Mutual effect of U(VI) and phosphate on the reactivity of nanoscale zero-valent iron (nZVI) for their co-removal

Nanoscale zero-valent iron (nZVI) has been widely considered as a promising permeable barrier material for remediating U(VI)-contaminated waters. Little information is available regarding co-removal of U(VI) and oxyanion contaminants by nZVI, yet in the majority of areas polluted by U(VI), co-existence of phosphate is found to be common especially in eutrophic water. Herein, the mutual influence of U(VI) and phosphate on the effectiveness of nZVI in co-removing U(VI) and phosphate is investigated by macroscopic and microscopic approach. The results indicate that nZVI can effectively co-remove U(VI) and phosphate and the processes intensively depend on the solution pH and the additional order due to the formation of nZVI-U(VI)-phosphate complexes and will change the morphology of nZVI through the formation of a new phase. Furthermore, the maximum removal capacity of nZVI increases by 21.63% at pH 6.0 for U(VI) ions and by 34.28% at pH 7.0 for phosphate when both U(VI) and phosphate are present simultaneously. In short, the co-presence of U(VI) and phosphate has a great impact on the reactivity and morphology of nZVI. The findings will be beneficial to broaden the potential feasibility of nZVI in simultaneous radionuclide and phosphate pollution cleanup. (C) 2019 Elsevier B.V. All rights reserved.