RU2226225C1 - Method of cleaning and concentrating chlorine complexes of platinum metals by electrolysis method - Google Patents

Abstract

FIELD: hydrometallurgy of platinum metals; refining processes engaged in extraction and purification of platinum metals from primary raw materials and secondary materials. SUBSTANCE: proposed method includes separation of aqua solution of complex compounds of platinoids from solutions of admixtures by means of electro-membrane method. Electrolysis of working solution is performed in four-path electrodialysis converter with the use of cationite and anionite membranes and porous diaphragms mounted in such way that first cationite membrane separates circulating solutions of cationite path from working solution path and porous diaphragm separates working solution from purified solution. Process is conducted at current density of 2.4-3.0 A/sw dm and temperature of 30-60 C; grade MK-40 membrane is used as cationite membrane and grade MA-40 membrane is used as anionite membrane; perfluorinated diaphragm at average diameter of 0.1 mcm is used as porous diaphragm MFFK-1. 2 or 4% solution of NaOH is used as catholyte and anolyte. EFFECT: possibility of performing thorough purification of platinum metals at high concentration coefficients. 3 cl, 2 dwg, 4 ex

Description

This invention relates to the hydrometallurgy of platinum metals, in particular their purification from contaminants from crude refractory salts. Its results can be used in the processing of both primary and secondary raw materials containing some platinum group metals.

Widely known and common methods of separation of various ions using ion exchange membranes. This relates primarily to electrodialysis water treatment, i.e. the possibility of desalination and concentration of ions with charges of various kinds in special chambers using anion-exchange and cation-exchange membranes [Grebenyuk V.D. // Electrodialysis. Technique, 1976, p.151]. Work on the separation of unlike complex ions and simple cations is presented to a lesser extent. However, in the book [Ion Exchange and its Application. M., 1959, s.298] a laboratory three-chamber electrolytic cell diaphragms ionite scheme where tested the possibility of separation of the ions having opposite charges, for example, purification of [MoO _4] ^- from Ca ^2+, Cu ^2+, and other cations. The lack of test results does not allow us to make a conclusion about the efficiency of the given cell.

The scientific and patent literature does not provide information on the use of this technique in the technology of refining platinum metals from metal contaminants. There is a reference to the use of electrodialysis using heterogeneous membranes in the analysis of noble metals [Bardin MB, Pushnyak AN, Voloshina M.Kh. Abstracts of the VII Meeting on the analysis of precious metals. - Norilsk, 1966, p.8]. However, neither the conditions of the experiments, nor the objects of research and the results obtained are not reported.

The closest analogue to the prototype should be considered the work [Yezerskaya N.A., Solovy T.N.// Izv. USSR Academy of Sciences, ser.chem, 1969, No. 5, p. 99], which describes an attempt to use high-voltage electrodialysis for the analytical separation of complex forms of platinum metals. Using a laboratory glass three-chamber electrodialysis cell equipped with a MK-40 cation-exchange membrane for separating the cathode chamber and a cellophane membrane from the anode chamber, the authors experimentally confirmed the fact that platinum metals can form different forms of different charge states as a result of hydrolysis, which must undergo electromigration differently. Upon separation, all iridium and only 60-80% of platinum and palladium pass into the anode space, and rhodium is not more than 60%. The main goal of the work - the individual electrodialysis separation of complex chlorides of various platinum metals with the aim of their subsequent analytical determination - was not achieved. The purification of platinum ions from some contaminants, for example, Cu ²⁺ , Ni ²⁺ , Fe ³⁺ , was also addressed in this work, although the experiments were carried out only with pure salts and model mixtures that simulated real production solutions. Copper and nickel in small concentrations penetrate through the cellophane membrane, partially precipitating on the electrode, while iron is deposited in the form of hydroxide on the membrane. When using the MK-40 cation-exchange cloth, most of these metals are absorbed by the membrane, poisoning it at the same time.

Thus, the prototype method only indicated the fundamental possibility of using electrodialysis to solve the problems of separation of both platinum metals among themselves, and their purification from typical metallic impurities. The main disadvantages of the prototype method include the laboratory scale of the cell, the main chamber of which had a volume of 70 ml, a low content of platinum metals (at the level of 1-2 mg), a periodic version of the work. Pouring distilled water into the side chambers initially assumed operation at high voltages (up to 600 V) and an extremely low current of 3-5 mA. The latter circumstance leads to low productivity and high process time even for such low-concentrated solutions. The main conclusion following the analysis of the results given in the prototype method indicates the preference for thin synthetic cellophane over a standard MK-40 ion-exchange membrane. However, the use of cellophane as a neutral membrane is impossible due to the fact that it does not possess the necessary properties that are shown to the chemical, thermal and technological resistance of membranes even for ordinary electrodialysis. The specifics of using this method for working with solutions of platinum metals, which are obtained from alkaline or acidic media, including aqua regia, completely excludes the use of cellophane.

