Difference between revisions of "DCOM Volume I Appendix I"
| Line 13: | Line 13: | ||
! Cations !! Anions | ! Cations !! Anions | ||
|- | |- | ||
| − | | Ca<sup>2+</sup> || HCO<sup>-</sup><sub>3</sub> | + | | Ca<sup>2+</sup> || HCO<sup>-</sup><sub>3</sub> or CO<sup>2-</sup><sub>3</sub> |
|- | |- | ||
| − | | | + | | Mg<sup>2+</sup> || SO<sup>2-</sup><sub>4</sub> |
|- | |- | ||
| − | | | + | | Sr<sup>2+</sup> || cl<sup>-</sup> |
|- | |- | ||
| − | | | + | | Fe<sup>2+</sup> || NO<sup>-</sup><sub>3</sub> |
|- | |- | ||
| − | | | + | | Mn<sup>2+</sup> || SiO<sup>-</sup><sub>3</sub> |
|} | |} | ||
Revision as of 11:11, 5 June 2020
Appendix I: Measurement of Water Hardness
Hardness and its Measurement
Hardness is expressed in terms of mg/l by weight in terms of calcium carbonate. Water having hardness not exceeding 70 mg/l is termed ‗soft‘ and above that 'hard'. In public water supplies, it used to be customary to reduce carbonate hardness to 35 - 40 mg/l and total hardness to between 50 and 100 mg/l. However as indicated above this is no longer recommended unless hardness exceeds about 130 mg/l, but should still be practised for strictly industrial supplies of hard water.
Hardness = ∑ divalent cations = Ca2+ + Mg 2+ + Fe 2+ + Mn 2+ + Sr 2+.....
Principle cations causing hardness in water and major anions associated with them are as follows:
Table I.1: Principle cations and anions associated with water Hardness
| Cations | Anions |
|---|---|
| Ca2+ | HCO-3 or CO2-3 |
| Mg2+ | SO2-4 |
| Sr2+ | cl- |
| Fe2+ | NO-3 |
| Mn2+ | SiO-3 |
