hydrom-s-07-00123[1]

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Elsevier Editorial System(tm) for Hydrometallurgy

Manuscript Draft

Manuscript Number:

Title: Caliche Heap Leaching

Article Type: Regular Article

Section/Category:

Keywords: Heap Leaching; Caliche; Sodium Nitrate

Corresponding Author: Prof. Luis A. Cisternas, Ph.D.

Corresponding Author's Institution: Universidad de Antofagasta

First Author: John A Valencia

Order of Authors: John A Valencia; David A Méndez; Jessica Y Cueto; Luis A

Cisternas, Ph.D.

Manuscript Region of Origin:

Abstract: The leaching of heaped Caliche minerals represents a valid

alternative for the extraction and transformation of this product, giving good

recovery levels with excellent economic projections and technical results when

compared with existing technology. This study reports on experimental tests of

the leaching of this mineral in columns in which we determined the recovery of

nitrate and magnesium at different heights through the bed of the mineral. The

columns were sampled at three different heights, recovering the strong solutionfrom sample ports at each height and calculating the recoveries of the target

materials at each height. These variables were analyzed as a function of time

and irrigation ratio, thus obtaining empirical kinetic expressions. A

mathematical model was constructed which represented the leaching process for

the solutes, considering the variation in height of the bed of the leached

mineral. The model showed a good fit for predicting the concentrations of

nitrate, since this species was associated with the basic assumptions of the

model.

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Caliche Heap Leaching

John A. Valenciaa, David A. Méndez a, Jessica Y. Cueto b, Luis A.

Cisternasa,b

a Department of Chemical Engineering , Universidad de Antofagasta, Antofagasta, Chile

bCenter for Mining Scientific Research and Technology (CICITEM), Antofagasta, Chile

Submitted to Hydrometallurgy

Original submission: April 2007

Keywords: Heap Leaching, Caliche, Sodium Nitrate

Abstract

The leaching of heaped Caliche minerals represents a valid alternative for the extraction and

transformation of this product, giving good recovery levels with excellent economic projections and technical

results when compared with existing technology. This study reports on experimental tests of the leaching of

this mineral in columns in which we determined the recovery of nitrate and magnesium at different heights

through the bed of the mineral. The columns were sampled at three different heights, recovering the strong

solution from sample ports at each height and calculating the recoveries of the target materials at each height.

These variables were analyzed as a function of time and irrigation ratio, thus obtaining empirical kinetic

expressions. A mathematical model was constructed which represented the leaching process for the solutes,

considering the variation in height of the bed of the leached mineral. The model showed a good fit for

predicting the concentrations of nitrate, since this species was associated with the basic assumptions of the

model.

anuscript

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1. Introduction

Salitre is a white salt which is translucent and bright, composed primarily of sodium nitrate. It forms thin

crusts on the surfaces of rocks and walls of the mineral and often forms a superficial horizon of some soils in

Chile [1], Spain, Iran, Egypt, and India. Salitre is commercially important as a fertilizer, food preservative, in

glass manufacture, and in some medicines as a diuretic. It was historically important in the manufacture of gunpowder, and is currently used in explosives, fireworks (rockets), and matches, as well as in metallurgical

smelting agents. It is an important raw material for obtaining nitrogen in the manufacture of certain compounds

such as nitric acid, and as an oxidizing agent in many industrial chemical processes.

The main procedures for the extraction of nitrate from Caliche mineral were worked out by the Pedro

Gamboni (a Chilean) in 1853. Twenty years later the English mechanical engineer James T. Humberstone

adapted a countercurrent leaching process originally developed by Shank [7] for obtaining soda ash by the Le

Blanc [7] process. The latter method allows processing Caliche minerals containing 15% nitrates. After the

invention of synthetic saltpeter, the Shank process became uneconomical, and was replaced by a cold

leaching process developed by Guggenheim in the 1920’s [7]. Presently, this process is only used at two

worksites, including Maria Elena and Pedro de Valdivia in northern Chile. More detailed information in this

area has been presented by the study of Wisniak and Garces [7].

A current existing demand on the world market for low grade saltpeter in fertilizer manufacture has

promoted the exploitation of Caliche mineral in the Tarapacá and Antofagasta regions of Chile. This led to

modifications in the original methods of extracting nitrate. Since 1990 the leaching process has been used on

heaps of the mineral at Pampa Blanca, Chile, similarly to that used with some other metals [2,3], with the

leaching agent for Caliche being water. The leaching of piled minerals represents a valid alternative, with

excellent economic and technological possibilities and good levels of recovery when compared with current

extraction technology and transformation of the product.

