Solidification of heavy metal sludge using cement, fly ash and silica fume

405-414In this paper, the properties of solidified waste using ordinary Portland cement (OPC) containing silica fume (SF) and fly ash (FA) as a binder are reported. Silica fume and fly ash are used to partially replace ordinary Portland cement by 10% and 30% by weight, respectively. Plating sludge is used of 40, 50 and 60% by weight of the binder. A water to binder (w/b) ratio of 0.40 is used for all of the mixtures. The compressive strength of the solidified wastes is investigated. The leachability of heavy metals is determined by TCLP and XRD, and XRF is used to study the chemical properties, while the fractured surfaces are studied by SEM, and the pore size distribution is studied by MIP. The test results show that the setting time of the blended cement increased as the amount of plating sludge in the mix increased. In addition, the compressive strength of the blended cement increased with increasing curing duration time but at a decreasing rate. The compressive strengths at 28 days of the SF solidified waste mixes are 12.4, 2.7, 1.34 MPa and those of FA solidified waste mixes are 1.1, 1.0, 0.5 MPa at the plating sludge of 40, 50 and 60% by weight of the binder, respectively. The quality of the solidified waste containing SF and FA is better than that with OPC alone in terms of the effectiveness in reducing the leachability. The concentrations of heavy metals in the leachates are within the limits specified by the US EPA.