The Effect of Mass Transfer Resistance on the Adsorption Rate of Phenol in Soil Sediments

Abstract

This study was aimed at evaluating the effect of mass transfer resistance to the transport of phenol in soil sediments. Batch adsorption experiments were conducted using phenol in homogenous soil sediments (clay and sand). The Physico-chemical properties of the soil sediments were determined and sorption behaviour kinetically modelled using the Pseudo-first order, Pseudo-second order, Intra-particle, Elovich, and Power function models. The sorption behaviour was best modelled with the intra-particle model (R² ˃ 0.9628). The rate limiting step and mass transfer resistance were determined by the Boyd plot, Homogenous pore diffusion model (HPDM) and the modified Furusawa -Smith equation. The Boyd plots indicated external mass transfer as the rate-determining step for the phenol/clay and phenol/sand systems; the HPDM model gave a poor fit (R² ≈ 0.6) for the phenol sorbate systems, corresponding with projections from the Boyd plots. From the results of the study, the rate controlling step for phenol sorption in the sediments was predominantly due to external mass transfer resistance. A comparative analysis between the two sediments using the Furusawa -Smith equation gave the mass transfer coefficients for clay and sand to be 2.09205E-14 m s⁻¹ and 4.17537E-12 m s⁻¹ respectively, showing that as the particle size decreased, the more significant the effect of external mass transfer effect on the sorption rate.