Investigations Of Supported Bi- And Tri-Metallic Nzvi: Nitrate Reduction And Heavy Metal Removal

Abstract

<p>nZVI has been well documented as an effective reagent to remove contaminants, including organic and inorganic substances. However, the drawbacks of nZVI are agglomeration and bioaccumulation due to its magnetic property and nanosize. One of the solutions for these problems is putting nZVI on non-toxic support. Microsilicate600 (Misi), a silicate from a geothermal deposit in Rotorua, New Zealand, has been established to be useful in adsorbing nZVI. Doping nZVI with other metals to generate bimetallic and trimetallic materials is a method to increase its reactivity. These dopant metals function as catalysts in enhancing the electron transfer from Fe(0) core to contaminants. In this research project, the effect of doping metals on nZVI to generate bimetallic or trimetallic nZVI particles and effect of adsorbing these resulting particles on Misi were investigated. The reactivity of these materials towards the removal of different contaminants such as nitrate and toxic heavy metals was examined. Supported bimetallic nZVI@Misi were synthesised using different dopant metals, including Ni, Cu, Zn, and Pd. Supported trimetallic nZVI@Misi was synthesised by doping Pd and Cu on the surface of nZVI@Misi. Both supported bimetallic and trimetallic materials were prepared using different Misi preparations, contents of dopants, and synthetic methods. All these doped materials had higher reactivity than non-doped nZVI@Misi in removing nitrate. Misi that was calcined and FeOOH-coated is the most optimised-prepared support. Moreover, materials prepared via deposition method had higher reactivity in reducing nitrate than those prepared via co-reduction method. This is due to the distribution of dopant metals on nZVI, which was observed in TEM analysis. Of these materials, Ni-doped, Cu-doped, and Pd-Cu- doped nZVI@Misi were the most promising materials. They not only reduced nitrate effectively but also were not significantly affected by naturally occurring factors such as oxygen, chloride, sulfate, carbonate, and phosphate. During nitrate reduction, the generation of metal by-products was minimal. Interestingly, their reactivity in natural water was relatively similar to that in lab-prepared samples. The representative materials including supported Ni-doped, Cu-doped, and non-doped nZVI@Misi, were used for heavy metal removal. These materials effectively removed cadmium, lead, and chromium in both lab-prepared samples and natural water.</p>