Method for increasing the yield of magnesium oxide in a magnesium oxide manufacturing process

Abstract

The present invention relates to a method for increasing the yield of magnesium oxide in a manufacturing process producing essentially magnesium oxide through the valorisation of magnesium-containing waste, wherein the method comprises the steps of: providing acid-generating microorganisms selected from the group of acidophilic microorganisms; providing a first stream comprising sulphur; allowing the microorganisms to interact with the sulphur comprised in the first stream thereby promoting the conversion of the sulphur to form sulphuric acid; providing a second stream comprising magnesium from the manufacturing process producing essentially magnesium oxide; allowing the formed sulphuric acid to react with magnesium in the stream comprising magnesium to form solubilised magnesium sulphate; providing oxalic acid and allowing the oxalic acid to react with the formed solubilised magnesium sulphate to form magnesium oxalate as a precipitate; collecting the formed magnesium oxalate precipitate; and transferring the collected magnesium oxalate precipitate to the manufacturing process producing essentially magnesium oxide, wherein the magnesium oxalate is calcinated to magnesium oxide and thereby increasing the yield of magnesium oxide in the manufacturing process producing essentially magnesium oxide. The present invention also relates to a system using said method.

Description

[0001] METHOD FOR INCREASING THE YIELD OF MAGNESIUM OXIDE IN A MAGNESIUM OXIDE MANUFACTURING PROCESS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a method for increasing the yield of a magnesium oxide in a manufacturing process producing essentially magnesium oxide. The present invention also relates to a system for increasing the yield of a magnesium oxide in a manufacturing process producing essentially magnesium oxide.

[0004] TECHNICAL BACKGROUND

[0005] There is an increased awareness of the limited supply of natural resources, and continuous work within different industrial fields in order to align today's processes with the Sustainable Development Goals. In 2019, the Australian Government released its inaugural Critical Minerals List and associated national strategy. Since then, critical minerals have become more important as governments around the world purse ambitious policies to achieve low-carbon economies and safeguard clean energy-supply. Also, critical materials are essential in the modern-day economy. The technology revolution in advanced manufacturing, defence, renewable energy, and medical devices has increased demand for critical minerals as building blocks for new products. However, not the least during the COVID-19 pandemic, global supply chain vulnerabilities were exposed.

[0006] Magnesium is essential in the modern-day manufacturing economy. Approximately 70% of the world's supply is used in the manufacturing of vehicles, cell phones, laptops, and other electronics due to its relatively low density but good structural strength. About 10% of the world’s magnesium production is used in processing titanium from rutile ore, and another 10% is used in the production of high-grade steel. Magnesium is also widely used as a catalyst, e.g., in the form of magnesium oxide, for toxic waste remediation, and as a super-conductor. A significant proportion of magnesium oxide produced is used for the production of kiln bricks, a refractory and protective lining in kilns during the processing of other metals and materials. Thus, the access to magnesium is essential for economic development.

[0007] Magnesium carbonate naturally occurs in minerals such as magnesite also known as magnesium carbonate (MgCOs), periclase, which is a cubic form of magnesium oxide (MgO), brucite, which is magnesium hydroxide (Mg(OH)2), and dolomite, which is a mixture of calcium carbonate (CaCOs) and magnesium carbonate (MgCOs). The minerals may be extracted from rocks and processed by calcination or leaching with chemicals to provide magnesium carbonate, or from magnesium chloride derived from seawater by electrolysis. The use of chemicals involves the cost of procurement and associated costs for waste remediation. The extraction process is also very energy intensive and, therefore, economically undesirable. For example, in 2021 it was reported that China, which dominates global magnesium production, slowed magnesium production due to an ongoing energy crisis in the country which led to record high market prices of magnesium and threatened the car manufacturing sector.

[0008] In addition to the previously stated problems with current manufacturing methods for obtaining materials like magnesium, it has been shown that these industries generate waste streams which still contain significant concentrations of valuable materials, and which are usually stockpiled as waste.

[0009] Thus, there is a need for solutions that preserves the environment, reduce the dependence on finite resources, and reduces waste. There is also a need for processes that provide raw materials like magnesium in an energy efficient and sustainable manner.

[0010] SUMMARY OF THE INVENTION

[0011] The method according to the present invention provides an energy efficient approach for solving the above-mentioned problems. In view of the above, it is an object of the present technology to provide improved production methods for enriching or extracting economically valuable metals, such as magnesium, from magnesium-containing waste, such as magnesium mining waste (MMW). Stored MMW exists as a dry product, i.e. , magnesium waste (MgW) or a hydrated waste, designated as magnesium waste hydrate (MgW-H). The primary difference is that the magnesite contained in MMW is hydrated to brucite in MgW-H. Magnesium can selectively be solubilised from MMW. By adjusting pulp density, magnesium can be selectively solubilised to a greater than 95% share of the solubilized metals. Pulp density is defined as the percentage solid mass in a liquid volume, e.g., 2 g of solid in 100 ml is 2% pulp loading density. Pulp is defined as the collective solids in a bioreactor at a given time. This has previously been indicated by the present inventors in Van Wyk et al., Journal of Applied Microbiology, 2025, 136(5). After selective solubilisation, the metal in solution may be extracted or precipitated to produce nearly pure product streams. In Van Wyk et al. exposure to oxalic acid resulted in a net gain of mass for both wastes (29.5% gain for MgW and 14.6% for MgW-H), most likely due to the formation of metal oxalates as evidenced by the appearance of an insoluble white precipitate. MMW is primarily a combination of magnesium carbonate (magnesite) and magnesium oxide (magnesia). MgW-H is hydrated magnesium mining waste. This is found to primarily be brucite (magnesium hydroxide). The present invention describes a manufacturing process that exploits a counterintuitive effect where manipulation of the pulp density affects the relative proportions of solubilised metals. In the present case, upwards of 95% of the metals in solution may be magnesium. Thus, counterintuitively to what has been described in the prior art, according to the present inventive method, by adjusting the pulp density upwards increases the proportion of magnesium in solution relative to other metals analysed e.g. calcium, manganese and iron. Thus, a serendipitous and counterintuitive effect is that magnesium is enriched in the aqueous phase over other metals analysed, and so providing a relatively pure solubilised magnesium stream.

[0012] Another object is to provide a method for manufacturing solid magnesium, such that the method is designed to be simple, i.e. , easy to perform and cheap to use, with commercially available and affordable materials.

[0013] Another object is to provide a continuous method for enriching magnesium out of mining waste material, wherein the method may be implemented at the place of mining, and by extension, reduce storage costs and environmental hazards.

[0014] Another object is to provide a method that provides an economically valuable product that enriches the primary production stream, while allowing for the preservation of primary stockpiles.

[0015] Another object is to provide a method that obtains magnesium salts from waste residues from completely separate manufacturing processes, such as bio-sulphur or Bio S, which may be utilised and combined with waste residues containing magnesium, in order to take care of as much waste materials as possible and thus minimizing the impact on the environment.

[0016] Another object is to provide a method that enables the possibility to meet requirements and legislation related to waste handling for certain types of processing industries.

[0017] Another object is to provide a method that reduces mining process waste to zero by utilising the wastes, and producing valuable product streams, which, as far as the present inventors are aware, has not been achieved in the mining industry.

[0018] Thus, to achieve at least one of the above objects and also other objects that will be evident from the following description, a method for increasing the yield of magnesium oxide in a manufacturing process producing essentially magnesium oxide through the valorisation of magnesium-containing waste is as defined in the independent claim. Preferred variations to the inventive concept will be evident from the dependent claims.

[0019] In a first aspect, the present invention relates to a method for increasing the yield of magnesium oxide in a manufacturing process producing essentially magnesium oxide through the valorisation of magnesium-containing waste, wherein the method comprises the steps of: a) providing acid-generating microorganisms selected from the group of acidophilic microorganisms; b) providing a first stream comprising sulphur; c) allowing the microorganisms to interact with the sulphur comprised in the first stream thereby promoting the conversion of the sulphur to form sulphuric acid; d) providing a second stream comprising magnesium from the manufacturing process producing essentially magnesium oxide; e) allowing the formed sulphuric acid to react with magnesium in the stream comprising magnesium to form solubilised magnesium sulphate; f) providing oxalic acid and allowing the oxalic acid to react with the formed solubilised magnesium sulphate to form magnesium oxalate as a precipitate; g) collecting the formed magnesium oxalate precipitate; and h) transferring the collected magnesium oxalate precipitate to the manufacturing process producing essentially magnesium oxide, wherein the magnesium oxalate is calcinated to magnesium oxide and thereby increasing the yield of magnesium oxide in the manufacturing process producing essentially magnesium oxide.

[0020] In a further embodiment, step e) further forms a refractory material as by-product, and wherein the method comprises a further step of reacting said by-product with the second stream comprising magnesium from the manufacturing process producing essentially magnesium oxide and phosphate to produce magnesium phosphate cement.

[0021] Hence, the present invention also relates to a method for producing cement as a third revenue stream, wherein a stream comprising unleached MMW, such as magnesium from a manufacturing process producing essentially magnesium oxide, is added to refractory material produced in the method according to the first aspect, and further combined with water and phosphate, such as phosphate containing waste, to produce magnesium phosphate cement (MPC). The refractory material fulfils the role of an aggregate and is produced in step e) in the method according to the first aspect as a by-product to the formed solubilised magnesium sulphate. The source of phosphate may be provided from the dairy industry, for example from acid-casein production from dairy industries which generates waste streams that are rich in nitrogen and phosphate. The by-product and the second stream comprising magnesium from the manufacturing process producing essentially magnesium oxide and phosphate to produce magnesium phosphate cement are leached and unleached waste which in this context is called waste. The proportions of waste: phosphate: water going into the further step of reacting said by-product with the second stream comprising magnesium from the manufacturing process producing essentially magnesium oxide and phosphate to produce magnesium phosphate cement may be 1 :0.5-0.75:0.1 -0.25, preferably 1 :0.5:0.1 , as measured by weight.

