ADAMSON UNIVERSITY

College of Engineering
Chemical Engineering Department
San Marcelino Street, Ermita, Manila

UNIT OPERATIONS 2 LABORATORY

EXPERIMENT 8
Batch Leaching of NaCl-Sand Mixture
with Water as Solvent

SUBMITTED BY:
ALFARAS, Alexander Allen S.
MURILLO, Ma. Cristine Bernadette A.
RUEDAS, Aina Dennice E.
VILLARETE, Meredith Mae Q.

SUBMITTED TO:
Engr. Pinky Joy Janaban

November 7, 2018
I. ABSTRACT
Leaching is concerned with the extraction of a soluble constituent from a solid by means of
a solvent. The process may be used either for the production of a concentrated solution of a
valuable solid material, or in order to remove an insoluble solid, such as a pigment, from a
soluble material with which it is contaminated. The one of the three modes of extraction;
single stage was done in this experiment using the beaker scale extraction operation. This
experiment uses mainly of the sand, NaCl and water mixture together with the series of
laboratory beakers. The extractions were carried out at different values of solvents for each
case. The solutions are withdrawn off after extraction process for the determination of
density using westphal balance. The density-concentration plot aids in the calculation of the
amount of solute in the final extract and raffinate for different cases. The efficiencies were
computed using the formula for extraction efficiency. The obtained efficiencies showed that
a large amount of solute was removed from the solution.

II. OBJECTIVES
1. To make a single – stage and multistage beaker-scale extraction operation.
2. To calculate single stage extraction efficiencies.

III. MATERIALS / EQUIPMENT

 7 pcs of 100 mL beakers
 NaCl
 Water
 Clean dry sand
 12 pcs – 1L beaker
 Westpal Balance

IV. EQUIPMENT SET UP

Figure 1. Typical Leaching Set-up.

V. THEORY

Extraction uses the property of solubility to transfer a solute from one phase to
another phase. In order to perform an extraction, the solute must have a higher solubility
in the second phase than in the original phase. In liquid-liquid extraction, a solute is
separated between two liquid phases, typically an aqueous and an organic phase. In the
simplest case, three components are involved: the solute, the carrier liquid, and the solvent.
The initial mixture, containing the solute dissolved in the carrier liquid, is mixed with the
solvent. Upon mixing, the solute is transferred from the carrier liquid to the solvent. The
denser solution settles to the bottom. The location of the solute will depend on the
properties of both liquids and the solute.

Solid-liquid extraction is similar to liquid-liquid extraction, except that the solute

is dispersed in a solid matrix, rather than in a carrier liquid. The solid phase, containing the
solute, is dispersed in the solvent and mixed. The solute is extracted from the solid phase
to the solvent, and the solid phase is then removed by filtration. Mass transfer rates within
the porous residue are difficult to assess because it is impossible to define the shape of the
channels through which transfer must take place. It is possible, however, to obtain an
approximate indication of the rate of transfer from the particles to the bulk of the liquid.

Figure 2. Schematic Extraction.

In leaching it is assumed that there is sufficient solvent present so that all the solute
in the entering solid can be dissolved into the liquid, equilibrium is reached when the solute
is dissolved. Hence, all the solute is completely dissolved in the first stage. It is also
assumed that the solid is insoluble, and no adsorption will happen for the solute in the solid,
meaning that the solution in the liquid phase leaving a stage is the same as the solution
remaining with the solid matrix in the settled slurry leaving the same stage. The settled
solid leaving a stage always contains some liquid. This solid-liquid stream is called the
underflow or slurry stream. The liquid is called the overflow stream. The concentration of
oil or solute in the overflow stream is equal to that in the liquid solution accompanying the
slurry or underflow stream. Hence, on an xy plot the equilibrium line is on the 45o line.

Figure 3. Countercurrent leaching: A, launder; B, rake; C, pump.

