FR2631043A1 - PROCESS FOR LEACHING GOLD - Google Patents

Abstract

Disclosed is a process for the extraction of gold from gold-bearing solid materials using a dilute aqueous alkaline solution of an alkali metal cyanide which is brought into contact with solid materials containing gold. gold in the presence of a substance which produces oxygen in situ, contact being maintained until at least a portion of the gold goes into solution. The invention is characterized by the fact that an effective amount of a sparingly soluble divalent metal peroxide is used as the substance which generates oxygen in situ, calcium peroxide being most suitable for this purpose. The technique can be used for leach recovery from gold-bearing solids of all types such as crushed ores or waste materials.

Description

P-PFOEDE OF LIXrI-CN OF GOLD Case L 88/04 (117xp)

INTEX CHEMI S LI

  The present invention relates to the leaching of

  gold and more particularly the improvements

  in relation to the extraction of gold from

  gold-containing solids using lixic agents

aqueous alkaline solution.

  Traditionally, gold has been obtained in the native state using a pan. In different ores that

  contain gold, it is only present in one

  proportion distributed in the ore; Therefore,

  efficient gold extraction involves grinding the mine-

  to a very fine particle size such as a granulometry

  lower mesh size 100 mesh (150 P) and the leaching of

  particles in a stirring vessel with a solution

  aqueous alkali metal cyanide, particularly sodium cyanide, and this generally by blowing air or oxygen into the liquor. Grinding or crushing the ore to very fine grain size can be an expensive operation; he

  This has resulted in increased interest in the extractive industry.

  gold for processes that do not require extensive grinding operations. One consequence is that

  in recent years we have been interested in leachate

  gravity, which in principle is a simple and inexpensive operation that does not require complicated equipment and for which coarse grinding of solids is sufficient although finely ground materials can also be processed. As such, gravity leaching has been favorably considered by industries

  processing minerals for use in mines

  low grade or for waste products.

  In gravity leaching, a pile of solid materials containing the desired metal is formed on an impermeable base and the leachate solution is

  introduced on or near the top of the pile, generally

  by spraying or spilling. The solution of lixi-

  viation infiltrates the pile under the influence of

  and is brought to the base which is usually lightly

  properly inclined towards a point of

  the resulting loaded liquor is then treated

  by additional operations to separate and isolate

  ler the desired metal. The pile generally has the shape of a truncated cone or pyramid with a

  flat top surface and inclined edges; in practice

  This heap is generally several meters high and contains several hundred tons of solids, although the precise dimensions and shape depend on the type of metal extraction and are determined by

  partly by the physical constraints of the site.

  For gold gravity leaching from solid materials, it is obvious to use aqueous leaching solutions as leach solutions.

  alkaline cyanides because they have been successfully used

  in the lixiviation with stirring. However, the use

  the most effective solution of such a leachate solution.

  tion results from the presence of oxygen. The duration of

  your leaching agent in the pile is long, well

  it depends, among other parameters, obviously

  the size of the pile and the porosity of the

  of. The solubility of oxygen in such solutions

  cyanide is relatively low and

  the quantity present in solution at the time of introduction is rapidly consumed as the

  solution seeps into the pile. Therefore, the effectiveness

  leachate cited for gold mining is shrinking progressively

  depending on the increasing depth in the pile, while the risk of reprecipitation of gold is 3spas decreased. In addition, the possibility that the solution may retain its oxygen content until it has infiltrated through the gold-bearing mineral material in the pile decreases for increasing depths as a result of oxygen-consuming reactions with other ore constituents that occur in the course of

  road. In practice, the overall efficiency or speed of

  xiviation of gold in the pile is compromised. In con-

  sequence, the pile can be replaced while a proportion

  significant amount of gold that can be mined is still

  present, which is both wasteful and

  loses relatively high handling costs

subjects.

