RU2234544C1 - Method of reworking of auriferous arsenical ores and concentrates - Google Patents

Abstract

FIELD: hydrometallurgy; extraction of gold from auriferous arsenical ores and concentrates of different mineral composition.

SUBSTANCE: proposed method includes floatation concentration of starting raw material, bio-oxidation of concentrate, two-stage neutralization of products of bio-oxidation, sorption cyanidation and desorption of gold and silver. Floatation of ores and concentrates are performed in presence of 1-2 mg/l of cyanides; bio-oxidation is performed at two stages at temperature of 34-36 C, after which bio-oxidation product pulp is subjected to neutralization. Sorption cyanidation is performed in neutralized pulp of bio-oxidation products at concentration of cyanides of 400-500 mg/l. Neutralization of pulp of bio-oxidation products may be performed at first stage by means of carbonates from floatation concentration tailings. Part of pulp together with bacterium biomass from second stage of bio-oxidation may be returned to first stage.

EFFECT: enhanced economical efficiency of process.

5 cl, 1 dwg, 7 tbl

Description

The invention relates to the field of hydrometallurgy and is used to extract gold from the so-called refractory gold-arsenic ores and concentrates of various mineral composition, in which finely dispersed gold is contained in sulfide minerals and is not available for producing gold in a traditional industrial process using cyanides to dissolve it with subsequent extraction from solutions precipitation or sorption on coal or ion exchange resin.

In refractory ores, sulfide minerals are usually represented by pyrite (FeS ₂ ), pyrrhotite (FeS), arsenopyrite (FeAsS) and antimonite (Sb ₂ S ₃ ). They also often contain carbonaceous substances containing organic carbon, which is sorption-active with respect to the gold cyanide complex.

Fine and submicroscopic gold in ores is in close association mainly (sometimes almost completely) with arsenopyrite. The presence of finely divided gold in other sulfide minerals is often determined by the finely disseminated arsenopyrite or its intergrowths with these minerals.

Pyrometallurgical (firing, smelting) and hydrometallurgical (autoclave leaching, bacterial oxidation) methods are used to open finely dispersed gold from sulfide minerals in industry. Bacterial oxidation began to be applied later than other methods, but its advantages in comparison with other methods attract more and more attention to the use of this process for the extraction of gold from refractory gold-arsenic ores and concentrates. The advantages of sulphide biooxidation as a preliminary operation over sorption leaching of gold are its economic efficiency (low capital and operating costs) with a relatively high extraction of gold and silver, environmental safety without dust and gas emissions and the absence of environmental pollution with soluble compounds. The process does not require the involvement of highly qualified specialists and allows the use of traditional industrial equipment.

A known method for the extraction of precious metals from refractory gold-arsenic ores, including the stage of bacterial oxidation (biooxidation) and the subsequent dissolution of gold using chlorine, hypochlorites or thiourea (GB patent No. 2180829, 1987). There is also known a method of separating gold from arsenopyrite ores, involving the biooxidation of sulfides and cyanide leaching of gold (US patent No. 4822413, 1989). However, these methods are not economical enough, and the degree of gold recovery is not high enough.

Analogs of the present invention are technologies using the BIOX® processes (Dew, DW, et al. The BIOX® process for biooxidation of goldbearing ores or concentrates. Biomining: Theory, Microbes and Industrial processes, ed. DE Rawlings, Chapter 3. Berlin: Springer Verlag, 1997) and BacTech (Miller, PC The design and operating practice of bacterial oxidation plant using moderate thermophiles (the BacTech process). Biomining: Theory, Microbes and Industrial processes, ed. DE Rawlings, Chapter 4. Berlin: Springer- Verlag, 1997) for the biooxidation of sulfide concentrates obtained from the processing of refractory gold-arsenic ores. The processes are carried out using a complex of bacteria oxidizing sulfide gold-bearing minerals, sulfur and ferrous iron at temperatures of 40-45 ° С (BIOX®) and 45-50 ° С (BacTech).

