Chromium Leaching In Hydrometallurgy Of Zinc Purification Process In The Behavior And Dechlorination Of Experimental Research

It is determined that the chromium content of zinc concentrate and zinc calcine from a zinc plant are 0.043% and 0.052% respectively which is about half of the copper content (0.088%) and much more than cobalt content and nickel content. It was also found the existence of chromium in neutral leachate (1.06 mg·L-1). The chlorine content of zinc bearing dust which produced from the dispose of zinc leaching residue by fuming process in this zinc plant is 0.146%. If return the dust to the leaching process, the chlorine content of leachate will be 292 mg·L-1 which is more than the chlorine permitted content in zinc electrolyte (100 mg·L-1 or less).The result of literatures reviewing shows that the behavior of chromium in roasting, leaching and purification has not aroused enough attention, and the related research has not been reported. The researches aims at dechloridation by ion exchange and pre-dechloridation of zinc bearing material whose chlorine content is high have achieved favorable result in some specified areas, but the application of ion exchange on chlorine removal from leachate of normal zinc hydrometallurgy has not been reported, neither the report about removal of difficultly soluble chloride from zinc bearing material. Develop the work that mention above has great significance on deeply understanding the behavior of chromium in roasting, leaching and purification, and the technological conditions mastery of dechloridation by ion exchange and the process exploration of pre-dechloridation from zinc bearing material whose chlorine content is high. Base on the above issues, investigation on the behavior of chromium in roasting, leaching and purification, the technological conditions of dechloridation from zinc electrolyte by ion exchange and the process exploration of pre-dechloridation from zinc bearing material whose chlorine content is high was carried out. Some results have been concluded as below through the investigation.The study on the behavior of chromium in roasting, leaching and purification indicated that chromium containing ore could react with zinc oxide (the product of roasting), the formed production is hard dissolve in acid. If zinc concentrate is roasted completely, the reaction of chromium containing ore and zinc oxide is complete, as result of that the chromium content of neutral leachate and acid leachate is less than 0.5 mg·L-1. Chromium in leachate could be removed in the first step of traditional three steps purification process, the optimum technological conditions are:Cu/Cr=2, pH >4.0, DZn>2.5 g-L-, t=1h, T>65℃., the residual chromium in leachate after purification is less than 0.5 mg-L-1. Cr (Ⅵ) is a kind of "activator" which could help zinc powder to removal cobalt and nickel. Addition Cr (Ⅵ) could reduce the oxidize redissolution effect of cobalt and nickel in antimonate purafication process. Add Sb (Ⅲ) and Cr (Ⅵ) as "activator" of cobalt and nickel removal by zinc powder, the removal rate of cobalt and nickel is 86.95% and 89.61% respectively under the optimum technological conditions.The study on removal of chlorine by ion exchange shows that it is impossible to transform Cl-type 201X7 ion exchange resin to SO42--type completely, it can only transform partly. The more SO42- contains in ion-transfer reagent the better type transformation effect could get, time has little influence on transformation effect. Static exchange experiment result indicates that the dynamics of 201×7's exchange with Cl-in zinc electrolyte fits better with Particle Diffusion Control. It needs long time to reach exchange equilibrium, the removal efficiency of chlorine is 20%-30%. The experiment result of dynamic exchange shows that the resin was breakthrough when the volume of feed solution is more than 15 times of resin volume. The practical chlorine exchange capacity of 201 X 7 ion exchange resin is 7.43 Kg-Cl/(ton resin) which is 5.8% of theoretical chlorine exchange capacity. The effect of regeneration is mainly depend on SO42- content of regeneration agent, when SO42- content of regeneration agent is 250 g-L-1, the regeneration efficiency of invalidation resin is 83.40%.The study on pre-dechloridation from zinc bearing dust which produced from the dispose of zinc leaching residue by fuming process shows that chlorine presence in zinc bearing dust which produced from the dispose of zinc leaching residue by fuming process is mainly as difficultly soluble chloride. The effect of chlorine pyrometallurgy removal from the dust is mainly depending on two factors:oxidation atmosphere and mass transfer rate. The study of chlorine removal with hydrometallurgy from the dust shows that Na2CO3 solution is good at the removing of difficultly soluble chloride from the mentioned material, the removal efficiency of chlorine is 92.46% with the premium conditions, zinc content of Na2CO3 solution is 0.2 g·L-1.