  It has already been considered to use hydrogen peroxide

  as an additive. In a paper by Norris, Brown and Caropreso entitled "The use of peroxygen chemicals in the heap of gold and silver leaching" (use

  of peroxygenated reagents in gravitational leaching

  of gold and silver ores) presented at the meeting

  SME-AIME in March 1983, this use is pro-

  in order to improve the speed and / or efficiency of

  metal leaching. However, the tests were done

  2D by the rolling bottle technique, in which the extraction conditions are inevitably significantly different from the gravitational leaching conditions. Therefore, at best, we can say that the recommendation

  was not properly proven. This topic has been clarified

  at a later meeting of SME-AIME in October 1983 in a paper presented by Smith and Craft, entitled "Pilot scale heap leaching at the Pinson Mine, Humboldt County, Nevada" (gravity leaching at the scale of a

  pilot at Pinson Mine, Humboldt County, Nevada). The

  know were done on piles of about 14 feet (4.27 m). The addition of hydrogen peroxide to the solution

  sodium cyanide at a content of 1200 ppm for a solution of

  The 35% solution is indicated as having no apparent effect on the degree of dissolution (i.e., gold) or on the rate of recovery. These tests confirm that

  the peroxide is only difficult to use in the

  xiviation by gravity of gold with heaps of usual dimensions. The present invention aims at providing means

  by which the total efficiency and / or speed of lixi-

  gold from solid materials containing gold can be improved and includes the provision of

  5. means to be used in processes of lixi-

gravity.

  According to the present invention, it is proposed

  assigned for the extraction of gold from solid

  containing it in which a dilute aqueous alkali solution of an alkali metal cyanide is brought into contact with solid materials containing gold in the presence of a substance which produces oxygen in situ,

  contact being maintained until at least one

  of the gold passes into solution, characterized in that an effective amount of a weakly soluble divalent metal peroxide

oxygen in situ.

  Advantageously, the divalent metal peroxide

  releases oxygen slowly into the lixic agent solution

  aqueous alkaline cyanide which results in either a

  more efficient release of oxygen at its point of con-

  summation, a maintenance in a simple and inexpensive way

  of continuous in situ production of oxygen for

  to grow or replace atmospheric oxygen without the need

  to use equipment or apparatus for regulating

  expensive to regulate the feed with another product such as highly soluble hydrogen peroxide. According to a particularly interesting aspect of

  The present invention provides a method for extracting

  gold from solid materials that contain it

  in which a dilute aqueous alkaline solution

  an alkali metal cyanide is introduced on the surface.

  the top face of a pile of said solid materials

  This solution infiltrates into the solid material, thus causing the passage of gold in solution after which the solution is collected, said process being improved by the incorporation into the pile consisting of said solid materials, an effective amount of 'a metal peroxide

  bivalent solid, poorly soluble.

  An effective amount is an amount that results in an increase in either the total amount of gold that can be extracted from solid materials, or the amount that can be extracted during a suitable leaching period, or both. in both cases the comparison is expressed with respect to a process which does not use such a quantity of metallic peroxide

  bivalent but which, on the other hand, takes place

identical operative procedures.

  The poorly soluble term used in the con-

  The text of peroxides shall be understood to apply to a peroxide that dissolves to a degree that is not significantly greater than the dissolution of the most soluble alkaline earth metal peroxide in water. C. Among these peroxides is the peroxide of

  magnesium, strontium peroxide, peroxide

  ryum, zinc peroxide and calcium peroxide among which calcium peroxide is preferred because of

  it is a combination of good

  cacity and an acceptable ecological character.

  The effectiveness of solid peroxides depends to some extent on how they are distributed

  in the mass of auriferous solids which undergoes leachate

  tion. As a result of the non-mobility characteristics of the solid particles in gravity leaching, it is particularly advantageous to distribute the divalent metal peroxides through the pile during its erection, and in particular to ensure that they are present in the body.

  part or the area of the heap that is farthest from the

  puts or sides of it. There are several ways

  to make such a distribution, the most practical

  to incorporate peroxide, most often under

  form of a dry solid, in the heap during his erection.

  This distribution may include a mixture of ore and peroxide particles or alternating layers of the two substances, the ore generally being the

  lower layer. In practice, distribution is like

  will probably be more a compromise between the two

  aforementioned types, areas rich in peroxide being

  in the solid ore that makes up the rest of the pile.

