softening

Question 1

what is alkalinity?

Answer 1

the capacity of water to neutralise an acid

Question 2

what is softening? how is it performed?

Answer 2

a chemical process which hardness-causing ions (Ca % Mg) are removed from water via the lime - soda ash method or by ion exchange

Question 3

what is an acceptable level of hardness?

Answer 3

between 75 and 120 mg/L as CaCO3

Question 4

what is a limitation of the lime-soda ash process?

Answer 4

• cannot completely remove hardness of water

- minimum calcium hardness = 30 mg/L and minimum magnesium hardness is 10 mg/L as CaCO3

Question 5

what is the generic amount used for excess lim?

Answer 5

62.5mg/L as CaCO3 or 1.25 me/L

Question 6

what are the 3 process variations for the lime - soda ash scheme?

Answer 6

• excess lime treatment (stoichiometric addition of lime)
• selective calcium removal (addition of lime to remove Ca2+ but no excess lime because the removal of Mg2+ is not needed)
• split treatment