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METALS REMOVAL FROM ACID

MINE DRAINAGE BY ION
EXCHANGE
MEND Report 3.21.1(b)

This work was done on behalf of MEND and sponsored by

Falconbridge Ltd.
Homestake Canada Ltd.
Teck Corporation
the Ontario Ministry of Northern Development and Mines and
the Canada Centre for Mineral and Energy Technology (CANMET)
through the CANADA/Northern Ontario Development Agreement (NODA)

MINERAL SCIENCES LABORATORIES

April 1995

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METALS REMOVAL FROM ACID

MINE DRAINAGE BY ION
EXCHANGE
MEND Report 3.21.1(b)

P. Riveros and E.W. Wong

WORK PERFORMED FOR:
W. Napier,

Homestake Canada Inc.

M. Filion,

Teck Corporation

W. Cowan,

Ministry of Northern Development and Mines

R. Michelutti, Falconbridge

April 1995

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EXECUTIVE SUMMARY
The extraction of Sb, Cd, Cu, Ni and Zn from acid mine drainage solutions using various ion exchangers
was studied with batch and column tests. The extraction was studied at low pH, at mildly acidic pH and
at neutral pH. The interference caused by the presence of Al, Ca, Mg and Fe was monitored.
It was found that most commercial ion exchangers do not exhibit a marked selectivity for the metals of
interest. Consequently, the co-extraction of iron is a major obstacle for the application of ion exchange
to acid mine drainage solutions. The selectivity did not improve significantly when Fe(III) was reduced
to Fe(II). The co-extraction of calcium becomes a problem at higher pH when lime is used to neutralize
the solution. The most promising results were obtained with copper and antimony, which were amenable
to extraction even at low pH.
While the selective extraction of Cd, Ni or Zn was not feasible under most conditions, the simultaneous
extraction of all three metals can be done at neutral pH using either a chelating resin or a synthetic
zeolite. This fact could be used to reduce the amount of lime that is normally added to ensure the
complete precipitation of metals.

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CONTENTS
1 BACKGROUND .......................................................................................................................... 1
2 EXPERIMENTAL ...................................................................................................................... 2
2.1 SOLUTIONS, REAGENTS AND MATERIALS...............................................................................2
2.2 EXPERIMENTAL TECHNIQUES.....................................................................................................2
2.2.1 Batch tests........................................................................................................................................................ 2
2.2.2 Column tests .................................................................................................................................................... 2
2.2.3 Chemical analysis ............................................................................................................................................ 3

3 RESULTS AND DISCUSSION.................................................................................................. 3

3.1 NEUTRALIZATION OF ACID MINE DRAINAGE........................................................................3
3.1.1 Behaviour of metals during lime neutralization ............................................................................................... 3
3.1.2 Lime consumption ........................................................................................................................................... 3
3.1.3 Toxicity of the neutralization sludge ............................................................................................................... 4

3.2 SCREENING OF ION EXCHANGERS.............................................................................................4

3.2.1 Metal extraction at natural (low) pH................................................................................................................ 5
3.2.2 Metal extraction from solutions containing iron as Fe(II) ............................................................................... 7
3.2.3 Metal extraction at low pH in the absence of iron ........................................................................................... 7
3.2.4 Metal extraction at mildly acidic pH................................................................................................................ 7
3.2.5 Metal extraction at near neutral pH ................................................................................................................. 8

3.3 EXTRACTION OF COPPER..............................................................................................................8

3.3.1 Loading capacity.............................................................................................................................................. 8
3.3.2 Selectivity ........................................................................................................................................................ 9
3.3.3 Extraction kinetics ........................................................................................................................................... 9
3.3.4 Column extraction............................................................................................................................................ 9
3.3.5 Elution ........................................................................................................................................................... 10
3.3.6 Extraction at mildly acidic pH ....................................................................................................................... 10
3.3.7 Summary........................................................................................................................................................ 10

3.4 EXTRACTION OF ANTIMONY......................................................................................................11

3.5 EXTRACTION OF CADMIUM........................................................................................................11
3.5.1 Column extraction.......................................................................................................................................... 11
3.5.2 Extraction kinetics ......................................................................................................................................... 11
3.5.3 Elution ........................................................................................................................................................... 12
3.5.4 Other tests ...................................................................................................................................................... 12

3.6 EXTRACTION OF ZINC ..................................................................................................................12

3.7 EXTRACTION OF NICKEL ............................................................................................................13
3.8 BULK EXTRACTION OF CADMIUM, NICKEL AND ZINC .....................................................13

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4 ECONOMIC CONSIDERATIONS.......................................................................................... 14
5 CONCLUSIONS AND RECOMMENDATIONS .................................................................... 15
6 REFERENCES ......................................................................................................................... 16

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Tables
Table 1 Composition of feed solutions. ..................................................................................................................... 17
Table 2 List of ion exchangers. ................................................................................................................................. 18
Table 3 Behaviour of metals during lime neutralization........................................................................................... 19
Table 4 Consumption of lime versus equilibrium pH. Solution B. ........................................................................... 20
Table 5 Consumption of limestone (Continental, technical grade) versus equilibrium pH. Solution B. ................. 20
Table 6 Some physical characteristics of the neutralization sludge. Solution C. .................................................... 21
Table 7 Leachate extraction procedure (Toxicity test) for two neutralization sludges. ............................................ 22
Table 8 Extraction of metals from solution A. Equilibrium distribution between 1 mL resin and 100 mL solution.23
Table 9 Distribution coefficients. Solution A. .......................................................................................................... 24
Table 10 Metal extraction from Solution B. Equilibrium distribution between 1 mL of resin and 100 mL of
solution. ..................................................................................................................................................... 25
Table 11 Distribution coefficients. Solution B. ........................................................................................................ 26
Table 12 Adsorption of metals from solution B after reduction treatment. Distribution between 1 mL of resin and
100 mL of solution. .................................................................................................................................... 27
Table 13 Distribution coefficients. Solution B after reduction treatment. ............................................................... 28
Table 14 Metal extraction from the Falconbridge solution. Equilibrium distribution between 1 mL of resin and
300 mL of solution. .................................................................................................................................... 29
Table 15 Distribution coefficients. Falconbridge solution. ...................................................................................... 30
Table 16 Metal extraction under mildly acidic conditions. Solution C. Equilibrium distribution between 1 mL of
resin and 100 mL of solution. .................................................................................................................... 31
Table 17 Distribution coefficients. Solution C partially neutralized. ...................................................................... 32
Table 18 Metal extraction at near neutral pH. Distribution between 1 mL of resin and 30 mL of Solution B. ....... 33
Table 19 Distribution coefficients for a lime-neutralized solution. .......................................................................... 34
Table 20 Saturation profile of XFS-43084. Solution B............................................................................................ 34
Table 21 Extraction kinetics for Dowex XFS-43084 (1 mL) and Solution A (100 mL)............................................. 35
Table 22 Column elution of XFS-43084 with 1 M sulfuric acid. .............................................................................. 35
Table 23 Column extraction from a partially neutralized solution. Dowex XFS-43084 in the Na form.................. 36
Table 24 Column extraction from a partially neutralized solution. Amberlite IRC-718. ........................................ 37
Table 25 Column elution of Amberlite IRC-718 with 1 M sulfuric acid. .................................................................. 38
Table 26 Column extraction of antimony with Amberlite C-467. ............................................................................. 38
Table 27 Elution of Duolite GT-73 with 0.5M sulfuric acid. .................................................................................... 39
Table 28 Extraction kinetics for Duolite GT-73 (2 mL) and Solution A (100 mL).................................................... 39
Table 29 Column extraction of zinc and calcium with Amberlite IR-120. ................................................................ 40
Table 30 Column extraction of Cd, Ni and Zn with Amberlite IRA-93. .................................................................... 41
Table 31 Column extraction of Cd, Ni and Zn with Clinoptilolite. ........................................................................... 42
Table 32 Column extraction of Cd, Ni and Zn from a neutralized solution with Zeolite 4A..................................... 43
Table 33 Column extraction of Cd, Ni and Zn from a neutralized solution with Amberlite IRC-718....................... 44
Table 34 Comparison of Annual reagent costs of three alternatives for the treatment of acid mine drainage. ....... 45

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Figures
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9

Simplified flowsheet of a conventional lime neutralization process........................................................... 46

Simplified flowsheet of a proposed process comprising lime neutralization and ion exchange. ............... 47
Behaviour of metals during lime neutralization......................................................................................... 48
Consumption of lime as a function of pH................................................................................................... 49
Copper equilibrium distribution isotherms. ............................................................................................... 50
Adsorption kinetics of copper by Dowex XFS-43084................................................................................. 51
Column extraction of copper with Dowex XFS-43084............................................................................... 52
Column extraction of Cd and Zn with Duolite GT-73................................................................................ 53
Adsorption kinetics of cadmium by Duolite GT-73. ................................................................................... 54