The objective of the present invention is a method for purification and concentration of platinum metal chlorocomplexes by electrodialysis, the aim is to create a continuous electrodialysis method of high performance, easily adaptable to existing refining production schemes, the technical result of which is the deep purification of platinum metals at high concentration ratios.

The technical result is achieved by the fact that in the method for purification and concentration of platinum chlorocomplexes by electrodialysis, which includes the separation of an aqueous solution of complex compounds of platinum metals from solutions of impurities using the electro-membrane method, the electrodialysis of the working solution is carried out in a four-channel electrodialysis converter using cation exchange and anion-exchange membranes and as porous apertures of perfluorinated membranes of the MFFK-1 brand with an average pore diameter of 0.1 μ and using as catholyte and anolyte NaOH solution, the first cationite membrane is installed with the possibility of separating the circulating solutions of the catholyte tract from the path of the working solution, and the porous diaphragm with the possibility of separating the working solution from the purified solution, while electrodialysis is carried out at a current density of 2.4 - 3, 0 A / dm ² and a temperature of 35-60 ° С using MK-40 grade as an cation exchange membrane, MA-40 anion exchange grade, as well as the fact that 2-4% NaOH solution is used as catholyte and anolyte.

Thus, the main distinguishing features of the proposed method are the use as a working dialysis diaphragm not of an anion-exchange membrane, which is impermeable to these complex anions, but of a neutral chemically resistant membrane MFK-1g with a small bar effect, carried out in parallel with the cleaning cycle to replace the neutralizing charge of the complex anion by other cations, the arrangement of membranes in a unit electrodialysis cell, selection of temperature and electrical conditions, etc. cession electrodialysis.

Modern electro-membrane technologies should not only allow the purification of platinum metal ions, but also carry out cationic exchange, which ensures the production of compounds with higher solubility. The latter circumstance is a prerequisite, since this reduces the number of processed solutions, reduces the volume of apparatus and tank equipment, reduces energy consumption.

Thus, the set of ion-exchange membranes and the order of their installation in the apparatus should ensure the separation of platinum metal anions from contaminating cations and facilitate the target exchange of cations of the initial salt.

Of the many experimental facts collected in the coordination chemistry of platinum metals, it is well known that in aqueous solutions, as well as chloride media, the latter are represented by complex multiply charged general anions:

[MCl ₆ ] ^n- , where M = Pt (IV), Pd (II), Ir (III), Rh (III) n = 2-3.

Some changes in the internal coordination sphere, for example, during hydrolysis can lead to a change in the charge state of the ion, but in all cases they remain complex anions. The vast majority of polluting ion impurities under these conditions are simple cations of various metals. The separation scheme involves the transition under the influence of an electric field of a direct current of cations through a cation exchange membrane, and ions of noble metals through another sort of membrane.

Laboratory experiments have shown that electromigration of noble metal ions through the MA-40 brand anion exchange membrane is extremely difficult and practically does not occur. This circumstance excluded further selection of ion-exchange membranes with other types of resins, since it is well known that all of them have an undesirable reducing effect in relation to solutions of precious metal salts. But the permeability of the platinoid complexes through cellophane observed in the prototype also cannot be used in the technological apparatus due to its insufficient mechanical strength and chemical instability even in dilute nitric acid solutions. To solve this type of problem, all conditions are met by a perfluorinated membrane on a polypropylene base of the MFK-1g brand with an average pore size of ≈0.1 μ and a water productivity of 2.3 m ³ / m ² · h at a pressure of 0.5 atm.

The layout of the membranes of the electrochemical cell is shown in figure 1, and their translation in the electrodialysis apparatus is shown in figure 2. As can be seen from the drawings, two cation-exchange and one fluoroplastic membranes form circulation channels for solutions of the initial contaminated potassium salt of platinum and its dialuate. A solution of sodium hydroxide is initially supplied to the anode and cathode chambers. When a direct current is turned on, cations of potassium, copper, nickel, iron, and other metals migrate to the cathode chamber. The complex hexachloroplatinate ion is involved in the transfer of current through the perforated membrane and remains in the chamber on the right. Sodium ions pass from the anode chamber there, forming already in solution a sodium salt of platinum. If it is necessary to obtain hydrochloric acid at the outlet, a solution of hydrochloric acid is required to be pumped through the anode chamber.

For example, a conversion of sparingly soluble salts of the form K ₂ PtCl ₆ or NH ₄ PtCl ₆ into their sodium analogue with a solubility of 42 wt% or acid H ₂ PtCl ₆ , which is a six-water crystalline hydrate, is possible.

Similar transformations are realized by analogy for the complexes Pd (II), Rh (III), Ir (III), Ru (IV).

It was a combination of these two distinctive features that was used in the future and was reflected in the design of the pilot electrodialysis unit used in the platinum cleaning cycle.

