Enrichment of Uranium from Aqueous Solutions with Nanoscale Zero-valent Iron: Surface Chemistry and Application Prospect

In the processes of uranium mining and nuclear power utilization, water pollution caused by radioactive contaminants (e.g., uranium) is becoming increasingly serious. Nanoscale zero-valent iron (nZVI) and its composites can be used to enrich low-concentrated uranium ions from radioactive wastewater effectively. Published works have demonstrated that nZVI has great application potential to treat uranium-contanined radioactive wastewater. However, published researches on the performance and mechanisms for U(VI) immobilization by nZVI between different papers are not unanimous. Based on the research progress, this review summarizes the aqueous and solid reaction mechanisms (e.g., adsorption, reduction and precipitation) between nZVI and U(VI) ions, and specifically discusses the effects of solution factors (e.g., pH, U(VI) concentration, cations, anions and dissolved oxygen) on U(VI) immobilization. Before the field-scale application of nZVI to remedy uranium wastewater, deep researches should be conducted to investigate: (i) the phase transformation of nZVI in uranium wastewater and the synergistic effect of solution factors on the ability of nZVI to separate uranium; (ii) based on the characteristics of radioactive solution and wastewater treatment processes, the structure of nZVI particles needs to be optimized and their long-term stability and ecotoxicity needs to be evaluated; (iii) confirm the mathematical correlation between the performation of nZVI to immobilize uranium and wastewater components and operation parameters, and then extabilish the monitoring and regulating method for wastewater treatment technology.