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1 BACKGROUND
Most Canadian mining operations contain sulphide minerals, either in the ore or the surrounding waste
rock. When these sulphide minerals, particularly pyrite and pyrrhotite, are exposed to oxygen and water,
they begin to oxidize almost immediately. In the absence of calcareous materials, the initial chemical
reactions produce acid, which liberates the heavy metals associated with the waste deposit. Bacteria and
ferric iron catalyze the chemical reactions. Rainfall and snow melt flush the toxic solutions from the
waste sites into the downstream environment.
Acid drainage solutions usually contain significant concentrations of base metals, such as cadmium, iron,
lead, copper, zinc and nickel. If left untreated, the acid drainage can contaminate ground water and local
watercourses, damaging the health of plants, wildlife and fish (Filion et. al, 1990).
The conventional method to treat acid drainage is lime neutralization (Figure 1). Normally, Fe(II) is
oxidized to Fe(III) in order to enhance the precipitation of iron. Upon the addition of lime, calcium
sulphate and metal hydroxides precipitate into a bulky sludge, which is allowed to settle and
subsequently stored in ponds. Questions have been raised about the long term stability of the
neutralization sludge; for example, metals may be leached out if exposed to acid rain over a long period
of time (Penn Environmental Consultants, 1973). Another concern about lime neutralization is that the
treated effluent has a high pH due to the excess of lime added to ensure the complete precipitation of all
metals. A subsequent pH adjustment with acid may become necessary in the future to meet stricter
limitations of effluent pH (see for example MISA regulations for Ontario beginning 1997).
Ion exchange is a mature technology and numerous metallurgical applications have been reported (Bolto
and Pawlowski, 1987; Dorfner, 1990). The most important ion exchangers are synthetic polymeric resins
to which specific active groups have been attached. Ion exchange resins are usually classified as anionic,
cationic or chelating depending on the structure of the active groups. Inorganic ion exchangers, or
zeolites, are also available. These are either natural or synthetic aluminosilicate minerals, which are
usually less selective and have lower capacity than polymeric resins. However, in recent years
considerable interest has been raised on the use of zeolites for the treatment of effluents due to their low
cost and high resistance to harsh conditions (Dorfner, 1990).
In the case of acidic drainage, the bulk extraction of all metals, although technically feasible (Penn
Environmental Consultants, 1973), is not economically attractive because the most abundant metals, i.e.
iron, aluminum and calcium, have little value. By contrast, the selective extraction of some metals which
are valuable and/or toxic may significantly improve the economic and environmental aspects of lime
neutralization. This project addresses the selective extraction of metals, but does not propose the use of
ion exchange as a replacement for lime neutralization.
Figure 2 shows how the conventional lime neutralization process could be improved by ion exchange
stages. Specifically, removing some metals prior to lime neutralization, would reduce the metal content
and the toxicity of the neutralization sludge. Similarly, removing those metals that are still in solution
after the free acid has been neutralized, may be a better alternative for cleaning the effluent than adding
excess lime. Also, some revenue may be generated from the recovery of metals.
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This report describes a series of batch and column experiments intended to evaluate the extracting
capabilities of various ion exchangers. The feasibility of improving the economic and environmental
aspects of lime neutralization, by means of ion exchange, are discussed.

2 EXPERIMENTAL
2.1 SOLUTIONS, REAGENTS AND MATERIALS
Samples of acid mine drainage solutions were obtained from Homestake Canada and Equity Silver
Mines. A sample of mine water was provided by Falconbridge. The chemical analysis of these solutions
showed that only the Equity Silver solution had most of the metals of interest. The Falconbridge solution
contained mostly copper and nickel, but much less iron than is normally found in acid mine drainage
solutions (Wilson, 1994). The Homestake solution contained few metals other than iron. In order to
facilitate the experimental procedure, the concentration of selected metals was increased in some cases to
desired levels by adding one or more of the following compounds: CuSO4, 3CdSO4C 8H2O, NiSO4,
Fe2(SO4)3, Sb2O3, PbSO4 and ZnSO4C 7H2O.
All the experimental work was done with the three solutions shown in Table 1. The Equity Silver
solution was used to prepare Solution A, the Homestake solution was used to prepare Solutions B and C,
and the Falconbridge solution was used as received. The metal concentration in these solutions changed
slightly over the several months during which this project was developed (the numbers shown are the
initial concentrations when the solutions were prepared and they may differ slightly from those quoted on
specific tests).
A number of ion exchange resins was selected for the experiments on the basis of previous experiments,
published information and theoretical considerations. Samples were then obtained from the
manufacturers: Rohm and Haas, Bayer, Dow Chemical, Reilly Industries and Schering. A natural zeolite
(clinoptilolite) was obtained from Rocky Mountain Zeolites (Colorado) and a synthetic zeolite (Zeolite
4A) was obtained from Union Carbide. Table 2 presents a complete list of the ion exchangers used.

2.2 EXPERIMENTAL TECHNIQUES

2.2.1 Batch tests
The equilibrium and kinetic experiments were carried out by contacting appropriate amounts of resin and
solution with mechanical agitation. The resins were hydrated, washed with water several times and used
as such. The "wet settled volume" was used to measure the amount of resin, as is the common practice in
ion exchange applications. Therefore, the metal loadings are expressed as grams of metal per litre of wet
settled resin.

2.2.2 Column tests

Columns tests were carried out by passing the solution, using a peristaltic pump, through a 1-cm-diameter
column containing 5 to 15 mL of resin. The column effluent was sampled with an automatic fraction
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collector and analyzed. The flowrate of the solution through the column is expressed in bed volumes per
hour (BV/h). The "bed volume" is, by definition, the total volume occupied by the packed resin bed in
the column, including the space between the beads.

2.2.3 Chemical analysis

The concentration of metals in solution was analyzed by either atomic absorption or ICP
spectrophotometry. The metal loading on the resin was either estimated by solution difference or
determined by eluting the resins. In a few cases, the resins were completely digested in acids and the
resulting solution was analyzed for metals.

3 RESULTS AND DISCUSSION

3.1 NEUTRALIZATION OF ACID MINE DRAINAGE
The feed solutions were subjected to lime neutralization tests to study the behaviour of metals during the
process, to determine the lime consumption, and also to generate a sample of neutralization sludge. All
this information was needed for the analysis and discussion of the ion exchange tests.

3.1.1 Behaviour of metals during lime neutralization

It is well known that some metals hydrolyze and precipitate more readily than others when an acid
solution is neutralized (Monhemius, 1977). Furthermore, when a mixture of metals is present, there may
be a considerable amount of coprecipitation and other physicochemical effects, which make it impossible
to predict the behaviour of each metal from thermodynamic constants obtained under ideal conditions.
When lime is used, the formation of insoluble calcium sulphate introduces another complication. Thus,
the response of metals to lime neutralization in a given solution was determined experimentally.
Solution B was subjected to a stepwise lime neutralization and the concentration of metals in the
supernatant solution was determined as a function of the pH. The results presented in Table 3 and Figure
3 show that although most metals were precipitated readily on addition of lime, the complete
precipitation of some specific metals from solution was not attained until the pH was strongly alkaline.
While antimony, lead, copper, aluminum and iron were practically precipitated at pH 7, the concentration
of the other three metals was: Ni, 2.3 ppm; Cd, 33 ppm; and Zn, 19 ppm. A considerable excess of lime
was needed to eliminate these metals.

3.1.2 Lime consumption

Table 4 and Figure 4 present the consumption of lime needed to raise the pH of solution B from its initial
pH of 1.8 up to 11. It can be seen that the lime consumption was 3.6 g/L to reach pH 7 and 4.5 g/L to
reach pH 11. This means that 80 percent of the lime was used to neutralize the free acid and to
precipitate the large majority of the metals, while 20 percent was used exclusively to precipitate the last
traces of cadmium, nickel and zinc. It follows that a considerable amount of lime could be saved if Cd,
Ni and Zn were removed from solution using another method. Furthermore, this option may open the
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possibility of using limestone to replace lime. Limestone (calcium carbonate) is a cheaper product than
lime, but it is not widely used in this case partly because, being a weak base, it cannot yield a strongly
alkaline pH (SENES Consultants, 1994). Table 5 presents the consumption of limestone as a function of
the pH.

3.1.3 Toxicity of the neutralization sludge

Two large samples (2.5 litres each) of solution C were neutralized with lime to pH 10.5 and 4.5,
respectively. Table 6 presents the physical characteristics of the sludges. These sludges were filtered,
dried at 110C for 24 hours and subjected to the toxicity test of the Regulation 347, Environmental
Protection Act of Ontario (Leachate Extraction Procedure). This test determines whether metals are
leached out from a solid in significant amounts when contacted with a mildly acidic aqueous solution
(pH 5.2 adjusted with acetic acid).
The results of the toxicity tests for the two dry sludges are presented in Table 7. The composition of the
dry sludges show that, as expected, calcium and iron are the main components. When the solution was
neutralized to pH 10.5, the concentration of copper and zinc in the solids was very high, i.e. 0.8 and
2.89% respectively. The contents of toxic metals in the solids, especially Zn, decreases considerably
when the solution is only partially neutralized (pH 4.5), although it is still significant. Table 7 shows also
the amount of metals that were leached out, along with the leachate quality criteria that are used to
evaluate the toxicity nature of a solid. The Ontario Environmental Protection Act states that if a waste
produces a leachate containing any of the contaminants listed in Schedule 4 at a concentration in excess
of 100 times that specified in the Schedule, it is classified as "leachate toxic waste" or "hazardous waste"
and regulated accordingly. As can be seen, the concentrations of arsenic, cadmium, lead and mercury are
below the specifications of Schedule 4. However, if these sludges can be considered not hazardous, it is
mostly because many metals, such as Cu and Zn, are not listed in Schedule 4 at the present time. Since
the neutralization sludges released high amounts of copper and zinc into the leachate, it can be
anticipated that they may become an environmental liability, should other metals be included in future
regulations.

3.2 SCREENING OF ION EXCHANGERS

A large variety of ion exchangers are currently available. The two main groups are organic (resins) and
inorganic (zeolites). Ion exchange resins are normally classified as anionic, cationic and chelating. The
first two types are widely used for the purification of water. Anionic resins have amine groups and are
used for extracting amphoteric elements or metals that form anionic complexes. Cationic resins have
either sulphonic or carboxylic groups and are used to extract polyvalent cations. Chelating resins have
organic groups, which can form coordinate bonds with specific transition metals. Therefore, chelating
resins are more selective than cationic and anionic resins. Zeolites are exclusively cationic exchangers,
which exhibit some selectivity as a result of the regular size of the molecular pores within their
aluminosilicate structure. Thus, cations larger than the molecular pores are excluded from the zeolite.
The selection of ion exchangers for this work was based largely on CANMET's expertise in ion exchange
(Koren, 1991) and the results of an extensive literature review on the application of ion exchange to the
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treatment of acid mine drainage (Dinardo et al., 1991). The difficulty of the task at hand is to identify
ion exchangers that will exhibit a marked selectivity for the metal(s) of interest over the non-valuable
metals, such as iron, calcium and aluminum. Thus, only two cationic resins (Amberlite IR-120 and
Amberlite IRC-50s) were included in the screening (mostly for comparison purposes), as they are known
to be non-selective (Holmes et al., 1972). Instead, most of the resins selected for this project belong to
the chelating type, including two iminodiacetic resins (Amberlite IRC-718 and Lewatit TP-207), three
picolylamine resins (Dowex XFS-4196, XFS-4195, and XFS-43084), and one hydroxyquinoline resin
(TN-02328), all of which have exhibited good extracting properties for copper (Dorfner, 1991). A thiol
resin (Duolite GT-73), which extracts several metals having a strong affinity for the sulphide ion, was
also included. Amberlite IRA-743, Duolite C-467, Reillex 425 have polyol, aminophosphonic and
pyridine functionality, respectively, and have been proposed for various metallurgical applications.
Some anionic resins having primary, secondary and tertiary amine group (Duolite A-7 and Dowex WGR)
exhibit chelating properties for transition metals at neutral pH (Hazen, 1960) and were also included in
this work. Initially zeolites were not considered suitable for this project because these materials are not
stable in acid media. However, two zeolites (clinoptilolite and Zeolite 4A) were tested for the treatment
of neutralized effluent in the later stages of the project.

