Dear Lerato moroe, ...

Dear Lerato moroe,

Colloidal silica is non-ionic, and is typically found in surface waters. The removal of contaminants, such as silica, from water can be a challenging proposition. Silica (SiO2) exists in water in equilibrium with the bisilicate (HSiO3 -) ion as a very weak acid. In the ionic form, silica can be removed by strong base anion exchange resins operated in the hydroxide cycle. Since the two forms exist in equilibrium, silica can be almost completely removed from solution. When present as a single unit of silica, in equilibrium with bisilicate, the compound is termed reactive silica. Silica can also exist as a polymer, often referred to as colloidal silica. These long chains of individual silica units exhibit virtually no charged ionic character, and cannot be removed by the ionic process of ion exchange.

On exchange will  remove  this as long as the anion resin is the strong base type.  Silica in deionized water can easily be reduced to 20-50 ppb. Reverse osmosis will also remove silica  by 90-98%.

1. Lime softening is one of the most common methods for removing silica from water .
2. “An exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases, the term is used to denote the processes of purification, separation and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic ion exchangers.”
3. Electrocoagulation (EC) will successfully remove silica, heavy metals and other contaminants from aqueous solutions.
4. Ultra Filtration: The best way of ensuring maximum removal of non-reactive silica is to remove the bulk of it in the pretreatment plant and polish it with an ultra filtration (UF) system installed at the outlet of the mixed bed (MB) unit. UF is a pressure activated process employing a semi-permeable membrane with asymmetric structure.
5. This colloidal silica gets reduced to around 60% in the pretreatment system (in contact type of clarifier), however remaining 40% escapes through the normal Ion Exchange Plant.