Method and system for obtaining metals

Abstract

Disclosed herein is an in-situ leaching system comprising: a lixiviant source; and an injection well arranged to receive a leaching solution at ground level and to inject the received leaching solution into underground glassy volcanic rock; wherein: the leaching solution comprises lixiviant from the lixiviant source; and the leaching solution is for leaching the underground glassy volcanic rock.

Description

[0001] METHOD AND SYSTEM FOR OBTAINING METALS

[0002] Field

[0003] The invention relates to obtaining metals by the in-situ leaching of underground rocks. The process for obtaining metals may be performed in combination with a process for producing geothermal energy.

[0004] Background

[0005] There is an increasing demand for metals. Particularly valuable metals include rare earth metals, zirconium, niobium, tantalum, hafnium and zinc. Such metals may be used in the manufacture of electronic goods, batteries and many other devices.

[0006] There are a number of problems with using mines to source metals. The mining process may cause environmental damage. Excavation of mines is costly and takes many years to complete. Conventional mines tend to focus on a relatively small number of raw materials because of the processes that form ore deposits. The locations of suitable mines may also require operating in politically unstable and / or unsafe regions.

[0007] There is a general need to improve on known techniques for sourcing metals, in particular for sourcing valuable metals, and to identify novel natural sources of these metals.

[0008] Summary

[0009] Aspects of the invention are set out in the appended independent claims. Optional features are set out in the dependent claims.

[0010] List of Figures

[0011] Figure 1 schematically shows a metal extraction system according to embodiments. Description of Embodiments

[0012] Embodiments of the present invention provide a new technique for extracting metals from a previously unrecognised natural source. Embodiments use leaching to extract metals from underground rocks. The extracted metals may include valuable metals such as rare earth metals, zirconium, niobium, tantalum, hafnium and zinc.

[0013] The inventor has discovered that certain types of underground rocks contain valuable metals that may be recovered by leaching.

[0014] Leaching is a chemical process for selectively solubilising elements of interest from solid substances. A rock that contains metals, for example in the form of metal oxides, is a metal carrier. If the rock is porous and permeable, a liquid lixiviant (i.e. a leaching solution) may flow through the rock. The lixiviant dissolves and / or reacts with at least some of the metals in the rock to form a metal-containing solution, that is referred to throughout the present document as a metal solution.

[0015] The form of the metals, or ions of the metals, in the metal solution is dependent on the chemical composition of the lixiviant and the type of metal. If the lixiviant is sulfuric acid and / or contains a high concentration of sulfate ions, some of the metals in the rock, such as the rare earth metals, may form sulfate complexes that can be highly soluble in the metal solution. The rare earth metals may therefore be present in the metal solution as dissolved metal sulfates.

[0016] The metal solution may flow out of the rock to thereby remove at least some of the metals from the rock.

[0017] In a separate process from leaching, the metals, which may be in the form of metal ions or soluble metal complexes, may then be extracted from the metal solution. There are a number of possible techniques for the metal extraction from the metal solution. For example, the metal solution may be mixed with ammonium bicarbonate so that metal carbonates are formed that precipitate out of the solution.

[0018] If substantially pure metals are required, known techniques may be used for the further processes of separating the different types of metal compound present and obtaining substantially pure metals from the metal compounds. Each metal may have different forms when it is in the rock before leaching, when the metal is in the metal solution after leaching, and during the processes for obtaining substantially pure metals. Throughout the present document, references to metals include metals that may be any in form, including metal compounds, metal ions and metal elements. A particularly suitable rock for such a leaching process is a peralkaline rhyolite volcanic tuff. Table 1 shows typical main metal oxide compositions of peralkaline rhyolite volcanic tuff as a weight percentage (WT%). Table 1 also shows typical other metals that may be present in trace amounts that are given as parts per million by weight (PPM). The information in Table 1 was published in: Hutchison, W., Pyle, D.M., Mather, T.A., Yirgu, G., Biggs, J., Cohen, B.E., Barfod, D.N. and Lewi, E., 2016, The eruptive history and magmatic evolution of Aluto volcano: new insights into silicic peralkaline volcanism in the Ethiopian rift, Journal of Volcanology and Geothermal Research, 328, pp.9-33. The three columns in Table 1 respectively show the specific compositions of three different samples of peralkaline rhyolite volcanic tuff. The two samples of porphyritic obsidian rock were obtained from the same location. The sample of airfall pumice was obtained from a different but nearby location.

