Hydrometallurgical method for extracting precious metals from refractory sulfide ore. Download the book "Analytical chemistry of sulfur" (1.9Mb) Dissolution of pyrite in nitric acid

Research on the development of a new hydrometallurgical technology using nitrate leaching of the original “gold head” and subsequent smelting of the resulting cake was carried out on two samples of rich gravity gold-containing concentrate (“gold head”) from the Kholbinsky mine of JSC Buryatzoloto.

As a result of the research, it was proposed for Buryatzoloto OJSC to carry out work on testing and introducing the technology for processing the “golden head” with nitrate leaching. The introduction of this technology will eliminate the labor-intensive operations of roasting and smelting pigs, eliminate the release of toxic gases, reduce losses of precious metals (by 2-3%) and reduce the cost of processing the “golden head” by half.

In the process of processing gold-containing ores at gold recovery factories (GRPs) in the gravity enrichment cycle, a rich gold-containing concentrate is obtained, the so-called “gold head” (hereinafter referred to as GG), into which up to 50% of gold and silver can be extracted. Depending on the composition of the processed initial ore, this gravity concentrate contains the following minerals: sulfides (pyrite, arsenopyrite, galena, sphalerite, etc.), technogenic scrap (metallic iron, lead, copper) and oxides of iron, silicon, aluminum - up to 50% . The mass fraction of gold in GL, as a rule, is 1-10%. This concentrate is very resistant to cyanidation, since gold is relatively large and is in close association with sulfides and quartz. In order to reduce losses in the process of extracting precious metals, products with large and refractory gold begin to be isolated at the grinding stage and at the first stage of gravity enrichment of gold ore, then after gravity finishing they are processed in a separate technological cycle.

Currently, for the processing of carbon dioxide, a technology is used, the main operation of which is the oxidative roasting of the concentrate at a temperature of 500-700 ° C. Next, the resulting cinder is melted into a lead alloy (werkblei) and cupellated also at a high temperature (850-900 ° C). Sometimes the cinder (with a small amount of non-ferrous metals) is directly melted into a gold-silver alloy. In general, the technology using the roasting operation is characterized by high labor intensity, the release of toxic gases of sulfur, arsenic and lead, and the production of a significant amount of gold-containing industrial products (dust, slag, waste drops), from which additional gold must be extracted. All this leads to noticeable technological and mechanical losses of precious metals.

For the processing of rich gravity-resistant gold-containing concentrates, acid technology is promising, according to which the initial concentrate (OC) is treated with a solution of nitric acid, and the solid sediment (cake) is melted. This technology makes it possible to eliminate the labor-intensive firing operation, prevent the release of toxic gases and reduce losses of precious metals.

Using acid technology, studies were carried out on two samples of the “gold head” of the Kholbinsky mine of Buryatzoloto OJSC.

A characteristic feature of the GR samples is the predominance of sulfides in them and the presence of technogenic scrap, which is iron-copper - with a predominant amount of copper. In sample No. 1, the mass fraction of sulfides was more than 60%, including 35% galena. In sample No. 2, pyrite predominates - more than 80%, galena - 6.0%. The mass fractions of gold and silver in sample No. 1 are 14.52% and 3.76%, respectively; in sample No. 2 - 4.34% and 1.36%.

Such a gravitational concentrate with a rather complex mineral composition and the presence of technogenic scrap is characterized by increased persistence, therefore the existing technology for processing carbon dioxide at the enterprise includes three labor-intensive operations: roasting at 700-900 ° C (for 6 hours), smelting in an ore-thermal furnace using Werkblei and cupellation . Direct extraction of noble metals into the alloy does not exceed 96%. The resulting middling products (solid gas purification product, slag, broken bricks from the furnace and broken scraps from droplets) are returned to the feedstock processing technology (usually for grinding before cyanidation). The degree of extraction of precious metals from these middlings has not been determined.

