Transport parameters of lead (Pb) Ions migrating through saturated lateritic soil–bentonite column

Abstract

This paper describes experiments and analyses conducted to determine the transport parameters of lead (Pb) ions diffusing through compacted lateritic soil–bentonite column. Experimental programme included the batch sorption tests and diffusion tests conducted in cells containing water-saturated lateritic soil treated with up to 10% bentonite by dry weight of soil. Specimens for diffusion tests were compacted at approximately 2% wet of optimum moisture content with British standard heavy (BSH) effort and exposed to municipal waste leachate placed on top of the specimens. Migration of Pb ions was monitored by measurement of pore water concentrations at various depths along the soil mixture columns together with the soil transport parameters (i.e. distribution coefficient, Kd, retardation factor, Rd and diffusion coefficient, D*). Based on sorption data, linear sorption isotherms were derived. Kd values of 2.0, 2.2, 2.5, 2.7, 3.9 as well as Rd values of 11.0, 11.1, 12.5, 12.5, 16.7 were recorded for 0, 2.5, 5, 7.5, 10% bentonite contents, respectively. The distribution of Pb was limited to upper sections (1.6–3.2 cm) of the soil column in mixtures. Diffusion testing established D* values of 4.50, 3.15, 2.78, 2.42 and 2.06 × 10−10 m2/s for the same sequence of bentonite treatment which is consistent with very strong sorption on mixtures particularly with higher bentonite contents.