RU2342446C2 - Method of extraction of nonferrous and noble metals, mainly copper and gold, from sulfur waste - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention concerns hydrometallurgy of nonferrous and noble metals, mainly extraction of copper and gold from sulfur wastes which are wastes from sulfuric acid manufacturing, and can be used at dense, cuvet and percolation leaching. Method includes piling of sulfur wastes to antifilter basis, influence upon it of precipitations during its storage, collection of underspoil acid water, its additional if necessary acidation by sulfuric acid and copper leaching at values of pH and Eh of productional solutions 2.0-2.5 and 500-540 mV respectively. After reduction of copper concentration less than 100 mg/l there are reduced content of oxidant and acid in leaching solution, thiocarbamide is introduced in it, noble metals are leached, and mainly it is gold. Extracted in solution copper and gold are isolated by cementation.

EFFECT: reduction of reagent unit discharge, expenditures of energy and increasing of copper and gold extraction ratio.

4 cl, 6 tbl, 6 ex

Description

The invention relates to hydrometallurgy of non-ferrous and noble metals, mainly copper and gold, from pyrite cinders, which are waste products of sulfuric acid production, and can be used in heap, cuvette and percolation leaching.

At present, neither in domestic nor in foreign practice of gold mining, there is an effective technology that allows to extract precious metals from pyrite cinder of sulfuric acid production.

Numerous publications are known on the extraction of non-ferrous and precious metals from pyrite cinders.

So, according to the work of Plaksin I.N. and Zyryanova M.N. Complex processing of lead-zinc raw materials. M., 1963, ed. USSR Academy of Sciences, p.78-79, the most common method of processing pyrite cinder is chlorine firing with sodium chloride and subsequent percolation leaching. For this purpose, the cinder is mixed with sodium chloride and subjected to firing. The calcining gases are contacted with water and a mixture of hydrochloric and sulfuric acid is obtained, which is used to leach a chlorinated cinder, while extracting copper, zinc, sodium sulfate and sodium chloride, processed by known precipitation and cementation methods.

To extract gold, the remaining iron cake is treated with chlorine water and gold is extracted from the solution by cementation.

In the same book (p. 81), another option is given for preparing pyrite cinders for percolation leaching using firing in the presence of sulfuric acid, after which water leaching of copper, zinc and iron that have passed into a soluble state is carried out. After cleaning the solution from these elements by neutralization in 2 stages, gold and silver are recovered by cyanidation.

The main disadvantages of the proposed methods are increased energy costs associated with firing, the use of toxic reagents - chlorine and cyanide, the complexity and multi-stage process of processing pyrite cinders and its increased environmental hazard.

Known Canadian patent No. 827063 from 11.11.69 "Method for the extraction of gold from pyrite cinders", according to which the pyrite cinders of chlorinating or sulfating firing are subjected to air oxidation in the presence of steam and the oxidized material is leached with an aqueous solution having an optimal concentration of chlorine. The disadvantages of the method are increased energy costs and environmental hazard when using chlorine.

In the book of M. Meretukov Metallurgy of precious metals. Foreign experience. M .: Metallurgy, 1991, p.222-223 describes a method of hydrolytic processing of pyrite cinders, developed at the University of Barcelona (Spain), according to which chlorine gas is introduced into the pulp of pyrite cinders at ordinary temperature and pressure, at pH 2.5- 3.0 precipitates soluble iron with lime, gold and silver are isolated from the clarified solution on iron scrap, and zinc is precipitated at pH 9.5.

The same book (p. 212) describes a method for leaching pyrite cinder, which is ground to -0.06 mm, treated with a solution of sulfuric acid 150 g / l at a temperature of 333K, and arsenic, copper, zinc and iron are extracted, and the cake is treated with thiocarbamide 40 g / l to dissolve gold and silver, using air as an oxidizing agent. Thiocarbamide consumption is 6.6 kg / t.

By A.S. No. 1486534 USSR, MKI C22B 19/24, 15/10, copper and zinc from a pyrite cinder are extracted with a water-ammonia solution in the presence of sulfur pyrite. However, noble metals are not recovered.

It is known to extract gold and silver from pyrite cinders with acid thiosulfate solutions followed by cementation of noble metals with zinc dust: t = 70 ° C, thiosulfate ion concentration of 10-30 g / l, pH 1.5-2.0, however, the method is difficult in large scale due to the decomposition of thiosulfate (Belyavsky MA The behavior of gold and silver in thiosulfate and sulfide environments in relation to the problem of cinder processing. Abstract on the degree of candidate of technical sciences. MISIS. M., 1988).

