Copper

Example 1

The effect of Tu on the electrochemical behavior of a chalcopyrite electrode was studied in a conventional 3-electrode glass-jacketed cell. A CuFeS₂ electrode was using as working electrode, a saturated calomel electrode (SCE) was used as reference, and a graphite bar was used as counter-electrode. The CuFeS₂ electrode was polished using 600 and 1200 grit carbide paper. All experiments were conducted at 25° C. using a controlled temperature water bath. The electrolyte composition was 500 mM H₂SO₄, 20 mM Fe₂SO₄ and 0-100 mM Tu. Before starting any measurement, solutions were bubbled with N₂ for 30 minutes to reduce the concentration of dissolved 02. Open circuit potential (OCP) was recorded until changes of no more than 0.1 mV/min were observed. After a steady OCP value was observed, electrochemical impedance spectroscopy (EIS) was conducted at OCP using a 5 mV a.c. sinusoidal perturbation from 10 kHz to 10 mHz. Linear polarization resistance (LPR) tests were also conducted using a scan rate of 0.05 mV/s at ±15 mV from OCP.

Linear potential scans were conducted at electrode potentials ±15 mV from the OCP measured at each Tu concentration. All scans showed a linear behavior within the electrode potential range analyzed. An increase in the slope of the experimental plots was observed with increasing Tu concentration. The slope of these curves was used to estimate the value of the polarization resistance (Ret) at each concentration. These values were then used to estimate the values of the dissolution current density using equation 1:

$\begin{array}{cc}{i}_{\mathrm{dissol}}\approx \frac{\mathrm{RT}}{{\mathrm{nFR}}_{\mathrm{ct}}}& \mathrm{Eq}.\left(1\right)\end{array}$

FIG. 3 shows the effect of Tu on the dissolution current density and mixed potential of the CuFeS₂ electrode, and indicates that a maximum dissolution current density was achieved when Tu concentration is 30 mM. Increasing Tu concentration to 100 mM resulted in a decrease in the current density and mixed potential of the CuFeS₂ electrode. Moreover, after immersing the CuFeS₂ electrode in the 100 mM Tu solution, a copper-like film was observed on the surface of the electrode, which film could only be removed by polishing the electrode with carbide paper.

FIG. 4 is a bar graph showing the effect of initial Tu or FDS concentration on the electrochemical dissolution of a chalcopyrite electrode in sulfuric acid solution at pH 2 and 25° C. A concentration of 10 mM Tu in the leach solution resulted in a six fold increase in dissolution rate compared to no Tu, and a concentration of 5 mM FDS resulted in a six fold increase relative to 10 mM Tu. A concentration of 10 mM Tu in leach solution also containing 40 mM Fe(III) resulted in a thirty fold increase in dissolution rate compared to 40 mM Fe(III) alone.

A column leach of different acid-cured copper ores was conducted with Tu added to the leach solution. A schematic description of the column setup is shown in FIG. 5. The column diameter was 8.84 cm, the column height was 21.6 cm, and the column stack height was 15.9 cm. The irrigation rate was 0.77 mL/min or 8 L/m²/h. The pregnant leach solution emitted from these columns was sampled for copper every 2 or 3 days using Atomic Absorption Spectroscopy (AAS).

The specific mineralogical composition of these ores are provided in Table 1. The Cu contents of Ore A, Ore B, and Ore C were 0.52%, 1.03%, and 1.22% w/w, respectively. Prior to leaching, ore was “acid cured” to neutralize the acid-consuming material present in the ore.

That is, the ore was mixed with a concentrated sulfuric acid solution composed of 80% concentrated sulfuric acid and 20% de-ionized water and allowed to sit for 72 hours. For one treatment using Ore C, Tu was added to the sulfuric acid curing solutions.

The initial composition of the leaching solutions included 2.2 g/L Fe (i.e. 40 mM, provided as ferric sulfate) and pH 2 for the control experiment, with or without 0.76 g/L Tu (i.e. 10 mM). The initial load of mineral in each column was 1.6 to 1.8 kg of ore. The superficial velocity of solution through the ore column was 7.4 L m⁻² h⁻¹. The pH was adjusted using diluted sulfuric acid. These two columns were maintained in an open-loop or open cycle configuration (i.e. no solution recycle) for the entire leaching period.

