A method for separating magnesium and lithium in salt lake brine and its application.

Abstract

This invention relates to a method for separating magnesium and lithium in salt lake brine and its application, relating to the field of efficient and clean utilization of salt lake resources and modern salt chemical technology. This separation method constructs a precise selective magnesium precipitation window, allowing magnesium to precipitate deeply in the form of carbonates, while lithium remains largely in solution, thereby achieving the separation and removal of magnesium from high-magnesium brine. The magnesium precipitate obtained through online solid-liquid separation has a consistently low Mg / Li mass ratio below 1.0 × 10⁻⁶. ‑2 Subsequently, the filtrate is efficiently crystallized and recovered from lithium carbonate via co-ion effect or concentrated pyrolysis at higher temperatures (T2 = 85–100 °C) and lower pCO2. This invention achieves a highly efficient closed-loop cycle of NH3 and CO2, and has the advantages of strong universality, high selectivity, low cost, and environmental friendliness.

Description

Technical Field

[0001] This invention relates to the field of efficient and clean utilization of salt lake resources and modern salt chemical technology, and to a method and application for separating magnesium and lithium in salt lake brine. Background Technology

[0002] Approximately 60% of global lithium resources are found in salt lake brines, with brines exhibiting a high magnesium-to-lithium ratio (Mg / Li mass ratio typically greater than 20:1) being a significant component. These brines are extremely complex in composition, exhibiting not only significant disparities in magnesium and lithium concentrations but also extremely high concentrations of sodium, potassium, chloride, and / or sulfate ions, resulting in an ionic strength (I) typically well exceeding 6 mol•kg⁻¹. -1 This high-salt effect drastically alters the activity coefficients of ions, making it difficult to directly apply conventional precipitation separation theories in aqueous solutions, and posing a severe physicochemical challenge to the selectivity of magnesium-lithium separation processes.

[0003] Currently, the mainstream industrial process for treating this type of brine is the "lime / soda ash method." This method involves adding strong alkalis such as lime milk to precipitate magnesium hydroxide, followed by using soda ash to precipitate lithium carbonate. However, this route has several inherent and difficult-to-overcome drawbacks:

[0004] 1) Huge material consumption: Processing each ton of magnesium ions requires a large amount of lime or caustic soda, and introduces an equivalent amount of calcium chloride or sodium chloride into the brine, which increases the difficulty and cost of subsequent comprehensive utilization such as potassium extraction and boron extraction.

[0005] 2) Severe secondary pollution: It generates a large amount of low-value, difficult-to-treat magnesium hydroxide waste residue, resulting in enormous environmental pressure. At the same time, the large amount of calcium or sodium ions introduced accumulate in the mother liquor, increasing the burden of waste liquid treatment.

[0006] 3) Limited lithium recovery rate: Due to its colloidal properties and huge specific surface area, magnesium hydroxide precipitate is very easy to trap and adsorb lithium ions, resulting in a lithium recovery rate that can usually only reach 70-80%, which is a serious waste of resources.

[0007] 4) Selective deterioration in high-salt systems: Under high ionic strength, the activity coefficients of various ions deviate from the ideal state, resulting in poor selectivity of precipitation reaction and difficulty in ensuring product purity.

[0008] To overcome the aforementioned problems, carbonate-based processes, such as variants of the Solvay process, have been proposed for magnesium-lithium separation. However, existing technologies often treat magnesium removal and lithium precipitation as separate unit operations, failing to establish a stable process window of "selective magnesium precipitation without lithium precipitation" within a tightly coupled continuous system through precise process control. This is particularly problematic under the unique chemical environment of high ionic strength, where conventional thermodynamic pH... realSignificant discrepancies exist between theoretical and actual measurements, and the complex variations in ion activity coefficients make process control extremely difficult. Current technologies lack in-depth research and clear control strategies regarding the chemical equilibrium, reaction kinetics, and their decisive influence on separation selectivity under this high-salt effect, resulting in poor stability and reproducibility during industrial scale-up.

