Sodium softeners strongly acidic cation

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. 

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 ... 

Shown in Fig. 20 is a scheme for countercurrent softening of water [9,42]. Divalent cations, Me, are sorbed from strongly acidic cation exchanger in the Na form. Ion exchanger regeneration is then affected with the concentrated solution of NaCl softened earlier by the replacement of all multicharged cations with sodium. 

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