The Best Ways To Filter Out Silica From Water


Silica, also known as silicon dioxide, can be found in many forms, including in quartz, glass, and sandstone. Silica in water is harmless to human health, yet most people still prefer to filter it out as it leaves behind unsightly scale deposits on whatever surface it comes in contact with.

Silica can be removed from water through ion exchange, lime-soda softening, ultrafiltration, reverse osmosis, distillation and electrocoagulation. For residential use, reverse osmosis and distillation are the best methods for silica removal.

This article will describe what silica is, the forms it takes in water, how it enters our water supply, and importantly explain which water filters can remove silica from water.

What is Silica?

Silica digital illustration.

Silica (SiO2) is one of the common mineral compounds in the Universe. After oxygen, it is the most plenteous naturally occurring element on the Earth’s surface.

The combination of silicon (Si) and oxygen (O2) produces SiO2 and its combination with many other elements, especially aluminum, sodium, calcium and magnesium, create almost all of the world’s minerals and rocks.

It’s present in practically all granular materials, including rocks, minerals, and sand.

Orthosilicic Acid (OSA) is the name for silicon in its soluble state. Only in the form of OSA is silicon digestible and absorbed efficiently by the human body.

Silicon can also be made synthetically in some cases. There are many different industrial uses for silica. Manufacturing glass, fillers, extenders, silica bricks as a catalyst, specialty coatings, cleansers, ceramics, electronics optics, refractories, rubber, and ferrosilicon production are just some of the many industrial applications for silica.

Silicon used in industry is often extracted from sand. It can also be found in the minerals talc, mica, nepheline, feldspar, olivine, perlite, vermiculite, and kaolinite. 

Common Forms of Silica in Water

The majority of silica varieties are not very water-soluble under typical conditions. Ground and surface water contain only trace amounts of silica from contact with nearby rocks.

There are two types of silica in the water supply.

  • Reactive silica
  • Colloidal silica 

Reactive Silica

Silica that has been completely dissolved but has not been polymerized into a long chain is called reactive silica (for example, silicate minerals).

Since the silica has been dissolved, it can be removed with ion exchange resins or by reverse osmosis. The most effective method for removing dissolved silica is Reverse Osmosis as the ion exchange resins are tough to recycle and reuse.

Colloidal Silica

Colloidal Silica is also known as unreactive silica because they don’t undergo any ionic reaction. In this form of silica, the particles do not dissolve in water. This type of silica cannot be removed from the water using ion-exchange techniques or conventional filtration methods.

Water containing trace amounts of colloidal silica can result in significant silica levels and pH drops (water becomes acidic). Colloidal Silica can cause etching, scratching, and spots on glassware and other fixtures. Ultrafiltration (UF), flocculation, and clarification are some of the widespread silica removal techniques for colloidal silica.

What is considered high silica in water?

The silica concentration in water is usually between 0.2 and 3.0 milligrams per liter. However, sometimes there can be higher concentrations of silica in water, for example there are several brands of bottled water with more than 50 mg/L of silica.

There is no maximum amount of silica set by the Environmental Protection Agency (EPA), as it is not considered a harmful contaminant.

However, there are certain things that can affect the amount of silica in your water, including:

  1. The depth of the water.
  2. The temperature of the water.
  3. The salinity of the water.
  4. The turbidity of the water.
  5. The pH of the water.
  6. The presence of organic materials in the water.
  7. The presence of oxygen.

On top of these factors there is the different types of silica – dissolved (reactive) silica and silica particles (colloidal). These behave differently depending on the factors described above.

Also, water can contain silica as silicic acid, quartz, and various minerals as sediment. It also depends on the depth of the water.

Harmful Effects of Silica

It is important to remember that silica is not a toxic chemical. Silica is found naturally in rocks, soil, and sand. The amount of silica in drinking water is very small and cannot harm your health. This means that the drinking water isn’t contaminated with a hazardous chemical, which is good.

However, if you breathe dust made up of silica particles, it can enter your lungs and cause health problems. The main way you can get exposed to silica is by working in a place with rock crushers and sandblasters. These machines create silica dust and can cause you to breathe in this dust. 

Silica also causes damage to glassware and some other equipment. It can create scratching and spotting on glassware. This is due to its tendency to attack the surface of the glass, creating a scaly, duller, hazy appearance. In most cases, silica is removed to prevent glassware damage.

The presence of silica in water can present considerable challenges for industrial processes, particularly those involving boilers and steam. It is a hard, abrasive material that quickly forms deposits and sticks to surfaces.

When heated, silica molecules undergo a series of chemical reactions that form crystals. Silica deposits can form on boiler tubes and heat exchangers when subjected to high pressures and temperatures. 

These crystalline deposits reduce heat transport efficiency, leading to failure at an earlier stage. Deposits of silica on boilers or water heaters reduce their efficiency and require costly maintenance as well as downtime to clean them.

How water filters can remove silica from water

Silica can be removed from water by five main methods.

1. Ion Exchange Resin

Ion exchange is when a stream of water is filtered through a resin substrate to remove ionic contaminants, such as dissolved silica, and replace them with particles with a similar charge.

Overtime, these resins need recharging for them to be able to keep removing contaminants from the water.

There are two ways to regenerate the ion exchange resin: thermal regeneration and chemical regeneration.

