System for energy storage

Abstract

There is provided a system for energy storage, which can also be simultaneously enabled for metal production, wherein the system includes one or more electrolytic cells making up a battery of cells and wherein the battery of cells are connected to a power source, wherein the system includes both a metal recovery / electrodeposition step and an electricity generation step in cycles.

Description

[0001] SYSTEM FOR ENERGY STORAGE

[0002] FIELD OF THE INVENTION

[0003] This invention relates to a system for energy storage. More particularly, but not exclusively, this invention relates to a system for energy storage in a metallurgical process.

[0004] BACKGROUND TO THE INVENTION

[0005] In the field of mining and mineral processing, copper solvent extraction electrowinning (SXEW) is a metallurgical process known in the art as a purification and recovery process, by which copper and other metals are leached from ores and selectively recovered into a solution for electrolytic production of copper. Leaching is achieved using acidic or alkaline lixiviants / chemicals to produce a pregnant leach solution (PLS). The PLS is then contacted, in one or more stages, with a non-aqueous solvent mixed with a chemical extractant, collectively known as loaded organic (LO) that selectively extracts copper over other metals. The LO also can be stripped (reversal of extraction from extractant) of copper in one or more strip stages, using a strong sulphuric acid solution, to produce a loaded strip liquor (LSL), or advance electrolyte (ADE) and resulting in a stripped organic (SO). Metals that are in the PLS such as iron, manganese, nickel, zinc and cobalt, are not significantly transferred to the LSL / ADE, in the solvent extraction (SX) process and thus remain in the stripped PLS - which is then called the Raffinate (RAF).

[0006] A disadvantage of the above process is that impurities, such as iron, cobalt, nickel, manganese, molybdenum and certain sulphur compounds are carried through the SX process by chemical or entrainment means. These impurities often build up in the electrolyte and could negatively affect the copper cathode purity.

[0007] The electrolytic recovery process known in the art as electrowinning (EW), is shown in Figure 1. Specifically, electrowinning (part of SXEW) refers to a process in which metal ions, present in an electrically conductive solution, are reduced to metal and thus separated using a direct current. A relatively pure metal is recovered in this process.

[0008] Electrolysis of copper, also known as electro-plating of copper, has been used for many decades in the refining of copper and recovery of pure copper from solvent extraction strip liquors (LSL / ADE). This recovery process, by which a metal (typically copper) is separated from a leach solution (typically acidic) and concentrated into a strip liquor (LSL) which is electrolysed to electrowin (EW) a relatively pure metal (approximately >99.9 %) as the cathode (or on the cathode), the cathode being opposed typically by a lead alloy anode, is referred to as this solvent extraction electrowinning (SXEW). As part of a leach SXEW process, a copper EW tank house electroplates copper metal onto a stainless- steel cathode with lead anodes either side. A typical EW cell may have 33 cathodes and 34 anodes or more, spaced at about 90 mm anode to anode. Typically, 30 to over 100 cells are connected in series. Such a battery of EW cells requires a source of approximately 15,000 A to 45,000 A and 70 VDC to over 220 VDC. This power supply is in most cases supplied from a national grid, where high voltage alternating current (HVAC) is stepped down in several steps to low voltage (LVAC), and then rectified to direct current (DC). However, the power losses, in the form of heat, from transmission and conversion of HVAC to LVDC, are significant.

[0009] Electrorefining (ER), a further process known in the art, uses relatively less electrical power, and is a recovery process where the anode consists of cast blister copper of approximately 97 % copper. The copper is transferred to the cathode, typically a copper starter sheet, where it then electroplates as a relatively pure metal.

[0010] A disadvantage of the abovementioned processes is that a stable power supply is required for operation. This can be costly and can have a significant environmental impact as a result of diesel-powered back-up systems required. In some cases, vast battery systems can be used in conjunction with solar or wind power sources. However, such renewable energy technologies suffer from the disadvantage of periodic and unpredictable power generation. As such they are generally unsuitable for the powering of industry without huge battery storage systems which, in themselves, are expensive and mostly have a huge environmental life cycle impact.

[0011] OBJECT OF THE INVENTION

[0012] It is accordingly an object of the present invention to provide a system for energy storage, to address the issues identified above, at least to some extent, or which may provide a useful alternative to existing technologies.