A method of processing ores using these processes includes ore preparation, beneficiation (gravity with flotation or only flotation), biooxidation of the concentrate obtained, separation of bacterial solutions from solid biooxidation residues in which gold and silver are concentrated, neutralization of solutions in two stages using limestone in the first stage and lime in the second stage, sorption cyanidation of solid biooxidation products, desorption of metals and regeneration of the sorbent returned to the cyanide process Ia, electrolysis gold-containing solution - the eluate and precipitation of cathode melting to obtain an alloy of gold and silver - dore.

The main disadvantages of this method are:

- increased yield of refractory concentrates (up to 15% or more) directed to bacterial oxidation (even if there is a significant amount of practically non-ash bearing sulfide minerals in the initial ore, primarily pyrrhotite), which makes ore processing more expensive;

- increase in the process of biooxidation at 40-50 ° C sorption activity of carbonaceous substances present in concentrates;

- the presence of an expensive system of separation of solid from liquid in biooxidation products with the loss of gold in bacterial solutions in soluble form and with fine suspensions in the discharge of thickeners;

- cyanidation of solid biooxidation products at elevated NaCN concentrations (up to 0.1-0.15%), which leads to an increase in reagent consumption and the formation of thiocyanates (in the presence of a significant amount of unoxidized sulfides and elemental sulfur) with a decrease in gold sorption on the resin;

- consumption of sulfuric acid to maintain pulp pH in the optimal range during biooxidation of concentrates with a significant content of carbonates and pyrrhotite.

The technical result of the invention is to increase the efficiency of the processing of refractory gold-arsenic ores. A method of processing refractory gold-arsenic ores, the authors call the BIOS method (Fig. 1), involves flotation enrichment of the feedstock in the presence of 1-2 mg / l of cyanides, biooxidation of the concentrate in two stages at 34-36 ° C, two-stage neutralization of biooxidation products in the form pulps without preliminary separation of them into solid and liquid phases, sorption cyanidation of neutralization products at a cyanide concentration of 400-500 mg / l and desorption of gold and silver.

The presence of cyanides at the flotation stage allows to reduce the yield of concentrate directed to biooxidation and to improve its quality (if the ore contains a significant amount of practically non-ash-bearing pyrrhotite and the flotation cannot receive tailings dumped by the gold content). In the proposed biooxidation process, the sorption activity of carbonaceous substances with respect to the gold cyanide complex is reduced. In addition, the intensity of biooxidation can be increased by the rotation of the biomass of bacteria with pulp from the second stage of oxidation to the head of the process.

The enrichment of gold-arsenic ores includes gravity and flotation operations to produce a combined gravity-flotation concentrate that is sent to biooxidation to open finely dispersed gold enclosed in sulfides before it is extracted by sorption cyanidation. The methods of combined gravitational and flotation concentration are used in the presence in the ores of relatively large or film-coated gold oxides not recoverable by flotation. With a low content of such gold, ores are enriched only by flotation.

Gold-arsenic ores usually have a complex composition, and it is often almost impossible to obtain flotation tailings dumped by the gold content using gold dressing methods alone. Therefore, an additional operation of sorption cyanidation of flotation tailings is necessary to reduce the gold content in them to values that allow their discharge into the tailing dump. In this regard, there is the possibility of a slight increase in the gold content in the flotation tailings without a significant reduction in its extraction.

In gold-arsenic ores, gold is associated mainly with arsenopyrite, sometimes almost completely. Typically, iron sulfides — pyrite and pyrrhotite — present in these ores are depressed during flotation by CN ions ^— to a greater extent than arsenopyrite. In the BIOS method, this property of sulfides is used for the selective flotation of ores to produce a richer gold-arsenic sulfide concentrate. This allows to reduce the yield of concentrate sent to the biooxidation process, and to reduce the amount of acid-resistant equipment used with a corresponding reduction in capital costs and operating costs.

