Process for the extraction of metal species using liquid-liquid reactive extraction

Abstract

The invention relates to a method for the extraction of metal species from an aqueous solution using liquid-liquid reactive extraction.

Description

Technical Field

[0001] This invention relates to a method for extracting metallic substances from aqueous solutions using liquid-liquid reactive extraction. Background Technology

[0002] "Extraction" generally refers to any separation method in which an extractant is used to separate one or more components from a mixture of substances. In liquid-liquid extraction, a solute is extracted from a liquid by means of a liquid extractant, where the different solubilities of the components to be separated in two immiscible solvents are utilized. Typically, a hydrophilic phase (e.g., water) and a hydrophobic organic solvent are used as the immiscible solvents. One application of liquid-liquid extraction is the selective separation of metal ions, which is becoming increasingly important in the fields of electric vehicles and waste battery reprocessing.

[0003] Typically, reactive extraction is based on the so-called extraction isotherm, which indicates the distribution of the metal in the aqueous (AP) and organic (OP) phases for a given pH value. The extractability E represents the proportion of the metal M in the organic phase, and is a ratio based on the total amount of metal in both phases. Theoretically, E can take any value between 0 and 1, or between 0% and 100%.

[0004] In the field of battery recycling, in particular, the separation of cobalt, nickel, manganese, and lithium from aqueous solutions is of great importance. Existing technologies describe various methods for optimizing this separation.

[0005] Metal extraction is based on a specific form of extraction known as reactive extraction. In this form of solvent extraction, the compound to be extracted is transferred to another phase by reacting with substances dissolved in the extractant. The equations below illustrate the basic chemical reactions and the distribution of different substances in the aqueous and organic phases, typically indicated by underlined symbols.

[0006]

[0007]

[0008] Where M represents a metal ion, R represents an acid residue, and K represents the equilibrium constant.

[0009] As can be seen from the expression for the equilibrium constant, this equilibrium is pH-dependent. Therefore, at low pH values, i.e., from a highly acidic aqueous medium, metals with high affinity (represented by a high equilibrium constant K value) have been extracted, while metals with low affinity can only be extracted from the aqueous phase at higher pH values. The pH value can be set, for example, by adding a basic compound (such as NaOH), which captures the protons formed during the reaction.

[0010] Reactive extraction for the separation of metal ions is well known. Therefore, in the paper "Synergistic effect of Cyanex 272 and Cyanex 302 on separation of cobalt and nickel by D2EHPA" published by D. Darvishi et al. in Hydrometallurgy77 (2005) 227-238, the advantages that can be achieved in the separation of cobalt and nickel by activating the complexing agent D2EHPA with Cyanex 272 and Cyanex 302 are described.

[0011] PKParhi et al. reported the separation of nickel and cobalt from ammoniacal sulfate solution using Cyanex 272. Their results were published in "Separation of cobalt and nickel from ammoniacal sulfate solution using Cyanex 272", Separation and Purification Technology 59 (2008), 310-317.

[0012] In “Extraction / Separation of Cobalt by Solvent Extraction: A Review”, Appl. Chem. Eng. Vol. 26, No. 6, 2015, 631-639, B. Swain et al. outlined different methods for separating cobalt.

[0013] In their article “New Cationic exchangers for the recovery of cobalt(I), nickel(I) and manganese(I) from acidic chloride solutions: Modelling of extraction curves” published in Hydrometallurgy 180 (2018) 96-103, K. Omelchuk et al. described novel extractants for separating the mentioned metals.

[0014] NB Devi et al. described the separation of cobalt(II) and nickel(II) from sulphate solutions using sodium salt of D2EHPA, PC 88A and Cyanex 272 in Hydrometallurgy 49 (1998) 47-61.

[0015] EP 2 614 868 discloses the use of a liquid-liquid extraction unit to contact an aqueous phase with an organic phase, separate them, and obtain a desired extract from the separated aqueous and / or organic phases.

[0016] In “Simultaneous recycling of nickel metal hydride, lithium ion and primary lithium batteries: Accomplishments of European Guidelines by optimizing mechanical pre-treatment and solvent extraction operations”, published in Journal of Power Sources 212 (2012) 205-211, G. Granata et al. described the solvent extraction of Co and Mn, in which the extraction of Co Cyanex 272 was achieved at a Cyanex / Co ratio of 4 at pH 5, and the extraction of Mn D2EHPA was achieved at a D2EHPA / Mn ratio of 2 at pH 5-6.

