Evaluation of ions retention capacity of a residual soil of Rio de Janeiro, Brazil

摘要

The paper presents the results of laboratory experiments investigating the cation and anion sorption parameters of a saprolitic residual soil from the State of Rio de Janeiro. The soil is a sandy silt with 58% of fines (%<#200 ASTM sieve), and a plasticity index Ip of 29%. The soil clay fraction is constituted by kaolinite, goethite and traces of vermiculite, and the soil is representative of the materials used for construction of liners at various industrial and domestic wastes disposal sites in Rio de Janeiro. The soil was completely characterized, including the determination of the physical and geotechnical index properties, minera-logical composition, and physico-chemical parameters such as the Cation Exchange Capacity (CEC), the soil natural pH and the Zero Point of Charge pH (ZPC), the exchangeable complex composition and the organic matter content. Distinct series of Batch tests were performed to investigate the soil sorption behaviour relative to the ions K~+, Cl~- and phosphate (occurring primarily as HPO_4~(2-)), at two pH levels, 2.5 and 6.5. The soil Zero Point of Charge is around 3.5, close to the kaolinite typical value. The residual soil sorption behaviour was also compared to pure kaolinite, goethite and hematite samples measured sorption patterns for the phosphate ion at the same pH conditions.