Note: Descriptions are shown in the official language in which they were submitted.
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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
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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.
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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
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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.
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[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
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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%.
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[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
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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,
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(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:
CA 02824769 2013-08-22
= 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.
CA 02824769 2013-08-22
11
[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.
CA 02824769 2013-08-22
12
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
CA 02824769 2013-08-22
13
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
CA 02824769 2013-08-22
14
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.
CA 02824769 2013-08-22
[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.
CA 02824769 2013-08-22
16
[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.
CA 02824769 2013-08-22
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[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.
CA 02824769 2013-08-22
18
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
CA 02824769 2013-08-22
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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
CA 02824769 2013-08-22
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
CA 02824769 2013-08-22
21
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),
CA 02824769 2013-08-22
22
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
CA 02824769 2013-08-22
= 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.
CA 02824769 2013-08-22
24
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
CA 02824769 2013-08-22
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.
CA 02824769 2013-08-22
= 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.
CA 02824769 2013-08-22
27
[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.
,
CA 02824769 2013-08-22
28
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