New Technology And Theoretical Study On Wet Oxidation Of Zinc And Chlorine By Microwave Oxidation And Roasting

Zinc is indispensable to the development of social economic and national defense construction. At present, about 85% of the worldwide zinc metals are prepared by hydrometallurgy. With the requirements of electrolytic, zinc sulfate solution must be dechlorination purification treatment. There are many dechlorination technologies, such as silver ion precipitation dechlorination, ion exchange dechlorination and extraction dechlorination. But those methods have more or less restrictive conditions which limit its further industrial application. The Copper slag dechlorination method is widely used in industrial with respect to its availability of the raw materials, simple operating procedure, low production cost and high initial dechlorination rate. But there will be some residue which is comprised of CuCl and Cu2O precipitation as the main phase. This part of the residue is not yet a reasonable and efficient processing method. Therefore, to seek a kind of economic, effective and environmentally friendly processing CuCl residue technology is very important.Nowadays, people’s attention is attracted by the energy and environmental problem. Microwave as a green environmental protection, efficient and rapid heating mode is widely used in chemistry, material and metallurgy, etc. There is a significant different between microwave and conventional heating. Microwave heat materials by dielectric loss of itself, so there are many advantages was shown, for example, the selective heating higher thermal efficiency, easy to control, reduce the reaction temperature, etc.For CuCl residue which produced by copper slag method removal Cl from zinc sulfate solution, its main chlorine content is the CuCl. Under oxygen atmosphere, the main reaction is included melting, volatile and oxidation reaction. Under a certain temperature, CuCl can react with O2 to generate the intermediate phase Cu2OCl2, eventually forming CuO and Cl2. The copper oxide and chlorine can be recycled at the same time. CuCl of the residue has stronger microwave absorption than other components in the microwave field. Therefore, using the advantage of microwave selective internal heating, combined with oxygen, strengthen the oxidation dechlorination reactions. The research details are as following:1.The thermodynamics of the microwave oxidation roasting process were calculated to provide theoretical guidance for the experiment. Through the thermodynamic calculation of the possible chemical reaction of the roasting process, the ΔG-T figures under different temperature were obtained. Then combined the literature and TG-DTA analysis, the process of CuCl oxidation was discovered. And the existence rule of Ch in absorption liquid was found by the study of the E-pH diagrams of Cl2-H2O system.2.Cavity perturbation method was used to measure the dielectric properties of CuCl residue when temperature was between 13℃ and 450℃, and according to the measured data the microwave penetration depth was calculated. The dielectric constant of CuCl residue increased with temperature rising, and the change tend to be a linear relationship. The dielectric loss factor and loss tangent kept on a steady value between 13℃ and 300℃, then significantly increased from 300℃ to 450℃. The penetration depth stabilized between 7.8 cm and 8.4 cm in 13-300℃, and then dropped to 6.1 cm from 300 to 450℃. And the CuCl residue has a high heating rate in microwave field, could reach more than 500℃ in 15 min. So the method of microwave roasting dechlorination is feasible.3. The position and thickness of CuCl residue were optimized and the field distribution of rectangular microwave cavity with the condition of no-load or load was simulated in the process of microwave roasting by using HFSS software. The results shown that when the material is at the center of XOY plane of the cavity and the thickness of material is 13 mm, the microwave heating efficiency is the highest.4.The dynamics of the CuCl residue dechlorination was researched with the way of conditional and microwave oxidizing roasting. The results show that the microwave roasting not only shorten the processing time for 30 min, but also increased the dechlorination rate for 12% under the same conditions. According to the dynamics analysis found that the apparent activation energy of conventional and microwave oxidizing roasting were 52.69 and 42.36 kJ/mol, respectively. The main control step of both of the two methods was surface chemical reaction control. The conclusion was proved though the micro structure analysis methods of XRD, SEM-EDS and Raman and section-distribution of the elements.5.Both the conventional and microwave roasting experiments were designed using response surface methodology. The biggest dechlorination rate of 84% for conventional roasting was obtained at roasting temperature of 456℃ for 127 min under the oxygen flow rate of 170 mL/min. The optimized microwave roasting conditions were identified to be a roasting temperature of 438℃, heating duration of 104 min, oxygen flow rate of 163 mL/min and microwave power of 1183 W. A dechlorination efficiency of 93% could be achieve at the optimal process conditions.6.The dechlorination rate of 85% for amplified experiment (120kg) was obtained at roasting temperature of 450℃ for 3 h under the oxygen flow rate of 7-8 m3/h with stirring speed of 10 r/min. The energy consumption of microwave roasting process was about 0.5 kW-h/kg, and the energy consumption was low. The pilot-scale experiment conditions were identified to be a roasting temperature of 450℃, heating duration of 4 h, oxygen flow rate of 70-80 m3/h, stirring speed of 5 r/min and particle size of-120 mesh. A dechlorination efficiency of 86% could be achieve at the process conditions.In summary, aiming at the shortcomings of the existing processing CuCl residue process, put forward a new technology of microwave oxidizing roasting dechlorination. Using computer simulation, thermodynamic calculation, dynamics computation and response surface method to research the dechlorination mechanism, and XRD, SEM-EDS, Raman and section-distribution of the elements were used to proved strengthening mechanism. In conclusion, an effective way was provided for the clean utilization of those chlorine material by microwave roasting.