Softening of water by various methods
WATER AND ITS INDUSTRIAL APPLICATIONS
Softening of water by various methods
One of the reasons for existence of life on our planet is the distance from sun, which is just right for DiHydrogen Monoxide (DHMO) to exist in its liquid form on the planet. In fact, the liquid form of DHMO covers almost 70% of the earth’s surface. Yes, you guessed it right! DHMO is nothing, but the chemical name for our planet’s lifeline, ‘water’. Water is so important for life that in many cultures it is revered as a god or deity. Water also constitutes up to 70% of human body and is essential for proper body functioning and health. The importance of water for human beings can be understood from the fact that most of the ancient civilizations sprang up next to some major rivers. Even though water covers the majority of the surface, all the water found on the planet is not the same. Water is available in three forms, in the vapor state in the atmosphere, in the liquid state on the surface and as polar ice caps on elevated regions. The liquid state of water that exists on the planet differs in composition and properties. Browse through the article and distinguish the different types of water. The information would surely help you understand what distinguishes each type of water.
Different Kinds of Water
Fresh Water
Fresh water is naturally occurring water on the Earth’s surface and underground and typically contains less than 1% sodium chloride. More than 70% of world’s fresh water is consumed by agriculture. Only 2.75 percent of the water on Earth is fresh water, about two-thirds of it is frozen in glaciers, a quarter is groundwater and only 0.005 percent of it is surface water. Fresh water may be either ‘hard’ or ‘soft’.
Brackish Water
Brackish water is the type of water that has salinity between that of fresh water and seawater. Normally, brackish water contains between 1 and 2.5% sodium chloride.
Seawater
Seawater typically contains about 3.5% sodium chloride, although the salinity may be weak in some areas as a result of dilution with fresh water or concentrated by solar evaporation in other.
Distilled/ Demineralized Water
Basically stands for the water that is ripped of its impurities through the process of distillation.
Steam Condensate
Water condensed from industrial steam is called steam condensate.
Boiler Feed Water
The feed water make-up for boilers is always softened and subsequently de-aerated.
Potable Water
Potable water is fresh water that is sanitized with oxidizing biocides such as chlorine or ozone to kill bacteria and make it safe for drinking purposes.
Waste Water
Waste water is any water that is discarded after use.
On the basis of usability water is of two types:-
1. Hard water
2. Soft water
SOFT WATER: – Natural or treated water that does not contain a significant amount of dissolved minerals such as compounds of calcium or magnesium. It produces copious lather with a little amount of SOAP or detergent and does not form scales in boilers, heaters, and kettles.
HARD WATER: – Water that does not form an immediate lather with soap is called hard water. Hardness of water is due to the presence of soluble calcium, magnesium or iron compounds. The most common compounds are calcium bicarbonate Ca (HCO3)2, magnesium bicarbonate Mg (HCO3)2, calcium sulphate CaSO4 and magnesium sulphate MgSO4. The addition of soap forms an insoluble scum. The scum consists of insoluble salts of these metals. Removal of these salts from the solution makes the water soft. Water that forms an immediate lather with soap is called soft water. Such water does not have dissolved salts of calcium, magnesium and iron.
Types of Hardness: Depending upon the behavior of water towards soap, hardness is divided into two types.
1. Temporary hardness:
Hardness of water due to the presence of soluble bicarbonates of calcium and Magnesium is called temporary hardness. When water containing dissolved carbon dioxide passes over solid carbonates (chalk or limestone deposits etc.), these compounds get dissolved in water. Rainwater and distilled water are always soft because they do not have dissolved (soluble) salts.
2. Permanent hardness:
This is due to the presence of chlorides and sulphates of calcium and magnesium. Such a hardness can be removed by the addition of washing soda. This removes both the temporary and the permanent hardness of water.
Problems with hard water
The presence of certain metal ions in water causes a variety of problems. These ions interfere with the action of soaps. They also lead to build up of lime scale, which can foul plumbing, and galvanic corrosion. In industrial scale water softening plants, the effluent flow from re-generation process can precipitate scale that can interfere with sewerage systems.
The slippery feeling experienced when using soap with soft water occurs because soaps tend to bind to fats in the surface layers of skin, making soap molecules difficult to remove by simple dilution. In contrast, in hard-water areas the rinse water contains calcium and/or magnesium ions which form insoluble salts, effectively removing the residual soap from the skin but potentially leaving a coating of insoluble stearates on tub and shower surfaces, commonly called soap scum.
So it is very essential to remove the hardness of water which is known as softening of water.
METHODS OF SOFTENING OF WATER
Temporary hardness is removed in the following ways:
1. By boiling the water: On boiling, the soluble bicarbonate is decomposed into insoluble carbonate.
2. Chemical methods:-By adding slaked lime [Ca (OH) 2] to hard water, insoluble carbonates are formed. The insoluble calcium carbonate is the ‘fur’ (or scale) formed in kettles, boilers, pipes, etc.