Known patent No. 1790230 SU, IPC ⁶ C22B 7/00 "Method for the integrated processing of pyrite cinders", according to which the pyrite cinder from firing sulfur pyrite is pulped with water and leached with weak solutions of sulfuric acid, while the pulp stream is divided into two parts. Sulfuric acid is dosed in the first part and leached for another 0.5 hours. The solution is separated from the cinder and non-ferrous metals are isolated from it, and the cinder is treated with hydrochloric acid solutions of thiocarbamide and noble metals are recovered.

The disadvantages of this method include the increased costs of sulfuric acid and thiocarbamide.

Closest to the technical nature of the proposed method is the "Method of complex processing of pyrite cinder" (patent No. 1669193 SU, IPC ⁷ C22B 3/44, 15/00, 19/00), according to which a solution is passed through three stages of leaching with water, dosed sulfuric acid to a pH of 1.8-2.0, blister copper is isolated by cementation on iron scrap with an oxidation-reduction potential (ORP) of 0 - (- 80) mV from the clarified solution, the precipitate is separated off, and the ORP value of the solution is increased to 600-700 mV and dose soda until pH 6.0 is reached, the precipitate and the they are heat treated to obtain an iron pigment; zinc carbonate is isolated from the clarified solution by precipitation with soda at pH 7.8, and the cinder is treated with hydrochloric acid solutions of thiocarbamide and noble metals are recovered.

The disadvantages of the prototype include the multi-stage process, the presence of operations of sludge solutions, increased consumption of thiocarbamide and insufficient environmental friendliness of the process.

The problem to which the invention is directed, is to develop a method for leaching copper and gold from pyrite cinders of sulfuric acid production.

The technical result of the proposed technical solution is to reduce the specific consumption of reagents, energy costs and increase the degree of extraction of copper and gold.

The technical result is achieved by the fact that in the method of leaching non-ferrous and noble metals from pyrite cinder, including the formation of an anti-filtration base, dumping on it a pyrite cinder dump, filing sulfuric acid solutions into the dump, leaching, extraction of non-ferrous metals and subsequent processing of cinder with an acid solution of thiocarbamide in the presence of an oxidizing agent , the formed pyrite cinder dump is exposed to precipitation during aging, which leads to the formation of sulfuric acid and ion ferric iron, acidic wastewater is collected and, with a pH in the range of 1.5-1.8, it is used to leach non-ferrous metals, mainly copper, or acid is added to the wastewater to these values, providing pH and Eh values of production solutions in the intervals 2.0-2.5 and 500-540 mV, respectively, copper is extracted from the resulting solution by cementation, aerated mother liquors are aerated and used to prepare the leaching solution, and after reaching a copper concentration of less than 100 mg / l, they reduce the oxidized content la and acids in the leach solution, thiocarbamide is introduced into it, noble metals, mainly gold, are leached at pH and Eh values determined by the stability region of the gold-containing thiocarbamide complex and the minimum value necessary to retain gold in the solution, respectively, and found experimentally, and produce gold by cementation. Fe ³⁺ ions are used as an oxidizing agent in thiocarbamide leaching, the concentration of thiocarbamide is maintained in the range of 0.2-0.5 g / l, substances selected from the range are used for the deposition of copper and gold: iron scrap, scrap, powder, cast iron ingots, sponge iron.

Also for cementation of gold can be used cement slurry from the stage of deposition of copper.

The proposed method is as follows. Pyrite cinders of sulfuric acid production containing readily soluble forms of ferrous iron compounds and sparingly soluble oxides of ferric and magnetite in an acidic medium are stored on a prepared antifiltration base and exposed to precipitation. The purpose of such exposure is the maximum transfer divalent iron compounds in oxyhydrates ferric due to their oxidation by atmospheric oxygen penetrating the blade together with precipitation, followed by their dissolution generated acidic solutions of sulfuric acid and using the Fe ³⁺ ions to dissolve additional non-oxidized copper sulfides contained in the feedstock.

The chemistry of the oxidation process that occurs in the cinder can be described by the following reaction equations:

When atmospheric precipitation infiltrates through the dump, the generated sulfuric acid reacts according to reaction (2) with cinder according to reaction (3) and the formed Fe ³⁺ sulfate is hydrolyzed when the pH of the solution reaches ≥ 3.0 with precipitation of Fe ³⁺ hydroxide:

in this case, the acid formed by reaction (5) is spent on the interaction with acid-soluble oxides of the cinder dump.

