RU2294984C2 - Lead electrolytic refining method - Google Patents

Abstract

FIELD: lead metallurgy, possibly refining of black lead from impurities.

SUBSTANCE: method of electrolytic refining of lead comprises steps of anode dissolution and cathode reduction of lead in aqueous solution of electrolyte; using as electrolyte aqueous nitrate solution of salts of lead and sodium containing, g/l: lead (in the form of Pb(No₃)₂), 220 - 250; NaNO₃, 180 - 200; HNO_3- ,(1.5 -2)10^-3 (pH =4,5); carrying out electrolysis at electric current density 450 - 480 A/m², temperature 20 -25°C, electrolyte circulation rate 45 - 50 l/min.

EFFECT: improved efficiency of process, lowered exploitation expenses.

Description

The invention relates to metallurgy of lead and can be used in the refinement of rough lead from impurities. The crude lead obtained in the process of processing ore lead concentrates and secondary raw materials is characterized by the content of the amount of impurities (copper, antimony, arsenic, tin, bismuth, zinc, silver, etc.), at a level of 1 to 8%. Refining is carried out in order to obtain lead with a total impurity content of not more than 0.05-0.008 (GOST 3778-77).

A known method of fire refinement of rough lead from impurities [Loskutov F.M. Metallurgy of lead. M .: Metallurgy, 1965, 528 pp.], Which includes a set of operations for the sequential separation of impurity metals in the form of segregated compounds, most often with reagents introduced into the molten refined metal. Liquidated products are usually distinguished by a higher melting point and lower density than molten lead. They form independent phases on the surface of the refined metal, which are removed using mechanical techniques. The processes take place in the temperature range 340-650 ° C and the melts are mixed.

The disadvantages of the method of refining lead should include: multi-operation, high consumption of various types of reagents, high content of the base metal in various refining intermediate products, which reduces direct extraction of lead by about 25%; high process temperatures; environmental hazard processes.

The closest analogue to the invention is a method for electrolytic refining of lead, including anodic dissolution and cathodic reduction of lead in an aqueous electrolyte solution, which is proposed as a series of electrolytes: an aqueous solution of lead silicofluoride and hydrofluoric acid, a solution of lead borofluoride and hydrofluoric acid, phenol sulfonic and perchlorate solutions (Shivrin G.N. Metallurgy of lead and zinc. M: Metallurgy, 1982, p.162-166).

The disadvantages of this method include:

- the high cost of preparing electrolytes with a low lead content in them (80-90 g / l);

- low current density and, accordingly, the productivity of the cell;

- a relatively low current efficiency (up to 96-97%), which is primarily due to the reduction of hydrogen ions together with lead on the cathode;

- a large imbalance of the anode and cathode current outputs, leading to an increase in the concentration of lead in the solution, which, accordingly, necessitates the regeneration of the electrolyte associated with the removal of excess lead, which leads to the formation of incomplete production of lead (up to 3% of the mass introduced into processing lead);

- accumulation of tin in the cathode metal, which is associated with the cost of an additional refining operation.

The objective of the invention is to increase the productivity of the electrochemical process, to ensure the commensurability of the anode and cathode output of lead, reduce operating costs associated with the preparation of the electrolyte, the regeneration of spent electrolyte, as well as with additional refining of the cathode lead from tin.

This is achieved by the fact that in the method of electrolytic refining of lead, including anodic dissolution and cathodic reduction of lead in an aqueous electrolyte solution, an aqueous nitrate solution of lead and sodium salts of the following composition, g / l: lead (in the form of Pb (NO ₃ ) is used as an electrolyte ₂ - 220-250; NaNO ₃ - 180-200; HNO ₃ - (1.5 ÷ 2) · 10 ^-3 , and the electrolysis is carried out at a current density of 450-480 A / m ² , a temperature of 20-25 ° C and speed electrolyte circulation of 45-50 l / min, at a pH of 4.5.

The starting electrolyte is prepared by leaching cathode lead in a solution of nitric acid. The process of dissolution of lead is completed at pH 4.5, and this indicator corresponds to the above condition for the content of free HNO ₃ and lead. NaNO ₃ is added to the solution in order to achieve the desired concentration. The cost of preparing the electrolyte is not more than 20% of the cost of obtaining silicofluoride and sulfamine solutions.

