| Due to its simplicity and efficiency, the cyanidation process for the extraction of gold from ore has been employed for about 128 years since MacArthur’s work in 1887 was applied commercially. However, the cyanidation process generates a large amount of cyanide and copper containing gold mine effluents. Many countries and environmental protection agencies have imposed limiting standards for the discharge of cyanide-contaminated effluent. The treatment (removal or recovery) of cyanide and copper from gold mine effluent is necessary. However, some methods are energy and/or reagent intensive, or require special equipment and maintenance to removal the copper and cyanide from gold mine effluents. Thus, the development of an alternative treatment with high removal efficiency, less reagent consumption and low secondary pollutant discharge is an urgent necessity。Electrodialysis (ED) has proven to be an efficient and environmental friendly technology for industrial applications, which includes brackish water desalination, boiler feed and process water, demineralization of food products, table salt production, waste treatment in galvanic industries etc. However, there is only a few works on the application of ED to remove the toxic substances and reuse ionized species in gold mine effluent. To the best of our knowledge, the Ion-exchange membrane fouling has rarely been investigated in the treatment of gold mine effluent. Moreover, the traditional three-compartment ED only can remove cyanide without additional treatment, but the treatment of concentrated effluent with higher concentrations of toxic substances is still a serious problem. Thus the effective recovery of cyanide couldn’t be achieved in this traditional way. However, the new approaches of ED have rarely been investigated in the treatment of cyanide from gold mine effluent.In this research, the feasibility of using ED technology to treat gold mine effluents (Zhaoyuan gold smelter plant) was investigated. The specific details and result were as follows:In this research, a laboratory-scale electrodialysis (ED) system with an effective area of 88 cm2 was used to remove copper and cyanide in simulated and real gold mine effluents. The membrane fouling was characterized by FTIR, SEM-EDX, measuring the membrane resistance and static contact angle. The effects of applied voltage, initial concentration, and flux rate on removal rate of copper and cyanide were investigated. The highest copper (99.41%) and cyanide (99.83%) removal rates were achieved under following conditions:applied voltage of 25 V, initial concentration of C2 (concentration of copper and cyanide were 47 mg/L and 242 mg/L), and flux rate of 4.17 mL/s. Besides, the lowest concentration of copper (0.44 mg/L), cyanide (0.48 mg/L) and zinc (0.34 mg/L) in the treated effluent were all below the regulatory limits (copper, cyanide<0.5 mg/L, zinc<2.0 mg/L). The results showed the presences of CuCN, [Cu(CN)3]2-,Cu(OH)2, and Zn(OH)2 in the precipitation, and the fouling of anion-exchange membranes(AEMs) can be decreased significantly via pH adjustment.In addition, a novel approach of five-compartment ED was proposed for the treatment of cyanide from gold mine effluent. The removal of cyanide was performed by homogeneous ion exchange membranes and heterogeneous ion exchange membranes respectively (mode 1), and the recovery of cyanide was achieved with homogeneous monovalent anion exchange membranes (1-AEMs) and cation exchange membranes (CEMs) (mode 2). The operational parameter (applied voltage) was optimized to improve the removal and recovery efficiency. In addition, the pH variation during the process in each compartment was analyzed and the efficient recovery of alkaline solution (the main composition was NaOH solution) was also achieved in two modes. |
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