RU2469112C1 - Method for extracting cadmium from secondary raw material - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method involves leaching of cadmium from raw material in solution of sodium ethylene diamine tetraacetate with its further extraction from solution and regeneration of ethylene diamine tetraacetate. Cadmium leaching is performed in two stages. The solution obtained at the first stage is supplied for extraction of cadmium, and residue of the first stage is supplied to the second cadmium leaching stage. The solution obtained at the second stage is used for leaching of cadmium from raw material at the first stage. Besides, leaching at the second stage is performed in presence of hydrogen peroxide at maintaining its concentration in the range of 10-15 g/dm³ during 2-2.5 hours.

EFFECT: increasing cadmium extraction degree.

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Description

The invention relates to metallurgy, and in particular to methods for producing cadmium, and can be used in the processing of negative lamellas of nickel-cadmium batteries.

The most widely used methods are the processing of cadmium-containing raw materials based on sulfuric acid leaching, where in the first stage of the process almost all scrap components are converted into solution, and later metals are extracted using various methods (1. Pfrepper Gerd, Deicke Liane. / Method for the extraction of valuable metals from Ni- Cd-scrap. Verfahren zur Ruckgewinmmg von Wertmetallenaus Ni / Cd-haltigem Schrott // Pat. 282925 GDR, IPC 4 C22B 7/00, C22B 11/04. Akademie der Wissenschaften der DDR. N 3283460; Declared 08.05.89; Publ. 09/26/90).

The disadvantages of the sulfuric acid method are the low degree of cadmium extraction due to its losses with iron and nickel-containing intermediate products, technological difficulties in cleaning industrial solutions.

Closest to the proposed technical solution is a method of processing nickel-cadmium scrap (patent RU No. 2372412, 11/10/2009. Bull No. 31), including cadmium leaching with a solution of sodium ethylene diamine tetra-acetate, followed by regeneration of the solvent and precipitation of cadmium.

The use of sodium ethylenediaminetetraacetate provides a high level of production safety, the possibility of solvent regeneration, which increases the economic efficiency of production, and also leads to a high degree of cadmium recovery. However, the prototype method does not provide a sufficient degree of cadmium extraction in the presence of cadmium metal in the feed. Since sodium ethylene diamine tetraacetate is leached in a medium, complexes are formed only with cadmium oxides and salts, and sodium ethylene diamine tetraacetate does not form complexes with metallic cadmium (the amount of which is significant in raw materials). Thus, a large amount of cadmium is lost with iron cake, which leads to the formation of iron-cadmium residue, the use and disposal of which are difficult.

The objective of the invention is to increase the degree of extraction of cadmium, in the processing of raw materials which contains both metallic and non-metallic cadmium, and obtaining processed products, the use of which does not present any difficulties.

This problem is solved in that the cadmium leaching is carried out in two stages, and the solution obtained in the first stage is sent to extract cadmium, and the residue is sent to the second stage of cadmium leaching, while the solution obtained in the second stage is used to leach the raw materials in the first stage, and leaching in the second stage is carried out in the presence of hydrogen peroxide while maintaining its concentration in the range of 10 -15 g / DM ³ for 2-2.5 hours.

It is rational to use hydrogen peroxide to oxidize cadmium metal in raw materials and transfer it into solution, since this oxidizing agent effectively oxidizes cadmium, while not polluting the solution with extraneous ions.

The countercurrent two-stage leaching process, in the presence of an oxidizing agent, provides the most complete extraction of cadmium in the solution, allows to obtain an iron-containing precipitate suitable for further processing at the iron and steel enterprises, and also completely eliminates the possibility of iron entering the solution.

The essence of the invention lies in the fact that negative lamellas of nickel-cadmium batteries are subjected to two-stage leaching. In the first stage, leaching is carried out with a solution of ethylenediaminetetraacetate obtained after the second stage at a ratio of T: W = 1: 5, while the obtained solid residue of the first stage is leached with a fresh solution of ethylene diamine tetraacetate, with a concentration of sodium ethylene diamine tetraacetate and hydrogen peroxide: 100-120 g / dm ³ and 15 g / dm ³ , respectively. The total duration of the two stages of leaching is 2.5 hours.

