RU2796344C1 - Method for processing polymetallic sulphide materials of non-ferrous metals - Google Patents

Abstract

FIELD: hydrometallurgy.

SUBSTANCE: invention relates specifically to processing of polymetallic sulphide materials containing non-ferrous and precious metals. Polymetallic sulphide materials of non-ferrous metals are leached in a solution of nitric acid and nitrous gases are trapped. The leaching is carried out with catalysts, which are used as a pyrite concentrate and an aqueous solution of iron sulphate (III). The ratio of the total mass of pyrite and non-ferrous metal sulphides in polymetallic raw materials is (0.5-1):1, and the initial concentration of iron (III) ions in the leaching solution is 5-30 g/dm³.

EFFECT: reduction of consumption of nitric acid and increase of extraction of non-ferrous metals into the solution.

2 cl, 2 dwg

Description

The invention relates to hydrometallurgy, namely the processing of mineral and technogenic polymetallic sulfide raw materials containing non-ferrous and precious metals.

With the depletion of standard raw materials of non-ferrous metals, it becomes necessary to involve in the processing of poorer and more difficult to process ores and production waste. The deterioration in the quality of raw materials consists both in a decrease in the quantitative content of metals, and in an increase in the proportion of materials with fine dissemination of metal sulfides in each other and in minerals of waste rock. The latter determines the impossibility of obtaining high-quality monometallic concentrates (copper, zinc, lead, etc.). The obtained polymetallic concentrates are characterized by the presence of harmful impurities (arsenic, antimony, etc.), which complicate the processing of such raw materials by traditional pyrometallurgical processes.

Known pyrometallurgical methods for processing polymetallic sulfide concentrates [SU 996491 A1, RU 2191210 C2], which consists in their variable melting to obtain a matte. The main disadvantages of these methods are high energy consumption, a large amount of zinc-containing dust and the complexity of processing polymetallic matte.

Combined methods for processing polymetallic sulfide raw materials [RU 2607681 C1, WO 2012053614 A1] include successive pyro- and hydrometallurgical processes, the first of which are aimed at removing harmful volatile elements (for example, arsenic) from concentrates, converting valuable components into easily soluble forms in acids. However, the use of pyrometallurgical processes is accompanied by the formation of sparingly soluble compounds (ferrites, non-ferrous metal silicates), the formation of sulfur dioxide and arsenic-containing dusts, which requires the use of expensive and complex equipment for their capture and processing.

Hydrometallurgical methods for processing polymetallic sulfide raw materials are quite diverse. A known method of leaching finely divided sulfide raw materials [RU 2339708] in a solution of sulfuric acid at 20-95°C. To intensify the process, an oxidizing agent is added to the pulp - ferric salts, hydrogen peroxide and ozone, and ultrasonic treatment is used. The main disadvantage of this method is the long duration of the leaching process (at least 3-8 hours) and the unsatisfactory degree of extraction.

Autoclave technologies make it possible to intensify leaching processes and reduce their duration to 1-2 hours. For example, the method [US4084961A] describes the autoclave sulfuric acid leaching of a sulfide concentrate in sulfuric acid solutions with the addition of nitric acid as a catalyst for sulfide decomposition processes. Under autoclave conditions, nitric acid can be regenerated from the resulting NO. The use of this method is accompanied by the formation of elemental sulfur, which can lead to a decrease in the rate of dissolution of sulfides due to blocking their surface with a sulfur film. The subsequent recovery of precious metals by cyanidation from undissolved leach residues will be complicated by the increased consumption of reagents and low extraction of precious metals due to the presence of elemental sulfur on the surface of the particles.

The use of nitric acid and nitrate solutions in the leaching of non-ferrous metal sulfides is characterized by high values of the oxidizing potential, which distinguishes this option from the more common sulfuric and hydrochloric acid reagents.

For example, a number of methods suggest the direct dissolution of sulfide materials in nitric acid solutions with purging the pulp with oxygen [CA 1117772 A] or nitrogen oxides (NO ₂ , N ₂ O ₄ , N ₂ O ₃ ) [US 4647307 A], with the addition of iron nitrate [ SU 981413 A1], nitrite ions [SU1314692A1], and under pressure conditions [US 3793429 A]. As a result of using these methods, it is possible to transfer non-ferrous metals into solution with high efficiency, thereby ensuring the opening of precious metals. However, these methods require an increased concentration of nitric acid (not less than 100 g/l).