[0013] SUMMARY OF THE INVENTION

[0014] According to the invention, there is provided a system for energy storage, simultaneously enabled for metal production if required, wherein the system includes one or more electrolytic cells making up a battery of cells, wherein the battery of cells are connected to a power source and wherein the system includes both a metal electrodeposition step and an electricity generation step in cycles.

[0015] The power source may be a renewable power source selected from the group including, but not limited to a photovoltaic (PV) solar cell, or wind or hydro sources of electrical DC power. Alternatively, the power source may be a conventional power source. Metal may be leached into a pregnant electrolyte metal solution from ore, mineral concentrate, scrap metal, battery scrap, anode or e-scrap.

[0016] In the metal recovery step, the metal in solution may be recovered in the electrolytic cell or cells via an electrowinning (EW), electrorefining (ER) or via a solvent extraction electrowinning (SXEW) process.

[0017] The metal in solution may be recovered as a metal on, or at, a cathode of the electrolytic cell or cells. Other metals in solution may be oxidised or reduced into other valencies as part of the electrical power storage and production cycles.

[0018] One or more metals in solution may be recovered as metal salt(s) via solvent extraction (SX), ion exchange (IX), SXEW or precipitation from the solutions before or after SX or IX.

[0019] In the electricity generation step, the electrolyte metal solution, in turn, may be used as a feed solution to the electrolytic cells, wherein the electrolyte metal solution may be used as an oxidant in the electrolytic cells for the generation of electricity via a redox reaction.

[0020] The metal recovery / electrodeposition step and electricity generation step may occur on an alternating, cyclical basis. The metal may be selected from the group including, but not limited to, copper, nickel, cobalt, iron, manganese and zinc.

[0021] Voltage over the battery of cells may be controlled by changing the number of electrolytic cells in use at any given time.

[0022] Alternatively, voltage over the battery of cells may be controlled by changing the spacing between anodes and cathodes in the electrolytic cells in use at any given time.

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The invention will now be described further by way of non-limiting examples with reference to the accompanying drawing wherein:

[0025] Figure 1 shows a flow diagram of a prior art, standard industry practice (SIP) electrowinning (EW) process;

[0026] Figure 2 shows a flow diagram of the system of the invention; and

[0027] Figure 3 shows a flow diagram of the system of the invention, including a supercapacitor and invertor.

[0028] DETAILED DESCRIPTION OF THE INVENTION

[0029] The following description is provided as illustration of the principles of the invention and is not intended to limit the scope of the invention. In accordance with the invention, there is provided a system for energy storage, which is simultaneously enabled for metal production, wherein the system includes one or more electrolytic cells making up a battery of cells and wherein the battery of cells are connected to a power source.

[0030] The power source is a renewable power source selected from the group including, but not limited to; a photovoltaic (PV) solar cell, or wind or hydro sources of electrical DC power. Alternatively, the power source is a conventional power source.

[0031] Metal is leached into a pregnant leach solution (PLS) or electrolyte, from either ore, mineral concentrate, scrap metal, battery scrap, anode, e-scrap or the like.

[0032] In a metal recovery / electrodeposition step, the metal in solution is recovered in the electrolytic cell or cells via an electrowinning (EW), electrorefining (ER) with or without a solvent extraction (SX) process involved. These processes are operated by applying a voltage over the electrolytic cells.

[0033] The metal in solution is recovered as a metal on, or at, a cathode of the electrolytic cell or cells.

[0034] In an electricity generation step, the electrolyte metal solution, in turn, is used as a feed solution to the electrolytic cells, wherein the electrolyte metal solution is specifically used as an oxidant in the electrolytic cells for the generation of electricity via a redox reaction (i.e., generation of electricity via a redox flow battery type system).

[0035] The metal recovery step and electricity generation step occur on an alternating, cyclical basis or at a random ad hoc basis.

[0036] The metal is selected from the group including, but not limited to, copper, nickel, cobalt, iron, manganese and zinc.

[0037] Voltage over the battery of cells is controlled by changing the number of electrolytic cells in use at any given time. Alternatively, voltage over the battery of cells is controlled by changing the spacing between anodes and cathodes in the electrolytic cells in use at any given time.

