Sodium water softening

Sodium softening is used to remove soluble hardness from water, including calcium, magnesium, barium, and strontium. As discussed in Chapter 8.1.6, sodium softeners are commonly used to pre-treat RO feed water to reduce the potential for scaling the membrane with hardness scales. In the next two sections, the placement of the sodium softener, either before or after the RO system, as well as the use of sodium softeners versus antisealants are discussed. 

Traditionally, sodium softeners have been used as pretreatment to RO. Sodium softeners remove hardness and metals, such as iron and manganese, that scale, foul, or degrade RO membranes. Anecdotally, softeners are also used to help reduce suspended solids and SDI from surface or other highly fouling feed waters prior to RO. The sodium softener, in essence, acts as another barrier in front of the membrane. 

The disadvantage with using sodium softening as RO pretreatment is that the softener must treat not only the permeate volume but also the volume of water that will become the reject. In other words, the softener must be large enough to treat the entire feed volume to the RO. This brings up two issues  

The softener system must be relatively large, as the service flow rate through a softener vessel should be about 6-8 gpm/ft. A 500-gpm RO operating at 75% recovery (see Chapter 3.1) would require two 120-inch diameter vessel to soften the feed water and maintain the desired service flow rate while one unit is in regeneration. 

Chloride discharge may become a concern. One 120-inch diameter vessel will generate about 3,400 gallons of 10% brine waste just from the brining step alone. 

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A salt originally called sodium hexametaphosphate, with n believed to be 6, is now thought to contain many much larger anion aggregates. It has the important property that it sequesters , i.e. removes, calcium ions from solution. Hence it is much used as a water-softener. 

Sodium alumiaate is used ia the treatment of iadustrial and municipal water suppHes and the use of sodium alumiaate is approved ia the clarification of drinking water. The FDA approves the use of sodium alumiaate ia steam generation systems where the steam contacts food. One early use of sodium alumiaate was ia lime softening processes, where it iacreases the precipitation of ions contributing to hardness and improves suspended soHds removal from the treated water (17). Sodium alumiaate reacts with siHca to leave very low residual concentrations of siHca ia hot process water softeners. Sodium alumiaate is often used with other chemicals such as alum, ferric salts, clays, and polyelectrolytes, as a coagulant aid (18,19). 

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). 

The quahty of feed water required depends on boiler operating pressure, design, heat transfer rates, and steam use. Most boiler systems have sodium zeohte softened or demineralized makeup water. Feed-water hardness usually ranges from 0.01 to 2.0 ppm, but even water of this purity does not provide deposit-free operation. Therefore, good internal boiler water treatment programs are necessary. 

Tetrasodium pyrophosphate [7722-88-5] Na4P20y, is another important primary builder and detergent. In sequestration, it is not quite as effective as sodium tripolyphosphate and its usage in heavy-duty laundry powders has declined in recent years. Functionally, tetrasodium pyrophosphate is both a builder for surfactants (ie, water softener) and alkaH. 

Sodium C rbon te. Sodium carbonate softens water by forming insoluble calcium carbonate with calcium ions in hard water. Carbonate can also reduce calcium levels by ion pairing, although the benefit to detergency is questionable. Buildup of calcium carbonate on machine and fabrics, which can occur with time, is undesirable. Sodium carbonate [497-19-8] does not provide any suspending action. It does, however, provide alkalinity to the wash hquor and is an effective alkah. 

This type of water softener shouldn t be used if you re trying to reduce sodium intake. 

Where water softening is provided and there is no reduction in system water TDS, treatments are primarily based on inorganic corrosion inhibitor blends (nitrite, molybdate, etc.). Under these circumstances, there is no benefit in using an expensive organic oxygen scavenger to keep the TDS level low, and a common chemical such as catalyzed sodium sulfite may be used. 

A sodium ion-exchange water softener is required for all boiler plants operating at an MAWP of over 15 psig. 