[0017] In another published article, “Product recovery from Li-ion battery wastes coming from an industrial pre-treatment plant: Lab scale tests and process stimulations,” published in Journal of Power Sources 206 (2012) 393-401, G. Granata et al. described the recovery of Co and Li using Cyanex 272 partially saponified with NaOH and D2HEPA.

[0018] In the paper “Separation of cobalt and nickel via solvent extraction with Cyanex-272: Batch experiments and comparison of mixer-settlers and an agitated column ascontactors for continuous counter-current extraction” in Separation and Purification Technology 296 (2022) 121326, IRR Rodrigues et al. used Cyanex-272 to separate Co and Ni via solvent extraction with the pH set to 6.

[0019] US 3,666,446 discloses a pH adjustment method for separating Cu and Co, wherein the pH value is adjusted through an ion exchange reaction.

[0020] US 4,353,883 describes the separation of Co and Ni from an aqueous solution in the presence of an extractant, wherein the extractant is a phosphonic acid having at least 6 carbon atoms.

[0021] In “Resource recovery of critically-rare metals by hydrometallurgical recycling of spent lithium ion batteries”, published by R. Sattar et al. in Separation and Purification Technology 209(2019) 725-733, it is known that a two-stage solvent extraction with Cyanex 272 was performed at pH 5.0, in which Cyanex was saponified at 50%.

[0022] All these methods share the common fact that, despite the uncertainties associated with the importance of pH, separation is based on the extraction isotherm at a pH determined to be "optimal," where the pH often must be finely adjusted. Another drawback of the known methods is that they typically require a large excess of extractant.

[0023] pH is usually defined as the negative decimal logarithm of the hydrogen ion activity of a given solution: pH = -lg a (H + ) The technique described for separating metal ions uses pH as a control variable, which is generally accepted, although pH measurements are subject to many uncertainties in practice.

[0024] In particular, this means that the measured pH value is not suitable for inferring the actual H₂ of the solution. + Concentration, specifically pH, is an unsatisfactory and uncertain control variable in the context of the reactive extraction described herein, making it difficult to operate the process stably. This is especially true when the operating range includes a maximum value of only a few tenths of a pH unit. Summary of the Invention

[0025] Therefore, in this context, there is a need for an improved method to separate metallic substances from aqueous solutions and obtain them in a very pure form, preferably one that eliminates the need for pH as a control variable.

[0026] Within the scope of this invention, it has been surprisingly found that by using an activated extractant and by setting a definite stoichiometric ratio of the activated extractant to the metal to be extracted, pH can be omitted as a control variable for liquid-liquid reactive extraction of metals from aqueous solutions.

[0027] Therefore, the present invention first relates to a method for extracting metallic substances from aqueous solutions using liquid-liquid reactive extraction, the method comprising the following steps: a) Provide an aqueous phase containing at least one metallic substance to be extracted; b) Provide an organic phase containing an extractant for extracting the metallic substance to be extracted; c) Activate the extractant in the organic phase with an activating agent; d) Contact the aqueous phase with the organic phase from step c); e) Separate the aqueous phase and the organic phase containing at least partially extracted metallic substances. The activated extractant and the metal substance to be extracted have a defined stoichiometric ratio. Its characteristic is that no active pH control occurs.

[0028] Unbound by theory, it is assumed that the extractant promotes the transfer of metallic substances from the aqueous phase to the organic phase. Therefore, according to the invention, the extractant is activated. Because a predetermined stoichiometric supply of the activated extractant adapted to the separation problem is provided based on the metallic substance to be extracted, pH can be eliminated as a control variable for the operating point, and uncertainties associated with pH determination can be avoided. The ratio of the activated extractant to the metallic substance to be extracted represents the ratio of the amount of activator (e.g., Na+) matched to each other according to the invention to the amount of the metallic substance to be extracted.

[0029] In extraction, the general goal is to find an acceptable balance between the quality and purity of the extractable substance and the yield. Within the scope of the method according to the invention, it has been surprisingly found that the extractable substance can be recovered with high purity and high yield due to process control independent of pH.

[0030] Within the scope of the method according to the invention, the extractant is activated by an activator. Activation of the extractant preferably takes place before contact between the aqueous and organic phases. Therefore, the activator is preferably added to the organic phase in an amount necessary to match the amount of the metal to be extracted before contact with the aqueous phase. This pre-contact can be carried out continuously or in a batch mode.

[0031] The method according to the invention specifies that an activated extractant is provided at a predetermined ratio to the metal to be extracted. Surprisingly, it has been found that the separation performance and selectivity of the extraction can be controlled by adjusting this ratio, thus the method can preferably be carried out independently of active pH control. Therefore, in a preferred embodiment, the method according to the invention further includes the step of adjusting the stoichiometric ratio of the activated extractant to the metal to be extracted according to a previously determined ratio.