3.2.1 Metal extraction at natural (low) pH

A simple batch test was used to get an indication of the affinity of every ion exchanger for each metal.
The test consisted of contacting 1 mL of each ion exchanger with 100 mL of solution using mechanical
agitation during 24 hours. The resin loading was then estimated or determined as explained above. The
equilibrium distribution between the resin and solution was then tabulated.
Table 8 presents the equilibrium distribution of copper, iron and zinc between Solution A (at its natural
pH) and various resins. Copper and zinc were selected because these metals are usually present in AMD
solutions in concentrations high enough to justify their recovery (Wilson, 1994). Iron is invariably
present in AMD and it is likely to compete with the metals of interest for the ion exchangers. The resin
loadings were determined by eluting the resins with 1 M sulphuric acid, except Dowex XFS-4195 whose
metal loading was calculated by solution difference because this resin is known to be poorly eluted by
acids (Grinstead, 1984). A significant result was that all resins, except for Duolite GT-73, extracted
large quantities of iron. At the same time, several resins also extracted copper, but none of the resins was
a good extractant for zinc.
The affinity between a resin and a metal is commonly expressed by the distribution coefficient, D, which

D =

Metal loading on the resin (mg / L)

Aqueous metal concentration (mg / L)

is defined as follows:

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Distribution coefficients provide a good measure of the intrinsic affinity between a resin and a metal
because, unlike loadings, the solution concentration is taken into account. However, loadings are
important from a practical point of view because even if the affinity for a given metal is low, its resin
loading may still be high if the aqueous concentration of that metal is high. Both loadings and
distribution coefficients are useful to evaluate a resin/metal equilibrium.
Table 9 presents the distribution coefficients of copper, iron and zinc for each resin. It can be seen that
Dowex XFS-43084 is the best extractant for copper, on account of having the largest DCu among all the
resins and a relatively low DFe. Although Duolite GT-73 exhibits the highest selectivity for copper
because its DFe is zero, the DCu of Duolite GT-73 is an order of magnitude lower than that of Dowex
XFS-43084. Another important result is that none of the resins showed any selectivity for zinc.
A number of resins did not exhibit any promising capabilities and were eliminated from the screening
process at this point: Amberlite IRC-50s, Amberlite IRA-743, Reillex 425 and TN-02328. Dowex
XFS-4196 was also eliminated because its performance was inferior to both XFS-4195 and XFS-43084.
The weak-base resins, Amberlite IRA-93 and Duolite A-7, are clearly not active at low pH, but they may
show better performance at a higher pH.
Table 10 presents the results of another set of equilibrium tests, which were done by contacting 1 mL of
every ion exchanger with 100 mL of Solution B. In this case, the following metals were monitored: Al,
Sb, Cd, Ca, Cu, Fe, Mg, Ni and Zn. Every ion exchanger extracted large amounts of iron, which presents
a significant problem for the extraction of the metals of interest. Interestingly, Duolite C-467 extracted
much more antimony than any other resin. Significant copper loadings were observed with the
picolylamine resins (Dowex XFS-4195 and XFS-43084). The copper loadings of the two iminodiacetic
resins (Amberlite IRC-718 and Lewatit TP-207) was also significant, although slightly lower than those
of the picolylamine resins. Amberlite IR-120 attained the highest loadings of cadmium, nickel and zinc.
However, this cationic resin is clearly not selective as it extracts also the largest amounts of calcium, iron
and magnesium. This resin would be useful for the bulk removal of metals, but it is not suitable for the
objectives of this project.
A comparison of the distribution coefficients (Table 11) shows that Duolite C-467 has the highest
affinity for antimony. Although this resin also extracts other metals, its preference for antimony is
apparent. The distribution coefficients of the picolylamine resins (Dowex XFS-4195 and XFS-43084)
for copper are much higher than those for other metals, which offers good prospects for the extraction of
copper. Of the two resins, Dowex XFS-43084 can be considered the best choice for the extraction of
copper because XFS-4195 is difficult to elute (Grinstead, 1984). None of the ion exchangers exhibited a
strong affinity for either Cd, Ni or Zn at this low pH. Similarly, the extraction of Al, Ca and Mg is rather
low with all the resins, except with Amberlite IR-120. The distribution coefficients for iron are in
general intermediate, but because of its high concentration, iron is clearly the main interference for the
extraction of copper and antimony. The chemical analysis showed that iron was 100% present as Fe(III)
in all cases. However, it is known that fresh acid drainage solutions contain a considerable portion of
iron as Fe(II) form. Therefore, it was undertaken to determine the effect of reducing Fe(III) to Fe(II) on
the extraction of metals.

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3.2.2 Metal extraction from solutions containing iron as Fe(II)

Fe(III) was reduced to Fe(II) by adding 7 g/L of solid sodium bisulphite, NaHSO3, to the solution B and
allowed to react for 2 hours. The excess of SO2 produced was removed by sparging nitrogen gas through
the solution until no SO2 was detected with a Draeger tube. The chemical analysis showed that iron was
now 87.2% Fe(II). This solution was contacted as before with a number of selected ion exchangers and
the results are presented in Table 12 and Table 13. Surprisingly, it was found that reducing Fe(III) to
Fe(II) had relatively little effect on the extraction of iron. The largest difference was observed with
Dowex XFS-43084, which loaded 1,900 mg Fe/L instead of the 4,900 mg Fe/L when iron was present as
Fe(III). However, the copper loading remained at the same level (>7,000 mg/L), which means that
despite the increase in selectivity for copper over iron of Dowex XFS-43084, the latter is still extracted
to a significant extent, even when it is present as Fe(II). Similarly the selectivity of Duolite C-467 for
antimony over iron did not increase.

3.2.3 Metal extraction at low pH in the absence of iron

The solution supplied by Falconbridge was essentially iron-free (Table 1). Thus, it provided an
opportunity to measure the effect of Fe(III) on the extraction of other metals. The equilibrium
distribution between this solution (300 mL) and four selected resins (1 mL) is shown in Table 14 and the
corresponding distribution coefficients are presented in Table 15. Significantly high extractions of
copper and nickel were observed. The DNi of Dowex XFS-43084, Dowex XFS-43084, and Lewatit
TP-207 are fairly large, although smaller than the corresponding DCu in each case. The extraction of
zinc was somewhat better than in previous experiments, but still not promising. It can be concluded that
the prospects for extracting nickel increase significantly when iron is not present in the solution. The
extraction of copper and zinc also increase to some extent.

3.2.4 Metal extraction at mildly acidic pH

The extraction of most metals, except for Cu and Sb, was poor at low pH. In general, the ion exchange
extraction of metals improves as the pH increases. The following experiment was conducted to evaluate
the extraction of metals under mildly acidic conditions.
A sample of Solution C was neutralized with lime to pH 4.1. After filtration, the composition of the
filtrate was: Al 0.4 ppm; Ca 671 ppm; Cu 38 ppm; Fe 0.9 ppm; Mg 202 ppm; Sb 1 ppm; Zn 284 ppm.
Thus, raising the pH effectively removed iron, aluminum, and antimony from the solution. More than
half of the copper precipitated, the concentration of zinc did not change and the calcium concentration
increased as a result of the lime addition. This solution was contacted as before with a number of resins
at the same ratio of 1:100. Table 16 and Table 17 present the equilibrium solution/resin distribution and
the distribution coefficients, respectively. A few weak-base anionic resins (Amberlite IRA-93, Dowex
WGR and Duolite A-7) were included in the experiment because these resins exhibit metal complexing
capabilities through their free amine groups. This mechanism is only possible at neutral or mildly acidic
pH. While carrying out the experiments, it was observed that the equilibrium pH shifted considerably
from its initial value because of the hydrolytic reaction of some resins, in particular the weak-base resins.
In these cases, it was decided to run two experiments for each resin: one with the resin in the free amine
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form and another with the resin in the hydrogen or protonated form (i.e. preconditioned with an acid
solution). This fact accounts for the two pH levels found in the tables for the weak-base anionic resins.
The results show that the extractions of calcium, copper, magnesium and zinc increase substantially
under mildly acidic conditions with respect to acid conditions. Most of the resins extract large amounts
of calcium, which becomes the main interference once iron has been eliminated. The extraction of zinc
increases in most cases, although none of the ion exchangers showed a strong selectivity for this metal.
A number of chelating resins (Dowex XFS-43084, Amberlite IRC-718, Lewatit TP-207 and Duolite
GT-73) attained a very high DCu. The weak-base resins (Amberlite IRA-93, Dowex WGR and Duolite
A-7) exhibited some extraction capabilities, especially for copper. The performance of weak-base resins
is clearly very sensitive to the pH, which indicates that the elution of these resins could be accomplished
readily with a weak acid solution. Since the two iminodiacetic resins (Amberlite IRC-718 and Lewatit
TP-207) showed practically identical characteristics, only one of them was used in future tests.

3.2.5 Metal extraction at near neutral pH

For this test, a sample of solution B was neutralized with lime to pH 6. After filtration, the solution had
the following composition: Al 0 ppm; Ca 727 ppm; Cd 179 ppm; Ni 29 ppm; Cu 0.1 ppm; Fe 0 ppm; Sb
0 ppm; Zn 47 ppm. Table 18 presents the equilibrium distribution between the neutralized solution and
some selected resins. The equilibrium pH, which is slightly different from the initial pH in some cases, is
also tabulated. Table 19 presents the corresponding distribution coefficients. The data indicate that
Amberlite IRC-718 is a good extractant for cadmium, nickel and zinc. Duolite GT-73 exhibits a
relatively good affinity for cadmium over other metals. The two weak-base anionic resins (Dowex WGR
and Amberlite IRA-93) showed fairly high DZn, but other metals are also extracted.