The leaching of heaps consists of feeding the solvent onto a mass of mineral having a determined grade,

so that the solvent percolates through the mineral, carrying away the solute. The enriched solution is recovered

from the base of the mineral mass which rests on an impermeable mineral or plastic-covered base.

The leaching of Caliche differs specifically from the leaching of copper and precious metals minerals. With

Caliche there are several soluble species while in the case of copper and gold minerals there are few. In the

case of copper and gold minerals, dissolution occurs through a chemical reaction and the resulting solutions

are diluted; in the case of Caliche, dissolution is by simple solubility and the final solutions must be

concentrated.

The objective of the present research is to study the process of leaching of Caliche heaps, with particular

attention to the recovery of nitrate and magnesium. The latter is important because it is a control variable in the

Caliche leaching process. The objective was pursued by establishing experimental tests and then developing a

mathematical model representing the leaching process which would allow better understanding of the

phenomena involved, and leading to new possibilities for improving the technology.

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2. Experiment

2.1 Materials and equipment

Testing was carried out in columns using Caliche mineral from the Antofagasta Region of Chile. Specific

chemical analyses were carried out on the types and grade values of materials composing the mineral.

Analytical methodology applied included volumetric oxidation-reduction for iodine (I2), gravimetry for the

insolubles and sulphate (SO4), atomic absorbtion spectrometry (AA) for sodium, potassium, calcium, and

magnesium (AA; Varian Corp., model 220FS instrument), precipitation volumetry for chlorine (Cl-), nitrate

(NO3) and perchlorate (KClO4) were measured by molecular absorbtion using a UNICAM Corp. model UV2

instrument, carbonate (CO3) by acid-base volumetry, and moisture by difference in weight. The results are

shown in Table 1 (raw column).

Mineralogical composition was determined using X-ray diffraction using a Siemens model 5000 automated

and computerized diffractometer. This analysis provided a general impression of the species more or less

abundant in the sample; abundant species were those occurring at above 5% and the less abundant species

those occurring below this percentage.

The goniometer used was a vertical Braga-Brentano, with a wave-length radiation of 1,5406Å (CuKα1).

The secondary monochromator was of graphite, with 1mm/ 1mm/ 0.1mm slits. The scanning range was

between 3 and 79º (2θ), time interval 1.0 second, and the database used was that of the International Center

of Diffraction Data (ICDD). The results of this analysis can be seen in the diffractogram presented as Figure 1.

In summary, the main species observed included: nitrate (NaNO3), halite (NaCl), sodium anorthite

((Ca,Na)(SiAl)4O8) and quartz (SiO2). The minor species included: anhydrite (CaSO4), glauberite

(Na2Ca(SO4)2), loeweite ([Na12Mg7(SO4)13]·15H2O), calcite (CaCO3), polyhalite (K2Ca2Mg(SO4)4·2H2O),

probertite (NaCa(B5O7)(OH)4·3H2O), gypsum (CaSO4·2H2O) and illite-montmorillonite (insoluble clay).

A granulometric analysis of the mineral was carried out using the following Tyler screens: 1”, ¾”, ½”, 5, 8,

20, 30, 70 and 100. The results obtained are shown in Figure 2, together with the results of fits to the

distribution of particle size proposed in the Rosin-Ramler model [4], where x represents the particle size in

millimeters (mm), l is the mean size of the particle and m is the adjustable parameter characteristic of the

particle distribution.

−=

m

l

xexpied tan Re%Cumulative

(1)

In the case of the Caliche analyzed, the value of l was 12.156 mm, and of m was 1.624, with a correlation

factor R2 = 0.9943 and an estimated standard error of 0.0282.

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Preliminary leaching tests were carried out in columns which demonstrated that large amounts of fine

material was formed, causing problems due to channeling, and to transport of the fines. In order to avoid these

problems we decided to classify the mineral to be leached, loading the columns with material having particle

sizes greater than 3/8 inch (9.53 mm). In order to determine the effect of the classification procedure, the

chemical composition of the mineral was re-determined, producing the results presented in Table 1. Nosignificant differences were found between the initial results (raw) and those presented (class.) in Table 1.

2.2 Procedure

Leaching tests were carried out following methods typically used by the copper mining industry [1], but

using water as the leaching solution. The procedures for storage and transport of the solids used were based

on CEMA (Conveyor Equipment Manufacturer Association) and ASTM (American Society for Testing and

Materials) norms.

In order to simulate a leaching process for columns of different heights, a column was prepared which was

divided into three different heights of the mineral, where samples of the leaching solution could be removed

from the column at each of the three heights. Enriched solution samples extracted from each height could then

be analyzed for concentrations and recoveries of nitrate and magnesium. Divisions of the mineral at the

different heights in the column were established by installing a perforated plexiglas plate and a drain bib at

each height from which samples of the leaching solution could be extracted. A pad of glass wool was installed

at each level of the mineral to prevent the movement of fines from one level to the next.