Closest to the claimed technical essence is a method of processing sulfide material containing non-ferrous metals, [CN 110724816 B], which includes the following stages:

(1) preparation of a slurry consisting of water and sulfide material with a ratio of liquid to solid (L : S) 10 : (4-6);

(2) adding nitric acid and leaching in a sealed reactor at a temperature of 20-80°C and a final pH of the solution of 0.5-4.0;

(3) recovery of nitric acid from nitrogen dioxide formed during the decomposition of sulfides, and returning it to the leaching stage.

For the regeneration of nitric acid, it is proposed to use an absorption column.

From the description of examples of implementation of the prototype method, it follows that the best results are achieved at F : T = 3 : 2, temperature 80°C, duration 35 min, final solution pH 1-2, at which the degree of decomposition of sulfide ore was 98.2%. The main disadvantage of the prototype is the high specific consumption of nitric acid.

Under optimal conditions, nitrogen oxides released from the reactor are captured in an absorption column and regenerated to produce 98.3% nitric acid. At the same time, a significant part of nitric acid (nitrate ion) is involved in the solvation of iron and other metals dissolved from the reaction mass. This share of the acid is withdrawn from circulation, lost irrevocably and regarded as a consumable part. Practice shows that, despite the installation of a regeneration system, the specific consumption of nitric acid is at least 0.7-1.5 kg (in terms of 100% HNO ₃ ) per 1 kg of polymetallic concentrate. This negative indicator increases with the desire to speed up the process using higher initial concentrations of nitric acid. In other words, at high process rates, the specific consumption of nitric acid increases despite the high degree of regeneration of nitrogen oxides with the production of circulating leaching solutions.

The technical problem to be solved by the proposed method is the high consumption of nitric acid in the leaching of sulfide ores and concentrates. The technical result consists in changing the reagent mode.

The technical result is achieved in a method for processing polymetallic sulfide raw materials based on treatment with nitric acid solutions and nitrous gas trapping. Unlike the prototype, the treatment with nitric acid solutions is carried out in the presence of a catalyst, which is used as a pyrite concentrate and a recycled solution of iron (III) sulfate, while the ratio of the total mass of pyrite and non-ferrous metal sulfides in polymetallic sulfide raw materials is (0.5-1) : 1, and the initial concentration of iron (III) ions in the leaching solution is 5-30 g/DM ³ . As an aqueous solution of iron (III) sulfate, a circulating solution obtained by processing a previous batch of pyrite concentrate and polymetallic sulfide raw materials is used, followed by trapping nitrous gases with this solution.

The process of leaching individual sulfide minerals in nitric acid solutions is somewhat different, for example, the dissolution of chalcopyrite (CuFeS ₂ ), covelline (CuS), chalcosine (Cu ₂ S) is accompanied by the formation of elemental sulfur, during the decomposition of pyrite (FeS ₂ ), sulfur is oxidized mainly to the sulfate ion . It is known that the reactivity (dissolution rate) of pyrite and chalcocite is higher than that of chalcopyrite and covelline, which is reflected in a significantly greater thermal effect of the process [Prater JD, Queneau PB, Hudson TJ Nitric acid route to processing copper concentrates // Society of Mining Engineers , AIME. 1973 Vol. 254 P. 117-254].

There is evidence that the joint dissolution of two sulfides leads to a noticeable acceleration of the process for one and a slowdown for the other mineral, which is associated with their electrode potentials. These galvanic interactions between sulfides are one of the most important electrochemical factors that governs the dissolution of sulfides in hydrometallurgical systems [Aziz A., Shafaei S.Z., Noaparast M., Karamoozian M. Galvanic Interaction between Chalcopyrite and Pyrite with Low Alloy and High Carbon Chromium Steel Ball // Journal of Chemistry. 2013. Vol. 2013. ID 817218].