As the elaboration of the blade and the resulting acid acidification arising from under it water containing ions Fe ^2+, Fe ²⁺ is oxidized to Fe ^3+, which is accompanied by an increase in the values of Eh collected water and intensifies the process of dissolving the copper. Upon reaching the pH value of the collected water in the range of 1.5-1.8, they are used for leaching non-ferrous metals, mainly copper, while regulating the process so that the pH of the resulting production solutions is in the range of 2.0-2.5, which allows to transfer oxidized copper compounds into solution with minimal acid costs:

and when cementing copper, reduce the consumption of iron scrap for adverse reactions:

For additional transfer of copper sulfide compounds into the solution in production solutions, it is necessary to maintain the Eh value in the range of 500-540 mV.

This is achieved by the fact that the mother liquors after copper cementation, having a pH of 2.4-2.8 and containing Fe ²⁺ 2-4 g / l, are subjected to aeration, which leads to the oxidation of Fe ²⁺ in Fe ³⁺ and an increase in the value Eh to values of 600-650 mV, sufficient for the oxidation of sulfide copper compounds by the reaction:

Maintaining the value of Eh in the production solution in the range of 500-540 mV, provide copper recovery at the level of 86-88%. In the absence of atmospheric precipitation on the pyrite cinder dump, copper recovery does not exceed 80%.

In addition, at Eh values in the production solution of not more than 540 mV, the consumption of iron scrap also decreases and the reverse dissolution of the formed cement copper decreases:

If in the subsurface waters the pH values in the range of 1.6-1.8 do not reach, then they are additionally acidified to these values and sent for irrigation of the dump and leaching of copper.

Solutions after aeration are used to prepare the leach solution.

Obtained by leaching of cinder production solutions containing, g / l: Cu ²⁺ 0.6-1.2; Fe ³⁺ 0.5-1.0, sent to the cementation of copper with iron scrap:

Reaction (12) is accompanied by an increase in the content of iron ions to 2-4 g / l.

The extracted copper is captured in a cascade of sedimentation tanks, and cementation solutions are aerated and sent to the preparation of leaching solutions.

When the concentration of copper in the production solutions is less than 100 mg / l, the acid and oxidant content in the leach solution is reduced, thiocarbamide is added in an amount of 0.2-0.5 g / l and sent to gold leaching:

This range of thiocarbamide concentrations was chosen because, according to laboratory studies, at a concentration of thiocarbamide less than 0.2 g / l, the extraction and dissolution rate of gold sharply decrease, and at a concentration of more than 0.5 g / l, the unproductive consumption of thiocarbamide increases due to the formation of thiocarbamide complexes that have converted to a metal solution and its additional oxidation with Fe ³⁺ salts.

The restriction on the copper content in the solutions supplied to the gold leaching to less than 100 mg / L is caused by the fact that, during the thiocarbamide dissolution of noble metals, copper, when the concentration in the solution is more than 100 mg / L, forms an insoluble complex Cu [CS (NH ₂ ) ₂ ] ₃ SO ₄ , which leads to the loss of thiocarbamide and a decrease in the degree of extraction of gold from the cinder. In addition, increased concentrations of copper in the solution contribute to the destruction of thiocarbamide and the formation of gelatin-like compounds that can reduce gold recovery and degrade the filtering properties of the dump until the filtration is completely stopped.

Reducing the concentration of acid contributes to the precipitation of part of Fe ³⁺ to the precipitate to the minimum level sufficient for leaching gold, which reduces consumption and also the loss of gold in cementation operations.

In this case, the required pH of the solution is determined by the stability region of the thiocarbamide complex, and the value of Eh is determined by the minimum value necessary to retain gold in the solution.

In turn, the specific optimal pH and Eh values for gold leaching are established empirically, depending on the phase composition of the cinders and are determined by the temperature regime of oxidative firing of the initial sulfide-containing raw materials.

So, depending on the firing temperature of a sulfide-containing raw material, for example pyrite, in an oxidizing atmosphere, the following reaction products can be obtained:

As can be seen from the above reactions, depending on the temperature of the oxidative calcination, the reaction products can be salts and oxides of ferrous iron, oxides of ferric iron Fe ₂ O ₃ and oxides of mixed basicity Fe ₃ O ₄ , which requires different pH values and Eh solutions for gold leaching .

The final stage of gold leaching is its extraction from production solutions by cementation, which is carried out using substances selected from the range of: iron scrap, scrap, powder, iron ingots, sponge iron or cement sludge from the copper deposition stage.

The use of a separate scheme for the extraction of non-ferrous and precious metals from the heaps of pyrite cinders at the storage site allows you to extract up to 88% copper and up to 71% gold.

The inventive method is illustrated by the following examples.

The feasibility of processing pyrite cinder by atmospheric precipitation during the aging process is illustrated by example 1.