The experimental scheme is shown in Figure 3, and Table 2 lists the disposition of the mineral modules

which define the different heights in the column.

A low flow rate of water (4.8 l/h·m2) was delivered by a peristaltic pump in order to minimize transport of

fine particles by the leaching flow. The tests were carried out at room temperature, using potable water at a

temperature of about 25°C.

The mineral in the columns was initially filled until reaching saturation of the bed, maintaining this level

without draining up to 10 hours, then following by continuous dropwise irrigation. The water was fed into the

first module, from which it was drained (solution from height 1), then directed into the second module (solution

from height 2), and finally into the third (height 3).

Continuous monitoring was carried out, taking samples every 12 hours from the outputs of each module.

After 250 hours of irrigation, entry of water into module #1 was stopped and the leaching solution was allowed

to flow until each module had been drained. Representative bed samples were then taken from each module

in order to make mineralogical analyses of the residue, determine which salts had been leached, and making

other analyses of the solutions.

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Table 3 and Figure 4 shows the results of chemical and mineralogical analyses, respectively, of the

leached mineral residue left in the column. This sample was prepared from a composite of subsamples of

residues at each of the levels. Assays of nitrate and magnesium for each level are given in Table 5.

The results of the chemical analyses of the leached mineral showed that since most of the soluble species

had been removed, the percentage of insolubles in the residue increased from 60.19 to 88.86%. The

percentage recovery of nitrate reached 95.62%, magnesium 94.59%, sulfate 68.28%, iodine 95.35% and

chloride 99.83%.

The x-ray analysis showed the species in major abundance in the residue were quartz (SiO 2), bassanite

(CaSO4·0.5H2O) and sodium anorthite [(Ca, Na)(Al, Si)4O8]. The lesser abundant species included orthoclase

(KAlSi3O8), calcite (CaCO3), vermiculite [(Mg2.36Fe0.48Al0.16)(Al1.28Si2.72)O10(OH)2(H2O)6Mg], montmorillonite

[Ca0.2(Al,Mg)2Si4O10(OH)24H2O], probertite [NaCa(B5O7)(OH)4·3H2O], kaolinite [Al2Si2O5(OH)4], loeweite

[Na12Mg7(SO4)13·15H2O], moscovite [KAl2(Si3Al)O10(OH,F)2] and gypsum (CaSO4·2H2O).

When comparing the mineralogical results from the leached residue with those in the original mineral

sample, it can be seen in that the species containing the nitrate disappeared from the more and less abundantspecies resulting in a total recovery of nitrate of over 95%. In the case of the magnesium, the species which

contained this element in the raw mineral were loeweite and polyhalite. The first of these remained present in

the residue (probably partially dissolved), but the polyhalite was completely dissolved. It was apparent that the

dissolution kinetics of loeweite and polihalite were different, governing the solution behavior of the magnesium

as noted in assays of the strong solution from different levels, which gave two different solubility rate curves for

magnesium.

3. Results and Discussion

3.1 Leaching recovery as a function of irrigation time

The percentage recovery of nitrate and magnesium were determined from the initial grade value of the

mineral and from the final analysis of the leached residues in each module. The trends in percentages of

recovery of nitrate are shown in Figure 5 as a function of irrigation time.

The nitrate recovery curves showed that excellent percentages of recovery were obtained at heights 2 and

3 (Table 4) when compared with the recovery obtained at the lowest height. The best kinetic was observed at

the lowest height (Height 1) during the initial hours of irrigation. The lesser amount of recovery obtained at the

first height can be explained by the fact that the leaching time was less than at the others levels, resulting in

less dissolution of the nitrate at the lower level. This is shown by the lower levels of nitrate in the leached

residues in Table 4.

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The concept of the kinetic as mentioned above is more clearly demonstrated by analysis of the

magnesium results (Figure 6). That is, solution of the magnesium was more rapid in the lower portion of the

column. Nevertheless, there was a difference between the magnitude of solution of the magnesium and that of

nitrate, as in the case of magnesium the recovery is greater at Height 1 although the irrigation time at this

height was less than in the others as shown in Table 4.

3.2 Leaching recovery as a function of irrigation ratio.

A more detailed analysis of the behavior of the recovery of nitrate and magnesium is obtained when it is

observed as a function of irrigation ratio, which is defined as the volume of leaching solution added per ton of

mineral initially placed in the leaching system. The irrigation ratios obtained in the test were less at Heights 2

and 3, since they represented double and triple the mass that contained at Height 1.

