CA2824769A1 - Method for separating metals - Google Patents

Abstract

A method for separating metals in a mixture of metallic compounds is provided.
The method comprises the steps of mixing the mixture with a carboxylic acid, selectively converting at least one of the metallic compounds into a metal carboxylate complex, thereby producing a mixture of said metal carboxylate complex with unreacted metallic compounds, and separating the metal carboxylate complex from the unreacted metallic compounds.

Description

METHOD FOR SEPARATING METALS
FIELD OF THE INVENTION
[0001] The present invention relates to method for separating metals. More specifically, the present invention is concerned with a method for separating metals in a mixture of metallic compounds such as oxides, sulfides, silicates, phosphates, hydroxides and/or carbonates of metals.
BACKGROUND OF THE INVENTION

[0002] The development of environmentally-friendly and sustainable chemical synthesis and processing is one of the central tasks of modern science and technology. In this context, the clean synthesis of coordination or metal-organic compounds has been explored through a variety of techniques, including sonochemistry, microwave synthesis, electrochemistry, mechanosynthesis and alternative solvents [0003] Metal oxides and sulfides are rarely used as starting materials due to their low solubility and inert nature, resulting from high lattice energies (4-6 MJ moll) of most metal oxides. Consequently, laboratory transformations of metal oxides into metal-organic materials typically require energy-intensive processes. An example is the conversion of ZnO or cobalt(II) carbonate into porous frameworks via melt reactions lasting several days at 1200C-160 C.

[0004] In this context, mechanochemistry (neat grinding or milling, liquid-assisted grinding and ion-and liquid-assisted grinding) has provided routes to quantitative conversion of a small number of main group or do-metal oxides (ZnO, MgO, CdO and Bi203) into functional materials, including metal-organic compounds, porous metal-organic frameworks (M0Fs), pharmaceuticals and metallodrugs. Mechanochemistry has been less efficient in converting other types of metal oxides or sulfides into metal-organic materials. Typical transition metal oxides (e.g. NiO, CoO, MnO, Sc203), rare earth (lanthanide) metal oxides (e.g. Ce02, Nd203, Lu203), and actinide oxides (e.g. Th02, U308) have not been used as precursors in mechanosyntheses of coordination polymers.
Mechanochemical approaches applicable to ZnO and MgO are not easily transferred to transition, rare earth or actinide metal oxides. Instead, mechanosynthesis of coordination compounds of Co, Ni or Cu uses reactive acetates, carbonates, halides or hydroxides.

[0005] Microorganisms, in particular lichens, are capable of transforming inert inorganic minerals into metal-organic derivatives through excretion of small molecules known as lichen acids. Such very slow geological biomineralization, known as mineral weathering or neogenesis, is essential to the formation of secondary metal-organic minerals (also called "organic" minerals) from oxides, sulfides, carbonates or phosphates. Oxalic acid is one of very many known lichen acids. Oxalic acid generated by lichens or found as ammonium oxalate in guano can thus slowly convert copper ores into copper(II) oxalate mineral Moolooite.
Other examples of mineral weathering by microorganisms include the formation of readily extractable deposits of metal oxalate biominerals Humboldtine, Lindbergite and Glushinskite, based on iron(II), manganese(II) and magnesium respectively. In vitro experiments have also demonstrated the biomineralization of lead oxalate by Aspergillus niger or the lichen Diploschistes muscorum.

[0006] Byrn and co-workers have described the complexation of MgO by aging in the presence of carboxylic acid pharmaceuticals.

[0007] The inventors have shown that ZnO can be converted into zeolitic frameworks by aging with imidazole ligands at high humidity and with a catalytic amount of an ammonium salt.
SUMMARY OF THE INVENTION

[0008] In accordance with the present invention, there is provided:
1. A method for separating metals in a mixture of metallic compounds, the method comprising the steps of:
= mixing the mixture with a carboxylic acid, = selectively converting at least one of the metallic compounds into a metal carboxylate complex, thereby producing a mixture of said metal carboxylate complex with unreacted metallic compounds, and = separating the metal carboxylate complex from the unreacted metallic compounds.
2. The method of claim 1, further comprising milling the mixture of metallic compounds with the carboxylic acid prior to the converting step.
3. The method of claim 1 or 2, wherein the metallic compounds are oxides, sulfides, silicates, phosphates, =
hydroxides and/or carbonates of said metals, preferably oxides and/or sulfides.
4. The method of any one of claims 1 to 3, wherein the metals are two or more of manganese, copper, nickel, cobalt, zinc, lead, magnesium, silver, neodymium, bismuth, antimony, arsenic, tin, cadmium, praseodymium, lutetium, europium, and ytterbium.
5. The method of claim 4, wherein the metals are copper and zinc.
6. The method of claim 5, wherein the metallic compounds are copper oxide and zinc oxide.
7. The method of claim 5, wherein the metallic compounds are copper sulfide and zinc sulfide.
8. The method of claim 4, wherein the metals are copper and lead.

9. The method of claim 8, wherein the metallic compounds are copper oxide and lead oxide.

10. The method of claim 8, wherein the metallic compounds are copper sulfide and lead sulfide.

11. The method of claim 4, wherein the metals are lead and zinc.

12. The method of claim 11, wherein the metallic compounds are lead oxide and zinc oxide.

13. The method of claim 11, wherein the metallic compounds are lead sulfide and zinc sulfide.

14. The method of claim 4, wherein the metals are lead and silver.

15. The method of claim 14, wherein the metallic compounds are lead sulfide and silver sulfide.

16. The method of claim 4, wherein the metals are zinc and silver.

17. The method of claim 4, wherein the metallic compounds are zinc sulfide and silver sulfide.

18. The method of claim 4, wherein the metals are neodymium and lutetium.

19. The method of claim 18, wherein the metallic compounds are neodymium oxide and lutetium oxide.

20. The method of claim 4, wherein the metals are europium and ytterbium.

21. The method of claim 20, wherein the metallic compounds are europium oxide and ytterbium oxide.

22. The method of any one of claims 1 to 21, wherein the carboxylic acid is a solid.

23. The method of claim 22, wherein the carboxylic acid is oxalic acid, salicylic acid, acetylenedicarboxylic acid, fumaric acid, terephthalic acid, succinic acid, or benzoic acid.

24. The method of any one of claims 1 to 23, wherein in the mixing step, the mixture is mixed with the carboxylic acid and with a salt of the carboxylic acid, said salt comprising a cation and the carboxylic acid in deprotonated from as an anion.

25. The method of claim 24, wherein the cation is an organic cation, such as an ammonium, diammonium, or oligoammonium cation, an alkaline metal cation, or an alkaline earth metal cation.

26. The method of any one of claims 1 to 25, wherein the converting step is carried out a temperature above 0 C and below 100 C, preferably between about 15 C and about 85 C, more preferably between room temperature and about 65 C, even more preferably between room temperature and about 45 C, most preferably at about 45 C.

27. The method of any one of claims 1 to 26, wherein the converting step is carried out at a relative humidity above 0%, preferably above about 50%, more preferably above about 75%, even more preferably above about 85%, yet more preferably above about 95%, most preferably of about 98% or more.

28. The method of any one of claims 1 to 27, wherein the converting step is carried out at atmospheric pressure.

29. The method of any one of claims 1 to 28, wherein the metal carboxylate complex is separated from the unreacted metallic compounds by flotation.

30. The method of any one of claims 1 to 28, wherein the metal carboxylate complex is separated from the unreacted metallic compounds by dissolution and filtration.

31. The method of any one of claims 1 to 30, further comprising separating the metals in the unreacted metallic compounds using the method of claim 1.

32. The method of any one of claims 1 to 31, wherein more than one metallic compounds are converted into more than one metal carboxylate complexes, the method further comprising, after the separating step, the step of heating the more than one metal carboxylate complexes to produce corresponding more than one metal oxides, and separating the metals in the more than one metal oxides using the method of claim 1.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] In the appended drawings:
[0010] Figure 1 shows (a) two coordination polymer chains, connected by hydrogen bonds (yellow dotted lines) in the crystal structure of zinc oxalate dihydrate (CCDC code QQQB0D04).
Selected PXRD patterns for aging reactions of ZnO and oxalic acid dihydrate under 98% relative humidity (RH):
(b) oxalic acid dihydrate; (c) simulated for zinc oxalate dihydrate; (d) ZnO; (e) 1 day at room temperature;
(f) 5 days at room temperature; (g) 1 day at 45 C; (h) 5 days at 45 C; (i) 1 day at room temperature with 5 min pre-milling; (j) 5 days at room temperature with 5 min pre-milling and (k) 10 days at room temperature with 5 min pre-milling. (I) Completed 10 gram aging syntheses of zinc oxalate dihydrate and nickel(11) oxalate dihydrate.
[0011] Figure 2 shows a comparison of PXRD patterns for the aging reactions of ZnO and oxalic acid dihydrate at 98% relative humidity and different conditions (top to bottom):
commercial ZnO; oxalic acid dihydrate; manually prepared reaction mixture after 1 day at 45 C; manually prepared reaction mixture after 1 day at room temperature; manually prepared reaction mixture after 3 days at 45 C; manually prepared reaction mixture after 3 days at room temperature; manually prepared reaction mixture after 5 days at 45 C; manually prepared reaction mixture after 5 days at room temperature; manually prepared reaction mixture after 7 days at 45 00 (10 gram scale) ;briefly milled reaction mixture after 1 day at room temperature; briefly milled reaction mixture after 5 days at room temperature and briefly milled reaction mixture after 1 day at room temperature. For comparison, the simulated pattern of zinc oxalate dihydrate (CCDC code QQ0BOD04) is also given.
[0012] Figure 3 shows FTIR-ATR spectra of final products of aging reactions between oxalic acid dihydrate and: (a) ZnO: 5 days at 45 C; (b) Co0: 7 days at 45 C; (c); NiO: 7 days at 45 C; (d) CuO: 16 days at 45 C; (e) MgO: 9 days at 45 C; (f) MnO: 16 days at room temperature; (g) MnO: 16 days at 45 C; (h) Pb0: 14 days at 45 C and (i) MnO: aging of a pre-milled sample for 1 day at 45 C. The FTIR-ATR
spectrum of reactant H2ox.2H20 is given under (j).
[0013] Figure 4 shows a comparison of PXRD patterns for the aging reactions of NiO and oxalic acid dihydrate at 98% relative humidity and different conditions (top to bottom): commercial NiO; oxalic acid dihydrate; manually prepared reaction mixture after 1 day at 45 C; manually prepared reaction mixture after 1 day at room temperature; manually prepared reaction mixture after 3 days at 45 C;
manually prepared reaction mixture after 3 days at room temperature; manually prepared reaction mixture after 5 days at 45 C; manually prepared reaction mixture after 5 days at room temperature; manually prepared reaction mixture after 7 days at 45 C;
manually prepared reaction mixture after 25 days at room temperature; manually prepared reaction mixture after 7 days at 45 C (10 gram scale); briefly milled reaction mixture after 1 day at room temperature; briefly milled reaction mixture after 5 days at room temperature and briefly milled reaction mixture after 1 day at room temperature. For comparison, the simulated pattern of zinc oxalate dihydrate (ICSD code 150590) is also given.

