Application to real samples

Examples of using solid-liquid separation at an industrial level are scarce. Diphonix was used to extract REE from the nitric acid solution from apatite processing on a pilot scale at Akron public corporation (Ehrlich & Lisichkin, 2017). However, there are lab studies in literature where various adsorbents have been used to separate REEs from various natural samples such as bauxite mud (Hu et al., 2019; Ochsenkühn-Petropulu et al., 1995; Roosen et al., 2016; ZHOU et al., 2008); Silicate & niobium mining deposits (Hu et al., 2017); apatite, orthite, and slag (Kostenko et al., 2019; Ogata et al., 2016); bastnäsite (Dolak et al., 2015), acidic mine drainage (Hermassi et al., 2021; Ramasamy et al., 2019; Ramasamy, Puhakka, Iftekhar, et al., 2018; Ramasamy, Puhakka, Repo, Ben Hammouda, et al., 2018); spiked seawater (Callura et al., 2018; Noack et al., 2016); spiked river/groundwater and sewage water (Marwani et al., 2018; Yantasee et al., 2009); geothermal brines (Liu et al., 2021), acidic streams, dialysate (Yantasee et al., 2009); REE mineral leachate (Giret et al., 2018); industrial wastewater (Li et al., 2013); leached solution of spent Ni-MH cells (Gasser & Aly, 2013; Kołodyńska et al., 2019), thin-film phosphors leached solution (Schaeffer et al., 2017), phosphoric acid plant effluent (Al-Thyabat & Zhang, 2015), zinc mine ore (Fonseka et al., 2021), and coal fly ash (Brown & Balkus, 2021; Hovey et al., 2021; Mondal et al., 2019).
These adsorbents showed varying degrees of success for REEs extraction (Figure 4). REEs extraction from red mud used ion-exchanger Dowex 50W-X8 in combination with the solvent extraction method (Ochsenkühn-Petropulu et al., 1995). The whole separation process resulted in an average 93% recovery of Sc(III). High La(III) and Nd(III) recovery (98%) from spent Ni-MH cells were achieved using layered double hydroxide (or hydrotalcite) functionalized with Cyanex-272 (Fe-Mg-LDH-Cyanex-272) (Gasser & Aly, 2013). In another study, 95% of REE were separated at pH 4.2 from the waste sulfate solutions of uranium leaching solution using carboxyl adsorbent CYBBER LX 280, after an initial step involving Fe(OH)3 precipitation (Lokshin et al., 2013). Bidentate phthaloyl diamide (PA) functionalized KIT-6 showed high selectivity for Lu(III) from a leached solution of silicate and niobium mining deposit samples (legend 6-11, Figure 4) (Hu et al., 2017). The adsorbent tetradentate phenylenedioxy diamide (PDDA) functionalized KIT-6 showed a higher affinity for HREEs in the case of KIT-6-1,2-PDDA (legend 14 Figure 4) and LREEs with KIT-6-1,3-PDDA (legend 15 Figure 4) while extracting REEs from red bauxite residue (Hu et al., 2019). Silica gel functionalized with phosphonoacetic acid (PAA), N, N-bis(phosphonomethyl) gylcine (BPG), diethylenetriaminepentaacetic acid (DTPA), and diethylenetriaminepentaacetic dianhydride (DTPADA) were able to adsorb REEs from spiked brine samples with high efficiency (legend 16-26, Figure 4) (Callura et al., 2018; Noack et al., 2016). Nd(III)-ion imprinted polymer extracted 100% Nd(III) from bastnäsite leachate solution (Dolak et al., 2015). In fly ash leachate solution, bis(ethylhexyl)amido diethylenetriaminepentaacetic acid-functionalized silica showed selectivity for REEs over Fe and Al that were present in much higher concentrations than REEs (~700- to 90,000-fold excess) (Hovey et al., 2021). Eu(III) was selectively recovered (88% Eu(III) recovery, <10% recovery of competitive ions) from zinc mine ore leachate solution adjusted to pH 5.5 using PMIDA functionalized MOF (Cr-MIL-PMIDA) (Fonseka et al., 2021). The single-element Eu(III) adsorption at pH 5.5 was 90-91%; thus, the presence of a high concentration of competing ions did not affect the Eu(III) adsorption. The Langmuir maximum capacity (qm) for Eu(III) on Cr-MIL-PMIDA was 69.14 mg/g.