Silica can cause major problems to industrial equipment, but luckily there are various methods to remove it from a water supply, including lime softening, ion exchange, reverse osmosis, ultrafiltration, and electrocoagulation.
Let’s examine these technologies for the removal of silica from the water or wastewater streams.
Why is Silica Removal from Water Important?
While silica removal from water is vital for drinking water applications utilizing membrane treatment processes, its removal is also important in industrial processes as well.
Numerous industries rely upon effective treatment for silica removal from water to prevent the increased operation and maintenance costs on their process equipment due to silica fouling. Industries utilizing cooling towers, boilers, and several other specialized industries rely upon the proper removal of this element.
Let’s have a look at the main problems caused by silica in water.
High Silica Content in Water Problems
High silica content in water can cause major problems and can cause a range of negative effects that necessitate effective cleaning practices through industrial water treatment.
Silica can cause the deterioration of equipment and loss of functionality by:
Abrasion: Silica is an abrasive substance; it’s even used for sandblasting and carving applications. It will bring its abrasive effects to the inside of a boiler and eat away at it, causing premature wear and tear and costly repairs;
Reduced heating and cooling efficiency: Scale deposits build up on the side of equipment when silica deposits precipitate out of the water and concentrate on the heat transfer surface of the equipment. Scale is a good insulator, reducing the efficiency of the heat transfer mechanism and the equipment’s performance. It can also slough off and create pieces that interrupt the flow of water;
Effects on pressure ranges: Those deposits and pieces can impact a system’s ability to operate at optimal pressure ranges;
Membrane fouling: Silica particles can get lodged in membrane pores in reverse osmosis and nanofiltration systems. They block the flow of liquids through that membrane and can cause early tearing;
How to solve these problems? We recommend five methods for removing silica, depending on the type and characteristics of this colloid.
Lime Softening for Silica Removal
Lime softening is the most common approach for lowering silica levels in the water. To remove silica, you also need to add lime which is calcium hydroxide, to the water supplies.
The addition of lime eliminates the hardness of water by removing both magnesium and calcium carbonate. These two get precipitates, but they decrease the silica content as well.
The silica present in water gets attached to calcium carbonate and also magnesium carbonate. When lime causes these two to precipitate, silica in water automatically gets precipitated.
Moreover, you can remove these precipitants later through a variety of methods that we will mention in later in this article. Sometimes, it can cause the problem of silica scaling on other equipment, but overall, lime softening is an effective method.
Ion Exchange for Removing Silicon Dioxide
Ion exchange is also one of the most common methods for producing contaminants-free treated water. Silicon dioxide splits in water and becomes ionic silica. This ion has a negative charge. That is why an anion resin can attract and bind this reactive silica to remove silica particles.
The resin is made of caustic soda (NaOH) and has a strong affinity for silicon. The silica in its ionic form is a weak acid, and sodium hydroxide in the resin completely removes ionic silica. It basically exchanges the hydroxyl part (OH) with silica.
After silica is removed the pH of the treated water increases because of the abundance of hydroxyl ions that are produced. Therefore, you need an additional step to stabilize pH after silica removal.
The ion exchange method is not suitable for residential applications as it uses caustic soda. After every removal cycle, the resin needs to be changed and also washed. This recharging process prepares the system for the next cycle.
Reverse Osmosis for Silica Removal
Reverse Osmosis (RO) is the main process of current industrial desalination, but its performance is greatly affected by the quality of water source, especially by silica and calcium.
In high silica content waters or wastewaters, the risk of fouling is very high. Due to its complexity, silica fouling is difficult to control, which often causes less efficient design of RO system for correct and safe operation.
In these cases, a pre-treatment is always needed to reduce the silica presence and lower the risks of fouling and shut-down times for the RO equipment.
Ultrafiltration for Removing Colloidal Silica
Ultrafiltration is strictly limited to the removal of colloidal silica. It does not sit well with the presence of reactive silica in water. Moreover, you can get an ultrafiltration test module for determining the type of silica in water. Ultrafiltration uses filters of very small pore sizes that can remove silica easily.
If the water supply has granular silicates and dissolved silica, we can use ultrafiltration to remove colloidal silica. For other kind of silica other methods still work.
Electrocoagulation for Silica Removal
Electrocoagulation is a rather new technology fitted for purifying water for industrial applications. In addition to silica, this method effectively removes hard mineral deposits, plastic impurities, etc.
In an EC system, such as PREDEST, there is an electrocoagulation reactor in which the impure water is introduced. This chamber has two parallel plates for passing the electricity through water. The water is dispersed as it moves through both of these plates. And the electricity field separates all contaminants from water.
The electricity charges the contaminants and causes them to separate. This technique is also economically effective as it treats the water without using chemicals. With our EC test equipment you can test the efficacy of this technology in silica removal applications.
Water Treatment System Design for Efficiently Removing Silica
A treatment system needs to be carefully designed to remove silica from water and to satisfy the treatment requirements, especially in drinking water applications.
As we mentioned, five treatment technologies can remove silica from water, but each of them has its drawbacks. In the picture below we present a treatment system that can remove colloidal silica from water by using water softeners, electrocoagulation, and REWATER ultrafiltration equipment.
Instead, in the system below, the installation of water softeners and reverse osmosis is the preferred choice for removing dissolved silica.
In both systems the silica removal efficiency is very satisfactory, thus water without silica is produced after the treatment process is complete.
What Is the Best Method for Silica Removal from Water?
For silica removal treatment the most suitable method needs to consider the characteristics of the feed water and the type of silica we are dealing with.
YASA ET helps companies all around the world to find the best solution to their water and wastewater problems by running tests on the high-silica water and designs the most suitable solution after an accurate assessment.
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