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topic 12873

Silica removal from water

A discussion started in 2002 but continuing through 2018


Q. Dear Readers,

Can anybody tell me about silica removal process? I know two processes, soda lime and activated alumina ... but how much it is feasible, I don't know.

Please let me know how we can remove the silica from the water and what is the outlet limit of silica as per WHO.


Brijesh Goel
- Mumbai, Maharashtra, India

Readers: Were you looking for Removal of Silica Stains instead? Then please see letter 12873a


A. Silica can be removed from raw water easily with standard demineralization techniques. Normally silica is present in a weak acidic form. Ion 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%. Both of these techniques are non-specific for silica, meaning they also remove all other ionic components along with the silica. Normally these methods work well for most well or surface waters where silica is below 15-20 ppm. In some cases for very large flow rates you can remove silica with lime softening techniques. In lime softening the silica is co-precipitated along with magnesium present in the water (or added if necessary). High temperature softening greatly improves silica removal. For high silica waters as seen in Mexico, Hawaii or other sandy areas where levels are 50-60 ppm or higher, the ion exchange and RO options are more troublesome because you may exceed solubility limits for one, and also you are more likely to have significant levels or non-ionic colloidal silica. This will not ion exchange and may foul an RO membrane. Typically this must be removed with ultrafiltration.

Dan Cooper
- Roscoe, Illinois

thumbs up sign Nice answer. While I did not ask the question I learned a great deal from your post. Thank you.

John Holroyd
- Elkhorn, Wisconsin

thumbs up sign I'll have to agree. There were a couple of gems in that monograph.

John Tuohy
- Ireland


Q. I'm doing my research in desalination esp. removal of silica from concentrated brines using lime. As per Dan Cooper, Mg helps in removal of silica; but in my research it proved wrong. Where the SiO2 conc. was 150-200 it proved negative. Can anyone explain why did this happen and is there anything where alkalinity comes into picture?

Bhaskar [last name deleted for privacy by Editor]
desalination - El Paso, Texas


A. The optimum pH for silica adsorption onto Mg(OH)2 is around 10-11

Christian Tasser
- Irvine, California


Q. Hi

I have come across the same problem to remove Silica (approximately 30 mg/L) in bore water to drinking water standard. The main concern is the use of membrane filters after chemical oxidation using Chlorine gas and pH and alkalinity adjustment using Calcite Filters. The water temperature is around 20 to 25 degree. The water has low hardness, less than 10 mg/L, low pH 4 to 5, and relatively high soluble iron, hydrogen sulfide and aluminium.

Can anyone suggest the most feasible and practical solution in my case? As in silica? Aluminium? Does calcite filters help in reducing aluminium concentrations?

By the way, I chose Chlorine gas out of potassium permanganate, ozone, and chlorine dioxide. Is there any comments or special considerations from anyone?



Max Y [last name deleted for privacy by Editor]
Process Engineer - Australia


A. Water Treatment of Silica can be quite interesting as many people generalize for text book simplicity perhaps.

Oxidised silicon atoms can and do exist in many different chemical and mineral forms, hence a process that works at one location may not be successful in another.

Silicate and silica particles of otherwise identical mineral forms can have different surface charge, according to their geo-history or immediate pre treatment. This characteristic of silicon is beneficial to the silicon chip! but adds complexity for water treatment design.

Understanding the chemical and or mineralogy involving silicon is a fundamental first step in selecting and designing the most appropriate solid-liquid separation technology for a silicate removal process, for any successful drinking water treatment.

Stewart Shipard
- Perth, Western Australia

To minimize searching and offer multiple viewpoints, we've combined multiple threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.


Q. I am experiencing problem with Silica rejection by RO membranes. RO projection software shows silica rejection at level of 99.3 %, but reality is different-close to 90 %. Does anybody have proven numbers(reality) on silica rejection by membranes like CPA3? I do appreciate any information

Jerry Simik
- Guelph, Ontario, Canada


A. The problem may be the pH that you are operating at, particularly if you are using an acid feed to prevent hardness fouling. At lower than neutral pH values, there may be a significant amount of non-ionic, soluble silica that can pass through the membranes. Operation at a higher pH increases the degree of ionization of the silica and its rejection, but increases the vulnerability of your system to hardness fouling.

