Water softening can be accomplished through the addition of chemicals that form insoluble precipitates or through ion exchange. On a small scale, chemicals used for softening include ammonia, borax, calcium hydroxide (slaked lime), or tri-sodium phosphate, usually in conjunction with sodium carbonate (soda ash).
What are the chemicals used in water softening?
To remove precipitates, the lime-soda method of water softening must be followed by sedimentation and filtration. Water can be chemically softened on a large scale by adding just enough lime to precipitate the calcium as carbonate and the magnesium as hydroxide, after which sodium carbonate is added to remove the remaining calcium salts.
1-BORAX:Sodium tetra boratedeca-hydrate (Na2B4O7. 10H2O), also known as tincal. Borax, a soft and light, colourless crystalline substance, is used in a variety of applications, including the ceramics industry as a component of glass and pottery glazes, metallurgy as a solvent for metal-oxide slags, welding and soldering as a flux, and agriculture as a fertiliser additive, soap supplement, disinfectant, mouthwash, and a water softener.
2-AMMONIA: Ammonia (NH3) is a colourless, pungent gas that is made up of nitrogen and hydrogen. It is the most basic stable compound of these elements, and it is used as a starting material in the production of many commercially important nitrogen compounds.
Ammonia is used in a variety of metallurgical processes, including the hardening of alloy sheets through nitriding. Ammonia is a convenient portable source of atomic hydrogen for welding because it decomposes easily to yield hydrogen. Furthermore, because ammonia absorbs a significant amount of heat from its surroundings (i.e., one gram of ammonia absorbs 327 calories of heat), it is useful as a coolant in refrigeration and air-conditioning equipment. Finally, one of its minor applications is in the formulation of certain household cleaning agents.
3-CALCIUM HYDROXIDE:Calcium hydroxide (also known as slaked lime) is an inorganic compound with the formula Ca(OH)2. When quicklime (calcium oxide) is mixed or slaked with water, it produces a colourless crystal or white powder. Hydrated lime, caustic lime, builders' lime, slack lime, cal, and pickling lime are all names for it.
Calcium hydroxide is used as a flocculent in water and sewage treatment, which is a significant application. It forms a fluffy charged solid that helps remove smaller particles from water, resulting in a clearer product. The low cost and low toxicity of calcium hydroxide allows for this application. Because it is self-regulating and does not raise the pH too much, it is also used in fresh-water treatment to raise the pH of the water so that pipes do not corrode where the base water is acidic.
It is also used in the production of ammonia gas (NH3) via the reaction:
Ca(OH)2 + 2 NH4Cl → 2 NH3 + CaCl2 + 2 H2O
4-TRISODIUM PHOSPHATE: The inorganic compound tri-sodium phosphate (TSP) has the chemical formula Na3PO4. It is a white, granular or crystalline solid that is highly soluble in water and forms an alkaline solution. TSP is a cleaning agent, a builder, a lubricant, a food additive, a stain remover, and a degreaser. Tri-sodium phosphate is created by neutralising phosphoric acid with sodium carbonate, which results in the formation of disodium hydrogen phosphate. When disodium hydrogen phosphate reacts with sodium hydroxide, tri-sodium phosphate and water are formed as per below equation:
Na2CO3 + H3PO4 → Na2HPO4 + CO2 + H2O
Na2HPO4 + NaOH → Na3PO4 + H2O
Tri-sodium phosphate was once widely used in the formulation of a wide range of consumer-grade soaps and detergents, and it’s most common application has been in cleaning agents. A 1% solution has a pH of 12 (very basic), and it is alkaline enough to saponify grease and oils. TSP, when combined with surfactants, is an excellent cleaning agent for everything from laundry to concrete driveways. Because of its versatility and low manufacturing cost, TSP became the foundation for a plethora of cleaning products sold in the mid-twentieth century.