The technological scheme for processing carbon dioxide using nitrate leaching is shown in Fig.

Nitric acid is a strong oxidizing agent and, when interacting with sulfides, forms water-soluble compounds. The exception is galena, which decomposes to form insoluble lead sulfate. Technogenic scrap, represented mainly by iron and copper, completely goes into solution. After nitrate leaching (NAL) of GL, a solution containing most of the impurities and a solid product are obtained, in which noble metals, insoluble oxides (mainly oxides of silicon and iron) and lead sulfate (lead in oxidized form) are concentrated. The resulting solid product (cake) is separated from the solution, dried and melted to produce a gold-silver alloy.

As a result of leaching, a certain amount of silver (10%) may enter the solution. To extract it, after separating the cake, table salt is introduced into the solution, and silver is released from the solution in the form of insoluble chloride, which can be melted either together with the gold-containing cake, or separately, to obtain technical silver with a metal mass fraction of 98-99%.

The results of experiments with nitrate leaching of “golden head” samples and melting of the resulting cakes showed the following.

1. The opportunity for the Kholbinsky mine to eliminate the labor-intensive and high-temperature operations of roasting, smelting and cupellation, thereby preventing the release of toxic gases from roasting and smelting from pigs.

2. Increase the extraction of precious metals into the ingot by significantly reducing (by two times for sample No. 1 and five times for sample No. 2) the mass of the melted product (cake), reducing, accordingly, the amount of slag and eliminating middlings: droplet breakage and bricks. The expected increase in the extraction of precious metals is 2-3%.

3. In the “gold head” ACR process, silver is leached up to 8%. To reduce the extraction of silver into the solution, ACR conditions have been developed and proposed. At the same time, the extraction of silver into the solution decreased by almost 30 times.

4. After melting the dried cakes from the AKV “golden head” of sample No. 1 using a known charge (soda, borax, quartz), an alloy with a total mass fraction of gold and silver of 90% was obtained. And after melting cakes from the AKV “gold head” sample No. 2 using an experimental charge, alloys with a total mass fraction of gold and silver of 95-99% were obtained.

5. A significant amount of galena in the CG leads after ACR to a noticeable transition of lead into a commercial gold-silver alloy, which reduces the quality of the finished product. During the research, conditions were determined and a charge was selected for melting cake containing up to 25% lead to produce a gold-silver alloy with a total mass fraction of gold and silver of 95-99%.

6. Studies on nitric acid leaching of carbon dioxide (sample No. 2) showed that fairly complete decomposition of pyrite (more than 97%) is achieved when leaching with a nitric acid solution with a concentration of 500-550 g/l (see table). This is due to the fact that pyrite (more than 90%) is in a relatively large class (minus 0.5 + 0.25 mm) and more stringent conditions are required for its decomposition.

According to the Kholbinsky mine, the specific cost of processing 1 kg of carbon dioxide (sample No. 1) for the roasting technology is 93.6 rubles. The specific costs of technology with nitrate leaching of the same sample are 44.9 rubles, i.e. the costs of processing carbon dioxide using the developed hydrometallurgical technology are reduced by half.

On two samples of rich gravity sulfide gold-containing concentrate (“gold head”) of the Kholbinsky mine of Buryatzoloto OJSC, research was carried out to develop a new hydrometallurgical technology using nitrate leaching of the original MG and subsequent smelting of the resulting cake.

The conditions for leaching of refractory gravity concentrate (GC) containing sulfides (up to 80%) and technogenic scrap (up to 16%) have been determined. The conditions for ACR with minimal silver dissolution were determined. After ACR, cakes (solid products) are obtained with a higher (2-5 times) content of noble metals than in the original CG. Melting conditions have been developed to produce alloys with a total mass fraction of gold and silver of 96-99%.

A technical and economic assessment of the proposed hydrometallurgical technology for processing carbon dioxide was carried out. Compared to the existing technology for processing carbon dioxide at the enterprise using roasting, the costs of processing carbon dioxide using the developed hydrometallurgical technology are reduced by half.

