RU2254389C1 - Method of electrochemical refining of lead from bismuth - Google Patents

Abstract

FIELD: lead metallurgy; cleaning of black and secondary lead from bismuth.

SUBSTANCE: proposed method of electrochemical refining of lead from bismuth at cathode polarization of alloy being cleaned with the use of electrolyte of molten caustic soda; bismuth extracted from metal being refined is accumulated in electrolyte-melt of caustic soda followed by separation into self-contained product.

EFFECT: low cost of process for refining stage and self-contained product production stage.

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Description

The invention relates to metallurgy of lead and can be used to clean rough and secondary lead from bismuth.

The known method (Delimarsky Yu.K., Pavlenko I.G., Zarubitsky O.G. Ukrainian Chemical Journal. 1967, t.33, p.863.) Electrochemical refining of lead in the system: melt of crude lead (anode) - a melt of chlorides (48% PbCl ₂ , 35% KCl, 17% NaCl) - lead melt (cathode) at a temperature of 500 ° C, providing satisfactory purification of lead from bismuth. The anode alloy is mixed throughout the refining time. At an anode current density of 1.56 A / cm ² an alloy with a bismuth content of 0.001% was obtained. It has been established that the content of bismuth in the cathode lead naturally increases as its content in the anode alloy increases (as the anode alloy enriches by impurities, the probability of their transition to electrolyte and, accordingly, to cathode lead increases).

The disadvantages of the method include:

- significant energy costs for refining (2000-2500 kW · h per ton of lead);

- high melting point of the selected electrolyte. A known method of electrochemical refinement of a lead alloy from bismuth (Delimarsky Yu.K., Pavlenko I.G., Zarubitsky O.G. Electrochemical separation of lead and bismuth in melts involving intermetallic compounds. Non-ferrous metals No. 9, 1963), carried out in system:

All components of the system are molten, as the method is implemented at a temperature of 340-350 ° C. With the polarization of the cathode, representing an alloy of lead with bismuth, conditions arise for the reactions:

from which reaction (2) should be distinguished. The metal sodium reduced on the cathode surface interacts with lead to form a set of intermetallic compounds (NaPb ₅ , NaPb, Na ₂ Pb, Na ₅ Pb ₂ ), which are characterized by high solubility in molten lead, with a uniform distribution in it.

Upon reaching a certain concentration of sodium in the lead-bismuth alloy (3.5-4%), conditions are created for the interaction of lead-sodium compounds with bismuth present in the melt with the formation of the Na ₃ Bi intermetallic compound. This compound is poorly soluble in lead, and its melting point is 775 ° C. Compound Na ₃ Bi segregates from molten lead onto its surface and is washed off into an alkaline electrolyte with further dissociation according to the scheme:

The method is implemented on the installation (figure 1), consisting of a steel boiler 1, immersed in the shaft of the furnace (not shown). In the boiler 1 there is a refined lead-bismuth cathode alloy 2, on the surface of which there is an electrolyte 3 - molten caustic soda. An anode 4 made of porous flake cast iron is immersed in the alkali melt, molten lead 5 is poured into the working space of the anode 4. In the center of the anode 4 there is an opening for the shaft of the mixer 6, mixing the cathode alloy 2 and electrolyte 3.

With the polarization of the anode, which is molten lead, loaded into the anode space, separated from the electrolyte by a porous septum, the reactions proceed:

Along with reactions (4) and (5) proceeding at the anode, there is a high probability of the occurrence of reaction (6) - the formation of metallic bismuth on the anode. Obtaining a bismuth product at the anode occurs as a result of successive processes:

- diffusion of bismuth compounds from the electrolyte through porous blocking to the anode alloy;

- the formation of bismuth metal on the anode (reaction 6);

- dissolution of metallic bismuth in the anode alloy.

The method is implemented at current densities from 0.5 to 2 A / cm ² .

The disadvantages of the method include obtaining low quality bismuth product (the anode alloy contains up to 15% of the recoverable element), as well as the complexity of the design of the anode assembly.

The objective of the present invention was to obtain a high-quality bismuth product isolated from a lead-bismuth alloy, with reduced operating costs for redistribution.

To achieve the desired technical result in the method of electrochemical refining of lead from bismuth during cathodic polarization of the alloy being purified using molten sodium hydroxide as an electrolyte, bismuth extracted from refined metal accumulates in the electrolyte - sodium hydroxide melt and can be concentrated into an independent product.

When implementing the proposed method, the probability of the cathodic reaction (2) remains unchanged. At the anode sections of the chain, bismuth ion (Bi ^3– ) is discharged to form Bi ⁰ (reaction 6), which accumulates in the alkaline electrolyte. The probability of the reverse dissolution of bismuth in the lead alloy is absent due to the fact that cathode lead is characterized by a high sodium content (up to 3-4%). The latter excludes the possibility of dissolution of bismuth in lead.

Bismuth released on the steel anode accumulates in the electrolyte in the form of a suspension. Its content in the melt can reach 30% or more. During electrolyte regeneration by leaching in water, a concentrate containing up to 95% bismuth is obtained.

The design of the cell is greatly simplified, while operating costs are reduced.

The inventive method can be implemented on the installation, the scheme of which is shown in (Fig. 2.) The installation consists of a boiler 1, which is loaded with lead-bismuth alloy 2, on the surface of which there is an electrolyte - sodium hydroxide melt 3. An anode is immersed in the electrolyte - steel a disk 4, which is suspended on the rods 5 to the frame 6. In the center of the anode there is an opening for the shaft of the mixer 7, with which the cathode lead-bismuth alloy 2 is mixed.

The method is described in the examples.

The prototype experiments were carried out on the installation, a diagram of which is shown in figure 1. The mass of the lead-bismuth alloy (cathode) is 2 kg, the mass of the lead alloy (anode) is 100 g. The experimental results are shown in Table 1.

Table 1
The results of experiments on de-deoxidation of lead (prototype) Name Duration of electrolysis, h 0 1,5 3,5 6.0 Voltage 0 2,35 2,31 2,3 Specific energy consumption, kWh / kg 0 0.74 1.06 1.44 The content of bismuth in the cathode alloy,% 0.12 0,035 0.01 0.002 The bismuth content in the anode alloy,% (at anode current output of 100%) 0.12 1,6 2.2 2.25

Experiments on the proposed method were carried out on the installation, the diagram of which is shown in figure 2. The mass of lead-bismuth alloy (cathode) 2 kg The results of the experiments are given in table.2.

As shown by the results of an experimental verification, using the proposed method provides a similar prototype residual bismuth content in refined lead. After leaching an alkaline electrolyte in water, an insoluble residue with a bismuth content of 95.3% was obtained.

table 2
The results of experiments on decontamination lead (the proposed method) Name Duration of electrolysis, h 0 1,5 3,5 6.0 Voltage 0 2.03 2.0 2.0 Specific energy consumption, kW · h / kg 0 0.64 0.92 1.25 The content of bismuth in the cathode alloy,% 0.11 0,031 0.0085 0,0006 The content of bismuth in an independent concentrate (after leaching in water),% 95.3

The proposed method allows you to:

- extract bismuth from lead alloy into an independent high-quality concentrate;

- simplify the design of the cell;

- reduce operating costs both for the redistribution of refining, and for the redistribution of an independent bismuth product.

Claims (1)

The method of electrochemical refining of lead from bismuth during the cathodic polarization of a purified alloy using molten sodium hydroxide as an electrolyte, characterized in that bismuth extracted from refined metal is accumulated in an electrolyte - sodium hydroxide melt - with subsequent isolation into an independent product.

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