  In order to avoid any confusion, it should be mentioned that peroxides of low solids should not be incorporated into the pile as a dry solid but, on the contrary, they can be incorporated in the form of an aqueous sludge, either directly on the job or by

  agglomeration with at least a portion of gold solids

  res. In situ separation of mud water can occur easily if the ambient temperature is high during the erection time of the pile. While she is at

  the mobile state, the mud can penetrate into a certain

  underneath the remaining surface of the pile, which

  facilitates the distribution of the peroxide therein. We

  on the other hand, that a reasonably

  peroxide in the pile is potentially

  that and that irregularities may also be acceptable

  to a certain extent. It will be appreciated that the mobility of the particles in stirred or tank leaching means that the leaching agent and the ore particles are continuously mixed with one another.

  results in a distribution of all the solids in the

lange.

  Although the mechanism by which the presence of poorly soluble peroxide improves the extraction of gold is not fully understood, it is thought that the peroxide is decomposed slowly in situ, which releases into the pile of oxygen that can be absorbed by the solution or slowly dissolve in the liquor as

  that it passes on solid peroxide, which has the conse-

  that when the liquor subsequently enters into

  tact with the ore, it can either release oxygen at the point of leaching or otherwise take

part in cyanurization.

  It is possible that the two international mechanisms

  are coming. In any case, we will observe that the advantage

  results in providing a means of better

  oxidation conditions up to the core of the heap whose duration is longer, this means being able to have a duration

  comparable to the time that can be desired for leachate

  heap. Note also that in the process in question, there is at least qualitatively a degree of agreement between the type of process, a stable material of long duration and a rate of decomposition and / or dissolution of the chosen peroxides. By such a choice of peroxides, it is possible to maintain the advantage of

  improved conditions of extraction during a proportion

  substantially higher duration. leachate

  only when no peroxide of this type is used. Moreover, by the choice and the distribution of these peroxides, it is possible to obtain an increase which it has not been practically possible to achieve at

using soluble peroxides.

  During investigations of which the present invention

  resulted, using high columns of material

  simulating gravitational leaching conditions, it has been found that the increase in gold extracted over a given extraction time period varies with

  the proportion of peroxide used.

  It is often desirable to choose the quantity

  Added peroxide content in a range from 1 to 20 parts

  per 1000 parts (proportion by weight) of

  particularly, the choice can be made in a range of 2 to 10 parts per 1000 parts. Such areas are considered for low grade gold solids for which leaching operations

  by gravity are generally considered suitable.

  In these solids, the gold content is generally in a range of 1 to 10 ppm (weight ratio). We will note

  however, the use of higher ratios of

  oxide to gold solids is not ruled out for chemical considerations and could well be

  envisaged if extractions

  rapidly, especially if the circumstances

  justify the additional costs of such

  significant amounts of peroxide.

  The amount of peroxide that may be desired can be directly related to the gold content of the gold material. By expressing this quantity in

  parts of peroxide per 1000 parts of material

  gold ratio and the gold content in the conventional manner in ppm (also weight ratio), the ratio peroxide: gold is preferably selected in a range from 0.2: 1 to 4: 1 and in many cases 0.4 : 1 to 2: 1. Particularly effective results have been obtained for

a ratio of 0.5: 1 to 1.2: 1.

  A second factor of some importance,

  specifically in relation to the use of peroxide

  in a leaching process, compared to the factors of im-

  Similar lift in both peroxide-using processes and not using peroxide is the pH of

  the leach solution. It is preferable for reasons

  protect the environment from using a pH that is

  pH 9 and, from the point of view of effective use

  of the peroxide by the leach liquor, it is

  It is particularly desirable to choose the pH in a range of about pH 10 to about 12.5. This is the beach

  effective practice for the use of calcium peroxide

  and also for other peroxides.

  Various other factors associated with iixivia-

  are common to both peroxide and non-peroxide processes.

  processes using peroxide and can be useful

  chosen or controlled using the same criteria in the technique of the invention as in the corresponding prior art techniques which are free of peroxide,

  know those using atmospheric oxygen as oxy-

  ing. Such factors include important considerations

  such as the concentration of cyanide

  in the leaching agent, the leachate ratio to gold solids, the particle size of the gold-bearing solids, how to introduce the leaching agent into the heap, the flow rate of leachate in the heap, and

the operating temperature.