[0014] Figure 5 shows a comparison of PXRD patterns for the aging reactions of MgO and oxalic acid dihydrate at 98% relative humidity and different conditions (top to bottom):
commercial MgO after calcination;
oxalic acid dihydrate; manually prepared reaction mixture after 1 day at 45 C; manually prepared reaction mixture after 1 day at room temperature; manually prepared reaction mixture after 3 days at 45 C; manually prepared reaction mixture after 3 days at room temperature; manually prepared reaction mixture after 5 days at 45 C; manually prepared reaction mixture after 5 days at room temperature; ;
manually prepared reaction mixture after 9 days at 45 C; manually prepared reaction mixture after 9 days at room temperature; briefly milled reaction mixture after 1 day at room temperature; briefly milled reaction mixture after 5 days at room temperature; briefly milled reaction mixture after 1 day at 45 C; briefly milled reaction mixture after 5 days at 45 C. For comparison, the simulated pattern of magnesium oxide dihydrate (CCDC
code QQQBDJ04) is also given.
[0015] Figure 6 shows a comparison of PXRD patterns for the aging reaction of a manually prepared mixture of CuO and oxalic acid dihydrate at 98% relative humidity and different temperature conditions (top to bottom):
commercial CuO; oxalic acid dihydrate; reaction mixture after 1 day at 45 0C;
3 days at 45 0C; 3 days at room temperature; ; 5 days at 45 C; 5 days at room temperature; ; 6 days at 45 C;
6 days at room temperature; ; 9 days at 45 C; 9 days at room temperature; ; 16 days at 45 C; 16 days at room temperature and 25 days at room temperature.
[0016] Figure 7 shows a comparison of PXRD patterns for the aging reaction of a briefly milled mixture of CuO
and oxalic acid dihydrate at 98% relative humidity (top to bottom): commercial CuO; oxalic acid dihydrate;
manually prepared mixture after 16 days at 45 C; manually prepared mixture after 25 days at room temperature;
milled mixture after 1 day at 45 C; milled mixture after 1 day at room temperature; milled mixture after 5 days at room temperature and milled mixture after 10 days at room temperature.
[0017] Figure 8 shows a comparison of PXRD patterns for the aging reactions of MnO and oxalic acid dihydrate at 98% relative humidity and different conditions (top to bottom):
commercial MnO; oxalic acid dihydrate; manually prepared reaction mixture after 3 days at 45 C; manually prepared reaction mixture after 3 days at room temperature; manually prepared reaction mixture after 6 days at 45 0C; manually prepared reaction mixture after 6 days at room temperature; manually prepared reaction mixture after 9 days at 45 C; manually prepared reaction mixture after 9 days at room temperature; manually prepared reaction mixture after 16 days at 45 C; manually prepared reaction mixture after 16 days at room temperature;
reaction mixture involving pre-milled MnO after 1 day at 45 C; reaction mixture involving pre-milled MnO
after 1 day at room temperature. For comparison, the simulated patterns of metastable a-polymorph of manganese(II) oxalate dihydrate (CCDC code FOZHUX11) and the stable y-form of manganese(II) oxalate dihydrate (CCDC code FOXHUX10) are also given.
[0018] Figure 9 shows a comparison of PXRD patterns for the aging reactions of Pb0 and oxalic acid dihydrate at 98% relative humidity and different conditions (top to bottom): commercial Pb0; oxalic acid dihydrate;
manually prepared reaction mixture after 30 days at room temperature; manually prepared reaction mixture after 1 day at 45 C; manually prepared reaction mixture after 3 days at 45 C;
manually prepared reaction mixture after 5 days at 45 C; manually prepared reaction mixture after 9 days at 45 C; manually prepared reaction mixture after 14 days at 45 C; briefly milled reaction mixture after 1 day at 45 C; briefly milled reaction mixture after 5 days at 45 C; briefly milled reaction mixture after 10 days at 45 C;
briefly milled reaction mixture after 15 days at 45 C; briefly milled reaction mixture after 5 days at room temperature; briefly milled reaction mixture after 10 days at room temperature; briefly milled reaction mixture after 15 days at room temperature; For comparison, the simulated pattern of lead(II) oxalate (CCDC code JAHVUJ) is also given.
[0019] Figure 10 shows an overlay of FTIR-ATR spectra for the reaction mixtures involving calcinated MgO
and oxalic acid dihydrate.
[0020] Figure 11 shows an overlay of FTIR-ATR spectra for the reaction mixtures involving NiO and oxalic acid dihydrate.
[0021] Figure 12 shows an overlay of FTIR-ATR spectra for the reaction mixtures involving CuO and oxalic acid dihydrate.
[0022] Figure 13 shows an overlay of selected FTIR-ATR spectra for the reaction mixtures involving ZnO and oxalic acid dihydrate, as well as Co0 and oxalic acid dihydrate.
[0023] Figure 14 shows an overlay of selected FTIR-ATR spectra for the reaction mixtures involving Pb0 and oxalic acid dihydrate.
[0024] Figure 15 shows the thermogram of zinc oxalate dihydrate obtained by aging of ZnO and oxalic acid dihydrate at 45 C and 98% RH. Calculated ZnO residue: 43.0% ; calculated water loss: 19.0%.
[0025] Figure 16 shows the thermogram of magnesium oxalate dihydrate obtained by aging of MgO and oxalic acid dihydrate at 45 C and 98% RH. Calculated MgO residue: 27.1% ; calculated water loss: 24.3%.
[0026] Figure 17 shows the thermogram of manganese(II) oxalate dihydrate obtained by aging of MnO and oxalic acid dihydrate at room temperature and 98% RH. Calculated Mn02 residue:
48.6% ; calculated water loss:
20.1%.
[0027] Figure 18 shows the thermogram of manganese(II) oxalate dihydrate obtained by aging of MnO and oxalic acid dihydrate at 45 C and 98% RH. Calculated Mn02 residue: 48.6% ;
calculated water loss: 20.1%.
[0028] Figure 19 shows the thermogram of cobalt(II) oxalate dihydrate obtained by aging of Co0 and oxalic acid dihydrate at 45 C and 98% RH. Calculated Co304 residue: 43.9% ;
calculated water loss: 19.7%.
[0029] Figure 20 shows the thermogram of nickel(11) oxalate dihydrate obtained by aging of NiO and oxalic acid dihydrate at 45 C and 98% RH. Calculated Ni0 residue: 40.9% ; calculated water loss: 19.8%.
[0030] Figure 21 shows the thermogram of copper(II) oxalate obtained by aging of CuO and oxalic acid dihydrate at 45 C and 98% RH. Calculated CuO residue: 50.2% ; calculated water loss: 5.6%.
[0031] Figure 22 shows the thermogram of lead(II) oxalate obtained by aging of Pb0 and oxalic acid dihydrate at 45 C and 98% RH. Calculated Pb0 residue: 75.6% ; calculated water loss:
0%.

