Cadmium sorption and extractability in tropical soils with variable charge

Area of Science:

• Environmental Science
• Soil Science
• Geochemistry

Background:

• Cadmium (Cd) availability to plants and environmental impact are governed by its sorption onto soil colloids.
• Understanding Cd sorption and fractionation in soils is key to assessing its affinity with soil components.

Purpose of the Study:

• To evaluate cadmium sorption and desorption dynamics in diverse tropical soils (Oxisols, Mollisol, Entisols).
• To assess the relationship between soil properties and Cd sorption capacity using a thermodynamic approach.

Main Methods:

• Cadmium sorption and desorption experiments were conducted on six different soil types.
• A thermodynamic approach, including Gibbs standard free energy, was used to analyze sorption.
• Chemical fractionation was employed to determine Cd distribution among soil pools.

Main Results:

• Cadmium sorption data fitted the Langmuir model well, with sorption capacities varying from 0.33 to 11.5 mmol kg⁻¹.
• Higher Cd sorption capacity correlated positively with Gibbs standard free energy, indicating more favorable sorption.
• Initial Cd concentration did not significantly affect Cd distribution among soil fractions, with CaCl₂ being the predominant extractant.

Conclusions:

• Soil properties significantly influence cadmium sorption capacity and thermodynamic favorability.
• Cadmium predominantly partitions into the readily extractable fraction (0.1 mol L⁻¹ CaCl₂) regardless of initial concentration.