Here, the lime-soda ash treatment is commonly used by industry for reducing hardness of water. Lime-soda ash treatment for the reduction of hardness involves the addition of slaked lime [Ca (OH)2] to a hard water supply to remove the carbonate hardness by precipitation with the precipitation being removed by filtration.
Full Answer
What happens when lime and soda ash are added to water?
Soda ash, also called sodium carbonate or washing soda, is used in many water softeners. This chemical makes the water less acidic, allowing more effective washing with soap. It also increases the sodium level in the water--a health concern for people who limit their sodium intake. This chemical is readily available and inexpensive, making it a ...
How to dispose of lime-soda ash sludge?
lime and soda ash are added to water to raise pH to between 10.3 and 10.6, and calcium hardness will be removed from the water (but minimal magnesium hardness will be removed). ... above 11, after which it is blended with 20 percent of the source water. Split treatment can reduce the amount of carbon dioxide required to re-carbonate the water ...
What is the pH of lime soda ash sludge?
Is a process in which carbon dioxide is bubbled into the water being treated to lower the pH. Recarbonation maybe carried out in two steps. the first addition of carbon dioxide would follow excess lime addition to lower pH to about 10.4 and encourage the precipitation of calcium carbonate and magnesium hydroxide.
What is lime used for in water treatment?
· The detention slaker operates with a wide range of water-to-lime ratios (2.5:1 and 6:1), moderate temperature, and a 1 0-minute slaking time at maximum capacity. A water-to-lime ratio of from 3.5:1 to 4:1 is most often used. The operating temperature in lime slakers is a function of the water-to-lime ratio, lime quality, heat transfer, and ...
How is soda ash used in water treatment?
Sodium Carbonate (Na2CO3), usually known as Soda Ash, is commonly used in water treatment to increase the pH of acidic water. Soda ash systems are employed to act as first a pH adjuster with the added benefit of softening of the water. Soda ash systems are typically used as a point-of-entry injection system.
How is lime used in water treatment?
Lime softening is a water treatment process that uses calcium hydroxide, or limewater, to soften water by removing calcium and magnesium ions. In this process, hydrated lime is added to the water to raise its pH level and precipitate the ions that cause hardness.
What are the functions of lime and soda ash respectively used in water softening?
Lime is used to remove chemicals that cause carbonate hardness. Soda ash is used to remove chemicals that cause non-carbonate hardness. When lime and soda ash are added, hardness-causing minerals form nearly insoluble precipitates. Calcium hardness is precipitated as calcium carbonate (CaCO3).
What is action of soda ash in purification of water by soda lime?
Lime-soda ash treatment for the reduction of hardness involves the addition of slaked lime [Ca(OH)2] to a hard water supply to remove the carbonate hardness by precipitation with the precipitation being removed by filtration.
Why do we add lime to water?
Drinking lime water improves digestion. Limes are acidic and they help saliva break down food for better digestion. Additionally, flavonoids in limes stimulate secretion of digestive juices. If you experience constipation, the acidity of limes can clear the excretory system and stimulate bowel activity.
How lime soda method is used for water softening of hard water?
Lime soda process: In lime-soda process, hard water is treated with lime (CaO or Ca (OH)2) firstly, after that with soda. In this process, the hardness is removed by sedimentation as calcium carbonate or magnesium hydroxide.
How can we remove hardness of water?
A few methods to remove hardness from water are,Chemical Process of Boiling Hard Water.Adding Slaked Lime (Clark's Process)Adding Washing Soda.Calgon Process.Ion Exchange Process.Using Ion Exchange Resins.
What is softening in water treatment?
Water softening is a process in which the ions of calcium, magnesium and sometimes iron are removed. It is these ions in hard water that make it difficult for products with other positively charged ions to dissolve in the water. By doing this, the water softening removes the offending minerals from the water.
What is the principle of lime soda process?
LIME SODA PROCESS- Principle:: Calculated quantity of lime & soda are added to hard water to convert soluble impurities into insoluble one which are easily removed by filtration.
Why is caustic soda used in water treatment?
Sodium Hydroxide is a strong alkali which, among other facts, means that it is highly ionized and has a high pH. Thus, in wastewater treatment these products can be used to raise the pH level of the water. It is also helpful in the process of removing heavy metal particles from the water.
What is lime soda process which chemicals are used?
10.3 The Lime-Soda Process of Softening The aim of the lime-soda process is to convert calcium and magnesium compounds to the virtually insoluble forms, calcium carbonate (CaCO3) and magnesium hydroxide (Mg(OH)2). Magnesium carbonate (MgCO3), unlike calcium carbonate, does not precipitate in cold water.
What is lime soda ash used for?
Here, the lime-soda ash treatment is commonly used by industry for reducing hardness of water. Lime-soda ash treatment for the reduction of hardness involves the addition of slaked lime [Ca (OH)2] to a hard water supply to remove the carbonate hardness by precipitation with the precipitation being removed by filtration.