[0022] In a second aspect, the present invention relates to a system for increasing the yield of magnesium oxide in a manufacturing process producing essentially magnesium oxide according to the method of the first aspect, wherein the system comprises: a pH meter; at least one vessel, such as a bioreactor; a further vessel, such as settling tank, and a separator wherein the at least one vessel and the further vessel are arranged for allowing transfer and recycling of fluids.

[0023] In a further embodiment, the present invention relates to a system for increasing the yield of magnesium oxide in a manufacturing process producing essentially magnesium oxide and for producing magnesium phosphate cement according to the method of the first aspect, wherein the system comprises: a pH meter; at least one vessel, such as a bioreactor; a further vessel, such as a tank; a further vessel such as a reactor; and at least one separator, wherein the at least one vessel and the further vessel are arranged for allowing transfer and recycling of fluids.

[0024] Thus, the present invention also relates to a system for producing magnesium phosphate cement, wherein the system comprises at least a further vessel and a separator for reacting the produced refractory material with the second stream comprising magnesium from the manufacturing process producing essentially magnesium oxide and phosphate, to achieve magnesium phosphate cement.

[0025] Further features of, and advantages with the present invention will become apparent when studying the appended claims and the following detailed description. The skilled person will realize that different features of the present invention may be combined to create variants other than those described in the following, however the present invention is defined by the appended claims. Features of one aspect may be relevant to anyone of the other aspects.

[0026] SHORT DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 shows a schematic drawing of the method and the system for increasing the yield of magnesium oxide in a manufacturing process producing essentially magnesium oxide.

[0028] Figure 1A shows a schematic drawing of the method and the system for increasing the yield of magnesium oxide and producing magnesium phosphate cement from MMW.

[0029] Figure 2 shows a schematic drawing of the present method performed in a vessel, container or reactor, such as a bioreactor.

[0030] Figure 3 disclose a more detailed drawing of a bioreactor and the present method.

[0031] Figure 4 shows a schematic drawing of the present method performed in two consecutive vessels, containers or reactors.

[0032] Figure 5 10% MgCOs (m / v) was added to a mature F. caldus culture. Samples were taken at regular intervals and analysed by ICP-MS.

[0033] Figure 6 discloses a graph of a comparison between a sulphur feed of Bio S (♦) and Elemental S (•) in view of acid generation as measured by pH using an F. caldus culture.

[0034] Figure 7 discloses a graph of comparison between sulphur feed of Bio S (♦) and Elemental S (•) in view cell number using an F. caldus culture.

[0035] Figure 8 shows the pH profiles in view of increasing waste MgCOs pulp densities. Figure 9 shows the cell densities during contact between the F. caldus culture and the increasing waste MgCOs pulp densities.

[0036] Figure 10 discloses a graph of how pH may recover after exceeding the optimal physiological range for F. caldus and, the cells metabolize the biosulphur to recover and lower the pH via biogenic sulphuric acid generation after about 8 days. The two lines are replicates, in the sense that they are from two different reactors with two different pulp densities.

[0037] Figure 11 discloses addition of magnesium waste material to a semi- continuous culture bioreactor containing F. caldus. Graph A shows regular dosing intervals with magnesium-containing waste ore resulting in cyclic pH rise and recovery. Graph B shows the solubilised Mg2+concentration increased concomitantly with the addition of the waste ore.

[0038] Figure 12 discloses ICP-MS data for vessel reactors incubated with active F. caldus cells (A, C, E) and without active F. caldus cells (B, D, F), and grown on bio-sulphur vessels contained pulp density Mg-waste in 0.5 % (A, B), 1.0 % (C, D) and 5.0 % (E, F). Mg (■), Ca (♦), Fe (A), and Mn (•) were analysed during regular sampling periods over the 57-day period

[0039] DETAILED DESCRIPTION OF THE INVENTION

[0040] The present inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred variants of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the variants set forth herein; rather, these variants are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person. Although individual features may be included in different variants, these may possibly be combined in other ways, and the inclusion in different variants does not imply that a combination of features is not feasible. In addition, singular references do not exclude a plurality. In the context of the present invention, the terms “a”, “an” does not preclude a plurality.

[0041] Bioleaching is the extraction or liberation of metals from their ores through the use of living organisms. Metals extraction through bioleaching is a well-established method for extracting high value metals from ores or waste materials.

[0042] The method according to the present invention may be a continuous method or in two-part method through for the solubilisation of magnesium from process stream and subsequent precipitation of magnesium as magnesium oxalate, thus providing an environmentally sustainable solution to increasing the yield of magnesium oxide in a manufacturing process producing essentially magnesium oxide.

[0043] The present invention also provides a method for obtaining magnesium oxide from secondary resources, such as residues from primary extraction streams, such as by-product streams or waste streams. In addition, waste residues from completely separate manufacturing processes which e.g., primarily produce bio-sulphur or Bio S may be utilised and combined with the residues containing magnesium and to be further processed in order to obtain magnesium oxide. The valorisation of the magnesium wastes allows for the reduction of total wastes produced during e.g., mining processes, and by extension, reduce storage costs and environmental hazards.

[0044] The present method also provides an economically valuable product that enriches a primary production stream in ore mining, while allowing for the preservation of the primary production stream waste stockpiles.

[0045] The present method enables the possibility to meet requirements and legislation related to waste handling for certain types of processing industries.

[0046] A noted effect to the biogenic acid leaching of heterogenous magnesium carbonate-containing waste, which still contains up to 30% magnesium [m / m], is the improved ratio of solubilised magnesium to other metals. With increasing pulp densities of magnesium carbonate-containing waste the relative ratios of metals such as calcium, manganese and iron are reduced, resulting in purities of solubilised magnesium to the bulked metals, such as calcium, manganese or iron, of greater than 95%. In addition, approximately 99% of magnesium in the magnesium-containing waste is solubilised.

[0047] According to a first aspect, there is provided a method 100 for increasing the yield of magnesium oxide in a manufacturing process 200 producing essentially magnesium oxide through the valorisation of magnesium-containing waste as may be seen in Figure 1. The method 100 comprises the steps of: a) providing acid-generating microorganisms selected from the group of acidophilic microorganisms; b) providing a first stream comprising sulphur; c) allowing the microorganisms to interact with the sulphur comprised in the first stream thereby promoting the conversion of the sulphur to form sulphuric acid; d) providing a second stream comprising magnesium from the manufacturing process 200 producing essentially magnesium oxide; e) allowing the formed sulphuric acid to react with magnesium in the stream comprising magnesium to form solubilised magnesium sulphate; f) providing oxalic acid and allowing the oxalic acid to react with the formed solubilised magnesium sulphate to form magnesium oxalate as a precipitate; g) collecting the formed magnesium oxalate precipitate; and h) transferring the collected magnesium oxalate precipitate to the manufacturing process 200 producing essentially magnesium oxide, wherein the magnesium oxalate is calcinated to magnesium oxide and thereby increasing the yield of magnesium oxide in the manufacturing process 200 producing essentially magnesium oxide.

[0048] The steps a), b), and d) may be provided simultaneously, or sequentially, in any order.

[0049] The first stream may be a by-product or waste stream. Said by-product or waste stream may be provided from biomass processing industry, mining industry, oil and gas industry, or downstream process industries therefrom, fibre production, or any combination thereof. Said by-product or waste stream may be provided from biorefinery processes, mining of or processing of sulphide-containing ores, metal refinery processes, mining of or processing of coal, biogas purification processes, waste gas purification processes, bullet proof fibre or fabric production, and other biological processes producing sulphur containing waste, or any combination thereof. Said by-product or waste stream may be provided from coal mining, oil and gas industry or downstream process industries therefrom, biogas purification processes including sulphur removal, bullet-proof fibre or fabric production, or any combination thereof. Preferably said by-product or waste stream is provided from a biological desulphurisation process.

[0050] The sulphur comprised in the first stream may comprise biogenic sulphur, preferably the sulphur is biogenic sulphur or bio-sulphur.

[0051] Moreover, the first part of the method, i.e. , steps a) to c), according to the present invention, provides a method for the biogenic production of a mineral acid from bio-sulphur, which may be generated as a waste from an industry unrelated in magnesium mining, thus having the advantage of combining two waste streams for the production of a valuable resource. Biosulphur has desirable benefits and is particularly fit for purpose, as it promotes improved conversion to sulphuric acid when used as a feed for acid-generating microorganisms. The use of bioleaching and utilisation of microorganisms in the present method, provides a self-regulating system, with limited requirement for external energy input. With self-regulating means that the microorganisms or the bacteria produce acid until the media or the stream is too acidic for its metabolism to produce more. Then, acid production stops until the pH is raised by adding more basic waste material, i.e., the stream comprising magnesium, that consumes the protons and keeps the self-regulating system going. Samples may be taken from the reaction stream and / or the reactor at regular intervals and the pH and / or the cell densities may be recorded by standard methods, such as by use of a pH meter 80. The reaction may be monitored by a pH meter 80.

[0052] The second stream comprising magnesium may be a product stream, a by-product stream, or a waste stream. Said product stream, by-product stream or waste stream may be provided from mining industry, mineral processing industry, ore processing industry, metal processing industry or desalination plants, or any combination thereof. Said product stream, byproduct stream or waste stream may be provided from dolomite mining or processing industry, magnesite mining or processing industry, magnesium smelting processes, magnesium calcination processes or desalination processes, or any combination thereof. Preferably the second stream comprising magnesium is a by-product stream or a waste stream, preferably a magnesium-containing waste stream.

[0053] The stream comprising magnesium may be comprising magnesium in the form as brucite, magnesite, dolomite or periclase, or any mixture thereof. For example, the stream comprising magnesium may be comprising magnesium in the form of brucite in the range of 30-55 weight%, preferably in the range of 35-50 weight%, preferably in the range of 40-47 weight%, preferably about 45 weight%. The stream comprising magnesium may be comprising magnesium in the form of magnesite in the range of 25-55 weight%, preferably in the range of 30-50 weight%, preferably in the range of 35-45 weight%, preferably about 50 weight%, preferably about 40 weight%. The stream comprising magnesium may be comprising magnesium in the form of dolomite in the range of 1-20 weight%, preferably in the range of 5-15 weight%, preferably about 15 weight%, preferably about 7-8 weight%. The stream comprising magnesium may be comprising magnesium in the form of periclase in the range of 0-30 weight%, preferably in the range of 0.05-25 weight%, preferably about 1 weight%, preferably about 23 weight%.

