Purification of cobalt leachate

The main impurity elements in the leachate are iron and copper , and the secondary ones are lead , zinc , manganese , and arsenic . Iron is removed by the yellow-sodium iron sulphide method, copper is removed by sulfide precipitation, and other impurities are removed by hydrolysis precipitation.

First, yellow sodium iron sputum iron removal

The principle of the base rate of iron, sodium and iron is to form insoluble salts. Sodium sulphate [Na ₂ Fe ₆ (SO ₄ ) ₄ (OH) ₁₂ ] is a pale yellow crystal precipitate with good filterability and detergency. The formation process is complicated and requires strict control of the formation conditions. The factors are the concentration of sodium carbonate solution, temperature and pH, and the addition of seed crystals. The specific control conditions are as follows:

(1) Concentration of sodium carbonate

The concentration of 7% to 8% must be uniformly added. The usual method is to use a low-pressure wind to spray the alkali solution into the iron slag formation tank. When a high concentration of sodium carbonate, colloidal iron hydroxide easy to produce, resulting in increased slag containing a polyvalent metal, and filtered difficult: too low a concentration disadvantageously volumetric balance of the entire system, reducing the concentration of the solution.

(2) Temperature, oxidation and pH

Before the iron removal, the solution needs to be oxidized to oxidize Fe ^{2 +} to Fe ^{3 +} , the oxidant is generally NaClO ₃ , the oxidation temperature is ≥85°C, and the iron sputum formation temperature is ≥90°C, it is granular and has good filtration performance; The pH of the pre-solution is controlled at 1.5-1.7, the oxidation time is controlled at 1.5-2.0 h, the pH value at the end point is controlled at 2.5-3.0, the iron removal rate is 99%, and the solution is Fe ≤ 0.05 g ∕L; final pH control At 4.0 to 4.5, Fe ≤ 0.001 g ∕ L in the enthalpy after iron removal.

(three) seed crystal

The wet iron slag is added as a seed crystal, that is, when the iron filter is removed, a certain amount of slag is left at the bottom of the reaction tank, which can greatly accelerate the iron removal rate of the yellow sodium iron slag.

The composition of the iron slag after washing is: 0.5% to 1% Co, 1% to 3% Ni, 0% to 0.4% Cu, and Fe ≥ 24%.

Second, sodium sulfide precipitation in addition to copper

The basic principle of sodium sulfide in addition to copper is the formation of insoluble copper sulfide precipitates. The copper removal operation was carried out in a mechanically stirred enamel kettle, and the amount of sodium sulfide was Cu ^{2 +} : Na ₂ S = 1:5. The sodium sulfide is firstly mixed into a saturated solution, and slowly added to the kettle at a normal temperature, the initial pH is 2.0 to 3.0, and the final pH is 3.5 to 4.0 because the sodium sulfide is alkaline. The copper retention time is about 30 minutes. The copper content of the solution can be reduced to below 0003 g ∕ L while removing lead. The disadvantage of sodium sulfide in removing copper is that it may locally form NiS and CoS precipitates, causing the copper slag to contain nickel and cobalt too high and bringing sodium ions into the solution.

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