Sorption-Desorption Hysteresis of Cd and Pb on Alluvial Soils as Affected by Clay Content

ADSORPTION hysteresis in natural sorbents has important …….environmental implications for pollutant transport and bioavailability. The objective was to assess and compare the competitive adsorption and desorption capacities and adsorption hysteresis of Cd²⁺and Pb²⁺on four natural soils with different clay contents (10%, 20%, 40% and 50%, hereafter referred to S₁₀, S₂₀, S₄₀ and S₅₀) in terms of their physical and chemical properties. The adsorption-desorption hysteresis of Cd²⁺and Pb²⁺ were characterized using linear, Freundlich and Langmuir equations. In all soils Pb²⁺ was invariably sorbed and retained to a greater extent than Cd²⁺. Based on hysteresis index, Pb²⁺ was less mobile than Cd²⁺ in the studied soils. The adsorption and retention of Cd²⁺ and Pb²⁺were most influenced by pH, cation exchange capacity (CEC), total amorphous material percent (TAM%), total organic carbon percent (TOC%) and clay content. In all the soils Cd²⁺ exhibited greater hysteresis than Pb²⁺. The amounts of Cd²⁺ and Pb²⁺ desorbed from S₁₀ were more than from S₅₀, indicating that S₅₀ was a more effective sorbent for water and wastewater treatment and clay content was the individual soil property most markedly influencing Cd²⁺ and Pb²⁺ adsorption and retention.
 
Keywords: Hysteresis, Adsorption, Desorption, Heavy metals.
 
DSORPTION hysteresis in natural sorbents has important …….environmental implications for pollutant transport and bioavailability. The objective was to assess and compare the competitive adsorption and desorption capacities and adsorption hysteresis of Cd²⁺and Pb²⁺on four natural soils with different clay contents (10%, 20%, 40% and 50%, hereafter referred to S₁₀, S₂₀, S₄₀ and S₅₀) in terms of their physical and chemical properties. The adsorption-desorption hysteresis of Cd²⁺and Pb²⁺ were characterized using linear, Freundlich and Langmuir equations. In all soils Pb²⁺ was invariably sorbed and retained to a greater extent than Cd²⁺. Based on hysteresis index, Pb²⁺ was less mobile than Cd²⁺ in the studied soils. The adsorption and retention of Cd²⁺ and Pb²⁺were most influenced by pH, cation exchange capacity (CEC), total amorphous material percent (TAM%), total organic carbon percent (TOC%) and clay content. In all the soils Cd²⁺ exhibited greater hysteresis than Pb²⁺. The amounts of Cd²⁺ and Pb²⁺ desorbed from S₁₀ were more than from S₅₀, indicating that S₅₀ was a more effective sorbent for water and wastewater treatment and clay content was the individual soil property most markedly influencing Cd²⁺ and Pb²⁺ adsorption and retention.