Method and device for reducing metal oxide

Abstract

The proposed invention presents a novel technology of utilizing hydrogen and direct induction heating of metal oxide, such as indium oxide, tin oxide and their mixtures for recycling and reduction purposes to obtain high-grade indium-rich and tin-rich alloys. The invention discloses the fundamentals of the novel procedure as well as the description of a device to utilize the reduction procedure on an industrial scale.

Description

METHOD AND DEVICE FOR REDUCING METAL OXIDE

[0001] The invention refers to a method and a device for reducing metal oxide.

[0002] Metal oxides are widely used in modern products and there is a need to recycle these metal oxides to reduce waste and to reuse rare and expensive metals. As an example, this is discussed below for the instance of indium-tin oxides and individual oxide of it (I n2C>3, SnO, SnC>2).

[0003] Indium-tin oxides represent an important class of materials that is used in electronical, optical and architectural applications, such as energy efficient windows, flat panel displays and spectroelectrochemical applications. These materials are prepared with radio frequency sputtering of indium-tin oxide targets at which the targets after sputtering become etched and thus not anymore usable for indium-tin oxide film preparation. As result the indium-tin oxide needs to be recycled. Recycling of indium-tin oxides is of utmost importance due to the rarity and high value of the indium material, which results that the indium is rather extracted in either oxide or metal form from the indium-tin oxide and separated from the tin, which can be used for other applications or for re-use for new indium-tin oxide production.

[0004] The current industrial processes of extracting indium from indium-tin oxide is through reduction of indium-tin oxide and its individual compounds SnC>2 and ln2Os through the use of carbon as a reducing agent via so-called pyrometallurgical carbother-mic reduction. In this process the current state of the art uses pyrometallurgical furnaces, where oxide material and reductant (i.e. carbon) are heated up and react in a solid-solid and solid-gas state form. The carbon can be used in solid form or can be used as a reduction agent through its reforming into carbon monoxide via subsequent carbon combustion reaction (see Equation (1) and Equation (2)) and Boudouard reaction:Equation (1) 2 ■ C + O2 2 ■ COEquation (2) 2 ■ CO + O2-> 2 ■ CO2

[0005] Consequentially through these reactions the oxygen is extracted from the oxides resulting in metal formation and production of carbon dioxide as a side product as per equations (3) and (4):Equation (3) C + Sn( — CO2 + SnEquation (4) 3 ■ C + 2 ■ In2(h — 3 ■ CO2 + 4 ■ In

[0006] Such procedure is currently highly energy intensive as the reduction occurs at temperatures above 1100 °C in order to stabilize the reduction via carbon as given by the Ellingham diagram. Alternatively, the procedure for reducing SnC>2 can also performed with methane that is utilized as a carbon carrier for the reduction.

[0007] Against this background, the present invention is based on the technical problem of specifying a more energy-efficient process and a device for reducing or deoxidizing metal oxides. Furthermore, the present invention is based on the technical problem of specifying a process that does not emit carbon dioxide.

[0008] The technical problems described above are solved by the features of the independent claims. Further embodiments of the invention are set out in the dependent claims and the following description.

[0009] According to a first aspect, the invention refers to a method, comprising the following method steps: Providing a conductive metal oxide powder; Deoxidation of the conductive metal oxide powder by means of heat and a reducing agent. The method is characterized in that the heat is directly introduced to the conductive metal oxide powder using induction heating and in that the reducing agent comprises hydrogen.

[0010] The technical terms “reduction” and “deoxidation” are used synonymously throughout this text. In the present text, the terms “reduction” and “deoxidation” refer to the release of oxygen. That is, metal oxides are separated from oxygen in order to recover the metals from the metal oxides.

[0011] The technical term “conductive” encompasses the technical term “semi-conductive” according to this application. Hence, when the text refers to conductive metal powder, this encompasses to refer to both conductive as well as semi-conductive oxides.

[0012] For induction heating, the heating of the conductive metal oxide powder occurs through the production of local fluxes of eddy currents that are formed through the inductively generated magnetic fields. These fluxes then heat the inner part of the material via Joule heating and magnetic hysteresis losses.

[0013] The utilization of induction-based heating has the beneficial effect that the conductive metal oxide powder can be heated in a homogeneous manner, while even large volumes of conductive metal oxide powder can be heated in a homogeneous manner.

[0014] The utilization of induction-based heating has the beneficial effect that the conductive metal oxide powder can be heated fast and in a controlled manner, since the direct induction heating can be very well managed by the power input into the induction system. This allows for a direct control of the reduction process, a sequence of reduction for different metals as well as metal extraction and separation either in a physical manner or through evaporation.

