A process and plant

Abstract

The present invention relates to a process and plant for reacting carbon dioxide with an alkali metal to form an alkali metal carbonate precipitant. The process and plant including a breaking step in which a slurry feed is broken down and forms an aqueous suspension, and a contacting step in which feed gas including carbon dioxide is contact with the suspension to form an alkali metal carbonate. The breaking and contacting steps are carried out progressively.

Description

A PROCESS AND PLANTFIELD

[0001] The present disclosure relates to a process of reacting carbon dioxide with a metal silicate to form a metal carbonate and silica. The present disclosure also relates to a plant for reacting carbon dioxide with a metal silicate.BACKGROUND

[0002] Sequestering carbon dioxide to prevent it from being vented to atmosphere is a challenge that is being investigated worldwide, and a solution can go some way to addressing the present climate change crisis. A number of solutions have been proposed, all of which have advantages and disadvantages.

[0003] Sequestering carbon dioxide using silicate-based minerals to form mineral carbonates has been proposed previously. However to our knowledge there are difficulties in sequestering carbon dioxide at industrial levels using silicate-based minerals. It is an object of the present invention to provide an alternative process and plant.SUMMARY

[0004] The present invention relates to a process of reacting carbon dioxide with a metal silicate, the process including the step of: breaking a feed ore containing metal silicate and forming an aqueous suspension of particles of the feed ore including metal silicate; and contacting the aqueous suspension with a feed gas including carbon dioxide reacts with metal silicate so that a precipitant containing metal carbonate forms; wherein the breaking step and the contacting step are carried out progressively, such that as the breaking step progresses, further metal silicate will be made available and the contacting step can continue further to form a product containing additional metal carbonate.

[0005] One of the advantages of the present invention is that progressively carrying out the breaking step and the contacting step increases the conversion of metal silicate to metal carbonate and silica in the product per unit mass of the feed ore on a dry basis.

[0006] The present invention also relates to a process of reacting carbon dioxide with a metal silicate, the process including the steps of:breaking a feed ore containing metal silicate and forming an aqueous suspension of particles of the feed ore including metal silicate; contacting the aqueous suspension with a feed gas including carbon dioxide so a reaction between carbon dioxide and metal silicate can form a precipitant containing metal carbonate and silica, wherein the breaking step and the contacting step are carried out progressively, such that as the breaking step progresses further metal silicate will be made available and the conversion of metal silicate to product containing a metal carbonate and silica increases per unit mass of the feed ore (one dry basis).

[0007] That is to say, the amount of the precipitant containing metal carbonate can increase per unit mass of the feed ore as the breaking step progresses and the contacting step progresses. During the contacting step, a layer of silica and / or initial metal carbonate forms on an outer layer on at least part of the particles of the suspension which can inhibit the metal from taking part in a reaction with carbon dioxide. This limitation is at least to some extent reduced, by the breaking step and the contacting step being carried out progressively, such that as the breaking step progresses additional metal from within the particles or uncovered at the surface particles can react with carbon dioxide as the contacting step progresses further, thereby producing product containing additional metal carbonate and silica. In other words, the breaking step may have two actions, including splitting the particles to expose metal within the particles, and / or removing at least part of an outer layer from the particles to expose metal within the particles. The outer layer may include metal carbonate and / or silica.

[0008] The metal silicate may include one or more alkali metals. For instance, the alkali metal may be a group II metal, such as magnesium and calcium. The metal silicate may also contain other metal species including ferrous and other non-ferrous minerals. The ferrous and other non-ferrous minerals may be present in addition to, or instead of, the alkali component of the metal silicate.

[0009] Although it is possible that the breaking step and the contacting step may be carried out consecutively, it is preferred that the breaking step and the contact step can be carried out concurrently, or at least partially concurrently. For instance, the breaking step can be commenced, and thereafter, the breaking step and the contacting step can be carried out together. In addition, it is also possible that there may be pauses in the breaking step whilst the feed gas is supplied during the contacting step. Alternatively, it is also possible that there may be pauses in the feed gas being supplied whilst the breaking step is carried out.

[0010] The feed ore may be transported to the vessel by any suitable means including a conveyor. However, suitably the feed ore is transported as a feed slurry to the vessel.

[0011] Moreover, the breaking step and the contacting step may be carried out in a vessel concurrently or at least partially concurrently. The vessel may or may not be divided into stages.

[0012] In one example, the breaking step and the contacting step may be carried out in at least one batch stage in which an amount of the feed ore is fed to the breaking step and broken down to a particle size distribution whilst the contacting step may be carried out to allow the metal silicate made available by the first particle size distribution to react and form the product which is thereafter discharged.

