Precipitation of calcium compounds in solvent extraction systems

Abstract

The invention relates to a solvent extraction method for removing calcium. In the method, an aqueous extraction solution is dispensed in an organic phase having a lower density than the aqueous extraction solution. The steps of the method include dispensing droplets of an aqueous extraction solution in an upper portion of a solvent extraction unit, passing the droplets through an organic phase towards a bottom of the solvent extraction unit, collecting the droplets at the bottom of the solvent extraction unit into an aqueous phase layer, and removing the aqueous slurry containing the precipitated calcium compound from the bottom portion of the aqueous phase layer at the bottom of the solvent extraction unit. The invention also relates to a solvent extraction unit for carrying out the method according to the invention.

Description

Technical Field

[0001] The present invention relates to a solvent extraction method and a solvent extraction unit for removing calcium. Background Art

[0002] In the field of hydrometallurgy, solvent extraction is a widely used method for separating metal ions. Currently, such systems are designed to be used only with liquids, so precipitates and solids must be avoided at all costs. The presence of solids in current solvent extraction systems will cause several problems because the solids will block the flow and equipment, and may also form stable emulsions, which will have a negative impact on the separation process.

[0003] In some extraction methods, precipitate compounds may form when ions are mass transferred between two liquid phases. To avoid the above problems, the amount of the aqueous phase and / or the organic phase must be adjusted to keep the precipitate compounds in solution. This is especially true for calcium-containing compounds derived from, for example, raw materials, neutralizing agents, or influent water in a metal leaching process. Since calcium may cause problems in subsequent steps of the separation method, it is beneficial to remove the excess calcium.

[0004] Calcium-based neutralizing chemicals are usually inexpensive and readily available. Therefore, calcium-based chemicals, such as limestone (CaCO3) or lime (Ca(OH)2), may be good choices for pH control in the solvent extraction process. The disadvantage is that calcium compounds may easily precipitate in the presence of counter ions, thus clogging the equipment. This problem becomes particularly evident in sulfate-based solutions by forming gypsum, which tends to adhere to the surface of the equipment in solid form.

[0005] In the prior art, precipitation is avoided by increasing the relative volume of the aqueous phase so that chemical equilibrium has not been reached, thus keeping the calcium compounds in solution. This method may require a large amount of water, which may be a very limited resource in some places, such as some regions in Australia, Africa, and Asia. In addition, this will increase the amount of wastewater generated in the method. Moreover, the feed water may also contain a relatively high amount of calcium, especially in desert areas, thus reducing the efficiency of the calcium removal method. Current methods are usually carried out with the highest possible stage efficiency, reaching 98% or higher. In order not to use more water than necessary, the water leaving the extraction process is almost saturated with respect to calcium compounds (such as calcium sulfate).

[0006] Current extraction methods still rely on strong mixing to increase the reaction surface area and the mass transfer of metals between the aqueous and liquid phases. This creates further problems when there are precipitates or solid materials present, as strong mixing tends to create emulsions, and the solid materials become incorporated into them. In particular, gypsum is prone to forming crud, which is an emulsion of the organic phase, aqueous phase, and solids. The newly formed gypsum is highly reactive and tends to adhere to the inner surfaces of solvent extraction units and pipes. When gypsum is formed under strong mixing, organic matter is typically incorporated into the wet precipitate, and the mixing further guides the precipitate into contact with the inner surfaces of the equipment. The accumulation of gypsum in the equipment makes it necessary to perform regular maintenance shutdowns.

[0007] There are some prior art solutions that utilize alternative flow arrangements rather than mixing. For example, both EP2614868B1 and US2022 / 0332751A1 describe liquid-liquid extraction units. In EP 2614868B1, the unit is arranged as a countercurrent unit, where the aqueous phase in the form of bubbles enters from an upper inlet in one sidewall, and the organic phase in the form of bubbles enters from a lower inlet. US 2022 / 0332751A1 relates to a multi-stage device for liquid-liquid extraction, where the liquids are arranged to flow from one baffle to another. Neither of these two publications addresses the removal of precipitates, although US2022 / 0332751A1 briefly touches on the issue, stating that maintenance can be reduced due to the lack of pipes connecting each stage.