[0015] The utilization of hydrogen as a reduction agent has the beneficial effect that the reduction can be performed with net zero CO2 emissions from the process itself. This statement is provided in the scope of the process itself and does not include the origin of the used gases and electrical energy that is required for the process itself, thus their inherent CO2 bill is not accounted for here.

[0016] According to one embodiment of the method, it may be provided that pressure is applied to the conductive metal oxide powder during deoxidation, in particular, the pressure being applied through a piston, said piston being in direct contact with the conductive metal oxide powder.

[0017] Active pressing can condense the formed metal, which in turn enables reducing a risk of possible re-oxidation of the metallic material after the reduction procedure (i.eexposure to ambient air) due to a lower ratio of surface versus volume - compared to an uncondensed state. Additionally, with active pressure, different metals can be more easily separated from one another, since different metals have different forming and viscosity parameters.

[0018] According to one embodiment of the method, it may be provided that the conductive metal oxide powder is comprised of indium-tin oxide or consisting of indium-tin oxide.

[0019] The inventors have found that indium-tin oxide is particularly well suited to be processed using induction heating due to the semiconductive properties of indium-tin oxide as well as the individual oxides, i.e. SnC>2, SnO and ln20s.

[0020] According to this aspect of the present invention regarding indium-tin oxide, a singular reduction procedure that can both provide the means to obtain metal / alloys from indium-tin oxide and refinement of the produced metal by simultaneous evaporation and condensation of the tin metal over indium metal in a spatial manner due to differences in reduction time, temperature, viscosity and inductivity.

[0021] The reduction and separation of indium and tin from indium-tin oxide works particularly well if, in addition to the combination of induction heating and hydrogen as a reduction agent, pressure is applied during deoxidation.

[0022] According to one embodiment of the method, a particle size of the conductive metal oxide powder being 500 microns or less, in particular being 150 microns or being 100 microns or less.

[0023] For the procedure of indium-tin oxide waste material, which as an example can be spent indium-tin oxide sputter targets, or other oxide mixtures mainly composed of tin (Sn) and / or indium (In), which includes their pure forms of SnO2, SnO and ln2O3, can be firstly collected for prior preparation for the reduction process.

[0024] The collected material can be mechanically ground to get rough granulates, flakes or similar macroscopic pieces that enable smooth pulverization. The mechanical grindingcan be performed by repetitive pressing or double-screw grinding and mincing. The final step in the refinement process of the material can be pulverization, which can be performed by rolling and / or milling. It can be advised for achieving fast reduction rates to obtain a particle size of about 100 pm after the pulverization process. This allows to achieve high ratios of surface area versus volume that provide sufficient reaction surfaces and minimize the diffusion-based solid-state limitations of the reduction process, i.e. the permeation of hydrogen gas and the removal of the formed water from the reduction process.

[0025] The claimed process can chemically reduce indium-tin oxide in pure form as well as in contaminated state and can provide the means to separate the impurities from the targeted formed metals due to the unique combination of conductivity and fast reduction rates with hydrogen gas as well as by the low melting temperature of the targeted metals being indium and tin.

[0026] The method can also be used for reduction of the following conductive and semi-conductive metal oxides: FesC , FeO, NiO, CO3O4, AgO, lead oxide PbO and PbC>2, WO3, ZnO and Sb20s as well as the mixtures of all of the listed oxides and indium-tin oxides.

[0027] According to one embodiment of the method, the induction efficiency can be improved by encasing the metal oxide target material into a conductive and thermally stable material (i.e. graphite) crucible / vessel that can be inductively heated and transfer the heat to the metal oxide target material.

[0028] According to one embodiment of the method, the induction efficiency can be improved by mixing the material with conductive particles (i.e. graphite or metallic materials such as iron) that can be inductively heated and transfer the heat to the oxide. The size of the particles is to be selected based on inductive efficiency and operational frequency of the inductive source.

[0029] With the utilization of conductive vessel and / or conductive particles, the method can be extended to use on oxides that display low conductivity properties at room temperatures: Bi2C>3, CU2O, MoOs, MnsC , TiC>2, Fe20s and PdO.

[0030] The method is applicable to both pure and impure oxide materials that have reasonable composition of the applicable oxides. This also applies to oxide mixtures originating from the combination of low conductive and high conductive primary oxides such as the case of the battery oxide materials LiCoO2, LiMn2O4, LiFeC or the so-called Lithium nickel manganese cobalt oxides abbreviated as NMC.

