Methods to remove Hardness of Water

Excessive concentration of minerals like calcium and magnesium in groundwater that sips through layers of limestone or chalk results in temporary hardness. Most commonly the multivalent cations – Ca2+ and Mg2+ get mixed in water when a natural source of water comes in contact with minerals like calcite, gypsum, dolomite, etc. Temporary hardness of water can be removed by boiling as they do not have traces of sulfates and chlorides of magnesium and calcium. These substances do not precipitate with an increase in temperature. In addition to the application of a water softener, an ion-exchange column for demineralizing water also proves to be an effective solution to remove permanent hardness. 

How to Remove the Hardness of Water ?

There are several standard methods to remove the hardness of the water. 

Temporary hard water devoid of calcium and magnesium sulfate compounds can be processed by boiling. When the water is boiled the dissolved bicarbonate [Ca(HCO3)2] gets transformed into an insoluble carbonate – CaCO3 that settles at the bottom and can be eliminated by filtering in a later stage. The same principle is followed for magnesium bicarbonate [Mg(HCO3)2]. 

Also, the temporary hardness of water can be removed by following Clark’s cold lime softening method. Just like the boiling method, this process also focuses on converting the bicarbonate compound into a corresponding carbonate compound but with the use of slaked lime or calcium hydroxide. This softening method uses lime to react with the carbonic acid to produce precipitates of insoluble carbonates. 

The balanced equilibrium chemical equations can be expressed as:

2Ca(OH)2 + Mg(HCO3)2 = Mg(OH)2- + 2 CaCO3- +2H2O

Ca(OH)2 + Ca(HCO3)2 = 2H2O + 2CaCO3-  

Untreated water exhibiting about 110 ppm hardness can be softened up to 35 ppm of calcium or about 70 ppm magnesium by using Clark’s reagent. 

Permanent hardness in water is more resilient. We perform certain elaborate methods to remove the hardness of water:

Permutit Process: Zeolites are aluminosilicate crystalline compounds that are reliable concerning ion exchange. In addition to numerous benefits, they can purify water and air. Its artificial form has been introduced and marketed as a permutit. Chemical nomenclature follows the name as sodium aluminum orthosilicate [Na2Al2Si2O8.XH2O]. 

Permanent hard water with excessive concentration of calcium and magnesium multivalent cations is passed through the chunks of sodium permutit in a tall cylindrical vessel. The water gradually softens by eliminating the metal ions. 

Due to repeated usage, a calcium chloride layer is deposited over the permutit that can be removed by a brine solution. 

The permanent hardness of water can be removed by Calgon’s method. Here, the calcium and magnesium bivalent ions (Ca2+ and Mg2+) are adsorbed by the sodium ions displaced from the Calgon anion. After removal, the cations formulate a complex compound with the commercially available sodium-hexa-meta-phosphate [NaPO3]6. This method is executed in laundries to ensure lather formation in water treated with a soapy solution. 

Methods to remove the hardness of water by ion exchange involve a physical polymer medium that consists of many microbeads. Similarly charged ions replace the metallic cations to get rid of the hardness by cooperating with the installed functional groups which attract oppositely charged particles. With repeated use, the polymer or resin gets exhausted and regeneration is required before further operation. Based on the resin type, caustic soda, salt, or acid is used which discharges the contaminant ions through an effluent stream. 

Through discussion of the above procedures, we are now familiar with the ideas involving how to remove the hardness of the water. 

Problems arising from Usage of Hard Water

• Although the high concentration of calcium and magnesium chlorides, bicarbonates, and sulfates do not pose detrimental effects on human health, they emit an awful taste or smell. Thus it is surely not desirable to consume such water. 

• Cleaning of clothes using surfactants or daily activities like washing hands and bathing with soap is done to remove dust and germs. If one uses hard water for this purpose, lather formation is disturbed which hinders proper cleansing. 

• If dishes are washed using hard water, it creates a rigid film of dotted discharge over time. 

• In course of time, hard water leaves stains in the bodies of metallic taps and other bathroom fittings which creates a dull appearance. The white toilet seats and sinks also tend to turn brown due to the permanent hardness of the water. 

• A temperature rise promotes limescale accumulation in bathroom fixtures and hot water appliances. In this way, hard water reduces the efficiency of water geysers by making them less energy-efficient. The owner can face pipeline leakage problems arising from corrosion – a common phenomenon caused by hard water. 

Conclusion 

Hard water portrays an array of problems in daily human activities. The hardness level depends on the presence of calcium and magnesium chlorides, bicarbonates, and sulfates in water.  Various processes have been standardized in the industry to remove the permanent hardness of the water. Some include the ion exchange method while a few plants incorporate thermal processing.