[0008] Given the above problems of the prior art, there is still a need for a solvent extraction method and system that more effectively utilizes water resources during the calcium removal process. Summary of the Invention

[0009] The present invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0010] According to a first aspect of the present invention, there is provided a solvent extraction method for removing calcium. In this method, an aqueous extraction solution is distributed in an organic phase having a density lower than that of the aqueous extraction solution, and the method further includes the following steps:

[0011] - Distributing droplets of the aqueous extraction solution in the upper part of a solvent extraction unit,

[0012] - Causing the droplets to travel through the organic phase towards the bottom of the solvent extraction unit, collecting the droplets in an aqueous phase layer at the bottom of the solvent extraction unit, and

[0013] - At the bottom of the solvent extraction unit, removing an aqueous slurry containing precipitated calcium compounds from the bottom portion of the aqueous phase layer.

[0014] Accordingly, a first aspect of the present invention relates to a method for removing calcium in a solvent extraction system. Droplets of an aqueous phase are distributed in an organic phase, and calcium compounds are precipitated in the aqueous droplets. The droplets travel downward and are collected in an aqueous layer, from which a precipitate is formed.

[0015] According to a second aspect of the present invention, there is provided a solvent extraction unit having an aqueous extraction solution inlet and an organic solvent outlet at an upper portion of the unit. The solvent extraction unit further comprises:

[0016] - an extraction solution distributor located at a level below the organic solvent outlet and configured to distribute the aqueous extraction solution from the inlet in the form of aqueous droplets in the organic phase,

[0017] - an organic solvent inlet located at the bottom of the solvent extraction unit,

[0018] - a concentrator section for collecting the precipitate in the bottom of the solvent extraction unit, wherein the concentrator section is located at a level below the organic solvent inlet in the bottom of the solvent extraction unit and includes a structure for guiding the precipitate towards the bottom of the solvent extraction unit, and

[0019] - a slurry outlet connected to the concentrator section.

[0020] Accordingly, a second aspect of the present invention relates to a solvent extraction unit suitable for implementing the method of the first aspect of the present invention. The solvent extraction device is configured to generate droplets of an aqueous phase within the organic phase. In addition, the solvent extraction system includes means for collecting and removing solid matter.

[0021] The present invention is based on the finding that by utilizing an alternative reaction mode that allows precipitate formation, the amount of water required to remove calcium in a solvent extraction method can be significantly reduced. Current solvent extraction systems cannot tolerate precipitates, so the calcium component must be kept in solution. It has been found that by confining the formation of calcium precipitates to aqueous phase droplets, thereby preventing the precipitate from contacting the organic phase, the problem of precipitate accumulation within the extraction system can be avoided.

[0022] Significant advantages are achieved using the present invention. Contamination of the solvent extraction unit and maintenance downtime due to accidental precipitation can be avoided. In addition, since readily available and affordable reagents can be used, the profitability of the method can be increased. Sulfuric acid can be obtained at low cost, and using sulfuric acid in the current system requires a large amount of water to prevent the formation of gypsum in the presence of calcium ions. Therefore, the water consumption in the method and system of the present invention can be significantly reduced to about 5% of the water consumption in conventional methods and systems. Accordingly, the method and system of the present invention provide a more environmentally friendly and economical method for calcium removal during metal recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 shows a solvent extraction unit according to at least some embodiments of the present invention.

[0024] Figure 2 shows a solvent extraction unit of an advantageous embodiment, wherein the unit is provided with means for recycling the aqueous extraction solution.

[0025] In Figure 1 and 2 the aqueous solution is represented by the slant line (A), while the organic phase is represented by the white area (B) within the device. The aqueous phase droplets are collected in the aqueous phase layer at the bottom of the solvent extraction unit, which is also shown by the slant line. The horizontal dashed line shows the division between the upper part of the aqueous layer (representing the layer that is directed to any recycling line) and the bottom part including the concentrator section, from which the calcium-containing slurry is withdrawn. This dashed line is merely illustrative and does not represent any physical part of the device. Similarly, the ratio between the liquid phase and the organic phase can be different from that shown in Figure 1 and Figure 2 and accordingly the positions of the inlets and outlets can also vary. Detailed Description

[0026] Definitions

[0027] In the context of the present invention, the term "solvent extraction" includes all kinds of liquid-liquid extractions in which two liquid phases of different properties interact such that mass transfer can occur from one phase to the other.

