The uptake of europium by reduced graphene oxide-supported nanoscale zerovalent iron investigated by batch and modeling techniques

•The uptake of uranium by tea wastes was strongly dependent on pH and ionic strength.•The maximum adsorption capacities of tea wastes was 29.412 mg/g.•Adsorption data can be satisfactorily fitted by diffuse double layer model.

The reduced graphene oxide-supported nanoscale zerovalent iron (NZVI@rGO) composites were synthesized towards the uptake of europium (Eu(III)) in environmental cleanup. In this study, the effect of environmental factors on the uptake of Eu(III) from aqueous solutions on NZVI@rGO composites was investigated under ambient conditions by batch techniques. The uptake kinetics indicated that the uptake of Eu(III) on NZVI@rGO composites can be satisfactorily fitted by pseudo-second order kinetic model. The uptake of Eu(III) on NZVI@rGO composites was independent of ionic strength at pH > 5.0, indicating that inner-sphere surface complexation dominated the uptake of Eu(III) on NZVI@rGO composites. It is demonstrated that the maximum uptake capacities of NZVI@rGO composites for Eu(III) calculated from Langmuir models was 96.675 mg/g at pH 5.0 and T = 293 K. The thermodynamic parameters indicated that the uptake of Eu(III) on NZVI@rGO composites was an endothermic and spontaneous process. Based on surface complexation modeling, the diffuse layer model gave an excellent fits to the uptake of Eu(III) on NZVI@rGO composites with cation exchange complexes (X3Eu species) at pH < 4.5, mononuclear and monodentate complexes (SOEu2+ species) at pH 5.0–7.0, and mononuclear and bidentate complexes ((SO)2Eu(OH)2− species) at pH > 7.0, respectively. The results indicated that NZVI@rGO composites can be considered as a promising adsorbent for the uptake of trivalent radionuclides from wastewaters in environmental cleanup.