Investigation of the compatibility of xanthan gum (XG) and calcium polysulfide and the rheological properties of XG solutions.

Shear thinning xanthan gum (XG) solutions as the delivery media can solve the bypassing problem induced by heterogeneity, especially with low permeable zones in aquifers. Experiments were conducted to investigate the compatibility of XG and calcium polysulfide (CPS) aiming at chromium contamination in groundwater. Rheological properties of XG solutions DURING delivery were studied. Results indicated that (1) XG slowed down the reduction of hexavalent chromium by CPS, and the reaction fitted well with the second-order kinetics. (2) CPS dosage had a significant effect on the removal of chromium (VI), but it was less pronounced as the CPS concentration over 160 mg/L. (3) Cationic ions (e.g. Na and Ca) decreased the solution viscosity, while anionic ions maintained the viscosity and shear thinning properties of XG solutions. CPS decreased the viscosity of XG solutions. (4) The solution viscosity increased linearly with the XG concentration (less than 1500 mg/L) at a low shear rate. The presence of aquifer media resulted in a drastic decrease in solution viscosity due to physical molecular breakdown and biodegradation. (5) The rheological properties of XG solutions were described by a power law model. The presented empirical relations may also provide a theoretical basis for field applications.