A method for stepwise recovery of magnesium and calcium from high-salinity brine

Abstract

This invention relates to a method for the stepwise recovery of magnesium and calcium from high-salinity brine. The method includes the following steps: first, mixing the high-salinity brine with an extraction system for extraction to obtain an organic phase loaded with magnesium and calcium; then, mixing the magnesium- and calcium-loaded organic phase with a first back-extraction system for a first back-extraction to obtain a magnesium back-extraction solution and a calcium-loaded organic phase; subsequently, mixing the calcium-loaded organic phase with a second back-extraction system for a second back-extraction to obtain a calcium back-extraction solution; the high-salinity brine contains Cl... ‑ The concentration is ≥150 g / L, and the extraction system includes a combination of β-diketone extractants and neutral phosphorus extractants; the method achieves efficient separation and recovery of magnesium and calcium in high-salinity brine, Mg 2+ / Ca 2+ The separation coefficient is preferably as high as 2000 or more, Mg 2+ The recovery rate is preferably as high as 99.5% or more; Ca 2+ The recovery rate is preferably as high as 99.0%.

Description

Technical Field

[0001] This invention relates to the field of calcium and magnesium separation and recovery technology in salt lake brine, and more particularly to a method for stepwise recovery of magnesium and calcium from high-salinity brine. Background Technology

[0002] Magnesium (Mg) and calcium (Ca), as important metallic elements, have wide applications in various fields such as chemical engineering, construction, medicine, and agriculture. Traditionally, magnesium and calcium are mainly obtained from mineral resources. However, with the increasing prominence of environmental problems, finding new resource recovery pathways has become particularly important. High-salinity brines, as a natural resource rich in various metal ions, including seawater, salt lake brines, and certain industrial wastewater, contain high concentrations of magnesium and calcium ions. The rational development and utilization of these brine resources can not only provide an alternative source of magnesium and calcium but also reduce environmental pollution and achieve resource recycling.

[0003] However, the efficient recovery of magnesium and calcium from high-salinity brines faces a series of technical challenges. Firstly, the magnesium content in high-salinity brines... 2+ and Ca 2+ It is often accompanied by various other ions such as Na + K + and Cl - This increases the difficulty of separation; secondly, Mg 2+ and Ca 2+ Magnesium and calcium have similar chemical properties, making it difficult for traditional separation techniques to achieve highly selective separation. To address this issue, previous studies have attempted to recover magnesium and calcium using techniques such as chemical precipitation, solvent extraction, ion exchange, and membrane separation; however, these methods still have shortcomings in terms of processing efficiency and cost control.

[0004] For example, CN112174170A discloses a dual-alkali combined method for deep magnesium removal from salt lake brine. This process uses sodium carbonate and sodium hydroxide to precipitate magnesium and achieve magnesium precipitation separation. However, it not only consumes a large amount of alkali, but also makes the filtration process of the alkaline magnesium slag difficult and difficult to operate continuously. Moreover, the alkaline magnesium slag is a hazardous waste that is extremely difficult to handle and may even cause serious harm to the environment. In addition, the loss of lithium during the precipitation process leads to low recovery efficiency.

[0005] CN118531230A discloses a method and system for separating calcium, magnesium and lithium from brine with a low magnesium-to-lithium ratio. The method uses an extraction system containing aromatic carboxylic acid compounds as the extractant, and also adds N263 or dimethyl di(N-octadecyl)ammonium chloride quaternary ammonium salt as a co-extractant. Furthermore, it requires conversion by adding alkali before extraction can be performed. Therefore, this method still requires alkali consumption, and the extraction system is complex and costly. Moreover, it mainly separates calcium and magnesium from lithium, but does not achieve the separation of calcium and magnesium.

[0006] Therefore, there is an urgent need to develop a new method for the stepwise recovery of magnesium and calcium from high-salinity brines, which can improve the recovery efficiency and selectivity of magnesium and calcium, reduce energy consumption and costs, and reduce environmental impact. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for the stepwise recovery of magnesium and calcium from high-salinity brine. The extraction process of this method does not require the consumption of acids or alkalis, and can achieve efficient stepwise separation and recovery of magnesium and calcium from high-salinity brine under relatively mild conditions. No hazardous waste residue or acid / alkali waste liquid is generated, reducing the impact on the environment. Furthermore, the entire process is simple to operate, uses widely available raw materials, and has low separation and recovery costs.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] This invention provides a method for the stepwise recovery of magnesium and calcium from high-salinity brine, the method comprising the following steps:

[0010] (1) Extraction was carried out by mixing high-salt brine and extraction system to obtain an organic phase loaded with magnesium and calcium;

[0011] (2) Mix the magnesium-calcium-loaded organic phase and the first back-extraction system to perform a first back-extraction, to obtain a magnesium back-extraction solution and a calcium-loaded organic phase;

[0012] (3) Mix the calcium-loaded organic phase and the second back-extraction system to perform a second back-extraction to obtain a calcium back-extraction solution;

[0013] Among them, the Cl in the high-salt brine in step (1) - The concentration is ≥150 g / L (e.g., it can be 150 g / L, 160 g / L, 170 g / L, 180 g / L, 190 g / L, 200 g / L, 210 g / L, 220 g / L, 230 g / L, 240 g / L or 250 g / L, etc.), and the extraction system is a combination of β-diketone extractants and neutral phosphorus extractants.