The results of leaching tests on the Ore A, Ore B and Ore C are shown in FIGS. 6, 7, and 8, respectively. The presence of Tu in the lixiviant clearly has a positive effect on the leaching of copper from the chalcopyrite. On average, the leaching rate in the presence of Tu was increased by a factor of 1.5 to 2.4 compared to the control tests in which the leach solutions did not contain Tu. As of the last time points depicted in FIGS. 6 to 8, copper extractions for columns containing Ore A, Ore B, and Ore C leached with a solution containing sulfuric acid and ferric sulfate alone, without added Tu, were 21.2% (after 198 days), 12.4% (after 50 days), and 40.6% (after 322 days), respectively. With 10 mM of added Tu, these extractions were 37.9%, 32.0%, and 72.3%, respectively.

Referring to FIG. 8, 2 mM Tu was added to the leach solution originally containing no Tu from day 322 onward, after which the leach rate increased sharply. From day 332 to day 448, the copper leached from this column increased from 40% to 58%, and rapid leaching was maintained throughout that period.

The averages for the last 7 days reported in FIG. 9 indicate that the leaching rate for acid-cured Ore C leached in the presence of 10 mM Tu is 3.3 times higher than for acid-cured Ore C leached in the absence of Tu, and 4.0 times higher than acid-cured and Tu-cured Ore C leached in the absence of Tu.

FIG. 10 shows the effect of Tu on solution potential. All potentials are reported against a Ag/AgCl (saturated) reference electrode. The solution potential of the leach solutions containing Tu was generally between 75 and 100 mV lower than the solution potential of leach solution that did not include Tu. Lower solution potentials are consistent with Tu working to prevent the passivation of chalcopyrite.

“Bottle roll” leaching experiments in the presence of various concentrations of Tu were conducted for coarse Ore A and Ore B. The tests were conducted using coarsely crushed (100% passing ½ inch) ore.

Prior to leaching, the ore was cured using a procedure similar to what was performed on the ore used in the column leaching experiments. The ore was mixed with a concentrated sulfuric acid solution composed of 80% concentrated sulfuric acid and 20% de-ionized water and allowed to settle for 72 hours to neutralize the acid-consuming material present in the ore. For several experiments, different concentrations of Tu were added to the ore using the sulfuric acid curing solutions.

The bottles used for the experiments were 20 cm long and 12.5 cm in diameter. Each bottle was loaded with 180 g of cured ore and 420 g of leaching solution, filling up to around one third of the bottle's volume.

The leaching solution from each bottle was sampled at 2, 4, 6 and 8 hours, and then every 24 hours thereafter. Samples were analyzed using atomic absorption spectroscopy (AAS) for their copper content.

The conditions for the bottle roll experiments are listed in Table 2. Experiments #1 to #6 were conducted using only the original addition of Tu into the bottles. For experiments #7 to #11, Tu was added every 24 hours to re-establish the Tu concentration.

A positive effect of Tu on copper leaching was observed. For the coarse ore experiments, a plateau was not observed until after 80 to 120 hours. Tu was added periodically to the coarse ore experiments, yielding positive results on copper dissolution.

The effect of different concentrations of Tu in the leach solution on the leaching of coarse ore (experiments #1 to #11 as described in Table 2) is shown in FIGS. 11 and 10.

For ore B, Tu was periodically added every 24 hours to re-establish the thioruea concentration in the system and thus better emulate the conditions in the column leach experiments. As may be observed from FIG. 9, 8 mM and 10 mM Tu yielded higher copper dissolution results than the other Tu concentrations tested for ore A. A plateau in dissolution is not observed until after approximately 120 hours, which varied with Tu concentration as shown in FIG. 11.

As may be observed from FIG. 12, 5 mM Tu yielded higher copper dissolution results than the other Tu concentrations tested for ore B. As with ore A, a plateau in dissolution is not observed until after approximately 80 to 120 hours, which varied with Tu concentration as shown in FIG. 12. Periodic addition of Tu resulted in increased copper dissolutions and produced a delay in the dissolution plateau.

Interestingly, solutions containing 100 mM Tu did not appear to be much more effective on copper extraction than those containing no Tu, and even worse at some time points. This is consistent with the results of Deschenes and Ghali, which reported that solutions containing 200 mM Tu (i.e. 15 g/L) did not improve copper extraction from chalcopyrite. Tu is less stable at high concentrations and decomposes. Accordingly, it is possible that, when initial Tu concentrations are somewhat higher than 30 mM, sufficient elemental sulfur may be produced by decomposition of Tu to form a film on the chalcopyrite mineral and thereby assist in its passivation. It is also possible that, at high Tu dosages, some copper precipitates from solution (e.g. see FIG. 17) to account for some of the low extraction results.

