Titration of an aminophosphonate-chelating ion-exchange resin Duolite
C467 in hydronium form with 1 M NaOH in 1 M NaCl reflected the diproti
c nature of this exchanger. Two inflection points were detected: at pH
values 9.3 and about 6.1. ion-exchange capacity calculated from the s
econd inflection point was 4.80 meg per g of dry hydronium-form resin.
Sodium ion uptake exceeded this value by as much as 2.6 meq/g, which
is assumed to have been caused by sorption of NaCl electrolyte. Exchan
ge of the less acidic hydronium ion for sodium ion showed a constant c
ornered selectivity coefficient (K-H) value of -6.5 (logK(H)) in the s
odium ion conversion range 50-90%. The corresponding value for the exc
hange of the more acidic hydronium ion was between -4 and -5 in the so
dium ion conversion range 10-50%. Hydrolysis of the sodium-form resin
in NaCl solutions does not essentially convert the resin into hydroniu
m form but considerably increases the solution pH.