Fabrication of novel valorized ecofriendly olive seed residue/ anthracite/chitosan composite for removal of Cr (VI): kinetics, isotherms and thermodynamics modeling

The present work verified the adsorption of hexavalent chromium (Cr (VI)) from synthetic aqueous solution using synthesized highly efficient low-cost adsorbent prepared from H2O2-modified olive seed residue solid waste/Anthracite/Chitosan (MOSR/An/CS) composite. Characteristics of the fabricated MOSR/An/CS composite were estimated by XRD, SEM, TGA, DSC, FT-IR, SBET and zeta potential tools. The entire chromium uptake study was conducted via batch adsorption mode under various operating conditions. Kinetics data were analyzed using five kinetic models, while empirical equilibrium data was fitted using three isotherms. The results clarified that Langmuir best described the adsorption of Cr (VI) ions with maximum monolayer coverage of 137.7 mg/g. Pseudo-first-order mode nicely fitted the kinetics adsorption. Further, Elovich, intraparticle diffusion, and Boyd models validate that more than one mechanism contributed to the adsorption of Cr (VI). The positive DH (110.11 kJ/mol), suggesting that the method of adsorption is endothermic and favorable at low temperatures, also indicated the chemisorption of Cr(VI). The positive value of DG varying from (14.53 to 8.1115 kJ/mol) at the temper- ature range measured confirms the possibility of the process as a non-spontaneous adsorption reaction. The Ea value was found to be 110.11 kJ mol-1 which mean that the adsorption of Cr(VI) onto MOSR/An/CS composite is chemisorption. The developed MOSR/ An/Cs composite exhibited decent reusability after five sequential adsorption cycles and showed higher adsorption affinity towards Cr (VI) ions. MOSR/An/ CS composite could also be effectively used as an effective eco-friendly and recyclable sorbent for the elimination of Cr (VI) from wastewater.