3.3 EXTRACTION OF COPPER

Copper is eliminated quite effectively from solution by lime neutralization (see Table 3). However, as
discussed in section 3.1.3., a high concentration of copper in the neutralization sludge may contribute
significantly to its toxicity. While this fact provides an environmental incentive, the relatively good price
of copper provides an economic reason for the recovery of copper from acid mine drainage.
The experimental results showed that the two picolylamine resins (Dowex XFS-4195 and XFS-43084)
were able to extract copper effectively at low pH. While the elution of Dowex XFS-4195 is difficult,
Dowex XFS-43084 is amenable to elution with sulphuric acid (Grinstead, 1984). Therefore, Dowex
XFS-43084 was chosen for further evaluation. At mildly acidic conditions, the iminodiacetic resins
(Amberlite IRC-718 and Lewatit TP-207) also extracted copper effectively and were also selected for
further tests.

3.3.1 Loading capacity

Figure 5 presents equilibrium copper distribution isotherms for Dowex XFS-43084 and solutions A and
B. In both cases the copper loading exceeds 30 g/L, which is a very promising result. The copper

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extraction is more efficient from Solution B than Solution A, probably because the former contains less
iron.

3.3.2 Selectivity
The selectivity trends of Dowex XFS-43084 were studied by means of a saturation profile. This
procedure involves subjecting a small amount of resin to a series of successive contacts with fresh
aliquots of the feed solution. The cumulative loading of metals on the resin after each contact is
calculated and plotted. The purpose is to determine the changes in metal loadings as the resin approaches
saturation.
Table 20 presents the saturation profile of Dowex XFS-43084 obtained by means of 6 successive
contacts with solution B, each at a 100:1 solution-to-resin ratio. It can be seen that the resin exhibits a
preference for copper over iron, which is manifested by a slight displacement of the loaded iron by
copper as the resin becomes saturated. The distribution coefficients of copper and iron at saturation can
be estimated as 373 and 6.3, respectively. The separation factor (defined as the ratio between both
distribution coefficients) is then: SCu/Fe = DCu/DFe = 59.2. This value is favourable for copper and
indicates that it would be possible to "scrub" the iron off the loaded resin with a dilute copper solution.
For example, a portion of the weak electrolyte if there was an electrowinning circuit.

3.3.3 Extraction kinetics

The extraction kinetics of copper were studied by contacting 1 mL of Dowex XFS-43084 with 100 mL of
the Solution A using strong mechanical agitation. The solution was sampled and analyzed periodically
for copper. The results are presented in Table 21, along with the fractional approach to equilibrium
(calculated assuming that equilibrium is reached at 24 hours). From the graphical representation of these
data (Figure 6), the equilibrium half time, t2 (the time at which the resin has attained 50% of the
equilibrium loading), can be estimated to be about 1.5 hours. It should be pointed out that this value
depends on the resin-to-solution ratio and it is useful for comparison purposes only. As such, this result
indicates that the extraction kinetics of copper with Dowex XFS-43084 is relatively slow, which is a
common finding with chelating extractions.

3.3.4 Column extraction

Two column experiments were carried out to determine a suitable flowrate for the extraction. Figure 7
presents breakthrough curves for the extraction of copper from Solution A at two flowrates: 6 and 3
BV/h. These experiments were done with columns containing 10 and 15 mL of Dowex XFS-43084,
respectively. Better results were obtained with the slower flowrate, i.e. 3 BV/h, which is consistent with
the slow kinetics observed during the batch tests. The residence time (or contact time) of the solution as
it passes through the resin bed can be calculated as follows:
Residence time (h) =

Voidage of the Resin Bed

Flowrate ( BV / h)

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Assuming a typical voidage of 40%, the residence time for a flowrate of 3 BV/h is 8 minutes. This is a
relatively long residence time, which implies that a large resin inventory will be required for an
application. It is possible, however, to increase the kinetics by using finer resin particles.

3.3.5 Elution
The elution of copper from Dowex XFS-43084 was done readily and efficiently with 1 M H2SO4, passed
at 3 BV/h, as shown in Table 22. The copper elution attained a peak concentration of about 20 g Cu/L
and the elution was completed with about 10 bed volumes. In this case, the eluate was contaminated with
iron because no scrubbing was done. Since the affinity of this resin for copper is much higher than it is
for iron, the prospects of scrubbing iron from the saturated resin appear to be good. Additional tests,
preferably in a larger scale, would be required to determine the operation parameters of the scrubbing
stage. This was considered to be outside the scope of this project.

3.3.6 Extraction at mildly acidic pH

As expected, the extraction of copper improves as the pH is raised and a larger number of resins can
extract copper at mildly acidic pH. However, a significant fraction of copper may be eliminated from
solution due to precipitation and co-precipitation.
A sample of solution C was neutralized with lime to pH 4.5 and filtered. The filtrate had the following
composition: Ca 711 ppm; Cu 54 ppm; Fe 0.0 ppm; and Zn 274 ppm. This solution was passed through
a column containing Dowex XFS-43084 at 3 BV/h. As shown in Table 23, the extraction of copper was
excellent. No breakthrough for copper was observed even after passing 175 bed volumes of solution.
Limited amounts of calcium and zinc were extracted, mostly at the beginning of the experiment.
A similar experiment was carried out with one of the iminodiacetic resins. In this case, the filtrate had
the following composition: Ca 804 ppm, Cu 50 ppm, Fe 0.0 ppm and Zn 311 ppm. This solution was
passed through a column containing Amberlite IRC-718 at 3 BV/h. As in the previous case, the copper
extraction was excellent since no breakthrough for copper was observed despite treating more than 800
bed volumes of solution (see Table 24). The elution of Amberlite IRC-718 with 1 M sulphuric acid at 2
BV/h is presented in Table 25 and it can be seen that copper was efficiently eluted. A significant amount
of zinc was found in the eluate along with smaller amounts of calcium.

3.3.7 Summary
The extraction of copper from acid mine drainage appears to be very promising. At low pH, the
extraction is feasible with Dowex XFS-43084, a picolylamine resin. Although the kinetics are relatively
slow and some iron co-extraction takes place, both drawbacks could be overcome by using finer particles
and scrubbing the loaded resin, respectively. Under mildly acidic conditions, copper can be extracted
very efficiently with either Dowex XFS-43084 or one of the iminodiacetic resins.

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3.4 EXTRACTION OF ANTIMONY

As discussed above, the preliminary tests showed that an aminophosphonic resin, Duolite C-467, has a
good affinity for antimony. Table 26 presents the results of a column experiment, in which Solution C
(without pH adjustment) was passed at 10 BV/h through a column containing 10 mL of Duolite C-467.
The results were very promising: there was a breakthrough at about 100 BV, but the resin continued to
extract antimony even beyond 300 BV. A slower flowrate may be required to produce a sharper
breakthrough curve and higher efficiency. The loaded resin was removed from the column and was
dissolved in strong acids to determined its metal loadings. The analysis showed the following values: Ca
2,450 mg/L; Cu 750 mg/L; Fe 5,750 mg/L; Sb 2,750 mg/L; Zn 4,000 mg/L. Taking into account the
relative concentration of each metal in the feed solution, it can be seen that the affinity of Duolite C-467
for antimony is remarkably good.
Although the extraction of antimony was not investigated any further, the preliminary results show that
the extraction of antimony from acid mine drainage is promising.

3.5 EXTRACTION OF CADMIUM

Cadmium is usually found in relatively low concentrations in acid mine drainage solutions (Wilson,
1994). However, it is extremely toxic to most living organisms and it is currently listed in Schedule 4 of
the Ontario Environmental Act, as discussed above. As shown in Table 7, cadmium was readily released
during the toxicity test and in one case (pH 10.5), it almost exceeded the specification set for hazardous
wastes, even though the initial cadmium concentration in the AMD solution was only 4 ppm.
Cadmium does not precipitate readily on addition of lime. Table 3 shows that the concentration of
soluble Cd was 7.8 ppm at pH 8 and 1.2 ppm at pH 9 in the lime neutralization experiment done with
Solution B.
None of the resins showed any selectivity for Cd at low pH (Table 10 and Table 11). Under neutral
conditions, Duolite GT-73 exhibited affinity for cadmium, whereas Amberlite IRC-718 showed high
loadings of Cd, Ni and Zn (Table 18 and Table 19).

3.5.1 Column extraction

A sample of Solution A was neutralized with lime to pH 4 and filtered. The filtrate contained 157 ppm
Zn and 151 ppm Cd. The filtrate was passed at 5 BV/h through a column containing 5 mL of Duolite
GT-73 in the acid form (i.e. conditioned with 0.5 N H2SO4). As shown in Figure 8, a good separation of
zinc and cadmium was obtained since only the latter was adsorbed. The performance of Duolite GT-73
is moderately good; the breakthrough for cadmium was observed at about 20 BV and the total cadmium
loading was estimated at 7-8 g/L.

3.5.2 Extraction kinetics

Figure 9 presents the extraction kinetics of Cd with Duolite GT-73. As can be seen, the extraction
proceeds fairly quickly to equilibrium. The t2 was estimated to be slightly less than 30 minutes. Again,

11

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this value is for comparison purposes only and it is not a direct measure of the contact time needed for
the solution passing through the resin bed.

3.5.3 Elution
One elution test is shown in Table 27. A 0.5 M sulphuric acid solution was passed through the column at
3 BV/h. The elution under these conditions was not very efficient as the peak Cd concentration was only
625 ppm and after 23 BV the elution had not been completed. The efficiency of the elution would
probably improve with a more concentrated acid solution. An important result is that the zinc loading
was apparently very low, as there is practically none in the eluate. Thus, Duolite GT-73 may be useful to
separate Cd from Zn.

3.5.4 Other tests

A synthetic zeolite, exhibited a high affinity for Cd at neutral pH. Since this zeolite also extracted Ni and
Zn, it will be discussed in Section 3.8.