Degree of pyrite decomposition during ACV of 3G sample No. 2

Introduction

1. Review of literature sources and formulation of the research problem . 6

1.1. Kinetics of solid dissolution 6

1.1.1. Basic principles of the theory of dissolution processes 6

1.1.2. Methods for studying dissolution kinetics 11

1.2. Kinetics of dissolution and hydrochemical oxidation of metal chalcogenides. 16

1.2.1. Oxides 17

1.2.2. Sulfides 30

1.2.2.1. Pyrite 36

1.2.2.2. Sphalerite 55

1.3. Methods for planning experiments and mathematical modeling of the kinetics of dissolution processes 60

1.4. Statement of the research problem 69

2. Experimental part 71

2.1. Preparation of research objects 71

2.1.1. Pyrite 71

2.1.2. Sphalerite 73

2.2. Preparation and standardization of oxidizing solutions 73

2.2.1. Nitric acid 76

2.2.2. Hydrogen peroxide 77

2.2.3. Sodium hypochlorite 79

2.3. Measuring the rate of sulfide dissolution processes 82

2.4. Determination of metal cations content in samples 85

2.4.1. Sample preparation and digestion 85

2.4.2. Iron(III) 86

2.4.3. Zinc 88

2.5. Identification of solid reaction products 90

2.6. Determination of the solubility of metal nitrates in solutions of nitric acid 92

2.7. Obtaining kinetic models 93

3. Results and discussion 95

3.1. Pyrite in oxidizing solutions. 95

3.1.1. Nitric acid 95

3.1.2. Hydrogen peroxide 110

3.1.3. Sodium hypochlorite 126

3.2. Sphalerite in oxidizing solutions 132

3.2.1. Nitric acid 132

3.2.2. Hydrogen peroxide 146

3.2.3. Sodium hypochlorite 164

Conclusion and conclusions 188

List of sources used 192

Applications 237

Introduction to the work

Studying the kinetics and mechanism of dissolution processes is necessary to optimize known and develop new technologies for extracting metals from ore raw materials.

Dissolution is a complex heterogeneous multi-stage process. Its theoretical description is possible only in fairly simple cases. The various experimental methods used to study the dissolution of crystalline substances differ in the state of the solid phase and hydrodynamic interaction conditions. The most correct kinetic data on the dissolution of solids can be obtained by the rotating disk method, which ensures equal accessibility of the surface in terms of diffusion and the ability to calculate the diffusion flow of reagents to the interaction zone or reaction products into the volume of the solution. This method did the bulk of the work.

The most important direction of physical and chemical research in hydrometallurgy is the search for reagents and determination of the kinetic parameters of dissolution processes in order to select technological modes for the extraction of metals from ore raw materials. The work determines the kinetic patterns of hydrochemical oxidation of sulfides common in ores - pyrite and sphalerite - in the presence of nitric acid, hydrogen peroxide and sodium hypochlorite in a wide range of influencing factors.

To describe the dependence of the dissolution rates of these sulfide compounds on the concentration of the reagent, pH, temperature, intensity of stirring and duration of interaction, kinetic models were built. Since for a rotating disk the general form of the dependence of the dissolution rate on each of the listed factors is known, the technique of performing a full factorial experiment and obtaining

5 calculations of polynomials, which were then converted into kinetic models, allowing for their physicochemical interpretation.

The dependences of the specific rates of dissolution of pyrite and sphalerite on the influencing parameters in the presence of these oxidizing agents have been studied for the first time using the rotating disk method. The resulting new kinetic models are valid for wide ranges of changes in influencing parameters and make it possible to calculate the amount of metal passing into solution per unit surface area of ​​a crystalline compound for any combination of reagent concentration, pH, temperature, stirring intensity and duration of interaction.