Permanent hardness can be removed by the following methods:
Practical means for softening water rely on ion-exchange polymers or reverse osmosis. Other approaches include precipitation methods and sequestration by the addition of chelating) agents. Devices that claim to use magnetism or electricity as a “water softening” technique are fraudulent.
Ion-exchange resin
Conventional water-softening appliances intended for household use depend on an ion-exchange resin in which hardness ions mainly Ca2+ and Mg2+ are exchanged for sodium ions. Ion exchange devices reduce the hardness by replacing magnesium and calcium (Mg2+ and Ca2+) with sodium or potassium ions (Na+ and K+).”
Types of ion exchange materials
Ion exchange resins are organic polymers containing anionic functional groups to which the di-cations (Ca++) bind more strongly than mono-cations (Na+). Inorganic materials called zeolites also exhibit ion-exchange properties. These minerals are widely used in laundry detergents. Resins are also available to remove carbonate, bi-carbonate and sulphate ions which are absorbed and hydroxide ions released from the resin.
Regeneration of ion exchange resins
When all the available Na+ ions have been replaced by calcium or magnesium ions, the resin must be re-charged by eluting the Ca2+ and Mg2+ ions using a solution of sodium chloride or sodium hydroxide depending on the type of resin used. For anionic resins, regeneration typically uses a solution of sodium hydroxide or potassium hydroxide. The waste waters eluted from the ion exchange column containing the unwanted calcium and magnesium salts are typically discharged to the sewerage system.
Reverse osmosis
Reverse osmosis is the other major technology for water softening. It is mainly deployed on a large scale rather than for individual domestic applications. As described by NSF/ANSI Standard 44, it “reverses, by the application of pressure, the flow of water in a natural process of osmosis so that water passes from a more concentrated solution to a more dilute solution through a semi-permeable membrane. Most reverse osmosis systems incorporate pre- and post-filters along with the membrane itself.”
Chelating agents
Chelators are used in chemical analysis, as water softeners, and are ingredients in many commercial products such as shampoos and food preservatives. Citric acid is used to soften water in soaps and laundry detergents. A commonly used synthetic chelator is ethylenediaminetetraacetic acid (EDTA).
Distillation and rain water
Since Ca2+ and Mg2+ exist as nonvolatile salts, they can be removed by distilling the water. Distillation is too expensive in most cases. Rainwater is soft because it is naturally distilled during the water cycle of evaporation, condensation and precipitation.
QUESTIONS AND ANSWERS
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Q1. What is hard water?
ANS: – Hard water is the type of water that has high mineral content (in contrast with soft water). Hard water minerals primarily consist of calcium (Ca2+), and magnesium (Mg2+) metal cations, and sometimes other dissolved compounds such as bicarbonates and sulfates. Calcium usually enters the water as either calcium carbonate (CaCO3), in the form of limestone and chalk, or calcium sulfate (CaSO4), in the form of other mineral deposits. The predominant source of magnesium is dolomite (CaMg (CO3)2). Hard water is generally not harmful.
Q2. How is hard water measured?
ANS: – Hard water is usually measured in either PPM (parts per million) or GPG (grains per gallon).17.1 PPM or Mg/L = 1 GPG or PPM or Mg/L divided by 17.1 = GPG (grains per gallon).
Q3. What is meant by scaling or fouling?
ANS: – Fouling refers to the accumulation of unwanted material on solid surfaces, most often in an aquatic environment. The fouling material can consists of either living organisms (biofouling) or be a non-living substance (inorganic or organic).
Fouling phenomena are common and diverse, ranging from fouling of ships, natural surfaces in the marine environment (marine fouling), fouling of heat-transferring components through ingredients contained in the cooling water or gases, and even the development of plaque or calculus on teeth, or deposits on solar panels on Mars, among other examples
Q4.What do you mean by softening of water?
ANS: – Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water is more compatible with soap and extends the lifetime of plumbing. Water softening is usually achieved using ion-exchange resins.
Q5.What is the difference between hard water and soft water?
ANS: – It’s the amount of calcium and magnesium in the water. The Water Quality Association of the United States defines hard water as having dissolved mineral hardness of 1 GPG (grain per gallon) or more. Scales are given below:
Soft Water- less than 1 gpg
Slightly Hard- 1-3.5 gpg
Moderately Hard- 3.5-7 gpg
Very Hard- 7-10 gpg
Extremely Hard- over 10 gpg
The major difference between hard and soft water is-
While doing household chores, hard water is to blame for dingy looking clothes, dishes with spots and residue, and bathtubs with lots of film and soap scum. Even hair washed in hard water may feel sticky and look dull. Hard water can take a toll on household appliances as well and use up more energy. The elements of hard water are to blame for all of these negative factors, as soap is less effective due to its reaction to the magnesium and calcium. The lather is not as rich and bubbly. Naturally soft water exists in some areas. Softened water increases salt in the water and is slightly acidic. Over time softened water will erode soft metals in plumbing such as copper pipes and brass fittings.
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