We use certain chemical methods to remove the permanent hardness of water, which are: Treating the Water with Washing Soda In this method, we add washing soda, i.e., Na 2 CO 3 to the hard water. These deposits can make hard water unsuitable for many uses, and so a variety of means have been developed to "soften" hard water; i.e.,remove the calcium and magnesium ions. ⇒ Check: Differences Between Hard Water and Soft Water. Due to continuous use of zeolite the sodium present in it is exhausted. higher than that in the unsoftened water and there is no increase in the chloride content of the water during the remainder of a run between successive regenerations. Methods to remove permanent hardness - definition Washing soda process: Hard water is treated with a calculated amount of washing soda when chlorides and sulphates of calcium and magnesium present in hard water get precipitated as insoluble calcium and magnesium carbonates which can be filtered off. Water which does not give lather with soap is hard water. (viii) The process proves to be economical where salt is cheaply available. It converts C a 2 + and M g 2 + salts (soluble) to carbonates (insoluble). Zeolites are complex compounds of aluminium, silica and soda, which occur in nature and are therefore available in natural form. The first step in the regeneration of zeolite bed is to backwash the bed in the manner similar to a rapid sand filter, to loosen the particles and remove any material that might have been deposited on the bed. Permanent hardness is that which cannot be removed by boiling. In the third case the regeneration of zeolite bed may be carried out as and when its need is indicated by the results of laboratory tests or field soap test. In this process no chemical are added to water as in the case of lime-soda process, but instead of this hard water is passed through a bed of ion-exchange material or ion exchanger commonly known as zeolite, which has a property of interchanging base or ion. Thus when hard water passes through zeolite bed, calcium and magnesium are removed from water as these are substituted by sodium by ion exchange phenomenon. Content Filtration 6. Water that can be removed by boiling but it forms (insoluble) limescale due to the calcium and magnesium compounds and this removes the ions from the temporary hard water. The following reactions take place in this exchange process: Due to continuous use of hydrogen exchanger its hydrogen content is exhausted. (vii) The process is almost completely automatic and highly skilled labour is not required for its operation. What is permanent hard water. The sodium salts that are formed in these reactions are soluble in water and no hardness is imparted to water by these salts. large scale is practically unfeasible. Since for public water supply water of zero hardness is not required, the usual practice is to soften only a portion of water to zero hardness and then to mix it with unsoftened water so that the resulting hardness is about 50 to 90 p.p.m. These ions are generated when calcium sulfate (CaSO 4) and magnesium sulfate (MgSO 4) dissolve in water. The filters may be of ordinary type rapid sand filters or pressure filters. The hardness of water is harmful to the boilers as the deposition of salts occurs, which reduces the efficiency of the boiler. CaCl 2, CaSO 4, MgCl 2, MgSO 4. Sodium carbonate can be used for both temporary and permanent hardness to soften hard waste. At this stage zeolite needs to be regenerated to make it again effective for removal of hardness of water. Mechanical devices for continuous removal of the sludge are also ordinarily provided. However, permanent hardness can be removed only by means of chemical treatment. Reaction: Na2 Al2 Si2 O8.KH2O + Ca++→ 2Na+ + Ca Al2 Si2 O8.xH2O. Permanent hardness present in the water can be removed by treating it with soda water and using permutit process. Water Engineering, Water Treatment, Removal of Permanent Hardness from Water. Hardness in water is caused by dissolved magnesium ions and calcium ions. However, for public water supply water of zero hardness is not required. In this process hard water is passed through a bed of ion-exchange material or ion exchanger such as resin or carbonaceous material which is also called a hydrogen exchanger. When hard water is passed through a bed of permutit the following chemical reactions take place: The above equations indicate that both calcium and magnesium present in water are replaced by sodium and thus hard water is softened. Since 1 p.p.m is equal to 1 kg per