The details of the mechanism of the studied processes, the nature of intermediate solid products, the reasons and conditions for their formation, as well as the nature of the influence on the dissolution kinetics are determined. Thermodynamically substantiated schemes of the interaction mechanism corresponding to the observed kinetic dependences are proposed.

The work was carried out at the Department of Chemistry of Tver State Technical University. Its content corresponds to the “Priority directions of fundamental research of the Russian Academy of Sciences” (Appendix 4 to the order of the Presidium of the Russian Academy of Sciences dated December 2, 1996 No. 10103-449) in part 2.1.5. Scientific basis for efficient processing of renewable and non-traditional chemical raw materials and 2.2.3. Development of resource-saving and environmentally friendly processes for the integrated processing of ore raw materials and their waste.

The results of the work are of interest for the physical chemistry of the processes of hydrochemical oxidation and dissolution of sulfides and hydrometallurgical technologies.

Methods for planning experiments and mathematical modeling of the kinetics of dissolution processes

Let us consider general issues of pyrite oxidation. Interest in the kinetics and mechanism of pyrite oxidation is due both to the fact that it is the most common sulfide and the possibility of using FeS2 for the conversion of solar energy into electrical and chemical energy, as an anodic depolarizer in the production of hydrogen and a cathode in high energy density batteries. The oxidation of pyrite in aqueous solutions has been the subject of extensive research in extractive metallurgy (such as the separation of gold from refractory ores), coal processing, geochemistry, and in the formation of acidic mining waters. Additionally, pyrite oxidation is an important process in the geochemical cycles of sulfur and iron.

A convenient way to present regions of stable states depending on the redox potential and pH of the solution - Pourbaix diagrams for the "Fe-S-H2O" system are given in the works (Fig. 1.2). The influence of pH on the state of the pyrite surface is discussed in the work. Thermodynamic calculations have shown that the possible oxidation reactions of pyrite with the formation of H2S, HS and S2" are metastable, since they cannot be carried out within the limits of the electrochemical stability of water. With a sufficient amount of oxygen in the solution, the main product of pyrite oxidation is the SC 42 ion. Analysis of the resulting diagram Pourbaix "Eh - pH" for the system "FeS2 - O2 - H20" showed that at high values ​​of Eh the predominant product of pyrite oxidation is Fe(OH)3. At less positive (or more negative) ORP values, FeC03 can be formed (up to pH 8). ,6) or Fe(OH)2 (at pH 8.6). The degree of oxidation of the pyrite surface should increase with increasing pH, and the release of elemental sulfur can occur only at pH 1.5. A film of oxidation products is found on the freshly exposed pyrite surface. from an inner dense layer of sulfide carbonate or sulfide hydrate and an outer porous layer of Fe(OH)3, which makes it difficult for the electrolyte to access the FeS2 surface. Based on the Pourbaix diagram, it was concluded that intensive dissolution of this film begins at pH 1.5-1.7. At pH 0.5, pyrite is exposed with elemental sulfur formed on its surface.

The papers provide reviews of the kinetics of pyrite oxidation. Work has also contributed to advancing the understanding of these reactions.

It is generally accepted that the dissolution of pyrite under acidic and oxidizing conditions is an electrochemical process, which can be described by the following summary equations:

From equation (1.45) it follows that the oxidation of pyrite to sulfate ions involves a total transfer of 15 electrons. Since electron transfer reactions are usually limited to one or at most two electrons, the process involves several steps. A number of researchers suggest that the final reaction products - sulfur and sulfate ions - can be formed through intermediate forms: S03, S203 and Sn06 (n = 4 6). The absence of intermediate sulfoxyanions in the presence of Fe(III) indicates that Fe(III) oxidizes sulfoxyanions rapidly.

In works based on the theory of molecular orbitals, it was concluded that the formation of thiosulfates may be the first stage of the oxidation of sulfur atoms in pyrite. In the presence of pyrite, thiosulfate can be catalytically oxidized to tetrathionate. It is also known that Fe3+ ions have the ability to quickly convert thiosulfate into tetrathionate.

