softening Flashcards
1
Q
what is alkalinity?
A
the capacity of water to neutralise an acid
2
Q
what is softening? how is it performed?
A
a chemical process which hardness-causing ions (Ca % Mg) are removed from water via the lime - soda ash method or by ion exchange
3
Q
what is an acceptable level of hardness?
A
between 75 and 120 mg/L as CaCO3
4
Q
what is a limitation of the lime-soda ash process?
A
- cannot completely remove hardness of water
- minimum calcium hardness = 30 mg/L and minimum magnesium hardness is 10 mg/L as CaCO3
5
Q
what is the generic amount used for excess lim?
A
62.5mg/L as CaCO3 or 1.25 me/L
6
Q
what are the 3 process variations for the lime - soda ash scheme?
A
- 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
