Silica fouling in coal seam gas water reverse osmosis desalination

Silica fouling was studied in RO desalination of high salinity (30–60 g L⁻¹ as NaCl) coal seam gas (CSG) water for a range of silica concentrations, pH conditions and dissolved aluminium concentrations. Silica fouling patterns and the effect of various residual dissolved aluminium concentrations on silicate scale formation were recorded. The permeate flux decline data collected during each RO experiment showed that the deposition of the foulant layer on the membrane surface formed much faster in higher salinity and higher silica concentration water (∼50 mg L⁻¹) in the presence of elevated concentrations of dissolved aluminium (7.4–27.7 mg L⁻¹). It was found that the presence of elevated concentrations of dissolved aluminium reduces silica solubility to as low as 60–48 mg L⁻¹, leading to rapid aluminium-silicate deposition on the RO membrane surface. A mechanism of aluminium silica formation is discussed.