Controllable shell corrosion of coated nanoscale zero valent iron induces long-term potentiation of its reactivity for uranium removal

Coating a soluble shell material on the surface of nanoscale zero-valent iron (nZVI) particles to eliminate the problems of agglomeration and rapid aqueous corrosion of Fe(0) in groundwater is an effective strategy for long-term maintaining uranium removal efficiency. However, the precise role of controllable shell corrosion on uranium removal mechanism remains unclear. In this study, a homogeneously dispersed Mg(OH)2 shell coated on nZVI ([email protected](OH)2) prepared by one-step surface precipitation was exploited to investigate the relationship between shell corrosion and uranium removal mechanism. The results confirm that nZVI with uniform coating shell (Mg(OH)2/Fe(0) = 1:2, mass ratio) was synthesized by simply mixing magnesium hydroxide with Fe2+ and NaBH4 solution under the flowing stream of N2 (25 ± 1 °C). The longevity and reactivity release rate of coated nZVI depended upon the initial pH value of the aqueous solution. At initial pH = 5, coated nZVI showed a high reduction activity, its ORP measured was 1.3 times that measured at initial pH = 3, and the duration could be prolonged to more than 4.5 times. The exposed Fe(0) core rapidly elimination U(VI) by synergistic attributed to the adsorptive (44.1%) and reductive (55.9%) processes after the passivation shell was eroded by reaction with H+. The results provide an efficient approach to improve the long-distance transport capacity and controllable release of nZVI, which can maintain its long-term reactivity in groundwater remediation.