Calcium-decorated biochar modified with phosphorus from wastewater to promote U(VI) removal: Adsorption behavior and mechanism

In this study, waste shrimp shell and phosphorous-containing wastewater were used to synthesize calcium-decorated biochar modified with phosphorus (Ca-BC-P) and utilized to remove uranium from aqueous solutions. The results from static adsorption experiment demonstrated that Ca-BC-P exhibited good U(VI) adsorption performance in acidic environments, with a maximum theoretical adsorption capacity of 1074.29 mg g−1. The adsorption behavior perfectly fit Langmuir isotherm and the pseudo-second-order kinetic models, which revealed the nature of monolayer chemical adsorption by Ca-BC-P. Thermodynamic analysis showed that this process was spontaneous and endothermic. Ca-BC-P also displayed excellent selectivity and could be reused for several times while keeping a high U(VI) removal efficiency. When treating simulated acidic uranium mine wastewater, the removal efficiency of uranium reached 99.9 % with Ca-BC-P. The U(VI) removal mechanism was attributed to the precipitation of Ca(UO2)2(PO4)2·6H2O and surface complexation, nHAP on the surface of Ca-BC-P played a pivotal role during the adsorption process. Therefore, Ca-BC-P could be prepared economically and showed great potential for efficiently remove uranium from mining wastewater.