[0031] According to one embodiment of the method, hydrogen can be used in pure form as well as in a mixture with inert gas to provide diluted concentrations of hydrogen. For example, a mixture of hydrogen gas with inert gas such as argon (Ar) or nitrogen (N2) can be used.

[0032] Diluted concentrations of hydrogen can be used to achieve a higher degree of safety and enable a high degree of hydrogen utilization, thus reducing hydrogen losses and costs.

[0033] According to one embodiment of the method, before deoxidation and before hydrogen is fed into the conductive metal oxide powder, a housing encompassing the conductive metal oxide powder is evacuated, wherein a pressure level within the housing after evacuating being 5*10’1mbar or lower. This evacuation can be carried out using an evacuation system having a vacuum pump.

[0034] According to one embodiment of the method, the deoxidation of the conductive metal oxide powder is carried out as follows: firstly, the conductive metal oxide is heated to a defined temperature threshold using induction heating; secondly, when the temperature of the conductive metal oxide has reached the defined temperature threshold, hydrogen is continuously fed into the heated conductive metal oxide.

[0035] According to one embodiment of the method, an induction coil encompasses a section of a powder volume of the conductive metal oxide powder, wherein a deoxidationrate is monitored for this section, wherein, after a predetermined deoxidation threshold has been reached, a relative movement between the induction coil and the conductive metal oxide powder is carried out to deoxidize another section of the powder volume of the conductive metal oxide powder.

[0036] The induction coil can cover at least 10 cm or more of the feedstock of metal oxide powder in a vertical direction. The induction coil can cover at least 20 cm or more of feedstock of metal oxide powder in a vertical direction. The induction coil can cover the full height of a feedstock of metal oxide powder in a vertical direction.

[0037] According to one embodiment of the method, the powder volume and the induction coil being moved relative to one another with a constant feed rate. The induction coil can be cooled. The induction coil can be water-cooled. For instance, with at least 30 °C wa-ter / cooling media temperature.

[0038] It is possible to also reduce a single oxide under the pretention of having the oxide reduced to a single metal species.

[0039] According to one embodiment of the method, the conductive metal oxide powder is converted by deoxidation into a solid metal slab or block that contains at least two metals, which have been separated from each other to a defined degree of purity.

[0040] According to another aspect, the invention refers to a device, the device comprising: a reaction chamber for holding a conductive metal oxide powder, a supply system for supplying a reduction agent to the reaction chamber, a heating device for heating the conductive metal oxide powder. The device is characterized in that the heating device comprises an inductive heating device for directly heating the conductive metal oxide powder and in that the supply system comprises a hydrogen supply to provide the reduction agent hydrogen. Hydrogen can be provided in pure gas form or mixture with inert gases, i.e. argon and nitrogen gas.

[0041] According to one embodiment of the device, the device comprising a pressure application system to apply pressure to conductive metal oxide powder during deoxidation, such as a piston or the like.

[0042] According to one embodiment of the device, the device comprising a vacuum system for evacuating a housing encompassing the reaction chamber, such as a vacuum pump or the like, the vacuum system being configured to generate a vacuum of 5*10’1mbar or less within the housing and the reaction chamber.

[0043] According to one embodiment of the device, the inductive heating device comprises an inductive heating coil, which inductive heating coil encompasses the reaction chamber. The induction coil can have a height of at least 10 cm or more in a vertical direction. The induction coil can have a height of at least 20 cm or more in a vertical direction. The induction coil can cover the full height of the reaction chamber in a vertical direction.

[0044] According to one embodiment of the device, the reaction chamber is defined by a movable plate, wherein the plate is particularly a bottom plate that is vertically displaceable.

[0045] According to one embodiment of the device, the pressure application system comprises a piston defining the reaction chamber, said piston being arranged opposite the plate, wherein the piston and the plate being arranged to move the conductive metal oxide powder along the heating device during deoxidation.

[0046] According to one embodiment of the device, the pressure application system has a closable through-opening which opens into the reaction chamber, the through-opening being provided for introducing conductive metal oxide powder into the reaction chamber.

[0047] According to one embodiment of the device, the reaction chamber being defined by a ceramic cylinder, said ceramic cylinder being in particular a porous ceramic cylinder which allows gas to be introduced to the metal oxide material in the reaction chamber and allows gas escape from the reaction volume. The ceramic cylinder can be prepared withperforated mesh or made of material that has channels that enables gas flow but not movement of the metal oxide material and formed metal through it.