[0013] In another example, the breaking step and the contacting step may be carried out in two or more batches. That is, the breaking step and the contacting step may be carried out in a first batch stage. For example, the feed ore may be broken down to a first particle size distribution in the first batch stage, preferably whilst the contacting step is being carried out to allow the metal made available by the first particle size distribution to react and form metal carbonate. Following the first batch stage, the breaking step and the contacting step both continue in a second batch stage, where the first particle size distribution is reduced to a small second particle size distribution to make available additional metal, and the contacting step is carried out to react the additional metal to form additional product containing metal carbonate.

[0014] In another example, the breaking step and the contacting step are carried out in a continuous flow regime or a semi-continuously flow regime, in which the feed ore containing the metal silicate is continuously supplied or semi-continuously supplied to the process, and the product is discharged from the breaking and contacting steps continuously or semi-continuously. Although it is preferred that flows of the feed slurry and the product can be continuous, it is also possible that there may be pauses or interruptions in the flow of the feed slurry and / or the product. Moreover, it is possible that flow of the feed slurry and / or the product may occur in pulses.

[0015] The breaking step may include the use of any suitable breaking technique, such as and by no means limited to, any one or a combination of the following: i) tumbling milling, ii) vertical milling, iii) grinding, iv) crushing, v) jaw crushing, v) ultrasonic milling, and vi) autogenous milling. Tumbling milling and vertical milling may be carried out using milling devices that include crushing media such as balls and / or rods.

[0016] In one example, the breaking step may include breaking the feed ore using ultrasonic milling with or without any other breaking technique. In one situation, the breaking step may include aplurality of sub-steps, in which one sub-step uses the ultrasonic milling, and at least one other substep including any one or a combination of the following: i) tumbling milling, ii) vertical milling, iii) grinding, iv) crushing, v) jaw crushing, and v) autogenous milling, in which the sub-steps including ultrasonic milling is carried separately from the at least one other sub-step. In other words, the substep using the ultrasonic milling may be carried in one zone and the at least one other breaking step may be performed in a different zone. In other words, the feed ore and / or suspension being processed in the ultrasonic milling sub-step will be separate from the feed ore and / or suspension being processed in the at least one other breaking technique. As a result, an ultrasonic generator that performs the ultrasonic milling should ideally not be exposed to movement of the feed ore and / or suspension caused by the other breaking techniques. Moreover, the ultrasonic generator will not be exposed to crushing media such as moving balls and / or rods, crushing jaws, grinding wheels and so forth that damage the ultrasonic generator.

[0017] In another example, the breaking step may include breaking the feed ore using breaking technique including any one or a combination of the following: i) tumbling milling, ii) vertical milling, iii) grinding, iv) crushing, v) jaw crushing, and v) autogenous milling.

[0018] Generally speaking, a vertical milling device has an outer stationary casing, and an internal rotating column or screw, causing balls to be thrown up and spun round in a horizontal circular path. Thereby, milling the contents.

[0019] The process may also include a preliminary step in which raw ore is obtained from a mine and crushed to a size suitable for being transported to the process. For instance, the preliminary step may include passing the raw ore through a jaw crusher and then sizing, typically by means of sieving prior to being fed to the breaking step and the contacting step as the feed ore. The feed ore may have a maximum size of approximately 10mm, and suitably a size range of 0.01 mm to 5mm (optionally 2 mm to 5 mm). The discharged product may have a maximum size of approximately 2mm, and suitably a size of less than 1mm. Moreover, the majority of the particles of the product may be in the range from 0.1 to 10 micron, and suitably from 0.2 to 2 micron.

[0020] The feed gas may be obtained from a variety of sources, and has a range of concentrations of carbon dioxide.

[0021] In one embodiment, the feed gas may be rich in carbon dioxide, for example containing at least 80wt% carbon dioxide, and suitably at least 90wt% carbon dioxide.

[0022] In another embodiment, the feed gas may have a medium concentration of carbon dioxide, for instance in the range of 10 to 80wt%. In yet another embodiment, the feed gas may have a low concentration of carbon dioxide, for instance in the range of 2 to 10wt%.

[0023] The process may include a temperature controlling step to control the temperature of the process to an operating temperature ranging from 100°C to 210°C. Suitably, the operating temperature may be from 150°C to 200°C, more suitably from 180°C to 190°C, and even more suitably approximately 185°C.

[0024] In another example, the vessel may have external flanges or fins extending from the vessel and the external cooling medium may be ambient air.

