•Undiluted [P66614][Cl]-DEHEHP has obvious synergistic extraction effect for light rare earths.•RE(NO3)3 has been confirmed to be transferred into the ionic liquid phase.•The extraction of rare earths follows a two-step ion association mechanism.•The ion-association reactions will not liberate any organic component into the aqueous phase.•[P66614][Cl]-DEHEHP has a high loading capacity as 0.78 mol/L Pr.The coexistence of tricaprylmethylammonium nitrate ([A336][NO3]) and Di(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP) has been found an obvious synergistic extraction effect for rare earths nitrates. In this work, synergistic extraction behaviors without any diluent for rare earth nitrates based on tri(hexyl)tetradecylphosphonium chloride (Cyphos®IL 101, [P66614][Cl]) and DEHEHP have been further investigated. Pr(III) was still used as a model RE, and the maximum synergistic extraction distribution ratio was obtained at a volume ratio of 2:3 for [P66614][Cl] and DEHEHP. The synergistic enhancement coefficients have been tested for the whole rare earths. Results show that there is an obvious synergistic enhancement effect for light REs (La-Sm) and an anti-synergistic effect for Gd-Lu including Y. The effects of acidity, anions and metal ion concentrations on the extraction have been investigated. The extraction mechanism has been confirmed to be the typical ion-association reactions. The maximum loading capacity is 0.78 mol/L Pr at 293.15 K. The extraction ability of [P66614][Cl]-DEHEHP is superior to that of reported [A336][NO3]-DEHEHP, and is also greater than that of common acidic organophosphate-kerosene extraction system. Stripping, recyclability, and selectivity between REs and non-REs, has also been investigated.

Na-ion batteries are becoming increasingly attractive as a low cost energy storage device. Sodium vanadium fluorophosphates have been studied extensively recently due to their high storage capacity and high discharge voltage. Shape and size often have a crucial influence over the properties. The controlling synthesis of nanoparticles with special microstructures is significant, which becomes a challenging issue and has drawn considerable attention. In this study, Na3(VPO4)2F3 nanoflowers have been synthesized via a pH-regulative low-temperature (120 °C) hydro-thermal route. In particular, it is a green route without any organic compounds involved. The hydro-thermal reaction time for the formation of Na3(VPO4)2F3 nanoflowers has also been investigated. A weak acid environment (pH = 2.60) with the possible presence of hydrogen fluoride molecules is necessary for the formation of the desired nanoflower microstructures. Compared to the nanoparticles obtained by Na2HPO4·12H2O, the as-synthesized Na3(VPO4)2F3 nanoflowers showed an excellent Na-storage performance in terms of superior cycle stability, even without any further carbon coating or high-temperature treatment.

•A novel two-step decomposition strategy for mixed RE concentrate is proposed.•Bastnaesite (RECO3F) can be decomposed at the first air-oxidization step.•Monazite (REPO4) can be decomposed at the second Na2CO3-roasting step.•Both the roasting processes have no apparent lumps produced.•Respective recovery of F, P, Th, RE can be expected from H2SO4-leaching liquors.The decomposition of the mixed RE (rare earth) concentrate bastnaesite (RECO3F) and monazite (REPO4) has been investigated extensively for a few decades. In this work, a novel environmental friendly Na2CO3-based roasting decomposition strategy for the mixed RE concentrate has been proposed. It is a two-step strategy combining air-oxidation and Na2CO3-roasting. In the first step of air-oxidation, almost all of bastnaesite decomposes. While more than 95% of monazite decomposes in the second Na2CO3-roasting step. Thus, the consumption of Na2CO3 in the current proposed process would decrease greatly. The Na2CO3-roasting phenomena were compared among the reactions of Na2CO3-mixed RE concentrate, Na2CO3-pure bastnaesite and Na2CO3-the first leaching residue by H2SO4. The air-roasting temperature was optimized. In particular, the roasting temperature for the reaction of Na2CO3 and H2SO4-leaching residue has been optimized according to P- and Ce-leaching percents. Finally, following the proposed flowsheet under the optimized conditions, taking 50 g of mixed RE concentrate as feedings, the final solid residue occupies around 2.4%. In addition, about 70% of F and 87% of P can be transferred into H2SO4-leaching liquor and H2O-leaching liquor, respectively. 93.7% of Th and 96.6% of RE can be leached. Finally, a H2SO4-leaching liquor containing Th, Ce(IV), RE(III) and F can be obtained for the subsequent separation.

