Agar agar stabilized milled zerovalent iron particles for in situ groundwater remediation

The use of nanoscale zerovalent iron (nZVI) particles as a nontoxic material for effective in situ degradation of chlorinated aliphatic hydrocarbons (CAHs) into less harmless products has been inhibited by many factors, including the high production costs. For that reason, submicro-scale milled zerovalent iron particles were recently developed (milled ZVI, UVR-FIA, Freiberg, Germany) by grinding macroscopic raw materials of elementary iron as a cheaper alternative to products produced by solid-state reduction. However, currently milled ZVI particles tend to aggregate and sediment due to the rather large particle size (d90 = 16.9 µm). To prevent aggregation and consequently sedimentation of milled ZVI suspension (1 g L-1 of particle concentration) and consequently improve the mobility after in situ application, the use of a stabilizer is necessary. In this study, milled ZVI particles were stabilized by environmentally friendly polymer agar agar (>0.5 g L-1), which had a positive impact on the milled ZVI stability significantly decreasing sedimentation rate by increasing the suspension viscosity. Column transport experiments were performed for bare and agar agar stabilized milled ZVI particles in commercially available fine grained quartz sand (DORSILIT® Nr.8, Gebrüder Dorfner GmbH Co, Hirschau, Germany) under field relevant injection conditions of 100 m d-1. The maximal travel distance (LT) of 12 m calculated for agar agar (1 g L-1) stabilized milled ZVI suspension compared to the non-stabilized suspension (LT < 10 cm) revealed that agar agar as stabilizer significantly improve particle mobility. Finally, lab-scale batch degradation experiments were performed to determine the impact of agar agar on the reactivity of milled ZVI and investigate the apparent corrosion rate of particles by quantifying the hydrogen gas generated by anaerobic corrosion of milled ZVI. The results indicate that despite agar agar had positive impact on the milled ZVI stability and mobility, adverse impact on the reactivity towards trichloroethene was observed compared to the non-stabilized material. On the other hand, this study shows that the apparent corrosion rate of milled ZVI particles is not impacted by the presence of agar agar and longevity of particles action is significantly prolonged compared to the nZVI particles.