The following series of sulfides has been established in order of increasing potential: ZnS < PbS < Cu ₂ S ≈ CuS < CuFeS ₂ < FeS ₂ [Lutsik, V.I. Kinetics of hydrolytic and oxidative dissolution of metal sulfides: monograph / V.I. Lutsik, A.E. Sobolev. Tver: TSTU, 2009. 140 p.]. The presented series makes it possible to predict the acceleration of the dissolution of some minerals and the deceleration of others: minerals with a large potential will accelerate the dissolution of minerals with a smaller one. For example, with the joint dissolution of chalcopyrite and pyrite in sulfuric acid media, the latter (pyrite potential 0.63 V) will act as a cathode and its decomposition will be inhibited, while the surface of chalcopyrite will be the anode in this system (potential 0.52 V) and dissolve at a faster rate than in the absence of pyrite [Mehta AP, Murr LE Fundamental studies of the contribution of galvanic interaction to acid-bacterial leaching of mixed metal sulfides // Hydrometallurgy. 1983 Vol. 9. No. 3. P. 235-256]. This principle is taken as a basis in the Galvanox process, where the leaching of sulfide raw materials of non-ferrous metals is carried out in sulfuric acid media with the addition of pyrite and oxygen [US7846233B2, US8795612B2]. It should be noted that no materials containing title data on the dissolution of sulfides in nitric acid in the presence of pyrite have been found.

The electrochemical mechanism of the oxidative dissolution of a mixture of sulfides during nitric acid leaching is described by the following electrode processes using pyrite and chalcopyrite as an example.

Reaction on cathode sulfide (pyrite):

Reaction on anodic sulfide (chalcopyrite):

According to this model, upon physical contact between pyrite and chalcopyrite mineral grains, the latter dissolves first.

Pyrite particles not in contact with chalcopyrite also undergo oxidation.

In accordance with the foregoing, pyrite, acting as a catalyst that accelerates the dissolution of chaclcopyrite, on the other hand, is a source of an additional amount of Fe (III) ions. Fe (III) ions act as an oxidizing agent and increase the rate of dissolution of non-ferrous metal sulfides. The interaction of chalcopyrite and ferric ions can be represented by the following reaction:

At a high initial concentration of nitric acid and the corresponding value of the redox potential (ORP), iron goes into solution mainly in the form of Fe ³⁺ cations. This is facilitated by secondary processes involving nitrogen oxides:

It is characteristic that at the final stages of the process, when the concentration of free acid and redox potential decreases, iron goes into solution in the form of Fe ²⁺ .

A film of elemental sulfur formed on the surface of chalcopyrite grains causes diffusion difficulties and slows down the rate of the process. It has been established that elemental sulfur in the system under discussion dissolves from the surface of the mineral due to additional oxidation with nitrogen dioxide (NO ₂ ):

This feature to a decisive extent determines the course of dissolution in the active mode, when the surface of sulfides is not passivated by films of elemental sulfur. In addition, gold particles in the undissolved residue are also more available for subsequent leaching.

Nitrogen oxides act as an oxidizing agent during the decomposition of zinc, iron sulfides, etc. Thus, with the introduction of pyrite into the composition of the reaction mass, the process as a whole is accelerated and the degree of targeted use of nitric acid for the processes of decomposition of sulfides and the conversion of elemental sulfur into sulfate increases.

During the process, and especially at the initial stage, nitrous gases are formed in excess, do not have time to be spent on secondary processes (reactions 5 and 6), are released from the reactor and are captured in the absorption column. Studies have established that if nitrous gases are captured with solutions containing Fe (II), then such capture proceeds faster and more completely.

An analysis of the totality of processes in the system under discussion shows that it is logical to use the spent solutions of the decomposition of sulfide concentrates containing Fe ₂ (SO ₄ ) ₃ salt in the processing of a new portion of concentrates, which will minimize the cost of additional reagents and make full use of the oxidizing ability of nitrogen dioxide.

The source of pyrite can be low-quality gold-bearing pyrite concentrates or pyrite enrichment tailings, in which the content of finely disseminated gold can reach 1-4 g/t. Autonomous processing of such relatively poor raw materials for the extraction of precious metals is not economically justified. Nitric acid leaching of the mixture will make it possible to jointly process sulfide raw materials of non-ferrous metals and pyrite concentrates, to separate non-ferrous metals from leaching solutions, and to direct undissolved residues to the extraction of precious metals by cyanidation.

