EXTRACTION AND SEPARATION OF RARE-EARTH ELEMENTS BY TRI-NORMAL-OCTYLMETHYLAMMONIUM NITRATE AND BETA-DIKETONE USING WATER-SOLUBLE COMPLEXING AGENT

Extraction and separation of rare-earth elements by tri-n-octylmethylammonium nitrate (TOMAN) and beta-diketone (alpha-acetyl-m-dodecylacetophenone: LIX54) in the presence of water-soluble complexing agent (ethylenediaminetetraacetic acid: EDTA) was investigated. All EDTA make 1:1 complex with rare earth, and only free (not complexed) rare-earth ions can take part in the extraction. Although the distribution ratio of the metals decreases by addition of EDTA, the separation factor increases since extractability of the heavier rare earth is further reduced by formation of inactive EDTA complex. The effect of EDTA on the separation factor can be predicted using the distribution ratio of each element in the absence of EDTA, the ratio of stability constants of the complexes and the feed concentration of the species. Separation and recovery of rare-earth elements from the aqueous raffinate solution was feasible by extraction of metals using tri-n-butylphosphate (TBP) in acidic conditions. Simulation of Nd/Pr separation by continuous counter-current batteries showed that Pr was highly purified by addition of EDTA in aqueous phase.