Zeolite softening

Aikaiinity Bicarbonate (HCOs" ), carbonate (COs , and hydroxyl (OH ), expressed as CaCOs Foaming and carryover of solids with steam embrittlement of boiler steel bicarbonate and carbonate produce CO2 in steam, a source of corrosion Lime and lime-soda softening, acid treatment, hydrogen zeolite softening, demineralization, dealkalization by anion exchange, distillation, degasifying... 

The degree of concentration that can be achieved by RO may be limited by the precipitation of soluble salts and the resultant scaling of membranes. The most troublesome precipitate is calcium sulfate. The addition of polyphosphates to the influent will inhibit calcium sulfate scale formation, however, and precipitation of many of the other salts, such as calcium carbonate, can be prevented by pretreating the feed either with acid or zeolite softeners, depending on the membrane material. 

External treatment also meant the removal of calcium and magnesium hardness by zeolite softening using either a variety of silcate-based, natural zeolites [such as analcite, (Na AljS O, 2 2H20)], or manufactured carbon zeolites. 

Zeolite softeners were limited in application because of their potential for rapid fouling by ferric hydroxide or calcium carbonate, and a narrow operating pH range of 5.8 to 8.3 was therefore preferred to minimize this problem. 

Hoi-Lime Zeolite Softening. In this process hydrated lime is employed to react with the bicarbonate alkalinity of the raw water. The precipitate is calcium carbonate and is filtered from the solution. To reduce silica, the natural magnesium of the raw supply can be precipitated as magnesium hydroxide, which acts as a natural absorbent fur silica. These reactions are carried out in a vat or tank that is located just head of the zeolite softener tank. The effluent from this tank is filtered and then introduced into the zeolite softener. There is always some residual hardness leakage from the hot-process softener to be removed in the final zeolite process. The hot lime process operates at about 220T (I04°C). At this temperature the potential for the exchange of sodium for hardness ions is greater than at ambient temperature, and the result is a lower hardness effluent than is achieved at ambient temperatures. This system is shown schematically in Fig. 2. 

ZEOLITE SOFTENING (Boiler Water). See Water Treatment... 

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 ... 

Zcoclean. [Western Water Management] Zeolite softener resin cleaner. 

SODIUM ZEOLITE SOFTENING - The process of removing scale forming ions of calcium and magnesium and replacing them with the equivalent amount of sodium ions. 

ZEOLITE SOFTENING - Refers to the process, where zeolite chemicals are capable to exchange ions with the hardness causing impurities of the water. 

Also, according to Charles et al. (1985), specific oilfield waterflood operations have used mechanical and chemical technologies in an attempt to remove hydrogen sulfide from active waters. Some mechanical methods involve aeration, anion exchange resins, degassing, distillation, steam reforming, and zeolite softeners. Most of these methods are viewed currently as being expensive or impractical. 

Weston, R.S. (1937). Treating highly colored water. Water Works Engineering 90(3) 388-391. Weston, R.S. (1941). 11-year operating experiences with zeolite softening plant. Water Works Engineering 94(2) 179-180. P... 

Continuous deionization of the storage basin water softens the water, as it removes the calcium bicarbonate and other ions contributing to hardness. Godard, however, found that zeolite softened, deionized water influenced the pitting behaviour of aluminium to the same extent as untreated water [2.6]. 

Alkalinity Bicarbonate (HCOji, carbonate expressed as CaCOj Foaming and carry over of solids with steam. Embrittlement of boiler steel. Bicarbonate and carbonate produce CO, in steam, a source of corrosion in condensate lines. Lime and lime soda softening. Acid treatment. Hydrogen zeolite softening. Demineralization. Dealkalization by anion exchange. 

A number of lime-softening treatments were used in the past, but these have given way to more sophisticated treatments. Probably the most common for boilers up to 2.8 to 4.0 MPa is Zeolite softening. In this treatment, a sodium salt of a long-chain polymeric organic molecule comprises the ion exchange bed. As the feedwater passes... 

Another modification of the process hot-lime zeolite softening process (Fig. 11.12) is used to increase silica reduction and carried out at 98°C. Calcium carbonate is filtered from the solution. To reduce silica. Mg is precipitated as Mg(OH)z which acts as an absorbent for silica. The residual hardness is removed by sodium zeolite softener. The increased temperature improves the potential of the softener to exchange sodium for hardness ions. 

In a properly designed system there is little opportunity for scale formation, because there is no evaporation within the system and thus little makeup water is needed. Therefore, sohds in makeup water do not concentrate, and saturation values are not exceeded. However, when designing such a system, it is a good practice to include the use of a pretreatment, such as zeolite softening. 

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