screened to eliminate particles larger than 200 mesh.

A
Communications chemical analysis showed the following composition:
SiO2 62.9 pct
An Alternative Method for the AI203 24.4 pct
L%O 6.8 pct
Recovery of Lithium from Spodumene K20 0.7 pct
Na20 0.5 pct
LUIZ FERNANDO MEDINA and "Fe203 0.53 pct
MOHAMED M.A.A. EL-NAGGAR MgO 0.13 pct
CaO 0.11 pct
The tachyhydrite dried in an oven at 400 to 410 K for
Spodumene, Li:O. A1203" 4SIO2, a mixed silicate mineral
one hour was cooled in a desiccator and then crushed in a
which is resistant to chemical attack, is the major source
porcelain mortar and screened to separate and discard
of lithium and its compounds at present. Upon heating to
the particles larger than 200 mesh. The chemical analysis
temperatures above 1373 K the naturally-occurring a-
of this mineral revealed the following percentages in the
spodumene suffers an irreversible change to the less dense
dry sample:
and more reactive /3-form. The two most important pro-
cesses applied presently for the extraction of lithium from Na + 2.98 pct
spodumene are the acid method and the lime method. In the K" 1.44 pct
first method, spodumene crushed to - 2 0 0 mesh is heated to Mg +§ 14.43 pct
1423 to 1473 K for one hour. The product is attacked by Ca ++ . I0.19 pct
concentrated H2SO4 (93 pct) at 523 K for 10 minutes during C1- 69.89 pct
which time the Li in the mineral is substituted by hydrogen. SO4- 0.26 pct
When the mixture is leached by water, lithium is obtained in IR* 0.81 pct
the aqueous solution in the form of sulfate, Li2SO4. Recov- * IR residue insoluble in hot water
eries up to 85 to 90 pct are claimed by this method. In the
lime process, crushed spodumene, - 2 0 0 mesh, is mixed The two minerals were then mixed in a 50 ml capacity
with CaCO3 and heated to 1423 to 1473 K for two hours. platinum crucible in the predetermined proportions, usually
The sinter obtained is then cooled and subjected to water 1 g of spodumene and 8 g tachyhydrite. The crucible was
leaching. Lithium hydroxide, LiOH, is dissolved passing to then heated in a muffle furnace open to natural ventilation
the aqueous phase. The recovery in this method is approxi- during two hours at the selected temperature which ranged
mately 85 to 90 pct. from 923 K to 1473 K.
A less common method is chlorination roasting, in which The product in the form of a sinter was cooled in air and
the spodumene is sintered with NH4C1 and CaC12 in a rotary then ground in a porcelain mortar. It was observed that the
furnace at 1023 K. About 98 pct of the lithium contained in grinding was more difficult at higher reaction temperatures.
the mineral remains in the solid as chloride and can be water The ground sinter was then transferred to a 200 ml ca-
leached. The rest is usually lost to the gas phase. Similar pacity Erlenmeyer flask and leached with distilled water
results are obtained using a mixture of CaCOs and CaCI2; maintained at the boiling temperature and with continuous
however, the roasting temperature must be raised to 1423 magnetic agitation. The leaching continued for approxi-
to 1473 K. mately 4 hours. The pulp was then filtered in a buchner, the
In 1976 the Brazilian production of lithium ores amounted residue washed with distilled water and the filterate com-
to 5330 metric tonnes. 3 Chemical analysis of the Brazilian pleted with distilled water to 500 ml in a volumetric flask.
ores indicates a lithium content of 3.2 pct, which is too high The extracted lithium was analyzed by atomic absorption
if compared with other ores in which a 1 pct Li content is spectrometry.
considered excellent. In some experiments a complete analysis was made of the
Tachyhydrite (MgClz-CaCI2- 12H~O) is found in the State leach liquor to determine the masses of all the ions present.
of Sergipe in North-East Brazil. Layers of thickness that at The behavior of the two minerals, individually, during
times exceed 100 m are encountered. Reserves of such min- heating was investigated by the Differential Thermal Analy-
eral are estimated at approximately 4500 million tonnes. sis technique. When a sample of tachyhydrite weighing
The only other location known to have tachyhydrite is the 36 mg was heated in air at a steady heating rate of 20 K
west coast of Africa. per minute, it was observed that it gradually loses its
The spodumene utilized was crushed in a laboratory size water of crystallization, becoming unhydrous at 573 K.
jaw crusher and then ground in a ball mill, using porcelain Between 703 K and 823 K the weight loss suggests a de-
balls, to 90 pct smaller than 200 mesh. The product was composition of the MgC12 to MgO. This was confirmed by
chemical analysis.
LUIZ FERNANDO MEDINA is Assistant Professor, lnstituto de Spodumene, on the other hand, is stable, showing a mass
Quimica, The Federal University of Rio de Janeiro, Brazil. MOHAMED loss of 0.3 pct around 693 K and an endothermic reaction at
M. A.A. EL-NAGGAR, formerly Professor of Extractive Metallurgy, 1323 K characteristic of the transformation a-spodumene
Programa de Engenharia Metalurgica e de Materials, Coordination of /3-spodumene.
Post-Graduate Programmes in Engineering, The Federal University of Rio
de Janeiro, Brazil, is now Professor, Chemical Engineering Department, At the reaction temperatures used in this study the mixture
King Abdulaziz University, Jeddah, Saudi Arabia. can then be regarded as a mixture of spodumene plus MgO
Manuscript submitted May 6, 1982. and CaC12.

