RU2743567C1 - Method of producing zinc powder from zinc-containing wastes - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: invention relates to production of zinc powder from zinc containing wastes for cement cleaning of solutions of zinc sulphate from admixtures of cobalt, cadmium and antimony. Method involves leaching of zinc containing wastes, electrolysis of alkaline solution with precipitation of zinc powder, its separation from electrolyte and washing. At the stage of zinc-containing wastes leaching, lead containing dust of zinc or lead production is introduced into the solution in the quantity ensuring zinc to lead ratio in solution 143:61. Electrolysis of solution is carried out with deposition of zinc powder, particles of which have evenly distributed lead.EFFECT: obtaining zinc powder with plate-like particles with uniform distribution of lead therein and with narrow particle size range of 5–7 mcm, as well as increased activity of zinc powder due to inclusion of electrolytically precipitated lead in its composition and eliminated back dissolution of impurities during cementation cleaning.1 cl, 1 tbl, 1 ex

Description

The invention relates to powder metallurgy, in particular to the production of metal powders and can be used in the production of zinc powder from zinc-containing waste, for example, dust from electric arc furnaces.

There is a known method of obtaining zinc powder from wastes from the production of rongalit, according to which the solution after alkaline leaching of the waste is sent to the electrochemical deposition of zinc powder (USSR author's certificate No. 1468976, priority dated 08.21.1987).

The use of the powder according to the specified method in the carburizing treatment from impurities has the following disadvantages:

- high consumption of reagents: antimony trioxide and copper sulfate;

- the process is accompanied by the reverse dissolution of cemented impurities (cadmium, cobalt, antimony).

The closest in technological essence to the claimed is a method for producing zinc powder from zinc-containing waste - ferrous metallurgy dusts (Patent No. 2663918 Russia for CL. С25С 5/02, published 13.08.2018 Bulletin No. 23).

The process of leaching zinc-containing waste is carried out in an alkali solution to obtain a solution containing 43 g / dm ³ Zn and 350 g / dm ³ NaOH. Sodium lignosulfate is added to the resulting solution in the amount of 900-1500 g / t of zinc powder and the solution is sent to electrolysis. Electrolysis is carried out at a current density (cathodic) of 2500 a / m ² . Removal of the precipitate from the cathode was performed after 38-40 minutes, which corresponds to the passage of 60 F / m ^{2 of} electricity through the bath. The resulting zinc precipitate was subjected to filtration from the cement slurry, washing with dispersion, and drying under vacuum. The dry powder was used in a process to precipitate a cobalt impurity from a commercial zinc sulfate solution.

The disadvantages of this method are:

- high consumption of reagents when using powder in carburizing processes when cleaning zinc solutions from impurities;

- low productivity of the cementation process;

- low degree of purification of solutions from cadmium, cobalt and antimony. The patented method is based on the following goals:

- increasing the productivity of the cementation process;

- reducing the consumption of zinc powder when using it for carburizing cleaning from impurities;

- reducing the content of impurities in the sulfate zinc solution supplied to electrolysis to obtain metallic zinc;

- reducing the consumption of reagents for carburizing treatment.

This goal is achieved by the fact that in the known method of producing zinc powder from zinc-containing waste, including leaching waste (dust from electric arc furnaces), electrolysis of solution, separation of the precipitated powder from the electrolyte at the electrolysis stage. Lead-containing dusts of zinc production, formed during calcination of Waelz-oxides or lead production, are introduced into the leaching stage in an amount that provides the ratio of zinc to lead in a solution of 143 ÷ 61.

The supply of a lead-containing product allows:

1) To ensure the production of zinc powder with plate-like particles with a uniform distribution of lead in them and a grain size composition with a narrow range of particle sizes of 5-7 microns.

2) Increase the activity of zinc powder by including electrolytically deposited lead *

(* In alkaline solutions, lead and zinc have practically the same overvoltage of hydrogen, respectively, 1.1 V and 1.14 V and therefore simultaneously precipitate on the cathode. In acidic solutions in which zinc is used for cementation of impurities, the overvoltage of lead for cathodic hydrogen evolution on lead higher by 0.24 V in comparison with zinc, which makes it possible to exclude the reverse dissolution of cemented impurities (Co, Sb, Cd) during cementation with zinc powder with the addition of lead and increase the depth of solution purification, reduce the consumption of zinc powder for cementation. used to suppress the reverse dissolution of impurities).

