LU82183A1 - TREATMENT OF SULFUROUS MATERIALS TO RECOVER THE METALS CONTAINED - Google Patents

Description

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The present invention relates to a process for treating sulfurous materials containing gold and silver, with a view to recovering these metals.

Certain ores and certain metallurgical residues are known which contain gold and silver in a gangue of various sulphides, such as in particular the pyrites.

Precious metals are found there in various forms more or less easily accessible to leaching] Thus gold can be found partially trapped in the native state and silver is often present mainly in the form of Ag ^ S , part of which may exist in solid solution in PbS.

It is already known to extract precious metals from such starting materials, but the recovery yields obtained are rarely entirely satisfactory.

For certain ore deposits or for certain metallurgical residues, direct leaching using a cyanidation solution or an acidic thiourea solution can already give exploitable yields.

In the majority of cases, however, it turns out to be necessary to subject the sulfurous starting materials to a roasting operation intended to remove the labile sulfur, or even to oxidize the sulfides to oxides and SC ^.

The roasting of sulphides is commonly done either in two distinct stages, namely a roasting stage in a reducing medium (endothermic) and an oxidizing roasting stage (exothermic), or in a single stage of highly exothermic oxidizing roasting.

Until now, roasting of sulfurous materials such as pyrites has always been carried out in industrial practice at high temperatures. The roasting temperatures depend on the type of appliance used: deck oven, rotary oven or fluid bed oven. These temperatures are between 700 and 1000 ° C.

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The main reason for roasting at these temperatures is that in general higher roasting rates and lower residual sulfur contents are obtained when temperatures are higher.

The behavior of the different elements present in the sulfides depends on the roasting temperature. We know, in fact, that at lower temperatures we can more easily form sulfates.

“The general decomposition equation for these sulfates is as follows:

MeS04 -> MeO + S02 + 1/2 02- 'This equation depends on the temperature.

At around 700 ° C, for example, the formation of sulfate is observed for zinc and copper, while at higher temperatures (850 to 900 ° C) these sulfates are broken down into oxides.

Regarding iron, iron oxide is formed even at lower temperatures (500 ° C).

The characteristics of the iron oxide formed are however variable and depend on the temperatures and the duration of roasting.

If a roasted material is leached at temperatures below 650 ° C, in an acid medium, a partial dissolution of the iron present in these materials is observed.

Contrary to this generally accepted trend, applicants have now unexpectedly discovered that the recovery efficiency of precious metals from sulfurous materials can be considerably improved, by roasting and leaching, if the roasting operation is carried out. at a lower temperature.

The present invention therefore relates to a process for the treatment of sulfurous, gold-bearing and silver-bearing materials, by roasting of these materials and by leaching of the roasting residues using cyanidation solutions oi: of thiourea acid solutions, in which performs the roasting operation at a temperature below 650 ° in order to improve the recovery of gold and silver.

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In the method according to the invention, this ·· ;, roasting operation can take place either in 2 stages, in which case the endothermic reducing operation can be carried out at usual temperatures - while the exothermic oxidizing step is carried out at a temperature below 650 ° C, or in a single exothermic step, the temperature being maintained below 650 ° C throughout the roasting operation.

The preferred conditions of the process according to the invention correspond to roasting temperatures of between 500 and 650 ° C., more particularly between 550 and 625 ° C.

According to a particularly advantageous embodiment of the invention, it is possible, after the roasting operation, to subject the material obtained to a prior leaching in a slightly acid medium in order to substantially remove therefrom the soluble iron oxides and the soluble sulfates.

Then the residue from this operation is subjected to a leaching operation using an acid thiourea solution.

In this embodiment of the invention, it is preferable to carry out the prior leaching operation, intended to remove the soluble iron, in the presence of a reducing agent. This reducer can in particular and preferably * be chosen from SO2 and magnetic pyrites, such.

than pyrrhotite.

A completely preferred embodiment of the invention consists in carrying out the following sequence of operations: roasting in one or two stages of the sulfurous, gold-bearing and silver-bearing material at a temperature between 500 and 650 ° C; - leaching of the roasting residue using a sulfuric acid solution in the presence of SO2? - Leaching of the residue thus obtained using an acid solution of thiourea.