[0028] The functional principle of the solvent extraction system described herein is presented in a vertical extraction system. The distributed aqueous phase travels downward in the vertical system due to the density difference (i.e., by gravity). Accordingly, expressions such as "upper" or "upper part" should be understood as the upper half of the system or the upper half of the relevant section (layer, part, etc.) when viewed from the ground plane. Correspondingly, "bottom" or "bottom section" should be understood as the lower half of the system or the lower half of the relevant section when viewed from the ground plane.

[0029] The present invention relates to a solvent extraction method for removing calcium, wherein an aqueous extraction solution is distributed in an organic phase having a density lower than that of the aqueous extraction solution. The method comprises the following steps:

[0030] - distributing droplets of the aqueous extraction solution in the upper part of a solvent extraction unit, wherein the diameter of the distributed droplets is from 0.1 mm to 2 mm, preferably from 0.5 mm to 2 mm,

[0031] - causing the droplets to travel through the organic phase towards the bottom of the solvent extraction unit, collecting the droplets in an aqueous phase layer at the bottom of the solvent extraction unit, and

[0032] - At the bottom of the solvent extraction unit, an aqueous slurry containing precipitated calcium compounds is removed from the bottom portion of the aqueous phase layer.

[0033] In such a solvent extraction method, calcium is transferred to the aqueous extraction solution. The extraction solution contains counterions capable of forming a precipitate with calcium. Preferably, the extraction solution is acidic, and even more preferably, it is an aqueous solution of sulfuric acid. The aqueous solution passes through the calcium-containing organic phase in the form of droplets. The organic phase may contain, for example, an organophosphorus-based extractant such as the commercial reagent D2EHPA or Cyanex 272, or C9-C10 carboxylic acids, but is not limited thereto. Since the density of the aqueous droplets is higher than the surrounding organic medium, the droplets travel downward under the action of gravity. Calcium is transferred to the aqueous extraction solution that becomes saturated, and then, by reacting with the counterions present in the aqueous extraction solution, calcium compounds precipitate within the droplets. The aim is to achieve a controlled precipitation of calcium compounds within the droplets such that the precipitate is transferred together within the droplets to the aqueous phase layer formed by collecting the droplets at the bottom of the solvent extraction unit. The precipitate settles in the concentrator section at the bottom of the solvent extraction unit, and the precipitate can be removed from this concentrator section in the form of a slurry, i.e., a suspension containing the precipitated calcium compounds. Since calcium is allowed to precipitate in the reaction, there is no need to add water to maintain the calcium compound concentration below the solubility equilibrium point. Therefore, compared with the currently adopted methods, the water consumption of this method is significantly reduced. When sulfuric acid is used in the extraction solution, it has been found that the water consumption can be as low as 3-7% of the water consumption of the corresponding conventional method.

[0034] In a preferred embodiment, the aqueous extraction solution is recycled from the aqueous phase layer at the bottom of the solvent extraction unit to the droplet distribution stage at the upper part of the solvent extraction unit, where makeup water is added to the recycled aqueous extraction solution before droplet distribution. In this way, the water consumption can be further reduced. When an acidic extraction solution is used, acid can be added to the makeup water. The volume ratio of the aqueous phase to the organic phase is generally kept constant in the extraction system and can be, for example, 1:1 - 1:10, preferably a volume ratio of 1:2 - 1:10, 1:2 - 1:5, or 2:3 - 1:3. Fluctuations within a predetermined range can be allowed, for example, the volume of the aqueous phase can increase or decrease by up to 10% or up to 20%. By keeping the volume ratio substantially constant, the fluid circulation also becomes more reliable because phase mixing can be avoided. When a reagent (such as sulfuric acid) is added to the extraction solution to maintain the counterion concentration at a certain level, the amount of the added reagent can also be kept constant when the volume ratio and composition of the two phases are kept constant.

