Citric acid-modified bentonite for enhanced dye removal in cutoff walls

This study enhanced bentonite with citric acid (CA) to improve its performance, then citric acid-modified bentonite (CAB) cutoff materials were prepared, and their ability to limit methyl orange (MO) migration in organically contaminated sites were examined. To obtain CAB, CA was added at 50 % of the original bentonite (RB) mass and stirred at 50 degrees C for 3 h. According to the mechanical properties, gas permeability test results, the optimal ratio of the material was 33 % content of CAB, 22 % content of RB, 45 % content of cement. After CA modification, the bentonite layer structure presented the characteristics of stacking, winding, irregular size and increased number of bulges. Molecular dynamics simulations predicted strong interactions between CA molecules and the primary component of bentonite, montmorillonite (001) surface. Under varying MO concentrations, the barrier wall's seepage velocity stabilized after 50 days, with no breakthrough observed within 180 days. At an initial MO concentration of 20 mg/L, the detection times for MO on the outer side of cutoff walls with thicknesses of 0.6, 1, 1.2, and 1.5 m were approximately 1.25 years, 3.58 years, 5 years, and 7.81 years, respectively. Visual MODFLOW simulations showed that the CAB-4 cutoff wall effectively blocked MO pollution, restricting azo pollutant diffusion for up to 3600 days, highlighting its long-term effectiveness against azo dye pollution.