| Abstract Scope |
Supercritical carbon dioxide (sc-CO2) is an emerging green solvent for recovery of metals from secondary sources. The sc-CO2 is a non-polar solvent; thus, a suitable chelating agent is required to accommodate a polarity difference between the solute and solvent during the extraction of metal ions and organometallic compounds. This study investigates four different organophosphorus ligands including triethyl phosphate (TEP), tri-n-butyl phosphate (TBP), tributyl phosphine oxide (TBPO), and trioctyl phosphine oxide (TOPO), on the solubility and effect on extraction for neodymium from NdFeB magnet in sc-CO2. A COSMO-vac model was developed to estimate solubility of the four agents in sc-CO2, and it shows that the order of solubility is following: TEP > TBPO ~ TBP > TOPO. The coordination environment of neodymium was determined by UV-Vis measurement, resulting a TEP:Nd = 1, TBP:Nd = 3, TBPO:Nd = 3, and TOPO:Nd = 4. The highest extraction for neodymium is achieved with TEP, which is due to low coordination number resulting less hydrophobic interactions between aliphatic functionalities, and the smaller micellar assemblies has a higher solubility in sc-CO2; thus, a higher extraction efficiency is achieved. |