| In the process of zinc hydrometallurgy,the zinc sulfate solution obtained from zinc roasting leaching contains a variety of impurity ions.This will seriously affect the electrowinning of zinc.Therefore,purification becomes an indispensable step.Currently the main purification method in industry is the zinc powder replacement method.However,the zinc powder agglomeration and wrapping in the actual production process hinders the mass transfer process and leads to problems such as high zinc powder consumption and long replacement reaction time.In this thesis,a new process of ultrasonic enhanced high temperature zinc powder purification of zinc sulfate solution is proposed,and the influence law and mechanism of different factors on the purification efficiency are investigated.The main contents are as follows:(1)The theoretical basis for the purification of zinc sulfate solution by zinc powder was studied.A theoretical analysis of the replacement and removal of zinc powder from zinc sulfate solution was carried out from both thermodynamic and kinetic aspects.The magnitude of the thermodynamic driving force for the replacement of copper and cadmium by zinc powder under different temperature conditions was obtained.The control steps in the replacement and removal process of zinc powder were analyzed.(2)The influence law of different factors on the purification efficiency was investigated,and the differences between conventional and ultrasonic intensification conditions,and between room temperature and high temperature zinc powder purification of zinc sulfate solution were compared.Single-factor experiments on the amount of zinc powder,reaction temperature,reaction time,zinc powder temperature and ultrasonic power were carried out to investigate the influence law of different factors on the purification efficiency of copper and cadmium,and to obtain the optimized process conditions for the purification of room temperature and high temperature zinc powder under conventional and ultrasonic intensification conditions.Compared with the conventional purification of zinc powder at room temperature,the ultrasonic-enhanced high-temperature zinc powder purification of zinc sulfate solution reduced the amount of zinc powder by 16.67%,the reaction time by 83.33%.(3)The purification behavior under conventional and ultrasonic intensification conditions was investigated using XRF,XRD,SEM-EDS,and XPS analyses.By heating the zinc powder,the mass and heat transfer were accelerated and the zinc powder agglomeration and wrapping were reduced.Ultrasonic intensification further reduces zinc powder wrapping,destroys zinc powder agglomerates,eliminates dissolved oxygen,and reduces the probability of cadmium re-solubilization.Therefore,ultrasonic intensification of high-temperature zinc powder purification method improves the utilization of zinc powder and the purification efficiency of zinc sulfate solution.(4)The kinetic behavior of the purification process of zinc powder under conventional and ultrasonic intensification conditions and at room temperature and high temperature was investigated,and the experimental data were fitted using a one-level reaction kinetic model,which showed that the increase in solution temperature accelerated the diffusion of ions.In addition,the ultrasonic-enhanced high-temperature zinc powder purification was significantly higher than the expansion rate of zinc powder in solution under conventional conditions.The apparent reaction activation energies under different process conditions were also calculated,and the activation energies of Cu and Cd in the ultrasonic-enhanced high-temperature zinc powder purification solution were reduced by 14.80 and 16.30 k J/mol,respectively,compared with the conventional zinc powder purification. |
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