Analysis of Water Softening

Related information:

• Industrial water softener information
• Industrial water calculators
• Industrial reverse osmosis information

Ion Exchange Water Softening vs. Lime Softening

Advantages

Disadvantages

Process

Ion-exchange water softening

What is Ion Exchange?

When minerals dissolve in water they form electrically charged particles called ions. Calcium carbonate, for example, forms a calcium ion with plus charges (a cation) and a carbonate ion with negative charges (an anion). Certain natural and synthetic materials have the ability to remove mineral ions from water in exchange for others. For example, in passing water through a simple cation exchange softener all of calcium and magnesium ions are removed and replaced with sodium ions. Ion exchange materials usually are provided in the form of small beads or crystals which compose a bed several feet deep through which the water is passed.

Types of Ion Exchange Materials

• Ion exchange materials are basically of two types: cation and anion exchangers.

• Cation exchange materials react only with positively charged ions such as Ca++ and Mh++.

• Anion exchanger materials react only with the negatively charged ions such as carbonate (CO3-) and sulphate (SO4-).

• Zeolite materials are cation exchangers composed chiefly of sodium, aluminum and silica.

• There are several other types of cation exchange materials of an organic or resinous nature.

• The anion materials are usually organic in nature and are of two basic types: weak base and strong base types.

• Weak base exchangers don’t take out carbon dioxide or silica (actually carbonic acid and silica acid) but remove strong acid anions by a process that is more like adsorption than ion exchange.

• Strong base anion exchangers on the other hand can reduce silica and carbon dioxide to very low values.

• Cation exchangers usually poles which settle out readily. In these cases clarification equipment merely involves the use of settling basins use either a sodium or hydrogen cycle. That is, they may be designed to replace all cations in the water with either sodium or hydrogen.

• Strong base anion exchangers are generally operated on a hydroxide weak base on a carbonate cycle. Chloride anion exchange is also used in some processes.

Source

http://www.hamadaboiler.com/en/water/qa.htm#46

http://www.thewatertreatments.com/water-softener/ion-exchange-softening

Lime-soda softening

What are the Various Methods of Lime-Soda Softening?

The two general types are intermittent (batch type) and continuous. The older method of intermittent softening consists of mixing the chemicals with the water in a tank, allowing time for reaction and settling of the sludge, and drawing off the clear water. The more modern method of continuous lime-soda softening involves the use of specially compartmented tanks with provisions for

1. Proportioning chemicals continuously to the incoming water
2. Retention time for chemical reactions and settling of sludge, and
3. Continuous draw-off of softened water. Lime-soda softening may also be classified as hot or cold, depending on the temperature of the water. Hot process softeners increase the rate of chemical reactions and give better quality water.

Why are Coagulants Used in the Lime-Soda Process?

Just as coagulants are used for removing suspended matter in clarification processes, they serve to clump together precipitates in the softening process. Coagulants can speed up settling of sludge as much as 25 – 50 per cent. Sodium aluminate has a special advantage as a coagulant in lime-soda softening since unlike most other coagulants it is alkaline and also contributes to the softening reactions’, particularly in reducing magnesium. Effective use of coagulants helps remove silica in the softening process. Silica tends to be absorbed in the floc produced by coagulation of sludge.

Source: http://www.hamadaboiler.com/en/water/qa.htm#46

Initial cost & operating costs

Ion-exchange water softening

• Compared with lime-soda ash softening, ion-exchange has certain advantages.

• It is compact and has a low capital cost.

• The chemicals used are safer for the operator to handle and operation is much easier.

• The ion exchange process is more cost-effective when treating ground waters, as they are typically a non-carbonate form of water hardness.

Approximate Costs of Lime Softening

Also see these industrial and commercial water softeners and reverse osmosis (RO) calculators, as you may find them useful:

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