Investigation of yield stress fluids for enhancing organic pollutant removal from contaminated soils through microfluidics

• Yield stress fluid was used as a selective blocking agent for soil remediation. • Polymer blocking significantly improved pollutant removal over waterflooding. • Microfluidic experiments allowed to optimize operation parameters. • The findings aligned with results from previous core-flooding experiments. • Fluid distribution within the transparent micromodels was captured. This study presents a method for remediating soils contaminated by organic pollutants through the selective blocking of pores. This technique is based on the use of yield stress fluids, specifically concentrated biopolymer solutions, which, due to their distinctive rheological properties, preferentially flow through high-conductance flow paths. Following the injection of yield stress fluid, its presence redirects subsequent water flow towards the pores that are typically unswept during standard waterflooding. Laboratory experiments at the pore scale were conducted to validate this method and confirm previous findings from core-flooding experiments. Aqueous xanthan gum solutions were used as microscopic blocking agents in well-characterized micromodels exhibiting microscopic heterogeneities in pore size. The impact of polymer concentration, soil wettability and operating conditions (injection pressure and flow rate) on the residual pollutant saturation following treatment was analyzed, enabling the optimization of the remediation strategy. The use of xanthan gum as a blocking agent led to a significant improvement in pollutant removal compared to conventional waterflooding, delivering consistently better results across all cases studied. The method demonstrated strong performance in water-wet medium, with the average polymer concentration yielding the highest efficiency in pollutant removal.