What is lime softening in water treatment?
Lime softening is a process where hydrated lime or quicklime is added to raise pH and precipitate calcium. In enhanced softening, the pH is increased further in a second stage, to at least 10.6 to also remove magnesium.
How do you soften limestone?
Lime softening (also known as lime buttering, lime-soda treatment, or Clark’s process) is a type of water treatment used for water softening, which uses the addition of limewater (calcium hydroxide) to remove hardness (deposits of calcium and magnesium salts) by precipitation.
Can lime be used to soften hard water?
Water containing little or no noncarbonate hardness can be softened with lime alone. However, water with high noncarbonate hardness may require both lime and soda ash to achieve the desired finished water hardness. Softening with lime or lime- soda ash is generally less expensive than caustic softening.
Which chemical is often used with lime softening?
calcium hydroxide
Lime Softening Chemicals normally used are lime (calcium hydroxide, Ca(OH)2) and soda ash (sodium carbonate, Na2CO3). Lime is used to remove chemicals that cause carbonate hardness. Soda ash is used to remove chemicals that cause non-carbonate hardness.
How effective is lime softening?
The use of lime and soda ash permits hardness reduction down to 0.5 gr/gal, or about 8 ppm, as calcium carbonate. Magnesium is reduced to 2-5 ppm because of the lower solubility of magnesium hydroxide at the elevated temperatures. Hot process softening can also provide very good silica reduction.
How does lime soda treatment remove permanent hardness?
In this process, the hardness is removed by sedimentation as calcium carbonate or magnesium hydroxide. Lime is added either as calcium hydroxide or calcium oxide, and soda is added as sodium carbonate. The substances form hardness in water and the reactions of lime and soda can be written as follows.
How does a warm lime softener work?
The warm lime softening process operates in the temperature range of 120-140°F (49-60°C). The solubilities of calcium, magnesium, and silica are reduced by increased temperature. Therefore, they are more effectively removed by warm lime softening than by cold lime softening.
How can we regain the hardness of water by adding lime?
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.
How do you control lime in water?
Install a reverse osmosis (RO) unit on your drinking water to remove lime deposits (see Resources). The water softener just counters the minerals with sodium salts but to remove them for human consumption, a reverse osmosis unit is in order.
Why lime is used in water treatment?
Production. 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.
Does cold lime softening remove silica?
Cold lime softening, also known as Clark’s process, is used to reduce raw water hardness, alkalinity, silica, and other constituents.
What are the disadvantages of lime soda?
Disadvantage of Lime-Soda Process:
- For efficient and economical softening, careful operation and skilled supervision in required.
- Disposal of large amounts of sludge (insoluble precipitate) poses a problem.
- This can remove hardness only up to 15 ppm, which is not good for boilers.