[0038] The anode electrodes of the cells are composed partially or fully of coke, graphite, lead, titanium, an alloy of lead calcium, tin and or antimony cast around a copper hanger bar, other highly resistant metals / metal alloys or carbon / graphite and / or combinations thereof and can differ in different cells making up the battery of cells. The cathode electrodes are composed partially or fully of mild steel, stainless steel (higher-grade or typically 316L stainless steel with a bonded copper hanger bar), copper, nickel, cobalt, lead, titanium or other acid-resistant metals / metal alloys or carbon / graphite and / or combinations thereof and can differ in different cells making up the battery cell. The EW or electrolytic cells (depending on which step is being carried out - metal recovery step or electricity generation) of the invention have either flat anodes and cathodes, or anodes and cathodes which are tubular or of the cyclonic EW cell type.

[0039] The system of the present invention further includes an electrowinning tank of rectangular horizontal cross-section wherein the electrodes are substantially rectangular plates suspended in a vertical plane with supporting means at the upper edge of said electrodes, which support the electrodes from vertical tank sidewalls that are substantially perpendicular to said electrodes.

[0040] In one embodiment of the system of the invention, electrolyte is circulated upwardly into the EW tank through a distributor means, with jets located beneath said electrodes so that the electrolyte flow rate is substantially uniform along the length of the tank.

[0041] In a further aspect of the invention, the electrolyte metal solution is circulated through an external loop electrolyte system and upwardly between at least one cathode and at least one anode immersed in said electrolyte, thereby adjusting in said external loop, the concentration of dissolved gases, other metals in solution and the pH. A portion of, or all the connected electrolytic cells of the invention are used to produce an oxidised electrolyte which can chemically store energy. The electrolyte stores this energy until it is required to regenerate electricity. The oxidised electrolyte is then used to regenerate electricity by pumping the oxidised electrolyte back through the electrolytic cells, including the cells used to produce cathode copper, hereby producing a reduced electrolyte that is stored until surplus power is available for it to be re-oxidised.

[0042] In the system of the invention, the direct current (DC) electricity generated from reducing the oxidised electrolyte in the electrolytic cells, is used to electroplate metal in electrically connected cells and / or the DC electricity can also be converted to alternating current (AC) electrical power and / or can be stored in a DC battery or super capacitor type DC storage unit for immediate or later use.

[0043] Furthermore, in the system of the invention, various cells are connected to form various sections (for example an EW section and redox section and / or other cell sections as shown in Figure 2). Each of these cell sections can contain different electrolytes and differing concentrations of metals, acids, alkali’s, amino acids and other metal chelates.

[0044] The system of the invention preferably is powered or charged, with direct current (DC) power from PV solar cells (as per Figure 2), wind or hydro sources of electrical DC power. During periods of low or nil power supply (such as during the night), the discharge of power, from the system of the invention, is achieved by changing the type and / or flow of the electrolyte. For example, in a setup where copper is the metal used in the system, the copper electrowinning (EW) system is charged and discharged in the same manner as a grid scale DC battery (such as those based on lithium, molten salt or redox flow battery types).

[0045] An electrolyte with high oxidising potential is produced in dedicated electrolytic cells of the system of the invention and can be based on any metal that has more than one oxidised valance in the solution chemistry of the respective electrolyte. The base metals which have shown usefulness, and are used in the electrolyte, include copper, nickel, cobalt, iron and manganese. Other chemicals such as mineral acids, alkali’s, sulphur dioxide (SO2), metal chelate’s and amino acids are added to the electrolyte as required to optimise electrical charging, dis-charging, current output, EW and for the use in mineral or metal leaching.

[0046] In the system of the invention, various types of electrolyte solutions are stored separately from the electrolytic cells. These electrolyte solutions are circulated, as required, through the system depending on if the electrolytic cells are respectively electroplating, oxidising electrolytes or discharging to supply power externally. Concentrations of the various metals and other chemicals in the electrolytes can range from a trace to approximately 65 g.L’1with acids and alkalis at trace, to concentrations of up to 98 % w / v.

[0047] Electricity produced by the system of the invention is DC power, which is stored in DC batteries such as super capacitors (shown in Figure 3), or Li or Pb based batteries. As per Figure 3, DC electricity is converted into AC electricity via industry standard DC to AC inverters, for use elsewhere.