In accordance with the results of studies of the electrical conductivity of nitrate lead-containing solutions, it was found that this particular system, corresponding to the above composition, is characterized by an electrical conductivity of 0.1429 Ohm ^-1 · cm ^-1 , which corresponds to a specific electrolyte resistance of 7 Ohm · cm. The total resistance of the electrolyte is 5 · 10 ^-5 Ohms. Taking into account the current density of 450-480 A / m ^{2, the} total voltage drop of the electrolyte solution in the bath is 0.77-0.8 V. The voltage on the bath is 0.79-0.82 V and, accordingly, the energy cost of producing a ton of metal constitute 200-210 kWh.

From the experimental data it follows that the anode and cathode current outputs in the inventive system are comparable and make up 98.5-99%, which is primarily due to the low content of hydrogen ions in the solution (3.16 · 10 ^-5 g · ion / l, for pH 4.5). This pH value is characterized by an extremely low equilibrium concentration of tin in solution due to the occurring hydrolytic reactions. (According to the Purbe diagram [Chemist's Handbook, edited by B.N. Nikolsky, vol. III. M.-L .: Chemistry, 1964 - 1005 pp.], The equilibrium concentration of Sn ²⁺ at pH 4.5 is 3 · 10 ^-8 g · ion / l). The latter excludes the possibility of its restoration at the cathode.

The use of solutions with a high lead content (220-250 g / l) can increase the current density to 450-480 A / m ² (with an increase in the electrolyte circulation rate to 45-50 l / min), which corresponds to an increase in the productivity of electrolytic refining by about 3 times.

The proximity of the values of the anode and cathode current outputs is confirmed by the constancy of the content of lead and hydrogen ions in the electrolyte in time, and, accordingly, the duration of the campaign of operation of the same electrolyte is extended several times in comparison with existing prototypes.

The essential features of the proposed method for electrolytic refining of lead are:

- as a working electrolyte, an aqueous nitrate solution of lead and sodium salts is used, which differs from the prototype in high (about 3 times higher) lead content and low free acid content - (1.5 ÷ 2) · 10 ^-3 g / l compared with 45-105 g / l in the prototypes;

- electrolysis is carried out at a current density of 450-480 A / m ² (about 3 times more than in the prototypes);

- the circulation rate of the electrolyte is 45-50 l / min instead of 12-20 l / min according to the prototype.

The method is carried out on standard equipment used for electrolytic processes conducted in aqueous media, as follows. In an electrolysis bath filled with an electrolyte (g / l: lead (in the form of Pb (НО ₃ ) ₂ ) - 220-250; NaNO ₃ - 180-200; HNO ₃ - (1.5 ÷ 2) · 10 ^-3 ), immersed a certain number of anodes cast from crude lead containing impurities and cathode substrates made from refined lead. The voltage is supplied from a direct current source, while the current density should be 450-480 A / m ² . The electrolyte temperature is 20-25 ° C, the electrolyte circulation rate is 45-50 l / min.

During the implementation of the method, it was found that the anode and cathode current outputs are comparable and make up 98.5-99%. Analysis of the cathode deposit showed that the content of impurities in it is at the level of 0.04-0.008%, which corresponds to lead of grade C0-C2 (GOST 3778-77). Electricity consumption is 200-210 kWh per ton of cathode metal. Analysis of the electrolyte solution showed that the content of lead, tin and hydrogen ions in it remains constant over time.

Claims (1)

A method of electrolytic refining of lead, including anodic dissolution and cathodic reduction of lead in an aqueous electrolyte solution, characterized in that an aqueous nitrate solution of lead and sodium salts of the following composition is used as an electrolyte, g / l: lead in the form of Pb (NO ₃ ) ₂ - 220 -250; NaNO ₃ - 180-200; HNO ₃ - (1.5 ÷ 2) · 10 ^-3 , and the electrolysis is carried out at a current density of 450-480 A / m ² , a temperature of 20-25 ° C and an electrolyte circulation speed of 45-50 l / min at a pH of 4, 5.