[0035] To avoid mixing of phases and unnecessary solids being transferred to the recycle line, the recycle water outlet is optimally arranged at a level close to the interface between the organic and aqueous phases, but still such that the outlet of the recycle solution is always in complete contact only with the aqueous phase during operation. This means that the distance between the extraction solution outlet and the interface between the aqueous and organic phases should be large enough to allow the volume of the aqueous layer to decrease within a predetermined fluctuation range without the extraction solution outlet coming into contact with the organic phase. In this way, water is directed to recycle from the upper part of the aqueous phase layer within the solvent extraction unit.

[0036] Since the acidic extraction solution is neutralized when reacting with calcium, an acid can be added to the make-up water to maintain the pH value or its ionic concentration of the extraction solution at a substantially constant level, e.g., within ±15% of a predetermined value or starting value. Preferably, the volume ratio of the recycled aqueous extraction solution to the make-up water is 1:1 - 20:1, or even more preferably 5:1 - 20:1. Thus, the volume of the recycled aqueous solution is 1 - 20 times the volume of fresh water (i.e., make-up water) added to the process.

[0037] The droplets formed in the droplet distribution step should be large enough to be able to effectively travel through the organic phase and serve as a precipitation environment for calcium compounds. Precipitation starts when calcium is transferred from the calcium-bearing organic phase to the droplets of the aqueous extraction solution containing an anti-ion (such as sulfate ions). When the droplets are allowed to fall through the organic phase due to density differences, the formed precipitate will remain within the droplets provided that no mixing or only moderate mixing occurs. If the droplets are atomized into mist-like water droplets, each individual droplet will not provide a large enough volume for precipitation to occur without the precipitate itself coming into contact with the surrounding organic phase. In addition, such small droplets move very slowly in the organic phase. On the other hand, droplets that are too large will have a negative impact on the mass transfer of calcium ions from the organic phase to the aqueous extraction solution because the relative contact surface area between the phases decreases. To achieve the desired effect, the suitable diameter of the droplets distributed in the upper part of the solvent extraction unit is 0.1 mm to 2 mm, preferably 0.5 mm to 2 mm. Such droplets can be formed, for example, by a nozzle arrangement preferably including a plurality of nozzles, or by a distribution system including a plurality of openings that allow the formation of droplets of the desired size within the organic solvent used. Thus, the generated droplets are relatively small but still larger than the droplets formed by a turbine.

[0038] In an optimal system, when traveling through the organic phase towards the aqueous phase layer in the bottom of the solvent extraction unit, the droplets of the aqueous extraction solution substantially maintain their initial size. This can be achieved in the absence of mixing or when only a moderate mixing corresponding to a mixing tip speed of at most 1 m / s, preferably at most 0.5 m / s, is applied. In yet another preferred embodiment, when reaching the aqueous phase layer in the bottom of the solvent extraction unit, the diameter of the droplets is from 0.1 mm to 2 mm, preferably from 0.5 mm to 2 mm.

[0039] In another embodiment of the present disclosure, the droplets are dispensed by an extraction solution dispenser which is arranged at a level horizontally lower than the organic solvent outlet level in the solvent extraction unit. In the foregoing embodiment, the dispensing device guides the droplets downward into the organic phase, covering an area of at least 70%, preferably at least 85%, even more preferably at least 95% of the total horizontal cross-sectional area of the solvent extraction unit 1. This ensures a uniform distribution of the droplets in the organic phase.

[0040] In a particularly preferred embodiment of the present disclosure, the acidic aqueous phase contains sulfuric acid (H2SO4). Sulfate ions form gypsum when reacting with calcium, whereby the calcium-precipitating compound in the aqueous slurry is gypsum (CaSO4·2H2O). Sulfuric acid is the cheapest available inorganic acid, so it is highly advantageous to be able to use it in the solvent extraction process. In conventional systems where precipitation cannot be tolerated, this may not be possible or a large amount of water may need to be added to keep the formed calcium sulfate in solution. Simply put, by being able to utilize sulfuric acid in the method of the present disclosure, the profitability of the method is increased.

[0041] The calcium precipitate formed in the aqueous droplets is transferred to the bottom of the solvent extraction unit, which preferably serves as a concentrator for guiding solid matter to the bottom of the solvent extraction unit. The aqueous slurry containing the precipitated calcium compound is removed through the slurry outlet at the bottom of the unit, preferably from the lowermost section of the concentrator. The solid content can be, for example, 10, 15 or 20% to 25, 30 or 40%. According to one embodiment of the present disclosure, the solid content of the aqueous slurry containing the precipitated calcium compound removed from the solvent extraction unit is 10 - 60%, such as 10 - 40% or 10 - 20%. The aqueous slurry of gypsum can be relatively easily removed even at a relatively high solid content.