Example 1

Stale pyrite cinders and pyrite cinders of the current storage, containing,%: copper 0.1; zinc 0.4; iron oxide (III) 49.4; silica 8.4; total sulfur 3.2; gold 1.4 g / g, loaded into percolators, respectively, and aerated water simulating precipitation was passed through them in the infiltration mode to the value G: T = 1 at a stable water supply rate of 2 l / h m ² . The determined process indicators and their values are given in table 1.

As can be seen from the data in Table 1, all the pH and Eh indicators of the solutions obtained by leaching stale pyrite cinders by atmospheric precipitation are preferable to the leaching rates from cinders of current storage.

The feasibility of maintaining the pH in the range of 2.0-2.5 in solutions flowing from the dump, is illustrated in example 2.

Example 2

The stale pyrite cinders of the composition of Example 1 under similar conditions were treated with aerated water with the addition of sulfuric acid in quantities providing a pH of 1.5; 2.0; 2.5; 3.0 at the exit of the percolator. The analyzed indicators and determination results are given in table 2

table 2 Leaching of stale pyrite cinders with solutions of various acidity Analyzed Indicators Indicators at the exit of the percolator at pH values of the solution 1,5 2.0 2,5 3.0 Eh, mV 525 516 500 380

copper:

zinc:

Sulfuric acid consumption, kg / t twenty 15.1 14,4 12.3

As can be seen from the data in Table 2, lower concentrations of solutions at the outlet of the percolator correspond to higher concentrations of copper and zinc and their degree of extraction at higher values of acid consumption.

The most optimal option for pH values at the outlet of the percolator, allowing to obtain approximately the same extraction of copper and zinc compared to the interval of pH values of 1.5, is the interval of 2.0-2.5. Moreover, in the claimed range of pH values, the consumption of sulfuric acid is 25% lower than in the range of pH + 1.5. Similar results were obtained using collected acidic waste water as a leaching solution at a pH in the range of 1.5-1.8.

The feasibility of maintaining the values of the value of Eh in the production solutions flowing from the dump, more than 500 mV illustrates example 3.

Example 3

The stale pyrite cinders of the composition of Example 1 were treated with aerated water with sulfuric acid additives so that at the outlet of the percolator, the Eh value was 300, 400, 500, 600 mV, respectively. The analyzed indicators and determination results are given in table.3.

Table 3 The dependence of the degree of extraction of non-ferrous metals from stale pyrite cinders with acidic solutions with different Eh Analyzed Indicators Indicators at the exit of the percolator at the values of the solution Eh, mV 300 400 500 550 600 pH 2.0 2.0 2.0 2.0 2.0

copper

zinc

Acid consumption, kg / t 15.6 15.3 15.1 14.9 14.7

As can be seen from the data in Table 3, an increase in Eh in solutions leaving the percolator contributes to an increase in the degree of extraction of both copper and zinc. For copper, this dependence is more significant. At Eh values of more than 500 mV, the degree of copper recovery increases already slightly, i.e. the most optimal range of Eh is 500-550 mV.

The dependence of the filtration properties of the stockpiled pyrite cinder dump on the residual copper concentration in solutions during thiocarbamide gold leaching is illustrated in Example 4.

Example 4

The stale pyrite cinders of the composition of Example 1 were leached in percolators to a residual copper concentration in the solution of 10.0 mg / L and treated with acidic thiocarbamide solutions containing 25, 50, 100, 150 mg / L Cu ^2+, respectively, in the presence of Fe ³⁺ . The value of W: T when leaching gold 3.0. The analyzed parameters and determination results are presented in table 4.

Table 4 Dependence of the filtration properties of stale pyrite cinders on the concentration of copper in leaching solutions during thiocarbamide leaching Analyzed Indicators Thiocarbamide leach solution containing Cu ²⁺ , mg / l 25 fifty one hundred 150 The specific injectivity of leaching solutions, l / m ² .h 5,0 5,0 4.9 2.0 The content of Cu ²⁺ in solutions at the outlet of the percolator, mg / l 32,0 58.0 95.0 100.0

As can be seen from the data in Table 4, an increase in the concentration of copper in leach solutions over 100 mg / L leads to a decrease in the specific injectivity of the supply of leach solutions by 2.5 times with a simultaneous decrease in the concentration of copper in the solution, which is associated with the appearance of gelatin-like thiourea degradation products characterized by increased viscosity and reducing the filtration rate of the solution, and the formation of sparingly soluble copper compounds with thiocarbamide.

The feasibility of maintaining the concentration of thiocarbamide in the range of 0.2-0.5 g / l is illustrated in example 5.

