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

ABSTRACT

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 Ca²⁺) 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.

KEYWORDS:

• Xanthan gum
• viscosity
• calcium polysulfide
• hexavalent chromium
• groundwater

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Natural Science Foundation of China (NSFC) [grant number 41572214], [grant number 41530636]; the Doctoral Fund of Colleges and Universities [grant number 20130061120085]; Project 2016037 supported by the Graduate Innovation Fund of Jilin University. The support of these agencies is gratefully acknowledged.