  The leach solution preferably contains

  sodium as the alkali metal. The cyanide concentration in the leachant is normally at least 0.005 mole / liter and generally is not greater than 0.2

  mol / liter. In many processes, this value corresponds to

  will lay at a concentration * of 0.01 to 0.1 mole / liter, for example when introduced into the heap. It will be noted that

  the effluent charged solution will have undergone a certain reduction

  free cyanide, for example by absorption or reac-

  as a result of its interaction with auriferous solids

  during the gold extraction operation, for example when passing through the pile. In practice, we observe

  a tendency for a correlation between the speed of extrac-

  of gold and the concentration of cyanide in the lixiviant agent. Therefore, the process operator will be able to choose whether he prefers a relatively high concentration and a faster recovery of gold but risking in

  this case of higher losses of the reagents or if it pre-

  - 20 use a comparatively low cyanide concentration

  lower, thus necessitating the need to

  to leach for a period of time

  longer to obtain a similar efficiency of

  gold than that resulting from higher concentrations. In either case, the inclusion of slowly dissolving peroxide, such as calcium peroxide, with gold solids increases the speed and / or

  or the efficiency of gold recovery.

  Because Group IB metals are generally

  the best catalysts for peroxide destruction of cyanide ions under aqueous alkaline conditions, generally at pH values of 10 or higher, one would have expected

  that the presence of added metal peroxide

  a significant and even excessive excess of cyanide from the leachate

  passage in. the pile of auriferous solids. In fact, we ob-

  serve a certain increase in cyanide losses but

  these losses are approximately in proportion to the increase

  the speed of extraction of gold and consequently

  The expected disadvantage does not arise when determining the consumption of reagents per unit of product production.

  Gravity leaching operations are

  generally open air and therefore are

  to a certain extent at the mercy of the climate. In the pre-

  In this invention, it is advantageous to use the lixi

  at a temperature of 0 to 45 C, which is generally observed

  in the mass of the pile even if the ambient air temperature fluctuates outside these limits, that is to say at similar operating temperatures corresponding to the simple use of atmospheric oxygen. Leaching

  stirring is often carried out in periods of

similar temperatures.

  A generally important complementary factor

  for the leaching of gold, that the present invention

  with peroxide-free processes consists of the

  particle size of auriferous solids. This factor is total-

  under the control of the process operator when seeking to optimize an increased rate of extraction of

  gold and possibly an increased total efficiency of

  gold's recovery resulting from what the solids are

  crushed or crushed to a finer granulometry in

  as an increased cost of performing such grinding or crushing operations, until reaching a point where the particles are too fine to effectively withstand gravity leaching. The practical equilibrium point is often achieved by grinding the product taken from the mine at a nominal value less than one digit in a range of about a diameter of 5 mm to about 25 mm, so that the major proportion of solid ( by weight) still has a diameter greater than 1 mm. Of course, even

  in the range of 5 to 25 mm nominal maximum, the particle size

  average number decreases in proportion to the maximum diameter

  average and therefore the speed and efficiency of gold extraction tend to increase. For some

  particles with a diameter of less than 1 mm and in particular

  bind less than 100 mesh (150 microns) lixiviation with stirring is better. If the process is envisaged for leaching by gravity fines, grinding rejections or the reprocessed material which has been previously ground into

  lixiviation with agitation and which has undergone

  inefficiently, it is preferable that the parties

  These agglomerates are agglomerated to reach the above-mentioned particle size, the known techniques including the use of

  lime as binder. The leaching rate of gold at

  shot of particles of any particle size is

  however, improved under otherwise

  by the use of an effective amount of a

  bivalent metal oxide dissolving slowly.

  In gravity leaching, the leaching agent is usually introduced by spraying it, usually continuously on top of the heap or forming depressions at the top of the heap which are periodically filled. It is customary for the feed rate of the leaching agent to be regulated so that the heap itself is not drowned but, on the contrary,

  leachate infiltrates the solids and / or their

  face. These speeds shall be determined for each ore or other material undergoing leaching,

  they depend on the physico-chemical characteristics

  of this material. The use of peroxide under otherwise identical conditions increases the extraction of

* gold and / or its speed, whatever the grain size.

  A simple way to estimate the types of materials

  The gold-bearing materials suitable for use in the process of the invention are the same types

  which would be suitable in the absence of slowly

  corn. Such materials may include quartzitic minerals and metal sulfides. In the case o

  the material is particularly acidic, it can be pre-

  treated with a neutralizing solution which is generally

  usually constituted by a diluted alkali and which for

  Cost reasons include or consist of lime.

