Seeking advice on the details of removing cadmium and nickel using zinc powder in zinc sulfate solution
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When purifying the crude zinc sulfate solution from the factory (which contains a high amount of salt impurities as well as fluorine and chlorine) to produce basic zinc carbonate, the following problems arise: 1. Potassium permanganate is used to remove manganese, and the actual amount of potassium permanganate used is twice the theoretical amount. I don’t know why. In the tank before the manganese removal tank, hydrogen peroxide is used to remove iron. 2 Zinc powder replacement: 2 grams per liter of cadmium + a small amount of copper + 0.2 grams per liter of nickel; the amounts used are 2.5–3 times the theoretical amounts. The specific method used in the factory is to first add some zinc powder to increase the cadmium content in the slag; afterwards, the acidity is adjusted in the next tank, and more zinc powder is added until the solution meets the required standards. The mixing time is approximately 35–40 minutes, the temperature is 75 degrees, and the mixing speed is 62 revolutions per minute. I would appreciate some guidance: what is the normal cadmium and zinc content in high-cadmium slag? To what pH level does the acidity need to be adjusted? Will the cadmium and zinc residues at the bottom of the tank get dissolved back by the acid?
First, I didn’t understand it； Second, cadmium slag and cobalt-nickel slag must be separated.
First, during the iron removal process, an insufficient amount of hydrogen peroxide should be used; otherwise, the efficiency of manganese removal will be low. Second, for cadmium removal, a low temperature of less than 65 degrees is required, while for nickel removal, a high temperature of over 80 degrees is necessary. Additionally, cadium that is removed through displacement process will dissolve again, and the efficiency of nickel removal via displacement is low. It is recommended to use nickel-removing agents
Upstairs is correct! Excess hydrogen peroxide will consume potassium permanganate.
First: Except for Cd, zinc powder is added for displacement at a low temperature of 45°C for a time of 30 minutes – 3 to 6 times; once it meets the requirements, pressure filtration is carried out immediately.
For Ni: at a high temperature of 80–85 degrees, Sb2O3 and CuSO4 are added first as activators, followed by zinc powder in an amount 30–40 times that of Ni; the substitution process takes 2 hours. The second method uses a nickel-removing agent: at a medium temperature of 65–70°C, the activator is added first, followed by the nickel-removing agent, with a displacement time of 50 minutes.
Potassium permanganate, hydrogen peroxide, and ozone are all strong oxidizing agents capable of oxidizing iron and manganese ions in solutions. If the cadmium content is kept at 1 mg/l, cadmium-containing slag typically contains 7-12% cadmium and 45-50% zinc