As can be seen from the data table. 1, with an increase in the concentration of NaCN in water to 2 mg / L, the yield of the concentrate decreases by 4.1% with an increase in the Au content in the concentrate by 10.5 g / t, and arsenic by 0.87%. In this case, the sulfur content in the concentrate decreases by 1.07% with a decrease in recovery by 32.7%. Extraction of As decreased by 3.5% in concentrate and in the solution of cyanidation of flotation tailings, and Au extraction decreased only by 1.1% with a decrease in sulfur recovery by 32.7%, which indicates a predominant suppression of pyrrhotite. Raising the concentration of NaCN to 5 mg / L reduces gold recovery by 28.4%.

A decrease in the sulfur content in the concentrate due to the passivation of pyrrhotite during flotation leads to a decrease or exclusion of the additional supply of sulfuric acid to the biooxidation process to maintain pulp pH in the optimal range for the growth and development of bacteria. A decrease in the content of sulfide sulfur in the concentrate, especially associated with pyrrhotite, reduces the content of elemental sulfur in the biooxidation products with a corresponding decrease in the consumption of NaCN during cyanidation of these products, as well as an improvement in the conditions of sorption of gold from the pulp.

Significant amounts of so-called soils are often found in refractory gold-bearing sulfide ores. carbonaceous substances (HC), which are sorption-active in relation to the gold cyanide complex Au (CN) $\genfrac{}{}{0ex}{}{\text{-}}{\text{2}}$ . This leads to significant losses of gold during its extraction by cyanidation of the oxidation products of gold-sulfide flotation concentrates, in which hydrocarbons are concentrated.

The sorption activity of hydrocarbons is different depending on their transformation under natural conditions in the deposits. When processing ores and concentrates in various ways, the sorption activity of hydrocarbons with respect to Au (CN) $\genfrac{}{}{0ex}{}{\text{-}}{\text{2}}$ usually rises. So, during firing, the specific sorption activity of hydrocarbons sharply increases: a residual content of more than 0.1% of organic carbon in the firing ends causes unacceptable losses of gold with cyanide tails. With alkaline or acid autoclave leaching of ores and concentrates, the sorption activity of hydrocarbons also increases sharply with a corresponding increase in gold losses during cyanidation of autoclave products. Ways to reduce the sorption activity of HC using various organic substances are ineffective or require unacceptably high costs of expensive and scarce reagents.

During bacterial oxidation of refractory carbonaceous sulfide concentrates by the BIOS method, the sorption activity of carbonaceous substances with respect to the gold cyanide complex sharply decreases. The degree of decrease in this activity depends on the conversion of hydrocarbons, which determines their initial sorption activity, the concentration and activity of bacterial biomass, as well as the duration of treatment of concentrates (Table 2).

The sorption activity of carbonaceous substances with respect to the gold cyanide complex during bacterial oxidation for 5-6 days is reduced by 93-100%, depending on the activity of carbonaceous substances in concentrates.

In contrast to the BIOS method, when processing carbonaceous gold-arsenic concentrate according to the BIOX® method, the sorption activity of hydrocarbons increases and the loss of gold with cyanide tails increases.

The decrease in the sorption activity of hydrocarbons during the biooxidation of sulfide gold-bearing concentrates by the BIOS method reduces the loss of gold with tails of sorption cyanidation of biooxidation products. This reduces the volume of the required one-time loading of the sorbent with a corresponding decrease in its consumption.

In alternative methods of biooxidation of gold sulfide concentrates - BIOX® and BacTech - the oxidation process is carried out at elevated temperatures.

In the BIOS method, the optimal temperature limit of the biooxidation process is 34-36 ° C. A relatively high activity of bacterial biomass is maintained at temperatures of 30-33 ° C. But at temperatures of 37–40 ° С that are higher than optimal, comparatively high values of bacterial biomass activity remain for 1-2 days of the process, then an unacceptable decrease in biomass activity occurs with a corresponding decrease in the oxidation rate of sulfide minerals (Table 3).