Example 1

The first precipitate K ₂ PtCl ₆ obtained from the processing of platinum from KP-1 concentrate contained 0.32 wt.% Cu, 0.28 wt.% Fe, 0.18 wt.% Pb, 0.69 wt. .% Ni. A laboratory electrodialyzer equipped with a nickel cathode and an anode of iridized titanium, a set of corresponding membranes with an area of 0.8 dm ² each, is fed with a multichannel peristaltic pump as anolyte and catholyte with a 2% NaOH solution at a rate of 180 ml / min. A sample of platinum salt weighing 5 g is placed in a glass with 150 ml of water and its solution is sent to the cleaned tract. The channel of the pure product is initially filled with distilled water, acidified with HCl to pH 3. Dialysis is carried out at a temperature of 35 ° C and a current density of 2.4 A / dm ² for 2.5 hours. The residual platinum content in the initial solution is 9 μg / ml. The purity of Pt obtained from the purified solution far exceeds the requirements for the metal grade PLAP-0. Mass fractions of impurities in the purified platinum powder are: Cu - 3 · 10 ^-4 %, Fe - 2 · 10 ^-4 %, Pb - 4 · 10 ^-4 %, Ni - 3 · 10 ^-4 %.

Example 2

250 ml of an aqueous solution of technical palladium salt K ₂ PdCl ₄ weighing 9 g, containing a total of 3.4% of impurities, the main of which are Al, Mg, Cu, Zn, Fe, Ni, are pumped through the electrochemical cell described above. At a current of 3A and a voltage of 12 V, after 90 min a Na ₂ PdCl ₄ solution with a concentration of 28 g / L is obtained in the treatment channel. The cell productivity under these conditions is 8 g / dm ² · h. The purity of palladium refined in this way is 99.999%, which far exceeds the conditions of GOST 14836-82.

Example 3

A sample of K ₃ RhCl ₆ weighing 22 g is filled with 200 ml of water and this suspension is circulated in the electrodialysis cell. A 2% NaOH solution enters the cathode chamber, and 0.1 N is pumped through the anode. hydrochloric acid. When a current of 5A is passed and an average voltage of 12 V in the cell in the concentration channel, acid formation of H ₃ RhCl ₆ occurs due to migration of hydrogen ions from the anolyte solution to the cathode. After 1 h of work, the concentration of rhodium in the complex acid reaches 92 g / L. The chemical composition of the rhodium metal powder recovered by known methods satisfies ASTM B 616-78.

Example 4

The rough salt of the form K ₂ PtCl ₆ obtained from the first precipitation during the purification of platinum after its cementation by aluminum, according to atomic absorption analysis, has the following composition of basic metal impurities, wt.%: Al 4.1; Cu 0.4; Fe 0.5; Ni 0.4; Cr 0.2; Si 0.2; Pb 0.1. 19 kg of salt with a moisture content of 28% are added to a 60-liter enameled pressure vessel equipped with a cooling coil and pulped from 60 liters of distilled water. The receiving tank for a clean solution is filled with 0.1% NaOH solution, the feeding containers of anolyte and catholyte - 4% alkali solution. Stock solutions with the help of pumps circulate through an electrodialyzer of a press filter type having 38 purification chambers with a total area of working membranes of 18 m ² . The process is conducted at a current density of 320 A / m ² and a temperature of 50-55 ° C. As soon as the concentration of platinum reaches 60-70 g / l, 40 l of the solution is removed, the same amount of water is added and a new portion of salt weighing 1-2 kg is added. The productivity of the apparatus is ≈120 g / m ² · h with a specific energy consumption of 12 kW / h · kg. The results of the chemical composition of platinum metal on controlled impurities, according to spectral analysis, allow us to conclude that it meets the requirements of ASTM B 561-86.

Thus, the obtained experimental data allow us to conclude that the application of the electrodialysis method to solving problems of deep purification of platinum metals is very promising for existing refining plants.

Claims (3)

1. The method of purification and concentration of chlorine complexes of platinum metals by electrodialysis, including the separation of an aqueous solution of complex compounds of platinum metals from solutions of impurities using the electro-membrane method, characterized in that the electrodialysis of the working solution is carried out in a four-channel electrodialysis converter using cation exchange resin and anion exchange resin and as porous diaphragms - perfluorinated membranes of the brand MFFK-1 with an average pore diameter of 0.1 μm, using catholyte and anoly and NaOH solution first with the cation exchange membrane installed with the possibility of separating the circulating catholyte solutions tract tract from the working solution, the porous diaphragm and - with the possibility of separating the working solution from the purified solution. 2. The method according to claim 1, characterized in that the electrodialysis is carried out at a current density of 2.4-3.0 A / dm ² and a temperature of 35-60 ° C using an MK-40 brand membrane as a cation exchange membrane and a brand anion exchange membrane MA-40. 3. The method according to claim 1 or 2, characterized in that as a catholyte and anolyte use a 2 - 4% solution of NaOH.

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