[0009] Although existing technologies have explored magnesium-lithium separation using ammonia and carbonization methods, they generally suffer from the following drawbacks: First, they are mostly stepwise or separate-stage operations, failing to achieve efficient sequential separation within a continuous, tightly coupled reaction system; second, descriptions of process control often remain at the level of a single parameter (such as pH). real With a broad limitation of (or temperature), it failed to reveal the effect at high ionic strengths (I ≥ 6.0 mol•kg). -1 Under this special chemical environment, temperature (T) and pH real There is a strong nonlinear coupling relationship between magnesium, carbon dioxide partial pressure (pCO2), and other factors; thirdly, therefore, existing technologies fail to provide a precise, stable, and industrially reproducible three-dimensional process window to overcome the interference of high salt effect on ion activity, resulting in poor selectivity, large process fluctuations, and difficulty in achieving deep removal of magnesium in practical applications. This invention is proposed to address the gaps and defects of the aforementioned existing technologies.

[0010] Therefore, developing a novel method for the sequential separation of magnesium and lithium that is universally applicable (considering both chloride and sulfate systems), environmentally friendly, low-cost, and with a stable and controllable process has become a critical technological bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0011] To address the aforementioned problems, this invention provides a method for separating magnesium and lithium in salt lake brine. This method constructs a precise selective magnesium precipitation window, allowing magnesium to precipitate deeply as carbonate, while lithium remains largely in the solution, thereby achieving the separation and removal of magnesium from high-magnesium brine. The magnesium precipitate obtained through online solid-liquid separation has a consistently low Mg / Li mass ratio below 1.0 × 10⁻⁶. -2 Subsequently, the filtrate is efficiently crystallized and recovered from lithium carbonate via co-ion effect or concentrated pyrolysis at higher temperatures (T2 = 85–100 °C) and lower pCO2. This invention achieves a highly efficient closed-loop cycle of NH3 and CO2, and has the advantages of strong universality, high selectivity, low cost, and environmental friendliness.

[0012] This invention provides a method for separating magnesium and lithium in salt lake brine, comprising the following steps:

[0013] Ammonolysis alkalization: Ammonia or ammonia water is added to the salt lake brine to adjust the alkalinity and obtain an alkalized slurry;

[0014] Carbonization and dissolution: Carbon dioxide is introduced into the alkali slurry for pressurized carbonization, which causes magnesium and lithium in the salt lake brine to form magnesium bicarbonate and lithium bicarbonate, thus obtaining a carbonized liquid.

[0015] Primary pyrolysis: controlling temperature, pressure, and pH real The solution is pyrolyzed to decompose magnesium bicarbonate in the carbonization liquid into magnesium carbonate precipitate, resulting in a slurry containing magnesium precipitate.

[0016] Solid-liquid separation: The slurry containing magnesium precipitate is subjected to solid-liquid separation to obtain filtrate containing lithium bicarbonate and magnesium salt;

[0017] Secondary pyrolysis: The filtrate containing lithium bicarbonate is pyrolyzed to decompose and crystallize lithium bicarbonate into lithium carbonate.

[0018] During the research on existing technologies, the inventors discovered the following technical problems: (1) poor applicability of existing technologies to different salt systems (chlorides, sulfates); (2) high material consumption, serious secondary pollution, and poor economic efficiency of traditional alkaline methods; (3) low lithium recovery rate due to the adsorption and encapsulation of lithium by magnesium precipitates; and (4) difficulty in accurately controlling the selectivity of magnesium-lithium separation due to the salt effect under high ionic strength, resulting in poor process stability. To solve the above problems, the inventors proposed the above separation method, which can achieve sequential separation of magnesium and lithium from salt lake brine. The core of this method is that, in a continuous reaction process, the pH of the system is precisely controlled by the synergistic regulation of ammonolysis, carbonization, and two-stage pressure-controlled pyrolysis. real The -pCO2-T chemical potential creates and maintains a precise thermodynamic window under high ionic strength, allowing for efficient precipitation of magnesium ions while lithium ions remain stable.

