ABSTRACT:

This paper presents a study of metal diffusion through compacted lateritic clay, with a view to contribute to the utilization of local soils in the construction of clay liners for waste disposal sites in tropical countries. Twelve metals controlled by regulations for potable water, and general components of leachates from domestic and industrial wastes, were studied: aluminum, arsenic, barium, cadmium, lead, copper, chromium, iron, manganese, silver and selenium. Diffusion tests were carried out on compacted specimens, and solutions of each metal, with concentration of 100 mg/L and pH values of 1 and 4. Adsorption batch-tests were carried out with solutions of each metal, with concentrations of 1, 10 and 100 mg/L at pH 1. Results show that diffusion may be an important mechanism of transport of metals in acidic solutions through a compacted layer of lateritic clay; however, some metals are retained in the upper layer of the soil even at low pH values. At pH 4, metal migration is avoided by metal hydrolysis and increase in adsorption. Comparison of results at pH 1 and pH 4 testifies the importance of pH correction for contaminated wastes, as a situation of migration by diffusion with low retention can be changed to that of high retention in the upper centimeters of the clay liner.

INTRODUCTION

Compacted clay liners are fundamental elements in lining systems of industrial and domestic waste disposal sites. In tropical countries, lateritic clays are suitable materials for the construction of clay liners because of their availability and their appropriate geotechnical properties. Furthermore, such soils have been extensively used in recent decades in dam and road construction. However, little is known about the geomechanical and chemical parameters of lateritic soils for the performance-oriented design of lining systems (Manassero et al., 1998).

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