[0048] According to one embodiment of the device, the supply system for supplying the reduction agent to the reaction chamber comprises a tube that extends in a central position into the reaction chamber, the tube can be made in particular of a ceramic material, in particular a porous ceramic material. The tube can also be made from nonporous material, such as metal or the like.

[0049] According to one embodiment of the device, the device has a closable removal opening that is designed to remove a solid metal slab or block produced from the conductive metal oxide powder, the removal opening of the cylinder being arranged in particular at the bottom or near the bottom of the reaction chamber.

[0050] The invention is described in more detail below, with the aid of schematic drawings. The figures show:Fig. 1 a device according to the invention;Fig. 2 the device according to Fig. 1, filled with conductive metal oxide powder;Fig. 3 the device according to Fig. 1, filled with a metal block formed through reduction of the metal oxide powder;Fig. 4 process steps of the method according to the invention;Fig. 5 Indium and tin concentration of a metal block after processing.

[0051] Fig. 1 shows a sectional view of a device 2 according to the invention.

[0052] The device 2 has a reaction chamber 4 for holding a conductive metal oxide powder.

[0053] The device 2 has a supply system 6 for supplying a reduction agent to the reaction chamber 4. The supply system 6 comprises a hydrogen supply 14 to provide hydrogen as the reduction agent.

[0054] The device 2 has a heating device 8 for heating the conductive metal oxide powder. The heating device 8 comprises an inductive heating device 10 for directly heating the conductive metal oxide powder, said heating device 10 being an induction coil 10. The induction coil 10 is connected to a power supply 12 of the heating device 8 to control the heating power of the induction coil 10. The induction coil 10 is water-cooled.

[0055] The device 2 has a housing 16, which housing 16 encapsulates the reaction chamber 4 and the induction coil 10.

[0056] A pressure sensor 18 is connected to the housing 16 to monitor the pressure inside the housing 16. A vacuum pump 20 is connected to the housing 16 to evacuate the housing 16 before hydrogen is fed into the housing 16. The vacuum pump 20 is configured to generate a vacuum of 5*10’1mbar or less within the housing 16 and the reaction chamber 4.

[0057] The reaction chamber 4 is defined by a piston 22, a bottom plate 24 and a ceramic porous cylinder 26.

[0058] The bottom plate 24 is translational moveable in vertical directions as indicated by the arrows assigned to the bottom plate 24. To clarify the orientation of the device 2, the direction g of acceleration due to gravity is indicated in the drawing.

[0059] The piston 22 is translational moveable in vertical directions as indicated by the arrows assigned to the piston 22.

[0060] The porosity of the porous ceramic cylinder 26 is designed to trap metal and metal oxide in the reaction chamber 4, but to allow hydrogen to be introduced through the porous ceramic cylinder and water and unused reduction gas to escape from the reaction chamber 4 through the porous ceramic cylinder 26.

[0061] The piston 22 is part of a pressure application system 28 to apply pressure to conductive metal oxide powder during deoxidation. The piston 22 is made of ceramics to avoid sticking of metals to the piston 22 during processing.

[0062] The piston 22 has a closable through-opening 30 which opens into the reaction chamber 4. The through-opening 30 is provided for introducing conductive metal oxide powder into the reaction chamber 4.

[0063] The supply system 6 for supplying hydrogen into the reaction chamber 4 comprises a first tube 32 that extends in a central position into the reaction chamber 4. The vertical section of the first tube 32 is made of porous ceramic material to feed hydrogen into the reaction chamber 4.

[0064] The supply system 6 for supplying hydrogen into the reaction chamber 4 comprises a second tube 34 to fill the housing with hydrogen.

[0065] Both the first tube 32 and the second tube 34 are connected to the hydrogen tank 14 by means of a respective controllable gas regulation block 34 to control the hydrogen flow. Each gas regulation block can be configured for regulating the reaction gas flow, having a pre-feeding pressure system, together with a flow meter and an adaptive valve to form the gas inlet part of the device 2.

[0066] The device 2 has a closable removal opening 36 that is designed to remove a solid metal slab or metal block produced from the conductive metal oxide powder. The removal opening 36 of the cylinder 26 is near the bottom of the reaction chamber 4.

[0067] The inventive process will now be described based on the example of processing indium-tin oxide.

[0068] Indium-tin oxide is provided being the conductive metal oxide powder to be processed, having a particle size of about 100 microns.

[0069] I ndium-tin oxide powder 38 is fed into the reaction chamber 4 from the top via the through opening 30 of the piston 22. The moveable bottom plate 24 is in the initial position required for the reduction process.