[0042] In the steps of collecting the precipitate and removing the slurry, the problem of calcium precipitate adhering to the inner surface of the device can become an issue, especially in the case of gypsum. Therefore, it is preferred that at least the bottom of the solvent extraction unit (which comes into contact with the collected aqueous layer and the calcium precipitate slurry) is coated with a reagent that reduces surface friction, such as a polymer coating, such as a fluoropolymer coating, such as a polyvinylidene fluoride (PVDF), perfluoroalkoxy alkane (PFA), or polytetrafluoroethylene (PTFE) coating. For the same reason, it is advantageous to design the solvent extraction unit such that the shape of the bottom section of the solvent extraction unit directs the flow towards the slurry outlet. To protect the pump line from clogging and wear, it is advantageous to arrange a guiding plate connected to the slurry outlet line to direct solid matter away from any pump connected to the concentrator section.

[0043] As described above, the aqueous solution droplets are preferably kept intact when transferred towards the bottom of the solvent extraction unit. To achieve this, it is preferred to carry out the method without mixing. Alternatively, moderate mixing can be carried out such that the mixing does not break the droplets formed in the upper part into smaller droplets. Naturally, in the method of the present disclosure, any such gentle mixing or stirring can be carried out by any mixing means known in the art, such as by using one or more slowly rotating mixing blades or by the direction of liquid flow. In a preferred embodiment, any mechanical mixing is carried out with a tip speed of at most 1 m / s, preferably at most 0.5 m / s. This is a very low mixing rate compared to the mixing rates, such as 5 m / s, used in conventional solvent extraction units aimed at obtaining as high (e.g., >98%) a stage efficiency. In conventional units, a mixing rate of about 5 m / s can be applied to increase the contact surface between the two phases, thus making mass transfer more effective, while in the system of the present disclosure, a mixing rate in a similar range will break the droplets of the aqueous extraction solution into smaller droplets, thereby increasing the risk of contact between the precipitate and the organic phase. Therefore, the precipitate is also more likely to come into contact with the organic phase. When using such conventional mixing, the problem of calcium precipitate depositing on the inner surface of the unit occurs. Similarly, when the aqueous droplets remain intact, the amount of organic phase lost in the extraction stage is minimized.

[0044] When no mixing or only moderate mixing is applied, the stage efficiency is reduced. However, it has been found that, contrary to extraction systems used for metal recovery (i.e., production extraction), in the system of the present disclosure, the main purpose is to remove calcium that may cause problems later in the process, and a relatively low stage efficiency of 10 - 50% or even 10 - 20% is sufficient. It is not necessary to remove all of the calcium in one method stage as long as the calcium contained in the organic phase is not allowed to accumulate. The lower stage efficiency can also be compensated for by internal recycling of the aqueous phase.

[0045] The present invention also relates to a solvent extraction unit 1 having an aqueous extraction solution inlet 3 and an organic solvent outlet 7 at the upper part of the unit 1. Additionally, the solvent extraction unit 1 comprises:

[0046] - an extraction solution distributor 2, which is located at a level below the organic solvent outlet 7 and is configured to distribute the aqueous extraction solution from the inlet 3 in the form of aqueous droplets 4 in the organic phase,

[0047] - an organic solvent inlet 6, which is located at the bottom of the solvent extraction unit 1,

[0048] - a concentrator section 8 for collecting the precipitate in the bottom of the solvent extraction unit 1, wherein the concentrator section 8 is located at a level below the organic solvent inlet 6 in the bottom of the solvent extraction unit 1 and comprises a structure for guiding the precipitate towards the bottom of the solvent extraction unit 1, and

[0049] - a slurry outlet 5 connected to the concentrator section 8.

[0050] Such a solvent extraction unit is as Figure 1 shown and is suitable for implementing the method of the present invention. Compared with the solutions of the prior art, the solvent extraction unit of the present invention is configured to allow solid matter, typically in the form of a precipitate. When allowing the formation of a precipitate during the extraction or extraction process, the water feed can be reduced because there is no need to adjust the amount of solvent to keep the calcium compound in solution.

