WO2023211318A1 - Method of processing iron-based concentrates containing precious metals - Google Patents

Abstract

The invention relates to the precious metals industry. A method of processing iron-based concentrates containing precious metals includes repulping a concentrate in water, treating the pulp with an alkali metal chlorate and sulphuric or hydrochloric acid to turn the non-precious elements into a solution, heating the reaction mixture, separating a solution of impurities from a non-dissolved residue containing precious metals, and then dissolving said residue. The treatment using an acid and an alkali metal chlorate is carried out by alternately introducing doses thereof into the aqueous pulp of the concentrate, with the redox potential of the pulp being in a range of 0-350 mV relative to a silver chloride reference electrode, and heating the reaction mixture after the introduction of each dose of the reagents. The non-dissolved residue in which noble metals are concentrated is dissolved in hydrochloric acid under consecutive oxidation first by oxygen and then by chlorine. The method makes it possible to turn the bulk of the iron contained in the concentrate into a solution without forming harmful and explosive substances, to concentrate noble metals in the non-dissolved residue and to separate the residue from the solution.

Description

METHOD FOR PROCESSING IRON-BASED CONCENTRATES CONTAINING NOBLE METALS

The invention relates to the metallurgy of precious metals (BM) and can be used in the technology of processing iron-based concentrates containing noble metals.

Concentrates of this type can be formed during pyrometallurgical methods for processing various products of complex composition containing noble metals, which include spent catalysts from the petrochemical industry, as well as automobile catalysts. The main component of the resulting concentrates, as a rule, is iron, the mass fraction of which is (30-90)%. They may also contain nickel, copper, chromium, silicon, phosphorus, carbon, and aluminum in varying concentrations. Noble metals are present in various proportions, and their total concentration reaches (5-30)%.

The initial stage of processing any concentrates containing noble metals is their dissolution. In this case, problems of a diverse nature often arise. In some cases, they are associated with low activity of the raw material. In others, on the contrary, with a rapid process, accompanied by the release of harmful and dangerous substances. Another important task when working with such concentrates is to separate, at the initial stage, most of the impurities of base elements, which will significantly simplify the subsequent dissolution of the enriched product and will contribute to a high extraction of noble metals into the target products.

One of the common and most frequently used methods in practice is to dissolve concentrates in acidic environments during oxidation.

There is a known method for processing concentrates containing platinum group metals (Yu.A. Kotlyar, M.A. Meretukov, L.S. Strizhko. Metallurgy of precious metals. T.2., Textbook. M., Publishing House "Ore and Metals", 2005, pp. 269-273), including hydrochlorination in hydrochloric acid when heated, separation of the insoluble residue, treatment of the resulting solution with sodium nitrite (nitration), separation of the precipitate and subsequent extraction of platinum group metals from the solution by known methods.

The main disadvantages of this method can be considered: the formation of explosive hydrogen when pulping the concentrate in hydrochloric acid; rapid progress of the iron dissolution process, accompanied by an increase in temperature, a multiple increase in the volume of the reaction mixture and its possible release from the reactor, which reduces the productivity of the equipment and increases the risk of injury; the formation of large volumes of solutions with a high concentration of iron and a low concentration of platinum group metals in them. When processing such solutions, large masses of secondary industrial products containing platinum metals are formed, and, as a consequence, leads to their low extraction into finished products.

There is a known method for processing concentrates of platinum metals on an iron-nickel base for the extraction of platinum metals (Patent No. 2391419, Russia / Ilyashevich V.D., Mamonov S.N., Shulgin D.R., Pavlova E.I., Koritskaya N.G. ., Solomatov V.V.), including pulping the concentrate in water, heating, treating the pulp with nitric acid, heating, treating with hydrochloric acid, heating the reaction mixture, filtering the pulp and separating impurities of base elements from platinum metals by precipitating hydroxides by treating with sodium nitrite.

