Resin fouling

Resin Fouling. In addition to the physieal eauses of eapaeity losses listed previously, there are a number of ehemieally caused problems that merit attention, specifically the several forms of resin fouling that may be found. 

Ionic silica is not totally removable by DI. Colloidal silica is difficult to remove by both DI and reverse osmosis (RO) it may cause some resin fouling as well as leaking into the treated water. Where the cation effluent is maintained at a pH of 2.0 to 3.0, however, silica tends to both depolymerize and ionize thus enabling its effective removal in strongly basic, anion resin beds. 

Twin-bed DI often ceases to be economical when TDS levels begin to climb, and it can be subject to bacterial infection and resin fouling. Also, there are cost and safety issues associated with chemical regenerant storage, consumption, and discharge. As a technology, however, DI provides the widest possible versatility. 

Ion exchange resin fouling can result from the use of a contaminated regenerant and result in channeling of flow with its attendant problems. 

A problem common to produced water appHcations is the tendency for oil fouling of the resin. If weak acid or chelate resins are used, a two-step regeneration process is required which uses acid to remove calcium and magnesium from the resin, foUowed by a dilute NaOH solution to convert the resin to the sodium form. 

Pretreatment of aqueous streams may be required prior to using ion exchange. Suspended soHds that can plug an ion-exchange unit should be reduced to the 10 p.m level. Organics that can foul resins can be removed by carbon adsorption. Iron [7439-89-6] and manganese [7439-96-5], commonly present in ground waters, should be removed because they precipitate on the resin. 

Many larger installations also feature a batch stiU. Material to be separated may be high in solids content, or it might contain tars or resins that would plug or foul a continuous unit. Use of a batch unit can keep solids separated and permit convenient removal at the termination of the process. 

Expensive dernineralizer resins can be irreversibly fouled by these materials. 

Iron fouling is caused by both forms of iron ions the insoluble form will coat the resin bead surface and the soluble form can exchange and attach to exchange sites on the resin bead. These exchanged ions can be oxidized by subsequent cycles and precipitate ferric oxide within the bead interior. 

Silica fouling is the accumulation of insoluble silica on anion resins. It is caused by improper regeneration which allows the silicate (ionic form) to hydrolyze to soluble silicic acid which in turn polymerizes to form colloidal silicic acid with the beads. Silica fouling occurs in weak-base anion resins when they are regenerated with silica-laden waste caustic from the strongbase anion resin unless intermediate partial dumping is done. 

If the unit becomes badly fouled with suspended matter (for example, after a pipe brake has introduced excessive suspended matter into the system) it must be taken out of service and cleaned. This is done with an extended backwash, possibly at higher flow rates. If this does not remove the dirt, the manhole should be opened and the resin agitated with an air lance. Non-ionic detergents can be used, but not at the same time as the air lance or the resulting froth will be impossible to control. 

The anion resins used in de-ionization are prone to fouling if the water contains organic matter. The soft peaty waters mentioned above are particularly bad in this respect, and, at worst, can reduce resin life to a few weeks. 

The major chemical problem met in ion-exchange practice is the fouling or poisoning of the anion resins by organic matter. The various counter measures deployed include pre-flocculation, oxidation of the organic material, the use of specially developed resins, and treatment of the fouled resins by brine and/or hypochlorite. 

Reduced operating capacity due to iron fouling of the resin, which occurs because soluble iron (in the form of ferrous bicarbon-... 

Loss of resin from the softener due to poor regeneration procedures or excessive water pressure. The resin may either be lost down the drain or it may enter the FW system, whereupon it melts or disintegrates and causes fouling of waterside surfaces. 

A further problem that may cause contamination of the treated MU water is anion leakage as a result of organic fouling. This significantly affects anion resins, preventing ion removal by ion exchange and thus reducing bed capacity. 

Organic fouling also affects cation resins, albeit to a lesser degree. The fouling primarily stems from the attachment to the anion exchange site of a variety of low-level organic matter of variable molecular weight that is present in the raw water source. 

Hardness breakthrough with ion-exchange (base exchange, BX) softening NOTE Caused by Fe/Mn fouling, resin breakdown/loss, or inadequate regeneration. Increased risk of carbonate scale or phosphate sludge Loss of alkalinity and hence an increased silica deposition risk... 

Organic fouling of DI resins. Loss of treated water capacity Anion leakage... 

The condition of an exhausted resin bed is an ionically banded bed, with the most strongly held ions on the top of the bed. Iron is more strongly held than calcium, which may lead to iron fouling problems. Some practical considerations for a RW softener are ... 

Type 1 and 2 resins Refers to SBA resins. Type 1 resins are either standard (particularly good temperature and oxidation stability) or porous (higher capacity and resistance against organic fouling). The structure of type 2 resins is similar to type 1 but provides for maximum capacity and resistance to fouling. 

Although EDI may be used as a process for the production of basic pure water, in practice it suffers from the organic fouling potential of resins and the scale fouling potential of ED when higher TDS water sources are utilized. Appropriate pretreatment is therefore required. As a consequence, EDI is best suited for the production of very pure and ultrapure water by acting as a polisher to follow bulk water deionization by RO. Under these circumstances, it competes with both doublepass RO and MB units. 

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