'/. 4 Other particularities and details of the invention will appear during the following description of a few embodiments thereof, given purely by way of illustration.

Example 1.

A material containing Au 35 g / t, Fe 35.85%, S 29.5% is roasted in a reducing atmosphere for 2 hours at a temperature of 700 ° C.

It is then divided into several fractions which are roasted for 4 hours in an oxidizing atmosphere at different temperatures (500 ° Ci550eC, 600 ° C., 650 ° C and 700 ° c).

The different grilled products are then leached in a thiourea solution.

The operating conditions are as follows: dilution: 40 g of toasted product / liter of solution solution composition: water: 1 liter of thiourea: 20 g of pH 0.8 adjusted using sulfuric acid temperature: 60 ° C duration: 4 hours.

The leach residue is filtered and washed with half a liter of thiourea solution.

i Analysis and leaching yields of the different products! I t _ - 1 ~ ----- _

Temperature 500 ° C 550 ° C 600 ° C 650 ° C 700eC

toasting________

Fe Au Fe Au Fe Au Fe Au Fe Au% g / t% g / t% g / t% g / t% g / t toasted 48.75 49 51.70 51 52.35 52 52.80 52 53.1 53 residue of η 41 2 51.35 2.5 57.9 9.9 57.9 12 leaching '' residue weight üxiyia.tioii 0.32 0.535 0.685 0.875 0.9 grid.

setting yield 92.32 99.28 57.57 97.90 32.81 96.71 4.05 83.34 1.86 79.62 solution ί 15

Oïl notes that the yields of solution in gold are practically constant and close to ^ ... 100% between 500 and 600 ° C and that suddenly at 650 ° C

there is a decrease in yield of almost 15%.

Example 2.

HbSk The material, identical to that of Example No. 1, was

HrlÉP ^ 'roasted in a first test at 600 ° C for 4 hours and in a second test at 650 ° C for 4 hours also. ^ f§ / We got the following grilled products:

R ““ Temperature _600 ° C_650 ° C

R Fe 49.3% 51.3% R Au 48 g / t 50 g / t.

| S sulfate 1.28% 1.25% S sulfide 0.15% 0.15%

These two samples were leached in a thiourea solution.

The operating conditions are as follows: dilution 40 g of roasted product / liter of solution solution composition: water: 1 liter thiourea: 20 g pH: 0.8 adjusted by means of sulfuric acid temperature: 60 ° C duration: 4 hours.

The leach residue filtered and washed with half a liter of thiourea solution.

Final results

* Broiling temperature 600 ° C_650 ° C

residue weight of _ 0 723 0 917 grid weight U '/ Z3 °' 917 analyzes of the residue

Fe 52.5% 56.1%

At 2.8 g / t 11 g / t

Solution yields

Fe 23.01%. 0%

At 95.78% 79.83%

Claims (7)

2. Method according to claim 1, characterized in that the roasting operation takes place in two stages and that the exothermic oxidizing stage is carried out at a temperature below 650 ° C. 3. Method according to claim-1, characterized in that the roasting operation takes place in a single exothermic step, the temperature being maintained below 650 ° C throughout the roasting operation. 4. Method according to either of the preceding claims, characterized in that the roasting operation is carried out at a temperature between 500 and 625 ° C. 5. Method according to either of claims 1 to 3, characterized in that the roasting operation is carried out at a temperature between 575 and 625 ° C. 6. Method according to one or other of the preceding claims, characterized in that after the roasting operation, the residue is subjected to a prior leaching intended to substantially eliminate the soluble iron and the soluble sulfates formed during mesh below 650 and that the residue from this operation is then subjected to a leaching operation using an acid solution of thiourea. 7. Method according to claim 6, characterized in that the prior leaching operation intended to remove iron and soluble sulfates is carried out in the presence of a reducing agent. 8. Method according to claim 7, characterized in that the reducing agent used for the prior leaching operation is chosen from SO2 and magnetic pyrites such as pyrrhotite. QP-rneédë according to claim 1. characterized by ^ '»a \ 7 * - roasting in one or two stages of the sulfurous, gold-bearing and silver-bearing material at a temperature between 500 and 625 ° C; - leaching of the roasting residue using a sulfuric acid solution in the presence of SC> 2 # - leaching of the residue thus obtained using a thiourea acid solution. l ·