To investigate the stabilization of heavy metal sludge from COD wastewater treatment and broken fluorescent lamp residue by adding sodium sulfide before solidification with portland cement and spent silica-alumina. The experiments were performed to determine not only the factors affecting the solidification process but also the physical properties of the solidified specimens, such as the compressive strength, density and permeability. In addition, the extraction tests on mercury, chromium and iron were carried out. There were four experiments in this research. The first experiment was performed by using the heavy metal sludge waste/cementitious binders ratios of 0.25 0.50 and 0.7. The second experiment indicated the effect of water/cementitious binders ratio of 0.3 0.4 0.5 0.6 and 0.7. The third experiment indicated the effect of varying curing time of the solidified specimens at 1 3 7 14 and 28 days. The fourth experiment considers the stabilization efficiencies of heavy metal and considers cost estimation of the proper binder for solidification by portland cement. The results for solidification of heavy metal sludge from COD wastewater treatment using cement mixed with spent silica-alumina indicated that the optimum condition were waste/binder ratio of 0.50, 60% spent silica-alumina/cement ratio (cement:silica = 1:0.6), water/binder ratio of 0.50, sodium sulfide 1.75 time the stoichiometric amount and curing time of 7 days. The stabilization efficiencies of mercury and chromium were 88.39 and 82.77% respectively. The extractive reduction efficiency of anthraquinone was 61.97%. The estimation of treatment cost were about 5,110 baht per ton of dry heavy metal sludge. The result for solidification of broken fluorescent lamp residue using cement mixed with spent silica-alumina indicated that the optimum condition were waste/binder ratio of 0.75, 100% spent silica-alumina/cement ratio (cement:silica = 1:1), water/binder ratio of 0.50, sodium sulfide 1.75 time the stoichiometric amount and curing time of 3 days. The stabilization efficiencies of mercury was 82.17%. The extractive reduction efficiency of anthraquinone was 60.56%. The estimation of treatment cost were about 5,620 baht per ton of dry heavy metal sludge.