Example 5

The stale pyrite cinders of the composition of Example 1 were processed in percolators to a residual copper content of 10.0 mg / L and gold was leached with acidic thiocarbamide solutions in the presence of Fe ³⁺ .

Thiocarbamide concentration 0.1; 02; 0.5; 0.6; 1.0 g / l, respectively. The value of W: T = 3.

The analyzed indicators and determination results are given in table.5

Table 5 Dependence of the degree of gold recovery and the specific consumption of thiocarbamide on the concentration of thiocarbamide in the leach solution Analyzed Indicators The concentration of thiocarbamide in the leach solution, g / l 0.1 0.2 0.5 0.6 1,0 Leaching solution: Eh 390 mV; pH 2.7 The degree of extraction of gold,% 14.2 65.7 70,4 71.0 71.1 The specific consumption of thiocarbamide, kg / g of gold 1.51 0.65 1,52 1.82 3.02

As can be seen from the data in Table 5, the optimal concentration range of thiocarbamide for cinder leaching is in the range of 0.2-0.5 g / l, while its specific consumption is 0.65-1.52 kg / g of gold. A further increase in the concentration of thiocarbamide, practically without increasing the degree of extraction of gold, leads to its significant consumption.

The possibility of leaching gold from pyrite cinders after extracting copper and zinc from them is illustrated in Example 6.

Example 6

The stale pyrite cinders and cinders of current storage after copper and zinc were extracted from them were treated with acidic thiocarbamide solutions in the presence and without of -Fe ₂ (SO ₄ ) ₃ oxidizing agent. The concentration of thiocarbamide is 0.56 g / l, the value of W: T = 3. The analyzed parameters and determination results are presented in table.6.

Table 6 Gold leaching from pyrite cinders Leach solution With Au, μg / L Recovery% Pyrite cinder current storage Leaching solution: thiocarbamide - 0.5 g / l; pH 2.0-2.5; 303.3 65,4 Eh 520 mV; Fe ₂ (SO _{4) 3} - 3.0 g / l Leaching solution: thiocarbamide - 0.5 g / l: pH 2.0-2.5; 12,2 2.6 Eh 310 mV Stale Pyrite Cinder Leaching solution: thiocarbamide - 0.5 g / l; pH 2.0-2.5; 328.5 7.04 Eh 520 mV; Fe ₂ (SO ₄ ) ₃ - 3.0 g / l Leaching solution: thiocarbamide - 0.5 g / l: pH 2.0-2.5; 105.7 22.6 Eh 180 mV

As can be seen from the data in Table 6, the presence of an oxidizing agent - Fe ³⁺ promotes the leaching of gold from pyrite cinders. The absence of Fe ³⁺ significantly reduces the concentration of gold in the solution, while the extraction of gold from the cinders is much higher than from the cinders of the current storage, which is associated with the conversion of compounds - Fe ³⁺ to Fe ³⁺ during storage and atmospheric precipitation on pyrite dumps cinder.

Thus, the above examples convincingly show the advantages of the proposed solution and the possibility of its practical implementation.

Claims (4)

1. The method of extraction of non-ferrous and noble metals, mainly copper and gold, from pyrite cinder, including leaching of non-ferrous metals, the selection of non-ferrous metals from the cinder with an acidic solution of thiocarbamide in the presence of an oxidizing agent, characterized in that before the leaching of non-ferrous metals they build an anti-filtration base, form a pile of pyrite cinder on it, collect the precipitate formed under the influence of atmospheric precipitation in the process of maturation of the dump to Isolate solutions containing sulfuric acid and ferric ions, and at a pH in the range of 1.5-1.8, use them to leach non-ferrous metals or add acid to the same pH values in the waste water, providing pH and Eh values of the production solutions in in the ranges of 2.0–2.5 and 500–540 mV, respectively, copper cementation is precipitated from the obtained production solutions, the cementation liquors are aerated, and after the concentration of copper in the production solutions is less than 100 mg / l, the oxidizer and acid content in the leach are reduced In the solution, thiocarbamide is introduced into it, noble metals, mainly gold, are leached out at pH and Eh values determined by the stability region of the gold-containing thiocarbamide complex and the minimum value necessary to retain gold in the solution, respectively, and gold is isolated by cementation. 2. The method according to claim 1, characterized in that ferric ions are used as an oxidizing agent. 3. The method according to claim 1, characterized in that the concentration of thiocarbamide is maintained in the range of 0.2-0.5 g / L. 4. The method according to claim 1, characterized in that for the cementation of gold using a cement deposit from the stage of deposition of copper.