[0070] The indium-tin oxide powder 38 can be fed into the reaction chamber 4 in stages or portions, whereby the powder filled in can be compacted between the filling steps by means of the hydraulically actuated piston 22. Before compacting, the through-hole 30 of the piston 22 is sealed to create a completely closed piston face 40.

[0071] According to alternative embodiments, the reaction chamber can be designed in an inverted conical shape to provide continuous pushing of the material downwards and not in reverse. This is to avoid potential blocking inlets and outlets for the gases with feedstock or formed metallic material.

[0072] The piston 22 can compress the indium-tin oxide powder 38 until pressures of 10 MPa (megapascal) are achieved and stabilized. For stabilization 10 min of waiting time is performed. During this stabilization the housing 16 and process chamber 4 are vacuumized with the vacuum pump 20. Based on the safety perspectives of using hydrogen gas, the housing 16 and process chamber 4 are evacuated to pressure levels of at least 5x10’1mbar or lower.

[0073] After the evacuation is of sufficient levels, the induction coil 10 is started and the heating of the indium-tin oxide powder 38 occurs.

[0074] For the reduction of metal oxides such as indium-tin oxide, high temperatures are required to overcome the energy barrier for continuous reaction progression and to enable fast conversion kinetics. For this purpose, the utilization of direct induction heating is used, where the utilization of the high conductivity properties of the indium-tin oxide and individual oxides is used to obtain fast heating rates and good energy conversion leading to heating the material locally up to a maximum temperature of approximately 1500 °C, depending on the input power and frequency of the induction field.

[0075] The heating rate and achieved temperature can be controlled through the input power to the coil 10. The induction is performed with the power supply 12, being a high frequency generator 12 that has a frequency range of 50 kHz up to 10 MHz that sends out an AC current through the water-cooled copper coil 10 that surrounds the indium-tin oxide material that is targeted to be reduced.

[0076] For this type of heating, the heating of the oxide occurs through the inherent Joule heating and magnetic hysteresis losses, through production of local fluxes of eddy currents that are formed by the inductively generated magnetic fields. For protection of the inductive copper coil 10 from heat and contamination with the processed material, the coil is wounded around the ceramic cylinder 26 that is positioned inside the heating zone of the inductive copper coil 10.

[0077] For allowing proper gas flow, the ceramic cylinder 26 is designed with perforated mesh or made of material that has channels that enables gas flow but not movement of the indium-tin oxide material and formed metal through it. The inductive coil 10 can be designed arbitrarily to heat a larger or smaller section of the input feedstock, depending on the power rating of the generator, coil design and on the required time of heating and reduction rate. A coverage length in a vertical height direction of at least 10 cm is recommended to have sufficient volume of material heated and to avoid inefficient and slow reduction of the feedstock with respect to the input power.

[0078] A temperature sensor 42 is connected to the bottom plate 24. As the temperature readout of the bottom plate 24 registers 900 °C, hydrogen is introduced into the housing 16 and into the reaction chamber 4. In this example 100 % hydrogen is used. However, as mentioned before, diluted hydrogen can be used according to alternative variants of the claimed method. For example, a mixture of hydrogen gas with inert gas such as Ar or N2can be used.

[0079] An outlet 50 of the housing 16 can be attached to a recuperating, filtering and condensing system that allows the proper processing of the off-gas. The outlet isconnected to a pumping system which can be constructed of a roughening pump and an oil pump.

[0080] Having reached 900 °C and with the hydrogen introduced, the reduction is now in the initial stages performed in stationary manner, i.e. the bottom plate 24 of the reaction chamber 4 is not yet moved.

[0081] The reduction efficiency is controlled through the temperature measurement and gas pressure changes in outgas pressure monitoring. Outgas pressure monitoring can be achieved using sensors at the pump 20 or at the outlet 50. The outlet 50 can be connected to the pump 20, wherein the pump 20 can be used as the outlet 50.

[0082] The reduction of the introduced feedstock 32 occurs through a two-step reaction, namely firstly the tin oxide will reduce with hydrogen prior to the indium oxide based on the reduction potentials. Resultingly, the reduction will effectively begin at 1050 °C for tin oxide, while for indium oxide the reduction will be efficient at temperatures of at least 1300 °C. The reduction reactions are formed in a singular reaction step for the individual oxides and metals as presented in equation (5) and equation (6):Equation (5) 2 ■ H2 + SnC — 2 ■ H2O + SnEquation (6) 3 ■ H2 + 2 ■ In2(h — 3 ■ H2O + 4 ■ In

[0083] With the formation of metal melt via the reduction and high temperatures, the process through its introduction of pressure allows direct mobility of the metal from the formed cavities in the feedstock to the outer edges of the slab of block of the processed material.