[0032] Figure 23 shows PXRD patterns for selected reactions at 98% RH: (a) MgO; (b) magnesium oxalate dihydrate obtained by aging of MgO and oxalic acid dihydrate for 5 days at 45 C; (c) MnO; (d) manganese(II) oxalate dihydrate made by 1 day aging of pre-milled MnO and oxalic acid dihydrate at room temperature; (e) manganese(11) oxalate dihydrate made by 9 days aging of MnO and oxalic acid dihydrate at 45 C; (f) simulated for a-form of manganese(11) oxalate dihydrate (CCDC code FOZHUX11); (g) simulated for y-for of manganese(11) oxalate dihydrate (CCDC code FOZHUX10); (h) NiO; (i) nickel(11) oxide dihydrate made by 3 days aging of NiO
and oxalic acid dihydrate at 45 C; (j) cobalt(II) oxide dihydrate made by 6 days aging of Co0 and oxalic acid dihydrate at room temperature (to eliminate fluorescence, data was collected using CuKa radiation and energy-discriminating LynxEye detector); (k) CuO; (1) copper(11) oxalate hydrate made by 16 days aging of CuO and oxalic acid dihydrate at 45 C; (m) copper(II) oxalate hydrate made by 10 days aging of pre-milled CuO and oxalic acid dihydrate at room temperature; (n) Pb0; (o) lead(11) oxalate made by 9 days aging of pre-milled Pb0 and oxalic acid dihydrate at 45 C; (p) simulated for lead(II) oxelate (CCDC code JAHVUJ). (q) Visual comparison of samples of oxide reactants with corresponding oxalate products obtained by aging at 98`)/ORH, 45 C.

[0033] Figure 24 shows (a) fragments of crystal structures of a- (top) and y-forms (bottom) of manganese(II) oxalate dihydrate. PXRD patterns collected using CoKa radiation: (b) MnO; (c) MnO after 5 minutes milling; (d) reaction of MnO and oxalic acid dihydrate, room temperature, 98% RH; (e) reaction of MnO and oxalic acid dihydrate, 45 C, 98% RH; (f) reaction of pre-milled MnO and oxalic acid dihydrate, room temperature. 98% RH;
(g) reaction of pre-milled MnO and oxalic acid dihydrate, 45 C, 98% RH. Full set of PXRD patterns is given in the Supplementary Material.

[0034] Figure 25 shows selected FTIR-ATR spectra for the reaction of MnO and oxalic acid dihydrate.
Characteristic bands are labeled for a- (red line) and y-forms (blue line) of manganese(11) oxalate dihydrate.

[0035] Figure 26 shows (a) chemical equation for the proposed solvent-free separation of ZnO from CuO.
Selected PXRD patterns for the solid-state aging of a 1:1:1 mixture of ZnO, CuO and oxalic acid dihydrate: (b) after 5 days at 45 C, 98% RH; (c) bottom layer obtained by flotation of sample (a) using CH212; (d) top layer obtained by flotation of sample (a) using CH212; (e) reference zinc(11) oxalate dihydrate made by aging; (f) reference copper(II) oxalate hydrate made by aging; (g) commercial ZnO and (h) commercial CuO. To highlight the selective conversion of ZnO into the oxalate and retention of CuO upon aging of the reaction mixture, characteristic X-ray reflections of CuO and zinc oxalate dihydrate are designated with * and =, respectively. (i) Solid-state UV-Vis reflectance spectra (top to bottom): averaged spectrum of copper(11) oxalate hydrate and zinc oxalate dihydrate; spectrum of the reaction mixture after 5 days at 45 C, 98%
RH; spectrum of zinc oxalate dihydrate, and of copper(11) oxalate hydrate. PXRD and UV-Vis reflectance clearly indicate the selective transformation of ZnO into zinc oxalate dihydrate, leaving behind CuO.

[0036] Figure 27 shows the thermogram of a 1:1:1 mixture of CuO, ZnO and oxalic acid dihydrate after aging for 5 days at 45 C and 98% RH. The analysis of residue weight and weight loss steps indicates selective conversion of ZnO into zinc oxalate dihydrate. Theoretical residue weight for the selective conversion of ZnO is 59.9%, and increases with increasing fraction of reacted CuO. A more conservative assessment of selectivity is provided by the less reliably measured water loss step (measured step:11.9%, theoretical for pure zinc oxalate dihydrate: 13.3%), which suggests the conversion of ZnO and CuO in the relative ratio 9:1. However, a further indication of the absence of any significant amounts of copper(II) oxalate is the absence of the characteristic copper(I) oxide re-oxidation step above 400 C.

[0037] Figure 28 shows an overlay of selected FTIR-ATR spectra for (top to bottom): oxalic acid dihydrate (black); zinc oxalate dihydrate (blue); copper(II) oxalate hydrate (green) and the 1:1:1 mixture of CuO, ZnO and oxalic acid dihydrate after aging for 5 days at 45 C and 98% RH (red).

[0038] Figure 29 shows the thermogram of a 1:1:1 mixture of Pb0, ZnO and oxalic acid dihydrate after aging for 3 days at room temperature and 98% RH. Residue weight indicates the selective conversion of ZnO with respect to Pb0 (calculated residue weight for a mixture of zinc oxalate dihydrate and Pb0=73.8%. Almost identical selectivity is observed by conducting the separation at 45 C and 98% RH.

[0039] Figure 30 shows selected PXRD patterns for reactions involving Zn (blue), Ni(II) (green) or Co(II) (red):
(a) Znox= 2H20; (b) Niox.2H20; (c) Cook 2H20; (d) ZnO, H2ox.2H20 and[pn][ox], in ratio 2:2:1 after 5 days aging; (e) Znox-2H20 and [pn][ox] in ratio 2:1 after 5 days aging; (f) NiO, H2ox.2H20 and[pn][ox] in ratio 2:2:1 after 5 days aging; (g) Niox.2H20 and [pn][ox] in ratio 2:1 after 5 days aging; (h) CoO, H2ox.2H20 and[pn][ox]
in ratio 2:2:1 after 5 days aging; (i) simulated for the 2-D framework [pn][Zn2(ox)3].3H20 (SEYQA0); (j) ZnO, H2ox.2H20 and [pa]2[ox] in ratio 2:2:1 after 5 days aging; (k) NiO, H2ox.2H20 and[pa]2[ox] in ratio 2:2:1 after 5 days aging; (I) Niox= 2H20 and [pa]2[ox] in ratio 2:1 after 5 days aging; (m) CoO, H2ox.2H20 and[pa]2[ox] in ratio 2:2:1 after 5 days aging; (n) simulated for the 3-D framework [pa]2[Zn2(ox)3]-3H20 (SEYQIW). Reactions were done at room temperature, 98% RH. PXRD patterns of cobalt samples were recorded using CuKa radiation and an energy-discriminating LynxEye detector.

[0040] Figure 31 shows (a) the reactivity of ZnO, CoO and NiO towards H2ox-2H20 with and without organoammonium salts; and (b) the 1H-13C HETCOR SSNMR of [pa]2[Zn2(ox)3].3H20 (5 ms contact time) with tentative assignment. Absence of correlations to water is explained by structural disorder. For the nitrogen-bound CH2 moiety the lack of correlations at this long correlation time and increased peak width are rationalized by the nearby 14N quadrupole. The 130 CP spectrum along the top was acquired with a 2 ms contact time.

[0041] Figure 32 show FIR-AIR spectra for the products of reactions of (pn)(ox) with H2ox.2H20 and: (a) ZnO; (b) NiO; (c) COO and of (pa)2(ox) with H2ox.2H20 and: (d) ZnO; (e) MO;
(f) CoO. Reference FTIR-ATR
spectrum of Znok2H20 is given under (g).

[0042] Figure 33 shows a conventional metallurgical process (left) and a similar process incorporating an embodiment of the method of the invention (right).
DETAILED DESCRIPTION OF THE INVENTION

[0043] Turning now to the invention in more details, there is provided a method for separating metals in a mixture of metallic compounds, the method comprising the steps of (A) mixing the mixture with a carboxylic acid, (B) selectively converting at least one of the metallic compounds into a metal carboxylate complex, thereby producing a mixture of said metal carboxylate complex with unreacted metallic compounds, and (C) separating the metal carboxylate complex from the unreacted metallic compounds.
The Mixture of Metallic Compounds [0044] The starting material on which the present method is carried out is a mixture of metallic compounds.
More specifically, it is a mixture of two or more metallic compounds.

[0045] Generally, the metallic compounds are in solid form in the conditions in which the method is carried out.
Such solids should be in the form of a powder to allow subsequent reaction, especially in embodiments where the carboxylic acid is also a solid. For example, the powder particle size of the metallic compounds could be of about 100 micrometers or less. While there is no particular limit on the particle size that can be used, it should be noted that smaller particles will generally react faster and at lower temperatures.

[0046] In embodiments, the starting material is an ore or a mixture of metallic compounds produced by conventional processes used in the mineral industry. As explained below, the present method also applies to radioactive metals. Therefore, the starting material can also be a radioactive ore or a mixture of metallic compounds produced by conventional activity in the nuclear industry.

[0047] In embodiments, the starting material is metal waste, for example in oxide, sulfide, hydroxide or carbonate form.

[0048] In embodiments, the metallic compounds are oxides, sulfides, silicates, phosphates, hydroxides and/or carbonates of metals. These types of metallic compounds are commonly found in minerals. In fact, in embodiments, the metallic compounds are the minerals in classes 02 A to F, 04 A to E, 05 A to E, 08, and 09 of the Nickel¨Strunz classification.

[0049] In preferred embodiments, the metallic compounds are oxides and/or sulfides.

[0050] The metallic compounds in the starting mixture do not need to be, for example, all oxides or all sulfides.
There may be, for example, oxides of one or more metal, sulfides of one or more metal as well as carbonates of other metals. Additionally, in the starting mixture, a given metal does not need to be present in only one form, say as an oxide. Rather, the starting mixture can comprise a given metal, for example, both as an oxide and as a sulfide. The metallic compounds need not to contain only one metal or a metal in a single oxidation state.
Rather, they can also be mixed metallic compounds, metallic compounds containing the same metal in different oxidation states, or both. Finally, they do not need to comprise only one type of anion each, say 02- or C032-.
Rather, a metallic compound can comprise one or more of the above anions and it may also comprise supplementary anions, such as halides and hydroxide (OH-).

