Utilisation of zeolitised coal fly ash as immobilising agent of a metallurgical waste

In the work described in this paper, partially zeolitised coal fly ash from a Spanish power station has been studied as the immobilising agent of an arc furnace dust waste (s-WA). s-WA is a dust coming from the collecting systems of particulate material in a carbon-steel electric arc furnace (EAF). The hazardous metals normally found in this kind of waste are lead, cadmium, and chromium. In addition, the dust usually has a high zinc content resulting from the use of galvanised scrap. Because of its heavy metal content, s-WA is classified as hazardous waste, according to Spanish regulations. Different zeolitisation procedures, depending on the treatment of the fly ash with NaOH and KOH alkaline solutions, using reflux heating and different times of attack were tested. The zeolitised products were studied using XRD in order to characterise the solid phases produced. The solidification/stabilisation (S/S) trials of s-WA were carried out using the zeolitised ashes, as well as the original coal fly ash, in mixtures containing 20% (w/w) of ordinary Portland cement. To evaluate the efficiency of the immobilisation process, some specific criteria were defined, with regard to some physical (compressive strength) and chemical (pH and metal concentrations in TCLP leachates) characterists of the S/S solids. Finally, comparisons among the stabilising mixtures were made and the role of the zeolitisation of fly ash in the S/S process was evaluated. (C) 2002 Society of Chemical Industry.