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 calciumdecorated 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(UO 2 ) 2 (PO 4 ) 2 & sdot; 6H 2 O 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.