million litre (or 1 mg/l), 1.27 kg of lime CaO will be required per million liters of water for 1 p.p.m of CO2. Question is ⇒ Both temporary and permanent hardness of water can be removed on boiling water with, Options are ⇒ (A) calcium hydroxide, (B) sodium carbonate, (C) calcium oxide, (D) calcium carbonate, (E) , Leave your comments or Download question paper. Hard water contains dissolved magnesium and calcium ions. In this case, the hardness in water can be removed by boiling the water. Mineral deposits are formed by ionic reactions resulting in the formation of an insoluble precipitate. Equation (viii) indicates the chemical reaction between sodium carbonate (or soda ash) and calcium chloride already present in water and that formed by chemical reaction indicated by equation (vii), is removed by this chemical reaction. The reaction produces calcium sulphate and hence, there is no softening of water as such. Permanent water hardness occurs due to the presence of calcium sulfate. These chemicals are mixed in the required proportion and the mixture is fused in a furnace. Thus for 1 p.p.m of CO2 present, 1.68 p.p.m of hydrated lime Ca(OH)2 will be required, or 1.68 kg of hydrated lime Ca(OH)2 will be required per million litres of water for 1 p.p.m of CO2. Assertion : Permanent hardness of water is removed by treatment with washing soda. Hence amount of sodium carbonate (or soda ash) Na2CO3 required to remove I p.p.m of non-carbonate hardness from 1 million litres of water = 106/100 = 1.06 kg. The exchange value of Permutit is 35000 to 40000 gm of hardness per m3 of zeolite, which is much higher than that of glauconite or green sand. It removes the hardness of water by converting bicarbonates into carbonate. Hardness can be removed by adding sodium carbonate (washing soda) or by passing the water through an ion-exchange column. ⇒ Also Read: Heavy Water – Methods of Preparation and Properties. What is temporary hard water. (xii) The first cost and operating cost of the process are comparatively low. The recarbonated water is passed through filters to ensure complete clarification. (iii) It can be easily operated and does not require any skilled supervision. The hardness of water is due to the presence of soluble bicarbonates, chlorides and sulfates of calcium and magnesium. Content Guidelines 2. Image Guidelines 4. Basically, a salt based water softener works to remove high concentrations of calcium and magnesium from water through a process called “ion exchange.” This process “softens” hard water by substituting the hardness minerals (calcium and magnesium) with sodium chloride (salt). Answer Permanent hardness of water is due to presence of soluble chlorides and sulphates of M g2+ and C a2+. (iv) There is no problem of deposition of layer of calcium carbonate in the distribution system. (iv) Zeolite water softeners should be operated carefully to avoid injury or damage to the equipment, bed of zeolite and quality of water. ⇒ Check: Difference between Adsorption and Absorption. At this stage it needs to be regenerated to make it again effective for removal of hardness of water. (v) When ion-exchange capacity of zeolite has been exhausted it has to be regenerated. C l 2. (i) A large quantity of sludge (i.e., insoluble precipitates of calcium carbonate and magnesium hydroxide) is formed in this process which needs to be disposed-off by some suitable method. As such this disadvantage is not that serious. The flow of water through the bed may be upward or downward, but the downward flow is more common as there is less danger of loss of material and the filtering action of the bed is better. It should therefore be flushed annually with chlorinated water. As such this process is also known as base-exchange or ion-exchange process. Therefore, the use of sodium hydroxide is only recommended in this case; however, it may also be considered for the partial softening of water where CaH > M-alk. Terms of Service 7. Types of HardnessA. Base exchange process’ is a chemical method by which, softening of permanent hardness in water can be done on a large scale or for household purposes. Linens and clothes look dull and feel rough. (vi) There is reduction in total mineral content of water. Temporary hardness is due to the presence of calcium hydrogencarbonate Ca(HCO 3) 2 (aq) and magnesium hydrogencarbonate Mg(HCO 3) 2 (aq). Water is present in the oceans, rivers, ponds, lakes, glaciers, etc. 3. The most common artificially prepared or synthetic zeolite is Permutit. Permanent hardness of water can be removed