METALLURGICALTRANSACTIONSB VOLUME 15B, DECEMBER 1984--725

 Table I. Effect of Temperature on Lithium Recovery Table I1. Comparison between Theoretical Masses
after Roasting for Two Hours and Experimental Values Found through Chemical
Analysis of the Leach Liquor of the Sinter Obtained
Temperature. K Recoveries,Pct AverageValue from 10.3 g Tachyhydrite plus 1.0 g Spodumene
823 43 52 49 47 49 48
973 50 51 55 54 50 52 Mass Found Mass Found
1173 64 64 59 52 58 60 Theoretical after Reaction after Reaction
1273 69 68 68 65 67 68 Element Mass. g at 1423 K at 1473 K
1373 78 80 76 75 77 78 CI~ 1.7291 1.33 1.17
1423 88 89 85 86 -- 87 Li- 0.0375 0.032 0.024
1473 69 71 70 Ca-- 0.9774 0.78 0.70
Mg- - 0.5929 0.12
Table I demonstrates the dependence of the quantity of Na- + K+ 0.4
insoluble
lithium extracted from spodumene upon the reaction tem- residue 1.86
perature. The data show the calculated average of five runs
Total (mass 4.689 4.87 4.81
at each indicated temperature where the deviation was about
of sinter)
-+5.0 pct.
The recovery is plotted as a function of temperature in
Figure 1. It is evident that maximum recovery, about 87 pct,
REFERENCES
is achieved at 1423 K. Lower recoveries above this tem-
perature are due to the fusion of silicates forming a protec- I. A.N. Zolikman, O. E. Krein, and G. V. Samsov: Metallurgy of Rare
tive layer of glassy substance. Also, it could be partly due Metals, 2nd ed., Israel Program Scientific Translations, Jerusalem,
1966. p. 435.
to LiC1 volatilization.
2. Khalil Afgouni and J. H Silva: Lithmm Ore in Brazil, Arqueana de
When tachyhydrite is heated it loses its water of crys- Minerios e Metais Ltda. Rua Maria Figueiredo. 374, Paraiso, 044002-
tallization, which amounts to 51.18 pct of its mass. Above S. Paulo, 1978, pp. 1-13.
700 K it loses another 13 pct of its mass due to the trans- 3. Anuario Mineral Brasileiro, published by the National Department of
formation of MgCI2 into MgO. The total mass loss expected Mineral Production, The Ministry of Mines and Minerals, Brazil, 1980,
pp. 269-76.
when tachyhydrite is heated to the reaction temperature is
therefore 64.18 pct.
Experimentally, when a mixture of 10.3 g tachyhydrite
was reacted with 1 g spodumene at 1423 K, the mass of the
sinter was found to be 4.87 g.
Table II shows a comparison between expected the- Recovery of Elemental Sulfur
oretical values of some constituents and the corresponding during the Oxidative Ammoniacal
values obtained by chemical analysis. It is to be noted that
as the reaction temperature was increased, more losses in Leaching of Chalcopyrite
CI-, Li +, and Ca ++ were observed which might suggest
some chloride volatilization.
I. G. REILLY and D. S. SCOTT
1. Tachyhydrite can be used to open the spodumene struc-
ture for subsequent lithium recovery. This is essentially
an alternative method of the classical chlorination The discovery of elemental sulfur as a principal product
method and achieves similar recoveries. in the oxidation of copper sulfides during ammoniacal leach-
2. Maximum recoveries were obtained at 1423 K roasting ing is relatively new. Reilly and Scott ~ have reported the
for 2 hours with mixtures 8:1 by weight tachyhydrite: recovery of up to 60 pct of the sulfur content of synthetic
spodumene, and subsequent leaching in boiling water for covellite during an ammoniacal leaching study carried out in
4 hours. the presence of an immiscible organic sulfur solvent. Filmer
et al. 23 have reported the development of a low temperature
%
95
oxidative ammonia leach process in which part of the sulfur
content of the sulfides (upwards of 76 pct) reports as ele-
mental sulfur and can be recovered from the leach residues
85 by solvent extraction. Prior to this point it was generally
believed that elemental sulfur was not formed during an
ammoniacal leaching process.
E 75
The sulfur recoveries achieved in the above studies indi-
cate that elemental sulfur is a principal intermediate product
65
in the oxidation sequence of the sulfide through to its final
ca
form as sulfate. The work of Filmer et al. 3 also clearly
55 indicates that, in the case of covellite, the elemental sulfur
J I.G. REILLY is Professor, School of Engineering, Laurentian Uni-
45
800 900 1000 1100 1200 1300 1400 1SO
versity, Sudbury, ON, Canada, P3E 2C6. D.S. SCOTT is Professor,
Department of Chemical Engineering, University of Waterloo, Waterloo,
TK ON. Canada.
Fig. 1 --Recovery of lithium as a function of roasting temperature (roast- Manuscript submitted January 17, 1984.
ing time 2 h).

726--VOLUME 15B, DECEMBER 1984 METALLURGICAL TRANSACTIONS B