This method also has a number of significant disadvantages. The main ones include the release of significant volumes of nitrogen oxides during treatment with nitric acid, the disposal of which requires the use of special, expensive equipment; long duration of the concentrate dissolution process; the formation of solutions with a high concentration of base elements, mainly iron, and a relatively low concentration of platinum group metals. Subsequent processing of such solutions involves with high material costs and low direct extraction of platinum group metals into target products.

There is a known method for processing iron-based concentrates (Patent No. 2707457 (Russia). Registered on November 26, 2019. A method for processing iron-based concentrates containing platinum group metals./ Ilyashevich V.D., Lukina K.V., Gerasimova L.K. , Krivosheev N.O., Barkhatov M.Yu.), containing platinum group metals, including pulping the concentrate in water, introducing a calculated amount of alkali metal chlorate into the pulp, subsequent treatment of the pulp with acid until a given pH value is reached, heating the pulp and separating the solution from undissolved precipitate of platinum group metals.

This method is the closest in technical essence to the proposed method and is accepted as a prototype.

With all its advantages, the method also has a number of disadvantages. As noted, the basis of concentrates of this type is iron. However, in lower concentrations, other impurities of base elements may be present, which dissolve in hydrochloric or sulfuric acid in the presence of alkali metal chlorates. It is very difficult to establish the exact concentration of soluble impurities, and therefore their mass, in concentrates supplied for processing, since these may be mixtures of different batches, the composition of which differs significantly. The chemical activity of iron in them also varies depending on the content of impurities of other base elements, in particular, silicon, carbon, phosphorus and some others, which are found in concentrates, including in the form of sparingly soluble compounds with iron. Specially conducted additional studies have shown that the concentration of the oxidizing agent in the reaction mixture, determined by the prototype method, is in most cases either excessive, which leads to the dissolution of some of the platinum metals along with base elements, or not sufficient for their effective separation.

The technical result to be achieved by the proposed method of processing iron-based concentrates containing noble metals, consists in using a set of hydrometallurgical processing methods that make it possible to transfer the main part of base elements into solution without the formation of harmful and explosive substances, to concentrate noble metals in an undissolved residue, and then to transfer noble metals into solution in the safest way.

The specified technical result is achieved by the fact that in the known method of processing iron-based concentrates containing noble metals, including pulping the concentrate in water, treating the pulp with alkali metal chlorate and sulfuric or hydrochloric acid to transfer base elements into solution, heating the reaction mixture, separating the solution impurities from the undissolved residue containing noble metals, and its subsequent dissolution - treatment with acid and alkali metal chlorate is carried out by alternately introducing them in portions into the aqueous concentrate pulp, while maintaining the value of the oxidation-reduction potential (ORP) in the pulp in the range ( 0-350) mV, relative to the silver chloride reference electrode, and heating the reaction mixture after introducing each portion of reagents, before separating the undissolved residue, the pulp is treated with a solution of alkali metal organosiliconate, the undissolved residue, in which noble metals are concentrated, is dissolved in concentrated hydrochloric acid in successive oxidation first with oxygen and then with chlorine.

Also in special cases of implementation of the invention:

- oxidation with oxygen is carried out until a stable ORP value is achieved in the pulp in the range (100-500) mV, relative to the silver chloride reference electrode;

- oxygen is supplied to the reaction mass in the form of air or a mixture of oxygen with inert gases, nitrogen or carbon dioxide.