Resins containing these functional groups are generally available in one or more forms for example, strong acid cation resin is typically a sulfonated polystyrene type, available either in the hydrogen form (H+ ) or in the sodium form (Na+). The sodium form of this resin is used for water softening. 

Where sodium bicarbonate is present (as when MU water pretreatment includes a water softener), given enough time and temperature it decomposes to form hydrate alkalinity, carbon dioxide, and water ... 

AVT Barg BD BDHR BF BOF BOOM BOP BS W BSI BTA Btu/lb BW BWR BX CA CANDUR CDI CFH CFR CHA CHF CHZ Cl CIP CMC CMC CMC COC All-Volatile treatment bar (pressure), gravity blowdown blowdown and heat recovery system blast furnace basic oxygen furnace boiler build, own, operate, maintain balance of plant basic sediment and water British Standards Institution benzotriazole British thermal unit(s) per pound boiler water boiling water reactor base-exchange water softener cellulose acetate Canadian deuterium reactor continuous deionization critical heat flux Code of Federal Regulations cyclohexylamine critical heat-flux carbohydrazide cast iron boiler clean-in-place carboxymethylcellulose (sodium) carboxy-methylcellulose critical miscelle concentration cycle of concentration... 

Sodium carbonate is used in detergent formulas as a water softener, to lock up calcium and magnesium from the water. Calcium and magnesium would otherwise combine with the soap or detergents and form an insoluble scum that would stick to the clothes and the washing machine. 

Pentasodium pentetate, tetrasodium etidronate, and tetra-sodium EDTA are added as water softeners and to protect the dyes and perfumes from the effects of metal ions in the mixtures. These compounds lock up calcium and magnesium in the water, preventing them from reacting with the soap to form insoluble soap scum. 

Straight-chain detergents don t work in hard water. Phosphates were added to detergents to soften the water, but phosphates are excellent fertilizer for algae in rivers and oceans. The algae blooms deplete the oxygen in the water, which in turn kills fish. Phosphates were replaced with other water softeners such as sodium carbonate and EDTA. 

Scarlet GN, 119. See also FD C Red 4 scopalomine, 178 SD-40, 56, 70, 174 SD alcohol 40-B. See ethanol SDIC. See sodium dichloroisocyanurate seaweed extract. See agar, carrageenan sequestering agents, 19,49-54,242. See also water softeners serine, 123... 

Scale prevention methods include operating at low conversion and chemical pretreatment. Acid injection to convert COs to CO2 is commonly used, but cellulosic membranes require operation at pH 4 to 7 to prevent hydrolysis. Sulfuric acid is commonly used at a dosing of 0.24 mg/L while hydrochloric acid is to be avoided to minimize corrosion. Acid addition will precipitate aluminum hydroxide. Water softening upstream of the RO By using lime and sodium zeolites will precipitate calcium and magnesium hydroxides and entrap some silica. Antisealant compounds such as sodium hexametaphosphate, EDTA, and polymers are also commonly added to encapsulate potential precipitants. Oxidant addition precipitates metal oxides for particle removal (converting soluble ferrous Fe ions to insoluble ferric Fe ions). 

NaCl(s) + X2+(aq) XCl2(aq) + 2Na+(aq) Water softened by this method contains extra sodium ions. Explain why people with hypertension (high blood pressure) should avoid drinking water softened by this type of ion exchange. 

An enormous amount of Na2C03 is produced annually because of its use in glass, laundry products, water softeners, paper, baking soda, and sodium hydroxide by the reaction... 

Some zeolites have the ability to exchange sodium for calcium and thereby function as water softeners by removing Ca2+. After the zeolite has become saturated with Ca2+, it can be renewed by washing it in a concentrated NaCl solution to restore the Na+ ions. Zeolites are also used to prepare ion exchange resins, as molecular sieves and as catalysts. 

Porter-Clark The original name for the cold lime-soda process. A water-softening process using sodium carbonate and calcium hydroxide. It removes the non-carbonate, as well as the bicarbonate, hardness. Developed by J. H. Porter. See Clark. 

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