- 1.Soda Lime Process
- 2.Base exchange process ( Permuted )
- 4.Soda Alum
- 6.Chelation on sequestration.
Soda Lime Process: In this process, Hydrated lime and sodium carbonate are added to precipitate calcium and magnesium ions as compounds of low solubility.
For temporary hardness,
Ca(HCO3)2+Ca(OH)2 ———–à 2CaCO3↓+2H2O
Mg(HCO3)+2Ca(OH)2 ———à 2CaCO3↓+Mg(OH)2+2H2O
For Permanent Hardness,
CaSO4+NaCO3 ————–à CaCO3↓+ Na2SO4
MgSO4+NaCO3 ————–à MgCO3↓+ Na2SO4
MgCl2+Ca(OH)2 ————-à CaCl2↓+ Mg(OH)2↓
CaCl2+NaCO3 —————à CaCO3↓ + NaCl
The main parts of the process are
- Reagent tanks (Soda lime+Coagulants)
- Reaction tank
- Soft water storage tank
The soda lime and coagulants are intered in the reagent tank. Predetermined amount of hard water is pumped into the reaction at the time of intering of reagents. The agitation is brought about by a large propeller. The agitation is increased to get more amount of PPTI steam is passed through the sideway pipe to increase the temp. of the mixer. When the precipitation is completed, the water is supplied to the filters to remove CaCO3 and then finally to the soft water storage tank.
The rate of precipitation may be increased by:
- By increasing of temp. which hasten, crystallization and reduce stability
- By using an excess of reagent and stirring.
- By bringing the water into contact with performed particles of precipitate or grains of sand which can act as nucleus for the precipitation.
Base Exchange Process : This method depends upon the use of zealot or base exchange complexes. The zeolites are hydrated silicates or sodium and alluminium with a general formula…(Na2O)x(AlO3)y(SiO2)z(H2O)n
When zeolites or base exchange complexes are brought in contact with hard water following reaction occur.
For temporary Hardness,
Ca(HCO3)2+Na2O.Z ————-à CaO.Z + Na2CO3 + H2O
Mg(HCO3)2+Na2O.Z ————-à MgO.Z + Na2CO3 + H2O
For Permanent Hardness,
CaSO4 + Na2O.Z —————à CaO.Z + NaSO4
MgSO4 + Na2O.Z ————-à MgO.Z + NaSO4
In where Z is an abbreviation for the Al2O3SiO2H2O part of Zeolite. The soft water obtained from this base exchange process is of 0-20 hardness or levelness. After a long time the whole of the sodium in base exchange substance is replaced by calcium or magnesium, it is said to be exhausted because it will not soften any hard water more.
Then it has to be generated.
Regeneration: CaO.Z+2NaCl ———–à Na2O.Z+CaCl2
The CaCl2 and residual NaCl are washed away and the regenerated Na2O.Z can be used to soften the hard water again.
The zeolites are taken in the vessel as shown in figure with other required substances. When the hard water is passed through the inlet, comes in contact with zeolites, the water softened and soft water is collected from the downward outlet.
When sufficient amount of hard water has passed then the supply of hard water is closed and then flow is reserved and beds of zeolites and other substances are cleansed. Then the cleansed is regenerated by passing 10% NaCl through the zeolites and the zeolites are regenerated again.
- Zeolite softening carried out by passing water from the raw water pump directly through the zeolite to service there by avoiding repumping which is necessary for the soda lime plant.
- The space requirements are small.
- A product of almost zero hardness may be obtained.
- If raw water is high in permanent hardness, zeolite softening may be carried out following a cold lime treatment, since salt use in regeneration is less costly then the soda ash necessary for the soda lime process.
- No objectionable excess of chemicals added.
- There is no sludge to be disposed of demineralization.
Demineralization process: It is modern industrial water softening process. By this process it can be possible remove of hardness well as remove of all dissolve slats, i,e FeCO3, CaCl2
Demineralization process of water softening can be brought about in two ways.
1. 1st step – Hydrogen cation exchange.
2. 2nd step – Anion Exchange.
1st step Hydrogen cation exchanger/ 1st resin bed : In this process, sulphonated resin in hydrogen form is used.
For water softening,
CaCl2+H2R ——————à CaR↓ + H2SO4
(Here resin of hydrated form )
Ca(HCO3)2+H2R —————à CaR↓+2H2O+2CO2
For Regeneration, Done by less then of 2% H2SO4
CaR+H2SO4 ——————à CaSO4 + H2R ( Regenerated Hydrogen Cation Exchanger ) Regeneration is done by Acid
2nd Step Anion Exchanger: Amino resin is used as an anion exchanger and producing HCL is removed.
HCL+HOR1———-à ClR1 ( Soft water ) + H2O ( Resin of Hydroxide Form)
Precipitation regeneration reaction, 1% solution of caustic soda
ClR1+NaOH ————à Na2SO4+HOR2 ( Regenerated resin)
The regeneration is performed by using alkali.