Isotherm and Statistical Validity Modelings of Adsorption of Endocrine Disruptive Cr(VI) onto Calcinated Earthworm Cast

Abstract

Heavy metals discharge by diverse anthropogenic activities has been identified to be hazardous and pose dangerous health effects and environmental challenges. Adsorption is an alternative wastewater treatment technique used in the removal of these non-biodegradable toxic wastes from water. This study focused on isotherm and statistical validity modeling of adsorption of endocrine disruptive Chromium (VI) ions using Calcined Earthworm Cast (CEC). Equilibrium data obtained from the adsorption of Cr(VI) onto CEC by batch technique were fitted to eight isotherm models. Beyond the linear regression coefficient, the suitability of the isotherm model in describing the equilibrium data was established using nine statistical error validity models. Freundlich and Halsey isotherm models demonstrated the best fitting to the equilibrium data with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{R}^{2} &gt; 0.99$</tex> , close agreement between <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{qe},_{\exp}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{qe},_{\text{cal}}$</tex> as well as lower range of values of statistical model. Langmuir monolayer capacity <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mathrm{Q}_{\max}=129.37$</tex> mg/g) demonstrated superiority over those previously reported. Adsorption of Cr(VI) was by physisorption mechanism process based on the free energy value from DKR being less than 8 kJmol-1. Isotherm model parameters predicted the efficacy of CEC and its relevance in the design of wastewater treatment reactors. The performance and capacity of CEC are enlisted among sustainable materials for the treatment of endocrine disruptive compounds.