[0054] The solubilised magnesium may be ionic magnesium.

[0055] With acid-generating microorganisms means microorganisms that show optimal growth in highly acidic environments. Acidophilic microorganisms or acidophiles are microorganisms or bacteria that optimally grow in conditions having pH values below 5. The acid-generating microorganisms are capable of interacting in and promoting conversion of sulphur into sulphuric acid and have chemical leaching kinetics at a pH of 0.0- 5.0, preferably 0.5-5.0, preferably 0.6-4.8, preferably 0.8-4.5, preferably 1.0-

[0056] 4.5, preferably 1.0-3.5, preferably 1.0-3.0, preferably 1.0-2.5, preferably 1.2-

[0057] 2.5, and preferably 1.2-2.0.

[0058] According to one embodiment the microorganisms are capable of interacting in and promoting conversion of sulphur into sulphuric acid, and have chemical leaching kinetics at a temperature of 10-90°C, preferably 10- 80°C, preferably 20-75°C, preferably 25-60°C, preferably 28-55°C, and preferably 30-45 °C. According to one embodiment the microorganisms are selected from acidophilic bacteria and / or archaea.

[0059] According to one embodiment the microorganisms are selected from the group consisting of the following genera: Acidiphilium, Acidicaldus, Acidiferrobacter, Acidibacillus, Acidihalobacter, Acidithiobacillus, Sulfuricurvum, Sulfurococcus, Sulfuricurvum, Sulfurovum, Fervidacidithiobacillus, Sulfobacillus, Sulfolobus, Acidithiomicrobium, Sulfuracidifex, Acidianus, Metallosphaera, or any combination thereof.

[0060] According to one embodiment the microorganisms are selected from the group consisting of the following species: Sulfuricurvum kujiense, Sulfurovum aggregans, Sulfurovum denitrificans, Sulfurovum indicum, Sulfurovum lithotrophicum, Sulfurovum riftiae, Acidithiobacillus ferrivorans, Acidiferrobacter thiooxydans, Acidithiobacillus sulfuriphilus, Acidiphilium acidophilum, Acidithiobacillus thiooxidans, Acidibacillus ferrooxidans, Acidithiobacillus albertensis, Acidihalobacter aeolianus, Acidihalobacter ferrooxydans, Acidihalobacter prosperus, Acidihalobacter yilgarnensis, Acidithiobacillus ferridurans, Acidithiobacillus ferriphilus, Acidithiobacillus ferrooxidans, Sulfobacillus benefaciens, Sulfurococcus yellowstonii, Acidibacillus sulfuroxidans, Fervidacidithiobacillus caldus (prior also called Acidithiobacillus caldus), Sulfobacillus thermotolerans, Sulfobacillus acidophilus, Sulfobacillus thermosulfidooxidans, Acidicaldus organivorus, Acidithiomicrobium P2, Sulfuracidifex metallicus, Sulfuracidifex tepidarius, Metallosphaera cuprina, Acidianus manzaensis, Acidianus brierleyi, Metallosphaera hakonensis, Metallosphaera javensis, Acidianus sulfidivorans, Acidianus copahuensis, Metallosphaera sedula, Metallosphaera prunae, Sulfolubus islandicus, Acidianus ambivalens, Acidianus manzaensis, Sulfolobus acidocaldarius, Acidianus infernus, or any combination thereof; preferably the microorganisms are selected from the species Fervidacidithiobacillus caldus.

[0061] According to one embodiment at least step c) is carried out at a pH of 0.0-5.0, preferably 0.5-5.0, preferably 0.6-4.8, preferably 0.8-4.5, preferably 1.0-4.5, preferably 1.0-3.0, preferably 1.0-2.5, preferably 1.2-2.5, and preferably 1.2-2.0. According to one embodiment at least step c) is carried out at a temperature of 10-90°C, preferably 10-80°C, preferably 20-75°C, preferably 15-75°C, preferably 20-60°C, preferably 25-60°C, preferably 28-55°C, preferably 30-55°C, preferably 35-50°C, preferably 38-47°C, and preferably about 45°C.

[0062] According to one embodiment the method further comprises providing at least one of nutrients, water, air, or any combination thereof.

[0063] According to one embodiment steps c) and e) are carried out in one same vessel or container 10 or two different vessels or containers 20 and 30, preferably at least step c) and optionally step e) may be performed in a bioreactor 10 as may be seen in Figure 2.

[0064] According to one embodiment the method further comprises recycling of carbon dioxide formed in step e) within said one same vessel or container 10 or two different vessels or containers 20, 30 (see Figures 3 and 4). Thus, as seen Figure 3 there is provided a method 110, wherein steps a) to e) are carried out in vessel 10. Further, as seen in Figure 4 there is provided a method 120, wherein steps a) to c) are carried out in vessel 20, subsequently steps d) to e) are carried out in vessel 30. Furthermore, as seen in Figures 3 and 4, respectively, each of the methods 110 and 120, comprise steps f) and g) that are carried out in vessel 40 and separator 50, respectively.

[0065] In a second aspect there is provided a system 300, 310, 320 for increasing the yield of magnesium oxide in a manufacturing process 200 producing essentially magnesium oxide according to any of methods 100, 110 or 120, wherein the system comprises: a pH meter 80; at least one vessel 10, such as a bioreactor; a further vessel 40, such as settling tank; and a separator 50, wherein the at least one vessel 10 and the further vessel 40 are arranged for allowing transfer and recycling of fluids as outlined in Figures 1-4.

[0066] In an embodiment of the second aspect there is provided a system 330 for increasing the yield of magnesium oxide in a manufacturing process 200 producing essentially magnesium oxide and for producing magnesium phosphate cement according to any of methods 100, 110, 120, 130, wherein the system comprises: a pH meter 80; at least one vessel 10, such as a bioreactor; a further vessel 40, such as a tank; a further vessel 60 such as reactor; and at least one separator 50, wherein the at least one vessel 10 and the further vessel 40 are arranged for allowing transfer and recycling of fluids as outlined in Figure 1A.

[0067] The transfer of fluids or streams may be between the vessels or containers by some line or lines of connection, such as tubing, piping, valve or duct. The transfer of fluids or stream may also be back to the process stream of the manufacturing process 200 producing essentially magnesium oxide. Thus, the precipitated and separated magnesium oxalate from separator 50 may be transferred back to the manufacturing process 200 producing essentially magnesium oxide, e.g., to a rotary kiln wherein it is further calcinated to magnesium oxide.

[0068] In one embodiment, the at least one vessel 10, such as a bioreactor, is for batch use. In another embodiment, there may be two vessels 20 and 30 for sequential use. The system 300, 310, 320, 330 also comprises a vessel 40, such as a settling tank, wherein vessels 10 and 40, or vessels 30 and 40 are arranged for allowing transfer and recycling of fluids. In another embodiment, the system 300, 310, 320, 330 also comprises a vessel 60, such as a settling tank. The system 300, 310, 320, 330 also comprises a separator 50, such as a hydrocyclone, wherein vessel 10 and separator 50, or vessel 30 and separator 50 are arranged for allowing transfer and recycling of fluids.

[0069] The system 300, 310, 320, 330 comprises a pH meter 80 for control of the pH in the system. The pH meter 80 may be placed in vessel 10 or 20, or in a line connecting the vessels in the system 300, 310, 320, 330. The system may be for production of a magnesium oxide from magnesium-containing waste (MW).

[0070] The system may be for batch use as may be seen in Figure 3. The system may also be for sequential use as may be seen in Figure 4. In the present method, the first stream comprises sulphur and said sulphur may be a by-product or a waste material. The first stream may be a by-product or a waste comprising sulphur. The sulphur is preferably at least part of a by-product and / or a waste material. The first, and second streams, and the microorganisms may be contacted in any order, or simultaneously. Alternatively, the microorganisms may be present, followed by addition of the first and second stream, in any order or simultaneously. In a preferred embodiment, the first stream comprising sulphur is brought in contact with the microorganisms, followed by addition of magnesium carbonate. In another preferred embodiment, the first and second streams are provided to the microorganisms simultaneously.

[0071] In the present method the sulphur is contacted with microorganisms. The microorganisms then interact with the sulphur and promote conversion of the sulphur into sulphuric acid. The sulphuric acid which is formed from the sulphur then used to provide soluble magnesium by the reaction:

[0072] MgCOs + H2SO4 — Mg (soluble) + CO2

[0073] It is to be noted that the reaction formula is not complete, and additional components are formed but not shown, as the focus herein is on the magnesium and not additional components present, the other components have been disregarded above. The soluble magnesium obtained may be ionic magnesium, meaning that when the magnesium sulphate salt is in water solution it is in its ionic form, i.e., as magnesium cations, Mg2+, and sulphate anions, SO42’. Another way of presenting the reaction between magnesium carbonate and sulphuric acid is by the following two schemes:

[0074] MgCOs[s] + H2SO4 — MgSO4[aq] + H2O + CO2 [1]

[0075] MgSO4[aq] + C2H2O4 — MgC2O4[s] + H2SO4 [2]

[0076] The invention may be applied and implemented in any type of facility that may produce wastes with a significant magnesium carbonate component.

[0077] The second part of the method includes the addition of oxalic acid to solubilised magnesium solutions. The addition of oxalic acid in a stoichiometrically balanced reaction and results in the energetically favourable formation of magnesium oxalate, a white, insoluble precipitate. The chemical reactions are indicated below:

[0078] From this is it clear that in [1] magnesium is solubilised and in [2] the formation of magnesium oxalate removes the magnesium from solution as a precipitate with the regeneration of the sulphuric acid.

[0079] Magnesium oxalate readily degrades to magnesium carbonate [3], and then magnesium oxide [4] at a temperature between 420 °C and 620 °C, well below kiln temperatures used during the manufacture of magnesium oxide. The process may produce almost pure Magnesium oxide.

