Environmental hazard of oil shale combustion fly ash

Abstract

The combined chemical and ecotoxicological characterization of oil shale combustion fly ash was performed. Ash was sampled from the most distant point of the ash-separation systems of the Balti and Eesti Thermal Power Plants in North-Eastern Estonia. The fly ash proved potentially hazardous for tested aquatic organisms and high alkalinity of the leachates (pH>10) is apparently the key factor determining its toxicity. The leachates were not genotoxic in the Ames assay. Also, the analysis showed that despite long-term intensive oil-shale combustion accompanied by considerable fly ash emissions has not led to significant soil contamination by hazardous trace elements in North-Eastern Estonia. Comparative study of the fly ash originating from the 'new' circulating fluidized bed (CFB) combustion technology and the 'old' pulverized-fired (PF) one showed that CFB fly ash was less toxic than PF fly ash. Thus, complete transfer to the 'new' technology will reduce (i) atmospheric emission of hazardous trace elements and (ii) fly ash toxicity to aquatic organisms as compared with the 'old' technology.