Multireaction Modeling of Lead (Pb) and Copper (Cu) Sorption/Desorption Kinetics in Different Soils

Batch kinetic experiments were carried out to quantify and describe the sorption/desorption of Cu and Pb in ten soils that exhibited a wide range of properties. Sorption isotherms were quantified using the Langmuir equation, whereas modeling of sorption/desorption kinetics was described using multireaction model (MRM). Results revealed the nonlinear sorption behavior of Cu and Pb in all soils. The ten soils exhibited higher affinity to Pb (6.4 to 36.5 mmol kg−1) in comparison to Cu (3.6 to 22.4 mmol kg−1). Simulation of Cu and Pb kinetic data indicated that the rate of sorption reaction was two orders of magnitude higher than the rate of release. Considering one irreversible site in addition to one-reversible kinetic site improved the estimation of rates of reaction for both Cu and Pb in acidic and alkaline soils. All soils exhibited sorption/desorption hysteresis where Pb-releases ranged between <0.2% and 14.4% of the total sorbed. The respective Cu releases ranged from <0.85% and 23.4%. The multireaction model, which was successful in describing Cu and Pb for all ten soils, provided insight into the processes of sorption/desorption of Cu and Pb in all soils.