抄録
The cation-exchange properties of monovalent (K+, NH4+ and Li +) and divalent(Ca2+, Mg2+, Cd2+, Pb2+ and Ni2+) cations has been investigated for the Na-zeolite synthesized from coal fly ash by a hydrothermal reaction. The amount of NH4+ exchanged with the Na-zeolite was compared to that with a commercial product, A-4 zeolite. The effect of cations (H +, K +, Na + and NH4+) on the removal of PO43-was studied for the solution containing phosphate ions.
The cation-exchange capacity of the Na-zeolite synthesized from coal fly ash is as much as that of an A-4 zeolite. The monovalent and divalent caion exchange selectivity for Na-zeolite is shown to increase in the order of Pb2+ > Cd2+ > Ca2+ > K + > NH4+ > Ni2+ > Li+ > Mg2+. It is found that the cation-exchange selectivity is closely concerned with an electric charge and a hydration ion radius of the cation. Namely, the cation having a small hydration ionic radius might exchange much more with Na-zeolite, while the cation having a large hydration ionic radius might hardly exchange.
Phosphate ions can be removed by a quantitative precipitation formation with Ca2+ released from Ca-zeolite. In phosphate solutions such as K3 PO4, Na3 PO4 and (NH4)3 PO4, Ca2+ is released by an ion-exchange reaction between a cation in the solution and Ca2+ on the zeolite, while in H3 PO4 solution Ca2+ is supplied in the aqueous solution from the zeolite surface destroyed by the action of an acid. It is possible to remove simultaneously NH4+ and PO43- in (NH4)3 PO4 solution through an ion-exchange reaction of NH4+ with Ca-zeolite and a precipitation reaction of PO43-with Ca2+ released from Ca-zeolite.