[0019] In one embodiment, the salt lake brine is a high-magnesium brine.

[0020] In one embodiment, the Mg:Li mass ratio in the brine of the salt lake is ≥20:1, and the ionic strength I is ≥6.0 mol·kg⁻¹. -1 .

[0021] In one embodiment, the separation method further includes a pretreatment step prior to the ammonolysis and alkalization step, and a closed-loop circulation step for ammonia and carbon dioxide after the secondary pyrolysis; the pretreatment includes filtering the brine to remove suspended solids; the closed-loop circulation includes collecting and treating the ammonia and carbon dioxide-containing gases generated during the process for recycling.

[0022] In one embodiment, when Ca in the salt lake brine 2+ Concentration higher than 0.05 g·L -1 At that time, sodium carbonate was added for pre-softening, and Ca was added. 2+The concentration was reduced to ≤0.05 g·L. -1 Preferably, Ca 2+ The concentration decreased to ≤0.04 g·L -1 More preferably, Ca 2+ The concentration was reduced to ≤0.03 g·L. -1 .

[0023] In one embodiment, during the ammonolysis alkalization step, the alkalinity is adjusted to pH. real =8.5–11.0.

[0024] In one embodiment, the ammonolysis alkalization is carried out at a temperature of 5-40°C; preferably, the temperature is 10-35°C, and the alkalinity is adjusted to pH. real =9.5–10.8; more preferably, the temperature is 15–30°C, and the alkalinity is adjusted to pH. real =9.5–10.5, to ensure sufficient alkalinity reserves and minimal energy consumption for subsequent carbonization reactions.

[0025] In one embodiment, the carbonization and dissolution step involves pressurized carbonization to a pH value. real It is 7.8–8.2;

[0026] The conditions for pressurized carbonization include: temperature 5–40°C, and carbon dioxide partial pressure pCO2 = 0.5–5.0 atm.

[0027] In one embodiment, the conditions for pressurized carbonization include: a temperature of 28–38°C, a pCO2 of 1.5–4.0 atm, and an endpoint pH of [missing information]. real The temperature is 7.9–8.1; more preferably, the temperature is 30–35°C and the pCO2 is 2.5–3.5 atm, to achieve efficient dissolution of magnesium and lithium and inhibit scaling of equipment.

[0028] In one embodiment, during the initial pyrolysis step, the temperature T1 is controlled at 55–65°C, the partial pressure of carbon dioxide in the top gas phase (pCO2) is 0.15–0.35 atm, and the liquid phase pH is... real It ranges from 8.7 to 9.1.

[0029] A core innovation of this invention lies in the inventors' discovery, through extensive experiments and thermodynamic simulations, that in a non-ideal solution system like high-ionic-strength brine, simply controlling the pH... real Temperature alone is insufficient to accurately distinguish the precipitation behavior of magnesium and lithium. This is because pH... realElectrode readings are affected by the high salt effect and cannot directly reflect the true carbonate ion activity. This invention creatively introduces top-phase pCO2 as a key, independently controllable third-dimensional parameter. By precisely controlling pCO2, this invention can indirectly, but more accurately, anchor carbonate ion activity in the liquid phase. At a defined T-pH... real Within the -pCO2 window, temperature (55–65℃) primarily provides the thermodynamic driving force required for the decomposition of Mg(HCO3)2, while precisely controlled pH... real (8.7–9.1) and low pCO2 (0.15–0.35 atm) synergistically maintain the chemical potential of the system at a delicate equilibrium point: a potential sufficient for Mg to... 2+ The solution precipitates efficiently as carbonate (SI_MgCO3 > 0), but this is insufficient to trigger a large-scale decomposition of LiHCO3 and precipitation of Li2CO3. This stable thermodynamic platform, constructed based on the synergistic control of three parameters, is the key technology enabling this invention to overcome the interference of high salt effects and achieve efficient and selective separation, which is impossible to achieve with existing single- or dual-parameter control methods.

