Adsorption of Metal Ions from Carwash Wastewater by Phosphoric Acid Modified Clay: Kinetics and Thermodynamic Studies

Abstract

The adsorption kinetics and the thermodynamic parameters for the removal of metal ions from carwash effluent using phosphoric acid modified clay were investigated in this study. Kinetic parameters were determined by analysing the modified second-order and intra-particle models. In the second order kinetics, Cd²⁺ had adsorption capacity q_e of 7.5mg/g with the regression coefficients of linearization (R²) of 1.0 followed by Ni²⁺ with q_e of 1.36mg/g with R² of 0.949. For the intra-particle kinetics, Cd²⁺ had Kid of 1.0 with R² of 0.959, while Pb²⁺ had Kid of 0.144 with R² of 0.997. Adsorption generally increases with temperature and time. At 240minutes, all Cd²⁺ had been removed from solution, same at 50^oC with trend of removal following the order Cd²⁺? Pb²⁺? Cr³⁺ ?Ni^2+. ?H^o ranged from -1.4KJ/mol for Cr³⁺ to -6.0KJ/mol for Cd²⁺ indicating physical adsorption. ?S^o ranged from 12..7J/mol for Cd²⁺ to 100J/mol for Cr³⁺ while ?G were negative for all metal ions indicating that the adsorption was spontaneous and feasible.

Keywords: Carwash wastewater, adsorption, phosphoric acid modified clay, kinetics and thermodynamics