Sorption characteristics of a landfill clay soil as a retardation barrier of some heavy metals

The sorption characteristics of landfill silty clay soil (LSC), taken from AL Hammam landfill site, as a retardation barrier of Zn2+, Cd2+ and Pb2+ ions were investigated. LSC consists mainly of kaolinite, quartz and calcite minerals, is a part of thin blanket of Miocene rocks forming a vast persistent limestone plateau of the north part of the western desert of Egypt. The results showed that the percentage equilibrium uptake of the metal ions by LSC are 94.8, 92.7, and 86.0 for Zn2+, Pb2+, and Cd2+, respectively. The coefficient of diffusion's value was found in the range (3.32-6.8)0.10(-17) m(2)/s and increases with the increase in temperature. The distribution coefficient for Pb2+, Cd2+, and Zn2+ ranged from 404.9 to 568, 230.1 to 281.9, and 371.4 to 466.7 ml/g in the temperature range 298 to 333 +/- 1 K, respectively. The value of retardation factor and the sorption affinity onto LSC took the order Zn2+- > Pb2+ > Cd2+. The experimental investigation on ionic concentrations in sorption batches suggested that sorption behaviors of Zn2+, Pb2+, and Cd2+ ion metals onto LSC are mainly controlled by cation exchange. The wetting front of water movement in the LSC as an unsaturated soil reached to about 0.06, 0.19 and 0.25 cm after 6, 24 and 48 h of steady infiltration. The saturation hydraulic conductivity of the LSC (<2.0 mu m) fraction is 2.18 x 10(-10) m/s therefore, it matches the condition of suitability of soils as mineral liners for a landfill facility. The Peclet number values (<32) indicate dominance of dispersion over advection. The <2 mu m fraction of LSC may be used to attenuate Zn2+, Cd2+ and Pb2+ ions presented in AL Hammam landfill leachate from reaching the shallow groundwater. (C) 2016 Elsevier B.V. All rights reserved.