Calcium phosphate stabilization of fly ash with chloride extraction.
Municipal solid waste incinerator by products include fly ash and air pollution control residues. In order to transform these incinerator wastes into reusable mineral species, soluble alkali chlorides must be separated and toxic trace elements must be stabilized in insoluble form. We show that alkali chlorides can be extracted efficiently in an aqueous extraction step combining a calcium phosphate gel precipitation. In such a process, sodium and potassium chlorides are obtained free from calcium salts, and the trace metal ions are immobilized in the calcium phosphate matrix. Moderate calcination of the chemically treated fly ash leads to the formation of cristalline hydroxylapatite. Fly ash spiked with copper ions and treated by this process shows improved stability of metal ions. Leaching tests with water or EDTA reveal a significant drop in metal ion dissolution. Hydroxylapatite may trap toxic metals and also prevent their evaporation during thermal treatments. Incinerator fly ash together with air pollution control residues, treated by the combined chloride extraction and hydroxylapatite formation process may be considered safe to use as a mineral filler in value added products such as road base or cement blocks.
Nzihou
Ange
A
Centre Energétique-Environnement, Ecole des Mines d'Albi-Carmaux, France. nzihou@enstimac.fr
Sharrock
Patrick
P
D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000517:prevention & control*; D001672:Biocompatible Materials / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry; D002712:Chlorides / Q000032:analysis / Q000737:chemistry / Q000302:isolation & purification*; D017886:Durapatite / Q000737:chemistry; D004492:Edetic Acid / Q000737:chemistry; D017745:Incineration; D019216:Metals, Heavy / Q000737:chemistry; D012037:Refuse Disposal; D012995:Solubility
D000393:Air Pollutants; D001672:Biocompatible Materials; D002614:Chelating Agents; D002712:Chlorides; D019216:Metals, Heavy; D017886:Durapatite; D004492:Edetic Acid