Example 1

95 g of manganese (purity: 99.95%; purchased from Taewon Scientific Co., Ltd.) and 5 g of high-purity graphite (purity: 99.5%; purchased from Taewon Scientific Co., Ltd.) were placed in a water-cooled copper crucible of an argon plasma arc melting apparatus (manufactured by Labold AG, Germany, Model: vacuum arc melting furnace Model LK6/45), and melted at 2,000 K under an argon atmosphere. The melt was cooled to room temperature at a cooling rate of 10⁴ K/min to obtain an alloy ingot. The alloy ingot was crushed to a particle size of 1 mm or less by hand grinding. Thereafter, the obtained powders were magnetically separated using a Nd-based magnet to remove impurities repeatedly, and the Mn₄C magnetic powders were collected. The collected Mn₄C magnetic powders were subjected to X-ray diffraction (XRD) analysis (measurement system: D/MAX-2500 V/PO, Rigaku; measurement condition: Cu—K_α ray) and energy-dispersive X-ray spectroscopy (EDS) using FE-SEM (Field Emission Scanning Electron Microscope, MIRA3 LM).

FIGS. 2(a) and 2 (b) show an X-ray diffraction pattern and an energy-dispersive X-ray spectroscopy graph of the Mn₄C magnetic material produced according to Example 1 of the present disclosure, respectively.

As can be seen in FIG. 2(a), the Mn₄C magnetic material showed diffraction peaks of (111), (200), (220), (311) and (222) crystal planes at 2θ values of 40°, 48°, 69°, 82° and 88°, respectively, in the XRD analysis. Thus, it can be seen that the XRD patterns of the Mn₄C magnetic material produced according to Example 1 are well consistent with the patterns of the cubic perovskite Mn₄C. In addition, the Mn₄C magnetic material shows several very weak diffraction peaks that can correspond to Mn₂₃C₆ and Mn. That is, the diffraction peak intensity at 2θ values of 43° and 44°, which correspond to Mn and Mn₂₃C₆ impurities, is as very low as about 2.5% of the diffraction intensity of the peak corresponding to the (111) plane. Through this, it can be seen that the powders obtained in Example 1 have high-purity Mn₄C phase. The lattice parameter of the Mn₄C is estimated to be about 3.8682 Å.

FIG. 2(b) shows the results of analyzing the atomic ratio of Mn:C in the powder by EDS. The atomic ratio of Mn:C is 80.62:19.38, which is very close to 4:1 within the experimental uncertainties. Thus, it can be seen that the powder is also confirmed to be Mn₄C.

The M-T curve of the field aligned Mn₄C powder obtained in Example 1 was measured under an applied field of 4 T and at a temperature ranging from 50 K to 400 K. Meanwhile, the M-T curve of the randomly oriented Mn₄C powder was measured under an applied field of 1 T. The Curie temperature of Mn₄C was measured under 10 mT while decreasing temperature from 930 K at a rate of 20 K/min.

FIGS. 3(a) to 3(c) show the M-T curves of the Mn₄C magnetic material, produced according to Example 1 of the present disclosure, under magnetic fields of 4 T, 1 T, and 10 mT, respectively.

FIG. 3 shows magnetization-temperature (M-T) curves indicating the results of measuring the temperature-dependent magnetization intensity of the Mn₄C magnetic material, produced in Example 1, using the vibrating sample magnetometer (VSM) mode of Physical Property Measurement System (PPMS®) (Quantum Design Inc.).

According to the Néel theory, the ferrimagnets that contain nonequivalent substructures of magnetic ions may have a number of unusual forms of M-T curves below the Curie temperature, depending on the distribution of magnetic ions between the substructures and on the relative value of the molecular field coefficients. The anomalous M-T curves of Mn₄C, as shown in FIG. 3(a), can be explained to some extent by the Néel's P-type ferrimagnetism, which appears when the sublattice with smaller moment is thermally disturbed more easily. For Mn₄C with two sublattices of Mn_I and Mn_II, as shown in FIG. 1, the Mn_I sublattice might have smaller moment.

