Selective extraction of rare-earth elements from rocks using a high capacity cis-1,4-butanedioic acid-functionalized resin

A high-capacity carboxylic acid functionalized resin prepared by ring-opening metathesis polymerization containing cis-1,4-butanedioic acid (succinic acid) units was used for the extraction of rare-earth elements (REEs) from rock digests. Extraction efficiencies measured by means of ICP-AES were found to be in the range of 90-100% for standards containing 5 and 500 ppb of each REE, respectively. The optimum extraction pH was found to be between 5.3 and 5.5. Three different rock standard reference materials (SRMs), GSR-1 granite, GSR-2 andesite and GSR-3 basalt, were digested by fusion of the corresponding rock with lithium metaborate (LiBO2) and subsequent dissolution in nitric acid. As a consequence of the different compositions of the three investigated SRMs, the resulting digest showed different concentrations of the REEs as well as of SiO2, Fe, Al, Mg, and Ca. The entire extraction procedure was additionally supported by masking of the interfering metal ions using 5-sulfosalicylic acid. Small amounts of methanol were added to prevent silicate from precipitating, Following this setup, REEs occurring in the digest solutions in the range of 40 ppt to 150 ppb were retained selectively, with recoveries ranging for most elements from 75 to 110%, The high performance of the entire system is underlined by the fact that relative standard deviations were <10% for most of the REEs.