Novel geopolymer composite based on oil shale and chitosan for enhanced uranium (VI) adsorption: Experimental and theoretical approaches

•An environmentally friendly and inexpensive chitosan + geopolymers-oil shale composite was proposed.•Characterized by different methods have shown an interaction between chitosan and geopolymers.•The composite demonstrated good performance for the management of U(VI) wastewater.•A theoretical study was studied to know the adsorption mechanism.