Statistical analysis of process and composition factors affecting the leaching of heavy metals from fly ash solidified/stabilized wastes

Six process factors were studied using a combined 26-3 fractional factorial design and the composition was studied using an augmented simplex-centroid design. Process factors included acid strength, acid/waste ratio, slurry pH, ash/slurry ratio, pressure, and aging time. Statistical analysis of the TCLP data obtained after 18 h of leaching showed that the factors which significantly affected the results depended on the specific response metal being studied. Only the process factor, aging time, was statistically significant for all of the responses. The composition of the waste did affect only the cadmium response. The results obtained in this study will contribute to understanding the leaching behavior of hazardous materials contained in solidified/stabilized fly ash wastes.