Viscosity modification enhanced the migration and distribution of colloidal Mg(OH)2 in aquifers contaminated by heavy metals

Mg(OH)2 is extensively considered as an potential material for groundwater remediation because its injection could provide a long-term pH buffering system. In this study, colloidal Mg(OH)2 was regarded as an alternative reagent for the in-situ remediation of heavy metal polluted groundwater. However, experiments demonstrated that the transport performance of colloidal Mg(OH)2 in groundwater was depressed by the contamination of heavy metals and its stabilization performance for heavy metals was deteriorated. To solve these difficulties, the transport properties of colloidal Mg(OH)2 was enhanced by viscosity modification by adding xanthan gum (XG). Column tests were conducted to investigate the transport performance of colloidal Mg(OH)2 with and without viscosity modification, and to evaluate its stabilization effect for Pb and Cd polluted aquifer. Experimental results indicate that although the injection pressure increased during the migration of colloidal Mg(OH)2, the increased viscosity effectively could decrease the intensity of Brownian motion of Mg(OH)2 particles and reduce the collision efficiency between colloidal particles and aquifer media. Thus, deposition of Mg(OH)2 particles on aquifer media significantly reduced after viscosity modification, and its migration performance in groundwater was effectively enhanced. In contrast, the distribution of colloidal Mg(OH)2 was more uniform after viscosity modification, and immobilization of heavy metals in contaminated aquifer was noticeably improved, furthermore the exchangeable fraction of Pb and Cd is significantly reduced. Keywords: Colloidal Mg(OH)2, Xanthan gum, Sustained-release materials, Groundwater pollution, in situ remediation