[0032] The stoichiometric ratio can be adjusted, for example, based on the concentration of the metal to be extracted. Therefore, one embodiment of the method according to the invention is preferred, wherein the concentration of at least the metal to be extracted in the aqueous phase is determined in an upstream step.

[0033] The extractant is preferably selected from the group consisting of complexing agents and liquid ion exchangers, thus enabling it to form a complex with the metal to be extracted. In a particularly preferred embodiment, the extractant is selected from the group consisting of organophosphonic acids, organophosphonic acids, and organophosphates. Even more preferred extractants are selected from the group consisting of bis(2-ethylhexyl)phosphoric acid (D2EHPA), bis(1,3-dibutoxypropyl-2-yl)phosphoric acid (Bidiopp), bis(1,3-diisobutoxypropyl-2-yl)phosphoric acid (IPA), bis(5,8,12,15-tetraoxanonadecan-10-yl)phosphoric acid (TPA), bis(undecane-6-yl)phosphoric acid (UPA), bis(1,3-dioctyloxypropyl-2-yl)phosphoric acid (OPA), bis(1,3-di-2-ethylhexyloxypropyl-2-yl)phosphoric acid (EHPA), and bis(2,4,4-trimethylpentyl)phosphonic acid (Cyanex 272). Furthermore, mixtures using the extractants listed above have proven particularly advantageous, as have mixtures using branched monocarboxylic acids and other organic acids; therefore, they are preferred for use within the scope of this invention. Corresponding products are, for example, marketed under the trade name Versatic. TM Acid was obtained through commercial purchase.

[0034] The activator activates the extractant, for example, by deprotonation. Therefore, the activator is preferably matched to the extractant. The activator can be selected, for example, from the group consisting of alkali metal hydroxides and / or ammonia. In particular, the activator is sodium hydroxide or lithium hydroxide. In this case, the activation of the extractant and the subsequent extraction of the valuable metal can be represented by the following two equations, wherein the amount of activated extractant is matched to the amount of the metal to be extracted.

[0035] activation:

[0036] extraction:

[0037] Surprisingly, in controlling this process, it was found that when the extractant was activated with an aqueous sodium hydroxide solution, the sodium hydroxide could be completely absorbed by the organic phase. Using an aqueous sodium hydroxide solution with a concentration of at least 40% by mass or higher has proven particularly advantageous. (Used in Escaid) TM (For example, 20% by mass of D2EPAH, available from Exxon Mobil), yielded good results at 50°C with a 20% by mass diluted aqueous sodium hydroxide solution. Furthermore, activation with a 40% by mass aqueous sodium hydroxide solution surprisingly produced a single phase that remained stable even after cooling to room temperature. This approach greatly simplifies the technical implementation. No phase separation occurs, and the activation stoichiometry can be precisely controlled via accurate mass flow rates in a precisely defined manner, without relying on pH or other control variables. The desired activation ratio of the extractant can be adjusted directly or, alternatively, after activation, by mixing it into the unactivated organic phase.

[0038] The method according to the invention aims to separate metallic substances, with transition metals and rare earth metals being particularly preferred. The metallic substances are preferably selected from the group consisting of: cobalt, nickel, manganese, iron, copper, magnesium, aluminum, and lithium. Specifically, the metallic substances are cobalt, nickel, manganese, and aluminum.

[0039] The organic phase is immiscible with the aqueous phase. Therefore, within the scope of the method according to the invention, aliphatic hydrocarbons and aromatic hydrocarbons, and mixtures thereof, are preferably used as the organic phase. Among these substances, kerosene or Escaid, such as that available commercially from Exxon Mobile, is particularly suitable. TM 120 has proven to be particularly appropriate.

[0040] The method according to the invention is primarily applicable to large-scale industrial applications and is preferably carried out as a continuous process in a multi-stage countercurrent flow. In another preferred embodiment, the method according to the invention is carried out in an intermittent mode.

[0041] The method according to the invention not only allows for the extraction of metallic substances from aqueous solutions but can also be used for the selective separation of several metallic substances from each other. Therefore, an embodiment in which the aqueous phase contains at least one other metallic substance that is at least partially retained in the aqueous phase is preferred. Adjusting the corresponding stoichiometric ratio can not only improve separation performance but also limit the amount of other metallic substances co-transferred into the organic phase, thereby achieving a desired ratio of metallic substances in the organic phase. To ensure the purity of the major component, a washing step can be performed after extraction, more preferably for the purpose of enhancing extraction, wherein the charged organic phase is contacted, for example, with a pure solution of the major component and / or a mineral acid (especially sulfuric acid), thereby displacing minor components again from the organic phase, for example, separating transition metals in a sulfate system. Therefore, the method according to the invention also includes a washing step after extraction.