The authors of the works postulated that instead of elemental sulfur, iron-deficient pyrite Fei_xS2 is formed as a metastable product, which is further rearranged into elemental sulfur and stable sulfide; Fei+J,S2 Fei+y-x&2 + Fe2+ + 2xe.. Electrochemical experiments carried out in , showed that in a non-aqueous solvent, no significant anodic current is observed on the pyrite electrode. Based on this, the authors concluded that during the decomposition of pyrite in an aqueous solution, half-reaction (1.44) does not occur. Surface analysis by X-ray photoelectron spectroscopy has shown that the products of the pyrite dissolution reaction include substances such as elemental sulfur, polysulfides, and iron and sulfur oxides. Raman spectra showed that both elemental sulfur and polysulfides are formed on the surface of oxidized pyrite. The surfaces of pyrite after its reactions with aqueous solutions, using the method of photoelectron spectroscopy of X-rays, were also studied in the works.

Preparation and standardization of oxidizing solutions

The kinetics of interaction of FeS2 powder with solutions of H2O2 in perchloric acid was studied in the work. The dissolution of pyrite occurs in the kinetic regime (Eact = 57 kJ-mol"). The rate of H2O2 concentration was close to first order. The change in [HCl4] and [ClCl4] had no effect on W. The introduction of FTT ions into the reaction system gives a slight positive effect (IF - [Ґ]), while the addition of S042- ions leads to their adsorption and inhibition of the process (W 4 2).

In this work, the kinetics of oxidation of powdered pyrite with hydrogen peroxide in a solution of HC1 was studied. The process occurs in the kinetic regime (EaiiT = 65 kJ-mol-1; linear dependence of the rate constant on the reciprocal radius of the particles; order in H2O2 1.32). An absence of WOT[H] dependence was found, while SG ions had a negative effect on the rate.

Powdered pyrite was oxidized with hydrogen peroxide in solutions of phosphoric acid. The kinetic regime has been established (El. = 57 kJ mol-1; linear dependence of the rate constant on the reciprocal radius of the particles; first order in hydrogen peroxide). Phosphate ions have an inhibitory effect on the oxidation process of pyrite.

There is information in the literature about other substances whose interaction with the surface of pyrite causes a slowdown in the process of its dissolution: acetylacetone, humic acids, ammonium lignosulfonates, oxalic acid, sodium silicate, sodium oleate, acetate ions, urea, purine, /-ribose, etc. .

Let us discuss the oxidation of pyrite with solutions of nitric acid. The authors tested the behavior of synthetic FeS, natural pyrrhotite Fe7Ss, pyrite FeS2 and other metal sulfides when exposed to nitric acid. Lower sulfides predominantly formed elemental sulfur, while pyrite and chalcopyrite formed sulfate ions.

The kinetics of dissolution of pyrite powder in nitric acid was studied in the work. Disulfide ions from FeSs were oxidized to sulfate ions and elemental sulfur, and most of the sulfur in solution was in the SC 2- form. The reaction rate did not depend on the intensity of stirring. The found values ​​of apparent Ea1GG were 52 kJ-mol-1 at C = 25% and 25 kJ-mol-1 at 10%.

Anodic oxidation of pyrite in 0.22 M HNO3 at 26-80 C was studied by volamperometry. The proportion of FeS2 oxidized to S, regardless of temperature, decreased with increasing potential from 70% at q 0.82 V to 0% at 9 1"5 V.

The possibility of intensifying the process of dissolution of pyrite and marcasite in nitric acid through the use of microwave energy is indicated in the work. The results of studying the behavior of nickel-iron pyrrhotite in hot nitric acid are presented in.

