Chemical for Treating Silica Before Filtration

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Filtering silica is not easy so I would like to know how I can treat it in a tank by adding some chemicals to make the silica settle so that lower concentrations reach the filter and do not clog it?

What chemicals can be used for treating silica in a tank, especially colloidal silica which is gelatinous and non-diffusable?

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12 Answers

  2. James Cusack is Right - Nature has a way of Purifying Water through the Natural Cycle - necessarily so since it sustains Living Organism. See note above - Add DISINFECTANT! wHAT BRAND OF DISINFECTANT WOULD THAT BE? BLEACH? - CONTACT sCHAUMBERGER SYSTEMS INSTITUTE - KARLSRUHE UNIVERSITY - 00 44 (0) 77 56 44 10 37 FOR  licensable systems for Water Table Integrity and Delivery - Schumacher Sys. Co. - Central Europe - Visegrad Source and functional effect - Healthcare & Smart Meters

  3. 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.

  6. There is no way to remove dilluted silica by coagulation and fltration. 

    Colloidal silica could be removed using appropriate coagulants, like PAC and polyelectrolyte. The type of polyelectrolyte should be determined by Jar-test, comparing different types of those (the best available is not absolutely assumed, so only comparable test could indicate the appropriate for each occasion).

  7. have you tried adding a polymer to your coagulant?  Also we have one site where we use an up-flow "clarifier of sorts".  It is basically filled with resin beads (about 6 feet thick of resin beads) and the resin beads are charged with a coagulation to make them positive as silica sand typically has a negative charge naturally and then after the water flow up through the positively charged resin beads it gently overflows into a multimedia filter comprised of anthracite, granular activated carbon on top of a gravel bed.  The gravel bed then of course sits on an under-drain system (we have had huge success with the Phoenix under-drain system) and then flows into our baffled clearwell where we inject a disinfectant (Cl) before we distribute (0.1 ppm free or 0.5 ppm total)

  9. You reminded me of my case where silica was out of specification and damage controll was altered in a costly way. This is caused by chemical dosing which is be to monitored closely within 2hrs intervals. 

    Check your mixed beds and see removal of anions and nanions. 

    Check your process as well and able to trace chemical concentration that might lightened you with cause of high silica.  

    Good luck

     

     

  12. Chemical treatment may not be possible but a thin-film "terrace" configuration, seeded with diatoms (a common organism that uses silica in its life cycle) might mimic the silicate deposits in some natural hot springs.  Mild heating (say a few degrees) prior to the terrace might help too.  I always look to how Mother Nature removes something before I resort to chemicals.  Good luck