[0014] The method described in this invention utilizes Cl in high-salt brine. - Can be with Mg 2+ Ca 2+ MgCl2 and CaCl2 are formed respectively, and high Cl2 content is utilized. - Concentration (≥150 g / L) drives the transfer of MgCl2 and CaCl2 into the organic phase, while Mg in MgCl2 / CaCl2... 2+ / Ca 2+It can form coordinate bonds with carbonyl groups (C=O) in β-diketone extractants and phosphorus-oxygen double bonds (P=O) in neutral phosphorus extractants, thereby forming stable complexes to obtain calcium-magnesium loaded organic phases, achieving efficient extraction of magnesium and calcium from high-salt brine; subsequently, combined with first and second back-extraction, calcium and magnesium in the calcium-magnesium loaded organic phases are separated stepwise.

[0015] In the method described in this invention, magnesium and calcium in high-salt brine are extracted in the form of MgCl2 and CaCl2, respectively, and the extraction process does not require the consumption of acids or alkalis, so no acid or alkali waste liquid is generated, which is more environmentally friendly.

[0016] Preferably, the high-salinity brine in step (1) includes seawater concentrate and / or chloride-type salt lake brine, wherein the chloride-type salt lake brine may be obtained, for example, from the dissolution of magnesium chloride tailings from a salt lake.

[0017] Preferably, the high-salt brine contains Cl - The concentration is 180–260 g / L, for example, it can be 180 g / L, 190 g / L, 200 g / L, 210 g / L, 220 g / L, 230 g / L, 240 g / L, 250 g / L or 260 g / L, etc.

[0018] The present invention further prefers the Cl in the high-salt brine. - A concentration of 180–260 g / L is beneficial for Mg 2+ and Ca 2+ Sufficient transfer into the organic phase, increasing Mg 2+ and Ca 2+ Extraction rate and recovery rate; if the Cl - The low concentration will result in some Mg remaining. 2+ and Ca 2+ Residual in high-salinity brine, leading to Mg 2+ and Ca 2+ The extraction rate and recovery rate decrease; if the Cl - A high concentration of extractant will increase the viscosity of the extractant during the extraction process, affecting the normal operation of the equipment.

[0019] Preferably, the high-salt brine also includes Mg. 2+ Ca 2+ Na + K + and Li + .

[0020] Preferably, the Mg in the high-salt brine 2+The concentration is 0.1 to 40 g / L, for example, it can be 0.1 g / L, 0.5 g / L, 1.0 g / L, 1.5 g / L, 2.0 g / L, 2.5 g / L, 5.0 g / L, 10.0 g / L, 15.0 g / L, 25 g / L, 30 g / L or 40 g / L, etc., preferably 1 to 20 g / L.

[0021] Preferably, the Ca in the high-salinity brine 2+ The concentration is 0.1 to 40 g / L, for example, it can be 0.1 g / L, 0.5 g / L, 1.0 g / L, 1.5 g / L, 2.0 g / L, 2.5 g / L, 5.0 g / L, 10.0 g / L, 15.0 g / L, 25 g / L, 30 g / L or 40 g / L, preferably 0.5 to 20 g / L.

[0022] Preferably, the β-diketone extractant comprises any one or a combination of at least two of dodecylphenol-alkyl-β-diketone, dodecylphenyl-ethyl-β-diketone, or decylphenyl-ethyl-β-diketone, wherein typical but non-limiting combinations include combinations of dodecylphenol-alkyl-β-diketone and dodecylphenyl-ethyl-β-diketone, combinations of dodecylphenyl-ethyl-β-diketone and decylphenyl-ethyl-β-diketone, or combinations of dodecylphenol-alkyl-β-diketone and decylphenyl-ethyl-β-diketone, etc.

[0023] Preferably, the neutral phosphorus extractant includes any one or a combination of at least two of tributyl phosphate, dimethylheptyl methyl phosphate, trioctylphosphine oxide, or trihexylphosphine oxide, wherein typical but non-limiting combinations include combinations of tributyl phosphate and dimethylheptyl methyl phosphate, combinations of dimethylheptyl methyl phosphate and trioctylphosphine oxide, or combinations of trioctylphosphine oxide and trihexylphosphine oxide, etc.

[0024] Preferably, the molar ratio of β-diketone extractant to neutral phosphorus extractant in the extraction system of step (1) is 1:(0.5-3), for example, it can be 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5 or 1:3, etc.

