Softening, of water

It is not always necessary for the resin to be in the hydrogen form for adsorption of cations, especiaHy if a change in the pH of the Hquid phase is to be avoided (see also Hydrogen-ION activity). Eor example, softening of water, both in homes and at industrial sites, is practiced by using the resin in the form. 

The most important applications of ion exchange are the softening of water and the deionisation of water. 

Determine the amount of water to be treated per cycle and the amount of hardness to be removed. Softening of water requires use of a cation-exchange resin operated in sodium form to exchange divalent hardness cations for sodium regenerated with aqueous sodium chloride solution. Total amount of water to be treated is (100 gal/min)(60 min/h)(8 h/cycle) = 48,000 gal/cycle (182 m3/ cycle). 

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. 

Write the fundamental chemical equations for the softening of water by a zeolite, and the regeneration of the zeolite. 

Quantitywise the next most important application is for food conservation in the sectors of meat, dairy products and margarine. Of the numerous other uses the dye, detergent and leather industries and for softening of water (ion exchanger) are worthy of mention. 

Chemicals used for the softening of water, or for disinfection, have an influence on tastes and odors, being detrimental in some cases and beneficial in others. The primary reason for using chlorine in water supplies is for disinfection, but incidental benefits on tastes and odors have led to the study of the use of it for this purpose. Similar studies have been made of ozone, chlorine dioxide, and permanganate, and successful applications of these agents have resulted. The utility of these chemical treatments, however, is restricted to a limited number of taste- and odor-bearing compounds, and even in such cases, successful reduction of odor requires careful control of all conditions. 

A principal use of the process of ion exchange is to remove or concentrate ions in solution, usually inorganic ions. An example is the softening of water which involves the removal of calcium ions, which form an insoluble salt with... 

The conventional ion exchange process for the softening of water may be represented by the chemical equation... 

Aluminum and ferrosilicon anodes are suitable for the protection of hot water tanks. The use of aluminum anodes in a hot water apparatus has additional effects, an indirect protective action on subsequent piping, since a protective film (1-1.5 mm thick) is built up by anode-formed aluminum oxide hydrates. In addition to alkalization at the cathode, a shift in the calcium carbonate (CaCOj)-CO2 equilibrium leads to partial softening of water, with CaC03 being deposited at the cathode. 

The cation exchange properties of zeolites give rise to their largest single application in terms of volume, as detergent additives. They are used for the softening of water i.e. the replacement of calcium ions by sodium ions) in domestic... 

This exchange process is apphed for the softening of water. The reaction takes place until the capacity of the ion exchange solid material is used or the total number of attached ions is replaced by ions provided by the solution according to equilibrium. Note tliat this capacity is constant and does not depend on the concentration of the solution - in contrary to adsorption. 

A zeolite is a mineral containing sodium ions, which can be replaced by calcium ions. It can be regenerated by passing a concentrated solution of sodium chloride over it. Write the fundamental chemical equations for the softening of water by zeolite and for the regeneration of the zeolite. 

The ability of the polyphosphates to form water-soluble complexes with calcium has been known for a long time. The phenomenon of binding alkaline earth ions in soluble complexes, and thus preventing the formation of undesirable precipitates, is generally called sequestration. This was the subject of earlier patent literature. The role of these calcium-polyphosphate complexes in softening of water was described in Chapter 23 of the book edited by Bailar. The complexing of a number of metal ions with the various phosphates was reviewed in detail in 1958. ... 

---