[0019] The types of metals that may potentially be obtained in substantial quantities from these specific examples of peralkaline rhyolite volcanic tuffs therefore include all of the above listed metals in either their compound or elemental form.

[0020] Embodiments are not restricted to only leaching the peralkaline varieties of volcanic tuff and other types of rock may be leached. In particular, embodiments include leaching all types of glassy volcanic tuffs. Rocks with different compositions may be leached to obtain different metals. Further metals that may be obtained by leaching glassy volcanic tuffs include lithium, boron, rubidium, cesium and tin.

[0021] An advantageous property of peralkaline rhyolite volcanic tuffs is that their phosphorous content is very low. This results in little, or no, rare earth phosphates forming and precipitating during the leaching process.

[0022] Known locations of peralkaline rhyolite volcanic tuffs include regions in Ethiopia, Kenya, Eritrea, Yemen, Turkey, Mongolia, Western USA, North Korea, China and Italy.

[0023] Peralkaline rhyolite volcanic tuffs are suitable for leaching because they are typically glassy, porous and permeable.

[0024] Figure 1 schematically shows a metal extraction system according to embodiments.

[0025] The metal extraction system performs two main processes for obtaining metals from an underground rock. A first main process pumps a lixiviant underground to extract metals from the underground rock. This generates a metal solution that flows to the ground surface. A second main process, that is performed at the ground surface, then produces metals by removing the metals from the metal solution. The first main process is performed by a leaching system that is comprised by the metal extraction system. The leaching system injects a lixiviant (i.e. a leaching solution) into underground rock. The second main process is performed by a metal production system comprised by the metal extraction system. The metal production system obtains metal solution from the underground rock and extracts metals from the metal solution.

[0026] Figure 1 shows in cross-section three different layers of rock at the location of the metal extraction system. A first layer 101 , that provides the ground surface, is the overlying strata and may be, for example, about 300m deep. The first layer 101 preferably comprises substantially impermeable rock such as rhyolite, trachyte or basalt lava flows. A second layer 102, that is immediately below the first layer 101, may comprise the rock that is leached. The second layer 102 may have an internal depth of, for example, about 10m to 100m, and so it may start at about 300m below the ground surface and extend to about 310m to 400m below the ground surface. The rock in the second layer 102 may be the above-described peralkaline rhyolite volcanic tuff, or any other type of leachable rock. A third layer 103, that is immediately below the second layer 102, is the underlying strata. The third layer 103 preferably comprises substantially impermeable rock such as rhyolite, trachyte or basalt lava flows. The rock in the second layer 102 preferably has a substantially higher porosity and higher permeability than the rocks in the first and third layers 102, 103.

[0027] The above-described properties of the underground layers make it a particularly suitable location for the metal extraction system according to embodiments.

[0028] The leaching system of the metal extraction system comprises a lixiviant source 104, an injection wellhead 110 and an injection well 109. The metal production system of the metal extraction system comprises a production well 108, a production wellhead 107 and a metal extraction plant 105. The metal extraction system may also optionally comprise a heat exchanger 106, as will be described later.

[0029] The lixiviant source 104 comprises lixiviant for extracting metals from the rock in the second layer 102. The lixiviant is supplied to the injection well via the injection wellhead 110.

[0030] The injection wellhead 110 comprises a valve arrangement for controlling the fluid flows into the injection well 109 as well as the pressure of the injected fluid into the injection well 109. The injection well 109 comprises a fluid inlet 109a at the ground surface. The fluid inlet 109a may receive a fluid flow from the lixiviant source 104 and / or the metal extraction plant 105. The injection well 109 comprises a fluid outlet 109b that is underground and, as shown in Figure 1, the fluid outlet may be located in the second layer 102. The injection well 109 may comprise a pipe system for supporting the flow of fluid from its fluid inlet 109a to its fluid outlet 109b.

[0031] The production well 108 comprises an underground fluid inlet 108b. The fluid inlet 108b of the production well 108 may be located in the same underground layer as the fluid outlet 109b of the injection well 109. The fluid inlet 108b of the production well 108 may therefore be located in the second layer 102. The fluid inlet 108b may receive a fluid flow from the second layer 102. The production well 108 comprises a fluid outlet 108a that is at the ground surface. The production well 108 may comprise a pipe system for supporting the flow of fluid from its fluid inlet 108b to its fluid outlet 108a.

