Kinetic, adsorption, and thermodynamic study of removal of Cr6+ by iron-rich natural clay minerals

Abstract

The study explores the adsorption behavior of unmodified natural clay as an ecologically acceptable procedure in the treatment of toxic elements such as Cr6+ in wastewater. Batch experiments were conducted by stirring 30 ml of a Cr6+ solution and natural clay for 3 h at different temperatures, pH, Cr6+ loadings, and concentrations. Characterization of natural clay before and after adsorption was studied by XRD, FTIR, and BET for surface area, SEM, and EDX for surface topography. The Cr6+ content was analyzed by UV–visible spectrophotometer further, the mechanism of the process was illustrated by isotherm and kinetic studies. Cr6+ maximum sorption capacity obtained was 12.3 mg/g at pH 3. The overall process followed the Langmuir model elucidating monolayer adsorption as a major, in addition kinetics study (pseudo-2nd-order) describes accurately that chemisorption is a rate-controlling stage. Thermodynamics measurements indicated a spontaneous and endothermic process involved throughout the adsorption. Therefore, the study highlights the efficacy of unmodified natural clay as an efficient adsorbent for the elimination of Cr6+ from aqueous solution.