In this work, a novel IL-based synergistic extraction system utilizing the ionic liquid tricaprylmethylammonium nitrate ([A336][NO3]) and the commercial extractant di(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP) was developed for the extraction of rare earth (RE) nitrates. Pr(III) was used as a model RE and the effects of key factors, i.e. the ratio of [A336][NO3] to DEHEHP, the acidity of feed solutions, and the concentration of a salting-out reagent, were systematically studied. Our results demonstrate that the mixture of [A336][NO3] and DEHEHP had an obviously synergistic extraction effect for the extraction of Pr(III). The maximum synergistic enhancement coefficient of 3.44 was attained at XA = 0.4 (v%). Alternatively, a mixture of [A336][Cl] and DEHEHP hardly extracted Pr(III) from chloride media. Moreover, we investigated the Pr(III) extraction mechanism and demonstrated that Pr(III) can be extracted as the neutral complexation species Pr(NO3)3·xDEHEHP and the ion-type species [A336]y·Pr(NO3)3+y. These extraction processes can effectively hamper the release of organic cation-ligands into the aqueous phase. The synergistic extraction effect is mainly derived from the enhanced solubility of the extracted species in the ionic liquid phase. The extraction behaviors of Pr(III) could be properly described by Langmuir and pseudo-second-order rate equations. An increase in temperature was unfavorable for the extraction reaction but greatly improved the extraction rate. Interestingly, the mixed IL extraction system has an obviously synergistic extraction effect for light REs (LREs, La–Eu), but an anti-synergistic effect for heavy REs (HREs, Gd–Lu, Y), thus indicating that our synergistic extraction system is helpful for the separation of LREs from HREs. In addition, the high selectivity between REs and non-REs suggested that the recovery of REs from a complicated high-salt leachate could be highly possible. It demonstrates that the IL-based synergistic extraction strategy developed in this work is promising and sustainable, and as a result the development of an IL-based synergistic extraction process for the recovery of REs is straightforwardly envisaged.

Hydrothermal carbon spherules (HCSs) can be loaded with a variety of metal nanoparticles for various applications. In this work, three types of HCSs were prepared from saccharides (mono-, di- and poly-saccharides) by a modified hydrothermal method using glucose, sucrose and starch as sources. Au nanoparticles can be deposited onto the HCSs through a regular adsorption process. For comparison, the HCSs made from mono-saccharide glucose (HCSs-M) have a higher adsorption capacity for Au(III) from aqueous acidic chloride media. The adsorption behaviors for AuCl4− by HCSs-M were systematically investigated. HCSs-M shows a high selectivity for Au(III) towards Pd(II), Pt(VI), Rh(III) and some relevant base metals such as Fe(III), Co(II), Cu(II) and Ni(II). An extra reductant glycine can not only significantly improve the adsorption capacities and selectivity, but also accelerate the adsorption rate. The Langmuir isotherm model and the 2nd-order kinetics model can properly describe the adsorption behaviors of AuCl4−. The adsorption mechanism of Au(III) by HCSs has been confirmed by XPS, XRD, TG, FTIR, SEM and TEM techniques, which demonstrate that AuCl4− deposited onto the HCSs has been reduced to Au0. On the basis of this phenomenon, a reduction–deposition coupled mechanism has been proposed. The current research illustrates the prospect for HCSs to be used as effective adsorbents for the selective adsorption separation of Au(III) from chloride media. It also demonstrates the possibility to integrate the selective recovery of gold from complex industrial waste streams and the fabrication of functional carbon materials through loading with gold nanoparticles.