3) Exclude the reverse dissolution of impurities (Co, Sb, Cd) when carrying out carburizing treatment.

This increases the productivity of the carburizing process, and reduces the consumption of zinc powder for carburizing.

Example

To compare the existing and the proposed method used zinc powder obtained by electrolysis from an alkaline solution according to the prototype and according to the proposed method.

Zinc powder according to a known technology was obtained by electrolysis of an aqueous solution containing 350 g / dm ³ NaOH and 43 g / dm ³ Zn with the addition of technical lignosulfonate (LST) in the amount of 1300 g / t LST in an electrolysis bath with a stainless steel cathode and anode. The temperature of the solution was 40-45 ° C, the current density (cathodic) - 2500 A / m ² . The sediment was removed after 38-40 minutes. The obtained zinc powder was subjected to filtration from an alkaline solution, washing with dispersion and drying under vacuum.

Zinc powder according to the proposed method is obtained by electrolysis of an aqueous solution containing 350 g / dm ³ NaOH, 43 g / dm ³ Zn and 0.3-0.7 g / dm ³ Pb. The addition of lead to the solution was carried out in the form of an alkaline solution containing 51 g / dm ³ Pb, obtained after alkaline leaching of lead-containing dusts of zinc production (secondary fumes from calcining Waelz oxide).

The electrolysis was carried out in modes similar to the electrolysis mode according to the prototype, followed by filtration, washing with dispersion and drying under vacuum of the powder.

Samples of dry powder obtained according to the prototype and the proposed method were used in tests for the precipitation of impurities of cobalt, cadmium, antimony from an industrial solution of zinc sulfate containing:

Zn - 125 g / dm ³ ; Co - 4.1 mg / dm ³ ; Sb - 0.028 mg / dm ³ ; Cd - 8.9 mg / dm ³ .

The deposition was carried out according to the used industrial technology at a temperature of 60 ° C for 30 minutes and 60 minutes and the consumption of reagents, respectively: copper sulfate 125 mg / dm ³ and 187.5 mg / dm ³ ; antimony trioxide - 4.2 mg / dm ³ and 5.4 mg / dm ³ and the proposed technology within 30 minutes at a consumption of reagents: copper sulfate 125 mg / dm ³ , antimony trioxide - 4.2 mg / dm ³ .

At the end of the operation, the resulting precipitate was filtered off, and the final concentration of impurities in the solution was determined.

The test results for the proposed and existing methods are shown in the table.

From the data in the table, it can be seen that in the absence of lead additive, there is a low productivity of the solution purification process, a high consumption of reagents, including zinc powder, copper sulfate, antimony trioxide for purification, a high content of the purified solution.

The addition of lead to electrolysis in the form of an alkaline lead-containing solution with a lead concentration in the solution of 0.3-0.7 g / dm ³ in a Zn: Pb ratio in a solution of more than 430 does not allow reducing the cleaning time from 60 minutes to 30 minutes and increasing the productivity of the site cleaning solutions, exclude the reverse dissolution of impurities (cadmium, cobalt, antimony) and obtain a purified solution with a cobalt content of less than 0.4 mg / dm ³ , cadmium less than 0.3 mg / dm ³ and antimony less than 0.2 g / dm ³ ( requirements for industrial sulfate solution for the production of zinc metal by electrolysis). An additive that reduces the Zn: Pb ratio in solution to less than 61 does not increase the positive effect.

The use of the powder obtained by the proposed method allows to reduce the consumption of zinc powder for cleaning by 16% (from 2.5 to 2.1 g / dm ³ ), copper sulfate by 33% (from 187.5 to 125.1 mg / dm ³ ) and antimony trioxide by 22% (from 5.4 to 4.2 mg / dm ³ ).

Claims (1)

A method of producing zinc powder from zinc-containing waste for cementation treatment of zinc sulfate solutions from impurities of cobalt, cadmium and antimony, including leaching of zinc-containing waste, electrolysis of an alkaline solution with precipitation of zinc powder, separating it from electrolyte and washing, characterized in that at the stage of leaching zinc lead containing dust of zinc or lead production is introduced into the solution in an amount that ensures the ratio of zinc to lead in a solution of 143: 61, while electrolysis of the solution is carried out with the precipitation of zinc powder, the particles of which have lead evenly distributed in them.