Modification of zero-valent iron with xanthan gum and oxalic acid enhances Cr(VI) removal, reduces bacterial toxicity, and improves transport
摘要
The rapid aggregation and sedimentation, the high toxicity towards bacteria, and the passivation of surfaces hinder the application of zero-valent iron (ZVI) particles in groundwater remediation. To overcome the shortages, ZVI particles were modified using oxalic acid (an environmental-friendly low-molecular-weight organic acid) together with xanthan gum (a safe and cost-effective high-molecular-weight polymer). We found that ZVI modified with both oxalic acid and xanthan gum exhibited superior Cr(VI) removal performance than those modified solely with oxalic acid and unmodified ZVI. Due to the reduced Fe2+ release, the toxicity towards Escherichia coli by oxalic acid-xanthan gum modified ZVI was greatly inhibited. Via enhancing electrostatic repulsion through increasing the negative zeta potentials, modification of ZVI by oxalic acid and xanthan gum improved the dispersion of ZVI and reduced their sedimentation in suspension. Moreover, the mobile performance of ZVI in porous media was greatly improved by the modification with oxalic acid and xanthan gum due to the enhanced electrostatic repulsive interaction between ZVI and quartz sand. The observations held true in actual groundwater samples without and with heavy metal contamination. Clearly, the modification of ZVI by using oxalic acid and xanthan gum could be a feasible approach to enhance the practical application potential for the in-situ decontamination of groundwater.