Update
2 Dec 2010

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ION EXCHANGE

Concentration and capacity units

This ion exchange site uses almost exclusively metric units, including equivalents. However, other units have been used in the past and are still — unfortunately — used in some regions. Here are two conversion tables:

Units of concentration
(per volume of water)
Name Abbreviation
meq/L ppm CaCO3 °f °dH gr as CaCO3/gal
Milliequivalent per litre 1 meq/L = 1 50 5 2.8 2.921
ppm as calcium carbonate 1 ppm as CaCO3 = 0.02 1 0.1 0.056 0.0584
French degree 1 °f = 0.2 10 1 0.56 0.5842
German hardness degree 1 °dH = 0.357 17.86 1.786 1 1.043
Grain as CaCO3 per US gallon 1 gr as CaCO3/gal = 0.342 17.12 1.712 0.959 1

 

Units of capacity
(per volume of resin)
Name Abbreviation
eq/L g CaCO3/L °f g CaO/L kgr CaCO3/ft3
Equivalent per litre 1 eq/L = 1 50 5000 28 21.85
Gram as CaCO3 per litre 1 g as CaCO3/L = 0.02 1 100 0.56 0.437
French degree 1 °f = 0.0002 0.01 1 0.0357 0.00437
Gram as CaO per litre g CaO/L = 0.0357 1.786 178.6 1 0.780
kgr as CaCO3 per cubic foot kgr CaCO3/ft3 = 0.0458 2.29 228.8 1.281 1

The unit of mole should be avoided altogether in ion exchange, as it does not take valence into account and brings only confusion. For reference : 1 eq = 1 mole / valence.

Examples

1 mole Na+ = 23 g valence = 1 —> 1 equivalent Na+ = 23/1 = 23 g
1 mole Ca2+ = 40 g valence = 2 —> 1 equivalent Ca2+ = 40/2 = 20 g
1 mole PO43– = 95 g valence = 3 —> 1 equivalent PO43– = 95/3 = 31.7 g

© François de Dardel