Strongly acidic wastewater produced by copper smelting industries contains high concentrations of Cl(-I), Cu(II) and H2SO4. The common method for the treatment of this type of wastewater is neutralization, which produces large amounts of solid waste. To avoid the production of solid waste, it was proposed to selectively remove contaminants and then recycle the wastewater as diluted sulfuric acid. This study proposed a new complexation-precipitation method to effectively remove Cl(-I) using thiourea (TU) under the promotion of ascorbic acid (AC). The Cl(-I) removal efficiency was optimized, important effecting factors were investigated and the mechanisms of the AC-improved removal of Cl(-I) were studied. The results showed that, Cl(-I) removal efficiency reached 87.4 % under a TU/AC/Cl(-I) mole ratio of 1:3:1 and the residual Cl(-I) concentration was lowered from 1000 mg/L to 126.4 mg/L. The mechanism investigation showed that, AC first reduces Cu(II) to Cu(I), then, the produced Cu(I) is quickly complexed by TU to form the [Cu(I)x(TU)y]x+; finally, [Cu(I)x(TU)y]x+ precipitates with Cl(-I) in the form of [Cu(I)x(TU)y]Clx. This study provided a theoretical foundation of complexation-precipitation of Cl(-I) under strongly conditions and developed an effective method for removal of Cl(-I) from strongly acid waster.
Keywords: Cl(-I) removal; Complexation-Precipitation; Strongly acidic wastewater.
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