Transport Characteristics of Green-Tea Nano-scale Zero Valent Iron as a Function of Soil Mineralogy

Abstract

The transport characteristics of iron nanoparticles prepared with a green tea, polyphenol-rich solution, were investigated for two granular media, pure silica sand and sand coated with aluminium hydroxide. The GT-nZVI injection caused a sharp decrease in the effluent pH and increase in the redox potential, which is attributed to the presence of free Fe3+ and polyphenols in the suspension, respectively. The breakthrough curves for total Fe in the outflow indicated that some aggregation and deposition of nanoparticles occurred in both types of sand. However, the majority of the iron mass was detected in the outflow (73 % in the uncoated and 62 % in the coated sand), indicating good transport of the nanoparticles. XRF results indicated that no iron was retained on the Al-coated sand particles, while 4% of the injected Fe was deposited on the pure silica particles. This behaviour is attributed to the electrostatic interactions between the positively charged nanoparticles and the positively charged Al- coatings vs. negatively charged silica in the pH range of the experiments. The “missing” iron in the Al- coated sand columns was observed as a reddish brown precipitate in the 0.7 µm filter that was placed in the outflow of the columns; thus, increased agglomeration was observed compared to the pure silica sand columns. This study shows that soil geochemistry can have a significant effect on the transport characteristics of nanoparticles in porous media.