Molecular\nMechanisms\nof Humic Acid in Inhibiting Silica\nScaling during Membrane Distillation

Membrane distillation (MD) efficiently\ndesalinizes and\ntreats high-salinity\nwater as well as addresses the challenges in handling concentrated\nbrines and wastewater. However, silica scaling impeded the effectiveness\nof MD for treating hypersaline water and wastewater. Herein, the effects\nof humic acid (HA) on silica scaling behavior during MD are systematically\ninvestigated. The interaction mechanism between typical components\nof HA and active silica was evaluated by molecular dynamics simulations.\nWe find that the addition of HA alleviated the significant decrease\nin water flux, with recoveries surpassing 60% and 80% at 10 and 20\nppm of HA, respectively. Quantum chemical calculations indicate that\nthe presence of HA greatly raised the free-energy barriers of silica\npolymerization compared to the system without HA (489.7 vs 45.1 kJ\nmol<sup>–1</sup>). Moreover, the interaction between HA molecules\nand silica significantly weakened the diffusion capacity of silica\nscale in water (diffusion coefficient from 1.04 × 10<sup>–5</sup> to 0.08 × 10<sup>–5</sup> cm<sup>2</sup> s<sup>–1</sup>), consequently decreasing the likelihood of contact between silica\nscale and the hydrophobic membrane. Finally, a neural network analysis\nmodel for the HA and silica interaction was developed to design effective\ninhibitors for silica polymerization. Overall, this study develops\nnanoscale modeling and simulations to understand how HA inhibits silica\nscaling in membrane processes, guiding the formation of new approaches\nto enhance MD performance.