Let's consider the oxidation of pyrite with other oxidizing agents. During the oxidation of FeS2 and FeS with manganese dioxide at pH = 8, the only products of FeS oxidation were elemental sulfur and sulfate ions, whereas for; FeS2 predominantly found SO4 ions, as well as thiosulfate, trithionate, tetrathionate and pentathionate ions as intermediates. Thiosulfate ions were oxidized by manganese dioxide to tetrathionates, while the remaining intermediates were oxidized directly to SO4. The reaction products indicate that the oxidation of FeS2 proceeds by the so-called “thiosulfate” mechanism, and FeS by the “polysulfide” mechanism.

For the FeS2 oxidation reaction, the rate values ​​calculated from the amounts of sulfur and iron transferred into solution turned out to be equal to 1.02 and 1.12 nmol-m 2 s-1, respectively. Since these values ​​are in the same range as the previously published rates of pyrite oxidation by Fe3+ ions, and also since ferric ions are well known as an oxidizer of pyrite, the authors conclude that even in the presence of MnO2, Fe + ions can be oxidizing agents for e$2 and FeS. On the surface of iron sulfide, Fe + ions are reduced to Fe2+, which are then oxidized by manganese dioxide again to Fe3+. Despite the low solubility of ferric iron in a neutral environment, the literature indicates that it can nevertheless serve as an oxidizing agent if it remains adsorbed on the surface of pyrite. Thus, the Fe3+/Fe2+ redox couple ensures the transport of electrons between the surfaces of two solid compounds. The works provide information about the possible participation of other redox pairs (Fe /Fe$2 and MnOa/Fe) during the dissolution of pyrite in the presence of manganese dioxide in an acidic environment.

The results of a study of the kinetics of oxidation of powdered pyrite with potassium dichromate in a solution of sulfuric acid are presented in the work. The reaction proceeds in the kinetic regime, as evidenced by the absence of dependence of the rate on the intensity of stirring and Eshcr = 43 kJ-mol"1. The experimental orders for the reagents are 0.52 for dichromate and 0.85 for sulfuric acid, respectively.

A mechanism explaining the increase in the rate of pyrite oxidation in a neutral environment in the presence of bicarbonate ions was proposed in the work. The kinetics of pyrite oxidation in sodium carbonate solutions is described in the work, and in sodium hydroxide solutions in the communication.

The behavior of pyrite in sodium hypochlorite solutions was studied by the rotating disk method in the work. It has been established that it is practically independent of [H] at pH 7. In a weakly alkaline environment (pH = 8-5-9), a sharp drop in speed is observed, and at pH 9, the absence of dependence of W on pH is again noted. Equations have been proposed that describe the process of FeS2 oxidation with NaOCl solution in a strongly acidic (pH 3) and alkaline medium (pH 8). At pH = 6, a kinetic model was obtained, from which K298 follows - 1.48-10 dm3 cm 2-s 9 and Eact = 27.5 kJ-mol. The observed reaction order in NaOCl is equal to unity, and in terms of disk rotation frequency - (-0.5), which is typical for diffusion processes. Calculation of diffusion fluxes showed that the limiting stage is the removal of reaction products from the surface of the mineral. At pH 8, the oxidation rate is directly proportional to the square root of the duration of the experiment. The dependence of the rate on temperature (Eac1 = 10.5 kJ-mol"1), hypochlorite concentration (W C), and disk rotation frequency (W co0) was obtained. At pH S, the rate of the process is limited by the internal diffusion of the reagent or product in the pores of the film of the new phase a -Eios, forming on the surface of the mineral.

In this work, the electrooxidation of pyrite in NaCl solutions was studied. Pyrite oxidation was carried out in an electrolyzer filled with a 10% NaCl solution at a temperature of 35-40 C. The current efficiency of the pyrite oxidation process with electrochemically generated hypochlorite reached 97%.

