Synergistic mechanism of adsorption-diffusion at quartz-water interface for the dewatering of waste slurry using APAM flocculant: Insights from molecular dynamics simulation

Abstract

In this study, molecular dynamics simulations were performed to investigate the flocculation and soil-water separation mechanism of anionic polyacrylamide (APAM) flocculant. Results show that the adsorption behavior of APAM on quartz particles in the quartz-water interface is the basis for flocculation occurrence, and the adsorption ability improves with the increases in APAM dosage. APAM molecules compete with the water molecular layer and are directly adsorbed on the surface of quartz through hydrogen bonds, while most APAM structures are indirectly adsorbed on the quartz surface through van der Walls forces. The diffusion behavior is the key to determining effective flocculation. The apparent chain self-entanglement of APAM molecules hinders the diffusion of APAM on the water surface as the APAM dosage increases, corresponding to a decrease in the diffusion coefficient. This phenomenon results in APAM molecules failing to collide with enough quartz particles on the water surface. The bridging action generated by the balance between adsorption-diffusion behavior is the key to the flocculation and dewatering effect. Additionally, flocculation treatment tests of waste slurry using APAM with different dosages were conducted, and the size of the flocs at different APAM concentrations was examined by SEM, further confirming the existence of the optimal amount of APAM.