We demonstrate that a series of high-performance cathode materials, sodium vanadium polyanionic compounds, Na3(VO1−xPO4)2F1+2x (x = 0, 0.5 and 1), can be synthesized by a phase-transfer assisted solvo-thermal strategy at a rather low temperature (80–140 °C) in one simple step, exhibiting a high Na storage capacity of ca. 120 mA h g−1 and excellent cycling performance. This study makes a significant step to extend this strategy to the synthesis of functional materials from simple binary to complex multicomponent compounds.

•Phase transfer assisted solvo-thermal can get REF3 or Ln3+-doped YF3 nanocrystals.•REF3 or Ln3+-doped YF3 nanocrystals have disk-stacked cylinder nanostructures.•Acid-base-coupled extractant PN plays a key role for such a special nanostructure.•The nanocrystals possess valued down- and up-conversion luminescent properties.•The current approach could be extended to other metal fluorides nanoparticles.Monodisperse orthorhombic-phase rare earth fluorides nano-/microcrystals with a special shape of disk-stacked cylinder have been synthesized via a facile phase transfer assisted solvo-thermal route, where an acid-base-coupled extractant has been employed to transfer hydrofluoric acid into an oil phase as a fluoride source. The synthetic parameters have been optimized and a possible formation mechanism has also been proposed. More importantly, the adopted acid-base-coupled extractant in this route can be recycled. Surveying all of the lanthanides from La to Lu, most of the heavy rare earths, such as Tb, Dy, Ho, Er, Tm and Yb, can form LnF3 nanocrystals with the similar morphologies. Furthermore, Ln3+-doped YF3 (Ln = Tb, Yb/Er) nanocrystals have also been synthesized, and their down-conversion and up-conversion (980 nm) luminescent properties were examined. The current approach could be extended to synthesize other metal fluorides nanoparticles.

•The maximum βV/Cr by pure [C8mim][PF6] was 100.6 in case of pH 3.5.•The extraction mechanism could be the anion exchange between HV10O273− and PF6−.•A novel approach to prepare ionic liquids with metal oxo-anions as counter anion.•Vanadate-loaded IL phase can be quantitatively stripped by KPF6 and NaOH.•Pure [C8mim][PF6] could be used to recover V(V) from Cr(VI)-containing solutions.Separations among vanadium(V) and chromium(VI) remain challenging. The extraction behaviors of V(V) along with Cr(VI) by a few of pure imidazolium-based hydrophobic ionic liquids have been investigated. Among these hydrophobic ionic liquids, [C8mim][PF6] exhibits a special extraction for V(V) while a weak extraction for Cr(VI). The extraction behavior of V(V) by [C8mim][PF6] was particularly studied. The extraction of V(V) is strongly dependent on the acidity of the aqueous phase, and the maximum separation factor between V and Cr (βV/Cr) was calculated to be 100.6 in case of pH 3.5. The most probable extraction mechanism of V(V) has been proposed to be the anion exchange between the main species HV10O273− and PF6−. Furthermore, V(V) in IL phase can be quantitatively stripped by KPF6 solution under the basic condition (COH− = 1 mol/l). Recycle test indicates that the extraction capacity shows no apparent decline until the 9th continuous extraction–stripping cycle. The result also provides a new approach for the preparation of a novel ionic liquid with metal oxo-anions as counter anion.Graphical abstract