Since, there are three components: solute (A), inert or leached solid (B), and solvent
(C), a rectangular diagram is used to show the equilibrium data. The concentration of inert
or insoluble solid B in the solution mixture or the slurry mixture is defined as
𝑘𝑔 𝐵 𝑘𝑔 𝑠𝑜𝑙𝑖𝑑
𝑁= =
𝑘𝑔 𝐴 + 𝑘𝑔 𝐶 𝑘𝑔 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
For the overflow, N = 0, for the underflow, N depends on the solute concentration
in the liquid. The compositions of solute A in the liquid as weight fractions are
𝑘𝑔 𝐴 𝑘𝑔 𝑠𝑜𝑙𝑢𝑡𝑒
𝑥𝐴 = 𝑘𝑔 𝐴+𝑘𝑔 𝐶 = 𝑘𝑔 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 (overflow liquid)
𝑘𝑔 𝐴 𝑘𝑔 𝑠𝑜𝑙𝑢𝑡𝑒
𝑦𝐴 = 𝑘𝑔 𝐴+𝑘𝑔 𝐶 = 𝑘𝑔 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 (liquid in slurry)

For the entering solid feed to be leached, N is kg inert solid/kg solute A and yA =
1.0. For pure entering solvent N = 0 and xA = 0.
 Figure 4. Graph of a Leaching Process.

The following figure shows a single-stage leaching process where V is kg/h of overflow solution
with composition xA and L is the kg/h of liquid in the slurry solution with composition yA based
on a given flow rate B kg/h of dry solute-free solid.

Figure 5. Balance in One Stage.

By doing material balances, we have Figure 6. Graph of the Tie-Line.

Total solution (A+C): L0 + V2 = L1 +V1 = M

A: L0yA0 +V2xA2 = L1yA1 +V1xA1 = MxAM
B: B = L0N0 + 0 = L1N1 + 0 = MNM

A balance on C is not needed since xA + xC = 1 and yA + yC = 1, where M is the total flow

rate in kg (A+C)/h, xAM and NM are the coordinates of this point M. If L0 entering is the fresh solid
feed to be leached with no solvent C present, it would be located above the N versus y line in the
above figure.

Factors influencing the rate of extraction

The selection of the equipment for an extraction process is influenced by the factors which
are responsible for limiting the extraction rate. Thus, if the diffusion of the solute through the
porous structure of the residual solids is the controlling factor, the material should be of small size
so that the distance the solute has to travel is small. On the other hand, if diffusion of the solute
from the surface of the particles to the bulk of the solution is the controlling factor, a high degree
of agitation of the fluid is required.

There are four important factors to be considered:

Particle size. Particle size influences the extraction rate in a number of ways. The smaller
the size, the greater is the interfacial area between the solid and liquid, and therefore the higher is
the rate of transfer of material and the smaller is the distance the solute must diffuse within the
solid as already indicated. On the other hand, the surface may not be so effectively used with a
very fine material if circulation of the liquid is impeded, and separation of the particles from the
liquid and drainage of the solid residue are made more difficult. It is generally desirable that the
range of particle size should be small so that each particle requires approximately the same time
for extraction and, in particular, the production of a large amount of fine material should be avoided
as this may wedge in the interstices of the larger particles and impede the flow of the solvent.

Solvent. The liquid chosen should be a good selective solvent and its viscosity should be
sufficiently low for it to circulate freely. Generally, a relatively pure solvent will be used initially,
although as the extraction proceeds the concentration of solute will increase and the rate of
extraction will progressively decrease, first because the concentration gradient will be reduced,
and secondly because the solution will generally become more viscous.

Temperature. In most cases, the solubility of the material which is being extracted will
increase with temperature to give a higher rate of extraction. Further, the diffusion coefficient will
be expected to increase with rise in temperature and this will also improve the rate of extraction.
In some cases, the upper limit of temperature is determined by secondary considerations, such as,
for example, the necessity to avoid enzyme action during the extraction of sugar.
Agitation of the fluid. Agitation of the solvent is important because this increases the eddy
diffusion and therefore the transfer of material from the surface of the particles to the bulk of the
solution, as discussed in the following section. Further, agitation of suspensions of fine particles
prevents sedimentation and more effective use is made of the interfacial surface.

