Method of opening platinum-palladium concentrates with sodium chlorate

Abstract

FIELD: non-ferrous metallurgy.SUBSTANCE: invention related to the recovery of platinum-palladium concentrates containing platinum, palladium, platinum companion metals: rhodium, ruthenium, iridium, osmium, as well as gold, silver and base metal impurities. Said concentrate is hydrochlorinated in a hydrochloric acid solution with a concentration of 180-200 g / dm3 a sodium chlorate solution with a concentration of 700 g / dm3 until the required end-of-process oxidation-reduction potential of more than 1000 mV is achieved. The resulting pulp is filtered and the insoluble hydrochlorination residue is boiled in a hydrochloric acid solution with a concentration of 140-160 g / dm3, using a sodium chlorate solution with a concentration of 700 g / dm3. Moreover, when the required oxidation-reduction potential of 950-1050 mV is reached, the pulp is heated at 80-90 °C. The resulting pulp is filtered to obtain a chloride solution containing precious metals.EFFECT: ensures a reduction in hydrochlorination time, safe opening of the concentrate due to the elimination of chlorine gas, the elimination of additional chlorine equipment, an increase in the direct extraction of precious metals and a reduction in the number of operations.1 cl, 1 dwg, 1 tbl

Description

[0001] The present invention relates to the field of non-ferrous metallurgy, in particular, to the field of refining precious metals, namely to a method for refining platinum-palladium concentrates containing platinum, palladium, platinum companion metals (rhodium, ruthenium, iridium, osmium), gold, silver and base metal impurities.

[0002] According to the Information and Technical Handbook on Best Available Techniques ITS 14-2016 "Precious Metals Production", Moscow, BAT Bureau, 2016, p. 32, refining operations primarily utilize the decontamination of platinum-palladium concentrates in a hydrochloric acid solution with stirring and a temperature of 70-90°C using chlorine gas as an oxidizer. This process results in the platinum group metals and gold, as well as impurity elements, passing into the solution, from which, after filtration, gold, platinum, and palladium are sequentially separated, along with platinum's associated metals—rhodium, iridium, and ruthenium. Most of the silver remains in the insoluble chlorination residue. This method has been adopted as a prototype.

[0003] This method has the following disadvantages:

[0004] - the need to organize a chlorine facility, which is associated with the organization of a hazardous production facility with significant volumes of chlorine consumption and, as a consequence, the need for its storage, significant capital investments and operating costs;

[0005] - the duration of the concentrate hydrochlorination operation, which can reach 12-16 hours at a hydrochloric acid concentration of 300-350 g / dm3 3 and the solid:liquid ratio (hereinafter referred to as s:l) = 1:3.

[0006] Therefore, there is a need to develop a method that is free from the above-mentioned disadvantages.

[0007] According to the present invention, a method is proposed for opening platinum-palladium concentrates containing platinum, palladium, platinum companion metals - rhodium, ruthenium, iridium, osmium, as well as gold, silver and base metal impurities, including the stages of hydrochlorination in a hydrochloric acid solution, filtering the resulting pulp, boiling the resulting insoluble hydrochlorination residue in a hydrochloric acid solution and filtering the resulting pulp to obtain a chloride solution containing precious metals, characterized in that the hydrochlorination is carried out in a hydrochloric acid solution with a concentration of 180-200 g / dm 3 using a sodium chlorate solution with a concentration of 700 g / dm3 3 until the required indicator of the end of the oxidation-reduction potential process of more than 1000 mV is reached, the insoluble residue is boiled in a solution of hydrochloric acid with a concentration equal to 140-160 g / dm3 3, using a sodium chlorate solution with a concentration of 700 g / dm3 3 , and upon reaching the required oxidation-reduction potential of 950-1050 mV, the pulp is heated at 80-90°C.

[0008] The proposed method for opening platinum-palladium concentrates and insoluble concentrate residues with the conversion of at least 97.0% of all precious metals contained into a dissolved form involves a complete abandonment of the use of liquid chlorine in cylinders during the hydrochlorination operation in favor of a reagent - technical sodium chlorate (GOST 12257-93), prepared before the chlorination process with a concentration of 700 g / dm3 3 .

[0009] The technical result of the proposed invention consists of creating an efficient (by reducing the time of the main hydrochlorination operation from 12-16 hours to 4-6 hours) and safe method for decontaminating platinum-palladium concentrates with sodium chlorate. This technical result is also achieved by eliminating the use of chlorine gas in the main raw material decontamination operation, thereby eliminating the need for additional chlorine equipment: vessels operating under chlorine pressure, chlorine distribution, supply, and reduction units, and the labor costs associated with its operation.

[0010] Furthermore, the technical result consists in increasing the direct extraction of precious metals into target products, reducing the number of operations, including the resulting duration of the cycle for obtaining a chloride solution of precious metals suitable for further refining.

[0011] The basic diagram of the claimed method is shown in Figure 1.

[0012] The method proposed in the present invention is carried out as follows.

[0013] Water and hydrochloric acid are poured into the reaction apparatus, the required amount of concentrate or insoluble residue (IR) of the hydrochlorination concentrate is loaded with stirring, the gas duct valve to the absorber is opened, and then the reaction apparatus is heated to a temperature of 65°C. After reaching the set temperature, primary hydrochlorination is carried out - dosing in portions in a thin stream of 0.1-0.5 dm3 3 aqueous solution of sodium chlorate with a concentration of 700 g / dm3 3 , avoiding the introduction of larger portions of sodium chlorate solution at a time, until a stable oxidation-reduction potential (ORP) (relative to the silver chloride reference electrode) above 1000 mV is achieved. Upon completion of the hydrochlorination process, the pulp is cooled to a temperature of (40±5)°C with constant stirring and sent for filtration.