How much hardness does lime ash reduce?
Often when a city has a raw water source that has 35 to 40-grain hard water, the local water system will use the lime-soda ash treatment to reduce hardness to between 5 and 10 grains.
How to reduce non carbonate hardness?
Non-carbonate hardness is in turn reduced by the addition of soda ash (Na2C03) to form an insoluble precipitate which is also removed by filtration. This particular method of removing hardness sometimes used by municipal water plants to reduce the amount of calcium and magnesium in a water supply. While it is quite effective in reducing hardness, ...
What is slaked lime used for?
Slaked lime is used to remove calcium bicarbonate from water. In the water to be treated, the slaked lime ions react with the calcium bicarbonate to form the very slightly soluble calcium carbonate. This precipitated material is usually removed by first settling and then filtering. Calcium hydroxide plus calcium bicarbonate reacts ...
Do cities have to stop using salt water softeners?
Sanitary departments are then forced to build treatment plants to remove the salt and they in-turn pass these costs down to the consumer through higher monthly water bills. Thus many cities have decided that it is not worth the cost and effort and have banned the use of salt-based water softeners altogether.
Is lime soda ash effective?
Lime-soda ash treatment is especially effective if a water contains bicarbonate (temporary) hardness. Where calcium and magnesium are primarily in chloride or sulfite compounds, this treatment is noticeably less effective. Slaked lime is used to remove calcium bicarbonate from water.
Chemical Reactions
There are at least 7 different chemical reactions that take place during the Lime-Soda Ash water softening process.
Determining How much Chemicals to Add to the Water
1) Convert all concentrations of constituents that will react with lime in the water to mg/meq. (The table below will help you).
What is hydrated lime?
A very common product, also known as hydrated lime or CaO quicklime, lime can be ‘slurry-ized’ through the addition of water to dry lime powder. This slurry can be used to treat wastewater to increase pH and alkalinity and is commonly used in potable water to “soften,” or remove hardness minerals, such as calcium and magnesium from drinking water.
Why use lime slurries?
Lime slurries minimize the effects of potential scaling in the water distribution system. It is also the most commonly used product to maintain alkalinity levels because of its low cost and multiple treatment benefits, such as assisting in the removal of manganese and iron from water.
What are the three main options for alkalinity treatment?
With so many options for treating alkalinity, there are three main options that are typically represented in the marketplace for Wastewater Treatment Plants (WWTP) when faced with this question: magnesium hydroxide, lime slurry, and caustic soda. The following outlines the good and the bad of each, hopefully providing needed guidance for decision-making at WWTPs. Ultimately, the choice lies within the final requirements of the plant and driven by the discharge permit at the facility.
Does caustic soda raise pH?
Caustic Soda and Lime Slurry are definitely go to chemistries for the WWTP industry and they do provide the needed pH adjustments required. But on a pound to pound basis there is a fundamental difference between those two and magnesium hydroxide to also consider that does not have much to do with pH or alkalinity, but rather the true amount required to treat. For example, a given water sample may require 100 mg/L of magnesium hydroxide to raise the pH to 8.8. For the same sample, 138 mg/L of caustic soda and 135 mg/L of lime would be required.
Is sodium hydroxide a caustic soda?
Caustic Soda is commonly referred to Sodium Hydroxide or NaOH. Surprisingly, it can be commonly found in the home but in the industrial sense, it is mainly used for alkaline neutralization. Caustic Soda is found in all kinds of concentrations and is a common, popular way to neutralize and tame all kinds of acids. It is also considered easy to introduce to the system due to its solubility. However, at high concentrations, it is extremely hazardous to handle and several precautious must be in place to safely use in the treatment process. These would include enhanced PPE (personal protective equipment) and immediately accessible wash stations at a minimum.
Is lime slurry harmful?
The downside of lime slurry originates from its high solubility. Maintaining proper pH levels often becomes biologically prohibitive before ideal alkalinity levels and process stability can be reached. Another major concern is lime slurry will cause an increase in waste sludge, sometimes as much as 50% – adding more disposal costs to the operation. If that wasn’t already enough, hydrated lime slurry added in collection systems increases the operations and maintenance costs related to formation of scale and accumulated solids/sludge. In severe cases this can lead to line blockages.
Is magnesium hydroxide good for microbial wastewater?
So, comparing magnesium hydroxide, caustic soda, and lime slurry, while all can supply the required benefits, the whole treatment process should be reviewed and determine the best overall solution based on some of the side effects for each. Magnesium hydroxide can be difficult to store when not done properly but can supply significantly more alkalinity in a bio-available form to a microbial wastewater system without advers ely affecting pH . This creates a more suitable environment for bioremediation of BOD and nutrients like nitrogen and phosphorus. Moreover, because magnesium hydroxide supplies a lightweight, divalent cation, unlike the monovalent sodium in caustic and heavier calcium in lime, magnesium hydroxide helps to generate a denser, more easily dewatered sludge, with a higher percentage of cake solids – reducing waste disposal costs.