Lyle Kirman
consultant - Cleveland, Ohio

August 19, 2009

A. Check silica in reject water. If silica concentration is near or more than saturation of silica, then there are only two ways.

- lahore pakistan

December 27, 2008

Q. Silica value is coming very high in dm plant. in filter water silica value comes 7-10 ppm .



January 15, 2009

thumbs up signThanks for the responses. I deal with water used in our boiler and domestic use.The silica levels are very high about 100 mg/l after being passed through a softening plant. Please keep on posting on this topic.

Eddah bonareri
- Kenya, Nairobi

January 15, 2009

A. Because of the range of particle size, silica removal has no "one size fits all" solution. Ultrafiltration (UF) offers complete removal down to .015 microns. Particles smaller than .015 microns can become lodged inside the membrane pores, occluding them and causing an earlier than expected loss of production.

Neil Oliver
- Elburn, Illinois

April 23, 2009

Q. Hi,
I'm designing a plant to bottle further treated municipal water but I'm not sure with the silica levels (10 mg/L) whether they are too high or ok. What are the WHO limits? what are the effects of having high levels of silica in bottled water?

Phylis Chauke
- Bulawayo, Zimbabwe

May 13, 2009

Q. Hi

Does silica contribute to water conductivity. Some sites say it does and some say it doesn't!
Kind Regards

Naeema Essop
- Vanderbijlpark, Gauteng, South Africa

October 6, 2009

Q. Dear Brijesh, I like your question, but let me ask something: if we have DI water but silica is 20 ppm, we want it 0.1 ppm, will RO work for it?


Abdul khurram
water care - Lahore Pakistan

December 14, 2009

A. Dear All...for all of you who work in Industries. There are mainly 2 forms of Silica the first one is Reactive Silica and the second one is Colloidal Silica.
Reactive silica is what it is called when silica and bisilicate are in equilibrium with each other.
Colloidal silica is basically a polymer with virtually no charge so Ion Exchange methods cannot remove the same.
The only way of removing these is by Ultrafiltration or Reverse Osmosis which can reduce both of the above >98%. The initial investment will be high but it will help those dealing in HP Boilers. Any questions please feel free to ask me about this.

Sunderam Nagar
- India

January 5, 2010

Q. I have a DI system which forks into different environmental chambers used for testing Glass PV Panels. I have noticed a lot of Silica build up on the samples in the chambers lately. How can I go about removing the Silica?

Can I install a polisher to remove excess Silica at the user (chamber) end of the system?

Tyler Barbaree
quality technician - tucson, Arizona

September 27, 2010

Q. Our spring water contains 68 ppm of Silica. Due to heavy rains the water tables are high and we encountered algae contamination. We add Chlorine Dioxide at the source killing most of yeast & moulds. total counts are low. One big problem is, we notice that the Chlorine Dioxide (0.4ppm) raises the pH to 7.6 and also reacts with silica forming a white precipitate (floc like) and I think this causes inefficiency in killing the algaes. I also use Ozone at bottling time. Still getting large growths of algae after about 20 days. Can anybody help?
A. Cid

albert cid
water provider - QLD, Australia

December 23, 2010

A. We developed a product to remove silica from geothermal brine. In Arizona this presents a problem of course; the cycling up of silica often limits the capacity to produce power. The product works by using a microbe that accepts silica through the cell wall, giving enough surface area and charge to physically remove the silica. Info was published in one of the Power Generation publications.

Scott Frazier
- Ozark, Missouri USA

Ed. note: Please get back to us with what magazine and what issue if you remember. Thanks.

August 31, 2012

Q. I would like to know if there is a method of removing silica from boiler blowdown having a concentration of 150-200 ppm to below 5 ppm?

Scott, you mentioned microbes that remove silica. Can you post some technical information about this technology so that readers can view it.

