Extraction and separation of rare earths from chloride medium with mixtures of 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester and sec-nonylphenoxy acetic acid

摘要

BACKGROUND: 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (HEHEHP, H2A2) has been applied extensively to theextraction of rare earths. However, there are some limitations to its further utilization and the synergistic extraction of rareearths with mixtures of HEHEHP and another extractant has attracted much attention. Organic carboxylic acids are also a typeof extractant employed for the extraction of rare earths, e.g. naphthenic acid has been widely used to separate yttrium fromrare earths. Compared with naphthenic acid, sec-nonylphenoxy acetic acid (CA100, H2B2) has many advantages such as stablecomposition, low solubility, and strong acidity in the aqueous phase. In the present study, the extraction of rare earths withmixtures of HEHEHP and CA100 has been investigated. The separation of the rare earth elements is also studied. RESULTS: The synergistic enhancement coefficient decreases with increasing atomic number of the lanthanoid. A significantsynergistic effect is found for the extraction of La~(3+)as the complex LaH_2ClA_2B_2with mixtures of HEHEHP and CA100. Theequilibrium constant and thermodynamic functions obtained from the experimental results are 10-0.92 (KAB), 13.23 Id mo1-1(ΔH), 5.25 kJ mol~(-1)(ΔG), and 26.75J mol~(-1)K~(-AS),respectively. CONCLUSION: Graphical and numerical methods have been successfully employed to determine the stoichiometries for theextraction of La~(3+)with mixtures of HEHEHP and CA100. The mixtures have different extraction effects on rare earths,which provides the possibility for the separation of yttrium from heavy rare earths at an appropriate ratio of HEHEHP andCA100.