by the following methods: In this method lime [Ca(OH)2] and sodium carbonate [Na2CO3] (or soda ash) are used to remove permanent hardness from water. Before uploading and sharing your knowledge on this site, please read the following pages: 1. This process is similar to zeolite process with the difference that in demineralisation process the metallic ions viz., calcium, magnesium, etc., are exchanged for hydrogen ions. The proper amount of 5 to 10 per cent of salt solution is then introduced into the bed and it is allowed to stand in contact with the entire bed for sufficient time. It is then passed through a dryer containing steel chips or turnings, to remove remaining water and active oxygen. (vi) There is likelihood of growth of bacteria on the bed of zeolite. Rainwater is considered pure water because it does not contain any salt dissolved in it thought there are dissolved gases present. (x) In this process since no chemicals are added to water there is no danger of excess chemicals being present in the effluent. In other words it is the soap destroying property due to the presence of Bicarbonates, Sulphates and Chlorides of Calcium and Magnesium.” 2. We can remove this hardness by treating the water with washing soda. Disclaimer 8. Permanent hardness cannot be removed by boiling, but can be removed by ion exchange or other water softener devices. After filtration, the water we get is soft water. However, glauconites or green sands are more rugged than synthetic zeolites. Further, these softeners are usually equipped with automatic regeneration control to regenerate either at a fixed interval of time or after a certain quantity of water have been softened. Uploader Agreement. Copyright 10. Water Demand: Estimating and Variations | Water Engineering, Unconventional Machining Processes: AJM, EBM, LBM & PAM | Manufacturing, Material Properties: Alloying, Heat Treatment, Mechanical Working and Recrystallization, Design of Gating System | Casting | Manufacturing Science, Forming Process: Forming Operations of Materials | Manufacturing Science, Generative Manufacturing Process and its Types | Manufacturing Science. This occurs when causticity caused by calcium hydroxide or sodium hydroxide of 20 to 50 p.p.m is retained in the treated water for a period of about 4 to 5 hours. When this is the case, it is usually caused by the presence of calcium sulfate and/or magnesium sulfates in the water, which do not precipitate out as the temperature increases. Quick lime is preferred for large plants because it is less bulky and cheaper. In this method, the permanent hardness of water is removed by using resins. This is usually accomplished by recarbonation process in which carbon dioxide CO2 gas is diffused through the effluent so that the insoluble calcium carbonate and magnesium hydroxide combine with carbon dioxide to again form the soluble bicarbonates of calcium and magnesium as indicated by the following equations-. Sodium carbonate (or soda ash) can also be added to water as dry feed or as a solution. After attaining a certain degree of fusing it is allowed to cool. (ix) The process is independent of change in quality of raw water. When the soluble salts of magnesium and calcium are present in the form of chlorides and sulphides in water, we call it permanent hardness because this hardness cannot be removed by boiling. This type of hardness can be removed by boiling the water to expel the CO 2, as indicated by the following equation: Permanent hardness is due to calcium and … Soluble salts of calcium and magnesium change into insoluble salts due to the treatment with sodium carbonate (washing soda). Temporary hardness is that which can be removed by boiling. The regeneration of a zeolite bed may be carried out either at a fixed interval of time or after a certain quantity of water has been softened, or when the effluent obtained has reached a predetermined level of hardness. Most of the calcium carbonate CaCO3 and magnesium hydroxide Mg (OH)2 which are formed in this process get deposited in the sedimentation tank. Solution (By Examveda Team) Temporary hardness can be removed by boiling or by addition of Ca (OH) 2. It can be fed as dry feed or added as made-up slurry. However, in this case a longer detention time, varying from 2 to 4 hours, is provided to obtain greater clarification. Reason : Washing soda reacts with soluble calcium and magnesium chlorides and … Although in the process of recarbonation due to the formation of bicarbonates of calcium and magnesium some hardness is imparted to water, but