[0025] The purpose of cooling the vessel is to avoid the contents of the vessel from heating above an operating temperature that hinders the rate of reaction. The reaction of carbon dioxide and metal silicate is exothermic, and in the event that the operating temperature exceeds a threshold temperature, such as 210°C, the operating temperature can reduce the reaction rate.

[0026] The temperature control step may include controlling the flow rate of a feed slurry to the process to adjust the operating temperature of the process. In other words, there is direct heat transfer between the feed ore, preferably in the form of a feed slurry and the aqueous suspension and / or the feed gas. The feed slurry may have a lower temperature than the operating temperature of the crushing and contacting steps, thereby lowering the operating temperature of the vessel.

[0027] The temperature control step may include a recuperative heat exchange step in which the product discharge transfers heat to the feed ore, which is preferably a feed slurry. The recuperative heat exchange may occur via a heater exchanger.

[0028] The temperature control step may include cooling a vessel in which the process is carried out using an external cooling medium to counteract the effects of the heats of reaction. The heats of reaction include the exothermic reaction between metal silicate and carbon dioxide.

[0029] For example, the vessel may include a cooling jacket and the cooling medium may be a cooling fluid, such as cooling water or air, that passes through the jacket.

[0030] The vessel may be operated at an elevated pressure, and may be referred to as a pressure vessel.

[0031] The process may include a pressure control step including controlling the pressure in the pressure vessel to an operating pressure that will comprise the partial pressure of saturated steam and the partial pressure of the feed gas.

[0032] The pressure control step may include controlling the pressure at which the feed gas is supplied to the pressure vessel.

[0033] The operational pressure of the pressure vessel may be in the range of 15 to 20 bar gauge. This pressure range is operable over a temperature range of 100°C to 210°C, and suitably at approximately 185°C. In addition, this pressure range assumes only nominal pressure loss over the vessel. In the event that the feed gas is fed at a depth in the aqueous suspension, i.e., the gas is bubbled through the aqueous suspension, it may be necessary to supply the feed gas at a pressure above the operational pressure of 15 to 20 bar gauge.

[0034] The process may include pressurizing the gas stream to the operating pressure of the pressure vessel.

[0035] Depending on the source of the feed gas, the feed gas may be pressurized to some extent as result of upstream processes. In any event, the process may include pressurizing the feed gas. Pressurizing the gas will increase the temperature of the feed gas.

[0036] The process may be carried out without adding any additional acid to the slurry. In any event, carbon dioxide acidifies the aqueous suspension in the pressure vessel. The aqueous suspension may have a pH of less than 7.

[0037] The process may include recovering power from the product via a power recovery device that is driven by the pressure and flow rate of the product discharge from the vessel.

[0038] The process may include a dewatering step in which the product discharged from the vessel undergoes dewatering to produce a concentrate suitable for use as an element in concrete.

[0039] The present invention also relates to a plant for reacting carbon dioxide with a metal silicate to produce a metal carbonate and silica, the plant including:

[0040] A plant for reacting carbon dioxide with a metal silicate to produce a metal carbonate and silica, the plant including: at least one breaking device in which metal silicate in a feed ore is broken down in the presence of water to form an aqueous suspension including particles of metal silicate; a gas source connected to the breaking device for supplying a feed gas including carbon dioxide, the feed gas contacting the aqueous suspension in the breaking device so a reaction between carbon dioxide and metal silicate can form a precipitant containing metal carbonate and silica,whereby in operation, the metal silicate is broken down progressively and reacts with the feed gas, such that as metal silicate is made available whilst being broken down and reacts with the feed gas, additional product containing metal carbonate and silica is produced.

[0041] The breaking device may include any one or a combination of the following: i) a tumbling mill, ii) a vertical mill, iii) a grinding mill, iv) crushing mill, v) jaw crushing mill, v) an ultrasonic mill, and vi) an autogenous mill.

[0042] The tumbling mill may include a tumbling pressure vessel having crushing media therein for crushing the feed ore.

[0043] The breaking device may include an ultrasonic milling device for breaking the feed ore using ultrasonic energy. In this instance, the breaking device may also include any one or combination of impact milling devices: i) a tumbling mill, ii) a vertical mill, iii) a grinding mill, iv) crushing mill, v) jaw crushing mill, and vi) an autogenous mill. The impact milling device and the ultrasonic milling device may be arranged consecutively relative to each other. In other words, the ultrasonic milling device, such as an ultrasonic generator thereof will not be exposed to the impact milling device of feed ore being processed on the impact milling device which could cause to the ultrasonic milling device.

[0044] The plant may include a compressor for pressurizing the feed gas.

[0045] The plant may include a controller for adjusting pressure of the feed gas supplied to the milling device.