Pulp aeration in biooxidation reactors in conventional schemes is carried out using non-standard ring aerators made of stainless steel or plastic. A ring aerator is installed under the impeller of the mixer, and air from the holes along the perimeter of the aerator is supplied under the impeller blades. The disadvantages of this system are:

- weak dispersion of the air and, accordingly, its increased flow rate necessary to maintain the optimal concentration of oxygen in the pulp is not less than 3-4 mg / l;

- clogging of the ring aerator pipe with concentrate during long-term operation of the reactor, as well as during periods of reactor shutdowns or accidents with the corresponding need to unload the reactor and clean the aerator;

- increased formation of aerosols and increased evaporation from the surface of the pulp, especially when the aerator malfunctions with the formation of breakers on the pulp surface due to the uneven distribution of air in the aerator when it is partially filled with concentrate.

During biooxidation of the concentrate according to the BIOS method, tubular aerators made of plastic with a special coating are used for pulp aeration, which provide a high degree of air dispersion and prevent the concentrate from getting into the aerator tube, including during reactor shutdowns. These industrial aerators are used for aeration of wastewater. The use of aerators during biooxidation provides a reduction in air consumption when the required oxygen concentration in the pulp is reached - at least 2-3 mg / l. Tubular aerators are located under the blades of the impeller of the mixer.

The concentrate biooxidation process takes place in a continuous mode of bacterial cultivation with the concentrate pulp stream being fed into three parallel reactors in the first stage, followed by the combined biooxidation pulp stream being fed into 2, 3 or 4 successive reactors in the following stages.

To intensify the process of concentrate biooxidation and reduce or eliminate acid consumption (in the presence of significant amounts of acid-consuming minerals in the concentrate - carbonates, pyrrhotite, etc.), the pulp from the first second stage reactor to the first stage reactors is used by the BIOS method. The use of biooxidation for the circulation of pulp from the first reactor of the second stage is explained by the following factors:

- the remaining high activity in comparison with subsequent reactors of bacterial biomass in this reactor;

- a lower content in the pulp of this reactor of finely dispersed material, mainly in the form of secondary sediments from bacterial solutions;

- a lower concentration of organic metabolic products;

- a lower concentration of iron, arsenic and other toxic elements in the liquid phase of the pulp;

- lowering the pH of the pulp in this reactor to values of 1.4-1.6, which can significantly compensate for the flow of acid in the head reactors.

In addition, during the turnover of bacterial biomass in the head reactors, the influence of toxic components in the liquid and solid phases of the concentrate pulp decreases. At the beginning of the process, a highly toxic element such as trivalent arsenic passes from the concentrate to the solution. The concentrate pulp also contains flotation reagents and other chemical compounds that are toxic to bacteria. The use of pulp from the reactors of the third and further stages for turning to the head of the pulp process is impractical, despite the higher concentration of pulp acidity (pH 1.2-1.5). This is explained by a sharp decrease in the activity of bacterial biomass due to a high concentration of metals (primarily arsenic and iron) and other toxic components, metabolic products, a high content of finely divided secondary sediments, and a decrease in pulp pH.

The turnover of bacterial biomass in the BIOS method is used as necessary, depending on the acid intensity of the initial concentrate and, accordingly, the acid consumption, as well as the activity of the bacterial biomass in the first stage reactors. With high biomass activity in the pulp of the first stage, the use of a high-quality concentrate that meets the requirements of the conditions for the content of acid-consuming components, with the corresponding absence of the need for an additional supply of sulfuric acid to maintain pulp pH in the optimal range, eliminates the need for the circulation of bacterial biomass to the first stage of the biooxidation process.