[0032] The production wellhead 107 may comprise a pressure valve system for controlling the flow of fluids out of the production well 108 and the pressure of the fluid flow.

[0033] The metal extraction plant 105 receives fluid from the production well 108 via the production wellhead 107. The metal extraction plant 105 comprises apparatuses that are configured to perform one or more processes that extract metal from the received fluid. This may be performed by a number of known processes, such as by using ammonium bicarbonate to precipitate out the metals as metal carbonates. The metal extraction plant 105 may also perform a process for separating the different types of metal compound and obtaining substantially pure metals.

[0034] The metal extraction plant 105 outputs the fluid that has been processed by the metal extraction plant 105. This output fluid may be supplied to the injection wellhead for re-injection into the injection well 109. The output of the metal extraction plant also includes extracted metals by the process performed on the received fluid by the metal extraction plant 105.

[0035] The leaching process of embodiments comprises supplying lixiviant, in a lixiviant solution, to the rock in the second layer 102. The leaching process generates a metal solution in the second layer 102 that is extracted through the production well 108. Metal in the metal solution is then extracted by the metal extraction plant 105.

[0036] The lixiviant source 104 comprises lixiviant that is supplied to the fluid inlet 109a of the injection well 109 via the injection wellhead 110. At, or before, the injection wellhead 110 the lixiviant may be mixed with the output fluid from the metal extraction plant 105 and / or other fluids, such as water. This allows the composition of the leaching solution supplied to the second layer 102 by the injection well 109 to be controlled so that it has the desired composition and concentration of lixiviant, and other properties, for the leaching process.

[0037] The injection well 109 supplies the leaching solution to the second layer 102. Within the second layer 102, the leaching solution flows out of the fluid outlet 109b of the injection well 109 and through the rock in the second layer 102. As the leaching solution flows through the rock in the second layer 102, it dissolves and / or reacts with the rock in the second layer 102 to form a metal solution.

[0038] At least some of the metal solution flows to the fluid inlet 108b of the production well 108. The time required for fluids to flow from the fluid outlet 109b of the injection well 109 and to the fluid inlet 108b of the production well is dependent on how permeable and porous the rock in the second layer 102 is to the leaching solution, as well as the separation of the fluid outlet 109b and the fluid inlet 108b. The typical time for fluid to flow from the fluid outlet 109b to the fluid inlet 108b may be in the range of about 1 day to 1 month.

[0039] The fluid inlet 108b of the production well 108 receives fluids that are present in the second layer. The received fluids may include the metal solution. The received fluids may flow through the production well 108 and to the metal extraction plant 105.

[0040] The metal extraction plant 105 performs processes for extracting at least some of the metal from the metal solution. After the metal extraction processes have been completed, the remaining fluid may be output from the metal extraction plant 105 and supplied back to the injection well 109. Before the output fluid is supplied to the injection well 109, it may be processed, such as filtered or cleaned of other solutes such as silica.

[0041] Embodiments also include the fluid output from the metal extraction plant 105 not being supplied to the injection well 109. The fluid may alternatively be stored or, if it is environmentally safe, allowed to flow away as waste fluid.

[0042] Accordingly, embodiments provide a metal extraction system for extracting metals from underground rocks. The lixiviant source 104, injection wellhead 110 and injection well 109 provide a leaching system that injects a leaching solution into underground rock. The production well 108, production wellhead 107 and metal extraction plant 105 provide a metal production system that obtains metal solution from the rock and extracts metal from the metal solution. As described above, the rock in the second layer 102 may be peralkaline rhyolite volcanic tuff. This type of rock is a preferable target for the leaching process of embodiments. It may be a metal containing rock that is permeable and porous to the leaching solution and the metal solution. Due to naturally occurring geothermal heat, the typical temperature of the rock in the second layer may be 150°C to 200°C and this may be the temperature range within which the leaching process occurs. The pressure in the second layer may be about 30 bar to 300 bar.

[0043] The lixiviant source 104 comprises lixiviant that is the main active chemical in the leaching process. Embodiments include the actual leaching solution that is injected into the second layer 102 being only the lixiviant as supplied by the lixiviant source.

[0044] Embodiments alternatively include the actual leaching solution that is injected into the second layer 102 being the fluid output from the metal extraction plant 105. This may be appropriate if the fluid output from the metal extraction plant 105 comprises a sufficient concentration of lixiviant.

