Thermodynamics, kinetics and isothermal studies of chromium (VI) biosorption onto Detarium senegalense stem bark extract coated shale and the regeneration potentials

A low-cost adsorbent (Detarium senegalense stem bark extract coated shale (DSMS)) comprising pristine shale (PSH) coated with D. senegalense stem bark extract was prepared and utilized for the adsorption of Cr(VI). The DSMS and PSH were characterized by the SEM, XRD, FTIR, EDX, TGA, and BET. The batch adsorption experiment results showed that DSMS exhibited an excellent ability to adsorb chromium with a maximum removal occurring at pH 2, dosage of 0.05 g and 180 min contact time. The adsorption process was best described by the pseudo-second-order for DSMS and Elovich model for PSH which depicts chemisorption as the major mechanism responsible for the uptake of Cr(VI) onto the adsorbents. Langmuir model provided the best fit to the isotherm analysis on both materials. The maximum adsorption capacity of DSMS and PSH were 64.98 mg g(-1) and 29.97 mg g(-1) respectively. The thermodynamics revealed that the adsorption of Cr(VI) was feasible, endothermic and entropy driven. Furthermore, after five cycles of reuse, both DSMS and PSH demonstrated effective regeneration and reusability for Cr(VI) uptake. The structural properties, reusability, and high adsorption capabilities of DSMS indicate that they could be used as low-cost adsorbents in large-scale Cr(VI) wastewater treatment. Novelty statement Plant extracts are packed with a variety of polyphenolic compounds, such as aldehydes, alcohols, carboxylics, ethers, ketones, and phenols which contains several functionalities useful in the adsorption of toxic metals. Despite this, research on the use of plant extracts in the modification of adsorbent materials for enhanced adsorption is rare. This study reports for the first time the use of Detarium senegalense stem bark extract coated shale adsorbent for the efficient uptake of Cr(VI) ion.

Automated summary

DSMS shows excellent chromium adsorption capability, with the adsorption process mainly controlled by pseudo-second-order kinetics and Elovich model, while Langmuir model provides the best fit for adsorption isotherm analysis. The maximum adsorption capacities of DSMS and PSH are 64.98 mg/g and 29.97 mg/g respectively, with thermodynamics revealing that the adsorption of Cr(VI) is feasible, endothermic, and entropy driven. Additionally, after five cycles of reuse, both DSMS and PSH demonstrate effective regeneration and reusability.