Can the kind of high purity DI resin really make a difference in the quality of your product? Absolutely. The more you know about the different kinds of DI resin that are available, the easier it will be to choose the right type for your application.
There are three kinds of deionization processes, each requiring a different composition of resin. Which process you choose depends on your specific water application needs.
We’ll explain how DI resin works before discussing how it interacts with the three types of deionization processes.
What is Resin and How Does it Work?
There are two different kinds of resin: Cation and anion. Physically, both are quite small, about the size of caviar. However, their applications are quite different.
Cation is a negatively charged resin bead (about 2-3 microns in diameter). It is regenerated with a 6-7 percent hydrochloric acid solution.
When cation resin first enters the deionization process, positively charged hydrogen ions(H+) are attracted to the negative “exchange sites” on the cation resin beads.
Hydrogen ions are very lightly charged ions in water. Therefore, as water passes through the resin beads, all the other positively charged ions, such as magnesium or iron, stick to the cation resin and dislodge the lightly charged hydrogen ions. This process is known as “Ion Exchange” or “Deionization.”
What do we get at the other end of the cation exchange tank? Water that is virtually absent of every positively charged ion except for hydrogen, with a very acidic pH level (2-2.5).
Anion resin is always in line after the cation resin. The anion resin has positively charged “exchange sites” to remove the negatively charged ions in the water. Anion resin is regenerated with 2 – 4% sodium hydroxide leaving the hydroxyl ion(OH-) on the resin beads.
Then, in a similar exchange process as the cation resin, water runs through the anion beads, which attract the negative ions like chloride and sulfates.
This water combines with the now decationized water to form “hydrogen hydroxide” or pure H20.
The 3 Different Kinds of Deionization
There are three different kinds of deionization, all of which are determined by the type of resin used in the process.
We use two types of cation resin: Strong acid (used in water softeners) and weak acid (used for reduction of hardness associated with alkalinity). Which one you choose depends on your water application requirements.
1. Weak base deionization
This process uses a strong acid cation and a weak base anion to create the lowest quality of deionized water. The weak base anion allows CO2 and silica to flow through, giving the water a low pH.
Weak base deionization typically renders water with a resistivity of 50,000 ohms, or about 22 microsiemens.
Applications: Applications include a spot-free rinse for a car wash or window/glass cleaning. Water that is too high in silica can still create problems depending on the level in the feed water.
The amount of silica depends on where your feed water originates from; surface water has less silica than ground water.
2. Strong base deionization
This process uses a strong acid cation and a strong base anion to create mid-range quality deionized water. This upgraded form of deionization removes all the CO2 and silica from the water.
Strong base deionization guarantees water with a resistivity of over 200,000 ohms, or 4-5 microsiemens.
Applications: Applications include use by any manufacturer who doesn’t require the highest quality purified water. This water is also much less aggressive on metal because it is less acidic (pH levels of 8 – 9).
3. Mixed bed deionization
This final process uses a 40/60 ratio of strong acid cation to strong base anion. This combination will create the purest water available from a resistance standpoint.
Mixed bed deionization creates water with a resistivity level of more than sixteen megohms (16 million ohms). High purity mixed bed water can only be measured with a resistivity meter, preferably a temperature compensated resistivity meter.
Conductivity meters are not sensitive enough to measure high purity mixed bed water.
Applications: Applications include medical use, laboratories, research facilities, biotech manufacturing, pharmaceutical and electronics.
When measured at 18.3 megohms this water is completely neutral, with a pH level of 7.
The other consideration regarding deionized water is your necessary capacity of treatment. Deionization canisters can purify anywhere from a quarter gallon of water per minute all the way up to 500 gallons per minute.
However, if your application requires large amounts of deionized water, it may be wise to consider a reverse osmosis (RO) unit. An RO unit can remove a large percentage of the charged ions, taking a bulk of the work off the deionization canisters.
You can learn more about how an RO unit interacts with the deionization process in this post.
Resin is the life force behind the deionization process. Choosing the right type of resin depends on your specific water treatment application or need.
If you have any questions about the deionization process and selecting the right resin for your needs, click on the form below. Our engineering department will be happy to assist you!
We’ll do more than give you a quote—we’ll visit your site to analyze your industrial water needs.