RU2505613C2 - Method for electrochemical extraction of lead from lead/acid wastes of accumulator batteries - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves electrochemical deposition of lead from alkaline solutions on asymmetric pulsed current with variation of the periodic sequence of packets of positive n+ and negative n- current pulses, wherein the number of pulses in a packet is selected from n+=20 and the interval 1≤n-≤10.

EFFECT: high degree of extraction of lead from alkaline solutions, low costs, environmental safety and wasteless production.

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Description

The invention relates to the field of electrochemical production, in particular to methods for extracting lead from waste batteries. The invention can be used to obtain lead from alkaline solutions.

A known method of extracting lead from a solution containing plumbite and sodium sulfate by neutralizing with acid by reaction

Na ₂ PbO ₂ + 2H ₂ O ₄ → PbSO ₄ + Na ₂ SO ₄ + H ₂ O.

The precipitate of lead sulfate is returned to desulfation (Marachevsky A.G. ZhPH, 1998, No. 6, p. 881-890).

The disadvantage of this method is the implementation of additional technological operations - neutralization, filtration, washing the precipitate with water, which significantly increases the cost of the product (Na ₂ SO ₄ ).

The closest analogue prototype is the extraction of lead in the form of a cathode sponge from sulfamic and hydrofluoric electrolytes.

The disadvantage of this method is the incomplete degree of lead extraction, since lead is extracted from the test solutions at the limiting current and diffusion restrictions with time can significantly reduce its deposition rate. In addition, the formation of a slurry in the form of a crust on the anode creates additional resistance and interferes with the deposition of lead at the cathode (Applied Electrochemistry. Ed. 2nd, trans. And additional. Edited by NT Kudryavtsev. M., “Chemistry” , 1975, 552 p.)

The invention is aimed at increasing the degree of extraction of lead from alkaline solutions by the electrochemical method. This is achieved by the fact that to extract the lead at the cathode, an asymmetric pulse current is used, varying the periodic sequence of packets of positive n + and negative n _- current pulses, and the number of pulses in the packet is selected from the intervals n ₊ = 20 and 1≤n-≤10. The duration, pulse repetition rate and their amplitude are selected depending on the lead content in the alkaline solution and the impedance of the electrochemical cell.

The method is as follows.

For electrolytic extraction of lead, four solutions were prepared according to the following procedure. 30 g of lead-sulfate paste is dissolved in 100 ml of a 20% NaOH solution for 60 minutes when heated (t = 333 ÷ 353K). After cooling, the precipitate, including lead oxides, is filtered off and washed with distilled water to a neutral medium pH = 8 ÷ 9.

The precipitate is dried and calcined for the subsequent preparation of meerk. A 400 ml filtrate solution is divided into four 100 ml portions. In each of them, the Pb content was 0.25 g, respectively; 0.25 g; 0.2 g and 0.15 g. Each part is subjected to electrolysis. The first part is direct current, and the other three are asymmetric pulsed current.

In unsteady mode, the current is supplied to the electrolyzer from a source, which allows changing the ratio of current pulses of positive and negative signs, as n + 20 / n- (1 ÷ 10). For n + <20, the process speed decreases markedly, for n +> 20 its economic efficiency decreases.

Graphite anodes were used, polished titanium cathodes (surface area 20 cm ² ). Electrolysis is carried out with the separation of the cathode and anode space. Room temperature. The cathode current density i _a = 2 A / dm ² . Elemental analysis of the paste was carried out on a JEOL 6380 electron microscope. The lead content in the solution was determined by the atomic absorption method with an accuracy of 0.01%.

Example 1. The lead content in the solution of 0.25 g. A direct current is supplied to the electrolyzer. The residual lead concentration after electrolysis was 0.05 g.

Example 2. The lead content in the solution of 0.25 g. Alternating packets of current pulses are fed to the electrolyzer: 20 pulses of a positive sign, and then 1 pulse of a negative sign n + / n- = 20/1.

Example 3. The lead content in the solution of 0.2 g. 10 pulses of a positive sign are fed to the electrolyzer, and then 5 pulses of a negative sign

n + / n- = 20/5.

Example 4. The lead content in the solution is 0.15 g. 20 pulses of a positive sign and 10 pulses of a negative sign n + / n- = 20/10 are fed to the electrolyzer.

At all asymmetric pulsed current modes (Example 2-4), the most complete extraction of lead from the test solutions is achieved, and the residual lead concentration after electrolysis is not detected.

Using the proposed method can significantly reduce the economic costs of the technological process of processing waste batteries, ensure environmental safety and non-waste production.

Claims (1)

The method of electrochemical extraction of lead from lead-acid waste batteries, including electrolytic deposition of lead from alkaline solutions, characterized in that the electrolytic deposition of lead is carried out on an asymmetric pulse current with varying the periodic sequence of packets of positive n + and negative n-current pulses, and the number of pulses in the package is selected from n + = 20 and the interval 1≤n-≤10.