[0051] The metallic compounds in the starting mixture can be hydrated.

[0052] The metals in the metallic compounds belong to groups 2 to 15 of the periodic table. More specifically, this includes:

= the alkaline earth metals: beryllium, magnesium, calcium, strontium, barium, radium; tantalum, and dubniunn;
= the transition metal: scandium, yttrium, titanium, zirconium, hafnium, rutherfordium, vanadium, niobium, chromium, molybdenum, tungsten, seaborgium, manganese, technetium, rhenium, bohrium, iron, ruthenium, osmium, hassium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, zinc, cadmium, mercury, and copernicium;
= the post-transition metals: aluminium, gallium, indium, thallium, germanium, tin, lead, arsenic, antimony, bismuth, polonium, and astatine;
= the lanthanides: lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium; and = the actinides: actinium, thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium californium, einsteinium, fermium, mendelevium, nobelium, and lawrencium.

[0053] In embodiments, the metals are two or more, preferably two, of manganese, copper, nickel, cobalt, zinc, lead, magnesium, silver, neodymium, bismuth, antimony, arsenic, tin, cadmium, praseodymium, lutetium, europium, and ytterbium.

[0054] In embodiments, the metals are copper and zinc, copper and lead, lead and zinc, lead and silver, zinc and silver, neodymium and lutetium, or europium and ytterbium.

[0055] In embodiments, the metallic compounds are copper oxide and zinc oxide, copper sulfide and zinc sulfide, copper oxide and lead oxide, copper sulfide and lead sulfide, lead oxide and zinc oxide, lead sulfide and zinc sulfide, lead sulfide and silver sulfide, zinc sulfide and silver sulfide, neodyniunn oxide and lutetium oxide, or europium oxide and ytterbium oxide.
Mixing with a Carboxylic Acid [0056] The method of the invention comprises the step of mixing the mixture of metallic compounds with a carboxylic acid.

[0057] Here, a "carboxylic acid" is a compound comprising at least one carboxyl (¨COOH) functional group. As such, it is a compound of generic formula (R-COOH). This includes monocarboxylic acid, as well as acids with two or more carboxyl groups (called dicarboxylic, tricarboxylic, etc.). This also includes amino acids, which are comprise both amine and carboxyl functional groups.

[0058] In preferred embodiments, the carboxylic acid is in solid form in the conditions in which the method is carried out. This would typically include exclude monocarboxylic acids comprising less than 3 or 4 carbon atoms (depending on the other atoms present). As with the metallic compounds, this solid should be a powder to allow subsequent reaction. There are no particular size requirements for this powder. For example, the powder particle size of the carboxylic acid could be from about 50 to about 100 pm.

[0059] When it is of interest to keep the method of invention as environmentally-friendly as possible, non-toxic and/or non-halogenated acids should be preferred.

[0060] In embodiments, the carboxylic acid is oxalic acid, salicylic acid, acetylenedicarboxylic acid, fumaric acid, terephthalic acid, succinic acid, or benzoic acid.

[0061] In order for the subsequent conversion reaction to take place, the carboxylic acid must be mixed to the metallic compounds. The manner in which such mixing is achieved is not crucial to the invention as long as there is proper contact between the various reactants (which, in most embodiments, will all be in solid form).

[0062] Optionally, the mixing can be followed by or performed by milling. The present inventors have found that milling generally speeds up the subsequent conversion reaction. The more extensive the milling, the faster the conversion reaction. It is believed that this is because milling breaks the crystal lattice of the metallic compounds. There are no particular limits on how little or how much milling can be done. In some cases however, the separation rate can be lowered by extensive milling. The manner in which the milling is carried out is not crucial. A mortar and pestle as well as mills of various natures can be used.
Optional Salt of the Carboxylic Acid [0063] In embodiments, in the mixing step, the metal compounds are mixed with the carboxylic acid and with a salt of the carboxylic acid.

[0064] Herein, a "salt of the carboxylic acid" is a salt comprising as an anion the carboxylic acid in deprotonated form (R-000-) (this anion is called a "carboxylate").

[0065] The cation of this salt may be an organic cation, an alkaline metal cation (Lit, Nat, K+, etc.), or an alkaline earth metal cation (Mg2+, Ca2+, etc.) salt.

[0066] Organic cations are not particularly limited. They include for example ammonium cations. These can be, for example, of generic formula [NR1112R3134+, wherein R1, R2, R3, 1:14 are independently an hydrogen atom or an alkyl, alkenyl, alkynyl, aryl, o rallryl aryl (for example benzyl) group.
The organic cation may also be a diammonium cation, or an oligoammonium cation.

[0067] In embodiments, the cation is 1,3-propanediammonium or propylammonium.

[0068] Reaction with the salt of the carboxylic acid is selective, which is advantageous in separating the various metals in the starting mixture. As shown below, when this reaction occurs, the properties of the metal carboxylate complexes formed are modified. In particular, it can make them more soluble in water. Further, using such salt also changes the structure of the metal carboxylate complexes.
They can be discrete complexes or repeating open structures in two or three dimensions. Such structures have a direct impact on the density of the product. This allows tailoring the density and the solubility of the products for easier separation.

Selective Conversion into Carboxvlate Complexes [0069] The next step involves the selective conversion of at least one of the metallic compounds into a metal carboxylate complex.

[0070] The present inventors have found that metallic compounds as defined above will react with a carboxylic acid to form a metal carboxylate complex. This reaction will occur even when all the reactants are solids. There is no need for supplementary reactants or a solvent.

[0071] The inventors have found that some humidity (water vapor in the air) is generally necessary for this reaction to occur.
Further, it has been found that reaction speed increased with humidity. Thus, in embodiments, this reaction is carried out at a relative humidity above 0%, preferably above about 50%, more preferably above about 80%, even more preferably above about 90%, yet more preferably above about 95%, and most preferably of about 98% or more (up to 100%).

[0072] There is no need for harsh reacting conditions. In fact, this reacting proceeds at atmospheric pressure and room temperature. The temperature limits at which the reaction can be carried out are dictated by the need for humidity, thus, in embodiments, the reaction is carried out at a temperature between the freezing point and boiling point of water (which will slightly vary depending on the exact atmospheric pressure at the time the reaction is carried out). The inventors have however found that some heating will speed up the reaction. Thus, the conversion reaction can carried out a temperature above 0 C and below 100 C, preferably between about 15 C and about 85 C, more preferably between room temperature and about 65 C, even more preferably between room temperature and about 45 C, most preferably at about 45 C. It should be noted that the higher the temperature, the faster the reaction rate. Higher temperatures are also preferred when one desires reaction of a very inert metallic compound (for example Bi203). However, a lower temperature (such as 45 C) is usually a good compromise between reaction rate and energy input (which is expensive).

[0073] It is particularly surprising that this reaction occurs because (A) many metallic compounds (such as transition metal oxides and sulfides) are inert or even highly inert, (B) the acid used and reaction conditions are quite mild compared to the that typically encountered in metallurgical processes (wet processes in H2SO4, HCI, or HNO3, high pressures, high temperatures).

[0074] The selectivity of this reaction arises from the fact that the conversion does not occur at the same speed for all metallic compounds. In fact, the reaction times are highly dependent on the starting metallic compound and the carboxylic acid used.

[0075] As further explained below, the metal carboxylate complexes produced have properties different from the unreacted metallic compounds, which allows separating them. As such, the conversion reaction will be carried out for a time sufficient for at least one or some of the metallic compounds of the starting mixture to be converted into carboxylate complexes, but not sufficient for all of them to be converted. The carboxylate complex(es) will then be separated from the unreacted metallic compounds. Of note, when metallic compounds comprising more than one metal are converted into metal carboxylate complexes, more than one metal carboxylate complex will be produced. The produced metal carboxylate complexes can be further purified as explained below. Similarly, where the unreacted metallic compounds comprise more than one metal, they can be further purified as explained below.

[0076] It should be noted a variation in the reacting conditions will not affect equally the speed of reaction of all metallic compounds. Therefore, the reaction conditions can be adjusted so that the reaction time difference between two metallic compounds at play allows for selective conversion of only one of them.

[0077] It should also be noted that some of the above metallic compounds may react very slowly, or even not at all. This may be the case of compounds where the metal atoms have very high degrees of oxidation (+4, +5, or more). This is also the case of titanium dioxide, cerium dioxide, and zirconium dioxide. This does not mean that such compounds cannot be separated from other metallic compounds by the present method. To the contrary, these compounds can very easily be separated from compounds that react more quickly in given reaction conditions.

[0078] Of note, the produced metal carboxylate complexes can, in embodiments, be hydrated. In addition, the metal carboxylate complexes typically present themselves as coordination polymers or discrete complexes.
Separation [0079] As mentioned above, the inventors have noticed that the metal carboxylate complexes produced by the conversion have properties different from the unreacted metallic compounds.

[0080] One such property is their density. Typically, the metal carboxylate complex will have lower densities than the unreacted metallic compounds. For reference, typical metal oxide/sulfide densities are generally over 5 g/cm3, while metal oxalate densities are generally under 3 g/cm3. Furthermore, open structures tend to be less dense than discrete complexes. The inventors have thus conceived of separating the metal carboxylate complex from the unreacted metallic compounds by flotation.