After filtration, the resulting cake is washed with water, and the wastewater is combined with the filtrate sent for re-leaching.

Sulfuric acid is added to the obtained solution of the first leaching stage until the pH of the solution reaches 1.0-1.6. In this case, a precipitate of ethylenediaminetetraacetate is obtained, from which, after filtration, a new leaching solution is prepared, and a cadmium-containing solution, which goes through the stages of cadmium hydroxide precipitation, filtration, washing and calcination by methods similar to the prototype.

This produces cadmium oxide that meets the requirements of GOST 11120-75.

Thus, in this method, it is possible to combine high speed and the degree of extraction of cadmium.

Leaching parameters are determined empirically and can be illustrated by the following data.

Example 1

A portion of cadmium-containing raw materials of alkaline batteries with a particle size of 0.1 mm, containing CdO 21.45%, Cd 43.84%, Fe ₂ O ₃ 28.1%, was leached in a solution of sodium ethylene diamine tetraacetate 100 g / dm ³ , obtained during the second leaching. A sample was taken from the solution obtained after filtration and analyzed for cadmium content.

The residue after the first stage was leached, with the addition of various amounts of hydrogen peroxide, in a fresh solution of sodium ethylenediaminetetraacetate, the same concentration obtained by regeneration of precipitated ethylenediaminetetraacetate.

Based on the obtained data, the completeness of cadmium extraction was calculated. For comparison, one sample was leached according to the method of the prototype in one stage, without the addition of an oxidizing agent. The results are shown in table 1.

Table 1 The results of experiments on leaching negative lamellas of nickel-cadmium batteries No. p / p The concentration of H ₂ O ₂ , g / DM ³ (initial) Temperature ° C Leaching time, min The degree of extraction of Cd,% one 8 thirty 200 85,2 2 10 45 180 93.8 3 12 40 190 96.8 four fifteen fifty 150 98.5 5 17 fifty 150 98.5 Leaching according to the prototype, at a temperature of 25 ° C, W: T = 1: 5, the concentration of sodium ethylenediaminetetraacetate 100-120 g / DM ³ , pH = 8-9. Leaching duration 120 min 54.3

Example 2

It differs from example No. 1 in that the experiments used raw materials without metallic cadmium and the oxidizing agent was not used.

A sample of the active mass of the negative lamella of a nickel-cadmium battery with a particle size of 0.1 mm, containing CdO - 21.5%, Fe ₂ O ₃ - 51.1%, graphite - the rest, was subjected to two-stage countercurrent leaching in a solution of 100 ethylene diamine tetraacetate with a concentration of 100 -120 g / dm ³ and pH = 7. For comparison, one sample was leached according to the method of the prototype in one stage. The results are shown in table 2.

table 2 The results of experiments on leaching negative lamellas of nickel-cadmium batteries No. p / p Stage 1 leaching time, min Stage 2 leaching time, min The degree of extraction of Cd,% one fifty fifty 96.8 2 60 60 98.0 3 70 70 98.1 Leaching according to the prototype, at a temperature of 25 ° C, W: T = 1: 5, the concentration of sodium ethylenediaminetetraacetate 100-120 g / DM ³ , pH = 8-9. Leaching duration 120 min 82.5

Comparative analysis of well-known technical solutions, including the method selected as a prototype, and the present invention allows to conclude that it is the totality of the claimed features ensures the achievement of the perceived technical result. The implementation of the proposed technical solution can significantly increase the extraction of cadmium during leaching of raw materials in which cadmium is in the oxidized form, and almost double the extraction during processing of raw materials in which cadmium is in the form of a metal.

Claims (1)

A method of extracting cadmium from secondary raw materials, comprising leaching cadmium from raw materials in a solution of sodium ethylene diamine tetraacetate followed by extraction of cadmium from the solution and regenerating ethylene diamine tetra acetate, characterized in that the leaching of cadmium is carried out in two stages, the solution obtained in the first stage being sent for cadmium recovery and the solid residue of the first stage is sent to the second stage of cadmium leaching, while the solution obtained in the second stage of leaching is used to leach cadmium from raw materials in the first stage, and leaching in the second stage is carried out in the presence of hydrogen peroxide while maintaining its concentration in the range of 10-15 g / dm ³ for 2-2.5 hours