Abstract:Electroplating sludge is a typical hazardous waste with both resources and hazards. NH4Cl and CaCl2 were used as compound chlorination agents, and FeSO4?7H2O was introduced as the fortifying agent. By using the method of enhanced chlorination roasting, Cr, Ni and Cu in electroplating sludge were separated in steps by controlling and adjusting temperature field, and the step separation mechanism was explored. Thermodynamic calculation shows that the main phases of Ni, Cr and Cu in electroplating sludge (except Cr2O3) can be chlorinated by HCl or Cl2 into corresponding metal chlorides. The experimental results show that NH4Cl is decomposed to produce HCl at about 400 ℃. First, the main phases of Ni, Cr and Cu in the electroplating sludge are chlorinated, and a small amount of CrCl3 is volatilized at about 500 ℃. At 700 ℃, the decomposition of FeSO4?7H2O produces SO2 and O2, which promotes the decomposition of CaCl2 to produce Cl2 for secondary chlorination. The generated NiCl2 volatilized in large quantities at 800 ℃, and the volatilization process can be described by zero-order chemical reaction kinetics model, namely the phase boundary reaction control. The volatilization of CuCl2 begins at about 900 ℃ and completes at 1 100 ℃. The purity of CuCl2(H2O)2 crystals collected at this temperature is 94% and the volatilization process at high temperature can be described by the first-order reaction kinetics model and the 1/2 order reaction kinetics model. Therefore, the phase separation and efficient recovery of Cr, Ni and Cu can be realized by directional phase transformation of chlorinated agent under controlled temperature field. This study provides a new method and an important theoretical basis for the recovery of valuable metals from electroplating sludge and has significant reference for the recycling of other polymetallic solid wastes.