PROCESS OF RECOVERING ZINC SULPHATE OF LOW FLUORINE CHLORIDE FROM ZINC SECONDARY OXIDE SLAG
The secondary zinc oxide slag can be used to prepare zinc electrolyte to realize the reuse of zinc.The main technical difficulty lies in the separation of fluorine chloride and zinc.If the fluorine chloride cannot be effectively removed,it will accumulate in the hydrometallurgical zinc system,corrode the electrode,and reduce the quality of electric zinc.The feasibility of preparation of qualified zinc sulfate crystals by acid leaching combined with cooling induced crystallization was investigated by treating zinc oxide slag from a smelter in Guangdong Province.Zinc sulfate heptahydrate crystals were obtained by adding zinc suboxide slag and sulfuric acid to saturated zinc sulfate solution,leaching at temperature and cooling.The results show that the fluorine content of zinc sulfate crystal is 0.013%～0.017%and the chlorine content is 0.001 9%～0.003 9%,which is significantly lower than the fluorine and chlorine content of zinc oxide slag when the dosage of zinc oxide slag is 12.5～37.5g/L.The content of fluorine and chlorine in the zinc sulfate crystal prepared by washing with zinc oxide slag was further reduced.If the zinc sulfate solution with a zinc concentration of 120 g/L is obtained by dissolving the crystals,the corresponding fluorine ion concentration in the solution is 25.04 mg/L and chloride ion concentration is 30.05 mg/L,which proves that the combined technology of washing and cooling crystallization can recover the zinc sulfate crystal with low fluorine chlorine.
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