DefinePK

Abstract

Solidification/Stabilization is an effective, yet economic remediation technology to immobilize heavy metals in contaminated soils, sediments and sludges. The main objective of this research was to study the effect of replacing cement with rice husk ash (RHA) on compressive strength and leachability of Pb from the stabilized sediments. Cement and Rice husk ash were used as stabilizing agents to immobilise lead contaminated sediment. In this study, artificially contaminated sediment was prepared by spiking Pb(NO3)2 to achieve an average of 1000 ppm target concentration to bracket a worst case scenario. The Pb- impacted sediment was stabilized with 10% cement and 5, 10, 15 and 20% rice husk ash (RHA) by total dry weight of the mixture and was cured for 7, 14 and 28 days. The unconfined compressive strength test (UCS) and the toxicity characteristic leaching procedure (TCLP) was used to evaluate the effectiveness of the S/S treatments at 7, 14 and 28 days. The result of the Toxicity characteristic leaching procedure (TCLP) leaching test conducted on the lead spiked solidified samples indicated that with addition of 15% RHA at 7, and 14 days the Pb concentration was below the leachability limit of 5 mg/l, subsequent 28 days of curing, the concentration of lead was all below the leachability limits except the control sample. The effect of pH on the leachability of lead (Pb) was also considered in the study, the leachability of lead in the TCLP at 7, 14 and 28 days respectively decreases from 13.49 mg/l to 1.89 mg/l as the pH of the leachates increases from 3.57 - 5.13. It was also observed that the higher the strength of the solidified sample the lower the leaching rate of lead in the TCLP. The X-ray diffraction (XRD) results indicated that lead in Pb(NO3)2 had precipitated to form Pb(OH)2 within the cement hydration environment which explained the high treatment efficiency due to low solubility of the precipitates. Results have indicated that the partial replacement of cement with RHA in the binder system has increased the strength and reduced leachability of Lead from the treated sediment samples compared to the untreated ones.