Removal Of Arsenic From Acid By Precipitation

In the process of turnning the flue gas of copper other non-ferrous metal smelting to acid,it produces amounts of contaminated acid.The composition of contaminated acidis extremely complex that contains principal component SO42-,fluorine, chlorine, arsenic of high concentrations, other heavy metal ions and so on.It will cause serious destruction of ecological balance if it is directly to the natural water body.Therefore, to seek cost-effective technology of the removal of arsenic is of great significance.Aiming at the current problems of removal technology of arsenic in the wastewater such as processing power is low, produceing a large number of hazardous solid waste, high economic costs, process complexity, the effluent water quality can’t satisfy,this paper studies the two-stage lime-neutralization-washing-flocculation precipitation, sulfide precipitatio-n of acid treatment process.The raw materials for experiments is copper smelter acid from a smelter of Yunnan Province.This paper studies arsenic removal effect of theprocesses.The research work and main results are as below.(1)The contaminated acid is dealed by the process of two-stage lime-neutralization in combination with flocculation and the neutralizing slags are washed. The results show the main content in slags in the first stage is CaSO4·2H2O. Washing the slags in the first stage with Na2CO3 solution and distilled water of liquid-solid ratio 10:1. They can both reduce the quantity of hazardous solid waste of a certain amount by turning the slag into ordinary solid waste from hazardous solid waste. The residues of arsenic drop to 3.6 mg/L from 13.69g/L after the process of two-stage lime-neutralization when the solution pH is 12.04. The arsenic content in the solution can drop to 0.1mg/L by adding PFSS.It satifies the emission standard of pollutants for sulfuric acid industry of GB26132-2010.(2)This paper studies the effect of the removal of arsenic in contaminated acid by sodium sulfide. The results show that the sodium sulphide additive quantity influence the arsenic removal rate most, followed by temperature, time. Arsenic removal rate rises as S/As mole ratio increases under the condition of that the reaction temperature is 45℃, reaction time is1h, mole ratio of S/As is from 3.3 to 4.5. The results show that arsenic content in the solution drop to 0.1mg/L from 4.53g/L,namely,the arsenic removal rate is 99.998% when mole ratio of S/As is 4.5.Arsenic removal rate rises as reaction temperature increases under the condition of that mole ratio of S/As is 4.5 and reaction time is 1h, reaction temperature is from 20℃-45℃.Arsenic removal rate is 99.998% and the residual amount of arsenic is 0.1 mg/L when reaction temperature is 45℃.The arsenic removal rate decreasedwhen the temperature is 50℃ due to possible return to dissolve ofarsenic. Arsenic removal rate rises as reaction time increases under the condition of that mole ratio of S/As is 4.5, the reaction temperature is 45℃ and the reation time is from 20-60 minutes. Arsenic removal rate is 99.991% and the residual amount of arsenic is 0.4 mg/L when reactiontime is 40 minutes.(3)This paper studiesthe effect of the removal of arsenic in contaminated acidby barium sulfide. It examinesthe effect of removal of arsenic on the consumption of sodium sulphide and the reaction temperature, reaction time.The results showed that the temperature influence the arsenic removal rate most, followed by time, the barium sulphide additive quantity. Arsenic removal rate rises as S/As mole ratio increases under the condition of that the reaction temperature is 45℃, reaction time islh, mole ratio of S/As is from 3.3 to 4.5.Arsenic removal rate is 78.67% and the residual amount of arsenic is 0.97 g/L when mole ratio of S/As is 4.5. Arsenic removal rate rises as reaction temperature increases under the condition of that mole ratio of S/As is 4.5,reaction time is 1hand the reaction temperature is from 20℃ to 50℃. Arsenic removal rate is 79.30% and the residual amount of arsenic is 0.93 g/L when reaction temperature is 50℃. Arsenic removal rate rises as reaction time increases under the condition of that mole ratio of S/As is 4.5,the reaction temperature is 35℃ and the reaction time is from20-60 minutes. Arsenic removal rate is 41.82 and the residual amount of arsenic is 2.64 g/L when reaction time is 60 minutes.