[0046] The plant may include a controller that controls an operating temperature of the vessel, by adjusting the temperature of the feed ore supplied to the milling device.

[0047] In the situation in which the feed ore is a slurry, the plant may include heater exchanger for recuperative heater exchange between the product and the feed slurry.

[0048] The plant may include a pretreatment stage in raw ore is crushed to a predetermined size, and mixed with water to form the feed slurry.

[0049] The plant may include a power recover device converting pressure energy in the product to electrical power. In one example the recovery device may convert pressure energy of the product to mechanical energy for partially driving other equipment items.

[0050] The plant may include a dewater stage in which the product discharged from the vessel undergoes dewatering to produce a concentrate suitable for use as an element in concrete.

[0051] Breaking (e.g. a feed ore) may comprise crushing (e.g. a feed ore). The breaking step may comprise (e.g. be) a crushing step. Feed ore that is broken down may comprise (e.g. be) feed ore that is crushed. Particles of metal silicate (e.g. broken down metal silicate) may comprise (e.g. be) crushed metal silicate. Further, it will be understood that method steps that are carried out concurrently may be (e.g. partially) overlapping steps (e.g. taking place during time periods which at least partially overlap).

[0052] The plant may include any one or a combination of the features of the process described herein. Similarly, the process may include any one or combination of the features of the plant described herein.

[0053] Throughout this specification the terms "concurrently" and "simultaneously" are synonymous.BRIEF DESCRIPTION OF THE DRAWING

[0054] Figure 1 is a flow diagram illustrating a process and plant for reacting carbon dioxide with a metal silicate according to a preferred embodiment.DETAILED DESCRIPTION

[0055] A preferred embodiment will now be described with reference to Figure 1.

[0056] Figure 1 illustrates a process 10 and plant 20 including a breaking device 11 in the form of a milling device 13, suitably a horizontal milling device 13 or a vertical milling device, and a gas source 12. A feed ore 14 comprising course metal silicate ore is fed to the milling device 13, preferably as a feed slurry, where it is crushed to form an aqueous suspension. The milling device 13 may include crushing media such as balls, rods and alike that progressively break the course ore of the slurry into smaller particles when tumbled. In addition, the milling device 13 receives a feed gas 15 including carbon dioxide from the gas source at an elevated pressure. One or more swivel couplings, not shown in Figure 1 may be fitted to the milling device 13 for connecting to the gas source 12, slurry source 14 and product 16. Carbon dioxide supplied from the gas source 12 can dissolve into the aqueous suspension of the milling device 13 which acidifies the suspension to some extent and assists in dissolving metal silicate in the milled particles. In addition, the metal silicate reacts with carbon dioxide to form metal carbonate and silica, which precipitates and is discharged as a product slurry 16 from the milling device 13. The product 16 can be discharged from the vessel 13 at a controlled rate based on the selected operating parameters, including butby no means limited to: i) average residence time of the feed slurry in the milling device 13, or ii) the mass of carbon dioxide converted to precipitant per mass of the feed ore.

[0057] In other words, the process 10 includes a breaking step 30 in which metal silicate supplied in a feed slurry 19 to the milling device 13 is broken down to form the aqueous suspension, and a contacting step 31 in which the aqueous suspension is contacted with the feed gas 15 including carbon dioxide to form a precipitant such as a metal carbonate and silica. The breaking step 30 and the contacting step 31 are carried out progressively, such that as the breaking step 30 progresses additional metal silicate will be made available from within the ore or uncovered on the surface, and the contacting step 31 can proceed further by the carbon dioxide contacting the additional metal silicate from the breaking step 30 to form product 16 comprising additional metal carbonate and silica.

[0058] The earth's crust comprises a vast array of metal silicate minerals, which may be described by the following notation:• (metal S)A (metal b)s ...(metal x)MSIN OP (H2O)Q (formula 1)

[0059] The metal silicates may include any one or a combination of: an alkali metal, iron and other non-iron minerals. In one example, the metal silicate may be Olivine which has the following basic formula: MgAFeBSiO4, where A+B add up to approximately 2. At one extreme, Fayalite Olivine contains almost all iron (Fe) and at the other extreme Forsterite Olivine contains almost all magnesium (Mg). These alkali metal silicates aways have traces of other metals present. For example, one European sample of Forsterite contains traces of aluminium, chromium, nickel, and manganese. The alkali metal silicates may be Group II metals, such as magnesium and calcium. These Group-ll metals both form solid carbonates that are very stable. Olivine is of particular interest because it has the highest proportion of magnesium of all the silicates, and so the smallest mass of mineral is required per unit of carbon dioxide sequestered. Olivine is also one of the faster reacting silicates.