3.6 EXTRACTION OF ZINC

Zinc is commonly found in acid mine drainage solutions, sometimes in relatively high concentrations
(Wilson, 1994). Zinc is usually not completely precipitated at neutral pH; as shown in Table 3, the
concentration of soluble Zn was 18.6 ppm at pH 7, 5 ppm at pH 8, and 0.5 ppm at pH 9.
None of the resins exhibited affinity for Zn at low pH. Under mildly acidic or neutral conditions, the
extraction of zinc is feasible, but with low selectivity. The most promising resins for zinc are Dowex
XFS-43084, iminodiacetic resins, and the cationic resin Amberlite IR-120.
The extraction of zinc and copper with chelating resins (Dowex XFS-43084 and Amberlite IRC-718 or
Lewatit TP-207) under mildly acidic conditions was already discussed in Section 3.3. Moderate
extractions of Zn were observed (Table 23, Table 24 and Table 25), but copper was extracted
preferentially in all cases.
A method has been proposed in which Zn is extracted from a partially neutralized AMD solution with
Amberlite IR-120, eluted with NaCl, precipitated as Zn(OH)2 and calcined to produce ZnO (Gilmore,
1977). The process was considered to be economically viable. To evaluate this approach, a sample of
solution C was neutralized to pH 4.5, filtered and passed through a column containing 10 mL of
Amberlite IR-120 in the sodium form (i.e. conditioned with 0.05 M NaOH) at 5 BV/h. The filtrate had
the following composition: Ca 650 ppm; Cu 24 ppm; Fe 0.5 ppm; Zn 269 ppm. Table 29 presents the
analyses of Ca and Zn in the column effluent and the estimated metal loadings. The data clearly show
that the resin became saturated very quickly and that it loaded three times more Ca than Zn. Although
Amberlite IR-120 can extract Zn, its lack of selectivity is a serious drawback for the development of a
large-scale application. This approach might be useful, however, in relatively clean solutions with a high
concentration of zinc.
The bulk extraction of zinc, cadmium and nickel at neutral pH is discussed in Section 3.8.

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3.7 EXTRACTION OF NICKEL

Nickel is frequently a component of acid mine drainage (Wilson, 1994); it is present in AMD of all
nickel mines and some gold, uranium and other mines. As shown in Table 3, nickel tends to stay in
solution at neutral pH in low but environmentally significant concentrations. For example, the soluble Ni
was 2.3 ppm at pH 7 and 0.4 ppm at pH 8.
The extraction of nickel from acidic drainage at low pH was poor (Table 10 and Table 11). However, a
number of chelating resins extracted Ni (and Cu) effectively from an iron-free solution from
Falconbridge (Table 14 and Table 15). At neutral pH, Amberlite IRC-718 extracted Ni very efficiently
along with zinc and cadmium. This will be discussed in Section 3.8.

3.8 BULK EXTRACTION OF CADMIUM, NICKEL AND ZINC

Cadmium, nickel and zinc are the metals which are most difficult to precipitate quantitatively with lime
(Table 3). Consequently, attempts were made to find an effective extractant for these three metals. Such
an extractant would provide an alternative way to clean and detoxify the effluent without raising the pH
to objectionable levels, as is the case with lime neutralization.
Based on the results of batch contacts with mildly acidic and neutralized solutions (Table 16, Table 17,
Table 18 and Table 19) a small number of ion exchangers was selected for the tests: 1) A weak-base
resin (Amberlite IRA-93); 2) A chelating resin (Amberlite IR-718); 3) A natural zeolite (clinoptilolite);
and 4) A synthetic zeolite (Zeolite 4A).
A sample of Solution B was neutralized with lime to pH 6 and filtered. The composition of the filtrate
was: Cd 153 ppm, Ni 25 ppm and Zn 287 ppm. This solution was passed through a column containing 5
mL of Amberlite IRA-93 in the free base form at 5 BV/h. The results, presented in Table 30, show that
the extraction of metals was very poor; only small amounts of Zn were extracted.
Another sample of Solution B was neutralized to pH 7.5 and filtered. In this case, the composition of the
filtrate was: Cd 151 ppm; Ni 27 ppm; and Zn 45 ppm. This solution was then passed through a column
containing 10 mL of clinoptilolite at 5 BV/h. Table 31 shows that the metal extraction with clinoptilolite
was not efficient. Limited amounts of Cd, Ni and Zn were loaded on the zeolite, but the removal of
metals from the solution was incomplete.
The experiment was repeated with Zeolite 4A. A sample of Solution B was neutralized to pH 7.5 with
lime and filtered. The composition of the filtrate was as follows: Ca 636 ppm; Cd 33 ppm; Cu
<0.04 ppm; Fe <0.07 ppm; Ni 6.4 ppm; Sb 0.73 ppm; and Zn 11.2 ppm. This solution was then passed
through a column containing 5 cc of Zeolite 4A (ground to -20+65 Mesh) at 5 BV/h. The results are
presented in Table 32. As can be seen, the extraction of cadmium and zinc was extremely good; the
breakthrough for both metals was observed at about 300 bed volumes and even after that the extraction of
both metals continued until the end of the experiment. By comparison, the extraction of nickel was
considerably lower.
A sample of Solution B was neutralized to pH 7 with lime and filtered. The filtrate had the following
composition: Ca 805 ppm; Cd 26 ppm; Cu <0.05 ppm; Ni 5.2 ppm; Fe <0.04 ppm; Sb 0.7 ppm; and Zn
13

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8.7 ppm. This solution was passed at 10 BV/h through a column containing 5 mL of Amberlite IRC-718.
Table 33 shows that the extraction of the three metals was very efficient. The breakthrough for Cd was
observed at about 170 bed volumes and the one for Zn was observed at about 220 bed volumes. No
breakthrough for nickel was observed even after 479 BV of solution had been treated.
In conclusion, both Zeolite 4A and Amberlite IRC-718 are effective extractants of metals at neutral pH.
Zeolite 4A extracts Cd and Zn very strongly and Ni to a lesser extent. Amberlite IRC-718 can remove all
three metals very efficiently.

ECONOMIC CONSIDERATIONS

A detailed economic analysis is beyond the scope of this project. Although some potential applications
have been identified, a complete flowsheet was not developed. A proper economic evaluation would
require experimental data for each stage of the flowsheet, including elution and regeneration of the ion
exchanger, metal recovery from the eluate, resin recycling and reagent consumption. Furthermore, the
economics of a specific application, such as the recovery of copper, would be necessarily site-specific
because it would depend on the volume and composition of the solution. Therefore, only some
preliminary estimates will be made in this section.
As discussed before, an excess of lime is normally added to AMD solutions in order to ensure the
complete precipitation of metals. This report shows that the most difficult metals to precipitate are Cd,
Ni and Zn and that these threee metals could be removed efficiently with an ion exchange resin or a
zeolite. This raises the question whether the savings in lime consumption would offset the cost of an ion
exchange process. Although practically no tests were done on the elution and regeneration of the ion
exchanger, a preliminary comparison can be made on the basis of a hypothetical example. Normally, the
ion exchange resin would be eluted with dilute sulphuric acid and regenerated with dilute sodium
hydroxide. The zeolite would be eluted with a concentrated sodium chloride solution.
Table 34 presents an annual cost comparison of full neutralization to pH 11 followed by re-acidification
to pH 7, and two proposed alternatives: A) Partial neutralization to pH 6 followed by metal extraction
with an ion exchange resin and B) Partial neutralization to pH 6 followed by metal extraction with a
zeolite. The flowrate has been chosen arbitrarily as 10,000 m3/day.
In this example, the cost of the ion exchange resin alternative is only slightly cheaper than full
neutralization; however, sulphuric acid is available in many locations at much lower cost. The cost of the
zeolite alternative is considerably lower than the cost of full neutralization. An important consideration
is that the two ion exchange alternatives offer the possibility of metal recovery if the concentration
warrants it. Since a high pH is not required for the last two alternatives, limestone could also be used for
the neutralization instead of lime. Limestone is often overlooked as a neutralization agent because of its
poor reactivity at near neutral pH even though it can be highly cost effective. Where pH values must be
raised to above 6.5, a second stage of alkaline addition is normally required (NaOH, CaO). For strong
strength AMD solutions, limestone can meet typically 90 to 95% of the alkali demand at perhaps one
third the cost of quicklime. Furthermore, sludges may be more granular and dense (SENES Consultants,
1994).
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5 CONCLUSIONS AND RECOMMENDATIONS

It was found that most commercial ion exchangers do not exhibit a marked selectivity for the metals of
interest, i.e. Sb, Cd, Cu, Ni and Zn. Consequently, the co-extraction of iron is a major obstacle for the
application of ion exchange to acid mine drainage solutions. The selectivity did not improve
significantly when Fe(III) was reduced to Fe(II). The co-extraction of calcium becomes a problem at
higher pH when lime is used to neutralize the solution. The most promising results were obtained with
copper and antimony, which were amenable to extraction even at low pH.
While the selective extraction of Cd, Ni or Zn was not feasible under most conditions, the simultaneous
extraction of all three metals can be done at neutral pH using either a chelating resin or a synthetic
zeolite. This fact could be used to reduce the amount of lime that is normally added to ensure the
complete precipitation of metals. A preliminary cost comparison based on a hypothetical example
indicates that the ion exchange alternatives are cheaper than full neutralization, especially if synthetic
zeolites can be used.
It is recommended that additional work be undertaken to further develop the ideas generated in this work:
A) Copper extraction and recovery, B) Antimony extraction and disposal, and C) Bulk extraction of Cd,
Ni, and Zn from neutral effluent with resins and/or zeolites. These experiments should address the
recovery of metals from solution (cementation, electrowinning), so that a proper economic evaluation can
be done. Special emphasis should be given to assess the performance of zeolites with respect to
recycling, kinetics, and fouling.