VI. PROCEDURE
A. Construction of Density – Concentration Plot for NaCl solution

Using seven (7) 100mL beakers, weigh corresponding amount of NaCl to make 0, 4, 8,
12, 16, 20, and 25% (by weight) salt dissolved in water. Then, add clean dry sand equivalent
to the amount of the water added. Stir properly and measure the liquor density of each beaker.
Lastly, plot the density (y-axis) against the weight percent NaCl (x-axis).

B. Preparation of the Fresh Feed

Weight 4 dry 1-L beaker and label from numbers 1-4, then place into each beaker the
sand-salt mixture pack. The pack contains150g sand; the amount salt is unknown. Pour 150mL
of water into each beaker and mix thoroughly. Then measure the liquor density of beaker IV.
This is the fresh feed liquor density and after that, determine the weight percent composition
of the fresh feed.

C. Single Stage Extraction Operation

Pour another 50mL of water to beaker 1, 100 mL to beaker 2, and 200mL to beaker 3.
Then stir well and allow settling. Decant the supernatant liquid from each beaker with a volume
equal to that added in step C-1 into separate containers. Then determine the densities of the
liquors in each beaker. Convert densities to weight percent salt using the density-concentration
plot. Lastly, calculate the single-stage salt extraction efficiencies.
VII. RESULTS & DISCUSSION
A. Construction of Density – Concentration Plot for NaCl solution

Density (g/ml) %
0 0
0.04167 4
0.07765 8
0.13698 12
0.19077 16
0.25015 20
0.33345 25

A density-concentration plot for the NaCl-sand solution (Figure 7) was constructed

from the calculated densities of the prepared NaCl with varying weight percent. This graph
was used to determine the corresponding weight percent of the different solutions obtained
in the experiment.

Density VS. Concentration

0.4
0.35
0.3
0.25
Density

0.2
0.15
0.1
0.05
0
0 5 10 15 20 25 30
Concentration

Figure 7. Density vs. Concentration of A.

As shown by Figure 7, the density increases as concentration increases. Density is

directly proportional to concentration of A.
 B. Preparation of the Fresh Feed

Mass of Water Density

Salt+Sand (ml) (g/ml)
(g)
72 100 0.72
64 88.9 0.71991
136 188.9

Table 1. Composition of Fresh Feed.

Table 1 shows the overall composition of the fresh feed. The composition of the
fresh feed is determined using the density-concentration plot for NaCl solution. The total
mass of solution in the feed is 136 g.

C. Single Stage Extraction Operation

Number of Stages Extraction Efficiency

1 10.35570855
2 31.04933071
3 83.56885564

Another method of operation in leaching is the multiple-stage extraction. In this

operation, the material to be treated and the solvent to be used are contacted many times.
Since leaching is limited by equilibrium, several subsequent stages for further extraction
are used to recover residual solute from the raffinate stream.
In the single stage extraction operation, the smallest amount of solvent used for
extraction will give the smallest amount of extracted component. This is because the
driving force for the transfer of the salt from the feed into the water solvent is the
concentration between the feed (underflow) and the solvent (overflow), and the distribution
of the salt is the same in both overflow and underflow once equilibrium is reached, granting
that enough time for mixing was done to evenly distribute the salt. This means that a
 smaller amount of solvent can only leach out a smaller amount of salt and a larger amount
of solvent can extract more salt before reaching equilibrium.
For multistage extraction operations, having more stages means higher extraction
efficiency. The table shows that as the number of stages increases, the extraction efficiency
also increases. A single stage for the extraction process using 150 mL solvent only gives
10.35% efficiency, whereas multiple stages give efficiencies of more than 80%. For a
certain amount of solvent, dividing it into several stages will give a more efficient
extraction because it creates more equilibrium stages.
The amount of salt that can be extracted increases due to the addition of another
stage which corresponds to introduction of a new driving force or concentration gradient
for diffusion of salt into the extracting solvent. Since at each stage, the solute particles in
the underflow would distribute uniformly with the overflow phase and would approach
equilibrium, a uniform concentration exists between the two streams. The introduction of
the fresh solvent into the next stage will disrupt the equilibrium and the diffusion of solute
can occur again. The amount of solute in the underflow stream continues to decrease as it
would achieve equilibrium once more with the fresh solvent at each succeeding stage.
Thus, a higher amount of solute would be extracted as the number of stages is increased.

