Process Analysis Of Metallic Chromium Electrodeposition From Ionic Liquids Using High Chromium Residue

In China,the environmentally friendly treatment of the high chromium residue is still a technique problem.With the rapidly developing of the metallurgical industry,a large number of unstable high chromium residue is produced which has a harmful effect on the environment.By the treatment of electrodeposition,the metal chromium with good toughness can be extracted from the high chromium residue,and this process has a great significance to the resource recycling and environmental protection.In the conventional electrodeposition process,the aqueous solution system has some defectiveness such as the low current efficiency and the hydrogen evolution.By contrast,the ionic liquids system owing more advantages is suggested to extracte chromium by electrodeposition of high chromium residue,such as the wide electrochemical window,the operability at room temperature,the reducing of the hydrogen evolution,the improving of the current efficiency and the reducing of the energy consumption.In this work,CrCl3·xH2O ionic liquid was prepared by vacuum distillation of leaching liquor of the high chromium residue.The technological parameter and electrodeposition mechanism have been studied systematically.This method can reduce the production cost greatly,simplify the production process,reduce the pollution of the environment and realize the value-added utilization.To recovery the resource,the trivalent chromium in the high chromium residue was reduced into zero-valent chromium in this paper.By analyzing the chemical composition and producing process,it was found that chromium element was mainly distributed in the chromium hydroxide among the high chromium residue,and the other impurities were mainly composed of soluble sulfur,sodium and insoluble silicate.According to the composition of the high chromium residue,the leaching experiment was carried out to gather the trivalent chromium into the ionic liquid.The optimal parameters in the leaching process were that:leaching solid-liquid ratio 1:15,pH 0.1,leaching temperature 80?,leaching time 60 min and stirring rate 200 r·min-1.Under the above reaction conditions,the leaching rate of chromium was 90.35%.CrCl3·xH2O was prepared of chromium leaching liquor by the process of vacuum distillation at 100?.Viscosity and electrical conductivity have been studied to determine the optimum preparation conditions of the ionic liquids.At last,a green viscous liquid was obtained by mixing the CrCl3·xH2O and choline chloride in a molar ratio of 67%at 70?.The cyclic voltammograms of the ChCl-CrCl3·xH2O ionic liquid system at different scanning rates and scanning temperatures were analyzed.The results show that,the reduction of trivalent chromium in the ChCl-CrCl3·xH2O ionic liquid system was an irreversible process.The effects of electrodeposition potential,electrodeposition temperature and electrodeposition time on the current efficiency,composition,morphology and particle size of the electrodeposition products were investigated.The optimum conditions of the electrodeposition were that:electrodeposition potential-4.1 V,electrodeposition temperature 60?,and electrodeposition time 3 h.