  The slow-dissolving peroxides used in

  the invention may be produced off-site and incorporated

  in the process as in the heap in the form of

  formed or preformed solid particles. Alternatively,

  In a less expensive process, the peroxides are formed at the site by a reaction between the corresponding metal oxide or hydroxide and aqueous hydrogen peroxide using approximately equimolar ratios, the corresponding formulas being respectively: MO + H 2 O 2 = M02 + H20 or

M (OH) 2 + H 2 O 2 = M02 + 2H 2 O,

  in which M represents the metal. He is particularly

  the use of calcium as a metal in such a process, since lime is generally a more readily available and less expensive

  in remote places where gold ores are generally

  found. Such on-site production can be

  using a small continuous flow reactor

  naked by producing a mud that can be pumped directly-

  on the desired area of the pile during erection or premixed with some gold solids. This avoids the drying costs of the product that would otherwise be

  necessary. Of course, if you wish, you can use

  excess of oxide or metal hydroxide, so that

  maximizing the use of the more expensive reagent than

  titrates hydrogen peroxide. The resulting solid peroxide

  so that constitutes the product can therefore contain

  residual and unreacted metal hydroxide.

  The mud also contains water. When a diluent is present a correction (pro rata) must be made in the total weight of material containing the peroxide that is

  used to allow the dilution of the peroxide

  its weight ratio to gold solids

  and / or their gold content. Thus, for example if the sludge contains 28% by weight of calcium peroxide and it is desired to use 4 kg CaO per ton of ore containing 5 ppm gold, the appropriate amount of sludge is 16 kg per ton. The charged liquor, which is separated from gold-depleted solids, i.e. the liquors flowing from the base of the pile is collected to be subjected to a conventional gold recovery technique from a solution, such as passing through a carbon column or pulverizing with carbon or the older method of precipitation using

  zinc. The solution of cyanide depleted in gold, possibly

  after the additional purification steps, is available for recycling through the heap or into a tank, as the case may be, and of course in practice its alkalinity and cyanide concentration have been restored

  at the level desired by the operator for a fresh solution

  che. The advantage of the process of the invention is that it

  and to increase the extraction of gold from residual solids in leaching processes. Indeed-

  The advantage can be obtained in two ways. In a first way, the daily and / or total production

  from a fixed quantity of solid materials

  such as a pile can be increased and a second

  However, leaching can essentially be achieved by

  same daily and / or total production of gold in

  less favorable conditions, such as greater particle size

  (resulting in lower grinding costs) or

  lower cyanide concentrations.

  After the description in general terms of the

  vention, it will be expressed in a complementary manner

  and more in depth using the examples that follow.

  Examples 1 to 16 In these examples, those bearing the numbers 3, 4, 7, 8, 11, 12, 15 and 16 are executed according to the present invention while those bearing the numbers 1, 2, 5, 6,

  9, 10, 13 and 14 are given for comparison.

  All these examples are made by recycling a

  dilute alkaline solution of sodium cyanide at room temperature

  the laboratory environment in a consistent way through

  to a 2.5 m high column with an internal diameter of 0.1 m packed with approximately 30 kg of gold ore. When the peroxide dissolves

  slow, CaO2 has been used in all the examples identi-

  below, which are in accordance with the invention, the

  Particles of calcium peroxide were evenly distributed in the ore by mixing the two solids together in a rotary mixer. The agent

  leaching solution drips onto the top surface

  ore with a filter paper simulating a

  spray. The leaching was continued for one

  maximum of 28 days and the liquor has been analyzed

  periodically to determine the amount of gold that has been extracted from the ore. If the analysis indicates that the amount of gold is no longer increasing, the test has been stopped. The results given below are either the quantity at the end of the test

or after 28 days or earlier.

  A different combination of operational factors

  In each example, these variations in the composition of the lixiviant agent, the ore and its content are shown in Table 3. The ore is a pyritic ore containing approximately 5.7 ppm of gold and containing more than sphalerite, chalcopyrites,

  pitchblende and gangue materials, which

  an example corresponding reasonably to a mine-

rai Witwatersrand reef.