[0080] MgC2O4 — MgCOs + CO [3]

[0081] MgCOs MgO + CO2[4]

[0082] Altogether, the present invention derives value from magnesium carbonate locked in mining waste, which contains up to 30% magnesium by mass, by the efficient solubilization. Herein, more than 95% of magnesium contained in the waste is solubilised by biogenic sulphuric acid, preferably more than 97% is solubilised, most preferably more than 99% is solubilised. Oxalic acid is added to the magnesium-containing leach solution, such as a pregnant leach solution (PLS), forming magnesium oxalate precipitate. In industry, pregnant leach solution (PLS) is a liquid phase that contains the metals of interest. The precipitate is collected, dried and added to the primary mining ore prior to calcination. During the calcination process the magnesium oxalate is converted to magnesium oxide, the primary product of the primary plant operation. This process results in an enriched product and also a reduced total waste of up to 87% of the collected mining waste may be solubilised. Precipitation of magnesium oxalate may be optimised through optimising the process conditions. For example, the stoichiometry of the magnesium and oxalic may be optimised. Further, the reaction temperature in step f) may be optimised such that step f) may have a reaction temperature of at least 25 °C, or a reaction temperature in a range of 25-80 °C. Even further, precipitation optimisation may be through optimising mixing and filtration of magnesium oxalate to replace the settling step.

[0083] In addition, the liquor is regenerated as sulphuric acid is the main product of the addition of oxalic acid to magnesium sulphate. This further reduces operational cost as the acidified medium can be reused.

[0084] Oxalic acid used in the process may be derived through industrial chemical means by the oxidation of carbohydrates or glucose using nitric acid or air in the presence of vanadium pentoxide. Alternatively, oxalic acid can be produced biologically through several organisms, including Aspergillus niger, by culturing on a variety of sugar-containing feeds, such as syrups and molasses.

[0085] The first stream comprising sulphur contains sulphur in solid form. Sulphur may be present in the form of particles, e.g., granules, powder, aggregates, or any combination thereof, preferably in powder form. Sulphur in particle form may have a particle size of 0.1-1.5 pm, such as 0.15-1.3 pm, 0.2-1.2 pm, or 0.23-1.1 pm, and preferably a particle size of 0.23-1 .1 pm, measured using a Malvern Zetasizer Nano ZS. The Malvern Zetasizer Nano ZS is a high performance two angle particle, zeta-potential, and molecular size analyser for the enhanced detection of aggregates and small particles. Samples may be measured at very low or high concentration using dynamic light scattering with Non-lnvasive BackScatter (NIBS) optics. Size may be measured in the range of 0.3 nm to 10 pm. Zeta-potential may be measured in the range of 3.8 nm to 100 pm. The flow mode option enables the system to be connected to a size exclusion chromatography (SEC) or a Field-flow fractionation (FFF) system to use as a detector for the size of proteins or nanoparticles. The MPT-2 Autotitrator, is an automator to help size particles and determine zeta potential and thus allows the study of the effect of changes in pH, conductivity, or any additive to be automated. A range of disposable and reusable cells are available to optimize the measurement in terms of sample volume, concentration and flow measurement.

[0086] The sulphur comprised in the first stream may e.g., comprise biogenic sulphur, also denoted bio-sulphur or Bio S herein. A biogenic substance is a product made by or of life forms. Biologically produced sulphur may be the end-product of microbiological sulphide oxidation, a process carried out by microorganisms. Biogenic sulphur is sulphur compounds which result from biological processes. Biogenic sulphur is considered being wettable, i.e. , having a wetting effect. Without being bound by theory, it is assumed that the wetting effect may be provided by the particle size of the sulphur particles provided by the microorganisms and / or possibly traces of hydrophilic polymers, such as negatively charged biopolymers, produced with the sulphur may be attached to the microbiologically produced sulphur particles. Biogenic sulphur is herein shown to have better reactivity and performance to sulphur prepared by conventional mechanical or chemical means. Biogenic sulphur in particle form, e.g., as powder, may be provided having smaller particle sizes compared sulphur in particle form prepared by conventional mechanical or chemical means. Biogenic sulphur contains trace amounts of other nutrients, such as organic carbon, as it has been obtained via a biological process. The trace amounts of e.g., carbon may be used as nutrition for the microorganisms present in the method. The sulphur may be biogenic sulphur.

[0087] The first stream may comprise sulphur obtained from industry processes or other processes and may relate to by-products and / or waste materials. The sulphur comprising by-product and / or waste stream may be obtained from biomass processing industry, mining industry, oil and gas industry, or downstream process industries therefrom, fibre production, or any combination thereof. The waste stream may be obtained from biorefinery processes, mining of or processing of sulphide-containing ores, metal refinery processes, mining of or processing of coal, biogas purification processes, waste gas purification processes, bullet proof fibre or fabric production, and other biological processes producing sulphur containing waste, or any combination thereof. The sulphur comprising by-product and / or waste stream may be obtained from coal mining, oil and gas industry, or downstream process industries therefrom, biogas purification processes including sulphur removal, bullet proof fibre or fabric production, or any combination thereof. The waste stream may be obtained from a biological desulphurisation process, e.g., from any of the above-mentioned industries or processes. The second stream may be a product stream, a by-product stream, and / or a waste stream. The magnesium carbonate is preferably originating from product stream materials, by-product stream materials, and / or waste materials or waste streams from different industries, and manufacturing processes. The product stream, by-product stream, and / or waste stream may be provided from mining industry, mineral processing industry, ore processing industry, metal processing industry, desalination plants, or any combination thereof. Preferably said product stream, by-product stream, and / or waste stream from is provided from dolomite mining or processing industry, magnesite mining or processing industry, magnesium smelting processes, magnesium calcination processes, desalination processes, or any combination thereof. It is especially preferred is waste streams or waste materials are used as the second stream.

[0088] For example, Table 1 shows an example of second stream comprising magnesium from a manufacturing process producing essentially magnesium oxide.

[0089] Table 1. Second stream comprising magnesium from a manufacturing process producing essentially magnesium oxide stream. MgW is Magnesium waste.

[0090] MgW-H is hydrated magnesium waste.

[0091] In the present method microorganisms are included. The microorganisms are selected from the group of acidophilic microorganisms. The microorganisms are preferably capable of interacting in and promoting conversion of sulphur into sulphuric acid, and may have chemical leaching kinetics, at a pH of 0.0-5.0, such as 0.5-5.0, 0.6-4.8, 0.8-4.5, 1.0-4.5, 1.0-3.5, 1 .0-3.0, 1.0-2.5, 1 .2-3.5, 1 .2-3.0, or 1 .5-3, preferably at a pH of 1 .0-3.0, such as 1.0-2.5, 1.2-2.5, or 1.2-2.0.

[0092] The microorganisms are preferably capable of interacting in and promoting conversion of sulphur into sulphuric acid, and may have chemical leaching kinetics, at a temperature of about 10-90°C, such as 10-80°C, such as about 20-75°C, about 25-60°C, about 28-55°C, or about 30-45 °C, preferably at a temperature of about 25-60°C, such as about 28-55°C, or about 30-45 °C.

[0093] The microorganisms may be selected from acidophilic bacteria and / or archaea.

[0094] The microorganisms may be selected from the group consisting of the following genera: Acidiphilium, Acidicaldus, Acidiferrobacter, Acidibacillus, Acidihalobacter, Acidithiobacillus, Sulfuricurvum, Sulfurococcus, Sulfuricurvum, Sulfurovum, Fervidacidithiobacillus, Sulfobacillus, Sulfolobus, Acidithiomicrobium, Sulfuracidifex, Acidianus, Metallosphaera, or any combination thereof.

[0095] The microorganisms may be selected from the group consisting of the following species: Sulfuricurvum sp., Sulfuricurvum sp., Acidiferrobacter sp., Sulfuricurvum kujiense, Sulfurovum aggregans, Sulfurovum denitrificans, Sulfurovum indicum, Sulfurovum lithotrophicum, Sulfurovum riftiae, Acidithiobacillus ferrivorans, Acidiferrobacter thiooxydans, Acidithiobacillus sulfuriphilus, Acidiphilium acidophilum, Acidithiobacillus thiooxidans, Acidibacillus ferrooxidans, Acidithiobacillus albertensis, Acidihalobacter aeolianus, Acidihalobacter ferrooxydans, Acidihalobacter prosperus, Acidihalobacter yilgarnensis, Acidithiobacillus ferridurans, Acidithiobacillus ferriphilus, Acidithiobacillus ferrooxidans, Sulfobacillus benefaciens, Sulfurococcus yellowstonii, Acidibacillus sulfuroxidans, Fervidacidithiobacillus caldus (prior also called Acidithiobacillus caldus), Sulfobacillus thermotolerans, Sulfobacillus acidophilus, Sulfobacillus thermosulfidooxidans, Acidicaldus organ ivorus Acidithiomicrobium P2, Sulfuracidifex metallicus, Sulfuracidifex tepidarius, Metallosphaera cuprina, Acidianus manzaensis, Acidianus brierleyi, Metallosphaera hakonensis, Metallosphaera javensis, Acidianus sulfidivorans, Acidianus copahuensis, Metallosphaera sedula, Metallosphaera prunae, Sulfolubus islandicus, Acidianus ambivalens, Acidianus manzaensis, Sulfolobus acidocaldarius, Acidianus infernus, or any combination thereof. The microorganisms may preferably be selected from the species Fervidacidithiobacillus caldus.