[0042] The method according to the invention is an improvement on conventional separation methods that rely on pH as a controlled variable. Therefore, embodiments in which the method is not subject to any pH-dependent control are preferred. Although pH can be measured as an indicator within the scope of the method according to the invention, it is preferable to add the required amount of activator at the desired location by precise gravimetric measurement, preferably via a Coriolis mass flow meter. Particularly when using an extraction column, it is preferable to use an activated extractant and a determined stoichiometric ratio.

[0043] The method according to the invention can be carried out in a mixer-settler battery or in an extraction tower, with performance preferred in the extraction tower. Suitable extraction towers are known to those skilled in the art, and preferably have material exchange elements for increasing the contact area and mixing between the organic and aqueous phases.

[0044] The present invention also relates to an apparatus for performing the method according to the invention, wherein the apparatus comprises a reactor for contacting an aqueous phase with an organic phase, and wherein the reactor has at least one outlet for collecting the aqueous phase and / or the organic phase.

[0045] The suitable reactor in the apparatus according to the invention particularly includes a mixing and clarification tank assembly and an extraction tower, wherein the extraction tower is preferred. Using an extraction tower significantly reduces space requirements, and the circulation rates of the organic and aqueous phases can be kept low. Furthermore, the use of an extraction tower ensures a certain degree of continuity in the countercurrent flow, where only one phase boundary needs to be adjusted at the top or bottom of the tower. Moreover, the construction cost of the tower is significantly lower compared to a large mixing and clarification tank assembly.

[0046] In another preferred embodiment, the device according to the invention further includes a module for pre-contacting the organic phase with the activator.

[0047] The present invention is further explained by the following embodiments and accompanying drawings, but these embodiments and drawings should in no way be construed as limiting the concept of the present invention. Attached Figure Description

[0048] Figure 1 An exemplary process for the extraction efficiency in the separation of Mn, Cu, Co, and Ni ions is schematically illustrated, where for E=0, the corresponding metal is completely retained in the aqueous phase, and E=1 indicates complete transfer to the organic phase. Thus, for example, with changes in solution acidity, an organic phase containing most Cu and Mn ions and an aqueous purified product in which most Co and Ni ions are retained can be obtained. Therefore, the separation of different metals can be selectively controlled according to the dominant acidity.

[0049] Figure 2 and Figure 3 This represents the extraction isotherms of cobalt and nickel, determined experimentally. Figure 2 This indicates a separately recorded isotherm, while Figure 3 The extraction isotherms represent aqueous solutions containing equal concentrations of the two metals. According to the method of the invention, competitive behavior regarding the shortage of the extractant supply can be clearly observed. Because cobalt has a higher affinity for the extractant, it inhibits the co-extraction of nickel, causing the isotherms to diverge sharply. The undesirable nickel fraction can then be removed from the organic phase containing both metals by contact with a washing solution containing only cobalt, or by washing with a mineral acid such as sulfuric acid. It should be noted that a single extraction stage is shown here. High yields and high purity can then be achieved simultaneously by employing countercurrent operation in both the extraction and washing processes. Suitable apparatus includes a mixing and clarification tank and a column. Detailed Implementation

[0050] Example The method according to the invention was tested in the first batch of settings.

[0051] A 600 mL solution containing equimolar amounts of Co and Ni (40 g / L Co and 39.88 g / L Ni) was prepared from the corresponding chloride salt and contacted with 1576 mL of an organic solution containing 20 mol% bis(2-ethylhexyl)phosphoric acid (DEHPA) as the extractant under stirring. A 50% NaOH solution was used as the activator at 40 °C. Table 1 shows the stoichiometric ratios of the extractant, the aqueous sodium hydroxide solution, and the Co to be extracted. After phase separation, the contents of Co and Ni in the organic and aqueous phases were determined, respectively. Table 2 summarizes the analytical results.

[0052] Table 1:

[0053] Table 2:

[0054] *Distribution coefficient: D=M OP / M AP Where M = Co, Ni; OP: organic phase; AP: aqueous phase As can be seen from the table, the method according to the present invention achieves efficient separation of Co and Ni through reactive extraction of Co from the aqueous phase. The separation factor (ω=D) is obtained from the partition coefficient D determined based on the measured concentration. Co / D Ni The separation factor was 79. Comparative experiments conducted at pH 3.5, using the same extractant and under the same extraction conditions showed a separation factor of 3. Therefore, the method according to the invention can achieve a significant improvement in selectivity.

