Rare earth elements (REE) have been used extensively in igneous, sedimentary, and metamorphic petrology to trace source of rocks and minerals during crustal and mantle evolution [1]. The trace amounts of such metals can contaminate the surrounding watershed and ecosystem [3], representing a serious threat to human health and local ecosystems, e.g. through accumulation of metals in food chains. Commercial fertilizers have been used for decades and will probably continue to be used for many future decades. Hence, even low annual accumulation may finally build up concentrations in soil, especially where fertilizers with high heavy metal or rare earth element concentrations are used. Industrial use of rare earth elements, however, has increased about 50 times in the world during the last 40 years. Generally, the techniques employed for REE removal include precipitation, ion exchange, desorption, filtration, liquid-liquid extraction, and reverse osmosis. Precipitation methods are particularly reliable, but require large settling tank for the precipitation of voluminous alkaline sludge and a subsequent treatment is needed. Ion exchange has the advantage of allowing the recovery of metallic ions, but it is expensive. Due to the specific affinity of rare metals and metal complexing group (e.g., crown ether), the thermal and chemical stability of these complexes needs further improvements. In this work, we obtained the stability constant of the complex formation between dicyclohexyl-18-crown-6(DCH18C6) with Eu3+, La3+, Er3+ and Y3+ cations using conductometric method. A polyvinyl holoride (PVC)-based liquid membrane ion-selective electrode (ISE) for Y3+ cation was fabricated with dicyclohexyl-18-crown-6(DCH18C6) as ionophore. Diocthylphetalate (DOP) as plasticizer and eterahydrofuran (THF) as a solvent were used. The results of calibration curve for this electrode at optimized conditions exhibit a Nerstian response of 19±2 mV for Y3+ ion. Linear response over oncentration range of 1×10-6 - 1×10-2 M at 25°C was obtained. The response of ISE for Y3+ was fairly constant over the pH range of 5-10. The detection limit for this electrode is 1×10-6 M. The lifetime of the electrode is 2 months. The concentration of Y3+ was determined in wastewater and results agreed with those of atomic absorption spectrometry method.

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