[0048] The present invention is a means to use conventional EW cells (producing copper cathodes) in a way similar to a redox flow battery, to then also provide power in a cyclical manner such that, at least, the full power requirements of the cells are met by solar PV power supplied directly as DC, as well as availing surplus electrical power for other loads.

[0049] In other words, the system of the present invention utilises a novel approach of optimising production of, storing and making use of oxidised species in electrolysis cell electrolytes, to regenerate electricity from the same on a cyclical basis, similar to the nature of a redox flow battery, while still allowing production of metal cathode products, on a cyclical basis. That is, the same EW operation is cyclically used to store and discharge stored chemical energy as electrical power with or without the requirement to produce electroplated metal for sale. This system utilises a combination of features and operating ranges to make continuous electrowinning of even low copper concentration solutions, such as less than about 10 gram per liter (g.L-1), practical, while simultaneously producing oxidised electrolyte for later use in generating electricity.

[0050] The system of the present invention has application with copper solvent extraction electrowinning (SXEW) systems as used at many copper and polymetallic mines as well as hydrometallurgical refineries around the world. Furthermore, this invention has wide application in the copper and or polymetallic ore processing or refining industry where a lower cost of electrical power is desired, and a cheaper oxidant is desirable for the purpose of leaching metals or minerals to release contained metals into solution. This invention can significantly reduce the carbon footprint of a mine or refinery which involves EW, when connected to a renewable electricity supply such as a solar PV electricity source, without a massive battery array and the associated cost of such.

[0051] By adjusting the size of tanks for storing the electrolytes and adding redox flow battery assemblies, the storage system can be sized to support multi-megawatt implementations suitable for use with industry or power grid applications.

[0052] Thermal integration with energy generating systems, such as compressed air energy storage, fuel cell, wind and solar systems, can further maximise total energy efficiency. The redox flow battery system can also be scaled down to smaller applications, such as a gravity feed system suitable for small and remote site applications.

[0053] Example of the invention

[0054] During conventional copper production in EW cells, a voltage of around 2 V to 2.2 V is applied across the anodes and cathodes. However, by utilising the system of the present invention, less voltage (resulting in energy savings) can be utilised by the modification of the electrolyte solution chemistry as is contingent with this invention. As shown in Figures 2 and 3, in this invention, the EW cells can be powered directly be a solar PV array. Therefore, the voltage will be variable during the day as solar intensity fluctuates. During peak solar PV power production, oxidised electrolyte production is maximised and stored separately to the electrolytic cells, and the supercapacitors are fully charged. Then, towards the afternoon, when the solar intensity reduces, the super capacitors slowly discharge, continuing the EW and other electrolytic processes.

[0055] Initially, as solar intensity drops during each afternoon, the voltage applied to the EW battery of cells decreases and the voltage that each EW cell sees will drop below 2 V and lower as the super capacitor discharges.

[0056] Depending on the electrolyte chemistry and the ingredients employed to optimise the process, the electrowinning process will slow down and almost stop as current pushed into the cells, by the potential between cathode and anode, trends towards zero. The production of AC power from the same source will continue as the super capacitors are still discharging, although then at a voltage that is lower than required for the EW processes. As the cell voltage decreases further, the electrolysis reactions are reversed and cells switch to a redox flow type battery that is discharging as some copper is then redissolved from the cathodes which now become the anodes in a redox battery producing current, rather consuming current. This DC current is then produced from the cells and feeds into the super capacitors and the DC to AC inverters (Figure 3).

[0057] In either case, a point will be reached where other power demands of the rest of the operation will require more electricity production from the redox flow battery than the supercapacitor can supply. At this point, the EW electrolyte will be rapidly drained from some or all EW cells via plugged drain ports in the bottom of each EW cell, into a dedicated storage tank(s) for the reduced circulating electrolyte (CRE). During the night, this CRE (at approximately 35 g / L copper) will be passed via SX strip mixer settlers, to load it all to STE SO- 55 g / L copper before EW recommences the following day. Oxidised electrolyte is then pumped into the cells. By the changing of the CRE electrolyte to an oxidising electrolyte (OXE) that was oxidised during peak solar PV production during the day, the EW cells become redox flow cells and electricity can be generated from the EW cells. The oxidising electrolyte (OXE) of higher oxidising potential produces a reverse DC current, switching the EW cells into redox flow cells and such DC current produced can be inverted into AC electricity for use within that industry or exported to a local power grid.