[0014] The insoluble precipitate is washed with water on the filter. After filtration, it is batched and sent to the digestion stage to ensure high direct extraction of precious metals. The digestion of the insoluble precipitates from the chlorination of the initial concentrates is carried out in a hydrochloric acid solution with a concentration of 140-160 g / dm3. 3 when feeding a sodium chlorate solution with a concentration of 700 g / dm3 into the pulp 3 Similar to hydrochlorination of concentrates, the ORP reaches 950 to 1050 mV. Once this potential is reached, the pulp is heated in the apparatus at a temperature of 80°C to 90°C for 1-2 hours. Upon completion of the process, the pulp is cooled to a temperature of 40±5°C with constant stirring and sent for filtration. This ensures additional extraction of precious metals into the solution by dissolving components of the material not fully recovered in the first stage.

[0015] It should be noted that the distinctive features of the proposed method are that the primary hydrochlorination is carried out in a hydrochloric acid solution of a lower concentration of hydrochloric acid (180-200 g / dm 3 versus 300-350 g / dm 3 ) and without the use of gaseous chlorine, using a sodium chlorate solution with a concentration of 700 g / dm3 3 and as a consequence, due to the more active course of the chemical reaction, a reduction in the time of the main hydrochlorination operation to 4-6 hours versus 12-16 hours during chlorination with gaseous chlorine until the required indicator for the end of the ORP process (oxidation-reduction potential) of more than 1000 mV is achieved.

[0016] The final product of the operations—the insoluble digestion residue—contains up to 3% of the remaining precious metals from the hydrochlorination step and is subject to further processing. The target product—the hydrochlorination solution (after hydrochlorination of the initial concentrate and the insoluble digestion residue)—contains at least 97% of the precious metals from the hydrochlorination step and is sent to further precious metal refining operations in the form of dissolved chloride compounds.

[0017] The parameters of hydrochlorination operations and the quantitative characteristics of the reagents are presented in Table 1.

[0018]

[0019] When 1g of sodium chlorate reacts with hydrochloric acid, 1.998g of chlorine gas is formed according to the reaction:

[0020] NaClO3+6 HCl=3 Cl2+NaCl+3H2O.

[0021] Chlorine is a strong oxidizing agent, and when it interacts with platinum group metals and gold contained in concentrates, in the presence of a complexing additive of hydrochloric acid, their water-soluble complex compounds are formed.

[0022] Pt+2Сl2+2НСl=H2[PtCl6],

[0023] Pd+Cl2+2HCl=H2[PdCl4],

[0024] Pd+2Cl2+2НСl=H2[PdCl6],

[0025] 2Rh+3Cl2+6HCl=2H3[RhCl6],

[0026] Ir+2Cl2+2HCl=H2[IrCl6],

[0027] Ru+2Cl2+2HCl=H2[RuCl6],

[0028] 2Au+3Cl2+2HCl=2H[AuCl4].

[0029] Osmium, which is present in the feedstock as a solid solution based on palladium and platinum, is oxidized by chlorine to form highly volatile osmium tetroxide by the reaction

[0030] Os+4Cl2+4H2O=OsO4+8HCl.

[0031] The silver contained in the feedstock is oxidized to form silver chloride, which remains as an insoluble residue

[0032] 2Ag+Cl2=2AgCl.

[0033] The base metal impurities contained in the concentrate: iron, copper, nickel, lead, selenium, tellurium, arsenic - are also oxidized by chlorine and pass into the sodium chloride solution in the form of simple chlorides and complex sodium chloride salts according to the reactions:

[0034] 2Fe+3Cl2=2FeCl3

[0035] Cu+Сl2=CuCl2,

[0036] Ni+Сl2=NiCl2,

[0037] Pb+Cl2+2NaCl=Na2[PbCl4],

[0038] Se+2Cl2+2NaCl=Na2[SeCl6],

[0039] Te+2Cl2+2NaCl=Na2[TeCl6].

[0040] Almost all of the chlorine formed interacts with the concentrate, which made it possible to replace gaseous chlorine with sodium chlorate during the operations of opening the concentrate (and boiling the insoluble precipitate).

[0041] To achieve high extraction of platinum group metals and gold from the feedstock, the chlorine consumption during hydrochlorination ranges from 100% to 120% of the stoichiometry of the oxidation reactions of the feedstock components. In this process, palladium(II) is oxidized to the tetravalent state, forming a palladium(IV) chlorocomplex according to the reaction

[0042] H2[PdCl4]+Cl2=H2[PdCl6].

[0043] The latter has strong oxidizing properties and, along with chlorine, takes direct part in the oxidation reactions of noble metals.

Claims

A method for opening platinum-palladium concentrates containing platinum, palladium, platinum associate metals: rhodium, ruthenium, iridium, osmium, as well as gold, silver and base metal impurities, including the stages of hydrochlorination in a hydrochloric acid solution, filtering the resulting pulp, boiling the resulting insoluble hydrochlorination residue in a hydrochloric acid solution and filtering the resulting pulp to obtain a chloride solution containing precious metals, characterized in that the hydrochlorination is carried out in a hydrochloric acid solution with a concentration of 180-200 g / dm 3 using a sodium chlorate solution with a concentration of 700 g / dm3 3 until the required indicator of the end of the oxidation-reduction potential process of more than 1000 mV is reached, the insoluble residue is boiled in a solution of hydrochloric acid with a concentration equal to 140-160 g / dm3 3 , using a sodium chlorate solution with a concentration of 700 g / dm3 3, and upon reaching the required oxidation-reduction potential of 950-1050 mV, the pulp is heated at 80-90°C.

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