The term irrigation ratio is widely used in the mining industry instead of leaching time, since the

operational conditions may vary and the leaching time may be a variable, which is difficult to quantify. In

contrast, the volume of leaching solvent is easily quantified.

With respect to the recovery of nitrate as a function of irrigation ratio, it can be noted that at the greatest

height, the kinetic begins slowly until reaching an irrigation ratio near 0,3 m3/ton, then beginning to accelerate

until reaching and exceeding the kinetic curves of Heights 2 and 3. The contrary case is observed at the lowest

level (Height 1) which shows a rapid kinetic with the lowest irrigation ratios, but as these increase, the kinetic

slows, becoming practically constant for irrigation ratios greater than 1,2 m3/ton. As might be expected, in the

middle level (Height 2), there is intermediate behavior between the two extremes mentioned. Nevertheless,

the greatest recovery is obtained from the middle level, and this can be attributed to the fact that a sufficientirrigation ratio is not obtained at the greatest height (Height 3) for obtaining a greater nitrate recovery (Figure

7).

The behavior of the recovery of magnesium as a function of the irrigation ratio at the lowest level (Height

1) has the more rapid kinetic, which is subsequently reached by the kinetics of the other levels, although these

do not produce the same recovery as the first, since they never achieve an irrigation ratio of greater than 1.0

m3/ton.

The experimental data were fit to empirical expressions, finding that the following models provided

satisfactory fits for Heights 2 and 3:

( )b xaexperycov Re ⋅−−=1 (2)

For the lowest level (Height 1) the following form was obtained:

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( )c xb

xaerycov Re

+⋅

⋅= (3)

Where x is the irrigation ratio. The parameters of empirical expressions 2 and 3 are given in Table 5,

together with the coefficient of fit R2 and a standard error estimated for each of the fits.

3.2 Leaching model

Models have been found in the literature which have analyzed the heap leaching process, considering

unreacted.core model with generation of ash[3, 4]. Therefore those works have not included the variation of

particle size without generation of ash, with which is generated a decrease in the height of the bed as we wish

to demonstrate as follows.

We will consider that the column is cylindrical in section, and represents an element of volume within the

heap. This cylinder is then subdivided into Si sections, with the volume of each section represented by VS,i

equal to the volume of a cylinder, i.e. VS,i = A hi, where hi is the height of the cylindrical section and A

represents the transverse area of the bed. The length of the column L, can vary as the reaction proceeds as

will be seen below. Figure 9 shows the division of the column into sections which have an input flow of q0 to its

upper portion and output flow qL from its lower portion. Dissolution of one or various species occurs in each

section.

The model developed below considers the following assumptions:

1. A piston flow through the mineral bed is assumed, although due to the mathematical complexity of the

resolution, the model is represented by completely mixed reactors in series. In this way, for each

given height, sections are defined representing the completely mixed reactors which when summed

as a whole represent the piston flow.

2. It is assumed that the leaching solvent encounters mineral particles which are not mixed with

insoluble or other soluble species.

3. It is assumed that dissolution is for shrinking spherical particles, without the production of ash, so that

the particles progressively decrease in size, and with this there is a variation in the height of the bed,

which decreases with leaching of the material.

4. The porosity of the bed was considered constant, and the geometry of the mineral particles was

considered to be spherical.

5. The temperature for any effect was considered constant, that is, no consideration was given to salt

crystallization, changes in density, and kinetics of the dissolution resulting from temperature changes.

6. The size distribution of the mineral particles to be leached was not considered. A single mean particle

size was assumed.

Figure 10 shows a section which assumes the existence of spherical particles of gangue and soluble

species having the same initial radius. The section has a total volume of VS,i.

The sum of the volume at VG,i, of the species susceptible to leaching is :

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∑=

=J

j i j i G V V

1,,

(4)

And the volume of the solution in the interstices is Vi. The relation between volume Vi and VS,i is given by

the porosity ξi.

iS

ii

V

V

,

=ξ

(5)

or

i

J

1 j

i jiG

ii

VVV

V

++

=ξ

∑=

,,

(6)

It is assumed that the particles are spherical, and thus, the volume of each type of particle that will be

leached in the section of the column is:

3

i ji ji j r 3

4 NV

,,,

π=(7)

Where N j,i is the number of particles of species j contained in volume V j, whose particle radius is r j,i.

The porosity of the bed may change with time, in relation to change in the volume of the solution V i and

less species which are dissolved V j,i. This leads to an equation for the change of porosity over time:

+

++

−

++

=ξ ∑∑∑ =

==

J

1 j

i ji2

i

J

1 j

i jiG

ii

i

J

1 j

i jiG

i

dt

dV

dt

dV

VVV

V

dt

dV

VVV

1

dt

d ,

,,

,,

(8)

If we consider the porosity to remain constant, an expression can be obtained for the change in the

solution volume over time in relation to the change in volume of leached species.