[0051] The solid matter formed in the method is collected in a concentrator located at the bottom of the solvent extraction unit, and the slurry (i.e., a suspension of solid matter and aqueous solution) is removed from this concentrator through the slurry outlet 5 in the bottom of the solvent extraction unit 1. The concentrator 8 guides the solid matter towards the bottom of the reactor. This is preferably achieved by providing a concentrator having a structure (such as circular or conical) that tapers towards the bottom. The slurry outlet 5 can be connected to the lowermost part of such a concentrator section. The concentrator can include additional structures, such as guide plates, baffles or shields, which guide the solid matter in a desired direction, typically towards the bottom of the solvent extraction unit, and / or protect any pumps or additional outlets located in the concentrator section from the influence of the precipitate. Since solid calcium compounds may have the property of easily sticking to the walls of the equipment, such as gypsum, it is preferred to coat any surface with a coating that reduces surface friction. In particular, steel surfaces are prone to contamination, whereby gypsum tends to accumulate on the surface and block the flow connections. By providing such a low-friction coating for the inner surface of the solvent extraction unit 1, especially for the inner surface of the concentrator section 8, the need for system maintenance is reduced and the flow of the slurry is improved. Different types of low-friction coatings are known in the art. Many polymer coatings, such as polytetrafluoroethylene (PTFE), paints and linings are suitable for this purpose.

[0052] In a particularly preferred embodiment of the present disclosure, the solvent extraction unit 1 further includes an extraction solution outlet 9, which is located at the bottom of the solvent extraction unit, at a level below the organic solvent inlet 6 and above the slurry outlet 5, wherein the extraction solution outlet 9 is fluidly connected to the make-up water supply line 10 and the extraction solution inlet 3. The extraction solution outlet 9 fluidly connected to the extraction solution inlet 3 provides the possibility of circulating the aqueous extraction solution, thereby further reducing the water consumption of the system. Since at least a part of the aqueous solution introduced via the inlet 3 is removed through the slurry outlet 5, fresh make-up water needs to be introduced to compensate for the aqueous solution removed together with the slurry, so as to maintain the system balance. The make-up water can be introduced via the supply line 10, i.e., the make-up water inlet, which is also fluidly connected to the extraction solution inlet 3. An acid or another aqueous solution containing a reactive counterion can be added to the make-up water to maintain the precipitation reaction at a desired level.

[0053] In another embodiment of the present disclosure, the extraction solution distributor 2 includes a plurality of fluid distribution openings arranged at a certain distance from each other, and the ratio of the distance between two adjacent openings to the diameter of the opening is: 2:1 - 20:1, preferably 3:1 - 10:1 or 5:1 - 10:1. Therefore, the distance between the openings is sufficient to form separate droplets, that is, the distance between the droplets is not too close so that they will combine, but still within a range where sufficient efficiency can be achieved. To form droplets with a desired size of 0.1 - 2 mm, the openings can be in a similar range of 0.05 - 2 mm or 0.1 - 2 mm. The arrangement of the droplet openings with a uniform distribution can minimize the degree of interaction between the droplets and can maximize the droplet distribution within the organic phase volume, because the droplets are dispersed and generated in a controlled manner.

[0054] In a further preferred embodiment, the extraction solution distributor 2 extends through at least 70% of the total horizontal cross-sectional area of the solvent extraction unit, preferably through at least 85% of the total horizontal cross-sectional area of the solvent extraction unit, and even more preferably through at least 95%. By arranging the distributor so that as wide an area as possible can be accessed, the efficiency of the system is improved. In addition, by arranging the distributor, the droplets fall straight down in the vertical direction, thereby minimizing the interaction between the surrounding droplets. Compared with point distribution, for example, using a single nozzle system arranged in the area of the vertical central axis of the system, the droplets formed in point distribution are also dispersed in the horizontal or partially horizontal direction, making the droplet flow more unpredictable. The distributor system can be arranged such that the organic phase can pass through the distributor system, for example, by arranging a network of multiple distribution systems or distribution openings.