The essence of the proposed method is as follows. The concentrates that are proposed to be processed according to the claimed method are formed mainly in the process of pyrometallurgical concentrating smelting of various products of complex composition containing noble metals, which include spent catalysts from the petrochemical industry, as well as automobile catalysts. They are based on iron, which is found both in the form of metal and chemical compounds with phosphorus, silicon, and carbon. They may also contain nickel and copper in varying concentrations. Accordingly, the chemical activity of these phases when dissolved in hydrochloric or sulfuric acids during oxidation also varies greatly. Since the task at the first stage of processing is to dissolve the bulk of the impurities and concentrate noble metals in the undissolved residue, this operation is carried out in a certain range of ORP values in the pulp in order to exclude the dissolution of noble metals. It has been experimentally established that if the dissolution of concentrates is carried out in an acidic medium with heating while maintaining the ORP value in the range from 0 to 350 mV, then the bulk of the iron and other impurities goes into solution. In this case, the noble metals remain almost completely in the undissolved residue and the process takes place without the release of gaseous hydrogen and phosphine. At lower or higher ORP values, respectively, either the degree of dissolution of impurities decreases and the formation of explosive hydrogen and phosphine is possible, or a significant part of the noble metals goes into the solution along with the impurities. The acidic environment in the pulp is maintained by the introduction of hydrochloric or sulfuric acid, since in neutral and alkaline media sodium chlorate does not exhibit oxidizing properties towards these impurities and they do not dissolve.

Due to the presence of soluble silicon compounds in the resulting pulps, problems arise in the subsequent operation of separating the solution from the sediment. Filtration occurs very slowly, which greatly reduces the productivity of the technological equipment used. To increase the speed and quality of filtration, the pulp is pre-treated with a solution of a reagent from the class of alkali metal organosiliconates, for example, sodium methyl siliconate, which precipitates soluble silicon compounds in the pulp and significantly increases the rate of subsequent filtration of the pulp. Probably, the silicon removal process can be represented as follows:

The dissolution of the residue that was not dissolved at the first stage, in which noble metals are concentrated, is carried out by oxidation in concentrated hydrochloric acid. Under such harsh conditions, further destruction occurs of iron-containing phases that were not destroyed during dissolution at the first stage (phosphides, carbides, silicides, intermetallic compounds), however, in the absence of oxidizing agents, the process proceeds with the release of explosive hydrogen:

Fe + H ₂ SO ₄ = FeSO ₄ + H ₂ (1)

Fe + 2HCL = FeCL ₂ + H ₂ (2)

In the presence of oxygen, dissolution proceeds through the resulting reactions without the formation of hydrogen

Fe + H ₂ SO ₄ + l/2O ₂ = FeSO ₄ + H ₂ O (3)

Fe + 2HCL + l/2O ₂ = FeCL ₂ + H ₂ O (4) and no negative aspects, for example, foaming, thermal effects that can lead to overheating of the reactor and emission of pulp from it, do not occur even with a large excess of oxygen-containing gas mixture, which is observed when using a stronger oxidizing agent at this stage, for example, chlorine. After the most chemically active iron-containing phases in such environments are destroyed, which occurs when the ORP value in the pulp reaches the range (100-500) mV, the oxygen-containing gas the mixture is replaced with a stronger oxidizing agent - chlorine and the dissolution of noble metals is carried out according to known methods.

EXAMPLE 1

To conduct a series of experiments, an iron-based concentrate obtained at the enterprise was taken with the following composition, typical for such concentrates, %: Pt-2.1, Pd-5.3, Rh-0.9, lr-0.1, Ru-0.5, Au-0.4, Ag- 1.6, Fe-48.3, Cu-5.0, Si-4.9, P-7.0.