∑∑∑

∑

=

==

=

++

+

++

+

=J

1 j

i j

i

J

1 j

i jiG

ii

i

J

1 j

i jiG

J

1 j

i jiG

dt

dV

VVV

V

dt

dV

VVV

VV

0,

,,,,

,, (9)

Returning to the definition of ξi, and knowing that:

dt

dr r N4

dt

dVi j2

i ji j

i j ,

,,

, π=(10)

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We obtain:

∑=ξ−

ξπ=

J

1 j

i j2

i ji j

i

ii

dt

dr r N

1

4

dt

dV,

,,

(11)

For convenience, it is taken into account that Vi = ξi A hi. Thus, in changing the volume of the solution, we

also change the height of the cylindrical section hi.

dt

dr r N

1

4

dt

dhA

i jJ

1 j

2

i ji j

i

i ,

,,∑=ξ−

π=

(12)

The variation in radius of leached particles is related to the supposition that these particles dissolve

without leaving ash, and their size becomes reduced radially. Simultaneously, the speed in reduction of themass of each particle is proportional to the surface area available for the dissolution and the difference in

concentration between the particle surface (saturation concentration, Csat j,i) and the concentration in the bed

(C j,i), following a solution mechanism shown in Figure 11 for a single particle. If we define the mass of a single

particle as follows:

3i ji j r

3

4,,

πρ(13)

With a constant particle density ρ j,i, the change in the mass of the particle is:

( )i ji j

2

i ji j

i j2

i ji j CCsatr 4k dt

dr r 4

,,,,

,

,,

−π−=ρπ (14)

Simplifying,

( )i ji ji j

i j

i jCCsatk

dt

dr ,,,

,

,

−−=ρ (15)

Where k j,i is a kinetic constant in m/h, Csat j,i is the saturation constant and C j,i is the concentration of

chemical species j in volume Vi. The negative sign implies that the mass is becoming smaller, and is

contributing to the volume of solution Vi.

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Based on the equations obtained, it is possible to conceive of each cylindrical section of the column as a

completely mixed reactor which functions in a quasi-steady state, due to the change in the volume of the

solution. For a section i, the material balance for each dissolved species can be written assuming the

controlling volume is the solution that carries away the dissolved species, thus having a positive sign for the

expression of the reaction speed. The material balance is as follows:

( ) ( ) i jii ji j2i ji ji j1i j1ii ji CqCCsatr k N4CqCV

dt

d,,,,,,,,

−−π+= −− (16)

In this equation, qi represents the flow of solution which exits the present section i, while q i–1 is that which

comes from the preceding section. The definitive expression remains in the following form:

( )i jii ji j

2

i ji ji j1i j1i

i j

iii

i ji CqCCsatr k N4Cqdt

dChA

dt

dhCA

,,,,,,,

,

,

−−π+=ξ+ξ −− (17)

The speed of percolation of the solution is different in each segment of the heap. This can be due to

compaction of the material which provokes greater resistance to the passage of the fluid. Thus the material

that reaches segment i is retarded prior to reaching this portion of the heap. The model can integrate this

delay in the following way:

( ) i j i i j i j i j i j i j i j

i j

i i i

i j i C qC Csat r k N t C t qdt

dC h A

dt

dhC A ,,,

2,,,1,

,, 4)()( −−+−−=+ − π τ τ ξ ξ (18)

In this last equation, q(t-τ) and C j,i – 1(t – τ) are qi and C j,i with a delay τi specific for each segment of thecolumn.

Since the variation in height depends on changes in the volume of the dissolved species, we must write

this same material balance for all the species susceptible to being dissolved.

We can determine the change in concentration C j,i, for the case of nitrate obtained from the experiments

carried out and from the model (Figura 12). The parameters which were input for resolution of the model were:

the dissolution kinetic constant 1.8·10-5 m/h; two sections for each height (i.e. the sum of the column divided

into six sections), the initial mineral particle size to be leached was 6.35·10-3 m, the feed flow to the columns

was 1.14·10-4 m3/h, the porosity of the bed was considered to be 0.2 and the lag times in sections 3 and 4

(representing Height 2) was 30 h each, and for sections 5 and 6 (representing Height 3) the lag times were 39

h each.

