Preparation of black nickel and removal of cobalt

The qualified leachate is pumped into a φ2.0m×1.5m mechanical stirring tank, and an appropriate amount of NaOH is added to form Ni(OH) ₂ precipitate, so that Ni=20g/L and pH=10～12 in the Ni(OH) ₂ slurry. Then, the slurry was pumped into an oxidation electrolytic cell, and air was bubbled in for electrolysis. The anode is a nickel initial pole piece, the cathode is a stainless steel piece, the tank voltage is 2.4-3.2V, the tank current is 2800-3000A, the temperature is 45-52°C, the electrolysis is 20-24h, the color changes from green to black, and the black nickel conversion rate can reach 65%. ~75%. The black nickel slurry is transferred to a φ3.0m×1.9m sodium washing tank, and the black nickel after washing the sodium can be used for removing cobalt and washing water to the sewage treatment station.

The cobalt was removed in the middle of a φ2.5 m×3.0 m air stirred tank at a temperature of 70-80 ° C, a residence time of 1.5 h, and Ni(III):Co=1.2 (mol ratio). The effluent cobalt removal slurry is subjected to two-stage pressure filtration, and the filtrate is adjusted to pH 3.2 to 3.4, and then sent to a nickel electrolysis process, and the filter residue is slurryed and sent to a cobalt system for treatment. Black nickel has a good effect of removing cobalt, and the removal rate of cobalt can reach 98%, and about 60% of copper and iron are simultaneously removed. Typical solution components and cobalt removal efficiency before and after cobalt removal are listed in Table 1. The chemical composition of the obtained cobalt slag is shown in Table 2.

Table 1 Average composition and removal rate of cobalt before and after cobalt removal

Table 2 Typical chemical composition of cobalt slag

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