  The particle size distribution of the ore introduced

  in the column corresponded respectively to the

  are designated respectively by level '-' and '+' in Table 3. The sample of ore of level - is obtained

  by grinding coarsely the ore of level + (no-

  minal diameter -15 mm) at a nominal value of 5 mm in diameter.

Table 1

  Size of parts-% by weight of "-% by weight of" + "cules nominal mm 5mm nominal -15mm

+ 13.2 0 4

+ 9.5 - 13.2 6 28

+ 6.3 - 9.5 22 32

+ 3.35 - 6.3 16 17

+ 1.7 - 3.35 12 6

+ 0.85 - 1.7 5 3

+ 0.425 - 8 5 4

  - 0.425 Balance The five factors that are varied in these

  examples are the nominal pH of the leaching agent, the pre-

  the presence or absence of calcium peroxide, the concentration

  tion of cyanide, the flow rate of the lixi-

  and the particle size of the ore. The levels designated by - or + for ease of reference - are summarized

in Table 2.

Table 2

  Factor Effect Levels -w ^ _r At + "At pH 12 10 B CaOz / g / kg ore 0 3.75 C [CN-], mol / l 0.01 0.05 D flow rate ml / minute 1.6 10 E ore dimension, mm -5 -15

Table 3

  Example Factor Amount of gold Extraction N A B C D E extracted relative ppm

1 - - - - + 2.3 80

52 + - - - - 1.6 55

3 - + - - - 2.13 73

4 + + - - + 2.55 88

- - + - - 1.83 63

6 + - + - + 2.5 87

7 - + + - + 2.9 100

8 + + + - - 2.3 80

9 - - - + - 1.7 58

+ - - + + 2.2 76

11 - + - + + 2.58 89

12 + - + - 2.2 76

13 - - + + + 2.48 86

14 + - + + - 1.6 56

- + + + - 2,2 76

16 + + + + + 2.6 90

  Comparing the results shown in Table 3, it is possible to classify the effectiveness of the combinations of

  factors for the extraction of gold under simul-

  lixiviation by gravity and determine which factors are particularly beneficial. The relative quantities are included in the far right column to facilitate such comparisons. These results can be arranged, the first in the lead, as follows: 7; 16; 11; 4, 6, 13; 1 = 8; 10 = 12 = 15; 3; 5; 9; 14 and 2. Of the five factors, both factor B and E can be considered to be influential

  particular by determining the amount of gold extracted.

  This can be observed either from a detailed statistical study

  results to demonstrate the importance with which each of these variables is meaningful or

  more summary by a simple side-by-side comparison of

  different examples. The four best results are obtained when both B and E are at the "+" level and the four worst results - when both B and E

  are at the level "-". This demonstrates that factor B, the first

  the presence or absence of calcium peroxide is not only

  However, if the less pronounced effect of factor C is also taken into account, then the distribution effect of calcium peroxide in the ore during leaching has a greater significance index.

  high as the change in cyanide concentration, a

  which for an impartial person could be

  to be a particularly significant factor. The difference

  The difference between presence and absence can be estimated from the average of each set of eight outcomes. Those without calcium peroxide gave average gold extraction values of 2.03 ppm, that is, 70% of what was obtained with the best result, while those with calcium peroxide gave average values. higher, namely 2.44 ppm of gold that is to say 84% of what is obtained in the best result. The potential advantage of the addition of calcium peroxide is greater than what is actually demonstrated, in that the increase in gold extraction continues for many of these examples using peroxide

  calcium while for most examples do not use

  calcium peroxide, the increase in the ex-

  gold pulling was ending. As a result, the final difference between the two result sets could even be

higher.

  The results in Table 3 also indicate

  that pH variations in pH ranges from 10 to

  pH 12 of the lixivant agent do not change in a

  the amount of gold extracted and only when the peroxide

  Calcium was also present, very good extrac-

were obtained.

  The average amount of gold extracted in the 16 examples after 5 days was 1.77 ppm (+/- 0.006 ppm) and the calculated effect of calcium peroxide was + 0.356 pp +/- 0.012 ppm, so that in a confidence limit of 99.5%, his presence may be considered as

  a significant effect. Likewise, after 20 days, the quantity

  average gold extracted was 2.15 ppm +/- 0.03 ppm and the measured effect of the presence of calcium peroxide was + 0.42 ppm +/- 0.06 ppm so that with a 99% confidence limit, calcium peroxide pre-

feels a significant effect.

