Adsorption of rare earths with crown ether adsorbents

Abstract

Crown ether-phosphotungstic acid (PW) and crown ether-phosphomolybdic acid (PMo) precipitates, and also the granular entrapped crown ether-PMo (or PW) in polyacrylamide, were prepared and applied as adsorbents for rare earth metal ions. Adsorbents containing 15-crown-5, such as 15-crown-5-PMo, were better adsorbents than the other crown ether precipitates. The adsorption capacity of 15-crown-5-PMo for Eu³⁺ was determined and corresponded to about 0.166 mmol of Eu³⁺ per gram of the adsorbent. The effects of pH and metal ion concentration on adsorption were also investigated. Crown ether-PMo (or PW) precipitates underwent hydrolysis at pH 1, but the granular entrapped crown ether-PMo (or PW)-polyacrylamide adsorbents were not hydrolysed at pH 1. The adsorption of individual rare earth ions with 15-crown-5-PMo-polyacrylamide showed that Tb³⁺, Nd³⁺, Eu³⁺ and Gd³⁺ were readily adsorbed, but adsorption was difficult for Ce⁴⁺, Sm³⁺ and Dy³⁺.