Classification of coal fly ash based on pH, CaO content, glassy components, and leachability of toxic elements

Leaching of As and Se from coal fly ash: fundamental study for coal fly ash recycling

Coal fly ash (CFA) is a useful recycled resource for uses such as cement raw material. To manage and evaluate safety for effective utilization of CFA, the leaching concentration and amounts of toxic elements in CFA need to be determined. In this study, 38 types of CFA and aged CFA generated in Japan were used to measure the occurrence and leaching concentration range of As and Se. In addition, the leaching characteristics over the long term were examined using statistical analysis. Leaching concentrations of As and Se from CFAs were in the range of 0.001-0.163 mg/L (average: 0.025 mg/L, median: 0.014 mg/L) and 0.001-0.189 mg/L (average: 0.071 mg/L, median: 0.055 mg/L), respectively. In general, the concentrations of aged CFAs were less than those of the CFAs with a few exceptions. Leaching concentrations of As and Se in the tank leaching test changed with time, and As and Se concentrations in the dispersions increased with stirring time. In contrast, pH of the dispersion decreased with time. The relation between As or Se and CFA factors showed that As or Se and pH or Ca were highly correlated. However, in aged CFAs for long-term use, the correlation coefficient for the relation between As and other factors was low while that for Se-S was high. Considering the effective utilization of CFA as a long-term recyclable resource, the leaching processes of As and Se in CFA would change with time depending on the environmental conditions.

Leachability and adverse effects of coal fly ash: A review

Coal fly ash (CFA) is a valuable industrial solid waste, but conventional methods used for its disposal can lead to serious and long-lasting environmental issues. The study of technologies for CFA recycling has been of major concern, while the harm caused by CFA is only partially understood, limiting its reuse. In this review, the basic physico-chemical properties of CFA are introduced, followed by a systematic summary and discussion of the leachability of CFA via different leaching methods and the chemical speciation of some typical metal elements in CFA, which is related to its harmful effects. The specific harm that CFA causes to humans, wild animals, and plants and the study status of magnetic property of CFA are presented. Because of the pervasive concerns of many people, the utilisation of CFA in the USA and Europe and an economic and environmental analysis of its disposal is provided and discussed. Finally, some possible directions for future research involving CFA are proposed.