Why is lime used in water treatment?
In some water-treatment plants, alum sludge is treated with lime to facilitate sludge thickening on pressure filters.
How does lime help with water?
Lime is also used to combat "red water" by neutralizing the acid water, thereby reducing corrosion of pipes and mains from acid waters. The corrosive waters contain excessive amounts of carbon dioxide. Lime precipitates the CO 2 to form calcium carbonate, which provides a protective coating on the inside of water mains.
What is the process of removing carbonate from water?
Softening - In water softening, hydrated lime is used to remove carbonate "hardness" from the water. Hardness caused by other calcium and magnesium salts, called noncarbonate hardness, is generally treated by means of the lime-soda process, which entails the precipitation of magnesium by lime.
What is lime used for?
Lime is used by many municipalities to improve water quality, especially for water softening and arsenic removal.
What is the best way to remove silica from water?
Removal of Impurities - One of the most common methods of removing silica from water involves the use of dolomitic lime . The magnesium component of this lime is the active constituent in silica removal. Lime is also used to remove manganese, fluoride, organic tannins and iron from water supplies.
How much lime does a person need?
Every person in the U.S. needs 138 pounds of lime each year.
How does lime affect pathogens?
Effect on Pathogen Growth - By raising the pH of water to 10.5-11 through the addition of lime and retaining the water in contact with lime for 24-72 hours, lime controls the environment required for the growth of bacteria and certain viruses.
What is soda ash?
Soda ash is a trade name for sodium carbonate, which is refined from natural mineral deposits or manufactured via a chemical process. This raw material is used in more than just water treatment, including glass making, detergent manufacturing, dyeing, and other processes. It's a more price-stable and less volatile substitute for caustic soda in ...
What is the chemical in water softener?
Sodium carbonate is both mined and made in laboratories. Soda ash, also called sodium carbonate or washing soda, is used in many water softeners. This chemical makes the water less acidic, allowing more effective washing with soap. It also increases the sodium level in the water--a health concern for people who limit their sodium intake.
Where is sodium carbonate found?
Sodium carbonate has also been found in a volcano in Tanzania and in ultra-alkaline rocks. It is mined in a number of locations, including Wyoming and Kenya. Advertisement.
Is soda ash poisonous?
Wear gloves while handling it and avoid getting soda ash in your eyes or mouth. This chemical is not poisonous but can cause skin and mucus membrane irritation.
Does soda ash help with detergent?
This chemical prevents the trace elements from bonding with detergents, making the detergent more effective. Soda ash is often sold in the laundry section of department stores for direct use in washing machines. When added to water with a pH of less ...
Can you use potassium salts in water softener?
Water softeners can greatly increase the amount of sodium in your diet. Consider using potassium salts to soften your water instead. It could result in much better health, with minimal changes to your lifestyle. For people not on restricted sodium diets, soda ash water softeners pose little threat.
Does soda ash increase alkalinity?
When added to water with a pH of less than 7, soda ash increases the alkalinity. It can keep water from being as corrosive and reduce the amount of mineral scale that builds up in your pipes. Advertisement.
What is the pH of lime ash?
Calcium carbonate sludges are normally dense, stable inert, and dewater readily. Solids content in the sludge range from 5 to 30 total solids with a pH greater than 10.5.
What is the pH of water that removes calcium?
When water has minimal magnesium hardness, only calcium needs to be removed. Only enough lime and soda ash are added to water to raise pH to between 10.3 and 10.6, and calcium hardness will be removed from the water (but minimal magnesium hardness will be removed).
What is the capacity of water to neutralize acids?
Alkalinity (mg/l as CaCO3) is the capacity of water to neutralize acids. This is determined by the content of carbonate, bicarbonate and hydroxide. Alkalinity is a measure of how much acid can be added to a liquid without causing any significant change in pH.
What is the best solution for magnesium water?
Two-stage softening is sometimes used for treatment of high magnesium water (where excess lime is required). Excess lime is added in the first stage to raise pH to 11.0 or higher for magnesium removal. Following first stage treatment, carbon dioxide is added to reduce the pH to between 10.0 and 10.5, the best value for removal of calcium carbonate. If non-carbonate hardness removal is needed, soda ash will be added at this point. After second stage treatment, the water flows to a secondary recarbonation tank, where pH is reduced to between 8.3 and 8.6.
What can be used to reduce scale forming tendencies in water?
After the chemical softening process, the scale forming tendencies of water can be decreased by the use of carbon dioxide.
What is the pH of calcium carbonate?
Calcium carbonate precipitates out at a pH above 10 and magnesium carbonate, which remains in solution
Can you use caustic soda instead of soda ash?
Caustic soda soften ing might be used in place of soda ash. The decision to use caustic soda rather than soda ash depends on the quality of the source water and the delivered costs of various chemicals.