[0058] The reduced electrolyte (RDE) from such redox flow battery arrangement is stored for re-oxidation, during peak solar production, the following day. By the time the PV solar array starts to produce power the following day, the cells have been acting as a redox flow battery and the stored volume of oxidised electrolyte (OXE) is near depleted. Once sufficient copper has been electroplated from that reduced electrolyte, all the RDE (reduced OXE) is drained from the cells and replaced with the stored CRE to commence EW again as the solar PV reaches peak power output. The RDE is pumped to dedicated electrolysis cells during peak power production during the day and oxidised back to OXE ready for the night shift. The combination of electrolysis cells produces cathode copper from CRE and converts RDE to OXE during the daytime solar production, and at nighttime converts to a redox flow battery to produce electricity by the conversion of OXE to RDE.

[0059] As shown in Figure 3, a super capacitor, or other type of electrical storage device (Pb or Li battery), can be employed in the system of the invention. Said super capacitor can be connected directly across the main supply(s) to the battery of various electrolytic cells. Such a super capacitor or capacitors would delay and smooth the process of switching from EW to redox battery, as a positive flow of current would be maintained for some while after the solar PV power supply has dissipated. The power from the discharging super capacitors and the EW cells now operating as redox flow batteries, is used via inverters for the continued production of AC power - for use in the rest of the facilities or for export. In this manor, the DC supply to the inverters switches seamlessly from solar PV to supercapacitor to redox flow battery and back to solar PV within a day to night to day cycle possibly without switch gear.

[0060] In an alternative embodiment of the present invention, a solar array of many megawatts can be arranged in a series and parallel arrangement to supply electricity directly to the electrolytic cells of the system of the invention, via a DC-to-DC converter (such as a Bucks type DC-DC converter). A super capacitor is connected in parallel, that is charged up during peak solar PV power production and continues to supply power back into the system after the sun goes down. As the voltage of the capacitor decays as it discharges and the electrochemistry changes in the EW cells, the current demand of the EW cells drop off steeply. This is a function of electrochemistry requiring a certain potential / voltage to force the current through the resistance of the electrolytic cell and reduce the metal from solution (electroplating / electrowinning). As a result, the capacitor does a fine job at providing a trickle current to the EW step, as the voltage available from the super capacitor decreases.

[0061] The DC voltage from a solar array or other renewable energy sources may be variable. However, as mentioned, electrolysis processes do require a specific range of voltage between the anode and cathode for the electrolysis to be achieved efficiently. The present invention caters for this by several means, including, separately or in combination, the following:

[0062] - a Bucks type DC to DC voltage controller device;

[0063] - a physical bridge that is placed across the electrolysis cells bypassing a number of those cells in order to deliver a higher voltage to the active electrolysis cells;

[0064] - a means to connect into the series of cells, additional cells in series to reduce the applied voltage over the individual cells; and / or

[0065] - a super capacitor pack, or large lithium battery pack, connected in parallel to the electrolysis, before or after a Bucks step down device, or by itself.

[0066] It will be appreciated that various alternative embodiments are also possible in accordance with the present invention. For example, electrorefining (ER) of metals solely or in combination with EW processes is possible. Furthermore, it will be understood that some advantages of the present invention may be attained by selecting some of the features of the present invention without utilising other features. Accordingly, those skilled in the art will recognise that modifications and adaptations to the present invention may be possible or desirable in certain circumstances and may form part of the present invention.

Claims

CLAIMS1. A system for energy storage, simultaneously enabled for metal production, wherein the system includes one or more electrolytic cells making up a battery of cells, wherein the battery of cells is connected to a power source, and wherein the system includes both a metal recovery / electrodeposition step and an electricity generation step in cycles.

2. The system of claim 1 , wherein the power source is a renewable power source selected from the group including, but not limited, to photovoltaic (PV) solar cells, wind or hydro sources.