The kinetics of reduction of an aqueous chlorine solution at pH = 2 and 4 on a rotating disk electrode made of pyrite was studied. In this pH range, CI2 (aq) exists in the form of HOCI, and the solubility of Fe(III) decreases. The reduction of dissolved chlorine at a potential of 0.6 V (relative to N.K.E.), at pH = 2, occurs very little. The observed deviation from Lewin's equation for transport-controlled current density at a potential of 0.5 V (relative to n.e.) becomes significant at low disk speeds.

Determination of the solubility of metal nitrates in nitric acid solutions

Preparation of selected samples for analysis consisted of removing unreacted oxidizing agent from them while simultaneously converting them into a form convenient for determination. To do this, selected solution samples were placed in heat-resistant chemical cups and evaporated to dryness in a sand bath. The resulting solid residue was kept at the bath temperature for 2-5 minutes until visible signs of the decomposition reaction disappeared, after which the cups were removed from the bath and allowed to cool slightly. Then a precisely measured volume of 2 N hydrochloric acid solution (reagent grade) and distilled water were added to the samples in small portions, ensuring complete dissolution of the residue. The resulting solution was quantitatively transferred into volumetric flasks for analysis.

In cases where the selected samples contained suspended particles (for example, colloidal sulfur), before decomposition, 1-2 cm of concentrated sulfuric acid (reagent grade) was added to them and then the so-called “wet ashing” was carried out - evaporation on a sand bed. bath until white smoke forms. Moreover, due to the oxidation of colloidal impurities: concentrated H2S04, the solutions became transparent and colorless. If the added amount of sulfuric acid was not enough to completely eliminate the opalescence of the sample, the procedure was repeated. If, as a result of interaction with sulfuric acid, the solution acquired a yellow color, 5-10 cm of a concentrated H2O2 solution was added to it and again evaporated until the hydrogen peroxide was completely decomposed (no 02 bubbles) and white smoke appeared. Then the cups were removed from the bath and allowed to cool. A little distilled water and a precisely measured volume of a 10% (by weight) ammonia solution in excess were added to the resulting solution until a characteristic pungent odor appeared. After this, the cups were again placed in a sand bath and evaporated until the volume of the solution in them became minimal (almost until crystals precipitated). Then the cups were removed from the bath, and their contents, after cooling, were dissolved in a minimum volume of distilled water and quantitatively transferred into volumetric flasks for analysis.

At the same time, a Blank experiment was carried out, evaporating an ali-quota of distilled water in a sand bath and subjecting it to the processing procedure described above. The solution obtained as a result of similar actions served as a “zero” solution when analyzing the content of metal cations in the samples.

The concentration of Fe + cations in the solution was determined photometrically by the color of the complex with sulfosalicylic acid.

Sulfosalicylic (2-hydroxy-5-sulfobenzoic) acid produces three differently colored complexes with Fe3+ ions, differing from each other in composition. At pH = 2-3, a red-violet complex with an iron:reagent ratio of 1:1 exists in the solution. At pH = 4-7, a brownish-orange complex predominates with a component ratio of 1:2. At pH = 8-10, the yellow complex with a component ratio of 1:3 is stable. The violet complex, stable in an acidic environment, is insensitive (molar extinction coefficient is 2.6 × 10 at X = 490 nm). Therefore, to determine Fe3+, a yellow complex that is stable in an alkaline environment was used. The absorption maximum of this complex is in the region of 420-430 nm, and the molar extinction coefficient is 5.8-103. Solutions of iron(III) sulfosalicylate complex are quite stable.

The photometric determination technique was as follows. The solution obtained after decomposition of the sample, containing no more than 300 μg of Fe(IH), was transferred to a 50 cm3 volumetric flask. Then 2 cm3 of 2 N was added there. H2S04 solution (up to pH = 2-3), 5 cm3 of 10% (by weight) solution of sulfosalicylic acid and 5-10 cm3 of 5% (by weight) aqueous ammonia solution (up to pH = 9). The contents of the flask were brought to the mark with distilled water, mixed, and after 5-10 minutes the optical density of the resulting yellow solution was measured on a KFK-3 spectrophotometer in cuvettes 1 cm thick at a wavelength of 425 nm (blue filter).