[0030] By analyzing temperature, top gas phase carbon dioxide partial pressure, and liquid phase pH real Coordinated regulation is employed to create and maintain a thermodynamic window for the selective precipitation of magnesium ions, resulting in a magnesium-containing slurry. Specifically, the partial pressure of carbon dioxide in the top gas phase (pCO2) is used as a key regulating variable to precisely stabilize the activity of carbonate ions in the liquid phase under high ionic strength, thereby ensuring the desired temperature and pH. real Selective precipitation of magnesium under certain conditions.

[0031] In one embodiment, during the initial pyrolysis step, the temperature T1 is controlled at 58–63°C, the partial pressure of carbon dioxide in the top gas phase (pCO2) is 0.18–0.32 atm, and the liquid phase pH is... real It ranges from 8.8 to 9.0.

[0032] In one embodiment, the initial pyrolysis step further includes adding MgCO3 seed crystals to make the saturation index SI MgCO3 of magnesite in the carbonization solution range from +0.30 to +0.60;

[0033] The amount of MgCO3 seed crystals added is 0.1–1.0 wt% of the magnesium carbonate precipitate.

[0034] In one embodiment, the amount of MgCO3 seed crystals added is 0.2–0.8 wt% of the magnesium carbonate precipitate; preferably, the amount of MgCO3 seed crystals added is 0.3–0.6 wt% of the magnesium carbonate precipitate, so as to obtain precipitates with regular morphology and concentrated particle size distribution, which is beneficial to subsequent filtration.

[0035] In one embodiment, the magnesium concentration in the lithium bicarbonate-containing filtrate is ≤0.030 g·L⁻¹. -1 Mg / Li mass ratio ≤ 1.0 × 10 -2 .

[0036] In one embodiment, the separation method further includes a washing step following the solid-liquid separation step, the washing comprising washing the filter cake with a saturated mother liquor or a saturated salt solution at 50–70°C.

[0037] In one embodiment, the temperature of the saturated mother liquor or saturated salt solution is 55–65°C to reduce heat loss while ensuring the efficiency of entrained liquid recovery.

[0038] In one embodiment, the filter cake thickness of the magnesium salt is controlled to be ≤8 mm by controlling the filtration device; preferably, the filter cake thickness of the magnesium salt is controlled to be 3–7 mm; more preferably, the filter cake thickness of the magnesium salt is 4–6 mm to achieve the best balance between filtration efficiency and washing effect.

[0039] In one embodiment, the pyrolysis conditions in the secondary pyrolysis step include: temperature T2 = 85–100°C and top gas phase pCO2 ≤ 0.10 atm.

[0040] In one embodiment, the temperature T2 is 88–98°C and the top gas phase pCO2 is ≤0.08 atm; preferably, the temperature T2 is 90–95°C and the top gas phase pCO2 is 0.02–0.06 atm to promote the complete decomposition of LiHCO3.

[0041] In one embodiment, the decomposition and crystallization method includes the co-ion effect method or the concentrated pyrolysis method;

[0042] When the decomposition and crystallization are achieved through the common ion effect method, it includes: adding a precipitant to the lithium bicarbonate-containing filtrate, wherein the precipitant includes sodium carbonate, and the amount of the precipitant is 15–35 g / L of lithium bicarbonate-containing filtrate.

[0043] When the decomposition and crystallization are achieved by the concentration pyrolysis method, it includes: evaporating and concentrating the lithium bicarbonate-containing filtrate to a concentration ratio of 1.5-3.0 times, and then carrying out pyrolysis crystallization.

[0044] In one embodiment, when the decomposition and crystallization are achieved by the common ion effect method, the amount of the precipitant used is 18-30 g / L of lithium bicarbonate filtrate; preferably, the amount of the precipitant used is 20-28 g / L of lithium bicarbonate filtrate.