In a titanium reactor with a volume of 760 liters, equipped with steam heating and water cooling, devices for supplying reagents and mixing the reaction mixture, devices for monitoring pH values, ORP and temperature, 300 liters of water were poured, a mixing device was turned on, 70 kg of concentrate and a sodium chlorate solution were loaded based on 30% of the stoichiometrically required iron for dissolution. After this, with the help of dosing devices, concentrated hydrochloric acid was introduced into the reactor in portions of 1-2 liters with a gradual increase in the temperature of the pulp and control of the acidity of the medium and the ORP value in the pulp. When the ORP dropped below 100 mV, an aqueous solution of sodium chlorate with a concentration of 700 g/l was introduced in portions of 0.2-0.5 l, the pulp was kept for a certain time at a given temperature, then subsequent portions of reagents were poured. When a stable ORP value in the acidic region was achieved in a given range of values, the pulp was heated for 2 hours, cooled to a temperature of 50 °C, 4 liters of a 25% aqueous solution of sodium methyl siliconate was poured into the reactor, the pulp was stirred for 10 minutes, filtered and washed with water. The main solution and industrial waters were combined. The filtration rate was (500-550) l*h/ ^m2 . The undissolved residue was loaded into a titanium reactor with a volume of 760 liters, 150 liters of water were poured in, a mixing device was turned on, the pulp was heated to 40 °C and air bubbling was turned on at a speed of 5-6 m ³ /h. After this, 150 liters of 12 M hydrochloric acid were poured into the reactor and the bubbling process was carried out with air (or a mixture of oxygen with inert gases) under such conditions until an ORP value of 100-500 mV was achieved, relative to the silver-silver chloride reference electrode, the air supply was turned off, and the supply of chlorine gas was turned on at speed 3 m ³ /h and, according to known methods, dissolved the concentrate using liquid-phase chlorination. After completion of the process, the pulp was cooled and the solution was separated from the sediment by filtration on a suction filter. All obtained middlings were analyzed: solutions by mass spectrometry with inductively coupled plasma; sediments using X-ray spectral analysis. The results are presented in Table 1.

EXAMPLE 2

To conduct a series of experiments, an iron-based concentrate obtained at the enterprise was taken with the following composition, typical for such concentrates, %: Pt-2.1, Pd-5.3, Rh-0.9, lr-0.1, Ru-0.5, Au-0.4, Ag- 1.6, Fe-48.3, Cu-5.0, Si-4.9, P-7.0.

In a titanium reactor with a volume of 760 liters, equipped with steam heating and water cooling, devices for supplying reagents and mixing the reaction mixture, devices for monitoring pH values, ORP and temperature, 300 liters of water were poured, a mixing device was turned on, 70 kg of concentrate and a sodium chlorate solution were loaded based on 30% of the stoichiometrically required iron for dissolution. After this, with the help of dosing devices, concentrated sulfuric acid was introduced into the reactor in portions of 1-2 liters with a gradual increase in the temperature of the pulp and control of the acidity of the medium and the ORP value in the pulp. When the ORP dropped below 100 mV, an aqueous solution of sodium chlorate with a concentration of 700 g/l was introduced in portions of 0.2-0.5 l, the pulp was kept for a certain time at a given temperature, then subsequent portions of reagents were poured. When a stable ORP value in the acidic region was achieved in a given range of values, the pulp was heated for 2 hours, cooled to a temperature of 50 °C, 4 liters of a 25% aqueous solution of sodium methyl siliconate was poured into the reactor, the pulp was stirred for 10 minutes, filtered and washed with water. The main solution and industrial waters were combined. The filtration rate was (600-700) l*h/ ^m2 . The undissolved residue was loaded into a titanium reactor with a volume of 760 liters, 150 liters of water were poured in, a mixing device was turned on, the pulp was heated to 40 °C and air bubbling was turned on at a speed of 5-6 m ³ /h. After this they poured it into the reactor 150 l of 12 M hydrochloric acid and carried out the process of bubbling with air (or a mixture of oxygen with inert gases) under such conditions until the ORP value was reached equal to 100-500 mV, relative to the silver chloride reference electrode, turned off the air supply, turned on the supply of chlorine gas at a speed of 3 m ³ /h and using known methods, the concentrate was dissolved using liquid-phase chlorination. After completion of the process, the pulp was cooled and the solution was separated from the sediment by filtration on a suction filter. All obtained middlings were analyzed: solutions by mass spectrometry with inductively coupled plasma; sediments using X-ray spectral analysis. The results are presented in Table 2.