When the bacterial biomass is turned into the head of the process up to 5% of the pulp volume per hour, the bacterial biomass activity in the pulp of the first stage of biooxidation increases with a corresponding increase in the rate of oxidation of sulfide minerals, which leads to an increase in the rate of formation of sulfuric acid and a decrease in pulp pH with an additional reduction or elimination of consumption supplied acid to maintain pH in the optimal range (table. 4). At the same time, the content of arsenic and sulfur concentrate in sulfide form in the biooxidation products decreases with a corresponding increase in the oxidation state of sulfide gold-bearing minerals.

According to the existing scheme (BIOX®, BacTech), the pulp from the bioreactors after achieving a sufficient degree of sulfide oxidation and opening of gold is directed to the operation of separating solid from liquid, carried out by countercurrent decantation in the cascade of thickeners. The liquid phase is neutralized in two stages: crushed limestone (in the first stage) and “milk of lime” (in the second stage), after which it is discharged into the tailing dump. The solid phase is also neutralized with "milk of lime", alkalized to the required pH values of the pulp and sent to sorption cyanide.

The disadvantages of this scheme to neutralize the components of the biooxidation pulp are:

- loss of gold with fine suspensions (unavoidable due to the high dispersion of the solid phase in the pulp of biooxidation of the concentrate), as well as in dissolved form in the liquid phase of the pulp - discharge of the thickener (up to 0.2-0.5 mg / l);

- capital costs for acid-resistant equipment, automation, as well as operating costs;

- high water consumption for countercurrent washing of solid biooxidation products in thickeners.

The neutralization of biooxidation products by the BIOS method is carried out without preliminary separation of the solid and liquid phases of the pulp. Neutralization is carried out in two stages: at the first stage, the supply of crushed (to a particle size of 85-90% class - 0.074 mm) limestone or part of the ore flotation tailings when they contain a significant amount of carbonates (up to 20-50%), at the second stage - milk of lime. " Pulp neutralization conditions in the first stage: pH 4.0-6.0; when using part of the final flotation tails, the ratio is solid: biooxidation product: flotation tails = 1: 1-5; the neutralization time with stirring of the pulp is 0.5-1.0 hours. In the second stage, the pH rises to 10.5–11.0 by feeding lime in the form of “milk of lime”, after which the pulp is sent for sorption cyanide.

Benefits of neutralizing biooxidation pulp without separation of solid and liquid phases:

- the exclusion of operating costs and capital costs for expensive acid-resistant equipment and automation;

- elimination of gold losses with bacterial solutions and with fine suspensions in the thickener discharge;

- the exclusion of fresh water consumption for countercurrent decantation equal to the volume of the liquid phase of the bacterial solution in the biooxidation pulp.

As can be seen from the data (Table 5), the yield of the product of neutralization of the entire pulp, directed to cyanidation, almost doubles with an increase in the consumption of limestone by 1.25 times and lime (100% CaO) by 1.14 times. The yield of the neutralized product increases due to the formation of a precipitate of iron-arsenic hydrate-sulfate compounds and, mainly, gypsum CaSO ₄ . When cyanidating precipitates obtained from purely bacterial solutions with a content of 0.8 g / t of gold, the NaCN consumption was only 0.2 kg / t (which corresponds to the flow rate during cyanidation of flotation tails) with a cyanide content of 0.18 g / t.

According to the usual scheme, the biooxidation product of the concentrate washed from the bacterial solution is cyanide. The main goal of separating bacterial solutions from solid biooxidation products, in which gold exposed during oxidation is concentrated, is to reduce the consumption of cyanides absorbed by the precipitation components obtained by neutralizing these solutions.

Solid biooxidation products contain significant amounts of secondary sediment formed during the oxidation of the concentrate, depending on the pH of the pulp and the concentrations of iron, arsenic and other elements. These products contain sulfur in elemental form (especially significant amounts - up to 7.5% with high content in pyrrhotite initial concentrate), which drastically increases the flow due to the formation of cyanide thiocyanates and deteriorating conditions gold sorption of pulp, since CNS ions ^- are gold desorbents from ion exchange resins. The presence in the biooxidation products of rhodanides and especially elemental sulfur, as well as the high gold content in these products (up to 100-200 g / t) force to increase the concentration of cyanide in the solution to 0.1-0.15% or more, which, in turn, increases the consumption of NaCN.