[0081] This includes a simple flotation process in which the mixed metal carboxylate complex and the unreacted metallic compounds are suspended in a flotation liquid (not a solvent) having density in-between that of the metal carboxylate complex and that of the unreacted metallic compounds.
In such mixture, the metal carboxylate complex will tend to float, while the unreacted metallic compounds will tend to sink, which allows collecting them separately. A centrifuge can be used to speed this process.
Examples of appropriate flotation liquids are diiodomethane (CH212) with a density of 3.3 g/ cm-3, an aqueous polytungstate solution, or any other heavy liquid used in metallurgy or geology.

[0082] This also includes froth flotation, which is well known in the mineral processing industry. Froth flotation is a process for separating solids by taking advantage of differences in their hydrophobicity. Hydrophobicity differences between the solids are typically increased through the use of surfactants and wetting agents. More specifically, to carry out a separation by froth flotation, the solids (in the form of a fine powder) are mixed with water to form a slurry. One of the solids is rendered hydrophobic by the addition of a surfactant or collector chemical. The particular chemical depends on which solid is desired. This slurry (more properly called the pulp) of hydrophobic particles and hydrophilic particles is then introduced to a water bath which is aerated, creating bubbles. The hydrophobic particles attach to the air bubbles, which rise to the surface, forming a froth. The froth is removed and may be further refined as desired. This process would be aided by the density difference between the metal carboxylate complexes and the starting metallic compounds.
The less dense metal carboxylate complexes would float more easily than the starting metallic compounds. In fact, the organic carboxylate group(s) that is part of the metal carboxylate complexes could act similarly to the surfactant, making the compounds more hydrophobic and less dense.

[0083] Another such property is their solubility. Typically, discrete metal carboxylate complexes with alkaline and alkaline earth cations tend to be much more soluble in water (or aqueous solutions) than the other compounds at play. Thus, these metal carboxylate complexes can be separated be simple dissolution followed by filtration. This could be advantageous, for example in copper refining as it would provide a copper solution ready for electrolytic extraction (electrowinning).

[0084] Other means of separating solids with different solubilities and/or densities known to the skilled person can also be used.
Optional Further Purification [0085] It should be noted that it is not necessary that the selectivity of the above conversion reaction be perfect. Similarly, it is not necessary that the separation of the various solids be perfect. The method of the present invention (and/or other purification methods known in the art) can be used to further purify the metal carboxylate complex and the unreacted metallic compounds. This is particularly useful when the starting mixture of metallic compounds comprised three of more such compounds. In such cases, the method of the invention can be carried out to isolate one compound from the others, and then repeated to isolate the other compounds, one at a time.

[0086] In all cases, it should be noted that it can be desirable to further purify either or both of the produced metal carboxylate complex and the unreacted metallic compounds.
[00871 In one instance, the unreacted metallic compounds are simply subjected to the present method anew (i.e. mixed with acid, allowed to react, and separated). In the other instance, the produced metal carboxylate complex can first be heated to produce corresponding metal oxides (i.e. one type of metallic compounds defined above). Then, the metal oxides are subjected to the present method anew (i.e.
mixed with acid, allowed to react, and separated). In both cases, as before, the reaction conditions and the time allowed for the conversion may be adjusted to the metallic compounds at play.
Advantages [0088] The method of the invention, in its various embodiments, may present one or more of the following advantages.

[0089] Because of the mild reaction conditions involved, the method of the invention does not usually require significant energy input, minimizes energy use, and should thus be relatively inexpensive.
[0090] Despite these uncommonly mild conditions, the method of the invention is applicable to a large variety of transition metals, even when they are in the form of metallic compounds with high melting points, such as metal oxides.
[0091] Because it does not require solvents (in particular organic solvent as well as strong organic or inorganic bases and acids), the method of the invention is a cleaner and more environmentally-friendly process than its generally used counterparts. Further, there are fewer risks involved with this method. If desired, the use of acid-proof equipment can be avoided. The expenses, in terms of chemicals to be used, are reduced. Further, the waste water management needs are reduced or even eliminated.
[0092] The separation of metal compounds, such as metal oxides, in mineral concentrates is central to mineral manufacturing. The current metallurgical processes are however often energy-and solvent-intensive. As such, the method of the invention has considerable potential for reducing energy and solvent use in the mineral industry and thus promises much industrial benefits.
Definitions [0093] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.
[0094] The terms "comprising", "having", "including", and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to") unless otherwise noted.
[0095] Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All subsets of values within the ranges are also incorporated into the specification as if they were individually recited herein.
[0096] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.
[0097] The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed.
[0098] No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
[0099] Herein, the term "about" has its ordinary meaning. In embodiments, it may mean plus or minus 10% or plus or minus 5% of the numerical value qualified.

[00100] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
[00101] Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of specific embodiments thereof, given by way of example only with reference to the accompanying drawings.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENT
[00102] The present invention is illustrated in further details by the following non-limiting examples.
Example 1 Abbreviations [00103] H2ox, oxalic acid; pa, 1-propylamine; pn, 1,3-diaminopropane; PXRD, powder X-ray diffraction; FTIR-ATR spectroscopy, Fourier-transform infrared attenuated total reflection spectroscopy; NMR, nuclear magnetic resonance; TGA, thermogravimetric analysis; DSC, differential scanning calorinnetry.
Introduction [00104] Below, we established: (1) conditions that enable the conversion of laboratory-scale samples of metal oxides into metal-organic materials; (2) the applicability of this methodology to metals other than zinc and ability for scale-up; and (3) the usefulness of this methodology for separating metals. Metal oxalates were selected as models for this study.
Experimental section [00105] Preparation of samples: All chemicals (metal oxides and oxalic acid dihydrate) were reagent grade and obtained from commercial sources. MgO, MnO, CoO, NiO, ZnO and Pb0 were of 99%+ purity, obtained from Sigma-Aldrich, CuO was 96% purity from Riedel-de Haen and H2ox.2H20 was 99%+ purity from American Chemicals Ltd. ZnO and MgO have been calcined (400 C) to remove potential hydroxide and carbonate impurities, and were kept in a dry desiccator over P401o.
[00106] Aging reactions were conducted either in a walk-in incubator held at 45 0C, or at room temperature without particular means of temperature control. The samples aged at high humidity were kept at 98% RH
atmosphere established in a Secador cabinet equilibrated with saturated aqueous K2SO4. In a typical experiment, 1 mmol of a metal oxide was mixed with 1 mmol of H2ox.2H20 and ground in an agate mortar and pestle for 30 seconds. The solid mixture was then placed in a 20 mL open vial and stored under suitable conditions. All reactions were investigated by PXRD, TGA, FTIR-ATR and, in some cases, by UV-Vis reflectance spectroscopy, SSNMR spectroscopy and DSC.

[00107] In a typical reaction, a mixture of 0.163 g (2mmol) ZnO and 0.252 g (2mmol) H2ox.2H20 was gently ground manually (ca 30 seconds) using a mortar and pestle. Ground mixtures were then placed in open vials and aged at 45 C and 98%RH in a glass desiccator in which a constant humidity level was maintained by equilibrating the atmosphere with a saturated K2SO4 solution. The desiccator was placed in a large volume incubator set at 45 C. The same procedure was repeated for reactions involving all other metal oxalates, typically using a 1:1 stoichiometric ratio.
[00108] In large scale reactions towards Znok2H20 and Niok2H20, 4.88 g (60 mmol) ZnO or 4.48 g (60 mmol) NiO was mixed with 7.56 g (60 mmol) H2ok2H20 and aged at 45 C 98%RH for 7 days.
[00109] In a typical milling activated reaction, 0.177 g (2.5mmol) MnO was ground at 30Hz for 5 minutes with a yield of 82% (2.05 mmol) due to the material loss in transfer. The ground oxide powder was then mixed with 0.258 g (2.05 mmol) H2ok2H20 and the mixture aged at room temperature, 98%RH
or at 45 C, 98%RH for up to 10 days.
[00110] For the solid state oxide separation experiment of ZnO and CuO, a mixture of 0.163 g (2mmol) ZnO, 0.159g (2 mmol) CuO and 0.252 g (2 mmol) H2ox. 2H20 was gently ground manually using a mortar and pestle and then aged at 45 C 98%RH for 5 days.
[00111] Powder X-ray diffraction (PXRD): Room temperature PXRD patterns were collected in the 20 range 3 to 600 on a Bruker D8 Discovery X-ray diffractometer or on a Bruker D2 Phaser diffractometer using a Cu-Ic,(A=1.54 A) source, equipped with a Vantech area detector and a nickel filter. The X-ray tube was operating at the power setting of 40 kV and 40 mA power. Data analysis was carried out using the Panalytical X'pert Highscore Plus program.
[00112] Fourier-transform infrared attenuated total reflection (FTIR-ATR) spectroscopy: Fourier transform infrared spectra were collected using a Perkin Elmer Fourier Transform-Infrared Attenuated Total Reflection spectrometer in the range 400 cm-' to 4000 cm-1.
[00113] UV-Vis reflectance (UV-Vis) spectroscopy: UV-Vis reflection measurements were conducted on the Ocean Optics Jaz-Combo spectrometer using LS-1 Tungsten Halogen Light Source (360-2000nm), 0.4mm fiber optic reflection R400-Angle-UV probe with RPH-1 reflection probe holder, and WS-1 PTFE diffuse reflection standard. The spectrums were collected in the range of 400-800nm using Spectrasuite software.
[00114] Thermogravimetric analysis (TGA): TGA measurements were conducted on a TA Instruments Q500 Thermogravimetric System with a Pt pan under dynamic atmosphere of N2 or air with 40m1/min balance flow and 60m1/min purge flow. The upper temperature limit ranged from 500 C to 800 C
depending on the sample, with a heating rate of 10 C/min.
[00115] Differential scanning calorimetry (DSC): DSC measurements were conducted on a TA Instruments Q2000 Differential Scanning Calorimeter with a standard aluminum pan of 40 pL.
Nitrogen flow rate was set at 50m1/min and the upper temperature limit ranged from 105 C to 150 C depending on the sample, with a constant heating rate of 10 C/min.

