Rheology modification of reduced graphene oxide based nanoscale zero valent iron (nZVI/rGO) using xanthan gum (XG): Stability and transport in saturated porous media

Abstract

Xanthan gum (XG) was utilized to rheologically modify the reduced graphene oxide based nanoscale zero valent iron (nZVI/rGO) in the study, to enhance the stabilization and transportation of the remediation materials in-situ. The results demonstrated that the saturated adsorption capacity of XG on nZVI/rGO (CAds XG/CnZVI/rGO) was 0.133, and when CFree XG/CnZVI/rGO was over 0.072, XG-nZVI/rGO was rheologically modified, manifesting high charged density (<-38.3 mV), small mean diameter (<1.204 μm) and good sedimentation stability. Adsorbed XG played a significant effect on electrostatic stability of XG-nZVI/rGO, while free XG had important role on hindering aggregation and sedimentation of XG-nZVI/rGO. The potential of shear thinning increased with XG-nZVI/rGO concentration, manifesting that the flow behavior index (n) increased from 0.479 to 0.866 when CXG-nZVI/rGO increased from 0.51 to 1.00 g/L. In addition, a higher XG-nZVI/rGO concentration contributed to a lower mobility. Besides, there existed a critical injection velocity 1.39 cm/min. Aggregation would be promoted and lead to transport inhibition when injection velocity (v) was below this critical value, but disagglomeration and transport would be enhanced by high hydrodynamic shear stress when v was above the critical value. These findings provided a new perspective of rheological modification of remediation material for in situ use.