The Harmfulness of Hard Water in Fabric Washing and Treatment Solutions
Release Time:
2016-11-04 20:02
Source:
Jieshi
Currently, most fabric washing in laundries uses water washing methods. In some regions, after washing fabrics with water, spots may appear on the fabric surface, or the originally bright colors become dull and lackluster; the whiteness of white cotton gradually decreases, and the fabric fibers become hard and brittle. Facing these issues in water washing, some washing departments have taken measures such as increasing detergent dosage, intensifying washing force, and extending washing time, but the washing effect on fabrics is still poor. Additionally, after using steam irons for a period, many water scale deposits accumulate at the steam outlet. Why do these situations occur? The answer is that the water used for washing is too hard.
What should be done to achieve the ideal washing effect?
The concept of hard water and soft water and the formation of hard water
1. The concept of hard water and soft water and water hardness
(1) Hard water
Hard water contains a certain amount of carbonates of calcium, magnesium, aluminum, and manganese, as well as bicarbonates, chlorides, sulfates, and nitrates impurities. Since calcium and magnesium salts are widely distributed in nature, they are the main components of hard water.
(2) Soft water
Soft water is relative to hard water; generally, water that has had calcium, magnesium salts, and other substances removed is called soft water.
(3) Water hardness
Total water hardness generally refers to the total concentration of calcium and magnesium ions in water. Calcium and magnesium salts exist in various forms in nature, each with different properties, so there are differences in "hardness." Calcium and magnesium carbonates have low solubility and are unstable in water; they precipitate as water temperature rises. Therefore, the change of calcium and magnesium carbonates precipitating with increased water temperature is softened by boiling. The hardness formed by calcium and magnesium combined with nitrates, sulfates, and other non-carbonate salts cannot be changed by boiling and is called permanent hardness. Substances constituting permanent hardness can precipitate under high temperature and pressure, forming common water scale.
2. Causes of hard water formation
Domestic and industrial wastewater contains large amounts of acids, bases, and salts, which seep into the soil. Some substances chemically react with carbonates in the soil, dissolving calcium and magnesium salts in nature, increasing the calcium and magnesium ion content in groundwater, thus forming hard water.
3. Methods of expressing water hardness
Water hardness is generally expressed by the concentration (mol/L) of carbonate and non-carbonate substances in water. Specifically expressed as follows:
(0~0.71)×10-3 mol/L Very soft water.
(0.71~1.43)×10-3 mol/L Soft water.
(1.43~2.14)×10-3 mol/L Moderately hard water.
(2.14~3.21)×10-3 mol/L Relatively hard water.
(3.21~5.36)×10-3 mol/L Hard water.
Water quality exceeding 5.36×10-3 mol/L is very hard water.
The hazards of hard water in washing and ironing
1. The hazards of hard water to fabric washing
The lower the water hardness when washing fabrics, the better. If the washing water exceeds a certain hardness standard, it will affect the washing quality of fabrics and cause certain hazards. Mainly reflected in the following aspects:
(1) Reducing the effective function of detergents
Calcium and magnesium ions in hard water combine with surfactants in detergents to form metal salts, causing surfactants to lose activity and reducing the main function of detergents.
(2) Preventing complete removal of dirt on fabrics
Ions in water can combine with substances in detergents to form precipitates. Additionally, calcium ions affect the removal of colored dirt, causing some dirt to remain attached to fabrics after washing.
(3) Affecting the appearance and service life of fabric materials
Hard water makes originally bright fabric colors dull and lackluster, reduces the whiteness of white fabrics gradually; it can make fabric fibers brittle and hard, losing their original softness, shortening the service life of fabric materials.
(4) Increasing washing costs
Hard water washing increases detergent usage, increases rinsing times, and extends washing time, causing waste of water, detergent, and labor.
(5) Shortening the service life of washing equipment
Under the influence of temperature, the deposited scale will corrode the metal surface of the washing equipment, greatly shortening the service life of the washing equipment.
2. The harm of hard water to fabric ironing
(1) Clogging pipelines, reducing heat conduction
When ironing fabrics, due to the gradual accumulation of hard water deposits—scale, the steam pipes of equipment such as steam generators, ironing machines, and irons become narrow or even blocked. This reduces the heat conduction ability of the ironing equipment.
(2) Corrosion of ironing equipment
The scale produced by hard water when heated has certain corrosiveness. The chloride ions in the scale will corrode the container walls at high temperatures, forming iron salt scale, causing the walls of the ironing equipment to thin, which not only affects heat conduction but also poses a safety risk to high-pressure steam containers.
Softening of hard water
The softening process of hard water involves the exchange or replacement of hard substances in the water, mainly calcium and magnesium ions, with sodium-containing minerals. Generally, this occurs in a special container where calcium and magnesium ions exchange with the softening substance—sodium—on the resin as hard water passes through.
1. The exchange process of calcium, magnesium ions with sodium ions
Resin is a porous, insoluble exchange material. In water softening devices, millions of tiny plastic beads (spheres) are contained, each with negatively charged exchange sites that absorb cations. When the resin is in a fresh state, these exchange sites are occupied by positively charged sodium ions. As hard water containing calcium and magnesium ions passes through the resin tank, these ions contact the resin beads and exchange places with the sodium ions on the beads. The resin preferentially binds cations with stronger charges, meaning the calcium and magnesium ions replace the sodium ions. After this exchange process, the hard water undergoes a qualitative change, becoming soft water.
2. Resin regeneration process
After the exchange sites on the resin are occupied by calcium and magnesium ions, the resin needs to be regenerated to restore the exchange state between calcium, magnesium ions and sodium ions. The regeneration process uses a sodium ion-containing salt solution to contact the resin beads carrying calcium and magnesium ions, replacing the calcium and magnesium ions on the resin with sodium ions.
Additionally, water softening can also be achieved by adding chemical agents or heating.
Common softening agents include sodium phosphate, which does not damage fabric materials, has a pH close to neutral, and is used at a dosage of 1g sodium phosphate per 10L of water. When using heating softening methods, the water temperature should be raised above 100°C and then cooled down.
After mastering the correct washing process and learning how to make the water quality meet the standards suitable for washing, washing fabrics will achieve the ideal bright white and clean effect.
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