The results are shown in Figure 12. It can be noted that there was a delay in the decrease in nitrate

concentration at heights 2 and 3, representing 60 and 78 hours, respectively. This was due to the time taken

by the solution in percolating through the bed and completing irritation of the entire column. To this, we note

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that as the solution lowers through the bed it increases in concentration until reaching saturation, without

having extracted all the nitrate in the upper part of the column. The solution does not become saturated in the

first few centimeters of the column, although it does extract nitrate from the following (lower) portion of the

column. It should be noted that the results of the model fit well with the experimental data, which is attributable

to the fact that the nitrate closely follows the assumptions of the model. It is not possible to assume the same

with respect to the magnesium concentrations, since this species was found to be contained withinmineralogical species and as mentioned above they do not have the same solution kinetic and thus the model

is not well adapted to its experimental data.

When analyzing the specific case of the leaching of nitrate following the model, it is possible to verify the

decrease in height and radius of the particles resulting from this phenomenon. This is also verified

experimentally (Tables 2 and 4). Nevertheless the decrease in height resulting in this model does not prove to

be the same order of magnitude as in a real scenario since the former does not consider the solution of other

salts contained in the mineral which produce greater decreases in the height.

The model supposes that the extraction occurs as a function of the radius of the mineral particle, and due

to the difference in saturation concentration and solution in the interstices of the bed. The resolution of the

preceding is adjusted to the behavior of the solution contained within the bed, validating the proposed

supposition.

4. Conclusions

The tests of column leaching provide examples of a valid technique for the kinetic analysis of the leaching

process in heaps of soluble species. The variation carried out in the development of this study included divisionof the mineral bed into three different heights which was done in order to understand the variation in

concentration of the leaching solution at different heights in the column. It was possible then to evaluate and

adjust correlations which were convenient for recovery of the species, and establishing empirical kinetic

expressions for the behavior of nitrate and magnesium for each height.

The model developed was fit to experimentally obtained values for nitrate concentration, for the three bed

heights analyzed. It was possible to leave open the interpretation of the concentrations obtained by the model

for any height of the bed hi, but for resolving this it was necessary to carry out the fit by using the lag parameter

described for each section defined associated with each h i.

This study is the first approximation of modeling with variation in height, which could be complemented infuture studies by including the size distribution of the mineral loaded, variation in porosity in the column, and

the interactive effects of solution of one species on another.

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Acknowledgements

The authors wish to thank CONICYT for support through Fondecyt Project 1020892. Luis Cisternas thanks Mr.

Patricio Pinto Gallardo for his expert technical assistance in carrying out the leaching experiments.

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[5] Da Silva G., Relative importance of diffusion and reaction control during the bacterial and ferric sulphate

leaching of zinc sulphide. Hydrometallurgy, Vol 73, (2004), pp. 313-324.

[6] Liddell K.C., Shrinking core models in hydrometallurgy: What students are not being told about the pseudo-

steady approximation. Hydrometallurgy, Vol 79, (2005), pp. 62-68.

[7] Wisniak J, and Garcés I, The rise and fall of the salitre (sodium nitrate) industry, Indian Journal of Chemical

Technology 8 (5) (2001), pp 427-438

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Table 1

Results of chemical analyses of the Caliche mineral for column leaching in the present study in untreated form(RAW) and classified into particles >9.53 mm (CLASS.)

Element Unit Raw Class

I2 Insolubles

NaKCaMgClSO4 NO3 CO3 KClO4 MoistureIonic Balance

ppm%

%%%%%%%%%%

64754.94

9.360.992.100.784.60

14.9710.150.03< 0.12.23-0.39

50960.19

8.080.731.500.703.85

12.558.800.05<0.13.20-0.94

Table 2 Characteristics of leached modules.Height (modules) Column height,mm Mass of Caliche loaded, Kg.

1 910 27.20

2 1,820 54.40

3 2,730 81.60

Table 3

Results of chemical analyses on residue of leached Caliche mineral remaining in the leaching column.Element Unit Content

I2 InsolublesNaKCaMgClSO4 NO3 CO3 KClO4 MoistureIonic Balance

ppm%%%%%%%%%%%

3788.860.090.262.380.140.016.230.060.00<0.1

17.54-1.41

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Table 4

Results of column leaching tests and estimations of percentages of recovery as a function of residue assays.Residue

assays,%%, Recovery

HeightIrrigationtime, h

Irrigation Ratiom3/ton

Height of residue

mm

Mass of residue

kg NO3 Mg NO3 Mg1 250 1.36 600 17.39285 1.41 0.046 89.75 95.802 336 0.92 1.200 34.74247 0.60 0.058 95.65 94.683 420 0.76 1.800 52.14935 0.60 0.141 95.62 87.16

Table 5

Parameters for the kinetic fit of nitrate (NO3) and magnesium leaching of Caliche mineral in columns atdifferent heights.

