Dr. Hua Zhong
State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, China
Speech Title: Effect of xanthan gum on stability of magnetite nanoparticles and their transport in quartz sand

Abstract: Magnetite nanoparticles (MNPs) are a promising material for in-situ remediation of contaminated groundwater. However, its application was inhibited by low mobility of MNPs in saturated porous media due to aggregation and sedimentation of the MNPs. In this study, sedimentation test was firstly carried out to investigate the feasibility of surfactants (SDBS, Triton X-100) and polymers (i.e., polyvinylpyrrolidone (PVP), polystyrene sulfonate (PSS), carboxymethyl cellulose (CMC), sodium alginate (SA), xanthan gum (XG)) used as an additive for stabilization of MNPs. Next, the column test was conducted to study transport behaviour of the MNPs in the presence of polymers and in the five different pore water velocity conditions (0.53 cm/min, 0.66 cm/min, 0.80 cm/min, 0.93 cm/min, and 1.06 cm/min). It has been observed that surfactants have no ability of stabilizing MNPs, even with a suspension of surfactant and MNPs with a mass ratio of 100:1 (surfactant 2g/L and 20 mg/L MNPs). In contrast, the polymers were more effective to improve the stability of MNPs. The XG was the most effective among the polymers tested (XG > SA > CMC > PVP > PSS). 2 g/L was the critical concentration of XG, at which no sedimentation of MNPs with a concentration as high as 20 g/L was observed for more than 24 h. The results of the column study showed that XG greatly enhanced the mobility of MNPs in natural silica sand. More than 50% of MNPs passed through the sand column for all of the pore water velocities tested (0.53 cm/min to 1.06 cm/min) when an MNP input concentration was 4 g/L and the XG concentration was 2 g/L. This is in contrast to the observation that no breakthrough of MNPs took place in the absence of XG. MNPs transport in quartz sand in the presence of xanthan gum decreased first and then increased with an increasing pore-water velocity from 0.53 cm/min to 1.06 cm/min. The tests showed that XG is an excellent agent to facilitate MNPs transport and has a high potential for use in remediation applications.