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6 REFERENCES
1. Bolto B.A. and Pawlowski L., 1987. Wastewater Treatment by Ion Exchange. E.&F.N. Spon Ltd.,
New York.
2. Cripps J., Union Carbide. Personal communication to P. Riveros. 19 July 1994.
3. Dinardo O., Kondos P.D., MacKinnon D.J., McCready R.G.L., Riveros P.A., and Skaff M., 1991.
Study on metals recovering/recycling from acid mine drainage. CANMET Report MSL 91-39 (CR).
4. Dorfner K., 1991. Ion Exchangers. Walter de Gruyter, Berlin-New York.
5. Filion M.P., Sirois L.L. and Ferguson K., 1990. Acid mine drainage research in Canada. CIM Bull.
83(944), December 1990, 33-40.
6. Gilmore A.J., 1977. The recovery of zinc from a mine water containing small amounts of alkali and
heavy metals. CIM Bull., April 1977, 142-146.
7. Grinstead R.R., 1984. Selective absorption of copper, nickel, cobalt and other transition metal ions
from sulphuric acid solutions with the chelating ion exchange resin XFS-4195. Hydrometallurgy
12(1984) 387-400.
8. Hazen W., 1960. US Patent 2,954,276.
9. Koren D.W., 1991. Ion exchange research at CANMET. CANMET Report MSL 91-64 (LS).
10. Monhemius A.J., 1977. Precipitation diagrams for metal hydroxides, sulphides, arsenates and
phosphates, TRANS. IMM Section C, 86, 202-6.
11. Penn Environmental Consultants and Skelly & Loy, 1973. Processes, Procedures and Methods to
Control Pollution from Mining Activities. U.S. Environmental Protection Agency, EPA-430/9-73011.
12. SENES Consultants, 1994. Acid Mine Drainage - Status of Chemical Treatment and Sludge
Management Practices. MEND Report 3.32.1.
13. Wilson L., 1994. Canada-wide survey of acid mine drainage characteristics. MEND Report 3.22.1.

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Table 1

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Composition of feed solutions.

CONCENTRATION, mg/L

ALUMINUM
ANTIMONY
ARSENIC
CADMIUM
CALCIUM
COBALT
COPPER
IRON**
LEAD
MAGNESIUM
MANGANESE
NICKEL
ZINC
pH

SOLUTION A

SOLUTION B

SOLUTION C

FALCONBRIDGE

1,150
2
39
191*
455
13
192
1,950
1
947
16
12
150
2.5

14
7*
0
140*
271
0
99*
1,155*
2*
185
0
26*
313*
1.8

14
7*
0
4*
271
0
99*
1,155*
2*
185
0
1*
313*
1.8

------0
247
4
57
2
------123
4
2.8

* Concentration increased to this level by spiking; ** Iron was 100% Fe(III)

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Table 2

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List of ion exchangers.

ION EXCHANGER

SUPPLIER

CLASSIFICATION,
FUNCTIONALITY

Amberlite IR-120
Amberlite IRA-93
Amberlite IRA-743
Amberlite IRC-50s
Amberlite IRC-718
Dowex XFS-4195
Dowex XFS-4196
Dowex XFS-43084
Dowex WGR
Duolite A-7
Duolite C-467
Duolite GT-73*
Lewatit TP-207
Reillex 425
TN-02328
Clinoptilolite
Zeolite 4A

Rohm and Haas

Rohm and Haas
Rohm and Haas
Rohm and Haas
Rohm and Haas
Dow Chemical
Dow Chemical
Dow Chemical
Dow Chemical
Rohm and Haas
Rohm and Haas
Rohm and Haas
Bayer
Reilly Industries
Schering
Rocky Mountain
Union Carbide

Cationic, Sulphonic
Weak-base anionic
Chelating, Polyol
Cationic, Carboxylic
Chelating, Iminodiacetic
Chelating, Picolylamine
Chelating, Picolylamine
Chelating, Picolylamine
Weak-base anionic
Weak-base anionic
Chelating, Aminophosphonic
Chelating, Thiol
Chelating, Iminodiacetic
Weak-base anionic
Chelating, hydroxyquinoline
Natural zeolite
Synthetic zeolite

* Formerly marketed as IMAC TMR

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Table 3

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Behaviour of metals during lime neutralization.

EQUILIBRIUM
pH

1.8
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0

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CONCENTRATION OF METALS IN SOLUTION (mg/L)

Al

Ca

Cd

Cu

Fe(III)

Mg

Ni

Pb

Sb

Zn

14
15
5
0.5
0.2
<0.1
<0.1
<0.1
<0.1
<0.1

280
884
894
760
792
768
782
768
842
944

135
135
135
131
108
33
7.8
1.2
0.2
<0.1

99
96
78
16
0.1
<0.1
<0.1
<0.1
<0.1
<0.1

1,166
50
2.2
0.9
0.2
<0.1
<0.1
<0.1
<0.1
<0.1

182
186
196
194
192
188
179
152
77
3

25
26
26
24
16
2.3
0.4
0.1
<0.1
<0.1

1.9
1.0
0.1
<0.1
<0.1
<0.1
<0.1
<0.1
<0.1
<0.1

7.2
1.2
0.3
0.1
<0.1
<0.1
<0.1
<0.1
<0.1
<0.1

314
320
330
284
137
19
5
0.5
0.1
0.4

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Table 4

Table 5

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Consumption of lime versus equilibrium pH. Solution B.

CaO added
g/L

Equilibrium
pH

0.0
0.7
1.5
2.1
2.8
3.1
3.2
3.4
3.6
3.7
3.9
4.4
4.5

1.8
2.0
2.4
2.8
3.0
4.1
5.0
6.0
7.0
8.1
9.0
10.0
11.0

Consumption of limestone (Continental, technical grade) versus

equilibrium pH. Solution B.
Limestone added
g/L

Equilibrium
pH

0.0
2.8
4.2
7.6
7.8
8.2
8.3
9.7
10.7
10.9
13.2

1.8
2.7
2.8
4.0
4.2
4.6
5.0
6.0
6.9
7.1
7.1

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Table 6

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Some physical characteristics of the neutralization sludge. Solution C.

Test
No.

Initial
Solution
Volume
L

Final
pH

Lime
Consumption
g/L

Volume of
Settled
Sludge
mL

Weight of
Settled Sludge
g

S.G. of
Settled
Sludge
g/L

Weight of
dry solids1
g

1
2

2.5
2.5

10.5
4.5

4.00
3.15

162
115

198.3
131.1

1.22
1.14

25.4
20.2

Dried at 110C for 24 hours

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Table 7

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Leachate extraction procedure (Toxicity test) for two neutralization sludges.

LIME NEUTRALIZATION
TO pH 10.5

ALUMINUM
ARSENIC
CALCIUM
CADMIUM
COPPER
IRON
MERCURY
MAGNESIUM
LEAD
ANTIMONY
ZINC

LIME NEUTRALIZATION
TO pH 4.5

Composition of
Dry Solids1
(%)

Leachate
Composition2
(ppb)

Composition of
Dry Solids1
(%)

Leachate
Composition2
(ppb)

0.14
--18.45
--0.80
7.29
--0.85
0.01
0.06
2.89

28
<2.0
--413
63,000
--<2.0
--<1
24
906,000

0.18
--20.46
--0.64
10.28
--0.07
0.02
0.08
0.41

10
<2.0
--36
14,200
--<2
--4
3
122,000

Solids were dried at 110C for 24 hours

Determined by CANMET according to Regulation 347 of the Ontario Environmental Protection Act

From Schedule no. 4, Regulation 347 of the Ontario Environmental Protection Act

Leachate Quality
Criteria3
(ppb)

NL
50
NL
5
NL
NL
1
NL
50
NL
NL

NL = Not listed

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Table 8

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Extraction of metals from solution A. Equilibrium distribution between 1 mL resin and 100 mL solution.

ION EXCHANGER

BLANK
Amberlite IRA-93
Amberlite IRA-743
Amberlite IRC-50s
Amberlite IRC-718
Dowex XFS-4195
Dowex XFS-4196
Dowex XFS-43084
Duolite A-7
Duolite GT-73
Lewatit TP-207
Reillex 425
TN-02328

COPPER

IRON

ZINC

Solution
mg/L

Resin*
mg/L

Solution
mg/L

Resin*
mg/L

Solution
mg/L

Resin*
mg/L

198
196
198
197
149
103
114
43
191
177
161
175
95

0
10
13
15
4,245
9,500
7,815
14,350
605
1,480
3,115
1,570
8,395

1,890
1,866
1,835
1,703
1,700
1,727
1,753
1,819
1,846
1,883
1,713
1,733
1,669

0
2,050
4,950
18,300
17,150
13,550
12,250
6,750
2,090
750
19,750
12,750
17,950

154
147
154
151
151
148
150
152
152
151
148
153
154

0
0
50
50
100
350
100
100
150
50
200
100
50

* Determined by elution with 1 M H2SO4, except XFS-4195 which was calculated by solution difference.

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Table 9

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Distribution coefficients. Solution A.

ION EXCHANGERS

Amberlite IRA-93
Amberlite IRA-743
Amberlite IRC-50s
Amberlite IRC-718
Dowex XFS-4195
Dowex XFS-4196
Dowex XFS-43084
Duolite A-7
Duolite GT-73
Lewatit TP-207
Reillex 425
TN-02328

DISTRIBUTION COEFFICIENTS
Copper

Iron

Zinc

0
0
0
28
18
69
334
3
8
19
9
88

1
3
11
10
8
7
4
1
0
12
7
11

0
0
0
1
2
1
1
1
0
1
1
0

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Table 10 Metal extraction from Solution B. Equilibrium distribution between 1 mL of resin and 100 mL of solution.
ION
EXCHANGER

BLANK
Amberlite IR-120
Amberlite IRC718
Dowex XFS-4195
Dowex XFS43084
Duolite C-467
Duolite GT-73
Lewatit TP-207

Aluminum
mg/L

Antimony
mg/L

Cadmium
mg/L

Calcium
mg/L

Copper
mg/L

R*

R*

R*

R*

R*

15
8
13
14
14
15
14
14

0
700
200
100
100
0
100
100

5.9
5.9
4.9
5.5
5.9
1.2
4.3
4.9

0
0
100
40
0
470
160
100

151
106
146
135
147
143
137
144

0
4,530
500
1,600
400
800
1,400
700

262
195
258
261
260
253
248
259

0
6,700
400
100
200
900
1,400
300

100
85
55
11
25
90
89
56

0
1,500
4,500
8,900
7,500
1,000
1,100
4,400

Iron
mg/L
S

R*

Magnesium
mg/L
S

R*

0
188
0
1,145
863 28,200 162 2,600
957 18,800 187 100
1,079 6,600 186 200
1,096 4,900 185 300
1,087 5,800 183 500
1,104 4,100 182 600
960 18,500 186 200

Nickel
mg/L
S

R*

27
19
25
21
22
26
23
24

0
770
160
560
460
68
323
260

Zinc
mg/L
S

R*

0
312
269 4,300
309 300
303 900
309 300
301 1,100
300 1,200
308 400

S Solution
R Resin
* Estimated from concentration difference

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Table 11 Distribution coefficients. Solution B.