Results and Discussion [00116] Initially, a stoichiometric 1:1 mixture of oxalic acid dihydrate (H2ok2H20) with ZnO was prepared. The mixture was prepared by gently grinding the reactants in a mortar and pestle for 30 seconds. Powder X-ray diffraction (PXRD) analysis of the sample after 24 hours aging at room temperature (18 C-22 C) and high (98%) relative humidity (RH) revealed the formation of a new product (Figure 1).
[00117] Comparison with PXRDs patterns simulated for known zinc oxalate structures revealed the product was the 1-0 coordination polymer zinc oxalate dihydrate (Znok2H20, CCDC code OQQB0004) in the a-type structure. Within one week, the conversion to the 1-D coordination polymer was complete. The composition Znok2H20 was confirmed by thermogravimetric analysis (TGA) in air, which provided the assessment of weight fractions for included water (measured: 17.7%, calculated: 19.0%) and ZnO
residue (measured: 43.7%, calculated: 43.0%). Aging reactivity was further improved by storing the sample in 98% RH conditions at the mild temperature of 45 C. Under such conditions, complete formation of a-Znok2H20, as established by PXRD
(Figure 2), was achieved in 5 days. The reaction was readily scaled to 10 grams (Figure 11), and reached completion in seven days. Transformation was also detected by Fourier-transform infrared attenuated total reflection (FTIR-ATR) spectroscopy (Figure 3), specifically by the disappearance of 0-H stretching bands of H2ok2H20 at 3380 cm-1 and 3470 cm-1 and the appearance of the 0-H stretching bands of Znok2H20 at 3350 cm-1, as well as the appearance of characteristic Znok2H20 absorption bands at 1604 cm-1, 1356 cm-1 and 1311 cm-1.
Reactivity of other metal oxides [00118] The reactivity of further metal oxides and oxalic acid in 98% RH, at room temperature and at 45 C was studied.
[00119] Table 1 below lists the times required for the reflections of the metal oxide to disappear from the PXRD
pattern of the reaction mixture (Figures 4 to 9). This demonstrates that aging reactions are applicable to a variety of metal oxides. The reactions could also be observed by FTIR-ATR
spectroscopy (Figures 10 to 14, selected spectra) Table 1. Time (in days) for the disappearance of X-ray reflections of the metal oxide (with given melting points) in the PXRD patterns of mixturesa with oxalic acid dihydrate exposed to 98% RH
under different conditions.
Reaction time (days) Oxide RTb 45 0C RTb (melting point/ C) with pre-millingc MgO (2852) >9 gd 5d MnO (1945) >16 9d id Ni0 (1955) >25 3d >10 CuO (1201) >25 >16 1 0e,f ZnO (1975) >5 3d 5d Pb0 (888) >30 gd >10 a) Reactions were conducted using 2 mmol of the oxide and 2 mmol of H2ok2H20;
b) room temperature;
c) milling was conducted for 5 minutes in a 10 mL stainless steel jar;
d) PXRD pattern displayed no reflections of H2ok2H20 or the metal oxide;
e) very weak reflections of H2ox.2H20 were observable in the PXRD pattern; and f) identical result was obtained at 45 00 and 98% RH after 1 day.
[00120] Table 1 clearly illustrates the ability to transform metal oxides at mild conditions of temperature, despite their very high melting points. Results in Table 1 are relevant in comparison to mechanochennistry, as analogous milling transformations of CoO, NiO, MnO or Pb0 into metal-organic derivatives have not yet been reported. The composition of the products was elucidated by the similarity of the PXRD
patterns to those simulated for published structures of Mn(II), 00(11), Ni(II), Zn and Pb(11) oxalates (Figures 4 to 9).
[00121] Product composition was corroborated by TGA (Figures 15 to 22).
Notably, NiO demonstrated similar level of reactivity as ZnO, with complete transformation to the 1-D
coordination polymer Niox.2H20 isostructural to monoclinic Znok2H20 within three days at 98% RH and 45 C. The structural resemblance of Niox.2H20 to the zinc-based polymer was also evident from the similarity of the FTIR-ATR
spectra (Figure 3) of the solids and, similar to reactions of ZnO, the synthesis of Niox.2H20 was also readily scaled to 10 grams (Figure 11). The slowest reaction was observed for CuO, for which the oxide was no longer observable by PXRD after 16 days aging at 98% RH and 45 C. The product was partially hydrated copper(11) oxalate with traces of oxalic acid dihydrate evident in the PXRD pattern, explained by the technical 96% purity of CuO. Product was analyzed as CuoxØ5 H20.
[00122] Like the oxides in Table 1, Co0 also readily (within six days) converted to a pink material isostructural to Niox.2H20 and Znok2H20. Diffraction pattern of the product exhibited X-ray fluorescence which impaired the detection of trace Co0 or H2ox.2H20 using CuKa radiation. However, TGA was consistent with the formula Cook 2H20, and the FTIR-ATR spectrum was almost identical to those of isostructural Ni(11) and Zn oxalates (Figure 3). Subsequent PXRD study on a Bruker D2 diffractometer using CoKa and CuKa radiation after energy discrimination by the LynxEye detector (Figure 23j) confirmed the absence of reactants and formation of Cook2H20.
[00123] Although all metal oxide transformations in Table 1 are conducted under 98% relative humidity, the obtained products are not the highest known hydrates of corresponding oxalate coordination polymers. MnO
yielded Mnok2H20 although a higher hydrate is also known. Similarly, Pb0 yields an anhydrous polymer Pbox (CCDC codes JAHVUJ, JAHVUJ01, Figure 23n-p) although a dihyd rate is also known. Copper produced the well-known partially hydrated structure, despite the existence of a trihydrate. For Pb(II) and Cu(II) the low content of water in products was also evidenced by FTIR-ATR spectra lacking the broad water absorption band at 3400 cm-, (Figures 3, 12, and 14).
Effect of temperature [00124] For all oxides, except MnO, switching from room temperature to 45 C
increased the reaction rate without changing the product. However, PXRD measurements using CuKa radiation (Figure 8) showed that MnO
produced the a-polymorph of Mnok2H20 by aging at room temperature and only the reportedly more stable y-form at 45 C. The a-form is structurally similar the other metal oxalate dihydrates (CCDC code FOZHUX11). In the y-form inorganic connectivity between octahedrally coordinated Mn2+ ions is established by p3-bridging oxalate oxygen atoms (Figure 24a). The difference in polymorphic composition was also observable using FTIR-ATR (Figure 25). For example, the 0-H stretching bands in the a-form are located in a narrow region between 3300 cm-1 and 3360 cm-1, while the y¨form exhibits two broad maxima centered at 3090 cm-, and 3320 cm-1.
[00125] An earlier solution-based study by Huizing et al. indicated the a-polymorph is metastable with respect to the rform. Therefore, the temperature-dependent change in polymorphic composition of the aging product suggests the formation of a kinetic product at lower temperatures. The formation of the thermodynamically stable form at 45 C can be explained by higher mobility of molecules at a higher temperature. Subsequent PXRD study of the aged samples using a CoKa X-ray source (Figure 24b-g), to avoid the X-ray fluorescence of manganese-based samples, indicated the presence of the y-form also in the room temperature product. As the CuKa-based PXRD and FTIR-ATR measurements were all performed without delay and are mutually consistent, we explain the y-form detected in the PXRD patterns obtained using CoKa radiation as a result of a spontaneous room-temperature transformation during sample transport and storage.
[00126] The transformation of the a-polymorph to the y-form in moist air was noted by Huizing etal. and traces of the y-polymorph are visible in the samples of the a-form after 16 days at room temperature and 98% RH. The a¨q transformation is not thermally reversible, since heating of the a-form did not result in a structural transformation, shown by differential scanning calorimetry.
Activation by milling: enabling room temperature reactivity [00127] Although the ability to conduct aging reactions in the absence of solvent and at mildly elevated temperature represents a considerable improvement over solution-based processes, the energy benefit can be reduced for long reaction times. Consequently, we explored means to further accelerate the reactions by mechanically activating the reaction mixture by brief ball milling.
[00128] Initial milling (Retsch MM400 mill operating at 30 Hz) of the reaction mixture for 5 minutes enabled most aging reactions to proceed to completion at room temperature, completely eliminating the need for thermal treatment. Consequently, the energy cost for such mechanically activated reaction is reduced to the short period of operating the mill. At the laboratory scale this amounts to a small total input of 15 kJ per reaction, as measured in our laboratory for a Retsch MM400 mill which operates at 100W
(comparable to a light bulb) for two milling stations.
[00129] The exception was the reaction of CuO that displayed traces of H2ok2H20 even after 10 days. Most notable was the effect of milling on reactions of MnO, which completely converted to Mnok2H20 in one day (Figures 24f,g, 25). The product was the metastable a- Mnok2H20 with minor amount of the y-form. Reaction acceleration was also achieved by pre-milling only MnO, and we speculate the success of pre-milling is due to introducing defects in the oxide structure. If the milled mixture of MnO and H2ok2H20 was left to age at 45 C
and 98% RH the product was a mixture of the a- and y-forms, indicating that pre-milling of reactants facilitates the kinetic formation of the metastable form, whereas increased temperature favors the thermodynamically stable one.
Solvent-free separation of metal oxides [00130] The selective transformation of metal oxides in a mixture was attempted. Such a process is akin to a solvent-free chemical separation of metal oxides which, to the best of our knowledge, has previously never been reported.
[00131] We conducted aging of a 1:1 stoichiometric mixture of CuO, the slowest reacting metal oxide in our study, with ZnO, one of the most reactive oxides in the study. To enable the expected selective transformation of only the more reactive metal oxide (illustrated by the proposed equation in Figure 26a) the mixture contained only one equivalent of H2ox.2H20.
[00132] After five days aging at 45 C and 98% RH the initially black reaction mixture (5 grams) turned to gray.
PXRD analysis of the aged mixture indicated that the proposed solvent-free separation of the mixture indeed took place, by selective conversion of ZnO into Znok2H20. PXRD revealed the formation of a crystalline material isostructural to Znok2H20 and the complete disappearance of X-ray reflections of ZnO. In contrast, the X-ray reflections of CuO were clearly observable and reflections of Cu(II) oxalate did not appear in the pattern, consistent with oxalic acid selectively reacting with ZnO. Thermogravimetric analysis (Figure 27) based on the residue weight indicated the complete conversion of ZnO, whereas the less reliable analysis of water loss upon heating indicated the selective conversion of ZnO over CuO in the stoichiometric ratio 9:1. The FTIR-ATR
spectrum of the reaction mixture was consistent with the formation of Znok2H20, but could not confirm the absence of copper(II) oxalate (Figure 28). The near absence of copper(II) oxalate in the reaction mixture was also confirmed by UVNis reflectance spectroscopy. Spectrum of the aged mixture was almost identical to that of pure Znok2H20 and different from the spectrum expected for a 1:1 mixture of Cu(II) and Zn oxalates (Figure 26i). Thus, UVNis spectra are consistent with the absence of any significant amounts of copper(II) oxalate in the aged mixture.
[00133] The large difference in densities of Znok2H20 (density=2.2 g cm-3) and CuO (density=6.3 g cm-3) produced allowed to mechanically separate copper from zinc by flotation. The ability to conduct the reaction at 5 gram scale facilitated such density-based separation by flotation with a "heavy liquid" CH2I2 (density 3.3 g cm-3), often used in laboratory-scale mineral processing. Indeed, flotation and centrifugation separated the reaction mixture into top and bottom layers identified by PXRD as Znox.2H20 and CuO, respectively (Figure 26c,d).
Consequently, combining the solvent-free chemical separation of zinc and copper oxides with conventional flotation allows the separation of copper and zinc oxides without the need for aggressive solvents or high temperatures. It should be noted that the heavy liquid in flotation experiments does not act as a solvent, but serves for physical separation of substances without dissolving them. In large-scale applications, the heavy liquid could be replaced by aqueous systems through froth flotation procedures.
[00134] Preliminary results on accelerated aging mixtures of Pb0 and ZnO
indicate similar selectivity (Figure 29). Thus, a similar separation is expected.
Conclusion [00135] The transformation of a variety of metal (Mg, Mn, Co, Ni, Cu, Zn and Pb) oxides was accessible at room temperature in mixtures prepared by gentle manual mixing of powders, despite high melting points of the investigated oxides (800 C -2500 0C). Mechanical activation or mild temperature increase accelerated the reactions, enabled the complete transformation of all metal oxides, and provided control over the polymorphic composition of the product (exemplified by reactions of MnO).
[00136] The difference in aging reactivity of metal oxides towards oxalic acid enabled the unprecedented solvent-free chemical separation of metals in their oxide form without using strong acids or high temperatures. As transition metal oxides are often slightly soluble and highly inert, the ability to conduct their chemical separation in a solvent-free manner and under mild conditions is particularly surprising.
Following such chemical separation, the metals can be physically separated by conventional flotation.
Example 2 ¨ Selective Conversion of Metal Oxides and Sulfides [00137] The above method was applied to the selectively convert metals in various mixture of metal oxides and sulfides. Oxalic acid was used unless noted otherwise. As shown in the table below, selective conversion was achieved for various pairs of metals.
Mixture Stoichiometric selectivity in Comments Conditions oxide/sulfide conversion (method) ZnO+CuO 90:10 (TGA); 5 gram scale 98% RH, quantitative in Zn (PXRD, UVNis) 45 0C, days CuO+Pb0 95:5 Pb:Cu (PXRD) 5 gram scale 98% RH, 4500, 1 day ZnO+Pb0 quantitative in Zn (TGA); 5 gram scale 98% RH, quantitative in Zn (PXRD) 45 C, 3 days = 23 ZnS+CuS 91:9 Zn:Cu (TGA); 0.5 gram scale 98% RH, quantitative in Zn (PXRD) 45 C, days ZnS+PbS 83:17 Zn:Pb (TGA); 0.5 gram scale 98% RH, 90:10 Zn:Pb (PXRD) 45 C, 5 days PbS+CuS 90:10 Pb:Cu (PXRD) 0.5 gram scale;
98% RH, 45 C, 5 days PbS+Ag2S quantitative in Pb (PXRD) 2.5 gram scale 98% RH, 45 C;
5days ZnS+Ag2S quantitative in Zn (PXRD) 2.5 gram scale 98% RH, 45 C, 5days Nd203+Lu203 quantitative in Nd (PXRD, fluorescence) 1 gram scale; 98% RH, using acetylenedicarboxylic acid RI, 2days Eu203+ Yb203 quantitative in Eu (PXRD) 0.5 gram scale;
98% RH, using acetylenedicarboxylic acid RI, 2 days [00138] It should be noted that zinc materials (if converting) will form zinc oxalate dihydrate; lead materials will form anhydrous lead oxalate and copper materials will yield copper(II) oxalate that contains a variable (0.1-0.5 equivalents with respect to copper) amount of crystallization water.
[00139] Above, PXRD, fluorescence and UVNis analysis were achieved through comparison with standard measurements. Thermogravimetric (TGA) analysis was performed either by fully oxidizing the converted mixture in air and measuring the weight of the oxide residue (these measurements also provide a convenient first-hand evidence of high temperature (in excess of 800 0C) needed for aerobic oxidation of metal sulfides), or by measuring the lower-temperature water loss step (for example, dehydration of zinc oxalate dihydrate).
Example 3 ¨ Conversion of Various Metals Oxides Under Various Conditions [00140] The table below report the results obtained for various metal oxides, various acids and reaction conditions. In this table H2ox.2H20 is oxalic acid, H2sal is salicylic acid, H2ada is acetylenedicarboxylic acid, H2fum is fumaric acid, H2ta is terephthalic acid, H2suc is succinic acid, and H2ba is benzoic acid.