[0045] Embodiments also include the actual leaching solution that is injected into the second layer 102 being a mixture of fluids. In particular, the actual leaching solution may be a mixture of lixiviant supplied directly from the lixiviant source 104, the fluid output from the metal extraction plant 105 and / or other fluids such as water.

[0046] The composition of the leaching solution that is injected into the second layer 102 may be controlled in an attempt to maximize the effectiveness of the leaching process at extracting metal from the rock. The specific composition of the leaching solution may be determined in dependence on the composition of the rock being leached, the temperature of the rock being leached, the targeted metal(s) for recovery and the pressures at the leaching location.

[0047] The leaching solution may be, for example, an acid with a pH of about 4 or less. The leaching solution may alternatively be an alkali with a pH of about 10 or higher.

[0048] When the leached rock is peralkaline rhyolite volcanic tuff, the temperature within the leached rock is about 150°C to 200°C, and the pressure in the leached rock is about 30 bar to 300 bar, a suitable leaching solution is sulfuric acid with a pH of about 4 or less that preferably has a high sulfate content. In particular, the leaching solution may comprise sulfate-rich solutions that may be combined with other acids such as hydrochloric acid. There may be a first mass flow controller at the injection wellhead 110 for controlling the pressure of the leaching solution flowing into the injection well 109. There may be a second mass flow controller at the production wellhead 107 for controlling the pressure of the metal solution flowing out of the production well 108. The first and second mass flow controllers may be controlled independently of each other. The first and second mass flow controllers may allow the injection and / or production pressures to be adjusted so as to regulate the flow of the leaching solution through the rock and thereby control the leaching rate.

[0049] The metal extraction system of embodiments may be a stand-alone metal extraction system. That is to say, the only intended output product of the metal extraction system may be the metal extracted by the metal extraction plant 105.

[0050] It is known to use underground heat sources to generate geothermal energy. A geothermal energy production plant receives a hot fluid that has been heated underground. The hot fluid may be supplied to a heat exchanger where it heats a liquid, such as water or a low-boiling point fluid such as isopentane, or a refrigerant. The heated liquid may be used to drive a turbine, such as a steam turbine, and thereby generate electricity.

[0051] Embodiments also include the provision of a metal extraction system that is combined with a geothermal energy production system.

[0052] As shown in Figure 1, the metal extraction system may comprise a heat exchanger 106 upstream of the metal extraction plant 105. The output fluid by the production well 108 may flow through the heat exchanger 106 before flowing to the metal extraction plant 105. The heat exchanger 106 may be substantially the same as the heat exchangers used in known geothermal energy product plants. Accordingly, the heat exchanger 106 may heat a liquid, such as water. The heated water, that may be steam, may be used to drive a turbine, such as a steam turbine, and thereby generate electricity. Alternatively, the hot fluid may be used for direct use heating purposes such as domestic heating or greenhouses.

[0053] Embodiments alternatively include the heat exchanger 106 being located downstream of the metal extraction plant 105. This may be advantageous if the preferred temperatures of the metal extraction processes are substantially the same as the temperature of fluid that flows out of the production well 108. Embodiments alternatively include a first heat exchanger 106 being located upstream of the metal extraction plant 105 and a second heat exchanger 106 being located downstream of the metal extraction plant 105. This may increase the amount of usable geothermal heat that is obtained.

[0054] A combined geothermal energy and metal extraction system provides a number of advantages. In particular, the generated geothermal energy may be sufficient to power the metal extraction system and provide other local energy needs. The combined economic value of the obtained metal and energy may also be greater than that achievable by only a metal extraction system or only a geothermal energy production system.

[0055] Embodiments include a number of modifications and variations to the above-described techniques.

[0056] The leaching process of embodiments is not restricted to use in peralkaline rhyolite volcanic tuffs. Embodiments include the leaching process being performed in other types of metal containing rocks, such as other types of glassy volcanic tuffs and any other type of leachable rock.

[0057] Embodiments may be used to leach underground rocks at any depth. Embodiments are therefore not restricted to operations at the specific depths described with reference to Figure 1.

[0058] Embodiments also include the metal extraction plant 105 being remote from the leaching system. The metal solution from the production well 108 may be transported to remote metal extraction plant 105 where the metals are extracted.