•The maximum βV/Cr by pure [C8mim][PF6] was 100.6 in case of pH 3.5.•The extraction mechanism could be the anion exchange between HV10O273− and PF6−.•A novel approach to prepare ionic liquids with metal oxo-anions as counter anion.•Vanadate-loaded IL phase can be quantitatively stripped by KPF6 and NaOH.•Pure [C8mim][PF6] could be used to recover V(V) from Cr(VI)-containing solutions.Separations among vanadium(V) and chromium(VI) remain challenging. The extraction behaviors of V(V) along with Cr(VI) by a few of pure imidazolium-based hydrophobic ionic liquids have been investigated. Among these hydrophobic ionic liquids, [C8mim][PF6] exhibits a special extraction for V(V) while a weak extraction for Cr(VI). The extraction behavior of V(V) by [C8mim][PF6] was particularly studied. The extraction of V(V) is strongly dependent on the acidity of the aqueous phase, and the maximum separation factor between V and Cr (βV/Cr) was calculated to be 100.6 in case of pH 3.5. The most probable extraction mechanism of V(V) has been proposed to be the anion exchange between the main species HV10O273− and PF6−. Furthermore, V(V) in IL phase can be quantitatively stripped by KPF6 solution under the basic condition (COH− = 1 mol/l). Recycle test indicates that the extraction capacity shows no apparent decline until the 9th continuous extraction–stripping cycle. The result also provides a new approach for the preparation of a novel ionic liquid with metal oxo-anions as counter anion.Graphical abstractDownload full-size image

Hydrothermal carbon spherules (HCSs) can be loaded with a variety of metal nanoparticles for various applications. In this work, three types of HCSs were prepared from saccharides (mono-, di- and poly-saccharides) by a modified hydrothermal method using glucose, sucrose and starch as sources. Au nanoparticles can be deposited onto the HCSs through a regular adsorption process. For comparison, the HCSs made from mono-saccharide glucose (HCSs-M) have a higher adsorption capacity for Au(III) from aqueous acidic chloride media. The adsorption behaviors for AuCl4− by HCSs-M were systematically investigated. HCSs-M shows a high selectivity for Au(III) towards Pd(II), Pt(VI), Rh(III) and some relevant base metals such as Fe(III), Co(II), Cu(II) and Ni(II). An extra reductant glycine can not only significantly improve the adsorption capacities and selectivity, but also accelerate the adsorption rate. The Langmuir isotherm model and the 2nd-order kinetics model can properly describe the adsorption behaviors of AuCl4−. The adsorption mechanism of Au(III) by HCSs has been confirmed by XPS, XRD, TG, FTIR, SEM and TEM techniques, which demonstrate that AuCl4− deposited onto the HCSs has been reduced to Au0. On the basis of this phenomenon, a reduction–deposition coupled mechanism has been proposed. The current research illustrates the prospect for HCSs to be used as effective adsorbents for the selective adsorption separation of Au(III) from chloride media. It also demonstrates the possibility to integrate the selective recovery of gold from complex industrial waste streams and the fabrication of functional carbon materials through loading with gold nanoparticles.

Na-ion batteries are becoming increasingly attractive as a low cost energy storage device. Sodium vanadium fluorophosphates have been studied extensively recently due to their high storage capacity and high discharge voltage. Shape and size often have a crucial influence over the properties. The controlling synthesis of nanoparticles with special microstructures is significant, which becomes a challenging issue and has drawn considerable attention. In this study, Na3(VPO4)2F3 nanoflowers have been synthesized via a pH-regulative low-temperature (120 °C) hydro-thermal route. In particular, it is a green route without any organic compounds involved. The hydro-thermal reaction time for the formation of Na3(VPO4)2F3 nanoflowers has also been investigated. A weak acid environment (pH = 2.60) with the possible presence of hydrogen fluoride molecules is necessary for the formation of the desired nanoflower microstructures. Compared to the nanoparticles obtained by Na2HPO4·12H2O, the as-synthesized Na3(VPO4)2F3 nanoflowers showed an excellent Na-storage performance in terms of superior cycle stability, even without any further carbon coating or high-temperature treatment.

We demonstrate that a series of high-performance cathode materials, sodium vanadium polyanionic compounds, Na3(VO1−xPO4)2F1+2x (x = 0, 0.5 and 1), can be synthesized by a phase-transfer assisted solvo-thermal strategy at a rather low temperature (80–140 °C) in one simple step, exhibiting a high Na storage capacity of ca. 120 mA h g−1 and excellent cycling performance. This study makes a significant step to extend this strategy to the synthesis of functional materials from simple binary to complex multicomponent compounds.