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

MATEC Web of Conferences, Jan 2016

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.

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

MATEC Web of Conferences The Strength, Leachabilty and Microstructure Characteristics of Chromium Contaminated Stabilised Sediment Mohammed Kabir Aliyu 0 Ahmad Tarmizi Abd Karim 0 Chan Chee Ming 0 0 Faculty of Civil and Environmental Engineering, Universiti Tun Hussein Onn Malaysia , 86400 Parit Raja, Johor , Malaysia 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 ± 3oC) 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. 1 Introduction Solidification/Stabilisation (S/S) is a treatment technique by which contaminated soils, sediments or waste are mixed with a binder and/or specific additives with the aim of decreasing the mobility of the toxic contaminants by increasing the pH and fully or partially binding the contaminants in the solid matrix (stabilisation), but also of improving the physical properties (strength, compressibility, permeability and durability) of the final treatment products (solidification) [ 1 ]. The wide spread use of chromium has resulted in the contamination of soils and water. Chromium contamination is of great concern due to its toxic, mutagenic, and carcinogenic nature. The chromium is generated from steel and other alloy‘s production, pigments, chrome plating and leather tanning industries. Among the various forms of chromium, Cr (VI) is the form which is commonly found at contaminated sites and most important one because of its toxicity, solubility, and mobility characteristics [ 2, 3 ]. It can cause skin rashes, nose irritation, stomach upsets, respiratory problems, weakened immune systems, kidney and liver damage, lung cancer and sometimes even death. X-ray diffraction (XRD) has been found to be a useful application to characterize the crystalline phases of the solidified wastes [ 4, 5 ]. Information from such studies can be used successfully to obtain the immobilization mechanisms and reactions that occur in an S/S process [ 4, 6 ]. At present, Toxicity characteristic leaching procedure (TCLP) is used by the US EPA to evaluate whether a particular S/S process is effective in treating a given waste. The TCLP limit for chromium is 5 mg/l. Factors such as waste form, binder system, curing time and cement-to-waste ratio have been identified to affect the leachability of a waste after an S/S treatment [ 4, 7-9 ]. 2. Experimental Program 2.1 Materials TiO2 The main source of data for this study are sediments taken from Sembrong river at a site located between geographical coordinates of latitude 1° 52'.18.44'' N and longitude 103° 06' 15.71'' E, at Parit Sempadan, Parit Raja near Universiti Tun Hussein Onn Malaysia (UTHM). Holcim Top standard cement was used for this study. This type of cement is one of the cement that its quality complies with the Malaysian standard MS 522:2007. This type of cement is usually used as the main binder for ordinary construction and is readily available and also is environmentally friendly due to the reduced CO2 emission when it is produced. The rice husk used was burnt at a controlled temperature of 700ºC in the furnace for a period of 6 hours, with a heating rate of 5°C /min and then it was left overnight to cool. The burnt ash was then ground to produce ash size less than 75μm. 2.2 Sediment contamination procedure The natural sediment contains very low (below detection limits) concentration of chromium. Therefore to obtain synthetic contaminated sediment, the dried sediment samples was spiked with potassium dichromate (K2Cr2O7) to obtain approximately 1000 ppm target concentration to (...truncated)


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Mohammed Kabir Aliyu, Ahmad Tarmizi Abd Karim, Chan Chee Ming. The Strength, Leachabilty and Microstructure Characteristics of Chromium Contaminated Stabilised Sediment, MATEC Web of Conferences, 2016, 47, DOI: 10.1051/matecconf/20164705011