The Strength, Leachabilty and Microstructure Characteristics of Chromium Contaminated Stabilised Sediment

The effect of replacing cement with rice husk ash (RHA) on compressive strength and leachability of Chromium stabilised sediments was investigated. Artificially contaminated sediment was prepared by spiking sediment with solution of Potassium dichromate (K2Cr2O7) to achieve an average of 1000 ppm target concentration. Cement was added at 10% and rice husk ash at 5%, 10%, 15% and 20% to the total dry weight of the mixture, which were then cured at room temperature (27 ± 3°C) and humidity of 75 ± 5 % for 7, 14 and 28 days. The addition of RHA with cement to the spiked sediment increased the compressive strength (UCS) of solidified sample with increase in curing period. The reaction products and crystalline mineral phases were identified using X-ray diffraction (XRD) which shows the formation of various crystalline phases of the treated sediment after 28 days which explain the mechanisms responsible for immobilization of chromium under study. The UCS values of solidified samples at 7, 14 and 28 days exceeded the minimum landfill disposal limits of 0.34N/mm2 (340 kPa). It was observed that leaching of Cr (VI) was higher in acetic acid medium (TCLP) as compared to deionized water (DIW) medium. The leached chromium concentrations in the two different leachates (acetic acid, and deionized water) were all below the regulatory limits of 5 mg/l of U.S EPA. Results have indicated that the partial replacement of cement with RHA in the binder system has increased the strength and reduced leachability of chromium in the treated compared to untreated sediment samples.