Amin Manji
Consulting Company - Van, BC, Canada

December 9, 2011

A. Try electrocoagulation. We use it to remove a whole variety of suspended solids, emulsified oils, bugs, etc. Has been quite effective with silica. More cost effective than chemical flocculation. Capex is much higher than chemicals, but you make it up in opex.

Chuck Hanebuth
- Houston, Texas, USA

December 21, 2011

Q. I have a well, used for our house, that has high level's of silica (103 mg/L). What are my best AND least costly options? RO is an option but to centrally treat the water will cost over $15,000.

Any other good ideas for dealing with this?

Jeff O
- St. Helena, California, USA

December 28, 2011

Q. I am a student of one of the universities in A.P. I am trying to learn more information on removal of silicon from water.

- Andra Pradesh, India

Hi Vijayalakshmi,

So that we can keep moving forward, and not go around in circles, please ask for any desired clarifications about the many technologies already discussed, or post a more specific question. Thanks!


Ted Mooney, amadeya42.com Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

February 20, 2012

Q. What is the most efficient process to remove 180 ppm of silica (reactive or colloidal) to level of 5 ppm - is this by IE/RO/SBA or by EDI? Request your feedback..
Thank you. I appreciate it.


coimbatore vedavyasan
- Dubai, UAE

September 10, 2012

Q. Dear all

Kindly inform us to remove silica in high alkalinity water. Silica in bore well is 110 ppm, T. Alkalinity is 415 ppm, Total hardness is 150 ppm. We are consuming high ppm of lime and dolomite in the range of 950 ppm each to reduce the level up to 50 - 60 ppm. We are using FeCl3 as coagulant of 25 ppm and Poly electrolyte of 1 ppm.

We want to decrease the chemical consumption. PAC (Poly aluminium chloride) is not approved. Please reply at the earliest.


October 10, 2012

Q. Hi folks,
I am a crude stabilization unit process engineer.
We use condensate as make-up water to electrical desalting vessel.
In order to get the salts out of the crude oil, it first has to be mixed with demineralized water (condensate in our case).
The condensate is pure water having almost zero conductivity. Lately we had a little silica (3.2 mg/L) show up in that make up stream. The reason for that is our carbon beds used for condensate filtering. So right now we are not able to eliminate the cause for such silica contamination but we need to figure out how bad can be the effect of silica-containing condensate to the desalting process as well as to downstream equipment: oil heat exchangers and reboilers.
I know that colloidal silica may strengthen oil-in-water emulsion, but what about dissolved silica?
Anybody know whether silica stays in water phase or it can be partially transferred to the oil phase during the mixing in desalter vessel? Oil coming out of desalter is almost free of water; however I would expect scaling formation in heaters/reboilers if there is still some retained in "dry" oil.

Rustam Kudaibergenov
oil - Tengiz, Kazakhstan

February 18, 2013

Q. Dear all... we need information on what technology to reduce silica content (silica content 490 ppm, TDS 900 mg/l ), because we need silica content not more than 10 ppm and electrical conductivity < 10 us/cm. This water is for for industrial battery charging.

Thanks for many information.

Subur W
engineering - Indonesia

July 4, 2014

Q. Silica present in water, tests say Silica (mg/L) 5.72

Is it okay OR does it needs to be treated?
If treatment required, please suggest treatment. Thanks.

Musa Shafi
- Lahore, Pakistan

July 2014

A. Hi Musa. I don't quickly see any WHO limits for silica, but how much more study would have to be done depends on your situation. If you are responsible for a public water supply, you'll need to learn the standards inside out.

Folks: Please detail your situation, and do your best to frame your questions in terms of the many very insightful answers already offered! When questions are presented as requests for clarification of suggestions that have been offered, they usually elicit enthusiastic response; but if earlier answers are just blown off, and questions are posed as "start over for me because I can't be bothered putting in any work to try to appreciate what you wrote", the thread often dies).


