Silica scale formation and effect of sodium and aluminium ions -29Si NMR study

Silica scale formation on reverse osmosis (RO) membrane surface is a significant problem for operation of high recovery RO desalination plant. In this study we report the effects of sodium ions derived from sodium chloride and aluminium ions derived from aluminium chloride on dissolved silica species obtained from commercial sodium silicate solutions. Five dissolved silica species have been positively identified in sodium silica solutions. 29 Si NMR spectroscopy has proven to be particular well suited to obtain in situ information on the connectivity of silicon atoms in the solution and the impact of sodium and aluminium ions on connectivity between monomeric silica acid groups. Such information extends the understanding of how polysilicate ion mixtures change under different chemical conditions. Implications for RO desalination and silica scale formation on the membrane surface were discussed

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

Silica fouling in high salinity waters in reverse osmosis desalination (sodium-silica system)

Silica fouling patterns in a sodium–silica system and the effect of pH on residual dissolved silica concentrations are reported. The unique chemical affinity between sodium and silica (SO4) prevented silica scale deposition on the membrane surface during reverse osmosis (RO) desalination. It was found that high concentrations of sodium in solutions depressed silica solubility to 81–84 mg L−1 for a maximum NaCl salinity of 60–65 g L−1. Using a range of membrane examination techniques, it was found that no silica scale formed on the RO membrane surfaces from NaCl solutions free from cations such as Ca, Al and Fe. This was considered to be the result of sodium ions acting as a barrier between polymeric silica and the membrane surface