[0025] This invention further optimizes the molar ratio of β-diketone extractant to neutral phosphorus extractant in the extraction system to 1:(0.5-3). The two work synergistically under a specific molar ratio, which further improves the extraction effect of the extraction system on magnesium and calcium in high-salinity brine. If the molar ratio of β-diketone extractant to neutral phosphorus extractant in the extraction system is too low or too high, the synergistic effect will be poor, resulting in a poorer extraction effect on magnesium and calcium.

[0026] Preferably, the extraction system in step (1) further includes a diluent.

[0027] Preferably, the diluent comprises hydrocarbons and / or alcohols.

[0028] Preferably, the hydrocarbon includes any one or a combination of at least two of C7 to C13 hydrocarbons (e.g., C7, C8, C9, C10, C11, C12, or C13, etc.), wherein typical but non-limiting combinations include combinations of C7 hydrocarbons and C9 hydrocarbons, combinations of C8 hydrocarbons and C9 hydrocarbons, or combinations of C9 hydrocarbons and C12 hydrocarbons.

[0029] Preferably, the alcohol compound includes any one or a combination of at least two of n-octanol, isodecanol, or isotrigine, wherein typical but non-limiting combinations include combinations of n-octanol and isodecanol, combinations of n-octanol and isotrigine, or combinations of isodecanol and isotrigine, etc.

[0030] Preferably, the volume ratio of extractant to diluent in the extraction system of step (1) is (0.05-0.5):1, for example, it can be 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1 or 0.5:1, etc., preferably (0.1-0.4):1.

[0031] Preferably, the extraction system in step (1) further includes a phase modifier.

[0032] Preferably, the phase modifier comprises an ester compound.

[0033] Preferably, the ester compound includes any one or a combination of at least two of ethyl acetate, triisooctyl phosphate, or isoamyl isovalerate, wherein typical but non-limiting combinations include combinations of ethyl acetate and triisooctyl phosphate or combinations of triisooctyl phosphate and isoamyl isovalerate, etc.

[0034] Preferably, the volume ratio of the high-salt brine to the extraction system in step (1) is (0.2-5):1, for example, it can be 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1 or 5:1, etc., preferably (1-3):1.

[0035] The present invention further preferably uses a volume ratio of (1-3):1 between the high-salt brine and the extraction system, which is beneficial to increasing the Mg content. 2+ and Ca 2+ The extraction rate and recovery rate are affected by the following: if the volume ratio of the high-salt brine to the extraction system is too low, the utilization rate of the extractant will be low, and the extraction rate of sodium and potassium impurities will increase; if the volume ratio of the high-salt brine to the extraction system is too high, the calcium and magnesium extraction will be incomplete, resulting in more residues.

[0036] Preferably, the pH of the extraction in step (1) is 7 to 9, for example, it can be 7, 7.2, 7.4, 7.6, 7.8, 7.9, 8, 8.2, 8.5, 8.8 or 9, and preferably 7 to 7.9.

[0037] The present invention further preferably uses an extraction pH of 7-7.9 in step (1), which is beneficial for complete calcium and magnesium extraction. If the extraction pH is too low, it will lead to incomplete calcium and magnesium extraction, increased residues, and consequently, Mg... 2+ and Ca 2+ The extraction rate and recovery rate will decrease; if the pH of the extraction is too high, the extractant will be severely emulsified, and the extraction reaction will not be able to operate normally.

[0038] Preferably, the extraction temperature in step (1) is 10 to 80°C, for example, it can be 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C or 80°C, and preferably 20 to 40°C.

[0039] Preferably, in step (2), the first back-extraction system comprises water and / or a first acid solution.

[0040] Preferably, the first acid solution includes any one or a combination of at least two of hydrochloric acid, sulfuric acid, or carbonic acid, wherein typical but non-limiting combinations include combinations of hydrochloric acid and carbonic acid, combinations of hydrochloric acid and sulfuric acid, or combinations of sulfuric acid and carbonic acid, etc.

[0041] Preferably, the H in the first acid solution + The concentration is ≤0.5mol / L, for example, it can be 0.5mol / L, 0.45mol / L, 0.4mol / L, 0.35mol / L, 0.3mol / L, 0.25mol / L, 0.2mol / L, 0.15mol / L, 0.12mol / L, 0.10mol / L or 0.05mol / L, etc., preferably ≤0.2mol / L.

[0042] Preferably, the volume ratio of the magnesium-calcium-loaded organic phase to the first back-extraction system is (0.5-10):1, for example, it can be 0.5:1, 2:1, 5:1, 7:1 or 10:1, etc.

[0043] The present invention further preferably uses a volume ratio of (0.5-10):1 between the magnesium-calcium-supported organic phase and the first back-extraction system, which is beneficial to Mg 2+ and Ca 2+ For efficient separation, if the volume ratio of the magnesium-calcium-loaded organic phase to the first back-extraction system is too low, the magnesium concentration in the back-extraction solution will be low, increasing the cost of subsequent reuse; if the volume ratio of the magnesium-calcium-loaded organic phase to the first back-extraction system is too high, the magnesium back-extraction will be incomplete, reducing the utilization rate of the organic phase recycling process.

