Non-dispersive solvent extraction of neodymium using a hollow fiber contactor: Mass transfer and modeling studies

• Nd separation by NDSX was studied.
• DNPPA and TOPO mixtures were used.
• Transport data were modeled and agreed well with experiments.
• The NDSX method can be used for Nd recovery from acidic feeds.

Non-dispersive solvent extraction (NDSX) of Nd(III) from nitric acid feed solutions was carried out for the first time employing a hollow fiber contactor which used a mixture of di-nonyl phenyl phosphoric acid (DNPPA) and tri-n-octylphosphine oxide (TOPO) in petrofin as the carrier extractant. The transport efficiency was found to be reasonably good with quantitative metal ion recovery (>99.9%) in about 30 min. The effect of feed acidity, extractant concentration, flow rates of feed and extractant solution on the transport of neodymium was investigated in recycling mode. For possible applications to different types of feed solutions, NDSX studies were also carried out at varying Nd concentrations and linear increase in Nd mass transfer was seen resulting in quantitative transport in about 40 min for feeds containing as high as 1.6 g/L of Nd. Various diffusional parameters for the mass transfer of neodymium in the extractant solution were calculated. A mathematical model was developed for prediction of the extraction behavior of Nd(III) in the extractant solution and mass transfer coefficients were calculated. The developed model was successfully validated with the experimental results under different feed conditions.