Nanoscale zero-valent iron (nZVI) synthesis in a Mg-aminoclay solution exhibits increased stability and reactivity for reductive decontamination

Abstract

Nanoscale zero-valent iron (nZVI) has often been explored as a reductant for detoxification of pollutants in environmental clean-ups. Despite the large surface area and superior reactivity of nZVI, its limited stability is a major obstacle in applying nZVI for in situ subsurface remediation, e.g. for chlorinated solvents hotspots. In this study, water-solubilized magnesium-aminoclay (MgAC) was applied for the first time as a stabilizing agent in the synthesis of nZVI. With increased doses of Mg-aminoclay applied in the synthesis mixture, nZVI particle growth was inhibited and thin sheathed grape-like nZVI particles with higher crystallinity were produced. Stability of nZVI particles were evaluated using a sedimentation test and a dynamic light scattering technique. The characteristic time increased from 6.71 to 83.8 min, and particle (aggregate diameter) size decreased from 5132 to 186 nm with increasing amounts of applied MgAC. The higher stability of MgAC coated nZVI could be explained from the higher zeta potential, which indicates that the stabilization mechanism is increased electrostatic repulsion from the positively charged MgAC coating. The optimal weight ratio between MgAC and iron was found to be 7.5:1. The MgAC coated nZVI exhibited higher reactivity for nitrate reduction with the observed first order rate constants increasing from 1.17 to 42.0h(-1), and Fe(0)-normalized rate constants from 0.124 to 43.8 h(-1) mg-Fe(0)(-1). Consequently, the MgAC coated nZVI showed increased feasibility, compared to uncoated nZVI, for application in remediation of subsurface contaminations; where high stability and mobility as well as high reactivity for degradation of contaminants is desired.