[0084] Resultingly, the metallic tin has a preferential mobility towards the outer edges resulting in a kinematic-viscosity-based separation of tin and indium. Additionally, the partial evaporation of the formed metal and recondensation on the walls of the reaction chamber additionally supports the separation of the two targeted metals. With the subsequent formation of indium through the reduction of indium-tin oxide and its individual oxide, ln2Os,the indium is encapsulated and concentrated within the bulk of the slab of the processed material and later metallic slab.

[0085] This is additionally enabled by the fact that liquid indium has a lower kinematic viscosity than liquid tin and that tin has a higher melting point than indium. However, with the distillation of the indium oxide from tin due to the prior reduction of tin oxide and subsequent evaporation, the melting temperature of the oxide mixture is modified and lowered over time. Based on thermodynamic calculations, the melting temperature of the oxide can be lowered down to 1150 °C for the case of pure SnC>2, while the melting temperature of pure ln2C>3 sustains at 1900 °C. The lowered melting temperature consequentially enables higher reduction rates due to the higher mobility of the liquid oxide compared to its solid form. The combined sum of the physical differences enables a prominent separation of the tin and indium into a core-shell like formation of the metallic slab, as schematically presented Fig. 5.

[0086] The heating through induction naturally decays with the formation of dense metal material due to the reduction of the skin depth related to the skin effect that is firstly lowered by the improved conductivity of the metal versus oxide. Secondly, the effective heating of the metal portion is reduced with larger volume, i.e with higher densification and interconnectivity as then the skin effect concentrates the heat formation to the very thin surface part of the metal portion. Essentially, this enables high temperature formation at the interface of the oxide and formed metal and on the other allows faster cooling and detection of the reduction progression through the subsequent change in the inductivity of the processed volume of the material.

[0087] After sufficient time the reduction effect decreases, which is registered by the formation of metal and reduced rate of formation of water. As the metal forms the induction efficiency also drops due to change in impedance which can be monitored by an LCR meter (inductance-capacitance-resistance meter) at the induction coil 10.

[0088] When sufficient degree of reduction is determined an automated vertical motion of the indium-tin oxide feedstock material 38 is initiated. The bottom plate 24 is unlatchedand using a hydraulic-based releasing a slow descending of indium-tin oxide feedstock material 38 is performed, thus effectively moving the induction heated zone to move upwards with respect to the indium-tin oxide feedstock materials 38 bottom edge.

[0089] The rate of the vertical descending motion of the plate 24 is set based on the reduction rate that is dependent on the average particle size, concentration of hydrogen, diameter of the cylinder 26 and the input power and frequency of the power supply 12, which power supply 12 is an induction generator 12.

[0090] For this example, the rate of motion is set to be 1 cm per minute or less, when the cylinder diameter d is 50 cm, the coil diameter c is 70 cm, the coil effective height h is 20 cm and an input power of the induction generator 12 is 500 kW. The values are only provided as indicative values to provide meaningful and expected values for industrial-scaled systems.

[0091] After the entire feedstock material 38 is reduced and converted to metallic material, the coil 10 is switched off. The formed material is pushed to the lowest end of the cylinder 26 and is left to be cooled down.

[0092] Before removal of the formed metal block the upper piston 22 is to be moved away from the upper surface of the formed metal block 44. In case of sticking of the formed metal to the piston 22, the piston 22 can provide a slight overpressure to destabilize metal contact. Another option can be also to utilize a clamping system to keep the metal block 44 in place and then slowly move the piston 22 to physically detach the piston 22 from the top of the metal block 44.

[0093] The formed metallic block 44 should be removable directly through physical removal, which could require a forklift or similar device, depending on the dimensions of the processed metallic block 44.

[0094] For easy separation, the ceramic cylinder 26 and the piston 22 should have fine surface to avoid sticking of the formed metal to the ceramic cylinder 26 and the piston 22. Additionally, non-sticking, high-temperature-stable powder or coatings can be applied onthe surface of the cylinder 26 as well as the piston 22 to ease the removal of the metal block 44.

[0095] The solid metallic block 44 consists of an indium phase 48 and a tin phase 46. The drawing is schematic so the shown distribution does not reflect the real distribution of tin and indium within the metallic block 44. This is shown in more detail in Fig. 5. The diagram shows the indium concentration over the width w of the block 44. For the indium phase 48 in the center, the indium concentration can be as high as 95 %. For the tin phase 46 surrounding the center, the tin concentration can be as high as 95 %.

