Study On Treatment Of High Concentrated Acidic Wastewater Containing Copper And Zinc By Fractional Sulfidation

Abstract:Large amounts of complex wastewater containing heavy metals were produced every year in a number of industries such as nonferrous hydrometallurgy smelting, mining, electroplating, and steel industry. If discharged into natural water, the wastewater could badly pollute the ecological environment and lead to resource wastage. The treated effluent generated from lime precipitation was hard to meet the stringent limit, and contained a large amount of Ca2+that not favors the effluent reuse. The main drawbacks of traditional sulfide precipitation were its excessive sludge production that requires further treatment, and the difficulty of sludge disposal for heavy metal recovery. Therefore, a novel multiple step sulfide precipitation process for treatment of high concentrations acidic heavy metal wastewater containing Cu(II) and Zn(II) was proposed in this study. The main purpose of this process was recovery of heavy metal sulfide stepwise from wastewater and the major conclusions are as follows:Diagrams for the distribution ratio of S(II) species (S2-、HS-、H2S) an-pH、E-pH in S(II)-H2O system; the solubility equilibrium pM-pH、 E-pH in (Cu、Zn)-S-H2O system at298.15K were drawn respectively. The solubility equilibrium and ion existent morphology in (Cu、Zn)-S-H2O system could be found out from the diagrams. an-pH diagram indicated that the concentration of S2-ion occurs at pH>12.5. The S2-ion basically reached saturation point at pH16. E-pH diagram in S(II)-H2O system also showed that the dominant S(II) species exist almost in the form of S2-at the pH value over12.8. The diagrams for pM-pH in (Cu、 Zn)-S-H2O system pointed out that the minimal solubility for CuS (1.733×10-14mol-L-1) was obtained at pH7.75, and ZnS had the minimal solubility of1.463×10-9mol-L-1at pH8.36. The two E-pH diagrams showed it would have a production of precipitate of CuS and ZnS at the pH range of0～12.5and-2～16.5, respectively.The optimal technology parameters for the removal of Cu2+were were studied to treat high concentration single copper containing acidic wastewater with hydrogen sulfide. The removal percentage of Cu2+could achieve99.18%while the initial concentration of Cu2+was500mg-L-1; pH value was1.0; temperature was25℃; mole ratio of Cu to S was1.1:1; reaction time was50minutes. The kinetics analysis of the reaction indicated that this vapour-liquid contact reaction was a first-order reaction. The reaction rate constant k was0.09685S-1when the initial concentration of Cu2+was1g-L-1. In addition, CuS crystal were calculated and analysis theoretically using software of Material Studio6.0with quantum chemistry method. In CuS crystal, Cu atom loses electrons; S atom gains electrons. Cu-S and S-S covalent bond are found between atoms. The stability of copper-sulfur bond is higher than sulfur-sulfur bond. The sediment generated from the process forms a stable crystalline CuS structure, which benefits settling performance of sludge and could be effectively separated.The optimal technology parameters for the removal of Zn2+were studied to treat high concentration single zinc containing acidic wastewater with hydrogen sulfide. The removal percentage could achieve99.54%under the optimized conditions. The kinetics analysis of the reaction indicated that this vapour-liquid contact reaction was a first-order reaction. The reaction rate constant k was0.11931S-1when the initial concentration of Zn2+was500mg-L-1. In addition, ZnS crystal were calculated and analysis theoretically using software of Material Studio6.0with quantum chemistry method. In ZnS crystal, Zn atom loses electrons; S atom gains electrons. Zn-S covalent bond with higher covalent component is found between atoms. The stability of zinc-sulfur bond is higher than sulfur-sulfur bond. The sediment generated from the process forms a stable crystalline ZnS structure, which benefits settling performance of sludge and could be effectively separated.This research put forward a novel technology of "fractional sulfidation and separation" to remove high concentration copper and zinc containing acidic wastewater. Cu2+and Zn2+were stepped sulphured by hydrogen sulfide with simulated copper-zinc mixed wastewater sample. And copper and zinc sulfides were cascade precipitated by adjusting the solution pH value. The results showed that the much better separation effect of copper from zinc could be gained at the following conditions: the temperature was25℃, solution pH value was1, the volume percentage of H2S was20%, the initial concentration of Cu2+and Zn2+were below100mg·L-1and500mg·L-1, respectively. The separating percentage was above75%, up to99%or more. This technology could achieve the objectives of purifying wastewater, reducing the waste discharge and recycling relatively pure copper and zinc resources.62figures,15tables,131references.