RU2207390C2 - Method of processing of palladium refining hydroxide sediments - Google Patents

Abstract

FIELD: metallurgy of nonferrous metals, particularly, refining of platinum metals in processing of hydroxide sediments of palladium refining. SUBSTANCE: sediment contains the main components from nonnoble metals in form of ferrous hydroxide and noble metals in form of palladium. Presence of high content of ammonium and ammonia compounds (above 25%) makes it possible to supply sediments directly for opening by chlorination. To provide for recovery of noble metals from obtained hydroxides by chlorination, it is offered to prepare sediments by calcination in steel trays at temperature of 830-870 C. In this case, main mass of iron passes into insoluble ferrous-ferric oxide - magnetite, and palladium passes into metal form. EFFECT: increased direct recovery of palladium into solution, reduced losses of nonferrous metals and expenditures for conduction of process. 1 tbl, 7 ex

Description

 The invention relates to the field of metallurgy of non-ferrous metals, in particular to the refining of platinum metals.

 Hydroxide precipitates of palladium refining are formed at the stage of dissolution of the technical salt of trans-dichlorodiammine palladium in ammonia water. The main components of precipitation are complex hydroxides of iron, copper, tellurium, selenium and other non-ferrous metals, as well as metallic palladium, platinum and their ammonia-chloride complex compounds. Palladium is the main useful component of precipitation, its content is (15-20)%. Among base metals, the main one is iron, mainly in the form of iron (II) hydroxide.

 Hydroxide precipitation is an intermediate product that cannot be directly returned from the work in progress to the autopsy by chlorination. The reason for this is the presence in this product of a large number of ammonium and ammonia compounds, since chlorination forms sparingly soluble hydroxide complexes of platinum and palladium.

 A known method of processing hydroxide precipitation by melting (Zvyagintsev OE Refining gold, silver and platinum group metals. M: Metallurgizdat, 1945, p. 158). During the reductive melting of hydroxides, ammonium compounds decompose, and the oxide forms become elemental metallized. The resulting alloy is sent for chlorination.

The disadvantages of this method are
- partial conversion of platinum metals into slag and furnace lining (up to 15%);
- reduction of direct extraction of platinum, palladium and gold in the refining cycle due to the transfer of slag and lining for processing;
- the practical absence of a channel for the withdrawal of non-ferrous metals and iron from hydroxide precipitates.

 From the same source of information (p.140-143. Fig. 99.), a method for processing a precipitate of hydroxides by calcination is known.

 The latter method is the closest to the claimed, i.e. prototype.

 Attempts to use the prototype at the refinery did not give the result required by the regulations due to the lack of optimal conditions and conditions for calcining hydroxide precipitates.

 The technical result of the proposed method is to establish optimal calcination modes that increase direct extraction of palladium in a chlorination solution, reduce the degree of transition of non-ferrous metals into solution, and reduce the cost of processing hydroxide precipitates.

The implementation of the technical result is achieved by the fact that in the known method of processing hydroxide precipitates, including calcining them and subsequent processing to extract precious metals, calcining the precipitates is carried out in a steel pan at a temperature of 830-870 ^o C, and processing is carried out by liquid phase chlorination with the conversion of precious metals into solution.

The essence of the method is that at temperatures above 830 ^o With palladium oxide decomposes to metal, and the presence of a reducing agent prevents the reverse oxidation during cooling of the cinder, i.e. iron (II) oxide and metallic iron (baking sheet material), in the presence of which the formation of palladium oxide is impossible. During the calcination process, up to 70% of selenium is distilled into the gas phase.

 The bulk of the iron from the composition of hydroxides in the presence of metallic iron in the pan passes into iron oxide (II-III), i.e. into magnetite. A characteristic feature of both natural and synthetic magnetite is a very low degree of opening it in the process of liquid-phase chlorination. Therefore, insoluble residues (n.o.) of chlorination are a channel for the removal of iron from the process.

 The optimization parameter for the processing of hydroxide precipitates is the maximum degree of conversion to the solution during the chlorination of platinum, palladium, gold, and the minimum - iron and non-ferrous metals.

 Examples of the method of the prototype and the proposed regulations are presented in the table.

As an object of study, a sample of typical hydroxide precipitates (after drying) of the composition was used,%:
Pt 1.1; Pd 18.9; Rh 0.13; Au 0.4; Ag 0.3; Fe 12.8; Cu 2.1; Se 4.7; Te 4.3; Sb 0.3; Sn 2.1.

Hydroxides were chlorinated (HCl + NaClO ₃ ) directly (experiment 1), melted, then the resulting alloy was chlorinated (experiment 2), calcined at various temperatures and in different containers, the calcine was chlorinated (experiments 3-7).

From the above data it follows that the chlorination of hydroxides directly causes a large yield of insoluble residue and the content of Pt and Pd in it (more than 40%). Extraction into the solution of palladium does not exceed 77%, and platinum - 23% due to the formation of sparingly soluble salts (NH ₄ ) ₂ [MeCl ₆ ], where Me is Pt and Pd.

 Melting hydroxides onto an alloy is more efficient and allows the extraction of (96-99)% Pt and Pd at the stage of chlorination of the alloy. However, when melting hydroxides, the extraction of Pt and Pd into the alloy does not exceed 95%, i.e. total recovery at the level of (92-94)%. In addition, when the alloy is chlorinated, (97-99)% non-ferrous metals are extracted into the solution, which is undesirable.

Annealing of hydroxide precipitates at a temperature of 400 ^o C (experiment 3) leads to significantly worse performance than smelting. It was also noted at a temperature of 800 ^o C. The reason is the oxidation of palladium with its conversion during chlorination to insoluble oxide.

Calcination of hydroxides at a temperature of 830-870 ^o With dramatically improves the performance of subsequent chlorination, since at a temperature of more than 830 ^o With the decomposition of palladium oxide. Extraction of Pt, Pd, and Au into the solution is 97-98%, while Fe, Se, Sn - 33-50%. Iron and tin pass into sparingly soluble oxides, and selenium disappears.

Calcination at a temperature of 900 ^o C has no advantages, but causes technical difficulties with unloading the cinder, as it is partially fused into the container material.

Calcination of hydroxides at an optimum temperature of 830-870 ^o C in a steel pan is preferable due to the lower degree of transfer of iron into solutions, which does not exceed 20%. The degree of extraction of palladium in solution during chlorination of the cinder is maximum (~ 99%), since iron prevents the reverse oxidation of palladium.

The advantages of the claimed method are
- recycling of industrial products in the technological scheme of refining platinum and palladium;
- an increase in direct extraction of palladium in solution during chlorination by 15-17%;
- decrease in extraction into solution during chlorination (2-3 times) of the main non-ferrous metals of hydroxide precipitates (iron, tin, selenium).

Claims (1)

A method for processing hydroxide precipitates of palladium refining, including calcining the precipitates and subsequently treating them to extract noble metals, characterized in that the precipitation is calcined in a steel pan at a temperature of 830-870 ^o C, and the treatment is performed by opening by liquid phase chlorination with the transfer of noble metals into solution .

Images