Unit 1 water and its treatment Topic:-Difference between hard water and soft water

Hardwater	Softwater
1.Water which does not form lather with soap is called Hard water	1.Water which forms lather easily with soap is called soft water
2.Hardwater has dissolved salts of calcium and magnesium	2.Softwater does not have dissolved salts of ca and mg
3.Because of presence of impurities,boiling temperature,of water is increased,because of which a lot of time go water for heating	3.Less time and fuel is consumed for heating softwater
4.Because of presence of impurities lot of soap is consumed by hardwater	4.Softwater consumes less soap for washing and bathing purposes

Methods to remove permanent hardness There are three methods to remove permanent hardness:- Lime-Soda The method involves the treatment of water with lime[Ca(OH)2] and soda [Na2(CO)3] which reasults in the formation of insoluble precipitates of Calcium and Magnesium which can be removed by filtration.

(A)Cold Lime-Soda Process In this method, water to be softened is treated with calculated quantities of lime and soda at room temperature. Small amounts of a coagulant such as alum, aluminium sulphate, sodium aluminate etc., are also added. The coagulant helps the finely divided precipitate formed in the process to flocculate. Sodium aluminate also helps in the removal of silica and oil present in water.

(B)Hot Lime-Soda Process In this process, water is treated with the softening chemicals at a temperature of 94°-100°C. Since the process is carried out at a temperature close to the boiling point of the solution, the reaction proceeds faster and the softening capacity of the process increases several times. At this temperature, the viscosity of water is much less than that at room temperature. Hence, rate of aggregation of particles increases and there is hardly any need of adding any coagulant. Moreover, the dissolved gases also escape to some extent at the temperature of the process.

Zeolite or Permutit processThis is a very effective method. Chemical formula of zeolite is:-Na₂O·Al₂O₃·xSiO₂·yH₂O;where x=2-10,y=2-6 Hydrated sodium alumino silicate or sodium zeolite. Permanent hardness of water can be removed by permutit process. Permutite is an artifical zeolite used for softening of water. Through ion-exchange process, here cation-anion exchange chamber is used to obtain pure water. In calgon's process sodium hexa meta phosphate is used to soften the water.

Ion exchange or de-ionization processIon-exchange or Deionization or Demineralization Process - Recently ion-exchange resins have been used to remove all minerals from water. It is a process by which ions held on a porous, essentially insoluble solid are exchanged for ions in solution that is brought in contact with it. Ion-exchange Resin – An ion-exchange resin is a crosslinked organic polymer network having some ionisable group. It may be of two types depending upon the nature of the ionizable group.

(i) Cation Exchange Resin or Cation Exchanger - Such resins have - SO₃H, -- COOH or -OH (phenolic) group as the ionizable group. Since these resins exchange the cationic portion of minerals by their hydrogen atom, they are known as cation exchangers.

(ii) Anion Exchange Resin or Anion Exchanger – These resins have -NH₂, -NHCH₃, -N(CH₃)₂ or -OH group. They exchange the anionic portion of the minerals and they are known as anion exchanger. Uses of Ion-exchange Resin – Water treatment by ion-exchange resin includes softening deionization and de-alkalization of water. Therefore, hard water can be converted into soft water by making use of ion-exchange resins.