Nitrate MagnesiumHeight 1

a b c R2 Error a b c R2 Error 1 105,848 1,000 0,233 0,987 2,2·10-2 1,000 0,008 0,003 0,993 2,0·10-2 2 4,412 1,272 - 0,995 1,9·10-2 3,006 1,203 - 0,999 6,0·10-3 3 7,274 2,000 - 0,973 5,1·10-2 2,692 1,259 - 0,998 1,1·10-2

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Figure 1. X- ray diffractogram for caliche mineral studied from the Antofagasta Region, Chile.

35-0652 (N) - Illite-montmorillonite - KAl4(Si,Al)8O10(OH)4·4H2O - Y: 6.25 % - d x by: 1. - WL: 1.5405

33-0311 (*) - Gypsum, syn - CaSO4·2H2O - Y: 4.17 % - d x by: 1. - WL: 1.54056 - Monoclinic - a 6.28

12-0420 (I) - Probertite - NaCaB5O7(OH)4·3H2O - Y: 4.17 % - d x by: 1. - WL: 1.54056 - Monoclinic -

21-0982 (*) - Polyhalite - K2Ca2Mg(SO4)4·2H2O - Y: 12.50 % - d x by: 1. - WL: 1.54056 - Triclinic - a

05-0586 (*) - Calcite, syn - CaCO3 - Y: 18.75 % - d x by: 1. - WL: 1.54056 - Hexagonal (Rh) - a 4.989

29-1241 (*) - Loeweite, syn - Na12Mg7(SO4)13·15H2O - Y: 10.42 % - d x by: 1. - WL: 1.54056 - Hexa

19-1187 (I) - Glauberite, syn - Na2Ca(SO4)2 - Y: 16.67 % - d x by: 1. - WL: 1.54056 - Monoclinic - a 1

37-1496 (*) - Anhydrite, syn - CaSO4 - Y: 14.58 % - d x by: 1. - WL: 1.54056 - Orthorhombic - a 6.993

46-1045 (*) - Quartz, syn - SiO2 - Y: 45.83 % - d x by: 1. - WL: 1.54056 - Hexagonal - a 4.91344 - b 4.

41-1481 (I) - Anorthite, sodian, disordered - (Ca,Na)(Si,Al)4O8 - Y: 37.50 % - d x by: 1. - WL: 1.54056

05-0628 (*) - Halite, syn - NaCl - Y: 58.33 % - d x by: 1. - WL: 1.54056 - Cubic - a 5 .6402 - b 5.64020

36-1474 (*) - Nitratine - NaNO3 - Y: 100.00 % - d x by: 1. - WL: 1. 54056 - Hexagonal (Rh) - a 5.0711 -

Operations: Fourier 8.200 x 1 | Background 1.000,1.000 | Import

Muestra M-R-1 - File: MR1.RAW - Type: 2Th/Th lock ed - Start: 3.000 ° - End: 7 0.000 ° - Step: 0.020 °

L i n

o u n t s

0

50

3 10 20 30 40 50 60 70

ure

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0%

10%

20%

30%

40%

50%60%

70%

80%

90%

100%

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28

Mesh (mm)

PSD

Experimiental

PSD Rosin Ramler

Figure 2. Experimentally obtained granulometric particle size distribution (PSD) of Caliche mineral of the

present study compared with the theoretical Rosin-Ramler distribution [4].

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Strong

solution

Water E-3

910 mmOre

Ore

Ore

910 mm

910 mm

Solution samples

Solution samples

Solution samples

Peristalticpump

Strong

solution

Water E-3

910 mmOre

Ore

Ore

910 mm

910 mm

Solution samples

Solution samples

Solution samples

Peristalticpump

Figure 3. Schematic diagram of equipment used in the experiment.

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33-0311 (*) - Gypsum, syn - CaSO4·2H2O - Y: 4.17 % - d x by: 1. - WL: 1.5406 - Monoclinic - a 6.284

06-0263 (I) - Muscovite-2M1 - KAl2(Si3Al)O10(OH,F)2 - Y: 33.33 % - d x by: 1. - WL: 1.5406 - Monocl

29-1241 (*) - Loeweite, syn - Na12Mg7(SO4)13·15H2O - Y: 29.17 % - d x by: 1. - WL: 1.5406 - Hexag

14-0164 (I) - Kaolinite-1A - Al2Si2O5(OH)4 - Y: 16.67 % - d x by : 1. - WL: 1.5406 - Triclinic - a 5.155 -

12-0420 (I) - Probertite - NaCaB5O7(OH)4·3H2O - Y: 20.83 % - d x by: 1. - WL: 1.5 406 - Monoclinic -

13-0135 (N) - Montmorillonite-15A - Ca0.2(Al,Mg)2Si4O10(OH)2·4H2O - Y: 25.00 % - d x by: 1. - WL :

