STABILIZATION OF LEAD AND HYDROCARBON CONTAMINATED LATERITIC SOILS USING LIME-RICE HUSK ASH

Abstract

This study investigates the efficiency of the binder (Lime-Rice Husk Ash) combined at a ratio of 1:2 Lime: Rice Husk Ash and added as stabilizing binder to lateritic soil collected from Akure (Nigeria) artificially contaminated by lead and naphthalene at varied degrees of 5 and 10% by weight of the artificially contaminated soil samples. To achieve this goal, strength, environmental performance evaluation and microstructural tests were conducted for mixtures of varied degrees of lead and naphthalene contaminated lateritic soil samples. Strength characteristics tests which include unconfined compressive strength and direct shear tests were conducted on the samples, with samples showing increase in strength as the stabilizing binder was added to the samples. The 10% binder addition produced the maximum values for the strength tests which were in the range of 272.03–349.75kN/m2 and 271.76–388.61kN/m2 for the unconfined compressive strength on lead and naphthalene contaminated samples respectively. The cohesion and angle of internal friction values from the direct shear test were in the range of 440-836kN/m2 and 79.92°-60.43° for the lead and 130-544kN/m2 and 61.56°-42.72° for the naphthalene contaminated samples respectively. The leaching potential of lead contaminated soils at their natural pH indicated a trend of decrease in the lead concentration in the leachate as the binder addition was increased from 0% to 5% to 10% by weight of sample respectively in the range of 0.73 mg/l - 0.32 mg/l - 0.24 mg/l. These remain below the USEPA (United States Environmental Protection Agency) regulatory level of 5 mg/l for lead after an aggressive procedure, but not below the WHO (World Health Organization) maximum lead contaminant level for drinking water which is 0.015 mg/l. The Naphthalene contaminated soil had their leaching potential also reduced as the binder addition was increased from 0% to 5% to 10% by weight of sample in the range of 4.17 mg/l - 2.21 mg/l - 0.62 mg/l respectively but not below the regulatory level of 0.2 μg/l. The lateritic soil showed a good adsorption capacity for lead and naphthalene. This was evident from the retardation factors for lead which increased from 2.55-4.98-59.83 and naphthalene which retardation factors increased from 17.74-18.29-29.96 at binder levels of 0%, 5% and 10% respectively. The X-ray diffraction (XRD) analysis showed that predominant minerals present in the lateritic soil sample were Quartz, kaolinite and illite. The XRD analysis on contaminated samples with their binder addition showed the presence of new minerals (which were not present in the uncontaminated samples). These minerals include cerossite and mimetite for lead contaminated samples, albertite and ozokerite for naphthalene contaminated samples. The mineral composition also showed that the 5% binder was effective in stabilization of 500 ppm (this represents the lowest concentration) of lead contaminated soil, while the 10% binder was effective in stabilization of 2000 ppm (this represents the highest concentration) of lead contaminated soil. For naphthalene contaminated soil, 10% binder was effective for both 0.5% by weight of lateritic soil (this represents the lowest concentration) of naphthalene contaminated soil and 3% by weight of lateritic soil (this represents the lowest concentration) of naphthalene contaminated soil.