[0044] Preferably, in step (3), the second back-extraction system includes a second acid solution.

[0045] Preferably, the second acid solution comprises hydrochloric acid.

[0046] Preferably, the second acid solution contains H + The concentration is ≥1 mol / L, for example, it can be 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2.0 mol / L, 2.5 mol / L or 3 mol / L, etc.

[0047] Preferably, the volume ratio of the calcium-loaded organic phase to the second back-extraction system in step (3) is (0.5-10):1, for example, it can be 0.5:1, 1:1, 3:1, 5:1, 8:1 or 10:1, etc.

[0048] Preferably, step (2) the first back-extraction and step (3) the second back-extraction each independently include single-stage back-extraction or multi-stage back-extraction.

[0049] Preferably, the multi-stage back-extraction includes multi-stage countercurrent back-extraction.

[0050] Preferably, the number of stages in the multi-stage back-extraction is 2 to 5, for example, it can be 2, 3, 4 or 5 stages.

[0051] Preferably, the temperatures of the first back-extraction in step (2) and the second back-extraction in step (3) are each independently 10 to 80°C, for example, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C or 80°C.

[0052] Preferably, the concentration of magnesium ions in the magnesium back-extraction solution in step (2) is ≥20 g / L, for example, it can be 20 g / L, 30 g / L, 40 g / L or 50 g / L.

[0053] Preferably, the concentration of calcium ions in the calcium back-extraction solution in step (3) is ≥10g / L, for example, it can be 10g / L, 20g / L, 30g / L or 40g / L.

[0054] As a further preferred technical solution of the present invention, refer to Figure 1 The process flow shown is performed, and the method includes the following steps:

[0055] (1) Mix high-salt brine and extraction system in a volume ratio of (0.2-5):1 and extract at 10-80℃ to obtain an organic phase loaded with magnesium and calcium;

[0056] Cl in the high-salt brine -The concentration is ≥150 g / L; the extraction system includes a combination of β-diketone extractants and neutral phosphorus extractants; the molar ratio of β-diketone extractants to neutral phosphorus extractants in the extraction system is 1:(0.5~3); the extraction system also includes a diluent; the volume ratio of extractant to diluent in the extraction system is (0.05~0.5):1;

[0057] (2) The organic phase loaded with magnesium and calcium and the first back-extraction system are mixed in a volume ratio of (0.5-10):1 and the first back-extraction is carried out at 10-80°C and pH 7-9 to obtain a magnesium back-extraction solution with a magnesium ion concentration ≥20 g / L and an organic phase loaded with calcium.

[0058] The first back-extraction system includes water and / or H2O. + The first acid solution has a concentration ≤ 0.5 mol / L;

[0059] (3) The organic phase loaded with calcium and the second back-extraction system are mixed at a volume ratio of (0.5-10):1 and the second back-extraction is carried out at 10-80°C to obtain a calcium back-extraction solution with a calcium ion concentration ≥10 g / L.

[0060] The second back-extraction system includes H + The second acid solution has a concentration ≥1 mol / L.

[0061] Compared with the prior art, the present invention has at least the following beneficial effects:

[0062] (1) The present invention provides a method for the stepwise recovery of magnesium and calcium from high-salinity brine, wherein the method utilizes the high concentration of Cl in the high-salinity brine. - Driven Mg 2+ and Ca 2+ The molecules are transferred into the organic phase, and utilize the carbonyl group in β-diketone extractants and the phosphorus-oxygen double bond in neutral phosphorus extractants; the two work synergistically to react with Mg. 2+ and Ca 2+ Coordinate bonds are formed, resulting in a stable complex, with the extraction forms being MgCl2 and CaCl2; then, combined with the first and second back-extraction, Mg... 2+ and Ca 2+ The method achieves efficient separation; the extraction process is gentle, requires no acid or alkali consumption, reduces the formation of acid and alkali waste liquid, and the process flow is simple with low raw material costs.

[0063] (2) The method for stepwise recovery of magnesium and calcium from high-salinity brine provided by the present invention further improves the recovery of magnesium and calcium by optimizing process parameters such as the molar ratio of the extractant, the pH of the extraction process, the volume ratio of the first back-extraction process, and the number of stages of the first and second back-extraction processes. 2+ and Ca 2+Extraction rate and Mg 2+ and Ca 2+ The separation effect and recovery rate of Mg 2+ The single-stage extraction rate is preferably as high as 99.1% or more, Ca 2+ The single-stage extraction rate is preferably as high as 98.9% or more; Mg 2+ / Ca 2+ The separation coefficient is preferably as high as 2000 or above; Mg 2+ The recovery rate is preferably as high as 99.5% or more; Ca 2+ The recovery rate is preferably as high as 99.0% or more. Attached Figure Description

[0064] Figure 1 This is a process flow diagram of the method for stepwise recovery of magnesium and calcium from high-salinity brine provided by the present invention. Detailed Implementation

[0065] The technical solution of the present invention will be further illustrated below through specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0066] I. Implementation Examples

[0067] Example 1

[0068] This embodiment provides a method for the stepwise recovery of magnesium and calcium from high-salinity brine, the method comprising the following steps:

[0069] (1) The high-salt brine and the extraction system were mixed in a volume ratio of 2.5:1 and extracted at 50°C and pH 7.5 to obtain an organic phase loaded with magnesium and calcium.

