Black Dross: Processing Salt Removal from Black Dross by Thermal Treatment

Abstract

The salt removal from black dross by thermal treatment has experimentally been studied under different conditions in both a stationary resistance furnace and in a laboratory scale rotary furnace. The experiments were designed based on partial pressure calculations using the Thermo-Calc software (Thermo-Calc Software, Stockholm, Sweden). The salt removal efficiency was evaluated by scanning electron microscope (SEM) energy-dispersive x-ray spectroscopy and x-ray diffraction analyses, and the optimum conditions for treatment established, i.e., temperature, gas flow rate, holding time, rotation rate, and sample size. The overall degree of chloride removal was established to increase as a function of time and temperature, as well as by reduced pressure. Under atmospheric pressure, the highest degree of chloride removal from a 20 g sample was obtained after 10 h at 1523 K resulting in a 98% removal and a final chloride content of 0.3 wt.% in the residue. Under reduced pressure, the chloride concentrate was lowered to 0.2 wt.% after thermal treatment of a 20 g sample at 1473 K for 8 h. In the case of 200 g samples treated in a rotary furnace, the chloride concentrate was 2.5 wt.% after 14 h at 1523 K, representing a removal of 87%. Below 0.3 wt.% chloride content, the material is deemed a nonhazardous waste.