STUDIES ON HETEROMACROCYCLIC POLYETHER .1 2. LIQUID MEMBRANE-TRANSPORT PROPERTIES OF METAL-CATIONS BY OXA-CROWN, THIA-CROWN, SELENA-CROWN OR TELLURA-CROWN ETHER

The liquid membrane transport rates of the nitrate salts of Na+, K+, A g+ and Pb2+ by 10-tellurabenzo-15-crown-5 (TeB15C5) were firstly deter mined, and compared with those by the corresponding benzo-15-crown-5 ( B15C5), 10-thiabenzo-15-crown-5 (SB15C5) and 10-selenabenzo-15-crown-5 (SeB15C5), At the same time, the effects of the concentrations of SeB 15C5 in the membrane phase and K+ in the source phase on the transport rates of K+ were also investigated, The experimental data indicate th at the relationship is linear between the transport rates of K+ and th e concentrations of SeB15C5 and K+ respectively, The transport rates o f Na+, K+ and Pb2+ by TeB15C5 are larger than those by SB15C5 and SeB1 5C5, but the transport rates of Ag+ by SB15C5 and SeB15C5, especially by SeB15C5, are much larger than those by TeB15C5. SB15C5 and SeB15C5 show a very high transport selectivity for Ag+ over Na+, K+ and Pb2+, and can be used to separate and recover noble metals such as silver.