Water Hardness | Problem Caused by Hard Water in Wet Processing/Dyeing Industry

Hardness of Water:
Hardness is traditionally measured by chemical titration. The hardness of a water sample is reported in milligrams per liter (same as parts per million, ppm) as calcium carbonate (mg/l CaCO3). Calcium carbonate hardness is a general term that indicates the total quantity of divalent salts present and does not specifically identify whether calcium, magnesium and/or some other divalent salt is causing water hardness. Hardness can be a mixture of divalent salts. In theory, it is possible to have water with high hardness that contains no calcium. Calcium is the most important divalent salt in fish culture water.

If hardness in found in water or it must be softening before use in textile processing and this softening is done by two wags.

1. Undergo the hard water in at appropriating process.
2. Treating the hard water by using sequestering agent.

Hardness Scale:
  1. Parts per million (ppm) : parts of the salt present per 106 parts of water in term of CaCO3
  2. 10dh (german) hardness : parts of the salt per 105 parts of water in terms of CaO/10mg of CaO in 1L of water.
  3. 10dh (French) hardness : parts of the salt present per 105 parts of water interns of CaCO3
  4. 10dh (English/british) hardness/clarkscale : the number of grain of salt per gallon of water in terms CaCO3
  5. 10dh (american) haedness : 1mg of CaCO3 in 1L of water. 

Water Hardness PPM Scale
 
Grains Per Gallon
Milligrams Per Liter (mg/L)or Parts Per Million (ppm)
Classification
less than 1.0
less than 17.1
Soft
1.0 – 3.5
17.1 – 60
Slightly Hard
3.5 – 7.0
60 – 120
Moderately Hard
7.0 – 10.5
120 – 180
Hard
over 10.5
over 180
Very Hard

Relation Between Different Hardness Scales:

Unit of water hardness
Mg/l on ppm of CaCO3
1 British degree
14.3
1 American degree
17.2
1 French degree
10.0
1 Garman degree
17.9
1 mmol/l
100

Reasons of Rater Hardness:
The hardness of water is mainly due to the presence of soluble salt of Co and mg in the sample of water. Such soluble salt are chlorite, nitrites, sulphates and bicarbonate of these metal heavy metal like Fe and Al also can tribute in the hardness of water.

Type of Water Hardness:

1. Temporary hardness : 
When only bicarbonate salt of Ca and Mg are present in HO the hardness is called temporary hardness or bicarbonate hardness. This hardness is called temporary bicarbonate hardness because it disappears on boiling. When water is boil. The bicarbonate decomposed with liberation of insoluble carbonates which are re-formed.

2. Permanent Hardness:
When sulphate chlorite and nitrate salt of Co and Mg are present in H2O the hardness is called permanent hardness. Permanent hardness cannot removed by boiling because these salt are not precipitated when the water is boiled but remain in solution. Due to the presence soluble salt of Ca and Mg. Sope cannot formed foam or lather.

Gridding of water hardness/classification of water according to water hardness:


Description
m.mol/l
PPM
Very soft
0-0.7
0-70
Soft
0.7-1.4
70-140
Mild
1.4-2.1
140-210
Fairly mild
2.1-3.2
210-320
Herd
3.2-5.3
320-530
Very hard
5.3
530

Consequences of using hard water/problem caused by hard water in wet processing:
  1. Precipitation of soaps.
  2. Redeposition of dirt and insoluble soaps on fabric being washed. This can caused yellowing and lead to unlevel dyeing and poor handling.
  3. Precipitation of same dyes as Ca and Mg salt react with them.
  4. Seale formation on equipment and in boilers and pipelines.
  5. Reduction in activity of enzyme used for Sdeslging.
  6. Decreased solubility of sizing agent.
  7. Coagulation of some types of printing paste.
  8. In compatibility with chemical in finishing recipes.
  9. Decomposition of belching bath.
  10. In mercerigation form insoluble melt oxide and reduce absorbency and lusture .
ETHYLENE DIAMINE TETRA ACETIC ACID (EDTA) :


This scale loosely attach with pipeline removal by brushing:


Scald thickness
Heat lass
1mm
10%
3mm
17%
5mm
22%

Required quality to a boiler feed water:


Properties
Acceptable limit
Residual hardness
<10 ppm
Oxygen
<0.2 mg/l
Temporary CO2
0 mg/l
Permanent CO2
<25 mg/l
Fe
<0.05 mg/l
Cu
<0.01 mg/l
PH
8-9
Temperature
>900C

Methods of Water Softening:
  1. Lime-soda process
  2. Base-exchange process
  3. Demineralization process
1 . Lime-soda Process:


2 .Base Exchange Process:
Base exchange complex.
Zeolites sodium alumina silicate/NaAlSiO4.3H2O

Temporary hardness:

Ca(HCO3)2+2Na-permutit Ca-permutit↓+ 2NaHCO3↓

Permanent hardness:

NaSO4+Na-permutit Ca- permutit↓+ NaSO4
NaSO4+Na-permutit Mg-permutit↓+NaSO4
MgCl2+ Na-permutit Mg-permutit↓+2NaCl

3 . Demineralization Process:
Ion exchange resin.
a. Cation exchanger
b. Anion exchanger

This reagent can remove all the mineral salt to complete the Demineralization of hard water.

Sequestering Agent:
A chemical capable of reacting with metal ions so that they become a part of complex anion. The principle is use to extract Ca and Mg ions from hard water , Fe (11). Copper ions form peroxide bleach liqueur and uerious metal ions from dye bath. by for miny a soluble complex in which the metal is held in a non-ioningation from for example.

Sodium tetra metaphosphate → Na4P4O12
Sodium hexa metaphosphate → Na6P6O12

Author of This Article:
Mohebul Hasan
Green University of Bangladesh
Mobile: +8801715858015
Email: sajrul96@gmail.com

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