[0059] In Figure 1, one injection well 109 and one production well 108 of the metal extraction system are shown. Embodiments include the metal extraction system comprising a plurality of injection wells 109 and / or a plurality of production wells 108. By providing a plurality of production wells 108 around each injection well 109, the amount of metal solution that is collected may be increased.

[0060] Embodiments also include using each well as either an injection well 109 or a production well 108. That is say, an injection well 109 may be converted into a production well 108 by reconfiguring the arrangements at the ground surface for controlling the fluid flows into and out of the well. Similarly, a production well 108 may be converted into an injection well 109 by reconfiguring the arrangements at the ground surface for controlling the fluid flows into and out of the well.

[0061] When there is more than one production well 108, all of the metal solution received by each production well 108 may be transported for processing at the same metal extraction plant 105. Embodiments alternatively include the metal extraction system comprising a plurality of metal extraction plants 105. This may be appropriate if transporting the metal solution from all of the production wells 108 to the same metal extraction plant 105 is difficult.

[0062] The foregoing embodiments are only to illustrate the technical ideas and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement them accordingly, and cannot limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

Claims1. An in-situ leaching system comprising: a lixiviant source; and an injection well arranged to receive a leaching solution at ground level and to inject the received leaching solution into underground glassy volcanic rock; wherein: the leaching solution comprises lixiviant from the lixiviant source; and the leaching solution is for leaching the underground glassy volcanic rock.

2. The in-situ leaching system according to claim 1, wherein the leaching solution is for extracting metals, that may be in compound or other form, from the underground glassy volcanic rock by leaching.

3. The in-situ leaching system according to claim 2, wherein the extracted metals, that may be in compound or other form, comprise one or more of rare earth metals, zirconium, niobium, tantalum, hafnium and zinc.

4. The in-situ leaching system according to any preceding claim, wherein the leaching solution has a pH of about 4 or less, or a pH of about 10 or more.

5. The in-situ leaching system according to claim 3, wherein the leaching solution comprises sulfuric acid.

6. The in-situ leaching system according to any preceding claim, wherein the underground rock that the leaching solution is injected into comprises peralkaline rhyolite volcanic tuff.

7. The in-situ leaching system according to any preceding claim, wherein the temperature of underground rock that the leaching solution is injected into is in the range of about 150°C to 250°C.

8. The in-situ leaching system according to any preceding claim, wherein the underground rock that the leaching solution is injected into may start at about 300m below the ground level and extend to about 310m to 400m below ground level.

9. A metal production system comprising: a production well arranged to receive a metal solution from leached underground glassy volcanic rock and to provide a flow of the metal solution to ground level; and a metal extraction plant arranged to receive the metal solution from the production well and to perform metal extraction processes for extracting metals, that may be in compound or other form, from the metal solution.

10. A metal extraction system comprising: the in-situ leaching system according to any of claims 1 to 8; and the metal production system according to claim 9.

11. The metal extraction system according to claim 10, wherein: the metal extraction plant is arranged to supply an output fluid to the injection well; and the output fluid is the resulting fluid after the metal extraction processes have been performed on the received metal solution.

12. The metal extraction system according to claim 10 or 11, further comprising one or more heat exchangers arranged to extract heat from the metal solution output from the production well and / or the output fluid by the metal extraction plant.

13. The metal extraction system according to any of claims 10 to 12, further comprising: a first mass flow controller configured to control the pressure of the leaching solution flowing into the injection well; and / or a second mass flow controller configured to control the pressure of the metal solution flowing out of the production well.

14. A combined geothermal energy and metal extraction system comprising: the metal extraction system according to claim 12, or claim 13 when dependent on claim 12; and a turbine system arranged to generate electrical energy in dependence on heat from the one or more heat exchangers.

15. An in-situ leaching method comprising injecting leaching solution into underground glassy volcanic rock; wherein the leaching solution is for leaching the underground glassy volcanic rock.

16. A metal production method comprising: receiving a metal solution from leached underground glassy volcanic rock; and performing metal extraction processes that extract metals, that may be in compound or other form, from the metal solution.

17. A metal extraction method comprising: the leaching method according to claim 15; and the metal production method according to claim 16.

18. A combined geothermal energy and metal extraction method comprising: the metal extraction method according to claim 17 ; obtaining heat from the metal solution and / or the output fluid after metal extraction processes have been performed on the metal solution; and generating electrical energy in dependence on the obtained heat.

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