[0055] Therefore, the method according to the invention is a simple and effective alternative to pH-controlled extraction, since only the amount of the metal to be extracted needs to be known.

[0056] The separation performance can be further improved by using a continuous process. Therefore, the above experiment was repeated in a continuously operating mixing and clarification tank. The experiment was repeated using six mixing and clarification tank units, each with a volume of 350 ml, in which the organic phase was pre-contacted with a 200 g / L NaOH solution.

[0057] After a 16-hour test duration, based on the measured concentrations of Co and Ni in Table 3, the partition coefficients D(Co) = 20.77 and D(Ni) = 0.011 can be calculated. Based on this, the separation factor (ω = DCo / DNi) is obtained as 1888.

[0058] Table 3:

Claims

1. A method for extracting a metallic substance from an aqueous solution using liquid-liquid reactive extraction, the method comprising the following steps: a) Provide an aqueous phase containing the metal to be extracted; b) Provide an organic phase comprising an extractant for extracting the metal substance to be extracted; c) Activate the extractant in the organic phase with an activating agent; d) Contact the aqueous phase and the organic phase from step c); e) Separate the aqueous phase and the organic phase containing at least partially extracted metallic substances. The activated extractant and the metal substance to be extracted have a defined stoichiometric ratio. Its characteristic is that no active pH control occurs.

2. The method according to claim 1, characterized in that, The activation of the extractant is performed before the aqueous phase comes into contact with the organic phase.

3. The method according to at least one of the preceding claims, characterized in that, The method further includes the step of adjusting the stoichiometric ratio of the activated extractant to the metal substance to be extracted.

4. The method according to at least one of the preceding claims, characterized in that, In the upstream step, the concentration of at least the metal substance to be extracted in the aqueous phase is determined.

5. The method according to at least one of the preceding claims, characterized in that, The extractant is selected from the group consisting of complexing agents and liquid ion exchangers.

6. The method according to at least one of the preceding claims, characterized in that, The method also includes the step of washing the separated organic phase.

7. The method according to at least one of the preceding claims, characterized in that, The extractant is selected from the group consisting of: organic phosphonic acids, organic phosphonic acids, and organic phosphoric acids, particularly from the group consisting of: bis(2-ethylhexyl)phosphoric acid (D2EHPA), bis(1,3-dibutoxypropyl-2-yl)phosphoric acid (Bidiopp), bis(1,3-diisobutoxypropyl-2-yl)phosphoric acid (IPA), bis(5,8,12,15-tetraoxanonadecan-10-yl)phosphoric acid (TPA), bis(undecane-6-yl)phosphoric acid (UPA), bis(1,3-dioctyloxypropyl-2-yl)phosphoric acid (OPA), bis(1,3-di-2-ethylhexyloxypropyl-2-yl)phosphoric acid (EHPA), and bis(2,4,4-trimethylpentyl)phosphonic acid (Cyanex 272); mixtures of the aforementioned extractants, and mixtures of branched monocarboxylic acids with other organic acids.

8. The method according to at least one of the preceding claims, characterized in that, The activator is selected from the group consisting of alkali metal hydroxides, especially sodium hydroxide or lithium hydroxide.

9. The method according to at least one of the preceding claims, characterized in that, The metallic substance is selected from the group consisting of transition metals and rare earth metals, particularly from the group consisting of cobalt, nickel, manganese, iron, copper, magnesium, aluminum and lithium, especially the metallic substance being cobalt, nickel, manganese and aluminum.

10. The method according to at least one of the preceding claims, characterized in that, The organic phase is selected from the group consisting of aliphatic hydrocarbons and aromatic hydrocarbons and mixtures thereof.

11. The method according to at least one of the preceding claims, characterized in that, The method is operated as a batch process or a continuous process.

12. The method according to at least one of the preceding claims, characterized in that, The aqueous phase contains at least one other metallic substance, wherein the other metallic substance is at least partially retained in the aqueous phase.

13. The method according to at least one of the preceding claims, characterized in that, The method is not subject to any pH-dependent control, and is particularly characterized by the fact that no pH measurement occurs.

14. The method according to at least one of the preceding claims, characterized in that, The method is carried out in an extraction tower.

15. An apparatus for performing the method according to the invention, wherein the apparatus comprises a reactor for contacting an aqueous phase with an organic phase, and wherein the reactor has at least one outlet for collecting the aqueous phase and / or the organic phase.

16. The apparatus according to claim 15, characterized in that, The reactor is an extraction tower, and / or the apparatus further includes a module for pre-contacting the organic phase with the activator.

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