Insights in leaching characteristic assessment of solidified wastes using different leach tests

Solidified samples of fuel oil combustion bottom ash with two sets of Ordinary Port-land Cement (OPC) and Pozzolan added OPC were investigated with three sets of chemical leaching tests. Toxicity characteristic leaching test (TCLP) results classified waste material and its solidifica-tion products as hazardous. Although Ni and Cr have over-leached, but their close examination with Sequential Chemical Extraction (SCE) test revealed new insights as follows. Nickel fixation in cement matrix has shifted over 20% of leachable Ni from first 4 fractions of SCE test to residual fraction with less likelihood of leaching. Chromium fixation in matrix has made shifts on leachable fractions that are not generally in favor of a successful fixation in matrix. In the case of Cd leaching, the only obvious finding from SCE test is that solidification processes have made a slight shift between fractions in bound to Iron and Manganese oxide and fraction in bound to carbonates. Compared to TCLP results for different mixtures, it can be concluded that Cd fixation has been done properly and significant change in leaching probability was not caused by solidification processes. Results of "Alkalinity, Solubility and Release as a function of pH" test indicate over regulation in the case of Pb and Cr leaching in different pHs. Results indicate need for more delicate interpretation of TCLP test results when several management scenarios are available and practical.

Keywords
Cement, Solidification, Fuel oil combustion, Residue, TCLP, SCE, Alkalinity, Solubility, pH, Leach tests