[0060] The acidity of the suspension in the milling device 13 may or may not be controlled. If desired, additional acid solution such as hydrogen chloride or sulfuric acid can be added to the milling device 13 to help dissolve alkali metal. However, one of the benefits of the process is that no additional acidifying agent needs to be added during the breaking step 30 and / or the contacting step 31.

[0061] Although the breaking device 11 shown in Figure 1 includes a milling device 13 having a tumbling vessel which generally rotates on a horizontal axis and contains media such as crushing balls, it will be appreciated that the breaking device 11 may include other types of breaking devices such as an ultrasonic milling device, a grinding mill device, or a vertical milling device. Generally speaking vertical milling devices comprise an outer stationary casing, and an internal rotating column or screw that causes balls to be thrown up and spun round in a horizontal circular path that crush the feed ore. Ultrasonic milling devices typically comprise an ultrasonic wave generator which emits waves at frequencies above the upper limit of the human hearing range, namely above approximately 20kHz. The ultrasonic energy may provide activation energy to facilitate chemical reactions, but more notably is likely to increase cracking of the feed ore which may have an enhancing effect by increasing surface area in much the same way as other milling devices. In addition cracking or splitting, the ultrasonic energy may remove an outer layer of material from the particles which exposes metal to carbon dioxide. In any event, although not shown in Figure 1, it is possible that the breaking step 30 and breaking device 11 of the process 20 and plant 10 respectively may be provided solely by an ultrasonic milling device without the use of any other milling device. In other examples, it is also possible that the breaking step 30 and the milling device 13 of the process 20 and plant 10 respectively may include an ultrasonic milling device in combination with one or more other milling device such as a vertical mill, a grinding mill, a crushing mill, jaw crushing mill, and an autogenous mill. In these situations, it is preferred that ultrasonic milling device may be arranged upstream and / or downstream of the one or more other milling device so as to minimize the potential harm that could be caused to the ultrasonic milling device if impacted by media of the other milling devices or by the feed ore shattering. In any event, the gas feed 15 may be supplied to any one of the breaking device 11 including the ultrasonic milling device if present, or supplied to any other milling device of the breaking device 11. Similarly, the feed gas 15 may be supplied to all, or part of, the breaking step 30.

[0062] The gas source 12 may be any suitable gas source, including a post combustion gas source, a flue gas source, a syngas source, a precombustion gas source, an enriched carbon dioxide source, and so forth. The enriched carbon dioxide source may supply carbon dioxide that has been captured from a lean carbon dioxide source, such as a flue gas stream. In one example, the gas source 12 may comprise from 5 to 80wt% carbon dioxide. In another example, the gas source 12 may comprise 80wt% or more carbon dioxide. In another example, the gas source 12 may supply the feed gas 15 with more than 85wt% carbon dioxide, or suitably approximately 90wt% carbon dioxide.

[0063] The process 10 may include a preliminary processing step, not shown in Figure 1, in which raw ore 23, including alkali metal silicate is obtained from a mine and crushed to a size suitable for the plant and process shown in Figure 1. The preliminary processing step may include passing the raw ore 23 through a jaw crusher and then sized, typically by means of a sieve screening prior to being used as the feed ore 14 to the breaking step 30.

[0064] The feed ore 14 may have a maximum size of approximately 10mm, and suitably a size range of less than 5mm and even more suitably to a size range of 5 to 2mm. However, it will be appreciated that the feed ore 14 may have a finer fraction. Although it is possible that the feed ore 14 could be a transported to the milling device 13 using any technique such as a conveyor, suitably the process 13 includes mixing the feed ore 14 with water 22 in a mixing tank 17 to form a slurry 19 and pumping the feed ore 14 as a slurry 19 at pressure to the milling device 13 via slurry pump 18.

[0065] During the breaking step, the feed ore 14 may be progressively broken down from a maximum size of approximately 10mm into smaller particles, suitably having a maximum size of approximately 2mm, and suitably a size of less than 1mm. Moreover, the majority of the particles of the product may be in the range from 0.1 to 10 micron, and suitably from 0.2 to 2 micron.

[0066] During the breaking step 30 and the contacting step 31, a layer of silica and / or alkali metal carbonate precipitant may form on an outer layer of the particles of the suspension. This layer may inhibit any alkali metal within the particles taking part in a reaction with carbon dioxide. As already mentioned, the breaking step 30 will progressively break the particles down over a period, suitably up to 2 hours. As the breaking step progresses, fresh alkali metal will be made available to react with carbon dioxide dissolved in the suspension and form more alkali metal carbonate, thereby maximizing the amount of the carbon dioxide that reacts to form alkali carbonate per unit mass of the feed ore 14. The fresh metal may be made available by the breaking step splitting the particles and / or by removing an outer layer from the particles. The outer layer may include one or a combination of metal carbonate or silica.

