RU2123544C1 - Method of cadmium production - Google Patents

Abstract

FIELD: metallurgical industry. SUBSTANCE: method of cadmium production by electrolysis includes use of alkali-carbonate melt in which cadmium oxide in the amount of 2-6 wt.% is dissolved. The process is carried out at cathode current density of 0.3-0.9 A/sq.cm, anode current density of 0.25-1.0 A/sq.cm, interpolar distance of 0.3-4.5 cm with use of liquid or indifferent solid cathode and indifferent anode which is used in the form of nickel. EFFECT: reduced capital outlays and power consumption, higher output, improved ecological conditions in electrolysis. 3 cl, 2 tbl

Description

 The invention relates to the field of non-ferrous metallurgy, in particular to methods for producing cadmium.

 Known methods for producing cadmium from cake, dust, sublimates by dissolving them with acids, in particular sulfuric; precipitation from a solution of spongy cadmium, dissolution of a cadmium sponge, purification of the solution from copper, thallium and iron. Electrolysis of a purified solution of cadmium sulfate, remelting of cathode cadmium and its casting [1, 2].

 These methods are multistage, cadmium recovery is low, a lot of energy and water are spent on metal extraction, in addition, it is necessary to use a more active metal to precipitate cadmium, which also requires a significant amount of energy.

 So for 1 kg of cadmium, you need to spend about 0.5 kg of zinc or 0.2 kg of aluminum.

In most cases, the main stage of the process is the electrolytic extraction of cadmium from solutions with a low current density (100 - 1000 A / m ² ), and the melting of the obtained cadmium with additional refining under a flux layer.

The closest in technical essence is a method for producing spongy cadmium by electrolysis [3] of a chloride solution that has passed through purification and ion-exchange columns and contains 15-30 g / l of cadmium in a cell with a graphite anode and aluminum cathode at a current density of 100 - 1000 l / m ² and a potential difference of 3 - 7 V. The cadmium yield is ≈ 90% with a purity of 98 - 98.5%, the spent electrolyte is sent again to the ion-exchange columns. The specific energy consumption is 2 - 4 kW • h / kg cadmium.

 This process has the following disadvantages: the use of aqueous electrolytes negatively affects the environment when the used electrolyte enters the soil and water of rivers and lakes, low current density requires a large number of electrolyzers, i.e., large capital investments in equipment and workshop area, a large number of manual labor for cathode stripping.

 Additional energy is required for the melting of solid cathode deposits, which are partially oxidized.

The aim of the present invention is to increase productivity, reduce capital investment, improve the environmental situation during electrolysis, reduce energy consumption. This goal is achieved by the fact that cadmium oxide is dissolved in an alkaline-carbonate melt containing 80 - 90% alkali of sodium or potassium and 10 - 20% carbonate (sodium, potassium or calcium) at a temperature of 450 - 550 ^o C and restored by electrolysis at the cathode current density 0.2 - 1.5 A / cm ^2, preferably 0.3 - 0.9 A / cm ^2. During electrolysis, liquid cadmium is deposited at the cathode, and oxygen is released at the indifferent anode. The interpolar distance is maintained within 2-5 cm, preferably 3.5-4.5 cm. The concentration of cadmium oxide is maintained within 3-6% (wt.).

 Nickel is used as the material of the indifferent anode.

A decrease in the cathodic current density below 0.3 A / cm ² leads to a decrease in productivity, then the process becomes unprofitable, and an increase in the current density above 0.9 A / cm ² leads to a certain decrease in current efficiency (42 - 55%) and a large overexpenditure of electricity by increasing the ohmic voltage in the electrolyte.

 The interpolar distance in the range of 3.5 - 4.5 cm is most advantageous, since within these limits the maximum current efficiency and the greatest ohmic resistance in the interpolar gap are achieved. At a CdO concentration below 3%, the current efficiency sharply decreases due to the lack of cadmium ions in the electrolyte at high current densities, and at a concentration of more than 6% (weight), thick viscous precipitates of undissolved cadmium oxide are created in the electrolyte.

When the temperature drops below 450 ^o C, the current efficiency drops sharply (up to 20% and lower), the electrolyte thickens, and at temperatures of 550 - 600 ^o C, although a fairly high current output (60 - 70%), the electrolyte intensively evaporates, corrodes body and design of the electrolyzer.

 The use of cadmium oxide reduces the cost of the process, allows for a more environmentally friendly process, since liquid metal is released at the cathode, and pure oxygen is released at the anode.