3. The system of claim 1 , wherein, the power source is a conventional power source.

4. The system of claim 2 or 3, wherein metal is leached into a pregnant electrolyte metal solution from ore, mineral concentrate, scrap metal, battery scrap, anode or e-scrap and wherein, in the metal recovery / electrodeposition step, the metal in solution is recovered in the electrolytic cell or cells via an electrowinning (EW), electrorefining (ER) or via a solvent extraction electrowinning (SXEW) process.

5. The system of claim 4, wherein the metal in solution is recovered as a metal on, or at, a cathode of the electrolytic cell or cells.

6. The system of claim 4, wherein one or more metals in solution are recovered as metal salt(s) via solvent extraction (SX), ion exchange (IX), SXEW or precipitation from the solutions before or after SX or IX.

7. The system of claim 4 or 5, wherein, in the electricity generation step, the electrolyte metal solution, in turn, is used as a feed solution to the electrolytic cells, wherein the electrolyte metal solution is used as an oxidant in the electrolytic cells for the generation of electricity via a redox reaction.

8. The system of any one of claims 4 to 6, wherein the metal recovery / electrodeposition step and electricity generation step occur on an alternating, cyclical basis.

9. The system of any one of claims 4 to 6, wherein the metal is selected from the group including, but not limited to, copper, nickel, cobalt, iron, manganese and zinc.

10. The system of claim 9, wherein various electrolytic cells in the battery of cells are connected to form individual sections, including, but not limited to an EW, ER, SXEW and redox section, and wherein each of these cell sections can contain different electrolytes and differing concentrations of metals.11 . The system of any one of claims 1 to 9, wherein voltage over the battery of cells is controlled by changing the number of electrolytic cells in use at any given time.

12. The system of any one of claims 1 to 9, wherein voltage over the battery of cells is controlled by changing the spacing between anodes and cathodes in the electrolytic cells.

13. The system of any one of claims 1 to 12, wherein a portion of, or all the connected electrolytic cells of the invention are used to produce an oxidised electrolyte which can chemically store energy.

14. The system of claim 13, including at least one tank for storing the electrolyte.

15. The system of claim 14, wherein the electrolyte stores energy until it is required to regenerate electricity and wherein energy is regenerated by pumping the oxidised electrolyte back through the electrolytic cells, including the cells used to produce cathode metal, hereby producing a reduced electrolyte that is stored until surplus power is available for it to be re-oxidised.

16. The system of claim 15, wherein direct current (DC) electricity is generated from reducing the oxidised electrolyte in the electrolytic cells, wherein this electricity is used to electroplate metal in electrically connected cells.

17. The system of claim 16, wherein the DC electricity is converted to alternating current (AC) electrical power and / or is stored in a DC battery, super capacitor storage unit or any other type of electrical storage device (such as Pb or Li battery) for immediate or later use.

18. The system of claim 17, wherein, during peak production from the power source, oxidised electrolyte production is maximised and stored in the tanks separately to the electrolytic cells, and the supercapacitors are fully charged.

19. The system of claim 18, wherein, during off-peak production from the power source, as cell voltage decreases, the super capacitors slowly discharge, thereby continuing the EW, ER or SXEW processes.

20. The system of claim 19, wherein, as cell voltage decreases further and trends towards zero, the electrolysis reactions are reversed and cells switch to a redox flow type battery that is discharging as some metal is then redissolved from the cathodes, which now become the anodes, in a redox battery producing current, rather than a consuming current.

21. The system of claim 20, wherein the super capacitor, or other type of electrical storage device is connected directly across the power supply to the battery of the electrolytic cells, in order to smooth the process of switching from EW, ER or SXEW to redox battery, as a positive flow of current would be maintained for some while after the power supply has dissipated.

22. The system of claim 21 , wherein the DC power from the electrical storage device is continuously converted to AC power, within a cycle, via an inverter or inverters, without expensive switch gear.

23. The system of claim 20, wherein a solar array of many megawatts can be arranged in a series and / or parallel arrangement to supply electricity directly to the electrolytic cells of the system of the invention, via a DC-to- DC converter (such as a Bucks type DC-DC converter), and wherein the super capacitor is connected in parallel, charged up during peak power production and continues to supply power back into the system after power production goes down.

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