[0067] The process 10 may also include a temperature control step 32 in which the milling device 13 is maintained at an optimal temperature range for reacting carbon dioxide with the metal alkali. For example, the temperature control step may include operating the milling device 13 at an elevated temperature, for example, ranging from 100°C to 210°C. Suitably the temperature control step 32 may include operating the tumbling vessel 11 at an operational temperature from 180°C to 190°C, and even more suitably at an operation temperature of approximately 185°C. One of the benefits of the process 20 is that the energy used to operate the breaking step 30 will be converted into heat energy, mainly through friction between the particles of the suspension.

[0068] The temperature control step 32 may also include a recuperative heat exchange step 34 in which the product 16 discharged from the milling device 13 transfers heat to the feed slurry 19 prior to the breaking step 30 in a recuperative heat exchanger 21. The recuperative heat exchange step 34 reduces the heating load required to operate the milling device 13 at the optimal operating temperature.

[0069] The reaction of carbon dioxide and alkali metal is exothermic, and in an event that the operating temperature exceeds a threshold temperature, such as 210°C, the temperatures above the threshold temperature can reduce the reaction rate. To avoid the contents of the milling device 13 from heating above an operating temperature that hinders the rate of reaction, the temperature control step 34 may include reducing the operating temperature of the milling device 13, including cooling the milling device 13.

[0070] In one example, the temperature control step may include controlling the flow rate of a feed slurry 19 into the milling device 13 and / or cooling a recycling stream (not shown in Figure 1) about the milling device 13 to adjust the operating temperature of the milling device 13. In other words, there is direct heat transfer between the feed slurry 19 and the aqueous suspension and / or the feed gas 15 in the milling device 13. Although not shown in Figure 1, the temperature control step may include controlling the flow rate of a separate water stream (not illustrated) supplied to the milling device 13. The feed slurry 19 and the water stream may have a lower temperature than the operating temperature of the milling device 13, and adding the feed slurry 19 and the water stream can be used to lower the operating temperature of the milling device 13.

[0071] In another example, the temperature control step 32 may include cooling the milling device 13 using an external cooling medium. For example, the milling device 13 may include a cooling jacket and the cooling medium may be a cooling fluid, such as cooling water that passes through the jacket. The cooling medium leaving the jacket may then be used to heat other streams, including the feed slurry 19 or the feed gas 15. In another example, the milling device 13 may have external flanges or fins extending from the milling device 13 and milling device 13 can be cooled by heat being transferred to ambient air.

[0072] The process 20 also includes a pressure control step 33 to reduce the tendency of water in the slurry flushing on entering the milling device 13 and to reduce water evaporation in the milling device 13. The total pressure in the milling device 13 being the sum of the vapour pressure of the steam at the operating temperature and the partial pressure of the feed gas 15. The total operating pressure of the milling device 13 may range from 15 to 20 bar gauge.

[0073] As can be seen in Figure 1, the pressure control step 33 includes operating a compressor 23 and / or a control valve 24 downstream of an outlet of the compressor 23 to control the pressure of the feed gas 15 supplied to the milling device 13. In addition, compressing the feed gas 15 will raise the temperature of the feed gas 15 prior to being supplied into the milling device 13.

[0074] The process 20 may also include recovering power from the product 16 discharged from the milling device 13 using a power recovery device 25. The power recovering device 25 may be centrifugal or positive displacement in nature. In one example, a shuttle pump may be used as the power recovery device 25 for generating power by letting down pressure of the product 16. Power generated by the power recovery device 25 may be used to supply at least a portion of the power requirements of one or more of: i) a drive 26 for the milling device 13, ii) the compressor 23 for the feed gas 15, or iii) the slurry pump 18. In another example, the power recovery device 25 may convert pressure energy in the product to mechanical energy which could be used to partially drive equipment items such as the slurry pump 18.

[0075] The process 20 may also include a dewatering step 35 which can be carried out using any suitable solid-liquid separator 26. Examples include a settling pond or decanter centrifuge to produce recycle water 29 and a concentrate 27 containing an enriched stream of the alkali metal carbonate. The recycle water 29 may be recycled back to the mixing tank 17, as shown in Figure 1, to conserving water usage. In addition, another benefit is that the water recycle 29 will be hot which can to some extend preheat the feed slurry 19 in the mixing tank 17.