ION EXCHANGER

Amberlite IR-120
Amberlite IRC-718
Dowex XFS-4195
Dowex XFS-43084
Duolite C-467
Duolite GT-73
Lewatit TP-207

DISTRIBUTION COEFFICIENTS
Al

Sb

Ca

Cd

Cu

Fe*

Mg

Ni

Zn

88
15
7
7
0
7
7

0
20
7
0
392
37
20

34
2
0
1
4
6
1

43
3
12
3
6
10
5

18
82
809
300
11
12
79

33
20
6
4
5
4
19

16
1
1
2
3
3
1

41
6
27
21
3
14
11

16
1
3
1
4
4
1

* 100% as Fe(III)

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Table 12 Adsorption of metals from solution B after reduction treatment. Distribution between 1 mL of resin and 100
mL of solution.
ION
EXCHANGER

BLANK
Amberlite IRC120
Dowex XFS-4195
Dowex XFS43084
Duolite C-467
Duolite GT-73
Lewatit TP-207

Calcium
mg/L

Iron**
mg/L

Aluminum
mg/L

Antimony
mg/L

Copper
mg/L

R*

R*

R*

R*

R*

R*

R*

14
8
13
14
10
13
13

0
600
100
0
400
100
100

5.8
5.6
5.5
5.0
1.3
5.2
5.2

0
20
30
80
450
60
60

249
176
243
246
245
239
245

0
7,300
600
300
400
1,000
400

94
78
11
22
92
72
20

0
1,600
8,300
7,200
200
2,200
7,400

1,128
918
1,099
1,109
1,012
1,099
968

0
21,000
2,900
1,900
11,600
2,900
16,000

174
147
172
171
172
169
173

0
2,700
200
300
200
500
100

303
256
291
301
296
296
299

0
4,700
1,200
200
700
700
400

Magnesium
mg/L

Zinc
mg/L

S Solution
R Resin
* Estimated from concentration difference
** 87.2% as Fe(II)

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Table 13 Distribution coefficients. Solution B after reduction treatment.

ION EXCHANGER

Amberlite IR-120
Dowex XFS-4195
Dowex XFS-43084
Duolite C-467
Duolite GT-73
Lewatit TP-207

DISTRIBUTION COEFFICIENTS
Al

Sb

Ca

Cu

Fe*

Mg

Zn

75
8
8
40
8
8

4
5
16
346
12
12

41
2
1
2
4
2

21
755
327
2
31
135

23
3
2
11
3
17

18
1
2
1
3
1

18
4
1
2
2
1

* 87.2% as Fe(II)

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Table 14 Metal extraction from the Falconbridge solution. Equilibrium distribution between 1 mL of resin and 300 mL
of solution.
ION EXCHANGER

BLANK
Dowex XFS-4195
Dowex XFS-43084
Duolite C-467
Lewatit TP-207

Calcium

Cobalt

Copper

Nickel

Zinc

Solution
mg/L

Resin*
mg/L

Solution
mg/L

Resin*
mg/L

Solution
mg/L

Resin*
mg/L

Solution
mg/L

Resin*
mg/L

Solution
mg/L

Resin*
mg/L

247
247
246
245
243

0
75
75
800
1,150

4.2
4.1
4.2
4.2
4.2

0
0
0
0
0

57
12
16
31
9

0
13,500
14,000
8,500
15,000

123
82
88
122
96

0
11,750
11,750
0
8,500

4.4
3.8
4.4
4.0
4.1

0
250
200
525
250

* Determined by elution with 1 M sulphuric acid, except Dowex XFS-4195 which was eluted with 6 M HCl

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Table 15 Distribution coefficients. Falconbridge solution.

ION EXCHANGER

Dowex XFS-4195
Dowex XFS-43084
Duolite C-467
Lewatit TP-207

DISTRIBUTION COEFFICIENTS
Ca

Co

Cu

Ni

Zn

0
0
3
5

0
0
0
0

1,125
875
274
1,630

143
134
0
89

66
45
131
61

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Table 16 Metal extraction under mildly acidic conditions. Solution C. Equilibrium distribution between 1 mL of resin
and 100 mL of solution.
pH

BLANK
Amberlite IRA-93
"
Amberlite IR-120
Amberlite IRC-718
Dowex XFS-43084
Dowex WGR
"
Duolite A-7
"
Duolite GT-73
Lewatit TP-207
Clinoptilolite

4.1
6.6
4.4
2.9
2.5
3.3
6.3
4.7
6.2
4.6
2.9
3.6
5.0

Calcium

Copper

Magnesium

Zinc

Solution

Resin*

Solution

Resin*

Solution

Resin*

Solution

Resin*

671
623
643
382
643
663
627
644
607
643
647
640
539

0
4,800
2,800
28,950
2,800
800
4,400
2,700
6,400
2,800
2,400
3,100
13,200

38
3
6
30
3
1
4
19
4
20
6
4
33

0
3,500
3,200
800
3,500
3,700
3,400
1,900
3,400
1,800
3,200
3,400
500

202
186
188
149
198
198
187
197
189
185
166
199
183

0
1,600
1,400
5,300
400
400
1,500
500
1,300
1,700
3,600
300
1,900

284
234
280
228
192
264
242
280
260
275
257
204
260

0
5,000
400
5,600
9,200
2,000
4,200
400
2,400
900
2,750
8,000
2,400

* Calculated from solution difference

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Table 17 Distribution coefficients. Solution C partially neutralized.

pH

Amberlite IRA-93
"
Amberlite IR-120
Amberlite IRC-718
Dowex XFS-43084
Dowex WGR
"
Duolite A-7
"
Duolite GT-73
Lewatit TP-207
Clinoptilolite

6.6
4.4
2.9
2.5
3.3
6.3
4.7
6.2
4.6
2.9
3.6
5.0

DISTRIBUTION COEFFICIENTS
Calcium

Copper

Magnesium

Zinc

8
4
76
4
1
7
4
11
4
4
5
24

1,167
533
27
1,167
3,700
850
100
850
90
533
850
15

9
7
36
2
2
8
3
7
9
22
2
10

21
1
25
48
8
17
1
9
3
11
39
9

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Table 18 Metal extraction at near neutral pH. Distribution between 1 mL of resin and 30 mL of Solution B.
ION EXCHANGER

BLANK
Amberlite IRA-93
Amberlite IRC-718
Dowex WGR
Duolite GT-73

Equilibrium
pH

Calcium

Cadmium

Nickel

Zinc

Solution
mg/L

Resin*
mg/L

Solution
mg/L

Resin*
mg/L

Solution
mg/L

Resin*
mg/L

Solution
mg/L

Resin*
mg/L

727
672
341
663
622

0
1,650
11,580
1,920
3,150

89
81
0.8
40
5

0
240
2,646
1,470
2,520

29
16
0.6
18
25

0
390
852
330
120

47
11
0.8
7
38

0
1,080
1,386
1,200
270

6.0
5.1
6.5
6.2
4.3

Estimated by solution difference

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Table 19 Distribution coefficients for a lime-neutralized solution.

ION EXCHANGER

DISTRIBUTION COEFFICIENTS
Calcium

Cadmium

Nickel

Zinc

2
34
3
5

3
3,530
37
504

24
1,420
18
5

98
1,733
161
7

Amberlite IRA-93
Amberlite IRC-718
Dowex WGR
Duolite GT-73

Table 20 Saturation profile of XFS-43084. Solution B.

CONTACT
No.

1
2
3
4
5
6

AQUEOUS CONCENTRATION, mg/L

CUMULATIVE RESIN LOADING,

mg/L

Calcium

Copper

Iron

Zinc

Calcium

Copper

Iron

Zinc

259
259
258
258
259
258

26.4
31.3
41.1
58.6
66.5
77.0

1,096
1,127
1,132
1,145
1,149
1,154

310
311
312
313
312
312

0
0
100
200
200
300

7,170
13,850
19,550
23,500
26,660
28,770

5,000
6,900
8,300
8,400
8,100
7,300

200
300
300
200
200
200

1 mL of Dowex XFS-43084 contacted six consecutive times with 100 mL of Solution B.

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Table 21 Extraction kinetics for Dowex XFS-43084 (1 mL) and Solution A (100
mL).

TIME
hours

AQUEOUS COPPER
CONCENTRATION
mg/L

RESIN LOADING1
mg/L

FRACTIONAL
APPROACH TO
EQUILIBRIUM

0.00
0.17
0.33
0.67
1.00
1.50
2.00
3.00
4.00
5.00
6.00
8.00
24.00

194
163
154
137
126
105
103
87
80
73
68
63
41

0
3,100
4,000
5,700
6,800
8,900
9,100
10,700
11,400
12,100
12,600
13,100
15,300

0.00
0.20
0.26
0.37
0.44
0.58
0.59
0.70
0.75
0.79
0.82
0.86
1.00

Estimated from the solution analysis.

Table 22 Column elution of XFS-43084 with 1 M sulfuric acid.
SOLUTION PASSED
Bed Volumes

0.0
1.1
2.1
3.1
4.1
5.1
6.6
8.9
16.0

ELUATE CONCENTRATION, mg/L

COPPER

IRON

0
1,195
19,507
7,480
1,247
269
87
37
5

0
1,603
7,210
810
43
13
7
0
0

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Table 23 Column extraction from a partially neutralized solution. Dowex

XFS-43084 in the Na form.
SOLUTION
TREATED BV

10
20
30
40
51
61
71
82
92
103
114
125
136
147
157
175

COLUMN EFFLUENT
mg/L
Calcium

Copper

Zinc

488
707
711
749
715
717
719
713
719
717
712
716
707
717
712
703

0.3
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.1
0.1
0.0
0.1
0.0
0.0
0.2
0.1

3
52
138
202
235
259
274
284
292
288
289
301
285
280
274
273

Flowrate = 3 BV/h. Feed: Ca 711 ppm; Cu 54 ppm; Zn 274 ppm. pH = 4.5.