[0096] According to the invention, a process can be provided having the following steps (Fig. 4): (A) Providing a conductive metal oxide powder; (B) Deoxidation of the conductive metal oxide powder by means of inductive heat and hydrogen. Step (B) can in addition include the application of pressure to the conductive metal oxide powder during reduction.

[0097] With prior knowledge of the process and processing parameters related to the scale of the process and the quality / type of the input feedstock and the used reduction gas composition, the previously presented process can be performed in a more unmonitored manner. This can be partially done using process monitoring as given in the previous example and then used as reference values and parameters. Namely, when utilizing different concentrations of hydrogen gases, generator power, coil designs and quality of material, the process can be adjusted based on the base values without the required measurement devices described in the previously presented process. The approximations and calculations can be done based on simplistic thermodynamic calculations or empirical-based reaction kinetic description of the reduction process in relation to the selected processing parameters. Effectively, this can be done using the Ellingham diagrams of the individual oxides and metals, Pourbaix diagrams in relation to the gas composition and temperature and thermodynamic calculations via CALPHAD method using the principal ensemble of processing parameters and input feedstock and gas material.

[0098] In addition, an example for proof of concept of the claimed indium-tin oxide reduction principle has been performed by the applicant:

[0099] 10 g of waste ITO sputter targets were smashed and ground to a powder. The powder was afterwards put in a cylindrical casing and compressed to a cylindrical compact with external pressure of 100 MPa.

[0100] The compact was afterwards extracted from the casing and positioned on a copper plate. The plate was water-cooled in order to avoid its melting with exposures to high temperatures. The sample and copper plate were encased with a glass tube that is on one side connected to a gas inlet and on the other connected to an outlet tube that is connected to a pump.

[0101] The glass tube was encircled by a water-cooled coil with 4 windings that was connected to a 12 kW generator with an operating frequency of 192 kHz.

[0102] For the reduction testing a 10 % H2 mixture in Ar base gas was used.

[0103] Before the experiment the inlet gas valve was closed and entire system was vacuumized with the pump system for approximately 5 min. Afterwards the inlet gas valve was opened and the pumping valve was adjusted to have a steady flow of the reduction gas and outflow of the formed gas.

[0104] Afterwards the generator was switched on and the coil heated the sample cylinder within a span of 15 seconds to a red glowing state. The material immediately developed a clear formation of vapor phase and outgas related to the chemical reduction of the oxides to metal form.

[0105] The heated cylinder strongly expanded and developed a sponge-like structure that is typical of solid-state reduction processes. The material over time additionally developed flakes of dendritic structures that grew over time and encased the entirety of the cylinder surface. With time the red glow dissipated and the sponge-like material displayed reduced activity and outgassing.

[0106] After 15 minutes, the coil was switched off and the material and glass tube were cooled down. The reduced material was extracted and cross-sectioned and analyzed with scanning electron microscopy and X-ray photoelectron spectroscopy.

[0107] Both analyzing methods confirm a large portion of the oxide material has converted to metallic material registered by the morphological changes and changes in the chemical composition and binding state of the individual metals.

[0108] Additionally, the deeper portions and the surface portions of the reduced material were analyzed. The results show that high concentrations of tin are formed on the surface of the reduced material whereas in the inner sides an enrichment of indium is determined.

[0109] The resulting compositions indicated that indium enriched metal of 95 wt.% indium is achievable and that on the opposite end alloys enriched with 75 % tin and 25 % indium are possible. It should be noted that the tin-rich alloys present a small fraction of the alloy compared to the indium-rich one.

Claims

CLAIMS:

1. Method, comprising the following method steps:Providing a conductive metal oxide powder;Deoxidation of the conductive metal oxide powder by means of heat and a reducing agent;characterized in thatthe heat is directly introduced to the conductive metal oxide powder using induction heating and in thatthe reducing agent comprising hydrogen.

2. Method according to claim 1,characterized in thatpressure is applied to the conductive metal oxide powder during deoxidation, in particular, the pressure being applied using a piston, said piston being in direct contact with the conductive metal oxide powder.