[0070] In the extraction system, the extractant is dodecylphenol-alkyl-β-dione and tributyl phosphate in a molar ratio of 1:1, and dodecane is used as a diluent. The volume ratio of the extractant to the diluent is 0.25:1.

[0071] (2) The magnesium-calcium loaded organic phase and water were mixed in a volume ratio of 3:1 and subjected to a first back-extraction at 45°C to obtain a magnesium back-extraction solution with a magnesium ion concentration of 37.5 g / L and a calcium-loaded organic phase.

[0072] (3) Mix the calcium-loaded organic phase and H in a volume ratio of 5:1. + A 2 mol / L hydrochloric acid solution was subjected to a second back-extraction at 60 °C to obtain a calcium back-extraction solution with a calcium ion concentration of 25 g / L.

[0073] The composition and corresponding content of the high-salt brine described in this embodiment are shown in Table 1;

[0074] Table 1

[0075] Components <![CDATA[Cl - ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Ca 2+ ]]> <![CDATA[Na + ]]> <![CDATA[Li + ]]> <![CDATA[K + ]]> Concentration / g / L 200 5 2 86 1.0 10

[0076] Example 2

[0077] This embodiment provides a method for the stepwise recovery of magnesium and calcium from high-salinity brine, the method comprising the following steps:

[0078] (1) The high-salt brine and the extraction system were mixed at a volume ratio of 0.2:1 and extracted at 30°C and pH 7 to obtain an organic phase loaded with magnesium and calcium.

[0079] In the extraction system, the extractant is dodecylphenyl-ethyl-β-dione and dimethylheptyl methylphosphate in a molar ratio of 1:0.5, and isopropanol is used as a diluent. The volume ratio of the extractant to the diluent is 0.05:1.

[0080] (2) The magnesium-calcium loaded organic phase and water were mixed in a volume ratio of 3:1 and subjected to a first back-extraction at 80°C to obtain a magnesium back-extraction solution with a magnesium ion concentration of 24 g / L and a calcium-loaded organic phase.

[0081] (3) The organic phase loaded with calcium and a 1.5 mol / L hydrochloric acid solution were mixed at a volume ratio of 10:1 and subjected to a second back-extraction at 80°C to obtain a calcium back-extraction solution with a calcium ion concentration of 10 g / L.

[0082] The composition and corresponding content of the high-salt brine described in this embodiment are shown in Table 2;

[0083] Table 2

[0084] Components <![CDATA[Cl - ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Ca 2+ ]]> <![CDATA[Na + ]]> <![CDATA[Li + ]]> <![CDATA[K + ]]> Concentration / g / L 210 40 5 20 2.0 5.0

[0085] Example 3

[0086] This embodiment provides a method for the stepwise recovery of magnesium and calcium from high-salinity brine, the method comprising the following steps:

[0087] (1) The high-salt brine and the extraction system were mixed in a volume ratio of 5:1 and extracted at 80°C and pH 7.9 to obtain an organic phase loaded with magnesium and calcium.

[0088] In the extraction system, the extractant is decylphenyl-ethyl-β-dione and trioctylphosphine oxide in a molar ratio of 1:2, and isothietrol is used as a diluent; the volume ratio of the extractant to the diluent is 0.5:1.

[0089] (2) The magnesium-calcium loaded organic phase and 0.45 mol / L hydrochloric acid solution were mixed in a volume ratio of 3:1 and subjected to a first back-extraction at 30°C to obtain a magnesium back-extraction solution with a magnesium ion concentration of 30 g / L and a calcium-loaded organic phase.

[0090] (3) The organic phase loaded with calcium and a 2.5 mol / L hydrochloric acid solution were mixed in a volume ratio of 4:1 and subjected to a second back-extraction at 30°C to obtain a calcium back-extraction solution with a calcium ion concentration of 20 g / L.

[0091] The composition and corresponding content of the high-salt brine described in this embodiment are shown in Table 3;

[0092] Table 3

[0093]

[0094]

[0095] Example 4

[0096] This embodiment provides a method for the stepwise recovery of magnesium and calcium from high-salinity brine, wherein the method, except for the Cl in the high-salinity brine mentioned in step (1), - Except for the concentration of 120 g / L, everything else was the same as in Example 1.

[0097] Example 5

[0098] This embodiment provides a method for the stepwise recovery of magnesium and calcium from high-salinity brine, wherein the method, except for the Cl in the high-salinity brine mentioned in step (1), - Except for the concentration of 280 g / L, everything else was the same as in Example 1.