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Table 24 Column extraction from a partially neutralized solution. Amberlite

IRC-718.
SOLUTION
TREATED BV

10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
250
260

COLUMN EFFLUENT
mg/L
Calcium

Copper

Zinc

657
764
731
847
829
764
852
835
745
757
841
832
796
833
844
817
829
781
840
843
809
801
781
767
728
804

0.1
0
0
0
0
0
0
0
0
0
0
0
0.1
0
0
0
0
0
0
0
0
0
0
0
0
0

58
162
203
240
260
272
283
298
305
321
322
317
314
313
322
330
338
323
329
327
323
331
328
326
320
311

Flowrate: 3 BV/h. Feed: Ca 804 ppm, Cu 50 ppm, Zn 311, and Fe 0.05 ppm.
pH = 4.5.

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Table 25 Column elution of Amberlite IRC-718 with 1 M sulfuric acid.

SOLUTION PASSED
Bed Volumes

ELUATE CONCENTRATION, mg/L

CALCIUM

COPPER

ZINC

409
335
139
80
38
18
11
11
12

910
5,139
374
38
18
13
11
11
10

756
1,060
153
42
25
20
19
20
20

3.0
5.4
8.0
10.9
13.7
16.6
19.6
22.6
25.3

Flowrate: 2 BV/h
Table 26 Column extraction of antimony with Amberlite C-467.
SOLUTION TREATED
BV

CONCENTRATION OF ANTIMONY
IN THE COLUMN EFFLUENT
mg/L

20
40
60
80
100
120
140
160
180
200
220
240
260
280
300

<0.1
<0.1
<0.1
<0.1
1.0
1.0
1.1
1.2
1.2
1.3
1.3
1.3
1.4
1.4
1.5

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Flowrate 10 BV/h. Feed: Sb 8.8 ppm, pH 1.8

Table 27 Elution of Duolite GT-73 with 0.5M sulfuric acid.
ELUATE COMPOSITION, mg/L

SOLUTION
TREATED
BV

Cadmium

Zinc

0
607
625
195
77
47
36
31
26

0
17
17
8
4
3
2
3
2

0.0
2.6
5.8
8.6
12.4
14.5
17.7
19.9
23.5

Flowrate: 3 BV/h
Table 28 Extraction kinetics for Duolite GT-73 (2 mL) and Solution A (100 mL).
TIME
hours

AQUEOUS
CADMIUM
CONCENTRATION
mg/L

RESIN
LOADING
mg/L

FRACTIONAL
APPROACH TO
EQUILIBRIUM

0.00
0.17
0.33
0.67
1.00
1.50
2.00
3.00
4.00
5.00
6.00
24.00

159
105
92
74
65
55
49
40
35
31
29
23

0
2,700
3,350
4,250
4,700
5,200
5,500
5,950
6,200
6,400
6,500
6,800

0.00
0.40
0.49
0.63
0.69
0.76
0.81
0.88
0.91
0.94
0.96
1.00

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Table 29 Column extraction of zinc and calcium with Amberlite IR-120.

SOLUTION
TREATED
BV

8
25
42
59
72
83
93
103
113
123
133
143
153

EFFLUENT COMPOSITION
mg/L

RESIN LOADING1
mg/L

Zinc

Calcium

Zinc

Calcium

<0.2
<0.2
85
225
286
274
274
274
276
269
275
276
272

0.6
0.4
18
303
632
653
662
655
651
672
673
676
658

2,374
7,146
10,452
11,401
11,346
11,431
11,513
11,594
11,653
11,782
11,852
11,911
12,009

5,754
17,320
28,499
34,847
35,560
35,888
36,114
36,406
36,732
36,851
36,961
37,040
37,294

Estimated from the solution analyses. Flowrate = 5 BV/h

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Table 30 Column extraction of Cd, Ni and Zn with Amberlite IRA-93.

EFFLUENT COMPOSITION, mg/L

SOLUTION
TREATED
BV

22
44
66
87
108
129
149
170
192
213

Cadmium

Nickel

Zinc

105
163
156
158
151
153
146
150
153
151

8
22
25
26
26
25
26
25
25
24

4
39
57
68
78
77
78
78
73
78

Flowrate: 5 BV/h. Feed: Cd 153 ppm, Ni 25 ppm and Zn 287 ppm. pH = 6.0

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Table 31 Column extraction of Cd, Ni and Zn with Clinoptilolite.

EFFLUENT COMPOSITION, mg/L

SOLUTION
TREATED
BV

2.5
5.0
7.6
10.1
12.7
15.2
17.7
20.2
22.7
25.8
28.4
30.9
33.5
36.1
38.7

Cadmium

Nickel

Zinc

1
3
13
30
48
69
88
104
119
132
149
150
152
152
152

1
2
14
25
30
31
32
31
31
30
29
29
27
28
28

2
1
3
9
14
20
24
28
33
34
31
37
38
41
42

Flowrate: 5 BV/h. Feed: Cd 151 ppm; Ni 27 ppm and Zn 45 ppm. pH = 7.5

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Table 32 Column extraction of Cd, Ni and Zn from a neutralized solution with

Zeolite 4A.
SOLUTION
TREATED
BV

36
74
113
150
188
225
263
299
336
370
404
438
472
506
541
575

COLUMN EFFLUENT COMPOSITION, mg/L

CADMIUM

NICKEL

ZINC

<0.03
<0.03
<0.03
<0.03
<0.03
<0.03
<0.03
0.03
0.05
0.05
0.13
0.21
0.3
0.4
0.7
1.0

<0.2
0.1
2.8
3.5
4.0
4.1
4.9
4.5
4.5
4.6
4.3
4.5
4.8
5.1
4.8
5.2

<0.03
<0.03
<0.03
<0.03
<0.03
<0.03
<0.03
0.1
0.2
0.1
0.2
0.3
0.5
0.5
0.6
0.7

Flowrate: 5 BV/h. Feed solution: Ca 636 ppm; Cd 33 ppm; Cu <0.04 ppm; Fe <0.07 ppm; Ni 6.4 ppm;
Pb <0.4 ppm; Sb 0.7 ppm; Zn 11.2 ppm. pH = 7.5

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Table 33 Column extraction of Cd, Ni and Zn from a neutralized solution with

Amberlite IRC-718
SOLUTION
TREATED
BV

25
50
75
99
124
149
174
199
224
249
274
299
323
345
365
391
419
444
479

COLUMN EFFLUENT COMPOSITION, mg/L

CADMIUM

NICKEL

ZINC

0.02
<0.01
<0.01
<0.01
<0.01
0.04
0.18
0.4
0.8
2
3
4
7
9
10
15
14
19
23

<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2

0.1
<0.1
<0.1
<0.1
<0.1
<0.1
<0.1
<0.1
0.1
0.2
0.5
0.6
1.2
1.2
1.5
2.4
2.8
2.6
2.6

Flowrate: 10 BV/h. Feed solution: Ca 805 ppm; Cd 26 ppm; Cu <0.06 ppm; Fe <0.04 ppm;
Ni 5.2 ppm; Pb <0.4 ppm; Sb 0.7 ppm; Zn 8.7 ppm. pH = 7.0

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Table 34 Comparison of Annual reagent costs of three alternatives for the

treatment of acid mine drainage.
FULL LIME
NEUTRALIZATION
TO pH 11

LIME
NEUTRALIZATION
TO pH 6 AND
ADSORPTION ON A
RESIN

LIME
NEUTRALIZATION
TO pH 6 AND
ADSORPTION ON A
ZEOLITE

10,000
2.1

10,000
2.1

10,000
2.1

Reagent cost, $/year

Lime1
Sulphuric acid2
Sodium hydroxide3
Sodium chloride4
Resin5
Zeolite6

1,560,375
3,756
N/A
N/A
N/A
N/A

1,178,950
102,200
69,987
N/A
83,333
N/A

1,178,950
N/A
N/A
29,638
N/A
41,666

TOTAL

1,564,131

1,434,470

1,250,254

CONDITIONS

Flow, m3/day
Initial pH

Note:

The above estimates are based on a process running 24 h/day for 365 days/yr. This estimate
includes reagent cost only. Capital and labour costs would be similar for the three options.
Credits for the recovery of metal for the last two options are not included.

The lime consumption was determined experimentally as 4.5 kg/m3 for pH 11 and 3.4 kg/m3 for
pH 6. The quoted price of lime was $95 per ton.

The sulphuric acid consumption to adjust the pH from 11 to 7 was determined experimentally as
14.7 g/m3. The quoted price for sulphuric acid was $70 per ton.

The amount needed to regenerate Amberlite IRC-718 was determined experimentally as 8.5 BV
of 0.1 M NaOH. The quoted price for NaOH was $140 per ton.

This assumes that the elution of zeolite can be done with 10 BV of 1 M sodium chloride and that
90% of the NaCl can be recycled. The quoted price of NaCl was $35 per ton.

The cost of the resin was estimated assuming a life span of 10 years and a price of $15,000 per
m3. The resin inventory was calculated assuming a flowrate of 15 BV/h and two columns. The
total resin inventory was estimated as 55.56 m3.

The cost of zeolite was estimated assuming a life span of 10 years, a price of $7.5 per m3 (Cripps,
1994), a flowrate of 15 BV/h and two columns.

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Figure 1 Simplified flowsheet of a conventional lime neutralization process.

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Figure 2 Simplified flowsheet of a proposed process comprising lime

neutralization and ion exchange.
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Figure 3 Behaviour of metals during lime neutralization.

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Figure 4 Consumption of lime as a function of pH.

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Figure 5 Copper equilibrium distribution isotherms.

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Figure 6 Adsorption kinetics of copper by Dowex XFS-43084.

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Figure 7 Column extraction of copper with Dowex XFS-43084.

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Figure 8 Column extraction of Cd and Zn with Duolite GT-73.

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Figure 9 Adsorption kinetics of cadmium by Duolite GT-73.

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