| The comprehensive treatment and recycled usage of waste acid produced from the nonferrous industry is one of the most challenging issue in the world. In this paper, the waste acid containing arsenic from a Shandong Nonferrous Group has been used in this research for the preparation of arsenic trioxide. Five steps were designed for the treatment of waste acid including:dechlorination, defluorination from arsenic waste acid, recycling of sulfuric acid by diffusion dialysis, precipitation of arsenic, preparation of copper arsenite, leaching of copper arsenite, preparation of arsenic trioxide by evaporation crystalline. Both sulfuric acid and arsenic/copper are recycled via this novel process.The experimental of dechlorination by copper powder shows that higher amount of copper powder lead to better effect of the chlorine removal. The optimal experimental conditions are as follow:5times the amount of theoretical copper powder, reaction temperature20℃, reaction time1.5h,5.88g-L-1of copper ions in the solution. At the above-mentioned conditions,93.41%of chlorine can be removed when106.2g copper powder is added into13.5L waste acid.Silicon dioxide is used to remove fluorine from waste acid. The appropriate reaction temperature is80℃. Better fluoride removing effect is observed at longer the reaction time, greater the SiO2dosage and higher H+concentration conditions. Firstly,160g of SiO2is added into the waste acid containing F-1.65g-L-1and H2SO4255g-L"’at80℃, After2h of reaction and filtration, the filter residue is used for another same waste acid treatment.7.35L waste acid is obtained, the total removal rate of fluoride reaches96.6%.Sulfuric acid is recovered by diffusion dialysis by using anion exchange membrane. The impact of membrane type, diffusion time and other parameters on the sulfuric acid recovery rate and removal rate of impurity has been investigated. Better diffusion dialysis effect is recorded by Ⅰ-type anion exchange membrane compared with Ⅲ-type. Most of sulfuric acid can be recovered while majority of Cu, Fe and Zn is rejected by the membranes.The acidity of the waste acid was decreased and the certain amount of impurities was removed when the pH value of the system was neutralized to2by lime milk. Copper arsenite was precipitated with arsenic precipitation efficiency of97.81%when cupric sulfate was added into the neutralized solution, at the same time the Cu/As molar ratio was controlled at1.5:1and pH value of system was adjusted to8by sodium hydroxide. The contents of copper and arsenic in the precipitate of copper arsenite were enhanced through washing and purification.10%sulfuric acid was adopt to leaching copper arsenite at liquid solid ratio of5:1, and then a mixture of arsenic trioxide and cupric sulfate was obtained after the leachate was evaporated and crystallized. Finally through dissolution and filtration of the mixture, cupric sulfate remained in the solution while arsenic trioxide meeting the product standard of YS/T-99-1997As2O3-3was collected in the filter cake. |
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