[0099] Example 6

[0100] This embodiment provides a method for the stepwise recovery of magnesium and calcium from high-salt brine. Except for the extractant in step (1) which is dodecylphenol-alkyl-β-dione and tributyl phosphate in a molar ratio of 1:0.2, the rest of the method is the same as in Example 1.

[0101] Example 7

[0102] This embodiment provides a method for the stepwise recovery of magnesium and calcium from high-salt brine. Except for the extractant in step (1) which is dodecylphenol-alkyl-β-dione and tributyl phosphate in a molar ratio of 1:3.2, the rest of the method is the same as in Example 1.

[0103] Example 8

[0104] This embodiment provides a method for stepwise recovery of magnesium and calcium from high-salt brine. Except for the volume ratio of high-salt brine to extraction system (dodecylphenol-alkyl-β-dione as extractant and dodecane as diluent) in step (1) being 5.5:1, the rest of the method is the same as in Example 1.

[0105] Example 9

[0106] This embodiment provides a method for the stepwise recovery of magnesium and calcium from high-salt brine. Except for the extraction pH of step (1) being 8, the method is the same as that in Example 1.

[0107] In this embodiment, the high pH caused the extractant to emulsify, making the extraction reaction difficult to proceed.

[0108] Example 10

[0109] This embodiment provides a method for the stepwise recovery of magnesium and calcium from high-salt brine. Except for step (2), which uses a 0.5 mol / L hydrochloric acid solution for the first back-extraction, the method is the same as in Example 1.

[0110] II. Comparative Example

[0111] Comparative Example 1

[0112] This comparative example provides a method for stepwise recovery of magnesium and calcium from high-salinity brine, wherein the method, except for step (1) in which Cl is obtained from the high-salinity brine... - Except for the concentration of 140 g / L, everything else is the same as in Example 1.

[0113] Comparative Example 2

[0114] This comparative example provides a method for stepwise recovery of magnesium and calcium from high-salt brine. Except for step (1), in which the extractant is only dodecylphenol-alkyl-β-dione and the total volume of the extractant remains unchanged, the method is the same as in Example 1.

[0115] Comparative Example 3

[0116] This comparative example provides a method for stepwise recovery of magnesium and calcium from high-salt brine. The method is the same as in Example 1, except that the extractant in step (1) is only tributyl phosphate and the total volume of the extractant remains unchanged.

[0117] Comparative Example 4

[0118] This comparative example provides a method for stepwise recovery of magnesium and calcium from high-salt brine. The method is the same as in Example 1 except that the dodecylphenol-alkyl-β-dione in step (1) is replaced with 5-dodecyl-2-hydroxybenzaldehyde oxime.

[0119] In this comparative example, 5-dodecyl-2-hydroxybenzaldehyde oxime does not have magnesium / calcium extraction properties under the conditions set in this comparative example, making the extraction reaction difficult to proceed.

[0120] Comparative Example 5

[0121] This comparative example provides a method for stepwise recovery of magnesium and calcium from high-salt brine. The method is the same as in Example 1 except that the tributyl phosphate in step (1) is replaced with diphenylphosphine.

[0122] In this comparative example, diphenylphosphine does not have magnesium / calcium extraction properties under the conditions set in this comparative example, making the extraction reaction difficult to proceed.

[0123] III. Tests and Results

[0124] The Mg content in the methods provided in the above embodiments and comparative examples was tested and calculated. 2+ and Ca 2+ Single-stage extraction rate, Mg 2 + / Ca 2+ Separation coefficient and Mg 2+ and Ca 2+ The recovery rates are shown in Table 4.

[0125] Table 4

[0126]

[0127]

[0128] Note: " / " in Table 4 indicates that there is no relevant data, that is, the extraction reaction is difficult to carry out under the experimental conditions set in the corresponding examples or comparative examples.

[0129] As can be seen from Table 4:

[0130] (1) As can be seen from Examples 1 to 3, the method for stepwise recovery of magnesium and calcium from high-salinity brine provided by the present invention does not require the consumption of acids or alkalis during the extraction process, achieving efficient separation and recovery of magnesium and calcium from high-salinity brine. 2+ The single-stage extraction rate is as high as 99.1% or more, Ca 2+ The single-stage extraction rate is as high as 98.9% or more; Mg 2+ / Ca 2+ The separation coefficient is as high as 2000 or more; Mg 2+ The recovery rate is as high as 99.5% or more; Ca 2+ The recovery rate is as high as 99.0%.

