Cation Resin Overview
Cation resin is a negatively charged matrix with exchangeable positive ions (cations). Negatively charged ions are fixed and permanently attached – part of the resin structure. Because the bead is negatively charged only positive ions are attracted or exchanged.
For water treatment purposes cation resin can be purchased in the sodium (Na) or hydrogen (H) forms. Always confirm the resin is in the sodium (Na) form before loading the tank and installing in a home. If hydrogen (H) form is used in a residence the pH of the treated water will be very acidic at 2-3 pH. This is damaging to people and pipes. Hydrogen form cation is required commercially when deionizing or demineralizing water.
- The color of the resin has no impact on performance.
- Black cation is available at a premium.
- Cation resin is available as 6%, 8% & 10% crosslink. Higher crosslinked 12-15% cation resins are manufactured for special applications. The higher the crosslink, the higher the cost. A great article by ion exchange expert, Chubb Michaud, gets into the details of crosslinking. http://wcponline.com/2011/06/07/role-cross-linking-ion-exchange-resins/
- Chubb’s highlights:
- Higher cross-linking means higher density with more plastic and less water.
- Higher cross-linking produces a tougher matrix that is more resistant to both chemical oxidation and physical breakdown.
- Drawbacks include higher costs and slower kinetics (not a good thing for cold water). Although higher cross-linked resins have a higher total capacity, the kinetics in colder water may actually result in a lower operating capacity than a lower cross-linked resin and prove to be an incorrect choice.
- Chubb’s highlights:
- How long does resin last?
- In non-chlorinated water 6% resin lasts ~ 8 to 10 years; 8% much longer. In general, the resin will wear out in the same time frame as the other parts of the softener – the valve, tank, brine tank, etc.
- For iron removal applications we recommend using a phosphoric acid drip to keep the resin bed clean so it lasts longer.
- Use sodium form cation not hydrogen form.
- Don’t store outside if there is the possibility of repeated freezing and thawing.
- Don’t overfeed chlorine. Consider an activated carbon filter as pre-treatment.
Urbans Aqua stocks Purolite & Thermax cation resin for quick shipment.
Cation Resin Applications
Our rules of thumb when applying these resins:
- 6% – Residential use on well water without chlorine.
- 8% – Residential or Commercial/Industrial well on city water where 1 ppm or less of chlorine.
- 10% – Residential or Commercial/Industrial well on city water where chlorine/chloramine levels are greater than 1 ppm. Also used where there is a combination of hot water and oxidants- chlorine or chloramine).
Installation of an activated carbon filter ahead of the softener to remove the chlorine or chloramine will prolong the life of the resin.
Water Softeners – Hardness Reduction
Sodium (Na+) strong base cation resin is commonly used for household, commercial and industrial water softening applications. According to the Water Quality Association, water hardness in the United States ranges from 1 to 350 grains (gpg) per gallon or 17.1 to 5,985 ppm. However, most waters range between 3 and 50 gpg. USGS Water Quality Information
Softening with cation resin is a simple exchange function. The resin bead is negatively charged and attracts positive ions. When supplied in the sodium form (Na+) the resin will exchange sodium ions for hardness ions – calcium and magnesium. The bead is more strongly attracted to these ions and readily exchanges with the sodium. Once the resin is exhausted it is regenerated with a brine solution (NaCl). The brine overwhelms and releases the calcium and magnesium from the bead. The resin is converted back to the sodium form and ready for re-use.
- Free chlorine levels above 0.5ppm or any oxidant decrosslink and shorten cation resin life. Dow Resins Recommended maximum free chlorine levels
- In applications with high chlorine levels and temperature use a 10% crosslinked gel or macroporous resin.
Urbans Aqua stocks:
- Purolite C-100Na C100 Cation Resin Product Data Sheet
- Purolite SSTC6000E
- Purolite C-100EFM Purolite C100EFM
- Thermax Tulsion T42Na Resin Cation TULSION T-42 Na N & Tulsion T52Na Resin Cation TULSION T-52 Na N
- These cation resins are suitable for residential, commercial and industrial applications.
Water Softeners – Iron & Manganese Removal
The hard water problem is often compounded by contaminants like iron (rust stains) and manganese (black stains). Iron water has a distinctive taste.
- Manganese can be reduced with cation resin.
- Manganese is often a companion to iron and is similarly removed. The black or dark brown stain occurs when the soluble manganese ions are oxidized and converted to manganese dioxide.
- The USEPA Secondary Drinking Water Regulations require less than 0.05 ppm – it is an aesthetic problem and not harmful.
