Selective and fast recovery of neodymium from seawater by magnetic iron oxide Fe₃O₄

Neodymium (Nd) is a key element that widely applied in high-tech industries; therefore, to recover it efficiently from aqueous solutions is rather important. This work examines the recovery of spiked Nd from seawater media by magnetic iron oxide (Fe₃O₄). A rapid increase of Nd recovery from 0.04 to 22.27mgg^-1 was observed when the solution pH adjusted from 1.98 to 8.22 at 298K. A maxima Nd adsorption capacity was estimated to be 24.88mgg^-1 at 308K and 8.22 pH. A negative change in standard free energy (δG°=-5.87, -6.69, -7.68kJmol^-1 at 288, 298, and 308K, respectively) suggests that Nd adsorption is spontaneous. The positive δH° value (2.42kJmol^-1) supports its endothermic nature of the adsorption and agrees with the observed enhanced Nd adsorption at high temperatures. Besides, the positive δS° (10.84Jmol^-1K^-1) displays that the randomness increase at the solid-solution interface during Nd adsorption. More importantly, we observed that the Nd adsorption only decreased slightly while the NaCl ionic strength increased from 0.001 to 1.0N, implying the involvement of inner-sphere mechanism. These data indicated that the adsorbent of ferrite has a great potential in selective and fast recovery of spiked Nd from seawater matrix.