[0131] (2) Based on the combined information from Examples 1 and 4-5, as well as Comparative Example 1, it can be seen that, compared to Example 1, the Cl described in Example 4...- The concentration is too low, resulting in Mg 2+ The single-stage extraction rate decreased to 30.2%, Ca 2+ The single-stage extraction rate decreased to 25.6%, resulting in Mg... 2+ and Ca 2+ The recovery rate decreased; the Cl described in Comparative Example 1 - Concentrations below 150 g / L lead to Mg 2+ The single-stage extraction rate decreased to 17.3%, Ca 2+ The single-stage extraction rate decreased to 13.5%, resulting in Mg... 2+ and Ca 2+ The recovery rate decreased; the Cl described in Example 5 - A high concentration of Cl in the extractant increases viscosity during the extraction process, affecting the normal operation of the equipment and resulting in a poorer extraction effect. This indicates that the present invention, by selecting Cl from the high-salt brine... - The concentration is ≥150g / L, and more preferably 180~260g / L, which further improves the extraction and recovery effect of calcium and magnesium.

[0132] (3) Based on the combined results of Examples 1 and 6-7, it can be seen that the molar ratio of dodecylphenol-alkyl-β-dione and tributyl phosphate in the extractant described in Example 6 is too high, resulting in Mg 2+ The single-stage extraction rate decreased to 45.2%, Ca 2+ The single-stage extraction rate decreased to 12.3%, and the magnesium-calcium separation coefficient decreased; the molar ratio of dodecylphenol-alkyl-β-dione and tributyl phosphate in the extractant described in Example 7 was too low, resulting in Mg 2+ The single-stage extraction rate decreased to 93.3%, Ca 2+ The single-stage extraction rate decreased to 95.2%, the magnesium-calcium separation coefficient decreased, and magnesium and calcium could not be recovered in steps. This indicates that the present invention further optimizes the molar ratio of the β-diketone extractant and the neutral phosphorus extractant to 1:(0.5-2), which further improves the extraction efficiency and step recovery effect of calcium and magnesium.

[0133] (4) Based on the combined results of Examples 1 and Examples 8-10, it can be seen that the volume ratio of the high-salt brine to the extraction system (dodecylphenol-alkyl-β-dione and tributyl phosphate as extractants, and dodecane as a diluent) described in Example 8 is too high, resulting in Mg 2+ The single-stage extraction rate decreased to 65.3%, Ca 2+ The single-stage extraction rate decreased to 58.9%, resulting in Mg... 2+ and Ca 2+The recovery rate decreased; the pH of the extraction in Example 9 was too high, causing emulsification of the extractant and preventing the extraction from proceeding smoothly; the H in the first back-extraction in Example 10 was... + The high concentration of magnesium in the brine caused some calcium to be back-extracted, preventing the separation of calcium and magnesium. Therefore, this invention further optimizes the volume ratio of the high-salinity brine to the extraction system to (0.2–5):1, or the extraction pH to be 7–7.9, both of which improve the magnesium content in the high-salinity brine. 2+ and Ca 2+ The extraction efficiency is improved; and the first back-extraction system is further preferably water and / or H2O. + The first acid solution with a concentration ≤0.2mol / L further improved the separation effect of calcium and magnesium.

[0134] (5) As can be seen from the combined examples 1 and 2-5, since the extractants used in Comparative Examples 2 and 3 are all single extractants (Comparative Example 2 only uses dodecylphenol-alkyl-β-diketone, and Comparative Example 3 only uses tributyl phosphate), the magnesium and calcium extraction efficiency is drastically reduced. Comparative Example 4 uses a combination of 5-dodecyl-2-hydroxybenzaldehyde oxime and tributyl phosphate, where 5-dodecyl-2-hydroxybenzaldehyde oxime does not have the ability to extract calcium and magnesium under the extraction conditions. Comparative Example 5 uses diphenylphosphine, which does not have the ability to extract calcium and magnesium under the extraction conditions. This shows that the present invention selects a combination of β-diketone extractants and neutral phosphorus extractants in the extraction system. The synergistic effect of the two further improves the extraction efficiency of magnesium in the high-salinity brine. 2+ and Ca 2+ Extraction efficiency and recovery rate.

[0135] In summary, this invention utilizes the high concentration of Cl in high-salt brine. - Driven Mg 2+ and Ca 2+ The transfer to the organic phase, combined with a specific extraction system—a combination of β-diketone extractants and neutral phosphorus extractants—works synergistically to increase the Mg content in high-salinity brines. 2+ and Ca 2+ The extraction effect, combined with the selection of the back-extraction system in the subsequent first and second back-extraction processes, has achieved the technical effect of efficient separation and recovery of magnesium and calcium in high-salt brine.

[0136] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for stepwise recovery of magnesium and calcium from high-salinity brine, characterized in that, The method includes the following steps: (1) Extraction was carried out by mixing high-salt brine and extraction system to obtain an organic phase loaded with magnesium and calcium; (2) Mix the magnesium-calcium-loaded organic phase and the first back-extraction system to perform a first back-extraction, to obtain a magnesium back-extraction solution and a calcium-loaded organic phase; (3) Mix the calcium-loaded organic phase and the second back-extraction system to perform a second back-extraction to obtain a calcium back-extraction solution; Among them, the Cl in the high-salt brine in step (1) - The concentration is ≥150g / L, and the extraction system includes a combination of β-diketone extractants and neutral phosphorus extractants.

