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

Abstract

Silica fouling patterns in a sodium–silica system and the effect of pH on residual dissolved silica concentrations are reported.

Aqueous Silica and Silica Polymerisation

“…The solubility limit for silica in various waters vary, it is estimated, however, at approximately 120 mg/L at 25°C [5,[28][29][30]. Practical means an experimental silica solubility to verify the silica solubility in specific conditions -physical and chemical [1,2,5,31]. The solubility defined empirically is also a key for prevention of silica polymerisation and silica scale formation in RO desalination systems [5,[32][33][34][35][36][37][38][39][40][41][42][43].…”

“…In this chapter, the past and recent studies on various aqueous silica species and its impact are discussed. Behaviours of aqueous silica species were studies using reverse osmosis (RO) desalination systems and 29 Si NMR techniques and coagulation to gain better understanding of aqueous silica species polymerisation and practical implications of these techniques [1][2][3][4][5][6].…”

“…Practical silica solubility or the solubility defined empirically is a key for prevention of silica polymerisation in RO desalination systems [1][2][3][4][5]7]. Soluble or dissolved (reactive) silica contains different forms of silica or silica species ( Figure 1); monomer, dimers, trimmers and other polymers of silicic acid in different solutions [5,7,8,12].…”

“…Soluble or dissolved (reactive) silica contains different forms of silica or silica species ( Figure 1); monomer, dimers, trimmers and other polymers of silicic acid in different solutions [5,7,8,12]. These dissolved silica species (Q 0 < Q 1 < Q 2 < Q 3 aggregation) (Figure 1) can be presented in various ionisation states which depend on the pH of solutions and silica concentrations and presence of other anions and cations [1,2,5,8,[10][11][12][13][14][15][16]. Chemical reactions between these silica species and cations and anions often present in the Concentration Polarisation (CP) layer in super-saturation conditions during the reverse osmosis chemical separation of water molecules are commonly lead to irreversible silica scale formation on the membrane surface [17][18][19][20].…”

“…Chemical reactions between these silica species and cations and anions often present in the Concentration Polarisation (CP) layer in super-saturation conditions during the reverse osmosis chemical separation of water molecules are commonly lead to irreversible silica scale formation on the membrane surface [17][18][19][20]. Contrarily, not all highly super-saturated silica streams lead to scaling of membrane surfaces as it was shown in the past research [1,5,9].…”