FIG. 3(a) shows the temperature dependence of magnetization of the Mn₄C magnetic material produced in Example 1. The magnetization of Mn₄C measured at 4.2K is 6.22 Am²/kg (4 T), corresponding to 0.258μ_B per unit cell. The magnetization of the Mn₄C magnetic material varies little at temperatures below 50 K, and is quite different from that of most magnetic materials, which undergo a magnetization deterioration with increasing temperature due to thermal agitation. Furthermore, the magnetization of the Mn₄C magnetic material increases linearly with increasing temperature at temperatures above 50 K. The linear fitting of the magnetization of Mn₄C at 4 T within the temperature range of 100 K to 400 K can be written as M=0.0072T+5.6788, where M and T are expressed in Am²/kg and K, respectively. Thus, the temperature coefficient of magnetization of Mn₄C is estimated to be about ˜2.99*10⁻⁴μ_B/K per unit cell. The mechanisms of the anomalous thermomagnetic behaviors of Mn₄C may be related to the magnetization competition of the two ferromagnetic sublattices (Mn_I and Mn_II) as shown in FIG. 1.

FIG. 3(b) shows the M-T curves of the Mn₄C powders at temperatures within the range of 300 K to 930 K under 1 T. The linear magnetization increment stops at 590 K, above which the magnetization of Mn₄C starts to decrease slowly first and then sharply at a temperature of about 860 K. The slow magnetization decrement at temperatures above 590 K is ascribed to the decomposition of Mn₄C, which is proved by further heat-treatment of Mn₄C as described below.

According to one embodiment of the present disclosure, the saturation magnetization of Mn₄C increases linearly with increasing temperature within the range of 50 K to 590 K and remains stable at temperatures below 50 K. The increases in anomalous magnetization of Mn₄C with increasing temperature can be considered in terms of the Néel's P-type ferrimagnetism. At temperatures above 590 K, the Mn₄C decomposes into Mn₂₃C₆ and Mn, which are partially oxidized into the manganosite when exposed to air. The remanent magnetization of Mn₄C varies little with temperature. The Curie temperature of Mn₄C is about 870 K. The positive temperature coefficient (about 0.0072 Am²/kgK) of magnetization in Mn₄C is potentially important in controlling the thermodynamics of magnetization in magnetic materials.

The Curie temperature T_e of Mn₄C is measured to be about 870 K, as shown in FIG. 3(c). Therefore, the sharp magnetization decrement of Mn₄C at temperatures above 860 K is ascribed to both the decomposition of Mn₄C and the temperature near the Tc of Mn₄C.

FIG. 4 is a graph showing the magnetic hysteresis loops of the Mn₄C magnetic material, produced according to Example 1 of the present disclosure, at 4.2 K, 200 K and 400 K. The magnetic hysteresis loops were measured by using the PPMS system (Quantum Design) under a magnetic field of 7 T while the temperature was changed from 4 K to 400 K.

As shown in FIG. 4, the positive temperature coefficient of magnetization was further proved by the magnetic hysteresis loops of Mn₄C as shown in FIG. 4. The Mn₄C shows a much higher magnetization at 400 K than that at 4.2 K. Moreover, the remanent magnetization of Mn₄C varies little with temperature and is Δ3.5 Am²/kg within the temperature range of 4.2 K to 400 K. The constant remanent magnetization of Mn₄C within a wide temperature range indicates the high stability of magnetization against thermal agitation. The coercivities of Mn₄C at 4.2 K, 200 K, and 400 K were 75 mT, 43 mT, and 33 mT, respectively.

The magnetic properties of Mn₄C measured are different from the previous theoretical results. A corner Mn_I moment of 3.85μ_B antiparallel to three face-centered Mn_II moments of 1.23μ_B in Mn₄C was expected at 77 K. The net moment per unit cell was estimated to be 0.16μ_B. In the above experiment, the net moment in pure Mn₄C at 77 K is 0.26μ_B/unit cell, which is much larger than that expected by Takei et al. It was reported that the total magnetic moment of Mn₄C was calculated to be about 1μ_B, which is almost four times larger than the 0.258μ_B per unit cell measured at 4.2 K, as shown in FIG. 4.

FIG. 5 is an enlarged view of the temperature-dependent XRD patterns of the Mn₄C magnetic material produced according to Example 1 of the present disclosure.

