Hardness of Water in Textile Industry: Types, Reasons and Consequences

Last Updated on 15/01/2022

Water Hardness in Textile: Types, Reasons and Consequences

Mohebul Hasan
Dept. of Textile Engineering
Green University of Bangladesh
Email: sajrul96@gmail.com

 

Water Hardness in Textile:
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.

water hardness in textile

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. 1°dh (German) hardness: parts of the salt per 105 parts of water in terms of CaO/10mg of CaO in 1L of water.
  3. 1°dh (French) hardness: parts of the salt present per 105 parts of water interns of CaCO3
  4. 1°dh (English/British) hardness/Clark scale: the number of grain of salt per gallon of water in terms CaCO3
  5. 1°dh (American) hardness: 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 German degree 17.9
1 mmol/L 100

Reasons of Water Hardness in Textile Industry:
Water for a textile plant may come from various sources. These include surface water from rivers and lakes, and subterranean water from wells. The water may be obtained directly from the source or from the local municipality. Natural and pretreated water may contain a variety of chemical species that can influence textile wet processing in general, and dyeing in particular.

The various salts present in water depend on the geological formations through which the water has flowed. These salts are mainly the carbonates (CO32–), hydrogencarbonates (HCO3, more commonly named bicarbonates), sulphates (SO42–) and chlorides (Cl) of calcium (Ca2+), magnesium (Mg2+) and sodium (Na+). Although calcium and magnesium carbonates in limestone are relatively insoluble, the action of dissolved carbon dioxide in rain water can leach them out in the form of the more soluble bicarbonates (Equation 1).

Hard water contains calcium and magnesium ions and gives an immediate precipitate with soap. Soap is a water-soluble sodium salt of a high molecular weight carboxylic acid, such as stearic acid. Its calcium and magnesium salts are much less soluble and give a gummy precipitate with a soap solution in hard water (Equation 2). When this happens, the cleaning efficiency of the soap decreases dramatically. The dirt in suspension, as well as the precipitated calcium and magnesium soaps, can deposit back onto the material being washed. This gives a dingy fabric with a poor handle that will be difficult to dye in a level shade.

CaCO3(s) + CO2(aq) + H2O(l)  → Ca(HCO3)2(aq)   —— (1)

2CH3(CH2)16CO2 Na+ (aq) + Ca2+ (aq) → (CH3(CH2)16CO2 )2Ca2+ (s) + 2Na+ (aq)   —– (2)

The hardness of water is mainly due to the presence of soluble salt of Ca 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.

Types of Water Hardness:
Water hardness are 2 types; temporary hardness and permanent hardness.

1. Temporary hardness: 
When only bicarbonate salt of Ca and Mg are present in H2O 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.

Ca(HCO3)2 → CaCO3↓ + H2O
CaCO3 → CaO↓ + CO2

Temporary hardness:

  • Mg(HCO3)2
  • Fe(HCO3)2
  • Ca(HCO3)2

2. Permanent hardness:
When sulphate chlorite and nitrate salt of Ca 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 soap cannot formed foam or lather.

2C17H35COONa + COCl2 → 2C17H35COOCa + 2NaCl

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 in Textile Wet Processing:

  1. Precipitation of soaps;
  2. Redeposition of dirt and insoluble soaps on the fabric being washed – this can cause yellowing and lead to unlevel dyeing and a poor handle;
  3. Precipitation of some dyes as calcium or magnesium salts;
  4. Scale formation on equipment and in boilers and pipelines;
  5. Reduction of the activity of the enzymes used in desizing;
  6. Decreased solubility of sizing agents;
  7. Coagulation of some types of print pastes;
  8. Incompatibility with chemicals in finishing recipes.

Ethylenediaminetetraacetic Acid (EDTA):

Ethylene Diamine Tetra Acetic Acid (EDTA)
Fig: Structure of Ethylenediaminetetraacetic Acid (EDTA)

Problem of hard water in boiler and pipelines:

Ca(HCO3)2 → CaCO3↓ + H2O + CO2
Mg(HCO3)2 → MgCO3↓ + H2O + CO2

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 >90°C

Methods of Water Softening:

  1. Lime-soda process
  2. Base-exchange process
  3. Demineralization process

1. Lime-soda Process:

Ca(OH)2 → Hydrated lime
NaCO3 → Soda ash

a) Temporary hardness:

Ca(HCO3)2 + Ca(OH)2 → 2CaCO3↓+ 2H2O
Mg(HCO3)2+Ca(OH)2 → MgCO3+CaCO3↓+H2O
MgCO3+Ca(OH)2 → Mg(OH)2↓+CaCO3

b) Permanent hardness:

MgCl2+ Ca(OH)2 → Mg(OH)2↓+CaCl2
CaSO4+NaCO3 → CaCO3↓+Na2SO4
CaCl2+Na2CO3 → CaCO3↓+2NaCl

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

a) Temporary hardness:
Ca(HCO3)2 + 2Na-permutit Ca-permutit↓ + 2NaHCO3

b) 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. Copper ions form peroxide bleach liquor and various metal ions from dye bath. by for many a soluble complex in which the metal is held in a non-ioninzation from for example.

Sodium tetra metaphosphate → Na4P4O12
Sodium hexa metaphosphate → Na6P6O12

You may also like:

  1. Water Hardness Test Method
  2. Water Management in Textile Industry – An Overview
  3. Water Consumption in Textile Processing Industry
  4. What is Sequestering Agent? | Types, Mechanism and Uses of Sequestering Agents

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