Metal oxide Acid Temperature Humidity Time (days), (0C) (%) Reaction (yes or no), Amount produced (if > 1 g) NiO H2ox-2H20 45 7 5 d, no MO H2ox-2H20 60 100 1 d, complete MO H2ok2H20 AT 0 5d, no NiO H2ok2H20 AT 26 5d, yes ZnO H2ok2H20 45 7 5d, no ZnO H2ok2H20 60 3 5d, no ZnO H2ok2H20 60 100 1d, complete ZnO H2ok2H20 AT 0 5d, no ZnO H2ok2H20 RT 26 5d, yes B1203 H2sal 95 98 1d, yes B1203 H2sal 95 98 3d, yes Bi203 H2sal 95 98 7d, yes Bi203 H2sal 95 98 9d, yes Bi203 H2sal 80 98 4d, no Bi203 H2sal 95 98 3d, yes, 10 gram SnO H2ok2H20 45 98 1d, yes CdO H2ada RT 98 5d, complete CdO H2ok2H20 RT 98 5d, yes CdO H2fum RT 98 5d, complete CdO H2ta RT 98 5d, no CdO H2suc AT 98 5d, yes CdO H2ba 60 98 1d, yes CdO H2ba RT 98 5d, yes CdO H2ba RT 98 13d, yes Co0 H2ada 45 100 id, yes Co H2ada RT 100 id, yes CuO H2ada 45 100 ld, yes CuO H2ada RT 100 1d, yes Lu203 H2ada 45 100 id, yes Lu203 H2ada RT 100 2d, no MgO H2ada 45 100 1d, yes MgO H2ada RT 100 1d, yes MnO H2ada 45 100 1d, yes MnO H2ada RT 100 1d, yes Nd203 H2ada 45 100 1d, yes Nd203 H2ada RT 100 1d, yes NiO H2ada 45 100 ld, yes NiO H2ada RT 100 1d, no Pb0 H2ada 45 100 1d, yes Pb0 H2ada RT 100 1d, yes ZnO H2ada 45 100 1d, yes Pr203 H2ada RT 100 1d, yes Pr203 H2ada 45 100 1d, yes Eu203 H2ada RT 100 ld, yes Eu203 H2ada 45 100 1d, yes Yb203 1-12ada RT 100 id, no Yb203 H2ada 45 100 1d, yes Example 4¨ Conversion in the Presence of Salts of Oxalic Acid [00141] While conducting the experiments reported in Example 1, the following experiments were also carried out.
[00142] Our first attempts involved mixtures of ZnO, H2ox.2H20 and either 1,3-propanediammonium oxalate [pn][ox] or propylammonium oxalate [pa]2[ox] in the stoichiometric ratio 2:2:1.

