Removal of BTEX from refinery waste using HDTMAC-modified Ogwuta source clay: Adsorption equilibrium and thermodynamic inclinations

Abstract

The possible non-compliance of refineries to the demands of environmenteal protection laws has led to the discharge of poorly treated and contaminated wastewater to the environment. Carcinogenic compoiunds such as benzene, toluene, ethylbenzene, and xylene (BTEX) find their way to the ecosystem. This study is aimed at investigating the isotherm and thermodynamics of the uptake of BTEX using hexadecytrimethylammonium chloride (HDTMAC)-modified natural Ogwuta clay. Batch adsorption process was used at different BTEX concentrations and at temperatures of 303oK, 313oK and 323oK. Langmuir, Freundlich, Dubinin-Radushkevich (D-R), and Tempkin models were used to describe the process while changes in enthropy , enthalpy , and Gibbs free energy of the process were evaluated. The maximum monolayer coverage capacity (qm) of 1.83, 0.92, 0.86 and 0.69 mg/g of BTEX was lower than the calculated values of 4.94, 2.64, 2.76 and 2.20 mg/g respectively, implying uptake of pollutants through other mechanisms. The Dubinin-Radushkevich monolayer coverage range of 0.81-2.66 mg/g agreed with the monolayer coverage of the Langmuir model but with energy less than 1 kJ/mol. Freundlich adsorption intensities for BTEX were 1.64, 1.41, 1.11 and 1.22 respectively and R2 values of not less than 0.99 for each pollutant showed that the model best fits the process. Results of the thermodynamic parameters showed that the process was more feasible at increased temperature, endothermic and lead to increased randomness at the solid-liquid interface. This study has presented hexadecyltrimethylammonium chloride-modified Ogwuta source clay as a veritable adsorbent for organic pollutant decontamination both from laboratory and real-life sources.