Silica fouling during groundwater reverse osmosis (RO) treatment can have a significant impact on filtration performance. To better understand this phenomenon, the equilibrium kinetics of amorphous colloidal silica were studied at conditions relevant to RO of silica-rich alkaline groundwater. The impact of particle size was investigated using synthetic monodisperse silica nanoparticles. Bench scale experiments were conducted by monitoring dissolved silica concentration of aqueous suspensions of colloids of 100 and 300 nm diameter and pH 8.5 to 9.5. The equilibrium data was determined from existing established rate law equations. This study concluded that surface energy has a major impact on silica dissolution rate constant, particularly for colloidal silica. Observations of Ostwald ripening in bidisperse silica dispersions further confirmed these results, which indicate that dissolution and redeposition is responsible for the problematic silica fouling behaviour during RO treatment. 2D modelling based on inferred equilibrium data allows visualization of scale layer growth in agreement with cross-sectional scanning electron micrographs of autopsied membranes.
Keywords: Dissolution; Ostwald ripening; Particle; Radius of curvature; Silica.
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