| The heavy nonferrous metallurgy occupies an important position in the modern industry; waste acid is one kind of the main pollutants produced by heavy non-ferrous metal smelters. The arsenic and some heavy metal elements content is higher in the waste acid produced by the process of acid-making with smelting gas, so the waste aid is very difficult to recycle. The traditional method of the waste acid is neutralizing treatment, which can not suit the requirements of deep purification, but produce large amounts of calcium sulfate slag containing arsenic and other heavy metal elements; it can take up a lot of land and cause serious pollution to the environment. So the development of efficient and environmental treatment process are in demand. This research has develop two kinds of waste acid purification process combining the theory of thermodynamics and dynamics analysis, the first method is Sulfide precipitation method to remove As and Evaporation method to remove F and Cl. the second method is Sulfide precipitation -Copper salt-Electrolytic deposition method to remove As, Cl and Cu, the second process which need further research. The Sulfide precipitation-Evaporation method, not only get deep purification level, but also solve the problems of storage and waste acid recycling.In this research, As, F and Cl are removed by Sulfide precipitation-Evaporation method, finally get the high concentration of sulfuric acid. Firstly, improved the existing Sulfide precipitation method, not only the As but also the Cu, Pb, Cd can be removed to the deep content in the waste acid. The optimum technological conditions are determined, the actual dosage of sodium sulfide is 2 times of the theory, the reaction temperature is 55 ℃, the reaction time is 20mins, which in the waste acid the sulfuric content is 183.2g/L and the As content is 4.281g/L,waste acid and arsenic content of the experimental condition after treatment decreased to 100mg / L, Pb 12mg / L, copper content and cadmium content of Omg / L, pH decreased to 153.02g / L; Secondly, improve the Sulfide precipitation method by using hydrogen sulfide instead of sodium sulfide in case of the happening of the residue of mounts of sodium ion and acidity reduce,hydrogen sulphide arsenic removal of arsenic in solution can be in addition to below 20 mg/L. Finally, the evaporation step will be carried on after the Sulfide precipitation method to remove F and Cl, which by the experimental verification we know that the F, Cl ion in HF, HCl form with the evaporation of water vapor into acid mist comes out from the waste acid,fluorine chlorine removal rate reached more than 98%, and the solution of acid content can reach more than 60%.The above-mentioned method is gived the recycling of waste acid, even can make the process simple. However, the above method has a high energy consumption, equipment corrosive and other shortcomings. In order to further optimize the waste acid process, the Sulfide precipitation-Copper salt-Electrolytic deposition method has been studied. In this two method the first step to remove As are same. Secondly, use the Copper salt method to remove Cl, and the optimum technological conditions are determined, the actual dosage of copper powder and copper sulfate are 1.6 and 1.4 times respectively of the theory, the reaction temperature is 55℃, the reaction time is 1h,the condition after processing after arsenic removal of chlorine ions in addition to below 100 mg/L, the chloride rate above 98%. Finally, use the Electrolytic deposition method to remove Cu,the experiment of current efficiency of 92% or more, in addition to copper rate of 97%.The method of Sulfide precipitation method to remove As and Evaporation method to remove F and Cl is a closed cycle system, which not produce polluted water, gases and solid waste and achieve the goal of deep purification, which definitely has a good industrial application prospect. |
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