recarbonation is necessary to avoid the above noted troubles. Ca++/Mg++ ions are exchanged with Cl–, SO4-2 ions are exchanged with anion exchange resin (RNH2OH). In this method, sodium aluminum ortho silicate known as permutit or zeolite is used to remove the permanent hardness of water. This tank is similar to coagulation- sedimentation tank. The amount of water softening chemical i.e., lime and sodium carbonate (or soda ash) required to complete these reactions depends on the following: (i) Amount of free carbon dioxide present; (ii) Amount of half-bound carbon dioxide, which is a portion of that in the bicarbonate alkalinity; (v) Contents of commercially available lime and sodium carbonate (or soda ash). (v), is removed by this chemical reaction. Temporary hardness present in the water can be removed by heating hard water and treating it with lime water. For every grain of hardness removed from water, 8 mg/1 (ppm) of sodium is added. Lime-Soda Process: In this method lime [Ca(OH) 2] and sodium carbonate [Na 2 CO 3] (or soda ash) are used to remove permanent hardness from water. The thickness of zeolite layer varies from 75 cm to 190 cm. The resulting increased acidity in treated water can be removed by: (i) Diluting treated water with raw water, (ii) Neutralizing treated water with alkaline substance, or. In the absence of recarbonation a thick layer of calcium carbonate will be deposited in the filtering media and distribution system. Recarbonation of water is carried out in a recarbonation plant. Permanent hardness Permanent hardness (mineral content) is generally difficult to remove by boiling. The above equations indicate that sodium of salt solution replaces calcium and magnesium of the exhausted zeolite. Huge Collection of Essays, Research Papers and Articles on Business Management shared by visitors and users like you. The chemical reactions involved in the cation exchange process are as follows: The above equations indicate that calcium, magnesium and sodium present in water are replaced by hydrogen and thus hard water is softened. Report a Violation 11. Equation (v) indicates the chemical reaction between lime and magnesium sulphate. Low water pressure from showers due to clogged pipes. Assertion : H 2 O 2 has higher boiling point than water. Reason : H 2 O 2 has stronger dipole-dipole interactions than that shown by water. The smaller thickness of zeolite bed is most common because smaller the thickness of zeolite bed, greater will be the capacity of the softener. Water is the most important compound that is needed for the survival of life on earth. This page gives you information about the temporary water hardness. The hardness due to the presence of chloride and sulphate salts of calcium and magnesium is known as permanent hardness of water. Some of the most common signs of hard water include: How to Remove Permanent Hardness of Water? The zeolite bed is considered to be satisfactorily regenerated if the first 10 per cent of the water softened between successive regenerations shows a chloride content of less than 10 p.p.m. The Concentration of Ions. Account Disable 12. Permanent hardness is also called non-carbonate hardness. The chemical composition of such an exchange is expressed as H2R, where H represents hydrogen ions and R represents the organic part of the exchanger. Further molecular weight of CaCO3 (non-carbonate hardness) is 100 and molecular weight of sodium carbonate (or soda ash) Na2CO3 is [(2 × 23) + 12 + (3 × 16)] = 106. However, these may also be prepared synthetically. Insoluble carbonates are formed when washing soda reacts with the sulphide and chloride salts of magnesium and calcium and thus, hard water is converted to soft water. The gas then passes through excelsior or moisture trap for its partial drying. Water is permanently hard when calcium (Ca 2+), magnesium (Mg 2+), and sulfate (SO 4 2-) ions are present in it. Hard water has high mineral content. The reaction produces calcium chloride and hence, there is no softening of water as such. How is permanent hardness removed? Its chemical formula is 2SiO2 Al2O3Na2O. [gravityform id="1" title="false" description="false" ajax="true"]. (iii) to convert magnesium carbonate into magnesium hydroxide. When we boil water the soluble salts of Mg(HCO3)2 is converted to Mg(OH)2 which is insoluble and hence gets precipitated and is removed. , ( N a 2 + and M g 2 + and M g +! Process it is possible to reduce hardness of water soda ash ) and magnesium sulfate CaSO... 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