[0096] Depending on which microorganism or microorganisms selected for the present process, the temperature, pH, and other process inputs may vary. Some examples of microorganisms are shown below. Sulfuricurvum sp. has a pH optimum of 3.5 and a temperature optimum 15°C. Sulfurovum sp. has a pH optimum of 3.5 and a temperature optimum 15°C, Acidiferrobacter sp. has a pH optimum of 1 .75 and a temperature optimum 22.5°C. Acidithiobacillus ferrivorans has a pH optimum of 2.5 and a temperature optimum of 28-33°C, but grows at 10°C. Acidithiobacillus sulfuriphilus has a pH optimum of 3.0 and a temperature optimum of 25-28°C. Acidiphilium acidophilum has a pH optimum of 3.0-3.5 and a temperature optimum of 25-30°C. Acidithiobacillus thiooxidans has a pH optimum of 2.0-2.5 and a temperature optimum of 28- 30°C. Acidibacillus ferrooxidans has a pH optimum of 2.0 and a temperature optimum 30°C. Acidithiobacillus albertensis has a pH optimum of 3.75 and a temperature optimum of 30°C. Acidihalobacter aeolianus has a pH optimum at 1 .8, and a temperature optimum at 36°C, and grows in the presence of salt. Acidihalobacter ferrooxydans has a pH optimum of 1 .8, a temperature optimum of 36°C, and grows in the presence of salt. Acidihalobacter prosperous has a pH optimum of 2.0, a temperature optimum of 37°C, and grows in the presence of salt. Acidihalobacter yilgarnensis has a pH optimum of 2.5, a temperature optimum of 30°C, and grows in the presence of salt. Acidithiobacillus ferridurans has a pH optimum of 2.1 and a temperature optimum of 29°C. Acidithiobacillus ferriphilus has a pH optimum of 2.0 and some strains grow at 10°C. Acidiferrobacter thiooxydans has a pH optimum of 1 .0 and a temperature optimum of 33.5°C. Acidithiobacillus ferrooxidans has a pH optimum at 2.5 and a temperature optimum of 30-35°C. Sulfobacillus benefaciens grows at a temperature in the range of 40-80°C. Sulfurococcus yellowstonii has a pH optimum of 2.5 and a temperature optimum of 30-35°C. Acidibacillus sulfuroxidans has a pH optimum of 1 .8 and a temperature optimum of 43°C. Fervidacidithiobacillus caldus has a pH optimum of 2.0-2.5 and a temperature optimum of 45°C. Sulfobacillus thermotolerans has a pH optimum of 2.0 and a temperature optimum of 40°C. Sulfobacillus acidophilus has a pH optimum of about 2.0 and a temperature optimum of 45-50°C. Sulfobacillus thermosulfidooxidans has a pH optimum of 1 .7-2.4 and a temperature optimum of 50-55°C. Acidicaldus organivorus has a pH optimum of 2.5-3.0 and a temperature optimum of 50-55°C. Acidithiomicrobium P2 has a temperature optimum of 50°C. Sulfuracidifex metallicus grows at pH in the range of 1 .0-4.5 and at a temperature range of 50-75°C. Sulfuracidifex tepidarius has a pH optimum of about 3.5 and a temperature optimum of 65°C. Metallosphaera cuprina has a pH optimum of 3.5 and a temperature optimum of 65°C. Acidianus manzaensis has a pH optimum of 1 .35 and a temperature optimum of 65°C. Acidianus brierleyi has a pH optimum of 1 .5- 2.0 and a temperature optimum of 70°C. Metallosphaera hakonensis has a pH optimum of 3.0 and a temperature optimum of about 70°C.

[0097] Metallosphaera javensis has a pH optimum of about 3.0 and a temperature optimum of about 70°C. Acidianus sulfidivorans has a pH optimum of 0.8-1.4 and a temperature optimum of 74°C. Acidianus copahuensis has a pH optimum 2.5-3.0 and a temperature optimum of 75°C. Metallosphaera sedula grows at a pH in the range of 1 .0-4.0 and has a temperature optimum of about 75°C. Metallosphaera prunae grows at pH in the range of 1 .0-4.5 and a temperature optimum of about 75°C. Sulfolobus islandicus has a pH optimum of 3.5 and a temperature optimum of 76°C. Metallosphaera sedula has a pH optimum of about 2.0 and a temperature optimum of about 75°C. Acidianus ambivalens grows at pH in the range of 1 .0-3.5 and has a temperature optimum of about 80°C. Acidianus manzaensis has a pH optimum in the range of 1 .2-1.5 and has a temperature optimum of about 80°C. Sulfolobus acidocaldarius has a pH optimum in the range 3.0-3.5 and a temperature optimum of about 80°C. Acidianus infernus has a pH optimum of about 2.0 and a temperature optimum of about 90°C.

[0098] The present method includes different interactions and reactions. When the microorganisms are allowed to interact and promote the conversion of the sulphur comprised in the first stream into sulphuric acid at least this step of the method, i.e. , step c), may be carried out at a pH of 0.0-5.0, such as at a pH of 0.5-5.0, 0.6-4.8, 0.8-4.5, 1 .0-4.5, 1 .0-3.0, 1 .0-2.5, 1 .2-2.5, 1 .2- 2.0, 1.2-3.5, 1.5-3.0, 1.5-2.5, or 2.0-2.5, preferably at a pH of 1.0-3.0, 1.0-2.5, 1 .2-2.5, or 1 .2-2.0. In addition, when the formed sulphuric acid is allowed to react with magnesium carbonate comprised in the second stream to provide soluble magnesium also this step, i.e. step e), of the method may be carried out under the same conditions as the conversion of sulphur to sulphuric acid, i.e. at said pH of 0.0-5.0, such as at a pH of 0.5-5.0, 0.6-4.8, 0.8-4.5, 1 .0-4.5, 1.0-3.0, 1.0-2.5, 1.2-2.5, 1.2-2.0, 1.2-3.5, 1.5-3.0, 1.5-2.5, or 2.0-2.5, preferably at a pH of 1 .0-3.0, 1 .0-2.5, 1 .2-2.5, or 1 .2-2.0.

[0099] When the microorganisms are allowed to interact and promote the conversion of the sulphur comprised in the first stream into sulphuric acid at least this step of the method, i.e. step c), may be carried out at a temperature of 10-90°C, such as 10-80°C, 20-75°C, 15-75°C, 20-60°C, 25-60°C, 28-55°C, 30-55°C, 35-50°C, 38-47°C, or about 45°C, preferably at a temperature of 35- 50°C, such as 38-47°C, or about 45°C. In addition, when the formed sulphuric acid is allowed to react with magnesium carbonate comprised in the second stream to provide soluble magnesium also this step of the method, i.e. step e), may be carried out under the same conditions as the conversion of sulphur to sulphuric acid, i.e. at said temperature of 10-90°C, such as 10- 80°C, 20-75°C, 15-75°C, 20-60°C, 25-60°C, 28-55°C, 30-55°C, 35-50°C, 38- 47°C, or about 45°C, preferably at a temperature of 35-50°C, such as 38- 47°C, or about 45°C.

[0100] The same conditions for both parts of the present method, i.e., step c) and step e), are especially relevant when the interaction / promotion and reaction occurs in a vessel or container, such as a reactor or a bioreactor. However, if the interaction / promotion and reaction are not performed in the same vessel, recirculation between vessels in series may provide the same conditions in such vessels in series.

[0101] The present method may be disclosed as providing a dissolution of a stream comprising magnesium, such as magnesium carbonate containing waste material from, e.g., calcination processes, a use of waste material containing bio-sulphur from e.g., a biological sulphur reducing process such as from oil refineries or battery recycling plants, and selection of a sulphuric acid generating bacteria, e.g., preferably selection of Fervidacidithiobacillus caldus, as the most suitable for and unexpected efficient mode to generate high amounts of sulphuric acid and being able to efficiently work with the ingoing feed waste components. The present method provides e.g., a unique and unexpected interaction between Fervidacidithiobacillus caldus, magnesium carbonate waste, and bio-sulphur waste. The present method provides utilisation of waste streams to provide empirically valuable critical raw materials, and also provides improved sustainability by providing valueadding components from wastes and thereby reducing the environmental impact.

[0102] The utilisation of carbonate in addition to oxide in an acid / base reaction evolves carbon dioxide that in turn can be utilised by the microorganisms (such as e.g., Fervidacidithiobacillus caldus, herein also F. caldus) as a carbon source for cellular growth. This provides a carbon capture process reducing carbon dioxide release to the environment and is a positive contributor to net zero emissions.

[0103] The acid / base reaction is exothermic, wherein large-scale production reduces the need for heating to provide beneficial conditions for reactions as e.g., the optimum temperature of F. caldus is about 45° C. Furthermore, this reduces the need to heat a large-scale bioreactor to attain an optimum temperature for growth and metabolism. Finally, excess heat from the exothermic reactor can be used to raise the temperature of additional starting reactors, again reducing the use of electricity and lowering carbon dioxide emissions. The interaction between the acid production, via bio-sulphur oxidation by F. caldus, is countered by the acid consuming magnesium carbonate waste and provides a simple modulation system such that the pH represents the only measurement parameter to efficiently operate the bioreactor. With modulation system means two competing reactions to maintain homeostasis. If the bio-sulphur is in excess when running the present method, then the rate at which the magnesium carbonate is added would be the sole factor to control pH and therefore, microbial growth with its acid production.

[0104] Bio-sulphur or Bio S used in the present method may be a waste product produced via the processing of e.g., petrochemicals or recycling of Zn / C batteries. Today, storage of bio-sulphur requires use of valuable land, and costly storage such as in a pond to reduce dispersion and furthermore, its oxidation results in sulphuric acid that in itself is another hazard, due to being strongly corrosive. Thus, the present process’ use of bio-sulphur and is mediated bacterially and thus reduces the total economic and environmental waste burden.

[0105] Effluent from the present method, e.g., from the bioreactor, can be reused after the valuable magnesium has been recovered such that the weak sulphuric acid solution can be recycled into the system of the present inventive method to mitigate the use of potable water, with environmental benefit.

[0106] The use of bio-sulphur results in the more rapid and greater production of sulphuric acid and less bio-sulphur may be used as it disperses more efficiently and thus, is not as rapidly removed from a continuous bioreactor system relative to elemental sulphur. Thus, use of the bio-sulphur has an unexpected practical advantage over elemental sulphur not being prior known. F. caldus may using the present method acidify the process medium to a low pH value, which allows it to react with a larger volume of magnesium carbonate waste. This provides the possibility of a smaller capacity bioreactor being needed to treat the same amount of waste and therefore, reducing the plant facility footprint, materials to build the reactor, and capital expenditure. Further, the lower pH value that F. caldus operates at results in a reduced risk of contamination by other microorganism species, such as fungi. This also reduces any potential biofilm formation from contaminating species that would result in fouling and the need to clean the system. For example, effects of the bio-sulphur and bacteria selection may be visible in the examples below, and Figures 6 and 7.

