Exploring bentonite-based cat litter as a low-cost sorbent for copper removal

Abstract

This study investigates the potential of two types of cat litter, labelled by manufacturer as natural bentonite and bentonite, as an effective sorbent material for copper removal. XRF characterization confirmed the presence of key clay minerals (Si, Al) and oxides of Fe, Ca, Mg, Ti, K, Na, P, and S. SEM analysis revealed porous and non-homogeneous structure, while EDS analysis detected only trace amounts of copper prior to sorption, with significant uptake afterward in both cat litter samples. Non-linear regression of equilibrium data indicated that the Jovanovic isotherm model best described the sorption process, suggesting mobile and monolayer sorption without lateral interactions. Sorption kinetics followed the Elovich equation for low copper concentrations (≤3.053 mmol/dm³), highlighting rapid initial sorption rates. At higher concentrations (≥5.046 mmol/dm³), the Weber-Morris model was most accurate, indicating the influence of both film and intraparticle diffusion. The highest sorption efficiency and copper uptake were observed in systems with the highest impeller to critical impeller speed (N/N_JS) ratio, particularly in the unbaffled reactor with an SBT impeller (R_k = 61.867 %, q_k = 0.629 mmol/g). Overall, this work contributes to sustainable water treatment technologies by proposing a low-cost, readily available sorbent while also advancing the understanding of sorption kinetics and reactor optimisation. It also provides insights into how variations in the composition of the same type of clay can influence sorption efficiency. In this study, cat litter labelled as natural bentonite showed a higher sorption efficiency and capacity.