The thermomagnetic behaviors of Mn₄C are related to the variation in the lattice parameters of Mn₄C with temperature. It is known that the distance of near-neighbor manganese atoms plays an important role in the antiferro- or ferro-magnetic configurations of Mn atoms. Ferromagnetic coupling of Mn atoms is possible only when the Mn—Mn distance is large enough. FIG. 5 shows the diffraction peaks of the (111) and (200) planes of Mn₄C at temperatures from 16 K to 300 K. With increasing temperature, both (111) and (200) peaks of Mn₄C shifted to a lower degree at temperatures between 50 K and 300 K, indicating an enlarged distance of Mn—Mn atoms in Mn₄C. No peak shift is obviously observed for Mn₄C at temperatures below 50 K. The distance of nearest-neighbor manganese atoms plays an important role in the antiferro- or ferro-magnetic configurations of Mn atoms and thus has a large effect on the magnetic properties of the compounds.

Thus, it can be seen that the abnormal increase in magnetization of Mn₄C with increasing temperature occurs due to the variation in the lattice parameters of Mn₄C with temperature.

The powder produced in Example 1 was annealed in vacuum for 1 hour at each of 700 K and 923 K, and then subjected to X-ray spectroscopy, and the results thereof are shown in FIG. 6.

The magnetization reduction of Mn₄C at temperatures above 590 K is ascribed to the decomposition of Mn₄C, which is proved by the XRD patterns of the powders after annealing Mn₄C at elevated temperatures. FIG. 6 shows the structural evolution of Mn₄C at elevated temperatures. When Mn₄C is annealed at 700 K, a small fraction of Mn₄C decomposes into a small amount of Mn₂₃C₆ and Mn. The presence of manganosite is ascribed to the spontaneous oxidation of the Mn precipitated from Mn₄C when exposed to air after annealing. The fraction of Mn₂₃C₆ was enhanced significantly for Mn₄C annealed at 923 K, as shown in FIG. 6.

These results prove that the metastable Mn₄C decomposes into stable Mn₂₃C₆ at temperatures above 590 K. The presence of Mn₄C in the powder annealed at 923 K indicates a limited decomposition rate of Mn₄C, from which the Tc of Mn₄C can be measured. Both Mn₂₃C₆ and Mn are weak paramagnets at ambient temperature and elevated temperatures. Therefore, the magnetic transition of the Mn₄C magnetic material at 870 K is ascribed to the Curie point of the ferrimagnetic Mn₄C.

The Mn₄C shows a constant magnetization of 0.258μ_B per unit cell below 50 K and a linear increment of magnetization with increasing temperature within the range of 50 K to 590 K, above which Mn₂₃C₆ precipitates from Mn₄C. The anomalous M-T curves of Mn₄C can be considered in terms of the Néel's P-type ferrimagnetism.

Example 3

The following features are relevant to the disclosed invention(s):

This work demonstrated the fabrication of dipole antennas made from different MXene compositions of Ti₃C₂, Ti₂C, Mo₂TiC₂ as exemplars of the general MXene family.

The films exemplified here were binder free and fabricated simply from the MXene colloidal solutions in water (MXene ink). Since MXenes can be made in colloidal aqueous and non-aqueous (e.g., organic solvent) solutions, they can be used as ink to print, spray paint, etc. any shape, design and thickness to fabricate very thin, flexible and transparent antennas in one simple step.

Any kind of antenna fabrication method can be employed, for example printing, spraying, coating, painting, rolling MXene clay into films, cutting complicated shapes for different antenna designs.

MXene return loss and peak gain outperformed any synthetic materials. Although MXenes are theoretically not as conductive as copper, the present work showed that MXene outperforms copper, the mostly used and very well-known antenna material. The as synthesized binder free titanium carbide (Ti₃C₂) MXene film dipole antenna showed a return loss of about 50 dB. The MXene antenna's radiation pattern measurements showed a peak gain similar to the copper dipole antenna. Such a high antenna performance has never been reported for any nanomaterials.

With the variety of MXene composition, it was and will be possible to tune the antenna for different applications.

By controlling the flake size, the bandwidth of the antenna can further be controlled.

Fabricating MXene-polymer composites can protect MXene from oxidation and can further improve its flexibility. In order to make MXenes films mechanically more robust, 2D MXene flakes can be embedded in polymer matrices. Moreover, using a polymer as a matrix can further improve the oxidation resistance of MXenes.