Ted Mooney, amadeya42.com
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

July 9, 2014

A. If this is tap water, then 5 mg/L of silica is a relatively low number. Values of 25-50 mg/L are not uncommon.

However, if this is DI water, then further treatment is needed for most uses.

Lyle Kirman
- Cleveland, Ohio USA

Lab says 10 ppm of silica in DM water -- are they wrong?

August 15, 2014 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear sir,
I am generating dm water of pH 6.4, conductivity 1.2 µs/cm.
Our lab in-charge says 10 ppm silica in DM water ... is that a right or wrong report, please tell me.
If silica in dm water, why?
All parameter is offline.

patel jayeshkumar
- gujarat, India

August 2014

A. Hi Jayeshkumar. We appended your inquiry to a long and detailed thread which offers some great explanation of silica in DM water. Still, if you don't trust your lab analysis, you'll have to have some other person or service re-do it -- you can't possibly rely on an internet vote to override an actual chemical analysis :-)

Best of luck.


Ted Mooney, amadeya42.com
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

September 1, 2014

A. It is very possible that you have 10 mg/L of silica in your DI water. Silica is the first thing to leak off of an anion exchange resin and at pH values < 7 it is not ionized so it adds almost nothing to conductivity.

If you want to have less silica in your DI water, there are several possible ways to accomplish this. You could add a tank of mixed bed resin after your DI system, or you will need to regenerate the anion resin before the water reaches a conductivity set point. Regenerating the anion resin based upon a volume throughput rather than conductivity can accomplish this if your feed water analysis does not vary very much.

Lyle Kirman
consultant - Cleveland, Ohio

August 28, 2014

Q. Sir,
I am facing a problem in SBA supply by THERMAX PLANT. SiO2 of SBA is continuously increasing after regeneration system taken in line. What is the reason of SiO2 increasing? Maybe SBA EXHAUST but a doubt due to not possible that fresh SBA taken in. Chances of increasing SiO2 in SBA EXHAUST of SAC? Please give technical process if it's reason of SAC EXHAUST.


Dilip Singh Gohil
- Bharuch, Gujarat India

April 14, 2015

Q. Sir,

in bore well water analysis (in ppm):
Mg : 910
Ca : 910
Cl : 5424
SiO2 : 85
Na : 1212
SO4 : 344
TDS : 9407

Designing RO of 12 M3/ Hr. My concern is whether there is any extra treatment required for SiO2 removal?

Himanshu Gohel
- Ahmedabad Gujarat India

April 15, 2015

A. Due to the high silica concentration, the RO recovery is very limited. There are anti-scalents that are reasonably effective for silica, but even with these, the silica in the RO concentrate will probably be limited to about 200 ppm. This is only about 60% recovery.

Lyle Kirman
consultant - Cleveland, Ohio

April 21, 2015

A. The best way to improve your RO recovery, is to go for Lime soda softening and bring down silica level to about 10-12 ppm. This will soften the water and simultaneously improve the system recovery.

Jayant Kumar Joshi
Consultant - New Delhi, India

July 7, 2015

Q. What could be the possible method to remove 50-70 ppb of colloidal silica to NIL ?

Piyush Garg
- Gurgaon, Haryana, India

September 23, 2015

A. Go with UF

Vaibhav M. K.
- Mumbai, India

October 18, 2015

A. At a concentration of < 1 mg/L, I doubt that it is colloidal silica. More likely it is reactive, soluble silica.

Your best approach depends upon what else is in the water and what quality you want the treated water to be. RO will probably remove >98% of this silica, but some type of adsorption might be a better choice.

Lyle Kirman
consultant - Cleveland, Ohio

October 15, 2015

Q. We are facing problem of silica carry-over with steam and silica deposit in super heater tube inside & on turbine rotor in our borewell water silica content increase up to 28 ppm. We process borewell water as under softener-RO-DM Plant-Mix Bed unit but at mixed bed outlet silica content found 0.5 ppm.
At RO permiate silica is 5 ppm,
What should we do; please suggest.

gyanendra shrivastava
fertilizers - bilaspur,chattisgarh,india

October 18, 2015

Q. What is the tolerable levels of Silica in the rejects of RO? In other words, what is the solubility limits of Silica in RO rejects? Or What is the concentration limit of Silica in Rejects which will foul the RO membranes?

