Reduced aggregation and sedimentation of zerovalent iron nanoparticles in the presence of guar gum

Injection of Nanoscale ZeroValent Iron (NZVI) is a promising technology for remediation of groundwater contamination. However, the efficiency of this process is significantly hindered by the rapid aggregation of the iron nanoparticles. The aim of this study is to enhance the colloidal stability of the nanoparticles by coating them with the “green” polymer guar gum. The study evaluated the properties of guar gum and its influence on the surface properties, particle size, aggregation, and sedimentation of the iron nanoparticles. In this study, RNIP (Reactive Nanoscale Iron Particles) from Toda Kogyo Corp. were dispersed at a concentration of 154 mg/L in 0.5 g/L guar gum solution, and their aggregation and sedimentation behavior was compared to the ones of bare RNIP and RNIP modified with sodium polyaspartate. High performance size exclusion chromatography (HPSEC), charge titration, and viscosity assessment showed that guar gum is a nearly neutral high molecular weight polymer, which may be suitable for steric stabilization of the iron nanoparticles. Electrophoretic mobility measurements demonstrated the ability of guar gum to adsorb on the nanoparticles, forming a slightly negatively charged layer. Dynamic light scattering (DLS) experiments were conducted to estimate the particle sizes of the different suspensions and to determine the trend of aggregation at different ionic strengths. Guar gum showed the ability to reduce the hydrodynamic radius from 500 nm for bare particles to less than 200 nm and to prevent aggregation even at very high salt concentrations of 0.5 M NaCl and 3 mM CaCl2. Finally, sedimentation of the different dispersions was evaluated by light absorbance measurements, confirming the improved stability of the dispersions in the presence of guar gum. Although guar gum proved to be a suitable polymer to stabilize zerovalent iron nanoparticles, further studies are needed to assess the effects on nanoparticle transport in saturated porous media