ION EXCHANGE Update 16 Oct 2012

Approximate selectivity scales
cation exchange resins


The sulphonic resin here is a "nominal 8% DVB" product. Resins with higher cross-linking will have higher selectivity values, but the order remains unchanged.
CAUTION: the data are approximate, but the relative order should be right.
Monovalent Sulphonic
(SAC)		 Carboxylic
(WAC)
AmberliteTM example IR120 IRC86
Ion
Li+ 0.85 1.0
H+ 1.00  
Na+ 1.69 0.6
NH4+ 2.20  
K+ 2.46 0.5
Rb+ 2.54  
Cs+ 2.80 0.3
Cu+ 5.25  
Ag+ 7.54  
Tl+ 9.75  
Divalent Sulphonic Carboxylic Iminodiacetic
AmberliteTM example IR120 IRC86 IRC748
Ion
UO2++ 0.44    
Mg++ 0.63 0.3 0.8*
Zn++ 0.67 1.5 22
Co++ 0.71 1.9 17
Cu++ 0.73 2.0 550
Cd++ 0.75 1.0 28
Ni++ 0.75 1.4 55
Be++ 0.77    
Mn++ 0.79 1.4 5.0
Ca++ 1.00 1.00 1.00
Sr++ 1.25 < 1 0.6*
Pb++ 1.9 > 1 160
Ba++ 2.2 < 1 0.5*
Ra++ 2.5    
* Doubtful, but the order is Ca > Sr > Ba

For sulphonic (SAC) resins, the order of selectivity is:

Pb++ > Ca++ > Mg++ > Na+ > H+

This means that you can remove hardness (Ca & Mg) with a SAC resin in the Na form, but you cannot remove Na selectively in presence of other cations.

See also anion selectivity values.

© François de Dardel