3. Method according to any one of the preceding claims,characterized in thatthe conductive metal oxide powder consisting of a single metal oxide to be reduced or consisting of a mixture of two metal oxides to be reduced;or the conductive metal oxide powder comprising indium-tin oxide or consisting of indium-tin oxide;or the conductive metal oxide powder comprising at least one of the following oxides or mixtures thereof: ln20s, SnO, SnC>2, FesC , FeO, NiO, CO3O4, AgO, lead oxide PbO and PbC>2, WO3, ZnO and Sb20s;or the conductive metal oxide powder comprising conductive particles, such as graphite or metallic materials such as iron or encased in a conductive casing / cruci- ble made of graphite, as well as at least one of the following oxides or mixtures thereof: Bi20s, CU2O, MoOs, MnsC , TiC>2, Fe20s and PdO;or the conductive metal oxide powder comprising at least one of the following oxides or mixtures thereof: LiCoC>2, LiMn2O4, LiFeC .

4. Method according to any one of the preceding claims,characterized in thatthe particle size of the conductive metal oxide powder being 500 microns or less, in particular being 150 microns or being 100 microns or less.

5. Method according to any one of the preceding claims,characterized in thatbefore deoxidation and before hydrogen is fed into the conductive metal oxide powder, a housing encompassing the conductive metal oxide powder is evacuated, wherein a pressure level within the housing after evacuating being 5*10’1mbar or lower.

6. Method according to any one of the preceding claims,characterized in thatthe deoxidation of the conductive metal oxide powder is carried out as follows: firstly, the conductive metal oxide is heated to a defined temperature threshold using induction heating;secondly, when the temperature conductive metal oxide has reached the defined temperature threshold, hydrogen is fed to the heated conductive metal oxide.

7. Method according to any one of the preceding claims,characterized in thatan induction coil encompasses a section of a powder volume of the conductive metal oxide powder, wherein a deoxidation rate is monitored for this section, wherein, after a predetermined deoxidation threshold has been reached, a relative movement between the induction coil and the conductive metal oxide powder is carried out to deoxidize another section of the powder volume of the conductive metal oxide powder.

8. Method according to claim 7,characterized in thatthe powder volume and the induction coil being moved relative to one another with a constant feed rate.

9. Method according to claim 7 or 8,characterized in thata length of the section of the powder volume encompassed by the coil being at least 10 cm.

10. Method according to any one of the preceding claims,characterized in that the conductive metal oxide powder is converted by deoxidation into a solid metal slab that contains at least two metals, which have been separated from each other to a defined degree of purity.

11. Device, the device comprising:a reaction chamber for holding a conductive metal oxide powder,a supply system for supplying a reduction agent to the reaction chamber,a heating device for heating the conductive metal oxide powder,characterized in thatthe heating device comprising an inductive heating device for directly heating the conductive metal oxide powder and in thatthe supply system comprising a hydrogen supply to provide hydrogen as the reduction agent.

12. Device according to claim 11 ,characterized in thatthe device comprising a pressure application system to apply pressure to conductive metal oxide powder during deoxidation, such as a piston or the like.

13. Device according to claim 11 or claim 12,characterized in thatthe device comprising a vacuum system for evacuating a housing encompassing the reaction chamber, such as a vacuum pump or the like, the vacuum system isconfigured to generate a vacuum of 5*1 O’1mbar or less within the housing and the reaction chamber.

14. Device according to any one of claims 11 - 13,characterized in thatthe inductive heating device comprise an inductive heating coil, which inductive heating coil encompasses the reaction chamber.

15. Device according to any one of claims 11 - 14,characterized in thatthe reaction chamber is defined by a movable plate, wherein the plate is particularly a bottom plate that is vertically displaceable.

16. Device according to claim 15 and to claim 12,characterized in thatthe pressure application system comprising a piston defining the reaction chamber, said piston being arranged opposite the plate, wherein the piston and the plate being arranged to move the conductive metal oxide powder along the heating device during deoxidation.

17. Device according to claim 12,characterized in thatpressure application system has a closable through-opening which opens into the reaction chamber, the through-opening being provided for introducing conductive metal oxide powder into the reaction chamber.

18. Device according to any one of claims 11 - 17,characterized in thatthe reaction chamber being defined by a ceramic cylinder, the ceramic cylinder being in particular a porous ceramic cylinder which allows gas to be introduced to the reaction chamber as well as escape of the gas from the reaction chamber.

19. Device according to any one of claims 11 - 18,characterized in thatthe supply system for supplying the reduction agent to the reaction chamber comprises a tube that extends in a central position in the reaction chamber, the tube be- ing made in particular of a ceramic material.

20. Device according to any one of claims 11 - 19,characterized in thatthe device has a closable removal opening that is designed to remove a solid metal slab produced from the conductive metal oxide powder, the removal opening of the cylinder being arranged in particular at the bottom or near the bottom of the reaction chamber.

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