Nickel sulphide concentrate generally contains 4-5% nickel and 0.1-0.3% cobalt. During the pyrometallurgical smelting of nickel, cobalt is enriched in high-ice nickel or converter slag due to its affinity for oxygen and sulphur, which is between iron and nickel. The degree of oxidation of iron in high-ice nickel can be controlled during converter smelting, so that cobalt is enriched in high-ice nickel or converter slag, and can be extracted using the following methods:
1. Cobalt enriched in high-ice nickel enters the anode solution together with nickel during the nickel electrolytic refining process. During the cobalt removal process, cobalt enters the cobalt slag in the form of high-valent cobalt hydroxide, and the cobalt slag contains 6-7% cobalt and 25-30% nickel. One method of extracting cobalt from this cobalt slag is to dissolve it in sulfuric acid by adding sulfur dioxide to the cobalt slag in a sulfuric acid solution to obtain a solution containing nickel sulfate, cobalt sulfate and a small amount of impurities such as copper, impurities such as copper, iron, arsenic and antimony; then copper is removed by replacing it with activated nickel powder; air is passed through to remove iron by oxidation, and then chlorine gas is passed through for oxidation, soda is added to neutralise and precipitate cobalt. If the cobalt hydroxide obtained contains a high proportion of nickel, it can be dissolved again, and cobalt and nickel can be separated by precipitation, so that the nickel content is less than 1%; calcination is used to produce cobalt oxide for sale, or cobalt oxide can be made into crude cobalt metal, which is refined by electrolysis to obtain electrolytic cobalt. Nickel plants in Canada and the Soviet Union use this method to recover cobalt. Another method of extracting cobalt from cobalt slag is to dissolve the cobalt slag in a sulfuric acid solution using sodium sulfite as a reducing agent, to obtain a solution containing nickel sulfate, cobalt sulfate and a small amount of impurities such as copper, iron, manganese and zinc. Then, the ferric sodium yellow alum method is used to remove the iron in the solution, and the copper, iron, manganese, zinc, etc. are extracted using alkyl phosphates such as di(2-ethylhexyl) phosphate (D-2-EHPA) or other alkyl phosphate extractants, and the cobalt and nickel are separated. The cobalt chloride solution obtained during the extraction process is treated with ammonium fluoride to remove calcium and magnesium, and then ammonium oxalate is used to precipitate the cobalt. The cobalt oxalate obtained is calcined at 450°C to obtain cobalt oxide powder, which can be used as a final product or to produce metallic cobalt powder by the hydrogen reduction method.
2. Cobalt enriched in the slag of nickel smelting converters is transferred to cobalt matte together with nickel during the reduction smelting of sulfides. The composition of converter slag is generally: cobalt 0.25-0.35%, nickel 1-1.5%; the composition of cobalt matte is generally: cobalt 1-1.5%, nickel 5-13%. Cobalt matte can be directly leached (by acid leaching at atmospheric pressure or under pressure), or it can be roasted into soluble compounds and then acid leached. The leaching solution can be treated according to the cobalt slag cobalt extraction process.
