High Cfcs Zinc Oxide Dust Preparation Of Electrolytic Zinc Process

The complex zinc oxide materiels with high content of F and Clcan't be treated with traditional zinc hydrometallurgy process, so a newprocess for extracting and preparing electrowinned zinc from these zincmateriels in the system of Zn(Ⅱ)-(NH₄)₂SO₄-H₂O has been proposed inthis paper. Based on the large difference of zinc solubility in ammoniumsulfate solution at different temperature, zinc are leached into solutionfirst at high temperature, and then precipitated as double salt with lowcontent of F and Cl when the temperature decreases. The double saltmother liquor solution can be returned to leaching process after gettingrid of F and Cl. The whole process is a clean and closed-circuit flow, ithas great significance in treating complex zinc resource and sustainabledevelopment of zinc industry. At the same time, also has potentialapplication in the technical innovation of traditional zinchydrometallurgy.According to the principles of simultaneous equilibrium and aqueouselectronic charge neutrality, the thermodynamics of Zn(Ⅱ)-(NH₄)₂SO₄-H₂O system have been carried out calculated using the exponentialcomputation method, and the solubility curves of ZnO in ammoniumsulfate solution have been plotted. The results show that the totalammonium concentration and pH value of ammonium sulfate solution have remarkable influences on Zn²⁺ concentration. The theoretical vauleof Zn²⁺ equilibrium concentration tallies with experimental measuredvalue, the relationship between temperature and Zn²⁺ equilibriumconcentration has also been studied, and the ratio of liquid volume tosolid mass is established as 16:1.The influences of time, temperature, ammonium sulfateconcentration and pH valve on zinc leaching ratio have been studied, andthe results under ptimum conditions show that during the leachingprocess of zinc dust with high content of F and C1, the leaching ratio ofzinc, calculated based on the zinc content in leached residue, can reach85.16％, and the equilibrium ratio of zinc is 95.65％. The impurity such asPb, As, Sb, In enter into leached residue mostly, and F and Cl intoleaching solution;During the zinc double salt precipitation, F and Clwhich are harmful to zinc electrowirming process remain in double saltmother liquor, the precipitating ratio of zinc can reach 72.59％, theequilibrium ratio of zinc is 98.56％; The effects of Zn²⁺ initialconcentration, current density, temperature and electrode distances oncurrent efficiency and cell voltage have been investigated, the resultsunder optimum conditions show that the current efficiency can reach92.88％, electricity consumption is 3618kW·h, the remnant zincconcentration of waste electrolyte is 30g·L^-1; The content of zinc inelectrowinning zinc obtained without further impurity removing treatment is higher than 99.97％.