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Effects of organic ligands on fractionation of rare earth elements (REEs) in hydroponic plants: an application to the determination of binding capacities by humic acid for modeling |
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| Authors: | Ding ShiMing Liang Tao Zhang ChaoSheng Yan JunCai Zhang ZiLi |
| Institution: | aNanjing Institute of Geography and Limnology, Chinese Academy of Science, Nanjing 210008, China bInstitute of Geographic Sciences and Natural Resources Research, Chinese Academy of Science, Beijing 100101, China cDepartment of Geography, National University of Ireland, Galway, Ireland dDepartment of Soil and Agrichemistry, Anhui Agricultural University, Hefei 230036, China |
| Abstract: | Previous studies have revealed the fractionation processes of rare earth elements (REEs) in hydroponic plants, with a heavy REE (HREE, the elements from Gd to Lu) enrichment in leaves. In this study, effects on the HREE enrichment in soybean leaves with additions of carboxylic acids (acetate, malate, citrate, NTA, EDTA and DTPA) and two soil humic acids (HAs) were investigated. REE speciation in carboxylic acid and HA solutions was simulated using Visual MINTEQ and Model V, respectively. The results showed that the effects caused by carboxylic acids were strongly dependent on the differences between their binding strengths for light REEs (LREEs, the elements from La to Eu) and those for HREEs. A good correlation existed between these effects and the changes of free REE ions in solutions. This relationship was also observed for the HA treatments, provided that the intrinsic equilibrium constants of REEs for cation–proton exchange with HA (i.e., pKMHA) in Model V were estimated using a free-energy relationship with the stability constants for REE complexation with lactic acid. It is suggested that this set of pKMHA values is more suitable for use in Model V for the simulation of REE complexation with HA. |
| Keywords: | Fractionation Humic acid Metal Model Rare earth elements (REEs) |
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