[0107] The microorganism F. caldus may tolerate a sudden increase in pH value. In the event of an unintentional pH increase (such as uncontrolled addition of magnesium carbonate) a system or process using F. caldus recovers within a short amount time and the pH was restored to a preferred range. The increased bioavailability of the bio-sulphur over elemental sulphur likely aids in this recovery.

[0108] Acidophilic microorganisms such as F. caldus may be tolerant of many metals including magnesium, e.g., which does not appreciably inhibit F. caldus growth up to about 5 g / L. A high waste pulp density may be utilised with the added benefit of reducing plant facility footprint, reactor materials, and capital expenditure.

[0109] The minor recalcitrant component of the magnesium waste after treatment in the present inventive process will be benign and can be used in many downstream applications such as aggregates, road fill etc.

[0110] The present method may include further components used therein. The method may further comprise providing at least one of nutrients, water, air, or any combination thereof. Nutrients may be added in the method to feed the microorganisms. Water may be added to compensate for evaporation or for lost volume due to processing. If any nutrient deficiency is noted, these may be added at any time, however growth appears to not be an issue when the bacterium is cultured on the magnesium waste ores. Sulphur appears to be the major limiting nutrient and can be added as needed. Water may be added prior to, during, and / or after step c). If water is added after step c) it is preferably added before and / or during step e). Air may be added in the method to provide good environment for the microorganisms. Air may be added prior to, or during step c) when the microorganisms provide the sulphuric acid.

[0111] As indicated previously, the present method steps c) and e) may be carried out, in a reactor 10, such as a bioreactor, simultaneously, or sequentially in two separate vessels, containers or reactors 20 and 30. In a sequential method 120, step c) may be carried out in a vessel 20, preferably a bioreactor, and step e) may be carried out in a vessel 30, which optionally may be a bioreactor. As seen in Figure 3, method 110 of the present invention, steps c) and e) may be carried out in a reactor 10. Preferably at least step c) and optionally step e) are performed in a bioreactor 10. As seen in Figure 4, method 120 of the present invention, steps a) to c) may be carried out in a reactor 20 and steps d) and e) may be carried out in a reactor 30. Further, in each of method 110 and 120, step f) and subsequently step g) may be carried out in a vessel, container or reactor 40, such as a settling tank. In each of method 110 and 120, the formed magnesium oxalate precipitate may be collected in step g), which preferably may be performed by cyclonic separation. Cyclonic separation is a method of removing particulates from an air, gas or liquid stream, without the use of filters, through vortex separation. When removing particulate matter from liquids or fluids, a hydrocyclone may be used. Rotational effects and gravity are thus used to separate mixtures of solids and fluids. Preferably, the vessel 40, such as a settling tank, may be arranged with a separator 50, such as a hydrocyclone. The vessel 40, such as a settling tank, may also be arranged with a funnel. Thus, the separator 50 may also be a funnel tank or funnel reactor.

[0112] Subsequently, the collected magnesium oxalate precipitate may be transferred to the manufacturing process 200 producing essentially magnesium oxide in step h), which allows for each of the methods 110 and 120 to be completed.

[0113] The present method may be used in batch-wise production, or continuous production. The present method may preferably be a continuous production, since continuous addition of waste allows local adaptation of the culture to the specific waste i.e., heavy metals stress. In support, continuous addition of waste implies that the reactor never has to be shut down, drained, or otherwise reset between additions of waste, allowing for a more efficient process. The continuous operation allows for the downstream processes to operate continuously, too, further maximising production capacity. The first, and second streams, and the microorganisms may be contacted in any order, or simultaneously. The first and second streams may be added to a vessel, such as a reactor i.e. , a bioreactor, which vessel 10 or 20 may already contain microorganisms. The first stream comprising sulphur may alternatively be brought in contact with the microorganisms in a vessel such as a reactor i.e., a bioreactor, followed by addition of stream comprising magnesium.

[0114] Specifically, for continuous processes, continuous addition of components or streams are used.

[0115] In a sequential continuous process 120, microorganisms may be provided in a first vessel 20, such as a reactor, and this first vessel 20 is supplied with the first stream, and optionally further feeding the first stream or the first vessel with water and / or nutrients. In the first vessel 10 or 20 sulphuric acid is formed. The sulphuric acid may be forwarded to a subsequent second vessel or reactor 30. Water may optionally be added to the sulphuric acid containing stream, which may optionally be exiting the first vessel 20, before entry into the second vessel 30, or water may be added to the second vessel 30 or reactor. In the second vessel or reactor 30 the magnesium in the stream comprising magnesium, such as magnesium carbonate, is converted into soluble magnesium through the reaction with sulphuric acid, i.e., magnesium sulphate. During the reaction carbon dioxide is formed.

[0116] Carbon dioxide (CO2) is a compound that could be used to increase the efficiency of the process. As the microorganisms may use the CC as nutrient, a more limited amount of CO2 may need to be released or vented. C02will increase the growth rate of the microorganisms, which preferably are autotrophic carbon fixing microorganisms, such as autotrophic carbon fixing bacteria and / or archaea. The present method may comprise recycling of carbon dioxide formed in step e). The carbon dioxide formed in step e) may then be used by the microorganisms in step c). The recycling of carbon dioxide formed in step e) may occur within said same or different vessels and / or reactors (see Figures 3 and 4). Figure 1 shows a schematic drawing of the present method performed in at least one vessel, container or reactor. Figures 3 and 4 two possible embodiments of the present method 100 in more detail as method 110 and 120, respectively. In Figures 3 and 4, embodiments with possible recycling of carbon dioxide are shown. Also, the possible additions of nutrients, water, and / or air are shown in said Figures 3 and 4. The outlet of refractory material or residue refers to material that is resistant to decomposition in the process, i.e. , residual material or material that is left over. The refractory material may be separated from the soluble magnesium that is formed in reactor 10 or 30 and forwarded to vessel or reactor 60 for further processing according to method 100. The refractory material precipitate may be collected in step e) of method 100, which preferably may be performed by cyclonic separation. Thus, reactor 10 or 30, such as a settling tank, may be arranged with a separator 50, such as a hydrocyclone or a funnel. Vessel 60, such as a reactor for mixing the reaction components, may also be arranged with a separator 50, such as a hydrocyclone or a funnel. The waste going into vessel 60 may be unleached MMW, leached MMW or a mixture thereof. The components going into vessel 60 may be in the weight ratio (wt%) of waste: phosphate: water 1 :0.5-0.75:0.1-0.25, preferably 1 :0.5:0.1. All ranges within the tested ranges forms good strong cement, but generally the more phosphate you add the harder the MPC gets. Also, the proportions may be changed and an aggregate, such as the refractory material, added to modify the curing parameters.

[0117] Figure 2 discloses a more detailed drawing of a bioreactor 10 and the present method for conversion of solid magnesium to soluble magnesium. Use of a bioreactor 10 is a good way to provide the present method 100. As the sulphur, magnesium carbonate, and microorganisms all are present in the same vessel, the pH may be regulated, by the feeds and kept at a desirable value. Thus, the pH may be raised by adding waste, i.e., the stream comprising magnesium. The pH will fall with time due to biotic production of sulphuric acid, or by adding sulphuric acid if needed. Also, the carbon dioxide may be easily recirculated into the liquid mix to allow microorganisms easy access to the compound. According to the present method 100, a process example may be using Fervidacidithiobacillus caldus (previously called Acidithiobacillus caldus or Thiobacillus caldus', herein F. c). A bioreactor 10 according to Figure 2 may be used. The bioreactor may be run at a temperature of about 45°C. Ingoing feeds include MgCOs waste, and biogenic sulphur (S°), but may also include water, and nutrients. The bioreactor may be supplied with air and CO2 enriched gaseous phase of the headspace of the reactor, which may be forwarded into the liquid mixture of the reactor. CO2 formed during solid magnesium, such as MgCOs, dissolution may be used to increase F. c. growth. Any excess CO2 may be vented and removed from the bioreactor. The outputs are soluble Mg ions, CO2, and refractory material or waste gangue. As solid magnesium, such as MgCOs, raises the pH while H2SO4 lowers the pH, the process conditions may be controlled. A target pH for said microorganisms F. c. is about 2.0 to 2.5. The process is controlled by addition of the stream comprising magnesium, such as MgCOs, such that the pH is maintained within the target range. The pH may be monitored by a pH monitor or pH meter 80 that may be comprised in the reactor or bioreactor.

[0118] Figure 3 shows a schematic drawing of the present method 110 performed in one vessel 10, wherein the magnesium is solubilised as magnesium sulphate, followed by precipitation as magnesium oxalate in vessel 40. Figure 4 shows a schematic drawing of the present method 120 performed in two consecutive vessels, containers or reactors 20 and 30, wherein the magnesium may also be solubilised as magnesium sulphate in a stepwise procedure, followed by precipitation as magnesium oxalate in vessel 40. In Figure 1 , recycling of sulphuric acid. In each of Figures 3 and 4, respectively, the embodiment with possible recycling of carbon dioxide is shown. Also, the possible addition of nutrients, water, and / or air are shown in each of Figures 3 and 4, respectively. In the first vessel 10 or 20 addition of an additional base, or alkaline material, such as NaOH, may be needed to control the pH in view of the acid formation. However, adding more waste material is preferred in order to control the pH. Even if separate vessels are used, it may be possible to obtain similar performance as from the use of only one vessel. Performing the present method in one vessel, such as vessel 10, is however preferred. It is to be noted that an additional recycling stream may be included. In Figure 3, a recirculation of the liquid mixture or stream obtained in vessel 40 may be recirculated into vessel 10. In another embodiment, a recirculation of the liquid mixture or stream obtained in the second vessel 30 back to the first vessel 20 (see dashed line in Figure 4), in order to rectify the pH in the first vessel 20. Recirculation of the liquid mixture or stream obtained in vessel 40 may also be recirculated into either vessel 20 or vessel 30 as shown in Figure 4.