  Examples 17 to 19 In these examples which are all in agreement with

  the present invention, the apparatus and the method of

  previous examples have been repeated using

  a 50/50 mixture by weight of ore samples from -

  mm and -15mm at pH 12, at a flow rate of 10 ml / min and a cyanide concentration of 0.02 mol / liter. The amount of calcium peroxide used in Example 17 was 1.0 g / kg of ore, in Example 18. It was 1.5 g / kg of ore and in Example 19 it was 2, 5 g / kg of ore. In Example 17, calcium peroxide was regularly distributed in the lower half of the ore only while in Examples 18 and 19,

  it was distributed throughout the ore. The ex-

  gold traction was measured after 5 days for each of the examples and found to be intermediate in its

  effect of the absence of calcium peroxide in the

  ples 9/10 and the presence of 5 g / kg of calcium peroxide

  examples 11/12 with which a comparison

  can be done. The result in Example 17 was an increase in the extraction of 0.07 ppm gold, in Example 18 0.12 ppm gold and in Example 19 0.21 ppm gold . The result set indicates that the importance of increased gold extraction varies in correspondence with the increase in the relative amount of peroxide

calcium present.

  According to a variant of Example 19, after 30 days, an additional quantity of solid calcium peroxide, 10 g, was sprayed at the top of the column, which is equivalent to an additional amount of 0.3 g.

  kg of ore. The quantity of gold extracted undergoes an increase

  approximately 0.1 / 0.2 ppm compared to the expected level indicating that at least for a short time it is possible

  favorably the extraction of gold from a column in the

  what the level of calcium peroxide is exhausted.

  These examples demonstrate that when a solution of alkali metal cyanide is brought into contact with gold solids in the presence of poorly soluble alkaline earth metal peroxide, the extraction of gold from

the leaching agent is increased.

Claims (11)

  1. Process for extracting gold from   solid materials that contain it in which a solu-   dilute aqueous alkali metal cyanide is brought into contact with the solid materials containing   gold in the presence of a substance that produces oxy-   in situ gene, the contact being maintained until at least a portion of the gold goes into solution, characterized in that an effective amount of a low-soluble bivalent metal peroxide as a generating substance is used. oxygen in situ.   2. Method according to claim 1 characterized in that the dilute aqueous alkaline solution of alkali metal cyanide is introduced on the top surface.   of a pile of said solid materials, this solu-   infiltration into the solid material, thus causing the passage of gold in solution after which the solution is collected.   3. Method according to claim 1 or 2   in that the solution of alkali metal cyanide pre-   has a concentration of 0.005 to 0.2 mole / liter.   4. Process according to any one of the claims   tions characterized in that the cyanide of   alkali tal is sodium cyanide.   5. Process according to any one of the claims   tions characterized in that the cyanide of   alkali tal is used at a pH value of about pH 10 at about pH 12.   6. Process according to any one of the claims   tions characterized in that the quantity of   used metal oxide is chosen in a range of 1   at 20 parts per 1000 parts of gold weight portions).   7. Method according to claim 6 characterized in that the amount of metal peroxide is included   between 1 to 10 parts per 1000 parts of gold-bearing res (proportions by weight).   8. Process according to any one of   Claims 1 to 5 characterized in that the ratio of   a) the amount of metal peroxide per 1000 parts by weight of gold materials to b) the gold content of the material expressed in ppm (weight proportions) is selected in a range of 0.5: 1 to 1.2: 1.   9. Process according to any one of the claims   tions characterized in that the metal peroxide   The calcium used is calcium peroxide.   10. Process according to any one of the claims   tions characterized in that the metal peroxide   lique is incorporated in a pile consisting of   during the erection of this pile.   11. The method of claim 10   in that the metal peroxide is incorporated in said pile in the form of an aqueous sludge which has been produced in parallel by reaction between a hydrogen peroxide   aqueous solution and a corresponding metal oxide or hydro-   corresponding metal oxide or a salt which produces one of these.