[0055] It should be understood that the embodiments of the present invention disclosed herein are not limited to the specific structures, method steps or materials disclosed herein, but extend to their equivalents that would be recognized by those of ordinary skill in the relevant art. It should also be understood that the terms used herein are for the purpose of describing specific embodiments only and are not intended to be limiting.

[0056] References to "an embodiment" or "one embodiment" throughout the specification mean that the particular features, structures, or characteristics described in connection with that embodiment are included in at least one embodiment of the invention. Thus, the phrases "in an embodiment" or "in one embodiment" that appear throughout the specification do not necessarily all refer to the same embodiment.

[0057] As used herein, for convenience, a plurality of items, structural elements, constituent elements, and / or materials may be presented in a common list. However, these lists should be interpreted as if each member of the list is individually identified as a separate and unique member. Thus, without contrary indication, any single member of such a list should not be construed as a de facto equivalent of any other member of the same list solely based on their presentation in the common group. In addition, various embodiments and examples of the present invention may be referred to herein together with alternatives to its various components. It should be understood that such embodiments, examples, and alternatives should not be construed as de facto equivalents of one another, but rather as separate and autonomous representations of the present invention.

[0058] Although the above examples illustrate the principles of the present invention in one or more specific applications, it will be apparent to those of ordinary skill in the art that many modifications can be made in form, use, and details of implementation without exercising creativity and without departing from the principles and concepts of the present invention. Accordingly, the present invention is not intended to be limited except as by the following claims.

[0059] The following non-limiting examples are only intended to illustrate the advantages obtained through the embodiments of the present invention.

[0060] Examples

[0061] Example 1 - Calcium Removal

[0062] A 35 m 3 / h aqueous feed is sent to a solvent extraction process. In the extraction unit, calcium is extracted into the organic phase. The calcium-containing organic phase is directed to a liquid-liquid extraction step. The aqueous extraction solution is distributed in the organic solvent in the form of droplets, and the volume ratio of the aqueous solution to the organic solvent is 1:10. It is taken out from the bottom of the solvent extraction unit at 1 m 3Flow of the gypsum precipitate slurry is collected at 1 m / h. The gypsum slurry has a solids content of 10%. The aqueous solution is recycled from the bottom of the solvent extraction unit to the inlet, and makeup water is added at a rate of 1 m 3 / h, corresponding to the volume of the removed slurry.

[0063] In a conventional system where precipitation is not allowed, the extraction solution flow rate must be equal to the aqueous feed flow rate, i.e., 35 m 3 / h.

[0064] Industrial Applicability

[0065] The method and system of the present invention can be used to replace traditional solvent extraction for calcium removal.

[0066] In particular, the method provides a resource - efficient procedure for calcium removal in metal separation methods. The amount of water required is only a small fraction of that in traditional methods, and the method can also use affordable reagents.

[0067] List of Reference Numerals

[0068] 1. Solvent extraction unit

[0069] 2. Extraction solution distributor

[0070] 3. Extraction solution inlet

[0071] 4. Aqueous droplets (formed in the extraction solution distributor)

[0072] 5. Slurry outlet

[0073] 6. Organic solvent inlet

[0074] 7. Organic solvent outlet

[0075] 8. Concentrator section

[0076] 9. Extraction solution outlet

[0077] 10. Makeup water supply line

[0078] 11. Extraction solution circulation pump

[0079] List of Citations

[0080] Patent Documents:

[0081] EP 2614868 B1

[0082] US 2022 / 0332751 A1

Claims

1. A solvent extraction method for removing calcium, in which an aqueous extraction solution is partitioned in an organic phase having a density lower than that of the aqueous extraction solution, characterized in that, The method includes: - Dispensing droplets of the aqueous extraction solution in the upper part of the solvent extraction unit, wherein the diameter of the dispensed droplets is from 0.1 mm to 2 mm, preferably from 0.5 mm to 2 mm, - Causing the droplets to travel through the organic phase towards the bottom of the solvent extraction unit, collecting the droplets in the aqueous phase layer at the bottom of the solvent extraction unit, and - At the bottom of the solvent extraction unit, removing the aqueous slurry containing the precipitated calcium compound from the bottom part of the aqueous phase layer.

