Cobalt hydroxide is an inorganic substance with the chemical formula Co(OH)2. It is a rose-red monoclinic or hexagonal crystal. It is insoluble in water, slightly amphiphilic, hardly soluble in strong alkalis, but soluble in acids and ammonium salt solutions. The density is about 3.6g/cm³, the melting point is 1100-1200℃, and it is an amphoteric hydroxide. It is mainly used as a colorant for glass and enamel, a raw material for preparing other cobalt compounds, and a drying agent for varnishes and paints.
Two crystal phases of cobalt hydroxide
a-Co(OH)2 has a structure similar to hydrotalcite, and its typical feature is the structure of layered double hydroxyl composite metal oxide. Due to its large layered structure, its conductivity is good. This type of cobalt hydroxide usually has the color Blue cyan. However, this phase is not stable, is in a metastable state, and is easily transformed into the β phase.
β-Co(OH)2 has a brucite structure, the hydroxyl ions are closely packed in hexagons, and the cations are filled in all the octahedral voids between every two adjacent hydroxyl ions; it forms a coordinated octahedral structure layer. The structure layer is an ionic bond, and the structural layers are maintained by phases. Its color is often brick red or rose red.
Two production methods of cobalt hydroxide
1. Synthesis method: various cobalt-containing waste materials are dissolved in nitric acid and hydrochloric acid, and the obtained cobalt chloride solution is purified by hydrogen peroxide to remove iron. If necessary, sodium carbonate or ammonia water is added to ensure complete purification. The purified cobalt chloride solution is added with sodium hydroxide to generate cobalt hydroxide, which is then washed and centrifuged to obtain a cobalt hydroxide product. Its Co+2HCl=CoCl2+H2↑
CoCl2+2NaOH=Co(OH)2↓+2NaCl
2. Electrolysis method: It is obtained by electrolyzing table salt solution with cobalt as an anode.
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