According to the BIOS method, cyanidation of neutralization products of the entire biooxidation pulp is carried out at a cyanide concentration of 400-500 mg / l (or less than 0.05%). At the same time, the NaCN consumption decreases more than 2 times with virtually no decrease in gold recovery, the conditions for gold sorption on the resin improve due to a sharp decrease in the concentration of rhodanides in the solution (Table 6). The consumption of NaCN during cyanidation of the products of neutralization of the entire pulp also decreases by at least 1.5 times with a decrease of more than 2 times the concentration of rhodanides in the solution.

When refractory refractory gold-arsenic ores are concentrated, containing finely dispersed and submicroscopic gold, contained partly in sulfides, partly in a free state and in splices, production under industrial conditions of tailings dumped in gold using gravity-flotation methods is problematic. Therefore, it is often necessary and advisable to cite flotation tailings, which allows to increase gold recovery and stabilize ore processing by reducing the dependence of the concentration conditions on the composition of the ore. At the same time, it becomes possible to reduce the yield and improve the quality of the concentrate directed to the biooxidation operation without reducing the through extraction of gold. It is advisable to conduct cyanidation of flotation tailings in conjunction with cyanidation tailings of neutralized concentrate biooxidation products. In this case, additional extraction of gold from the tails of cyanide neutralization products occurs, and the residual cyanide in the pulp is used when cyanidation of flotation tails.

According to the BIOS method, when processing refractory carbonated gold-arsenic ores, the products of concentrate biooxidation are neutralized by flotation tailings to pH 4.5-5.0 and sent to the first cyanidation stage, the remaining flotation tailings with a high gold content (0.7-1.2 g / t) cyanide in the second stage together with the cyanide tails in the first stage. The concentrate yield under this scheme is reduced to 3.5% instead of 5% according to the scheme with processing of concentrate only, and the through gold recovery increases to 95% (Table 7). At a concentration of 0.04% NaCN in the first stage, its consumption decreases to 7.8 kg / t instead of 18.44 kg / t of neutralized biooxidation products at a 0.1% NaCN concentration (0.27 and 0.64 kg / t of ore, respectively ) The total consumption of 0.04% NaCN is only 0.53 kg / t of ore and 0.92 kg / t of ore at a 0.1% NaCN concentration.

Claims (5)

1. A method of processing refractory gold-arsenic ores and concentrates, including flotation enrichment of the feedstock, biooxidation of the concentrate obtained, two-stage neutralization of the products of biooxidation, sorption cyanide neutralization products and desorption of gold and silver, characterized in that the flotation enrichment of the feedstock is carried out in the presence of 1-2 mg / l of cyanides, biooxidation is carried out in two stages at a temperature of 34-36 ° С, biooxidation products are subjected to two-stage neutralization in the form of pulp without preliminaries their separation into solid and liquid phases, and sorption cyanidation is carried out at a cyanide concentration of 400-500 mg / L. 2. The method according to claim 1, characterized in that before the flotation concentration of the feedstock, gravity concentration is carried out. 3. The method according to claim 1, characterized in that the neutralization of the pulp of the biooxidation products in the first stage is carried out by carbonates from the flotation tailings. 4. The method according to claim 1, characterized in that the pulp from the stage of sorption cyanide is separated from the sorbent and sent for additional sorption cyanide together with the flotation tailings, while the desorption of gold and silver from the sorbents of both stages is carried out together. 5. The method according to claim 1, characterized in that part of the pulp with the biomass of bacteria from the second stage of biooxidation is returned to the first stage of biooxidation.

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