2. The method according to claim 1, wherein Recycling the aqueous extraction solution from the aqueous phase layer at the bottom of the solvent extraction unit to the droplet dispensing stage at the upper part of the solvent extraction unit, wherein makeup water is added to the recycled aqueous extraction solution before the droplet dispensing.

3. The method according to claim 2, wherein The volume ratio of the recycled aqueous extraction solution to the makeup water is 1:1 - 20:

1.

4. The method according to any one of the preceding claims, characterized in that, When reaching the aqueous phase layer at the bottom of the solvent extraction unit, the diameter of the droplets is from 0.1 mm to 2 mm, preferably from 0.5 mm to 2 mm.

5. The method according to any one of the preceding claims, characterized in that, The droplets are dispensed by an extraction solution dispenser which is arranged at a level horizontally lower than the organic solvent outlet level in the solvent extraction unit, wherein the dispensing device guides the droplets downward into the organic phase, covering an area of at least 70% of the total horizontal cross-sectional area of the solvent extraction unit, preferably at least 85% of the total horizontal cross-sectional area of the solvent extraction unit.

6. The method according to any one of the preceding claims, characterized in that The aqueous phase contains sulfuric acid (H2SO4), whereby the precipitated calcium compound in the aqueous slurry is gypsum (CaSO4·2H2O).

7. The method according to any one of the preceding claims, characterized in that, The solid content of the aqueous slurry containing the precipitated calcium compound removed from the solvent extraction unit is 10 - 60%, for example 10 - 40% or 10 - 20%.

8. The method according to any one of the preceding claims, characterized in that, The method is carried out without mixing.

9. The method according to any one of claims 1-7, characterized in that, Any mechanical mixing is carried out at a tip speed of at most 1 m / s, preferably at most 0.5 m / s.

10. A solvent extraction unit (1) having an aqueous extraction solution inlet (3) and an organic solvent outlet (7) at the upper part of the solvent extraction unit (1), characterized in that, The solvent extraction unit (1) further includes: - An extraction solution dispenser (2) which is located at a level lower than the organic solvent outlet (7) and is configured to dispense the aqueous extraction solution from the aqueous extraction solution inlet (3) in the form of aqueous droplets (4) in the organic phase, - An organic solvent inlet (6) which is located at the bottom of the solvent extraction unit (1), - A concentrator section (8) for collecting the precipitate at the bottom of the solvent extraction unit (1), wherein the concentrator section (8) is located at a level in the bottom of the solvent extraction unit (1) lower than the organic solvent inlet (6) and includes a structure for guiding the precipitate towards the bottom of the solvent extraction unit (1), and - A slurry outlet (5) connected to the concentrator section (8).

11. The solvent extraction unit (1) according to claim 10, characterized in that, The solvent extraction unit (1) further includes an extraction solution outlet (9) which is located at the bottom of the solvent extraction unit, at a level lower than the organic solvent inlet (6) and higher than the slurry outlet (5), wherein the extraction solution outlet (9) is in fluid connection with the makeup water supply line (10) and the aqueous extraction solution inlet (3).

12. The solvent extraction unit (1) according to claim 10 or 11, characterized in that, The extraction solution dispenser (2) includes a plurality of fluid distribution openings arranged at a certain distance from each other, and the ratio of the distance between two adjacent openings to the diameter of the opening is 2:1 - 20:1, preferably 3:1 - 10:

1.

13. The solvent extraction unit (1) according to any one of claims 10-12, characterized in that, The extraction solution dispenser (2) extends through at least 70% of the total horizontal cross-sectional area of the solvent extraction unit, preferably through at least 85% of the total horizontal cross-sectional area of the solvent extraction unit.

14. The solvent extraction unit (1) according to any one of claims 10-13, characterized in that, The concentrator section (8) includes a guiding plate which is arranged to protect any pump connected to the concentrator section (8) from sediment.

15. The solvent extraction unit (1) according to any one of claims 10 - 14, characterized in that, The inner surface of the solvent extraction unit (1), in particular the surface of the concentrator section (8), is coated with a polymer coating to prevent sediment from adhering to the inner surface of the solvent extraction unit (1). Preferably, the surface is coated with a fluoropolymer coating such as a polyvinylidene fluoride (PVDF), perfluoroalkoxy alkane (PFA), or polytetrafluoroethylene (PTFE) coating.

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