- Softener sizing is not affected by the presence of manganese. Like iron, it is not easily exchanged, will stick to the resin and require regular resin maintenance as noted above.
- Softening resin removes ferrous, or soluble iron, in water.
- The USEPA Secondary Drinking Water Regulations require less than 0.3 ppm for iron.
- Ferrous iron is often referred to as “clear water iron” and commonly found in ground or well water.
- When sizing a softener compensate for ferrous iron –> for every part per million (ppm) of iron add 1 grain of hardness. For example – if the water sample shows 5 grains hardness and 2 ppm of iron, you would size the softener for 7, not 5 grains.
- Ferrous Fe++ not Ferric Fe+++
- Ferrous iron sticks to the cation resin and isn’t easily exchanged. Regular use of resin cleaners or salt with resin cleaner additives is recommended.
- When ferrous iron meets oxygen (air) it changes to ferric iron. Ferric iron is insoluble and leaves the classic rust stains people are familiar with and often mistakenly refer to as hardness. Ferric iron is best removed through mechanical filtration not cation resin.
Using SST – Shallow Shell Resin for Softening & Iron Removal
How SSTC6000E differs from standard resin.
- Standard beads are completely activated from the core out to the surface of the bead.
- SST – Only 60% of the radius of the bead is active.
- Active sites for SST equal about 94% of the total bead volume vs.100% for standard.
- SST resin has an inner core. Standard resin does not.
How it works
- The diffusion path that the ions, in the case of softener – calcium and magnesium – is reduced. These ions don’t go all the way to the core. And it’s more efficient because the diffusion path is slower.
- Typical regeneration service cycles don’t allow enough time for brine to effectively convert 100% of a standard resin bead. Because SST resins have a core, regeneration service cycles are more effective and efficient. More of the calcium and magnesium collected during service cycle is exchanged.
- Rate of exchange going in and out of the bead is much faster resulting in a cleaner bead.
- Up to 20% reduction in salt.
- Less rinse water
- Slow rinse one bed volume vs. two to three bed volumes for standard resin.
- Fast rinse one and a half bed volumes vs. three to five bed volumes for standard.
- Quantifiable payback. Even though SST is twice the cost of standard cation, the typical payback is six to eight months.
- Rinse water
- Physically strong
- Tolerates very high flow rates
- Effectively removes ferrous iron when applied properly.
- SSTC6000E Technical Data
Using Fine Mesh Resin for Softening & Iron Removal
Fine mesh resin is also used in residential applications where iron is present.
- Fine mesh resin beads are smaller and will form a more compact bed with less void space.
- This results in a higher capacity resin because the kinetics of this bed are faster.
- The ion exchange happens more quickly than in standard sized resin.
- Be careful of the distributor screen slot size. 1/8×1/16” gravel sub-fill is suggested.
Lead, Aluminum, and Copper
- Lead seldom naturally occurs in water. More often it’s the result of dissolving brass, lead fixtures, lead solder or improperly treated city mains. Fine mesh resin is recommended because it will pick up particulate lead. Lead is so ionically sticky that one cubic foot of cation will remove up to 9 pounds. WQA 2016 Lead Fact Sheet
- Aluminum can be found in city water if alum polymer is overfed.
- Copper will be picked up by cation resin and turn it green. We’ve seen this in plating operations.
Urbans Aqua stocks Purolite & Thermax cation resin for quick shipment.
Strong Acid Cation in the hydrogen form (H+) in combination with strong base anion (SBA) in the hydroxide form (OH), is most often used for demineralization processes such as portable exchange tank (PEDI) operations. In this case, the hydrogen is exchanged for calcium, magnesium and sodium. (For more information please refer to section on demineralization for portable DI exchange operations.)
Some mixed bed resins have black cation and blonde anion. The first regeneration step of mixed bed is to separate the cation and anion. Anion which is lighter in weight and color is floated to the top; cation heavier and darker remains on the bottom. The color difference distinguishes where they separate enabling the regenerator to easily see and move each resin to the appropriate regeneration vessels.
Links to Specifications & Engineering Bulletins:
Visit our PDF Library for technical specifications and product manuals on cation resins.
Visit our SDS Library for safety data sheets on cation resins.
Urbans Aqua is a stocking wholesaler of Residential & Commercial Water Treatment Equipment and supplies including Ion Exchange Resin; Calgon & Haycarb Activated Carbon; FilterAg Plus; GreensandPlus; Pyrolox Advantage; KDF; Birm; Sand/Gravel; Clack, Fleck & AqMatic valves; Stenner Pumps & Parts.
We work exclusively with water treatment dealers.