Usually, DI resins have a five to ten years lifespan. These resins will be active until their beads have no physical and chemical damage. These resins must be carefully handled to maintain their entire lifetime. This article will help to identify the causes of resin failures.
What are the main factors that can be identified for resin failures?
As time passes, the resin can be fouled and damaged for various reasons. Resins start to age due to improper regeneration or contact with contaminating particles. Therefore, resins cannot hold the hydrogen ions and hydroxyl ions, hinder the ion exchange, and lose efficiency. Chemical attacks on the resin cause resin degradation. The following factors can be identified as the reasons for shortening the lifespan of resins.
- Iron and Manganese contamination
- Aluminum fouling
- Hardness precipitates
- Oil fouling
- Silica fouling
- Microbial fouling
- Thermal degradation
- Organic fouling
- Storage problems
Let’s move forward with brief descriptions for all of the above.
1. Iron and Manganese contamination.
Iron exists in water as ferrous or ferric inorganic salt or organic complexes. Ferrous irons can remove through the ion exchanging process, but ferric irons are insoluble and do not remove by the IX method. Cation resins catch the Ferric ions and prevent exchange. A potent reducing agent or an acid is able to remove these irons. When organically bound irons pass through the cation unit and foul the anion resins. Contaminated resins can remove along with the organic material. Manganese is another element present in some well waters and degrades the resins in the same manner as irons. These resins need an accurate, sensitive regeneration to prevent a reducing lifespan.
2. Aluminum fouling.
Usually, Aluminum is present in water as aluminum hydroxide. The presence of aluminum hydroxide in water results from alum or sodium aluminates that are used in settling or clarification steps in water treatment. In a softener system, these aluminum flocs can be attached to the resins while passing through the filters. In most cases in demineralization units, Aluminum isn’t a foulant due to the removal during the normal regeneration.
3. Hardness precipitates
The ions that cause the water hardness are Ca2+ and Mg2+. The most challenging precipitation is sulfate precipitation. This sulfate precipitation can raise the Strong acid cations in operation with the hydrogen cycle. At the end of the softener service cycle, the resin beads are saturated with calcium ions. If you regenerate this calcium saturated resin bed with sulfuric acid at high concentration levels or slow flow rate levels, the sulfate fouling occurs and fouls the resin. These calcium precipitation levels are difficult to re-dissolve. Therefore, the resin fouled with calcium sulfate precipitates is generally discarded. Still, there is a chance to reverse the mild fouling of calcium sulfate with prolonged soaked HCl (hydrochloric) acid. Always selecting the suitable regenerant with the help of the field consultants will help you protect the lifetime of the resins.
4. Oil fouling
Oil can be present in water for various reasons, and the oil in feed water may cause resin fouling. Oil gets caught by resins resulting in the ion exchanging to the water and from the water. Even in low oil concentrations, surfaces of resin beads are blocked with oil layers and cover the resin pores. With elevated concentration levels create the beads to be sticky and clump together. Oil can remove by selecting a suitable surfactant. It is essential to carefully choose the surfactant that doesn’t cause the resin fouling. For example, the anion resins with oil fouling need to be removed with non-ionic surfactant only.
5. Silica fouling
Low-temperature levels in strong base anion (SBA) resin will cause silica fouling in SBA resins. Suppose someone uses effluent caustic from the SBA unit to regenerate the weak base resin unit with a high silica range. In that case, it will also raise the silica fouling in weak base anion resins. Silica polymerization can occur in weak base resins at low pH levels. Silica fouling can recover with a prolonged soak in caustic soda solution at the temperature of 120 0F.
6. Microbial fouling
Long-term inactivation of the ion exchange unit with no service flow causes microbial growth in the resin bed. The microbial growth can generate a severe plugging of the resin bed and leads to mechanical damage because of the unusual pressure drops across fouling resins. Severe conditions may require appropriate sterilizers or surfactants.
Chlorine and chloramines are two types of oxidizing agents in the water treatment industry. These oxidants can degrade both anion and cation resins. As you are aware, the resins are cross-linked with divinylbenzene, and these links strengthen the resin bead. Oxidants attack these cross-links reducing the total strength of the polymer bead. The continuous attack on the resins loses its spherical shape and rigidity, allowing to compact the bed during service flow. It increases the higher pressure losses, decreases the unit performances, and leads to channeling. If chlorine is available in raw water, the precaution is to use an activated carbon filter before the IX unit.
Oxygen-saturated water destructs the strong base resins over time and accelerates organic fouling resin degradation.
8. Thermal degradation
The thermal effect most affects the acrylic resin and type II strong base anion resin types. Overheating anion resins during the service cycle or regeneration process is the reason for thermal degradation. The temperature limit of the type – II anion resins is at least 105 0F limit.
9. Organic fouling
Surface water contains a massive amount of natural and artificial organic particles. Usually, groundwater contains low levels of organic particles. Decomposed vegetation causes the natural organic in water and aromatic and acidic in nature. These contaminants include humic acid, fulvic acid, tannins, and tannic acid.
Organic fouling and degradation are the most common resin fouling. The initial blockage of the strong base resins site results in long final rinsing and reducing salt splitting capacity. If these organic foulants remain on resins, it starts to degrade. The functionality decreases the strong base site to weak base to non-active sites. Though the total capacity is high in the early stages of degradation, salt splitting capacity is lower. At this time, we can recover some of the operating capacity. High conductivity, lower pH levels of effluent water, and the color changes of the regenerant output water will help to identify the organic fouling of resin. You can prevent organic fouling by pre-chlorination, filtering through an AC filter, macro-porous weak base anions instead of a strong base, and identifying new specialized resins in the market.
10. Storage problems
Improper storage of resins can damage the beads and reduce the chemical properties. Sensitive caring of resin storage helps keep its original lifespan up to five years.
The main point is to control the temperature and oxygen exposure to the resins because it helps minimize the organic leachables during storage. Most resin manufacturers introduced plastic covers to keep that cover at the warehouses. If you unpack the bag, it is essential to cover the opening to prevent air entering the resin bags. The general condition of temperature to store resins at warehouses, containers, and trucks is mot higher than 90 0F. Freezing and thawing are other states caring points in shipping. It helps to generate sudden cracks in polymer beads.
This article introduced the factors that shorten the lifespan of resins: frequent regeneration, fouling, storage problems, and inaccurate awareness.
- Under-designed treatment plants result in frequent regeneration. Select well-experienced chemical engineering design for your industrial application work. The capital cost will be higher, but you can reduce your operation and maintenance cost with a highly durable plant.
- Resin fouling shortens the lifespan of resins, and various types of fouling can be identified.
- Improper storage conditions reduce the life span of original and used resins. Leaching and cracks can pop up with inaccurate storage conditions.
As a consumer of resins, it will be cost-effective with a long lifetime of resins types in your IX plant. At least keeping up a basic knowledge of the above will helps you to save money and long term efficient service.