Chromium release from waste incineration air-pollution-control residues

Cr release overtime was investigated in batch experiments for eleven air-pollution-control residues from eight different municipal solid waste incinerators covering all major flue gas cleaning technologies. Cr released during 168 h of contact with water showed significant variations among the residues studied. Also for the individual residue, large variations were observed depending on the liquid-to-solid ratio used in the leaching test and the degree of carbonation. It is argued that Al(O) present in the residues can control Cr leaching by reducing Cr(VI) released from the solid phase by dissolution and that exposure to oxygen-either prior to or during the leaching test-depletes the reduction capacity of Al(O) leading to increased Cr leaching. A dynamic model is shown to describe Cr release from all investigated residues by accounting for Al(O) oxidation with Cr(VI), O-2, and water as well as Cr(VI) dissolution. The paper reveals that Al-O-2-Cr(VI) interactions must be considered very carefully when interpreting Cr leaching data.