This is about water hardness a chapter of chemistry

1. Dr. Rekha Trivedi

2. Water Hardness and removal methods
Main content :
Industrial Application of water,
Definition of
Hardness,
Types of hardness,
Causes of hardness,
Determination and removal of
hardness

3. Water is used in various industries
• 1. Textile 2.Laundries
• 3.Paper
• 4.Bevarages
• 5.Sugar 6.In Boilers
• 7.Cooking
• 8.Dairies and pharmaceutical industries

4. Impurities of water
• Suspended impurities : Give turbidity colour
and odour to water (organic and Inorganic).
• Colloidal impurities: Finely divided silica and
clay.
• Dissolved Impurities: Like carbonates,
bicarbonates, chlorides and sulphates of
calcium and magnesium. Gases like O2 and CO2
etc.
• Microorganism: Include Bacteria fungi and
algae.

5. Impurities that causes boiler Problems
• Alkalinity: Due to OH-
,CO3
-2
and HCO3
-
• Hardness: The property of water which
prevents the lathering of soap.
• Types of hardness: Temporary and permanent
• Temporary or bicarbonate hardness: due to
the presence of HCO3
-
of Ca and Mg.
• Permanent: due to the presence of Chlorides
and sulphates of Ca and Mg.

6. Scum formation
• Soap scum or lime soap is the white solid composed of
calcium stearate, magnesium stearate, and similar
alkali metal derivatives of fatty acids. These materials
result from the addition of soap and other anionic
surfactants to hard water. Hard water contains calcium
and magnesium ions, which react with the surfactant
anion to give these metallic or lime soaps.
• 2 C17H35COO−Na+ + Ca2+ →(C17H35COO)2Ca + 2Na+
• In this reaction, the sodium cation in soap is replaced
by calcium to form insoluble calcium stearate (scum).

7. Hardness can be measured in
ppm, mg/L,°Fr, °Cl
1ppm=1mg/L=0.1 °Fr=0.07 °Cl
1. Calculation of hardness by using Chemical
equivalent in terms of CaCO3.
2. Classification of water hardness
Classifi
cation
Soft Slightly
hard
Mid hard Hard Very Hard
ppm/
mg/L
0-17 17-60 60-120 120-
180
180 and
above

8. Determination of Hardness
1. Temporary hardness: By acid base titration
using HCl and methyl orange.
2. Total, temporary and Permanent hardness:
By Complex metric titration using EBT, buffer
solution and EDTA.

9. Removal of hardness
1.By external treatment
 Lime Soda method
 Zeolite bed process
 Ion exchanger method
2.Internal treatment
 Colloidal conditioning
 Phosphate conditioning
 Calgon conditioning
 Carbonate conditioning

10. Cold lime soda and hot lime soda method
• Cold lime soda process

11. In Cold lime Soda process
• Coagulant is necessary because at room
temperature precipitate is finally divided. But
do not settle easily & cannot easily filtered.
• NaAlO2+2H2O−
−→NaOH+Al(OH)3NaAlO2+2H2O−
−→NaOH+Al(OH)3
• Mechanical stirrer is used to increase mixing &
rate of precipitate formation

12. Hot lime soda method

13. Hot lime soda method
advantages
• It is carried out at temperature 80−150 c80−150 c. It is used when small quantity of
∘ ∘
water is required. But it takes place at low hardness ie. 15-25 ppm. Due to hot condition-
• i) Reactions take place faster.
• ii) No need of coagulant
• iii) Hardness is low
• iv) Dissolved gases are expelled out at high temperature
• Advantages:- i) It is more economical
• ii) Less amount of coagulant is required.
• iii) It increases pH value, there by corrosion is reduced.
• iv) Also Fe, Mn & minerals are reduced.
• v) Pathogenic bacteria are reduced.
• Disadvantages:-
• i) The hardness is 50-60 ppm by cold process & about 15-30 ppm by hot process
• ii) Careful operation & skilled supervision are required.
• iii) Disposal of large quantity of sludge formed during process is a problem.

14. Zeolite bed process
• Reaction of hardness and zeolite

15. Zeolite or permutit process
• Zeolites are naturally occuring hydrated alumino
silicate minerals like: Na2O.Al2O3.xSiO2.yH2O
where (x=2-10 and y=2-6)
• Two types of Zeolite: natural and Synthetic
• Principle- Zeolite is micro-porous mineral which is
used as catalyst in many industrial purposes such
as water purification and air purification.

16. Process
• Softening and regeneration reactions- For softening of
water by zeolite process, hard water is percolated at a
specified rate through a bed of zeolite.
• Zeolite holds sodium ion loosely and can be represented
as Na2Z, where Z represents insoluble radical frame
work. When the water passes through the zeolite the
hardness causing ions (Ca+2,Mg+2 etc.) are retained by
the zeolite as CaZ and MgZ respectively, while the
outgoing water contains equivalent amount of sodium
salts. The block diagram and chemical reactions taking
place in zeolite softener are:

17. Regeneration of zeolite Bed
• After some time, when the zeolite is completely
changed into calcium and magnesium zeolites,
then it gets exhausted (saturated
with Ca+2Ca+2 and Mg+2Mg+2 ions) and it
ceases to soften water. It can be regenerated and
reused by treating it with a 10% brine (sodium
chloride) solution. Regeneration reactions are
• CaZ+2NaCl→Na2Z+CaCl2
• MgZ+2NaCl→Na2Z+MgCl2

18. Advantages of zeolite process
• Advantages- It removes the hardness almost
completely (about 10 ppm hardness only). The
process automatically adjust itself for variation
in hardness of incoming water. This process
does not involve any type of precipitation,
thus, no problem of sludge formation occurs.

19. Ion exchanger method

20. Ion exchanger Process
• Ion-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.

21. Types of Ion exchanger
• (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.

22. Ion exchanger reaction
• Process – In this process first we passed hard
water through cation exchange column, which
removes all the cations (like Ca+2
, Mg+2
etc.)
from it and equivalent amount of H+ ions are
released from this column to water.
Thus,
2RH+
+ Ca+2
-> R2Ca+2 + 2H+
2RH+
+ Mg+2
-> R2Mg+2
+ 2H+

23. Ion exchanger reaction
• After this process, hard water is passed through anion exchange
column, which removes all the anions (like SO4
-2
, Cl-
etc.) from it, and
equivalent amount of OH-
ions are released from this column to
water. Thus,
R'OH-2
+Cl-2
-> R'Cl-
+ OH-
2R'OH-
+ SO2-
4 -> R'
2 SO2-
4 + 2OH-
2R'OH-
+ CO2-
3 -> R'
2 CO2-
3 + 2OH-
H+
and OH -
ions get combined to produce water molecule
H+
+ OH-
+ H2O
The water coming out from the exchanger is free from cations as well
as anions. Ion-free water is known as a deionized or demineralized
water.

24. sstc 24
•Thank You