Sodium softeners resin

Sodium metabisulfate may be used to chemically reduce high chlorine content in order to prevent softener resin damage. Resins can tolerate chlorine levels less than 0..5 pprn. 

Sodium softeners are used to treated RO influent water to remove soluble hardness (calcium, magnesium, barium, and strontium) that can form scale on RO membranes. Once known as sodium zeolite softeners, zeolites have been replaced with synthetic plastic resin beads. For sodium softeners, these resin beads are strongly acidic cation (SAC) polystyrene resin in the sodium form. The active group is benzene sulfonic acid, in the sodium, not free acid, form. Figure 8.12 shows styrene-divinylbenzene gel cation resin. Equation 8.4 shows the softening reaction for calcium exchange ... 

Table 15.1 lists operating cost issues for sodium softeners and antisealant feed systems. The three largest expenditures listed in Table 15.1 are the salt and resin amortization for the sodium softener options and the antisealant itself for that option. To provide examples of these costs in greater detail, consider the following cases. 

The sodium softener selected to treat this water is a duplex, 150-gpm system with 54-inch diameter by 72-inch side sheet vessels. Each vessel contains 50ft3 of resin. Since the duplex system operates with one vessel on line and one vessel in stand-by, the total system regenerates 2.4 times per day. At a salt dosage of 15 pounds per cubic foot, the system uses about 1,800 pounds (820 kg) of salt per day or 27.4 tons per month, assuming a 100% operating factor. At a salt cost of 80 per ton, the total month cost for salt is about 2,200.3... 

The softener is a 48-inch diameter unit with 35ft3 of resin. The softener will regenerate once per day with 151b/ft3 of salt. At a salt cost of 80 per ton, the sodium softener would require about 638 per month to operate. 

In operation, metal ions (M ) in solution are preferentially bound to the insoluble matrix with the concomitant release of protons or another cation (M). The toxic metal ion (M ) is effectively held within the matrix. The most common examples of cation exchange are water-softening resins. Hard water (containing Ca ) can be treated with an ion-exchange matrix containing sodium ions. The sodium ions are exchanged with the calcium ions, with the resultant removal of calcium from solution (see Figure 14.3). 

Note that the resin shows a preference for iron and manganese over hardness. Although sodium softeners will remove these metals, they are not adequately removed from the resin during regeneration. Therefore, sodium softeners operating on well waters with high iron or manganese... 

Water is softened by removing calcium and magnesium ions from hard water in exchange for sodium ions at sites on cation-exchange resin. Water softeners typically use a gel polystyrene sulfonate cation-exchange resin regenerated with a 10% salt brine solution (25). 

These resins have found a wide range of application, being used on the sodium cycle for softening, and on the hydrogen cycle for softening, dealkalization, and demineralization. 

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