Adsorption of lead and cadmium by some volcanic ash soils

Abstract

The adsorption of cadmium (Cd) and lead (Pb) by three volcanic ash soils with varying chemical properties was studied. Soil samples were equilibrated with increasing amounts of both CdSO₄‐8H₂0 and Pb(NO₃)₂ in 1:5–1:20 soi1:solution ratios at several time intervals, in the presence of various surfactant concentrations (0.05–1.0%). Concentrations of Cd and Pb remaining in solution after equilibrium time were determined by atomic absorption. The study showed that there was a decrease in percentage of adsorbed Cd with an increase in soi1: solution ratio and an apparent adsorption plateau with shaking time. Adsorption of Cd varied according to soil types, being in the order of 80–96% at low surfactant and Cd concentrations in the soil with the highest organic matter content. At low surfactant concentration (up to 0.5%) most of the Pb was retained by the soils after a 15 minute shaking time, regardless of soi1:solution ratio. Substantial amounts of Pb, however, remained in solution in most soils at higher surfactant concentrations, presumably due to the ability of the surfactant accompanying cation to compete with Pb for adsorbing sites. Cadmium and Pb adsorption maxima and their relationship with some soil properties with regard to their implications in waste‐treatment processes also were discussed.

Key words:

• Heavy metals
• Surfactants
• Allophanic soils.