When substantiating the recommended limits of distinguishing features, it should be noted that the positive effect of the presence of pyrite in the reaction mixture is observed only when the ratio of pyrite to non-ferrous metal sulfides is at least 0.5:1. A large proportion of low-quality pyrite in a mixture of more than 1:1 is not economically justified. With a relatively small mass of additionally recovered gold, the additional consumption of nitric acid does not pay off.

The recommended range of Fe (III) content in leaching solutions is also dictated by technological reasons. A positive effect on the dissolution rate is observed when the content of Fe (III) is more than 5 g/l; when the content is above 30 g/l, the specific consumption of nitric acid does not decrease. As a recycled source of Fe (III), it was proposed to use a part of previously obtained leaching solutions used as an absorbent for nitrous gases.

Thus, the set of distinctive features of the proposed method:

- adding pyrite concentrate during leaching in the ratio of pyrite - non-ferrous metal sulfides in polymetallic sulfide raw materials (0.5÷1): 1;

- the introduction of salts of Fe (III) in the leaching solution in the amount of 5-30 g/l;

- partial use of solutions in circulation

compared with the prototype provide a reduction in the specific consumption of nitric acid.

An example of the implementation of the proposed method are the results of the following experiments.

As an object of research, we used a sulfide polymetallic concentrate of the Uchalinsky deposit with a copper content of 18%, zinc 4.8%, arsenic 3%, lead 2%, iron 17% (of which 8% in pyrite), gold 5 g/t, silver 96 g/t, and pyrite concentrate with iron content 34%, gold 3 g/t. The natural ratio of pyrite to non-ferrous metal sulfides in the polymetallic concentrate was 0.3:1. These sulfide materials were preliminarily crushed, sieved, and a fraction of 74–100 µm was used in the experiments. Weighed portions of the polymetallic concentrate were pulped with water at L : T = 3 : 2, and the required amount of nitric acid was added. Catalysts were added to the resulting mixture in a given amount: a solution of iron (III) sulfate and pyrite tailings. During the leaching, the temperature of the pulp was maintained at 80° C. and pH at 1.0 by adding nitric acid while continuously monitoring the pH. The leaching time was 20 minutes. The pulp after leaching was filtered, the solutions were analyzed by atomic absorption spectrophotometry for the content of copper, zinc, lead, arsenic, and the degree of extraction of metals was estimated from the results of the analysis. The results of the nitric acid leaching are shown in FIG. 1.

Additionally, experiments were carried out in which part of the solutions of nitric acid leaching with the content of Fe (II) 25-30 g/l and Fe (III) up to 20 g/l was used to capture nitrous gases when processing new batches of a mixture of pyrite and polymetallic concentrates. The content of Fe (III) in the trapping solutions increased to 45 g/l, and part of this solution was used in the preparation of a leaching solution with a given concentration of Fe (III). If necessary, the iron sulfate reagent (III) was added. The solutions were used repeatedly. In these experiments, the mass ratio of pyrite to the mass of non-ferrous metal sulfides was 1:1. Other experimental conditions are similar to those used in the first series. The results of these experiments are shown in Fig. 2.

For comparison, experiments were carried out under the conditions of the method of the prototype, that is, without the use of the proposed catalysts.

A comparative analysis of technical solutions, including the method presented as a prototype, and the proposed invention, allows us to conclude that it is the totality of the claimed features that ensures the achievement of the required technical result. The implementation of the proposed method makes it possible to reduce the consumption of nitric acid by 1.8 times and, under comparable conditions, increase the degree of extraction of non-ferrous metals by 24-44%.

Claims (2)

1. A method for processing polymetallic sulfide raw materials of non-ferrous metals, including leaching of raw materials in a solution of nitric acid and trapping nitrous gases, characterized in that the leaching is carried out in the presence of catalysts, which are used as a pyrite concentrate and an aqueous solution of iron (III) sulfate, while the ratio the total mass of pyrite and non-ferrous metal sulfides in polymetallic raw materials is (0.5-1):1, and the initial concentration of iron (III) ions in the leaching solution is 5-30 g/dm ³ . 2. The method according to claim 1, characterized in that as a solution of iron (III) sulfate, a recycled solution is used, obtained by processing a previous batch of a mixture of pyrite concentrate and polymetallic sulfide raw materials, followed by trapping nitrous gases with this solution.

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