2. The method according to claim 1, characterized in that, The high-salinity brine mentioned in step (1) includes seawater concentrate and / or chloride-type salt lake brine; Preferably, the high-salt brine contains Cl - The concentration is 180–260 g / L; Preferably, the high-salt brine also includes Mg. 2+ Ca 2+ Na + K + and Li + ; Preferably, the Mg in the high-salt brine 2+ The concentration is 0.1–40 g / L, preferably 1–20 g / L; Preferably, the Ca in the high-salinity brine 2+ The concentration is 0.1–40 g / L, preferably 0.5–20 g / L.

3. The method according to claim 1 or 2, characterized in that, The β-diketone extractant includes any one or a combination of at least two of dodecylphenol-alkyl-β-diketone, dodecylphenyl-ethyl-β-diketone, or decylphenyl-ethyl-β-diketone; Preferably, the neutral phosphorus extractant includes any one or a combination of at least two of the following: tributyl phosphate, dimethylheptyl methyl phosphate, trioctylphosphine oxide, or trihexylphosphine oxide; Preferably, the molar ratio of β-diketone extractant to neutral phosphorus extractant in the extraction system of step (1) is 1:(0.5-3).

4. The method according to any one of claims 1 to 3, characterized in that, The extraction system described in step (1) also includes a diluent; Preferably, the diluent comprises hydrocarbons and / or alcohols; Preferably, the volume ratio of extractant to diluent in the extraction system of step (1) is (0.05-0.5):1, more preferably (0.1-0.4):

1.

5. The method according to any one of claims 1 to 4, characterized in that, The volume ratio of the high-salt brine to the extraction system in step (1) is (0.2-5):1, preferably (1-3):1; Preferably, the pH of the extraction in step (1) is 7 to 9, more preferably 7 to 7.9; Preferably, the extraction temperature in step (1) is 10–80°C, more preferably 20–40°C.

6. The method according to any one of claims 1 to 5, characterized in that, Step (2) The first back-extraction system includes water and / or a first acid solution; Preferably, the first acid solution includes any one or a combination of at least two of hydrochloric acid, sulfuric acid, or carbonic acid; Preferably, the H in the first acid solution + The concentration is ≤0.5mol / L, preferably ≤0.2mol / L; Preferably, the volume ratio of the magnesium-calcium-loaded organic phase to the first back-extraction system is (0.5–10):

1.

7. The method according to any one of claims 1 to 6, characterized in that, Step (3) The second back-extraction system includes a second acid solution; Preferably, the second acid solution comprises hydrochloric acid; Preferably, the second acid solution contains H + The concentration is ≥1 mol / L; Preferably, the volume ratio of the calcium-loaded organic phase to the second back-extraction system in step (3) is (0.5-10):

1.

8. The method according to any one of claims 1 to 7, characterized in that, Step (2) the first back-extraction and step (3) the second back-extraction each independently include single-stage back-extraction or multi-stage back-extraction; Preferably, the multi-stage back-extraction includes multi-stage countercurrent back-extraction; Preferably, the number of stages in the multi-stage back-extraction is 2 to 5. Preferably, the temperatures of the first back-extraction in step (2) and the second back-extraction in step (3) are each independently 10 to 80°C.

9. The method according to any one of claims 1 to 8, characterized in that, The concentration of magnesium ions in the magnesium back-extraction solution in step (2) is ≥20 g / L; Preferably, the concentration of calcium ions in the calcium back-extraction solution in step (3) is ≥10 g / L.

10. The method according to any one of claims 1 to 9, characterized in that, The method includes the following steps: (1) Mix high-salt brine and extraction system in a volume ratio of (0.2-5):1, and extract at 10-80℃ and pH 7-9 to obtain an organic phase loaded with magnesium and calcium; Cl in the high-salt brine - The concentration of magnesium ions is ≥150 g / L; the extraction system includes a combination of β-diketone extractant and neutral phosphorus extractant; the molar ratio of β-diketone extractant and neutral phosphorus extractant in the extraction system is 1:(0.5~3); the extraction system also includes a diluent; the volume ratio of extractant to diluent in the extraction system is (0.05~0.5):1; (2) the magnesium-calcium loaded organic phase and the first back-extraction system are mixed at a volume ratio of (0.5~10):1 and the first back-extraction is carried out at 10~80℃ to obtain a magnesium back-extraction solution with a magnesium ion concentration ≥20 g / L and a calcium-loaded organic phase; The first back-extraction system includes water and / or H2O. + The first acid solution with a concentration ≤ 0.5 mol / L; (3) The organic phase loaded with calcium and the second back-extraction system are mixed at a volume ratio of (0.5-10):1 and the second back-extraction is carried out at 10-80°C to obtain a calcium back-extraction solution with a calcium ion concentration ≥10 g / L. The second back-extraction system includes H + The second acid solution has a concentration ≥1 mol / L.

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