It is proposed to use distilled water as a reference solution. To avoid systematic errors associated with the possible presence of iron ions in the reagents used, a “zero” solution was used as a reference solution, which had undergone the full processing procedure according to the above method, but did not contain iron ions.

To construct a calibration graph, a standard solution of Fe(III) salt with a concentration of iron ions of 1 mg cm-3 was prepared according to the method. To do this, 8.6350 g of ferric ammonium alum NFLtFetSO 12H20 (chemically pure grade) was dissolved in a 1 dm3 volumetric flask and 5 cm3 of concentrated sulfuric acid was added. The contents of the flask were brought to the mark with distilled water while stirring. Working solutions with an iron ion concentration of 20 μg-cm-3 were prepared on the day of the experiment by diluting 5 cm of a standard iron (III) solution with distilled water in a volumetric flask to 250 cm3.

Sphalerite in oxidizing solutions

The obtained value of activation energy in combination with the established orders of speed in C and Co confirms the conclusion about the autocatalytic nature of the interaction of sphalerite with nitric acid, occurring at C 13 mol-dm: in a mixed, close to kinetic regime.

Equation (3.48) allows you to visualize the influence on W of the most important factors: C(NZH)z), G and co. In Fig. Figures 3.16 and 3.17 show the surfaces of the dissolution rate of sphalerite depending on the combination of values ​​of C, G and w, C, respectively. It follows from them that an increase in C and T, as well as a decrease in co, lead to a monotonic increase in W), as a result of which, for the studied range of influencing parameters, the highest value of the rate (1.57-10 mol-dm -s) is achieved at maximum values ​​of concentration and temperature and the minimum value of the disk rotation frequency (respectively, at C = 12.02 mol-dm 3, T = 333 K and co - 1.6 s-1). From these figures it is clear that the degree of influence of these factors on the value of W decreases in the series: T C co.

Comparison of the kinetic parameters of the processes of dissolution of pyrite and sphalerite in nitric acid in the concentration range corresponding to the ascending branch of the dependence W = f2 and 2.5 M HNO3. processed in an autoclave at a temperature of 130-160 °C. The minimum temperature value corresponds to the moment of formation of volatile NO. At maximum temperature (160 °C), the vapor pressure in the autoclave reaches 1200 kPa. The total duration of the process is 4 hours. Checking the solubility of the resulting precipitate in HNO3 (at pH = 4) showed that after 4 hours of treatment, the concentration of As in the solution was 1.6 mg/l.

The work describes a method for nitrate treatment of Ag-As-rich flotation and gravity concentrates (silver content from 0.8 to 31.5 kg/t), in which bismuth, nickel, cobalt, copper and zinc are present as associated useful components. It is recommended that the mixture of concentrates be subjected to leaching with an HNO3 solution (acid consumption 124% of the concentrate weight) at a temperature of 125 °C, oxygen pressure 1 MPa; F:T=6:1, D for 30 minutes. In this case, 95-99% of the metals present, including arsenic and iron, pass into the solution. From the resulting solutions, the following are sequentially precipitated: silver in the form of chloride (by introducing NaCl); bismuth oxychloride-hydroxide; ferrous-arsenic sediment (neutralization of the solution with ammonia, respectively: up to pH = 0.4-0.8 and 0.8-1.8) and a mixture of nickel, cobalt, chalk and auger sulfides (treatment of the solution with ammonium sulfate at pH = 5-7 ). By calcining AgCl with soda at 600 °C, high-purity metallic silver powder was obtained. It is recommended to process other solid products using standard methods, also to obtain pure metals. The nitrate solution obtained after separation of the sludge is proposed to be used as a fertilizer. The degree of extraction of silver and other metals during chemical metallurgical processing of sediments reaches 99%.