Dechlorination of zinc dross by microwave roasting

Abstract

Traditional treatments of zinc dross have many disadvantages, such as complicated recovering process and serious environmental pollution. In this work, a new process of chlorine removal from zinc dross by microwave was proposed for solving problem of recycling the zinc dross. With better ability of absorbing the microwave than zinc oxide, the main material in zinc dross, chlorides, can be heated and evaporated rapidly during microwave roasting. Various parameters including roasting temperature, duration time and stirring speed were optimized. The microstructure of roasted materials was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The content of the chloride was analyzed by the method of chlorine ion selective electrode. The experiments indicate that the best duration time is 60 min with a stirring speed of 15 r/min during the microwave roasting process. The dechlorination rate reaches peak value of 88% at 700 °C. The chlorine is removed as HCl gas when water vapor is used as activating agent, which means that it can be recovered into hydrochloride acid.