The big advantage of using thermal regeneration is that it does not require chemicals. Unfortunately, thermal regeneration is used primarily in commercial settings.

Chemical regeneration is the more common way to regenerate the anion resin. It is also faster than thermal regeneration. The biggest drawback of using chemical regeneration is that it requires chemicals, which are very dangerous and costly. Chemicals are flammable, and they can cause serious harm to people. 

Fortunately, many filters use disposable ion exchange resin cartridges that are replaced rather than recharged.

The ion-exchange technique is effective at removing reactive silica, but is unsuitable for colloidal silica.

2. Lime-Soda Softening

At higher pH’s (alkaline), silica is removed via adsorption onto magnesium in a process called lime softening. For maximum effectiveness, magnesium chloride is used when adding magnesium.

In this sophisticated chemical precipitation method, calcium (CaOH) and Soda Ash make the water extremely alkaline – to extremely high levels. In this way, the calcium and magnesium hydroxides absorb the silica particles. 

This approach is quite expensive and needs substantial initial investment. Using this technique in a home setting is not feasible financially. Lime softening is typically used in large cooling towers, and huge boiler feeds – but it is certainly an effective means of removing silica from water.

3. Ultrafiltration

Ultrafiltration (UF) is used to remove colloidal silica. In this filtration process, a UF Pilot Stick is used to check whether there is colloidal silica in the water or not. If the result shows colloidal silica, then ultrafiltration can remove it. 

Many under-sink water filters use ultrafiltration to purify water. Although it is a mechanical filter, UF is very effective at removing 0.025-micron contaminants from water.

4. Reverse Osmosis

Reverse osmosis is the most effective method for removing all forms of silica from water at home. Water is pushed through a membrane and several other filters designed to block the passage of silica, fluoride, chlorine, and other impurities.

You can get silica-free water from all the water fixtures by installing a whole-house reverse osmosis, or use a point-of-use system to ensure silica-free drinking water.

5. Distillation

Distillation can effectively remove silica from water. The distillation process can remove contaminants that have a boiling point higher than water (212°F). It does this by heating the water until it turns to vapor, this is removed and then cooled and condensed in a separate chamber, with the water collected for drinking.

Anything that has not also turned to a vapor (i.e., boiled) is left behind. Silica has a boiling point of 4,046°F – and is definitely left behind, making distillation very effective.

5. Electrocoagulation

Electrocoagulation is an interesting process that has been used for many years to remove impurities from wastewater.

It is done with electricity. Two separate metal sheets (anodes and cathodes) are placed in a pair for electrocoagulation. By oxidizing the cathode (causing it to lose electrons) and reducing the water (causing it to gain electrons), electrochemistry is used to improve wastewater treatment.

This causes minerals to be removed from the water. It is then placed in a safe landfill for humans and animals.

Most of the water treated by electrocoagulation is recycled back into the environment. It can save a lot of energy and time. Unfortunately, it cannot be used for residential purposes – but it really is interesting.

How does Silica enter our water supply?

Silica enter our water in several different ways, but predominantly via weathering of rocks.

At the time of water flow

Minerals, sediment, and rocks are carried by water when it flows from one place to another. While these sediments are in suspension the water can dissolve a small amount of different silicate minerals, releasing silica into the water flow.

Weathering Processes

Many particles or colloids of silicate minerals are produced as a byproduct of the natural chemical and physical processes of weathering. When atmospheric carbon dioxide (CO2) dissolves in rainwater, carbonic acid (H2CO3) is formed. In the weathering process, this weak acid dissolves silicate rocks and releases dissolved silica, as well as calcium, magnesium and bicarbonate into the water.

This is why hard water (water high in calcium and magnesium) is also often high in silica.

Volcanic Activity

Crystalline silica typically forms in volcanic environments after lava eruptions, which occur when silicic magma is extruded from a volcano. 

Antarctic Weathering

Silicon is more abundant in the water within the spaces of marine sediments than at the sea surface. The weathering of Antarctica releases silicon (just like elsewhere on earth) and contributes to silica concentrations in seawater.

Does bottled water have silica?

The amount of silica in bottled water typically ranges from 38 mg/L to 92 mg/L. Up to 92 mg/L of silica can be found in some bottled waters. Silica water is very different from most mineral waters. Orthosilicic acid (OSA), a soluble form of silicon, is usually written on the label of bottled water as silica and measured in milligrams per liter.

Water Purification Guide has a complete list of all the bottled water high in silica available here.

Which water has the most silica?

ROI Roitschocrene and FIJI Natural Artesian bottled waters contain more than 85mg/L of silica. However, water from Mount Kirishima contains the highest concentration of silica on Earth. It is an active volcano in Japan on the island of Kyushu, in the prefectures of Kagoshima and Miyazaki.

Over the last 1,000,000 years, several eruptions have created aquifers’ underground water sources. Also known as the wettest place in Japan, this area gets a lot of rain every year. Through the Kirishima mountain range, the rain seeps into these aquifers, which produce groundwater that is rich in silica and a number of rare minerals.

Russell Singleton

Russell has a Bachelor of Science (Environmental and Marine Geoscience) with Class I Honors. He is currently completing his doctorate in science and is passionate about all earth processes, especially isotope geochemistry and paleohydrology.

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