Chemical fractionation of a fly ash sample by a sequential leaching method

A five-stage sequential leaching procedure was optimized for the analysis of the fly ash sample, CW6, as a candidate reference material. The distribution of particulate elements was achieved for Cd, Cr, Cu, Pb, Zn, and V into different fractions: (1) exchangeable, (2) bound to carbonate, (3) bound to Fe/Mn oxides, (4) bound to sulfide compounds, and (5) acid soluble, residual fraction. The leachability of the metals proved to be different, so various distribution patterns have been achieved. The results of the total elemental analysis and the sequential leaching method were compared and a good agreement was found. The uncertainty of the leaching method is reasonable, even when experimental parameters are strictly fixed and the analysis is quite tedious. The ratio of environmentally mobile fractions was compared to that from the conventional test method and a reasonable conformity has been found. This characterization method can be used to interpret the leaching behavior of element species and mode of binding to the matrix. Using the optimized sequential procedure, a new aspect can be interpreted to understand the behavior of toxic elements released from fly ashes into nature.