Comparative study of Cadmium adsorption on three contrasting soils from a highly industrialized region

Abstract

Evaluation of natural soils potentiality to effectively immobilize heavy metals is a fundamental tool for a sustainable management of an industrialized region. Three soil textures from Bahía Blanca Citýs industrial zone (Argentina) were analyzed to quantify Cd adsorption and assess its applicability for industrial land use. Soils textural classes corresponded to sandy loam (M1), sand (M2) and silt loam (M3). Batch adsorption kinetics and isotherms were carried out with a 1:10 soil:solution ratio. Adsorption kinetics was conducted for 240 min at constant initial Cd concentration (250 mg l−1) and varying pH (4–8 range). Adsorption isotherm was done for twenty Cd concentrations (range 0.5 mg l−1 to 460 mg l−1) and contact time of 24 h. Kinetics showed a fast instantaneous initially adsorption. Soil-water partitioning coefficient (Kd) was calculated for each concentration supplied to soils, showing a direct relationship between pH and Kd. Adsorption isotherms plots showed a nonlinear shape for M1 and M2 and a linear shape for M3. The affinity of Cd for soils is in the order: M3 > M1 > M2. Metal retention in M3 was upper than 97.8%. Langmuir, Freundlich and Dubinin-Radushkevich (DRK) adsorption models correctly reproduced experimental data. However, M1 (R2 = 0.992) and M3 (R2 = 0.985) fitted better to Freundlich model. Otherwise, M2 (R2 = 0.981) fitted better to Langmuir adsorption model. M3 presented the highest buffer and Cd retention capacity, possibly related to its clay content. Based on desorption studies, M3 presented the strongest binding site as 95% of metal removal was attributed to specific sorption. Silt loam is the most suitable soil coverage for industrial land of all analyzed soils.