[0076] The concentrate 27 may be heaped for longer term storage and sequestration of carbon dioxide. It is also envisaged that the concentrate 27 may be used as a component in the manufacture of concrete.

[0077] Those skilled in the art of the present invention will appreciate that many variations and modification can be made to the preferred embodiment described herein without departing from the scope of the present invention.

[0078] In the claim which follows, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" and variations such as "comprises" or "comprising" are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the apparatus and method as disclosed herein.Reference numeral table

Claims

CLAIMS1. A process of reacting carbon dioxide with a metal silicate, the process including the step of: breaking a feed ore containing metal silicate and forming an aqueous suspension of particles of the feed ore; and contacting the aqueous suspension with a feed gas including carbon dioxide reacts with metal silicate so that a precipitant containing metal carbonate and silica forms; wherein the breaking step and the contacting step are carried out progressively, such that as the breaking step progresses, additional metal silicate will be made available and the contacting step can continue further to form a product containing additional metal carbonate.

2. The process according to claim 1, wherein the metal silicate includes an alkali metal such as magnesium or calcium.

3. The process according to any one of the preceding claims, wherein progressively carrying out the breaking step and the contacting step increases the conversion of metal silicate to metal carbonate and silica in the product per unit mass of the feed ore on a dry basis.

4. The process according to any one of the preceding claims, wherein the breaking step and the contact step are carried out concurrently, or at least partially concurrently.

5. The process according to any one of the preceding claims, wherein the feed ore is a feed slurry.

6. The process according to any one of the preceding claims, wherein the breaking step and the contacting step are carried out by the feed ore and the feed gas being supplied concurrently or at least partially concurrently in a milling device.

7. The process according to any one of the preceding claims, wherein the breaking step and the contacting step are carried out in at least one batch stages in which an amount of the feed ore is fed to the breaking step and broken down to a particle size distribution whilst the contacting step is being carried out to allow the alkali-metal made available by the first particle size distribution to react and form the product which is thereafter discharged.

8. The process according to any one of the preceding claims, wherein the breaking step and the contacting step are carried out in two or more batch stages, in which the breaking step and the contacting step are carried out in a first batch stage, in which the feed ore is broken down to a first particle size distribution in the first batch stage whilst the contacting step is being carried out to allow the metal silicate made available by the first particle size distribution to react and form metalcarbonate and silica, and subsequently the breaking step and the contacting step both continue in a second batch stage, in which the first particle size distribution is reduced to a small second particle size distribution to provide additional metal silicate, and the contacting step is carried out to react the additional alkali-metal to form the product containing additional metal carbonate and silica.

9. The process according to any one of the preceding claims, wherein the breaking step and the contacting step are carried out in a continuous flow regime or a semi-continuously flow regime, in which the feed ore containing the alkali metal silicate is continuously supplied or semi- continuously supplied to the process, and the product is discharged from the breaking and contacting steps continuously or semi-continuously.

10. The process according to any one of the preceding claims, wherein the breaking step includes any one or a combination of the following: i) tumbling milling, ii) vertical milling, iii) grinding, iv) crushing, v) jaw crushing, v) ultrasonic milling, and vi) autogenous milling.

11. The process according to any of the preceding claims, wherein the breaking step includes a plurality of sub-steps, in which one sub-step uses the ultrasonic milling, and at least one other substep including any one or a combination of the following: i) tumbling milling, ii) vertical milling, iii) grinding, iv) crushing, v) jaw crushing, and v) autogenous milling, in which the sub-steps including ultrasonic milling is carried separately from the at least one other sub-step.

12. The process according to any one of claims 1 to 9, wherein the breaking step may include breaking the feed ore using breaking technique including any one or a combination of the following: i) tumbling milling, ii) vertical milling, iii) grinding, iv) crushing, v) jaw crushing, and v) autogenous milling.

13. The process according to any one of claims 1 to 9, wherein the breaking step includes tumbling milling and / or vertical milling in which either one uses a crushing media.

14. The process according to any one of the preceding claims, wherein the feed ore has a maximum size of approximately 10mm, and suitably a size range of 2 to 5mm.

15. The process according to any one of the preceding claims, wherein the product discharged has a maximum size of approximately 2mm, and suitably a major portion of the product has product size range of 0.2 to 2 micron.

16. The process according to any one of the preceding claims, wherein the feed gas is rich in carbon dioxide, for example containing at least 80wt% carbon dioxide, and suitably at least 90wt% carbon dioxide.

17. The process according to any one of the preceding claims, wherein the feed gas has a concentration of carbon dioxide in the range of 10 to 80wt%.