EXAMPLE 3

To conduct a series of experiments, an iron-based concentrate obtained at the enterprise was taken with the following composition, typical for such concentrates, %: Pt-2.1, Pd-5.3, Rh-0.9, lr-0.1, Ru-0.5, Au-0.4, Ag- 1.6, Fe-48.3, Cu-5.0, Si-4.9, P-7.0.

In a titanium reactor with a volume of 760 liters, equipped with steam heating and water cooling, devices for supplying reagents and mixing the reaction mixture, devices for monitoring pH values, ORP and temperature, 300 liters of water were poured, a mixing device was turned on, 70 kg of concentrate and a solution of potassium chlorate were loaded based on 30% of the stoichiometrically required iron for dissolution. After this, with the help of dosing devices, concentrated hydrochloric acid was introduced into the reactor in portions of 1-2 liters with a gradual increase in the temperature of the pulp and control of the acidity of the medium and the ORP value in the pulp. When the ORP dropped below 100 mV, an aqueous solution of potassium chlorate with a concentration of 700 g/l was introduced in portions of 0.2-0.5 l, the pulp was kept for a certain time at a given temperature, then subsequent portions of reagents were poured. When a stable ORP value in the acidic region was achieved in a given range of values, the pulp was heated for 2 hours, cooled to a temperature of 50 °C, 4 liters of a 25% aqueous solution of sodium methyl siliconate was poured into the reactor, the pulp was stirred for 10 minutes, filtered and washed with water. Basic the solution and industrial waters were combined. The filtration rate was (500-550) l*h/ ^m2 . Since the composition of the undissolved residues in all experiments is similar in composition, the process of dissolving it in hydrochloric acid during oxidation was carried out only with the product from the first experiment. The results for the dissolution of base elements are presented in Table 3.

Thus, the proposed method for processing an iron-based concentrate containing noble metals makes it possible to extract the main part of the iron and other base elements into solution, excluding, at the same time, the formation of an explosive air-hydrogen mixture and the release of highly toxic phosphine gas, and to concentrate the main part of the noble metals in a separate industrial product, quickly and efficiently separate it from the solution by filtration, and then dissolve it in a safe way.

Table 1

Distribution of metals during the dissolution of an iron-based concentrate containing noble metals.

** Emission of hydrogen gas was observed. table 2

Distribution of metals during the dissolution of an iron-based concentrate containing noble metals.

** Emission of hydrogen gas was observed. Table 3

Distribution of metals during the dissolution of an iron-based concentrate containing noble metals.

** Emission of hydrogen gas was observed.

Claims

Claim 1. A method for processing iron-based concentrates containing noble metals, including pulping the concentrate in water, treating the pulp with alkali metal chlorate and sulfuric or hydrochloric acid to transfer base elements into solution, heating the reaction mixture, separating the impurity solution from the undissolved residue containing noble metals, and its subsequent dissolution, characterized in that the treatment with acid and alkali metal chlorate is carried out by alternately introducing them in portions into the aqueous concentrate concentrate, while maintaining the value of the oxidation-reduction potential (ORP) in the pulp in the range (0-350 ) mV, relative to the silver-silver chloride reference electrode, and heating the reaction mixture after introducing each portion of the reagents, the undissolved residue, in which noble metals are concentrated, is dissolved in concentrated hydrochloric acid with sequential oxidation, first with oxygen and then with chlorine. 2. The method according to claim 1, characterized in that before separating the undissolved residue, the pulp is treated with a solution of alkali metal organosiliconate. 3. The method according to claim 1, characterized in that oxidation with oxygen is carried out until a stable ORP value in the pulp is achieved in the range (100-500) mV, relative to the silver chloride reference electrode, 4. The method according to claim 1, characterized in that oxygen is supplied to the reaction mass in the form of air or a mixture of oxygen with inert gases, nitrogen or carbon dioxide.