[0119] In an embodiment, the present invention relates to a method 100, 110, 120 or 130 and a system 300 wherein a novel revenue stream of non- hydraulic cement may be produced as a by-product from step e) of method 130. As illustrated in Figure 1A, leaching of the magnesium mine wastes (MMW) in vessel 10 or 30 selectively removes magnesium metal from the MMW, leaving an acid stable refractory residue, i.e. , the by-product of step e). This residue may be part of method 130, wherein the refractory material and phosphate is added to unleached MMW in vessel 60 of system 330, thus forming a magnesium phosphate cement (MPC).

[0120] MPCs are a magnesia-based binder involving the acid-base neutralisation reaction between MgO and a phosphate (e.g. ammonium dihydrogen phosphate or potassium dihydrogen phosphate), resulting in a non-hydraulic cementitious product. MPC has significant development potential and excellent properties. MPC materials may be applied in architecture and other fields such as wall spraying, floor levelling, structure repair, solid waste curing, biomedical engineering, and 3D structure printing. Using MMW as a source of magnesite or magnesia for the production of MPC is beneficial as it has been finely milled, thus presenting increased homogeneity and surface area available for chemical reaction, and it has been calcined, thus having the major energy expenditure already spent. Thus, an advantage is that using MMW for providing magnesite is less expensive than using pure magnesite in producing concrete.

[0121] Figure 1 A also shows a system 330 for forming a magnesium phosphate cement, wherein the system comprises: a vessel 60, for reacting MMW, refractory material from method 100, 110, 120, 130 and phosphate, thus forming a magnesium phosphate cement as a novel revenue stream. System 330 may also comprise a separator 50 for collecting the formed MPC.

[0122] Acid-casein production from dairy industries generates waste streams that are rich in nitrogen, usually in the form of protein and nitrate, and phosphate. The dairy waste stream may contain 1 -4 g / L phosphate and, after some dehydration, may be used to provide the necessary phosphate to produce MPC.

[0123] Thus, according to the present invention a new revenue stream can be created from MMW from the present method according to the first aspect and phosphate waste from dairy industries. This new revenue stream realises reduction in total waste (zero waste) of the method according to the present invention. Accordingly, the overall benefit of the present invention is that solid magnesium oxide together with MPC may be formed from mining waste with almost zero waste material from the process.

[0124] Examples

[0125] Example 1

[0126] A waste stream comprising MgCOs was leached with Fervidacidithiobacillus caldus (F caldus) that was maintained in MacConkey (MAC) medium at pH 2.5 and 45°C as an inoculum. A batch reactor system 300 containing 0.5 % pulp density (250 ml final volume in Erlenmeyer flasks) slurry of the waste MgCOs was created in triplicate. Samples received a 10 % inoculum volume and analysed for oxidative / reductive potential (ORP), pH, cell number, cell free fluid for Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The samples were incubated at 40 °C, 120 rpm.

[0127] Figure 5 discloses the results obtained. Leaching with F. caldus of MgCOs wastes resulted in significant mobilisation of Mg but also revealed divergent mechanisms for solubilisation. Media containing sulphuric acid generated by F. caldus from the biogenic sulphur contacted with MgCOs resulted in significant solubilisation on day 0, implying acidification with biogenic H2SO4 alone was responsible for solubilisation. Mg dissolution over time is seen as the waste MgCOs is acted upon by the biogenic acid. This indicates that a sulphuric acid, and a relatively low concentration thereof, will rapidly solubilise the Mg from the MgCOs waste.

[0128] Example 2

[0129] In this example acid generation is compared between different sulphur sources, i.e. , Bio S versus commercially purchased elemental sulphur. In this example, F. caldus prepared as described in Example 1 was contacted in Erlenmeyer flasks with elemental sulphur S° in the form of elemental sulphur obtained by synthetical chemicals, i.e., a sulphur obtained by chemical ways (commercial sulphur). The elemental sulphur was not obtained using microorganisms.

[0130] Figure 6 discloses the pH profiles. Elemental sulphur S°, provided by way of chemicals is herein shown as “elemental S”, and biogenic sulphur shown as “Bio S”. In Figure 6, it is clearly shown that the Bio S more quickly lowers the pH, indicating that the conversion of Bio S to sulphuric acid is more efficient than the Elemental S. In just 20 days pH 1 is obtained, which takes almost 50 days to obtain for the Elemental S. As more acid is produced in a shorter time, when it is then used for solubilising the magnesium carbonate more solubilised magnesium may be obtained in a shorter time as well.

[0131] Figure 7 discloses the cell densities from the above experiment. In Figure 7 it can be seen that the number of cells increases more rapidly with Bio S compared to Elemental S. This is reflected in the more rapid generation of sulphuric acid and concomitant decrease in pH shown in Figure 6. The results show that Bio S allows for an increased rate and total mass of acid generation versus Elemental S. It has unexpectedly been found that by Bio S improves the acid generation.

[0132] Example 3

[0133] A mature F. caldus culture was prepared in MAC medium as described in Example 1 and split into five equal volumes. Two percent (w / v) bio-sulphur was added. Increasing percentages (m / v) waste MgCOs were added on Day 1 and samples were taken at regular intervals. pH was recorded by a pH meter and cell densities were recorded by using a microscope and a haemocytometer. Figure 8 shows the pH profiles, from which it can be seen that the decreasing pH values show that the F. caldus culture was able to continue to generate sulphuric acid in increasing waste MgCOs pulp densities. This means that the F. caldus culture was able to oxidize the biogenic sulphur while exposed to increasing soluble Mg ion concentrations.

[0134] Figure 9 shows the cell densities during contact between the F. caldus culture and the increasing waste MgCOs pulp densities. From this it can be seen that the cells were able to divide and increase in cell number while exposed to increasing soluble Mg ion concentrations. Example 4

[0135] The example discloses the increase in pH for F. caldus used in reactors dosed with an excess of Mg waste material. Two 1 L reactors were dosed with an excess (0.8 and 1.5%) of waste ore comprising magnesium carbonate. The basic nature of the waste ore raised the pH above the optimum for the microbe. However, after approximately a week, the pH had recovered as a result of microbial bio-sulphur oxidation. This indicates that the microbe is able to overcome short pH exposures out of its optimum, and therefore demonstrates robustness of F. caldus and resilience of the process. It has been found that F. caldus may survive at a pH above 7 for at least one week. If there is a sudden pH increase, e.g., such as uncontrolled addition of magnesium carbonate, the present process using F. caldus recovers within a short amount time and the pH was restored to a preferred range (see Figure 10). The increased bioavailability of the bio-sulphur over elemental sulphur likely aids in this recovery. pH exceeding the physiological range for F. caldus may happen, however in such case, the cells metabolize the bio-sulphur to recover and lower the pH after 8 days. The two lines in Figure 10 are replicates, in the sense that they are from two different reactors with two different pulp densities, but their response is the same - recovery from a high pH insult. Example 5

[0136] Addition of magnesium material to a semi-continuous culture bioreactor containing F. caldus. Regular dosing intervals (see Figure 11 A) with magnesium-containing waste ore result in cyclic pH rise and recovery. With regular dosing interval means that the stream comprising magnesium is added whenever there is a dip in the pH below a defined pH, preferably the defined pH is 1 . For example, as pH is logarithmic, the pH may go from 2.5 to

[0137] 1 in 10 to 15 days. The pulp density was increased on the final two cycles (additions on Day 35 and 48). The solubilised Mg2+concentration (see Figure 11 B) increased concomitantly with the addition of the waste ore. This was carried out in 1 L bioreactors with 2% bio-sulphur, dosed approximately every

[0138] 2 weeks. The data indicates that the process can be operated in a semi- continuous manner over long periods. As the reactors were run semi- continuously with addition of media and a residence time of approximately 1 week, the solubilised metal steady-state was well tolerated by F. caldus.

[0139] If, with continued dosing of the stream comprising magnesium, such as Mg waste, the Mg concentration increases and the pH of the system decreases, this implies metal tolerance. The rate of pH decrease is pretty regular throughout the experiment, and thus this seems to indicate that the cells are quite satisfied, even at elevated Mg concentrations, e.g., more than 5 M or 16 g / L. The pH with time graph Figure 11 A shows that the F. caldus were metabolically active with addition of Mg as pH decreased post addition of waste (Figure 11 B).

[0140] Acidophilic microorganisms such as F. caldus are tolerant of many metals (see Table 2), including magnesium, which does not appreciably inhibit F. caldus growth up to 5 g / L (Figure 11 ). The acidithiobacilli are known as generally tolerant of high metal concentrations, particularly Zn, Cu and As, as these metals are part of the mineralogy of the ores that are treated. It is known that acidophiles are resistant via complexation of many metals with sulphate ions that reduces the toxicity. Thus, a high waste pulp density can be utilised with the added benefit of reducing plant facility footprint, reactor materials, and capital expenditure.

[0141] The minor recalcitrant component of the magnesium waste after treatment in the present process will be benign and can be used in many downstream applications such as aggregates, road fill etc.

[0142] Table 2 shows the upper-level concentrations of some common metals in a variety of acidophiles where metabolic activity was recorded. Table 2. Recorded upper-level concentrations of some common metals in a variety of acidophiles where metabolic activity occurs.

[0143] ND means “not determined”. Values of metal toxicity are often defined differently. Therefore, for this table the term “metal concentration whereby metabolic activity occurs” has been defined as the maximum metal concentration where either growth or a defined enzyme activity (e.g., ferrous iron oxidation) still occurs. The Escherichia coli minimum inhibitory concentration has been included as a neutrophilic example for comparison of the degree of metal resistance between these types of microorganisms. These data show a general tolerance of acidophilic microorganisms to metals and demonstrates their suitability for the dissolution of magnesium wastes.

