Continuous lime-soda process, Chemistry

Q. Describe Lime-soda method for softening of hard water. Discuss the advantages of the process and the chemistry involved in it.


Describe the continuous lime soda process of softening of hard water. Compare between continuous cold and hot Lime-soda process.


Continuous Lime-soda process: The basic principle in this method is to convert all the soluble hardness causing constituents into insoluble precipitates by appropriate chemical reactions. In this process, a suspension of calcium hydroxide (lime) and sodium carbonate (soda) is added to water in calculated quantities bases on the concentration of impurities.

Reactions involved in treatment:

(a)          Ca (HCO3)2 + Ca (OH)2 = 2CaCO3 +2H2O

(b)         Mg (HCO3)2 + 2Ca (OH)2 = Mg (OH)2 +  2CaCO3 + 2H2O

                MgCO3 + Ca (OH)= Mg (OH)2 +CaCO3  

(c)           Mg+2 + Ca (OH) = Mg (OH)2 + CaCO3

(d)         Ca+2  + Na2CO3 = CaCO3 + 2Na+

(e)         CO2 + Ca (OH)  =  CaCO3  + 2Na+

(f)              2H+  + Ca (OH)  = Ca+2 + 2H2O

(g)          Ca+2+ + Na2CO3  = CaCO3 + 2Na+

(h)         2HCO-3 + Ca (OH)2  =  = CaCO3 + 2H2O + CO2-3

(i)                Fe2+ + Ca (OH)2  =  Ca+2 + Fe (OH)2

(j)                Al2 (SO4)3 + 3Ca (OH)2 = 3CaSO4 + 2Al (OH)3

(k)          3CaSO4 + 3Na2CO3  =  3Na2SO4  + 3CaCO3

Since 100 parts of CaCO3 are equivalent to 74 parts of Ca (OH2), the lime required for removing hardness is

Lime required = 74/100 [Temperature Ca+2 + 2* Temperature Mg+2 + Permanent Mg+2 + Fe+2 + Al+3 + CO2 + H+ (HCl or H2SO4) + HCO-Na3+AlO2]

Soda required = 106/100[Permanent (Ca+2 + Mg+2 + Al3+ + Fe2+ + H+-HCO-3]

Advantages of Lime-soda process

1.      Fewer amounts of coagulants are required.

2.      The pH of soft water is higher which prevents corrosion of the distribution pipes.

3.      Amount of impurities such as iron and manganese are also decreased.

4.      Water produced after treatment is of alkaline nature. Amount of micro organism are reduced.

5.      It is very economical method.

Disadvantages of Lime-Soda process:

1.      This process cannot be used for domestic purpose because it is difficult to find amount of lime-soda required.

2.      It is not suitable for laundry industry, where calcium carbonate may end up on the clothing.

3.      Skilled and careful supervision is required for efficient and economical operation.

4.      It creates the problem of disposal of sludge.

5.      The hardness of water is not completely removed.

Comparison between cold and hot lime-soda process:

S. No

Cold lime-soda process

Hot lime-soda process


Reactions are slow

Reactions are fast and complete


Filtration is slow

Filtration is fast


Less efficient

Very efficient


Softening capacity is low

Softening capacity is high


Use of coagulant is necessary

No coagulants are required


Requirement of lime consumption is as per stochiometry

Less quantity of lime is required as temporary hardness is removed by boiling.


Steam is not used

Steam is used, which increases fuel consumption.


Residual hardness of soft water produced is 50-60 ppm.

Residual hardness of soft water produced is 15-30 ppm.

Posted Date: 7/21/2012 9:15:45 AM | Location : United States

Related Discussions:- Continuous lime-soda process, Assignment Help, Ask Question on Continuous lime-soda process, Get Answer, Expert's Help, Continuous lime-soda process Discussions

Write discussion on Continuous lime-soda process
Your posts are moderated
Related Questions
Q. in radioactive decay, a nucleus emits an alpha particle and two beta particle successively. show that the final nucleus is an isotope of original nucleus. Ans: Let the mass and

1. In water softening, which of the precipitates will settle out? 2. For particle sizes larger than 1μ in size 3. In non-ideal type II settling 4.The most usually used me

NMR Spectrum of benzyl methyl ether

Sir any method to learn the arrangement of functional group in poly functional compound ????

a 60.0g sample of water initially at 40.0 degree celcius is heated and converted to steam at 100 degree celcius. how much heat has been supplied to the sample during the pross. giv

Which kind of volcano is the most destructive? Well each type of volcano can be very destructive and if you are talking in human loss of life terms than the answer is any type

Two solutions are prepared using the same solute: Solution A: 0.27g of the solute dissolves in 27.4g of t-butanol. Solution B: 0.23g of the solute dissolves in 24.8g cyclohexane. W

lithium and beryllium markedly differ from other members of their respective groups.

Unlike components of the 3 d series, 4 d and 5 d elements have little simple aqueous cationic chemistry. The main exceptions are La3+ and Y3+, and Ag+, which builds some soluble

Energy of the electron in Hydrogen atom is given by: (1) E n = 131.38/ n 2 x kj mol -1         (2)  E n = 131.33/n xkj mol -1           (3) E n = 1313.3/ n 2 x kj mol