VIII. CONCLUSION & RECOMMENDATION

The experiment investigates the batch leaching of NaCl-Sand mixture with water as
solvent in a beaker scale set-up. The group generated a single-stage and multistage leaching
operation to measure the extraction of the salt-sand mixture by calculating the extraction
efficiencies in each stage involved. The results indicated that as the number of stages
increases, the extraction efficiency increases as well. The group recommends the use of a
Westpal balance to accurately identify the density of a given solution. In addition, ensure
that all the salt-sand mixture in each stage are properly transferred into the next one to
avoid errors in the computation.
IX. REFERENCE
https://www.jove.com/science-education/5538/solid-liquid-extraction
http://www.gunt.de/images/download/extraction_english.pdf
https://pubs.acs.org/doi/abs/10.1021/ie50481a041?journalCode=iechad
Perry, Chemical Engineering Handbook, 8th Edition
X. APPENDICES
EXPERIMENTAL DATA
A. Construction of Density – Concentration Plot for NaCl solution
% Salt + Sand Water
(g) (ml)
0 0 35
4 1.40 33.60
8 2.5219 32.4781
12 4.2167 30.7833
16 5.6072 29.3928
20 7.0033 27.9967
25 8.7523 26.2477

B. Preparation of the Fresh Feed

Mass of Salt+Sand Water

(g) (ml)
72 100
64 108

C. Single Stage Extraction Operation

Beaker I
Initial Final
Mass Sand+Salt (g) 72 50
Water (ml) 150 116.2
Density (g/ml) 0.48 0.430293
 Beaker II
Initial Final
Mass Sand+Salt (g) 72 56
Water (ml) 200 118.7
Density 0.36 0.471778

Beaker III
Initial Final
Mass Sand+Salt (g) 72 112
Water (ml) 300 120.3
Density 0.24 0.440565

ATTENDANCE SHEET

ALFARAS, Alexander Allen S.

MURILLO, Ma. Cristine Bernadette A.
RUEDAS, Aina Dennice E.
VILLARETE, Meredith Mae Q.

SAMPLE COMPUTATION
A. Construction of Density – Concentration Plot for NaCl solution
1.40 𝑔
𝜌= = 0.04167 𝑔/𝑚𝑙
33.60 𝑚𝑙
2.5219 𝑔
𝜌= = 0.07765𝑔/𝑚𝑙
32.4781
B. Preparation of the Fresh Feed
72 𝑔
𝜌= = 0.72 𝑔/𝑚𝑙
100 𝑚𝑙
64 𝑔
𝜌= = 0.71991 𝑔/𝑚𝑙
88.9 𝑚𝑙
C. Single Stage Extraction Operation
Beaker I:
Initial:
72 𝑔
𝜌= = 0.48 𝑔/𝑚𝑙
150 𝑚𝑙
 Final:
50 𝑔
𝜌= = 0.430293 𝑔/𝑚𝑙
116.2 𝑚𝑙
Extraction Efficiency:
0.48 − 0.430293
𝛾= 𝑥100 = 10.35570855
0.430293

DOCUMENTATION

Preparation of materials Weighing of NaCl Weighing of sand

Sand and NaCl mixed in Weighing of the decanted

Wet sand after decanting
beaker solution