[0144] Figure 12 discloses ICP-MS data for vessel reactors incubated with active F. caldus cells (A, C, E) and without active F. caldus cells (B, D, F), and grown on bio-sulphur vessels contained pulp density Mg-waste in 0.5 % (A, B), 1.0 % (C, D) and 5.0 % (E, F). Mg (■), Ca (♦), Fe (A), and Mn (•) were analysed during regular sampling periods over the 57-day period. Hence, this proves that with increasing pulp densities the relative proportion of Mg increases with a slight concomitant decrease in yield. This is beneficial in creating a high relative purity Mg2+solution that will promote high efficiency conversion to Magnesium oxalate. Example 6

[0145] Unleached magnesium-containing waste was added to the refractory material from vessel 10, which is an aggregate, and then further combined in vessel 60 with water and a source of phosphate, which may for example be provided from a dairy industry, such as from acid-casein production from dairy industries which generates waste streams that are rich in nitrogen and phosphate, to produce magnesium phosphate cement. This allows a third revenue stream, that was collected in separator 50, from the method according to the present invention, as well as reducing the process waste to zero - an industry first. Example 7

[0146] Unleached waste was combined with pure di potassium phosphate and water in a 1 :0.5:0.1 ratio. This was to provide a proof of concept for the production of magnesium phosphate cement (MPC). The dry components of the mixture were combined and mixed, and the water was added last. The slurry was mixed for 20 seconds and decanted into a mould. The slurry solidified after 2 minutes and the reaction forming the MPC was exothermic. The MPC was allowed to cure over two days and removed from the mould. In a further proof of concept, dairy waste whey was investigated as a source of phosphate. It was found (personal communication) that the whey contained 1- 4g phosphate per litre. This whey may be evaporated to obtain the phosphate salts used in the creation of the MPC. In addition, an aggregate, very likely the unleached component of the MMW may be added to the MPC to modulate the curing parameters. Thus, the production of MPC provides another value stream, and consumes three waste products (whey waste, unleached and leached MMW).

Claims

CLAIMS1 . A method (100) for increasing the yield of magnesium oxide in a manufacturing process (200) producing essentially magnesium oxide through the valorisation of magnesium-containing waste, wherein the method comprises the steps of: a) providing acid-generating microorganisms selected from the group of acidophilic microorganisms; b) providing a first stream comprising sulphur; c) allowing the microorganisms to interact with the sulphur comprised in the first stream thereby promoting the conversion of the sulphur to form sulphuric acid; d) providing a second stream comprising magnesium from the manufacturing process (200) producing essentially magnesium oxide; e) allowing the formed sulphuric acid to react with magnesium in the stream comprising magnesium to form solubilised magnesium sulphate; f) providing oxalic acid and allowing the oxalic acid to react with the formed solubilised magnesium sulphate to form magnesium oxalate as a precipitate; g) collecting the formed magnesium oxalate precipitate; and h) transferring the collected magnesium oxalate precipitate to the manufacturing process (200) producing essentially magnesium oxide, wherein the magnesium oxalate is calcinated to magnesium oxide and thereby increasing the yield of magnesium oxide in the manufacturing process (200) producing essentially magnesium oxide.

2. The method (100) according to claim 1 , wherein the first stream comprising sulphur is a by-product or waste stream; preferably said by-product or waste stream is provided from biomass processing industry, mining industry, oil and gas industry, or downstream process industries therefrom, fibre production, or any combination thereof; preferably said by-product or waste stream is provided from biorefinery processes, mining of or processing of sulphide- containing ores, metal refinery processes, mining of or processing of coal,biogas purification processes, waste gas purification processes, bullet proof fibre or fabric production, and other biological processes producing sulphur containing waste, or any combination thereof; preferably said by-product or waste stream is provided from coal mining, oil and gas industry or downstream process industries therefrom, biogas purification processes including sulphur removal, bullet proof fibre or fabric production, or any combination thereof; preferably said by-product or waste stream is provided from a biological desulphurisation process.

3. The method (100) according to claim 1 or 2, wherein the sulphur comprised in the first stream comprises biogenic sulphur, preferably the sulphur is biogenic sulphur.

4. The method (100) according to any one of claims 1-3, wherein the second stream comprising magnesium is a product stream, a by-product stream, or a waste stream, preferably said product stream, by-product stream or waste stream is provided from mining industry, mineral processing industry, ore processing industry, metal processing industry or desalination plants, or any combination thereof; preferably said product stream, by-product stream or waste stream is provided from dolomite mining or processing industry, magnesite mining or processing industry, magnesium smelting processes, magnesium calcination processes or desalination processes, or any combination thereof; preferably the second stream comprising magnesium is a by-product stream or a waste stream.

5. The method (100) according to any one of claims 1-4, wherein the stream comprising magnesium is comprising magnesium in the form as brucite, magnesite, dolomite or periclase, or any mixture thereof.

6. The method (100) according to any one of claims 1-5, wherein the acidgenerating microorganisms are capable of interacting in and promoting conversion of sulphur into sulphuric acid and have chemical leaching kinetics at a pH of 0.0-5.0, preferably 0.5-5.0, preferably 0.6-4.8, preferably 0.8-4.5,preferably 1.0-4.5, preferably 1.0-3.5, preferably 1.0-3.0, preferably 1.0-2.5, preferably 1.2-2.5, and preferably 1.2-2.0.

7. The method (100) according to any one of claims 1-6, wherein the acidgenerating microorganisms are capable of interacting in and promoting conversion of sulphur into sulphuric acid and have chemical leaching kinetics at a temperature of 10-90°C, preferably 10-80°C, preferably 20-75°C, preferably 25-60°C, preferably 28-55°C, and preferably 30-45 °C.

8. The method (100) according to any one of claims 1-7, wherein the acidgenerating microorganisms are selected from the group consisting of the following genera: Acidiphilium, Acidicaldus, Acidiferrobacter, Acidibacillus, Acidihalobacter, Acidithiobacillus, Sulfurococcus, Sulfuricurvum, Sulfurovum, Fervidacidithiobacillus, Sulfobacillus, Sulfolobus, Acidithiomicrobium, Sulfuracidifex, Acidianus, Metallosphaera, or any combination thereof.

9. The method (100) according to any one of claims 1-8, wherein the acidgenerating microorganisms are selected from the group consisting of the following species: Sulfuricurvum sp., Sulfuricurvum sp., Acidiferrobacter sp., Sulfuricurvum kujiense, Sulfurovum aggregans, Sulfurovum denitrificans, Sulfurovum indicum, Sulfurovum lithotrophicum, Sulfurovum riftiae, Acidithiobacillus ferrivorans, Acidithiobacillus sulfuriphilus, Acidiphilium acidophilum, Acidithiobacillus thiooxidans, Acidibacillus ferrooxidans, Acidithiobacillus albertensis, Acidihalobacter aeolianus, Acidihalobacter ferrooxydans, Acidihalobacter prosperus, Acidihalobacter yilgarnensis, Acidithiobacillus ferridurans, Acidithiobacillus ferriphilus, Acidiferrobacter thiooxydans, Acidithiobacillus ferrooxidans, Sulfobacillus benefaciens, Sulfurococcus yellowstonii, Acidibacillus sulfuroxidans, Fervidacidithiobacillus caldus, Sulfobacillus thermotolerans, Sulfobacillus acidophilus, Sulfobacillus thermosulfidooxidans, Acidicaldus organivorus, Acidithiomicrobium P2, Sulfuracidifex metallicus, Sulfuracidifex tepidarius, Metallosphaera cuprina, Acidianus manzaensis, Acidianus brierleyi, Metallosphaera hakonensis, Metallosphaera javensis, Acidianus sulfidivorans, Acidianus copahuensis,Metallosphaera sedula, Metallosphaera prunae, Sulfolubus islandicus, Acidianus ambivalens, Acidianus manzaensis, Sulfolobus acidocaldarius, Acidianus infernus, or any combination thereof; preferably the microorganisms are selected from the species Fervidacidithiobacillus caldus.

10. The method (100) according to any one of claims 1 -9, wherein at least step c) is carried out at a pH of 0.0-5.0, preferably 0.5-5.0, preferably 0.6-4.8, preferably 0.8-4.5, preferably 1.0-4.5, preferably 1.0-3.0, preferably 1.0-2.5, preferably 1.2-2.5, and preferably 1.2-2.0.11 . The method (100) according to any one of claims 1 -10, wherein at least step c) is carried out at a temperature of 10-90°C, preferably 10-80°C, preferably 20-75°C, preferably 15-75°C, preferably 20-60°C, preferably 25- 60°C, preferably 28-55°C, preferably 30-55°C, preferably 35-50°C, preferably 38-47°C, and preferably about 45°C.

12. The method (100) according to any one of claims 1 -11 , wherein step g) is performed by cyclonic separation.

13. The method (100) according to any one of claims 1 -12, wherein steps c) and e) are carried out in one same vessel or two different vessels, preferably at least step c) and optionally step e) are performed in a bioreactor.

14. The method (100) according to any one of claims 1 -13, further comprising recycling of carbon dioxide formed in step e) within said one same or two different vessels.

15. The method (100, 130) according to any one of claims 1 -14, wherein step e) further forms a refractory material as by-product, and wherein the method comprises a further step of reacting said by-product with the second stream comprising magnesium from the manufacturing process (200) producing essentially magnesium oxide and phosphate to achieve magnesium phosphate cement.

16. A system (300) for increasing the yield of magnesium oxide in a manufacturing process (200) producing essentially magnesium oxide according to the method (100) of claims 1 -14, wherein the system comprises: a pH meter (80); at least one vessel (10), such as a bioreactor; a further vessel (40), such as settling tank; and a separator (50), wherein the at least one vessel (10) and the further vessel (40) are arranged for allowing transfer and recycling of fluids.

17. A system (330) for increasing the yield of magnesium oxide in a manufacturing process (200) producing essentially magnesium oxide and for producing magnesium phosphate cement according to the method (100,130) of claims 1 -15, wherein the system comprises: a pH meter (80); at least one vessel (10), such as a bioreactor; a further vessel (40), such as a settling tank; a further vessel (60), such as a reactor; and at least one separator (50), wherein the at least one vessel (10) and the further vessel (40) are arranged for allowing transfer and recycling of fluids.

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