New Technology Dielectric Properties Of Zinc Oxide Fumes And Chlorine Removal Determination

Zinc oxide dust is one of the important raw materials of zinc and lead smelting system, and as the secondary resource, all kinds of zinc oxide dusts contain different contents of F and Cl. If the contents of them exceed the standard, the separation of valuable metals such as copper, lead, zinc, cadmium, indium, germanium and so on from impurities will not be unfavorable, and it can also cause serious impacts on zinc electrolysis process such as plate corrosion and loss, electric zinc quality decline, environmental pollution, etc. Thus, to study a new method of removing fluorine and chlorine is of great significance for the development and utilization of zinc dust resource, as well as realizing its reuse and comprehensive recovery. Moreover, it also has the potential advantage of energy conservation and consume reduction in zinc hydrometallurgy process.With the zinc oxide dusts containing high-contens Cl and low-contents F produced in the zinc leaching residue volatile kiln as raw materials, this work was devoted to the following stdudies:research on the dielectric properties of zinc oxide dust and its temperature increasing characteristics in microwave field. With the dechlorination rate as response values, the process parameters of dechlorination from microwave-roasted zinc oxide dusts by using the center combination design (CCD) of response surface methodology (RSM) was optimized based on a series of factor experiments. The main conclusions were as follows:(1) Study on the dielectric properties and temperature increase characteristics of zinc oxide dustThe dielectric properties (ε’、ε" and tan δ) of zinc oxide dust, which was derived from zinc leading residue treated in rotary kiln, was measured using a microwave cavity perturbation method, and the temperature increase characteristics of oxide zinc dust was studied under the different material quantity and microwave power, respectively. The results showed that zinc oxide dust dielectric constant and dielectric loss are proportional to its apparent density. Meanwhile, apparent density of zinc oxide dust exhibits a linear function relationship with dielectric parameters and the microwave penetration depth. Zinc oxide dust has a strong microwave absorbing ability, and it can be reached800℃in8min under microwave heating. The apparent heating rate increases with the increase of the power of microwave roasting and decreases with the increase of the material quantity. The absorbing properties and temperature increase characteristics of zinc oxide dust in microwave field provide a theoretical basis and experimental foundation for a new process of treating zinc oxide dust with microwave.(2) Study on optimizing the process parameters of dechlorination from zinc oxide dust by microwave roastingAccording to the characteristics that the absorbing ability of halides is relatively better than oxides of Pb and Zn, the new process of dechlorination from zinc oxide dust by microwave roasting was studied with the advantages of heating-selectivity for microwave in this work. Besides, the optimum dechlorination parameters under the condition of strengthening in the air were studied based on the thermodynamic analysis of lead and zinc halides.The center combination design (CCD) of response surface methodology (RSM) was used in the study, and the response surface equation with multiple cross-term was established. Meanwhile, the effects of roasting temperature, holding time and stirring speed, as well as their interactions with each other on the dechlorination rate of zinc oxide dust by microwave roasting were systematically studied. These results indicated that the roasting temperature, holding time and stirring speed can significantly effect the dechlorination rate. Under the condition of air flow rate300L/h, the optimum technique parameters (for the dechlorination rate of zinc oxide dust by microwave roasting) were roasting temperature of650℃， holding time of30min, stirring speed of60r/min, and the predicted value of the dechlorination rate from zinc oxide dust is97.13%. which is quite close to the actual experimental value (95.66%), and it shows that the regression mathematical model obtained by response surface methodology (RSM) was statistically suitable and feasible.The results shows that the zinc oxide dusts treated by microwave roasting could definitely satisfy the demands of chlorine content in the electrodepositional process of zinc, and the chlorine concentration is12.39mg/L in the leaching liquid. Compared with roasting in the muitiple hearth furnace and in the rotary kiln, as well as the method of alkali cleaning, microwave roasting treatment shows more advantages.