Assessment of heavy metal adsorption potential of lateritic soil used as landfill liner material in waste containment structures

Deptt. of Civil Engineering, Haldia Institute of Technology, Haldia, West Bengal, India

Increasing soil and groundwater pollution by heavy metals through anthropogenic reason is a major concern of present environment. The objective of the present study was to assess the potential of lateritic soil to be used as liner material in landfill, effluent drain and effluent pond particularly with respect to subsurface transport of Zn & Cu. In the present study, the adsorption and migration of the two metals (Zn & Cu) through lateritic soil were studied using batch adsorption tests. The laboratory scale batch adsorption experiments were performed to determine adsorption capacity of the soil by carrying out adsorption isotherms and kinetic studies at different initial concentrations (0.5, 1, 5, 10 mg/l) of adsorbate at a fixed pH of 8 and with different adsorbent doses (5, 10, 20, 30 g/L) and an equilibrium contact time of 120 minutes. The soil used as adsorbent in batch adsorption experiments was found to have low hydraulic conductivity of 3.17x10^-8 cm/s, and thus suitable to be used as a liner material in waste containment structures. The linear, Langmuir and Freundlich isotherm models were examined for fitting with the laboratory batch adsorption experimental results. The Langmuir isotherm provided best fit for Zn adsorption test data with R² (co-efficient of determination)=0.922 and RMSE(root mean square error) =0.000962 at a soil dose of 5.0 g/L. Similar trend was observed with Cu adsorption test results with R²= 0.989, RMSE =0.000588 at a soil dose of 5 g/L. The higher values of adsorption capacity (qZn =1845 mg/kg, qCu = 1796.8 mg/Kg) of the soil for both the metals indicate good attenuative potential of the soil with respect to Cu & Zn. It was concluded from the present study that the lateritic soil can be used as an effective adsorbent and a barrier material and can be used as a primary liner material in a waste containment structure for retarding the migration of contaminants and thereby protecting the precious groundwater.