The low temperature of the process 470 - 550 ^o C allows the use of Article 3 in the design of the electrolysis cell, relatively cheap chemical compounds are used in the electrolysis, and at the indicated process temperatures the evaporation of the melt is negligible, at the same time, the electrolyte conductivity is high at current densities of 0.5 - 0 , 6 A / cm ² , or 5000 - 6000 A / m ² , the voltage on the electrolyzer is not more than 3 - 3.5 V. This ensures energy savings, since the specific consumption is 1.3 - 1.5 kW • h / kg cadmium, which is much lower than that of the prototype. Productivity per 1 m ² of electrolytic cell area is 5 to 50 times higher than that of an electrolytic cell in which aqueous electrolytes are used.

 Therefore, there will be savings both in capital investments due to equipment and the building of the workshop, and due to labor productivity.

 In fact, 8 to 10 electrolyzers with a current strength of 50 kA recycle all the cadmium mined in Russia.

 Cadmium is obtained in liquid form, it does not need to be melted, i.e. spend additional energy, at the same time it can be cast into ingots and semi-finished products.

Example 1. In a crucible of beryllium oxide with a diameter of 43 mm and a height of 95 mm, 100 g of NaOH and 25 g of Na ₂ CO _{3 were} melted; heated at 500 - 550 "for 2 hours to remove moisture, then lowered 2 flat nickel electrodes equal to the diameter of the crucible, located horizontally, at a distance of 40 mm from each other. The current leads to them from nickel wire were protected by beryllium oxide tubes to prevent shorting The lower current supply served as the cathode, and the upper one served as the anode. A direct current was passed for 1.5 hours to decompose water with a current strength of 1.2 A and a voltage of 1.17 V.

 Then, cadmium oxide was periodically loaded into the melt and the current was increased to 10 A, maintaining a cadmium concentration of ≈ 5%. At the anode, oxygen began to be released, at the cathode, liquid cadmium. After passing 54.2 A / h, the current was turned off, the electrodes were removed and the contents of the crucible were poured into a graphite mold.

 Received 41 g of metallic cadmium in the form of an ingot, the current efficiency was 97.85%.

Example 2. In the same crucible, 100 g of KOH and 25 g of Na ₂ CO ₃ were melted, heated at 500 - 550 ^o C for 2 hours, water was electrolyzed for 1.5 hours, cadmium oxide was charged in portions of 5 g in equal time intervals at a current density of 0.5 A / cm ² .

 After passing 42.949 A / h, the current was turned off, the metal electrodes were removed and the contents of the crucible were poured into the mold, cadmium kings were separated and weighed, the current efficiency was 20%.

 By varying the current density, interpolar distance, temperature and cadmium content in the electrolyte, as well as the composition of the electrolyte, the following results were obtained, shown in table. one.

 The chemical composition of the metal from some experiments is shown in table. 2, where N samples correspond to N experience in table. one.

 Sources of information.

 1. Diev N.P., Hoffman I.P. Metallurgy of lead and zinc. -M .: Metallurgizdat, 1961, p. 388-401.

 2. Cadmium production at the Puhe-Zink plant in Dattelu / Germany / Dic Kadmiumgewiannung bci der Puhr-Zink CmbH in Datteu. Sch Schmidt Wilhelm "Erzmetall", 1979, 32, N 12, 522-524 (German, English, French, Spanish).

 3. A method for producing spongy cadmium by electrolysis of Vladuleseu Constantin Marius, Velea Teodor, Cornea Andrei, Obadan Merun. Procedeu de obtinere a buretelui de cadmiu pe cale electrochimica / Interpriderea metalurgica de metale neferoase / US Pat. CPP, cl. 22 B 17/04, N 66983, claimed. 12/15/75, N 81200, publ. 09/30/78.

Claims (2)

1. The method of producing cadmium by electrolysis, characterized in that the electrolysis uses an alkaline carbonate melt in which cadmium oxide is dissolved in an amount of 2-6 wt.% At 450-550 ^o C, and the process is carried out at a cathodic current density of 0.3 - 0.9 A / cm ² , anode density 0.25 - 1.0 A / cm ² , interpolar distance 3.0 - 4.5 cm using a liquid or indifferent solid cathode and an indifferent anode. 2. The method according to claim 1, characterized in that as the alkaline carbonate melt, the following compositions are used, wt.%:
NaOH - 80 - Na ₂ CO ₃ - 20
KOH - 80 - Na ₂ CO ₃ - 20
NaOH - 80 - CACO ₃ - 20
NaOH - 80 - Mg CO ₃ - 20
3. The method according to claim 1, characterized in that nickel is used as the anode.

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