18. The process according to any one of the preceding claims, wherein the process includes a temperature controlling step so the process is operated at a temperature ranging from 100°C to 210°C, suitably the operating temperature is from 150°C to 200°C, more suitably from 180°C to 190°C, and even more suitably approximately 185°C.

19. The process according to claim 18, wherein the temperature control step includes a recuperative heat exchange step in which the product discharged transfers heat to the feed ore.

20. The process according to claim 18 or 19, wherein the temperature control step includes cooling a vessel in which the process is carried out using an external cooling medium to counteract heats of reaction.

21. The process according to claim 20, wherein the vessel has a cooling jacket and the cooling medium is a cooling fluid, such as cooling water, that passes through the jacket.

22. The process according to claim 20 or 21, wherein the vessel has external flanges or fins extending from the vessel for transferring heat to ambient air.

23. The process according to any one of claims 18 to 22, wherein the temperature control step includes controlling the flow rate and / or temperature of the feed ore to adjust the operating temperature of the process.

24. The process according to any one of the preceding claims, wherein the process is carried out at an operational pressure that is elevated.

25. The process according to claim 24, wherein the elevated pressure is in the range from 15 to 20 bar gauge.

26. The process according to any one of the preceding claims, wherein the process includes a pressure control step include controlling an operating pressure at which at the least contacting step is carried out and optionally the breaking step, wherein the operating pressure comprises partial pressure of saturated steam and the partial pressure of the feed gas.

27. The process according to any one of claims 23 to 25, wherein the pressure control step includes controlling the pressure at which the feed gas is supplied.

28. The process according to any one of the preceding claims, wherein the process includes recovering power via a power recovery device that is driven by the pressure and flow rate of the product discharged.

29. The process according to any one of the preceding claims, wherein the process includes a dewatering step in which the product discharged undergoes dewatering to produce a concentrate suitable for use in concrete.

30. A plant for reacting carbon dioxide with a metal silicate to produce a metal carbonate and silica, the plant including: at least one breaking device in which metal silicate in a feed ore is broken down in the presence of water to form an aqueous suspension including particles of metal silicate; a gas source connected to the breaking device for supplying a feed gas including carbon dioxide, the feed gas contacting the aqueous suspension in the breaking device so a reaction between carbon dioxide and metal silicate can form a precipitant containing metal carbonate and silica, whereby in operation, the metal silicate is broken down progressively and reacts with the feed gas, such that as metal silicate is made available whilst being broken down and reacts with the feed gas, additional product containing metal carbonate and silica is produced.

31. The plant according to claim 30, wherein the breaking device includes any one or a combination of the following: i) a tumbling mill, ii) a vertical mill, iii) a grinding mill, iv) crushing mill, v) jaw crushing mill, v) an ultrasonic mill, and vi) an autogenous mill.

32. The plant according to claim 30 or 31, wherein the breaking device includes an ultrasonic milling device for breaking the feed ore using ultrasonic energy and any one or combination of the following impact milling devices: i) a tumbling mill, ii) a vertical mill, iii) a grinding mill, iv) crushing mill, v) jaw crushing mill, and vi) an autogenous mill, wherein the impact milling device and the ultrasonic milling device may be arranged consecutively relative to each other.

33. The plant according to any one of claims 30 to 32, wherein the tumbling device includes a horizontal mill having crushing media therein for breaking the feed ore.

34. The plant according to any one of claims 30 to 32, wherein the milling device is a vertical ball-mill, in which the outer casing is stationary, and an internal column rotates, causing crushing media to move in circular horizontal circular path.

35. The plant according to any one of claims 30 to 34, wherein the feed ore is a slurry, and the plant includes a heater exchanger for recuperative heater exchange between the product and the feed slurry.

36. The plant according to any one of claims 30 to 35, wherein the plant includes a controller that controls an operating temperature of the milling device, by adjusting the temperature of the feed ore supplied to the vessel.

37. The plant according to any one of claims 30 to 36, wherein the plant includes a compressor for pressurizing the feed gas.

38. The plant according to any one of claims 30 to 37, wherein the plant includes a controller for adjusting pressure of the feed gas supplied to the vessel.

39. The plant according to any one of claims 30 to 38, wherein the plant includes a power recovery device converting pressure energy in the product to electrical power.

40. The plant according to any one of claims 30 to 39, wherein the plant includes a recovery device for transferring pressure energy of the product to mechanical energy.

41. The plant according to any one of claims 30 to 40, wherein the plant includes a dewater stage in which the product discharged from the vessel undergoes dewatering to produce a concentrate suitable for use as an element in concrete.

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