ION-EXCHANGE PROPERTIES OF NASICON-TYPE PHOSPHATES WITH THE FRAMEWORKS [TI-2(PO4)(3)] AND [TI1.7AL0.3(PO4)(3)]

Ion-exchange properties in aqueous A(+) solution (A(+)=Li+, Na+, K+, Ag+, Rb+, NH4+) are investigated for the title materials at room temperature. In LiTi2(PO4)(3) and Al-containing Li1.3Ti1.7Al0.3(PO4)(3), Li+ is exchanged rapidly and selectively by Na+ and Ag+. The exchange rate of Li1.3Ti1.7Al0.3(PO4)(3) is faster than that of LiTi2(PO4)(3); this is probably related to a larger diffusion coefficient of Li+ in the former due to its high Li+ conductivity. Large ions such as K+ are not readily accepted by the anion frameworks. Accordingly, Li1.3Ti1.7Al0.3(PO4)(3) has excellent Na+ selectivity with fast exchange rate to extract even a very small amount of Na+ in reagent-grade KOH. The Na+-exchanged product of Li1.3Ti1.7Al0.3(PO4)(3) can exchange Na+ for Ag+ selectively. The reverse exchange also occurs easily. This material can be used to recover Ag+ in waste solutions.