Preliminary examinations of mechanistic control in the solidification of flue gas desulphurisation sludge and pulverised fuel ash

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Abstract
Cement‐based solidification of pulverised fuel ash and flue gas desulphurisation waste i s examined using mix designs adapted from a commercial process. Monoliths augmented with up to 3.75%w/w Portland cement exhibited dimensional stability and unconfined compressive strengths exceeding 2 MPa at 84 days set. Total aqueous‐extractable metals of 0.1–1.7 mg 1‐1, determined using rapid dynamic leach tests, indicated minimal, but progressive removal of cationic species from solidified waste forms at 7, 28 and 84 days. Distinction between the mechanistic processes of solidification and cation fixation is evidenced by microstructural investigations suggesting that well‐developed ettringite crystallites, formed in the presence of available sulphate, are instrumental in controlling the leachability of metals from waste matrices.