77-0022 (C) - Mg-Vermiculite - (Mg2.36Fe.48Al.16)(Al1.28Si2.72)O10(OH)2(H2O)6Mg. - Y: 29.17 % -

05-0586 (*) - Calcite, syn - CaCO3 - Y: 35.42 % - d x by: 1. - WL: 1.5406 - Hexagonal (Rh) - a 4.989 -

31-0966 (*) - Orthoclase - KAlSi3O8 - Y: 12.50 % - d x b y: 1. - WL: 1.5406 - Monoclinic - a 8.556 - b 1

41-1481 (I) - Anorthite, sodian, disordered - (Ca,Na)(Si,Al)4O8 - Y: 66.67 % - d x by: 1. - W L: 1.5406 -

41-0224 (I) - Bassanite, syn - CaSO4·0.5H2O - Y: 75.00 % - d x by: 1. - WL: 1.5406 - Monoclinic - a 1

46-1045 (*) - Quartz, syn - SiO2 - Y: 100.00 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 4 .91344 - b 4.

Operations: Fourier 8.200 x 1 | Background 1.000,1.000 | Import

Muestra Compos - File: Valencia-1.raw - Type: 2Th/Th locked - Start: 3.000 ° - End: 70.000 ° - Step: 0

L i n ( C o u n t s )

0

5

10

15

20

25

30

35

40

3 10 20 30 40 50 60 70

Figure 4. X-ray diffractogram of the residue of the column-leached Caliche mineral.

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0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300 350 400 450

Irrigation Time, [Hour]

N O

3 R e c o v e r y

, [ % ]

Height 1

Height 2

Height 3

Figure 5. Percentage recovery of nitrate (NO3) from different heights in the column as a function of irrigationtime.

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0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300 350 400 450


M g R e c o v e r y ,

[ % ]

Height 1

Height 2

Height 3

Figure 6. Percentage recovery of magnesium (Mg) from the column at different heights as a function of irrigation time.

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0

10

20

30

40

50

60

70

80

90

100

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Irrigation Ratio, [m3/ton]

N O 3 ,

R e c o v

e r y [ % ]

Height1

Height 2

Height 3

Empirical Model

Figure 7. Experimental recovery of nitrate (NO3) and kinetic fit, as a function of irrigation ratio.

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0

10

20

30

40

50

60

70

80

90

100

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Irrigation Ratio, [m3/ton]

M g R e c o v e r y ,

[ % ]

Height 1

Height 2

Height 3

Empirical Model

Figure 8. Experimental recovery of magnesium (Mg) and kinetic fit, as a function of irrigation ratio.

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hi

hL-1

h 1

h 2

hL

Area transve rsal A

q0

qL

L

hi

hL-1

h 1

h 2

hL

Area transve rsal A

q0

qL

L

Area transve rsal A

q0

qL

L

Figure 9. Division of the leaching column into sections.

Transverse area, A

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hi

ξi

Ganga Especie 1

Especie 2VS,i = A hi

t = 0

r 1i

r 2i

hi

ξi

Ganga Especie 1

Especie 2VS,i = A hi

t = 0

r 1i

r 2i

Figure 10.a. Distribution of the material in acylindrical section of the column prior to initiation of leaching of species, t = 0.

hi

ξi

Ganga Especie 1

Especie 2VS,i= A hi

t ? 0

r 1i

r 2i

hi

ξi

Ganga Especie 1

Especie 2VS,i= A hi

t ? 0

r 1i

r 2i

Figure 10.b Distribution of material in a cylindricalsection of the column after a time period during whichleaching of species has begun, t ≠ 0.

≠ 0Insoluble

Soluble 2

Soluble 1 Insoluble Soluble 1

Soluble 2

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Figure 11. Transient balance of material of a particle in being dissolved.

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0

50

100

150

200

250

300

0 50 100 150 200 250 300 350 400 450


N O 3

C o n c e n t r a t i o n [ g r a m p e r l i t r e ]

Leaching Model

Height 1

Height 2

Height 3

Figure 12. Results from the variable height model showing the experimental concentrations of nitrate (NO3) for

the three heights analyzed.

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Antofagasta (Chile), April 9, 2007

D.M. Muir Editor Hydrometallurgy

Dear Dr. Muir

Please find enclosed the work “Caliche Heap Leaching”, which I want you consider for publication in Hydrometallurgy.

Sincerely yours

Luis Cisternas, PhDFacultad de IngenieríaUniversity of AntofagastaCasilla 170Antofagasta- Chile

e-mail: [email protected]

ver Letter

hydrom-s-07-00123[1]

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