V Nirmalgandhi
Thirumalai Chemicals Ltd - Ranipet, Tamilnadu, India

October 27, 2015

A. A silica concentration of up to about 120 mg/L can be tolerated in most RO concentrates.

5 mg/L of silica in the permeate with only 28 mg/L in the feed is not very good rejection. You may need a tighter membrane. <1 mg/L should be possible.

Lyle Kirman
consultant - Cleveland, Ohio

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Colloidal silica in boiler water

October 10, 2016

Q. Sir...I am facing a big problem with new High Pressure Boiler cleaning. Silica is reaching out of control in super heated steam having value 3.2 to 4.0 PPM, but boiler feed water parameter is TDS-2, pH-8.6, P.Alkalinity-01, M.Alkalinity-02, Total hardness-00 and SILICA IS 00 PPM. Why does steam carry silica and where does it come from if FEED WATER SILICA is zero?

chirag singh
- ambala, haryana,india

March 16, 2017

A. Hi Chirag,

you gave a clue to the answer in your heading.."Colloidal" silica.
Firstly, silica adds very little to conductivity of water.. Many times I have seen water with TDS of <5bppm (measured with conductivity meter) have a Silica level of >>10ppm (measured with spectrophotometer, molybdo-vanadate method).

Colloidal silica will show up very little even in the chemical test, as it is a polymer and quite unreactive. Once it goes into your boiler, it is hydrolysed under high temperature and high pH of the boiler water and appears as if by magic, as suddenly it is monomeric and able to react with the test method.

As for silica's presence in the steam, above about 27BARg, silica is able to evaporate and travel as a gas/vapour with the steam... boiler water carryover is not necessary for this 'silica carryover' to occur, as the silica has become volatile at this temperature..
The silica will condense at the first big pressure drop, which is invariably, across your turbine, leaving silica deposits and consequent loss of balance, vibration, and eventual catastrophe!
I face these issues a lot in Papua New Guinea, which has hard, high silica water in most areas. RO is replacing Demin in many plants, but is not the "magic bullet" that the boiler owners were told it would be..
I try to convince them to base exchange soften before RO, so that we can fine tune the RO for silica rejection by increasing pH of RO feed...(increasing pH of RO feed without softening first will rapidly scale membrane with Calcium).

Andy Webster
Boiler Water Treatment Chemist - Brisbane QLD Australia

March 20, 2017

Q. How to remove 120 ppm silica( to get 60 % ro recovery with single stage;

Also, how to reduce COD? In my RO feed the COD is 700 ppm, so my membrane fouls instantly.

Please give a solution,


mahendra singh
- panipat, HARYANA, INDIA

June 23, 2017

Q. Hi there,

I tested town water this week and i received the following information from the lab.

Silicon 53g/m3
Reactive silica 88g/m3 as SiO2
Total Dissolved Silica 114g/m3 as SiO2 (silicon x 2.14 by calculation)

I understand that Total Silica = reactive silica + unreactive silica, so does the lab result give me unreactive silica?

Which of these silica forms can I remove by microfilter?

Thanks all.

Ming Yii
- New Zealand

November 14, 2017

Q. Sir, my plant is ion exchange and anion silica is 0.456 mg/Lit.
But the anion resin [is] in one vessel [and is a mix of] 2 types [of] resin, FFIP & 850. Please give me solution.

Lucky Kagankar
- Maharashtra india

November 2017

A. Hello Lucky. I'm not sure if I even understood the question, but in order to try to remove silica you have mixed two anion exchange resins in the one vessel for better performance than you got from either resin alone?


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

November 18, 2017

A. Silica leakage is lower if you regenerate the DI system counter-currently and regenerate the anion exchanger before exhaustion as determined by conductivity and also more frequently.

Lyle Kirman
Consultant - Cleveland Heights

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