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Cadmium sorption and extractability in tropical soils with variable charge

Colzato, Marina, Alleoni, Luís Reynaldo Ferracciú, Kamogawa, Marcos Yassuo
Environmental monitoring and assessment 2018 v.190 no.6 pp. 345
Entisols, Gibbs free energy, Mollisols, Oxisols, cadmium, calcium chloride, correlation, desorption, fractionation, soil colloids, soil nutrient dynamics, sorption isotherms, t-test, tropical soils, variable charge
The availability of cadmium (Cd) for plants and its impact in the environment depends on Cd sorption in soil colloids. The study of Cd sorption in soil and its fractionation is an interesting tool for the evaluation of Cd affinity with soil pools. The objective with this study was to evaluate Cd sorption and desorption in tropical soils with variable charge (three Oxisols), in a Mollisol and in two Entisols with diverse physical, chemical, and mineralogical attributes. We used a thermodynamic approach to evaluate Cd sorption and performed a chemical fractionation of Cd in the six soils. Data from Cd sorption fit the Langmuir model (r > 0.94), and the sorption capacity ranged from 0.33 to 11.5 mmol kg⁻¹. The Gibbs standard free energy was positively correlated to Cd sorption capacity (r = 0.74, except for the Quartzipsamments), and it was more favorable in soils with great sorption capacity. Distribution of Cd among fractions was not affected (t test, α = 0.05) by initial concentration, and there was a predominance of Cd extractable in 0.1 mol L⁻¹ CaCl₂.