Investigating washing treatment to minimize leaching of chlorides and heavy metals from MSWI bottom ash

Bottom ash residues are one of the major products of Municipal Solid Waste Incineration (MSWI). The application of these residues in building materials is undermined by high content of heavy metals (Pb, Zn, Cu, Mn, Sb, Mo, Cr, Ni and Cd), chlorides and sulphates. Bottom Ash (BA) 0-4 mm was investigated for the distribution pattern of these constituents. Fractionation and washing treatment were applied to bring the emission of these contaminants under the limit established by Soil Quality Decree. Two steps washing treatment was investigated to remove soluble contaminants and to liberate fine particles (≤ 0.125 mm) rich in heavy metals and chlorides from BA fractions. Different washing parameters were investigated such as washing time, liquid to solid (L/S) ratio and mass of liberated fine particles for the optimization of the treatment. BA was washed twice with the L/S=3 for the duration of 60 min in order to remove soluble chlorides and concentrate heavy metals in the fine particles liberated during washing.