Improvement of environmental quality of coal fly ash by applying forced leaching

A coal fly ash containing leachable trace elements in amounts higher than a llowed by Dutch law for its free application as granular building material was subjected to forced leaching using water, citrate-, oxalate-, EDTA- and carbonate-solutions. With water only, the free lime and substantial amount s of Mo (30%), Se (20-40%) and SO24- (40-50%) are removed. Using the extrac tion agents, these percentages increase to 60-90% and in addition 15-20% Cr , V and Sb are removed. The environmental quality of the washed fly ash was checked with the Dutch standard leaching test (NEN7343). Leachability of M o, Se and S decreased by a factor of 2-4 after washing with water and a fac tor 2-18 (including Cr) after washing with the extracting agents. Removing extractants and metals remaining in the moisture after filtration will furt her decrease leaching. For a feasible process reduction of reagent consumpt ion and simple methods for process-water recycling are needed. (C) 2001 Els evier Science Ltd. All rights reserved.