Tanit Chalermyanont, Surapon Arrykul and Nanthanit Charoenthaisong

pp. 269 - 276

Abstract

Clayey soils are usually used as barrier material in landfill liners because of its low hydraulic conductivity and high sorption capacity. Bentonite, which consists mainly of montmorillonite, has a high cation exchange capacity resulting in a high retention capacity of heavy metals. Sand is a permeable material but its hydraulic conductivity decreases significantly when mixed with bentonite. However, using a sand-bentonite mixture as landfill liners is questionable, because the hydraulic conductivity of the sand-bentonite mixture may increase when permeated with heavy metal solutions, which are normally found in landfill leachates. In this paper, transport of heavy metals through a compacted sand-bentonite mixture and its chemical compatibility were studied through the batch adsorption test, the column test, and the hydraulic conductivity test. Experimental results indicate that the sorption capacity of the bentonite, ranked in descending order, was Cr³⁺, Pb²⁺, Cd²⁺, Zn²⁺, and Ni²⁺, respectively. The diffusion coefficients of the sand-bentonite mixture were in the order of 10^-5 cm²/s and the
retardation factors were 130, 115, 111, and 90 for Pb²⁺, Ni²⁺, Zn²⁺, and Cd²⁺, respectively. The hydraulic conductivity of the sand-bentonite mixture was only compatible with a chromium solution having a concentration not greater than 0.001 M.

Keywords

• sand-bentonite mixture
• hydraulic conductivity
• heavy metals
• adsorption
• diffusion coefficient
• retardation factor