A stable shear-thinning XG-WAS@n-FeS slurry for simultaneous removal of Cr(VI) and TBBPA from water

A stable XG-WAS@n-FeS slurry was constructed for simultaneous removal of Cr(VI) and TBBPA. • Xanthan gum enhanced slurry viscosity, stability, and oxidation resistance. • TBBPA was transformed through successive debromination reactions. • Coexisting contaminants influenced TBBPA removal through site competition. Nanoscale ferrous sulfide (n-FeS) is a promising reductant for water treatment, but rapid oxidation, particle aggregation, and poor transportability restrict its practical use. In this study, n-FeS was immobilized on alkali-modified waste activated sludge (WAS), and xanthan gum (XG) was added as a structural regulator. This approach produced a stable, shear-thinning XG-WAS@n-FeS slurry for the simultaneous removal of Cr(VI) and tetrabromobisphenol A (TBBPA). Carboxyl and hydroxyl groups contributed to the binding of FeS within the XG-WAS matrix, which helped establish a stable reactive interface. The slurry exhibited lower viscosity at higher shear rates, confirming its shear-thinning behavior. Increasing the XG concentration also improved sedimentation stability and oxidation resistance. Cr(VI) was completely removed at all tested concentrations. By contrast, TBBPA removal decreased from 81.93% to 53.19% as the Cr(VI) concentration increased from 20 to 80 mg L −1 . It also decreased from 92.49% to 58.99% when the TBBPA concentration increased from 5 to 20 μM. These concentration-dependent trends reflect the finite reducing capacity of the slurry and the preferential consumption of electrons by Cr(VI). Humic acid, Ca 2+ , Mg 2+ , and Cl − enhanced TBBPA removal to varying degrees, while Cr(VI) removal remained complete. XPS analysis showed that Cr(VI) was reduced and immobilized as Cr(III) species. HPLC-MS analysis revealed the stepwise debromination of TBBPA to BPA. These findings demonstrate that XG-WAS@n-FeS is a stable and effective slurry for treating water containing both Cr(VI) and TBBPA. Download: Download high-res image (190KB) Download: Download full-size image