Heavy metal stabilization of industrial solid wastes using low-grade magnesia, Portland and magnesia cements

Abstract

In this study, stabilization/solidification of electric arc furnace dust and Pb-refining dust was investigated. Stabilization of both wastes was performed by mixing each raw waste with MgO, Portland cement, MgO with MgCl2 (magnesium oxychloride cement), and MgO with phosphate salts (magnesium phosphate cement), at ratios between 5 and 25 wt%. Stabilization/solidification processes were evaluated using EN 12457-4 standard leaching test and stabilized wastes were classified according to the 2003/33/EC Decision. Leachates of stabilized electric arc furnace dust with magnesium oxychloride and magnesium phosphate cement at 10 wt% and 5 wt%, respectively, presented lower concentrations than the regulation limits for disposal in non-hazardous waste landfills; however, the stabilized electric arc furnace dust using MgO or Portland cement at 25 wt% cannot be disposed in hazardous waste landfills. Stabilized Pb-refining dust using MgO or Portland cement at 25 wt% can be disposed of in hazardous waste landfills, whereas stabilized Pb-refining dust with magnesium oxychloride and magnesium phosphate cement at 20 wt% is suitable for disposal in non-hazardous waste landfills. The efficiency of magnesia cements stabilization is attributed to regulation of pH at 10–11, where metal solubility is diminished and positive surface charge of hydrolyzed MgO products results in high adsorption of metalloids oxy-anions.