= 26 [00143] After 5 days at room temperature and 98% RH, PXRD analysis (Figure 30) of the mixture of ZnO, H2ox-2H20 and [pn][ox] in 2:2:1 ratio revealed the presence of Znox= 2H20, but also X-ray reflections consistent with honeycomb-topology [pn][Zn2(ox)3].3H20 (CCDC code SEYQAO, Fig. 5a). Aging for a total of 16 days led to the complete disappearance of reflections of ZnO reactant and the Znox=
2H20 intermediate, and the diffraction pattern displayed an excellent fit to that expected for the pn2+
salt of the Zn2(ox)32-. Since Znok2H20 was an intermediate phase in the assembly of [pn][Zn2(ox)31-3H20, we attempted the room-temperature aging reaction of [pn][ox] with Znox= 2H20. After five days, the reaction mixture fully converted into [pn][Zn2(ox)3].3H20, as demonstrated by PXRD (Figure 30e). The formation of [pn][Zn2(ox)3].3H20 was supported by TGA which gave an excellent fit for the expected loss of three equivalents of water before 200 C
(measured weight loss=10.1c1/0, expected weight loss=10.3%), followed by the decomposition of the metal-organic residue into ZnO (measured residue weight=31.3%, calculated ZnO
residue for [pn][Zn2(ox)3]. 3H20=31.0 /0).
[00144] We studied aging of a mixture of (pa)2(ox), H2ox and ZnO at room temperature and 98% RH. After five days PXRD (Fig. 30j) indicated complete transformation of the mixture into the known 3-D metal-organic framework [pa]2[Zn2(ox)3]- 3H20 (CCDC SEYQIW, Fig. 31a).34 Composition was confirmed by TGA (measured water content=9.1%, calculated=9.5 /0; measured ZnO residue=29.4%, calculated=28.6 /0).
[00145] Cross-polarization magic angle spinning 13C solid-state NMR (SSNMR, Fig. 31 b) was consistent with the product being [pa]2[Zn2(ox)3]-3H20, displaying the signals of ox2- and pat. The 1H-13C HETCOR and 1H-1H
INADEQUATE experiments enabled tentative assignment of the 1H SSNMR spectra of [pa]2[Zn2(ox)3]-3H20, but with multiple signals expected from partially disordered water molecules unresolved. The HETCOR spectrum was consistent with the reported structure in which the framework interacts mostly with the methyl and ammonium moieties of the pa. The 13C SSNMR spectrum of [pn][Zn2(ox)3].3H20 obtained by aging was also consistent with the published structure.
Difference between Znox= 2H20, [Prign2(0x)3PH20 and [pa]2[Zn2(ox)3].3H20 were also evident using FTIR-ATR by the appearance of new features in the spectra of the 2- and 3-D MOFs, by the broadening of the 0-H stretching band at 3350 cm-, and, by the fine shift of 1604 cm-1 and 816 cm-1 bands of Znox= 2H20 to ca. 1580 cm-1 and 816 cm-1 in the 2-D and 3-D MOFs, respectively (Fig.
32a,d,g).
[00146] Further metal oxides were studied in that way. The results are shown in Figure 32. ZnO, NiO, Co0 aged with a mixture of oxalic acid dihydrate and 1,3-propanediammonium oxalate formed infinite open structures in two dimensions. ZnO, NiO, Co0 aged with a mixture of oxalic acid dihydrate and propylammonium oxalate formed infinite open structures in three dimensions.
[00147] Finally, a 1:1:1 stoichiometric mixture of CuO: H2ox.2H20: Na2ox was manually ground using a mortar and pestle for 1 minute. Reaction scale was 6 mmol (6 mmol : 6 mmol : 6 mmol), and the theoretical mass of product was 1.93 grams. The mixture was then aged at 60 C and 100% RH for 3 days. The reaction was complete according to PXRD. The product obtained was Na2Cuox2=2H20, a dark blue solid, and was identified by X-ray powder diffraction. This is a discrete complex that is soluble in water.

[00148] A 1:1:2 mixture of NiO: H2ox.2H20: Na2ox was manually ground using a mortar and pestle for 1 min.
Reaction scale is 6 mmol (6 mmol : 6 mmol : 12 mmol). The mixture was then aged at 60 C, 100% RH for 3 days. Only a mixture of Niox.2H20 and Na2ox has been found by PXRD. Niox.2H20 is poorly soluble in water.
Example 5 ¨ Prophetic Example: Integration of the Method of the Invention into a Conventional Metallurgical Process [00149] Figure 33 shows a conventional metallurgical process (left) for produce zinc from a zinc ore containing ZnS. The right side of the figure shows a similar process incorporating an embodiment of the method of the invention. This figure clearly shows the expected simplification of the process brought about by using the method of the invention.
[00150] The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.
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Claims (32)

1. A method for separating metals in a mixture of metallic compounds, the method comprising the steps of:
.cndot. mixing the mixture with a carboxylic acid, .cndot. selectively converting at least one of the metallic compounds into a metal carboxylate complex, thereby producing a mixture of said metal carboxylate complex with unreacted metallic compounds, and .cndot. separating the metal carboxylate complex from the unreacted metallic compounds.

2. The method of claim 1, further comprising milling the mixture of metallic compounds with the carboxylic acid prior to the converting step.

3. The method of claim 1 or 2, wherein the metallic compounds are oxides, sulfides, silicates, phosphates, hydroxides and/or carbonates of said metals, preferably oxides and/or sulfides.

4. The method of any one of claims 1 to 3, wherein the metals are two or more of manganese, copper, nickel, cobalt, zinc, lead, magnesium, silver, neodymium, bismuth, antimony, arsenic, tin, cadmium, praseodymium, lutetium, europium, and ytterbium.

5. The method of claim 4, wherein the metals are copper and zinc.

6. The method of claim 5, wherein the metallic compounds are copper oxide and zinc oxide.

7. The method of claim 5, wherein the metallic compounds are copper sulfide and zinc sulfide.

8. The method of claim 4, wherein the metals are copper and lead.

9. The method of claim 8, wherein the metallic compounds are copper oxide and lead oxide.

10. The method of claim 8, wherein the metallic compounds are copper sulfide and lead sulfide.

11. The method of claim 4, wherein the metals are lead and zinc.

12. The method of claim 11, wherein the metallic compounds are lead oxide and zinc oxide.

13. The method of claim 11, wherein the metallic compounds are lead sulfide and zinc sulfide.

14. The method of claim 4, wherein the metals are lead and silver.

15. The method of claim 14, wherein the metallic compounds are lead sulfide and silver sulfide.

16. The method of claim 4, wherein the metals are zinc and silver.

17. The method of claim 4, wherein the metallic compounds are zinc sulfide and silver sulfide.

18. The method of claim 4, wherein the metals are neodymium and lutetium.

19. The method of claim 18, wherein the metallic compounds are neodymium oxide and lutetium oxide.

20. The method of claim 4, wherein the metals are europium and ytterbium.

21. The method of claim 20, wherein the metallic compounds are europium oxide and ytterbium oxide.

22. The method of any one of claims 1 to 21, wherein the carboxylic acid is a solid.

23. The method of claim 22, wherein the carboxylic acid is oxalic acid, salicylic acid, acetylenedicarboxylic acid, fumaric acid, terephthalic acid, succinic acid, or benzoic acid.

24. The method of any one of claims 1 to 23, wherein in the mixing step, the mixture is mixed with the carboxylic acid and with a salt of the carboxylic acid, said salt comprising a cation and the carboxylic acid in deprotonated from as an anion.

25. The method of claim 24, wherein the cation is an organic cation, such as an ammonium, diammonium, or oligoammonium cation, an alkaline metal cation, or an alkaline earth metal cation.

26. The method of any one of claims 1 to 25, wherein the converting step is carried out a temperature above 0°C and below 100°C, preferably between about 15°C
and about 85°C, more preferably between room temperature and about 65°C, even more preferably between room temperature and about 45°C, most preferably at about 45°C.

27. The method of any one of claims 1 to 26, wherein the converting step is carried out at a relative humidity above 0%, preferably above about 50%, more preferably above about 75%, even more preferably above about 85%, yet more preferably above about 95%, most preferably of about 98% or more.

28. The method of any one of claims 1 to 27, wherein the converting step is carried out at atmospheric pressure.

29. The method of any one of claims 1 to 28, wherein the metal carboxylate complex is separated from the unreacted metallic compounds by flotation.

30. The method of any one of claims 1 to 28, wherein the metal carboxylate complex is separated from the unreacted metallic compounds by dissolution and filtration.

31. The method of any one of claims 1 to 30, further comprising separating the metals in the unreacted metallic compounds using the method of claim 1.

32. The method of any one of claims 1 to 31, wherein more than one metallic compounds are converted into more than one metal carboxylate complexes, the method further comprising, after the separating step, the step of heating the more than one metal carboxylate complexes to produce corresponding more than one metal oxides, and separating the metals in the more than one metal oxides using the method of claim 1.