[0045] In one embodiment, when the decomposition and crystallization are achieved by a concentration pyrolysis method, the concentration ratio is 1.8-2.8 times; preferably, the concentration ratio is 2.0-2.5 times.

[0046] The present invention also provides a method for preparing magnesium salts and / or lithium salts, wherein the separation method is used to treat salt lake brine to obtain magnesium salts and lithium carbonate.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] This invention discloses a method for separating magnesium and lithium in salt lake brine and its application. This separation method has the following advantages: (1) High versatility: The unique process window of this invention does not depend on a specific anion system and shows excellent separation effect on chloride-type, sulfate-type and mixed-type high-salt brines; (2) Green and environmentally friendly, with no secondary pollution: NH3 / CO2 is used as the recycling reagent, and no exogenous metal cations are introduced, thus eliminating the generation of a large amount of inefficient waste residue from the source. Magnesium is recovered in the form of high-quality magnesium carbonate, which can be used as an added-value product; (3) High selectivity and high resource utilization: Through precise "pH" real —pCO2—T synergistic control enables precise sequential separation of magnesium and lithium under high ionic strength, reducing the Mg / Li mass ratio of the magnesium precipitation filtrate to 1.0×10 -2 The following are the results: the lithium recovery rate can reach more than 90%; (4) low cost and significant economic benefits: the efficient closed-loop circulation of NH3 and CO2 (recovery rates ≥80% and ≥70% respectively) greatly reduces the consumption of chemical reagents, significantly reduces operating costs, and improves overall economic benefits; (5) simple raw materials and low temperature, suitable for operation in plateau areas, which fits the geographical characteristics of salt lakes.

[0049] This separation method is universally applicable to ionic strengths I ≥ 6.0 mol·kg⁻¹ -1 This method is applicable to chloride-type, sulfate-type, and mixed-type high-salt, high-magnesium brines. It involves ammonolysis and alkalization (pH...). real After pyrolysis (8.5–11.0) and pressurized carbonization (pCO2 0.5–5.0 atm), the temperature of the first stage of pyrolysis (T1 = 55–65 °C), the partial pressure of CO2 in the top gas phase (pCO2 = 0.15–0.35 atm), and the pH of the liquid phase are controlled in a single connected system through coordinated control. real (pH) real =8.7–9.1), a precise selective magnesium precipitation window was constructed, allowing magnesium to precipitate deeply in the form of carbonates, while lithium remained largely in solution, thus achieving the separation and removal of magnesium from high-magnesium brines. The magnesium precipitate obtained by online solid-liquid separation has a consistently low Mg / Li mass ratio below 1.0 × 10⁻⁶. -2Subsequently, the filtrate is efficiently crystallized and recovered from lithium carbonate via co-ion effect or concentrated pyrolysis at higher temperatures (T2 = 85–100 °C) and lower pCO2. This invention achieves a highly efficient closed-loop cycle of NH3 and CO2, and has the advantages of strong universality, high selectivity, low cost, and environmental friendliness. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the process flow for the separation method of magnesium and lithium in salt lake brine according to the present invention. Detailed Implementation

[0051] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0052] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0053] Unless otherwise specified, all reagents, materials, and equipment used in this embodiment are commercially available; unless otherwise specified, all test methods are conventional test methods in this field.

[0054] definition:

[0055] This invention defines ionic strength (I) using mol / kg solvent concentration, and its calculation formula is as follows:

[0056] in, Let be the molar concentration of the i-th ion. Its charge number. The "high ionic strength" brine referred to in this invention specifically refers to brine with I ≥ 6.0 mol·kg⁻¹. -1 The system. Under these conditions, strong interionic interactions (salt effect) cause the chemically effective concentration (activity) of ions to deviate significantly from their analytical concentration, and the activity of water decreases, rendering conventional thermodynamic calculations and process control methods ineffective. This is the key technical background that this invention needs to address.

[0057]

[0058] pH real

[0059] In the context of this invention, the term "pH" real "Specifically refers to a repeatable engineering control parameter, rather than a strict thermodynamic pH." real Its value is determined by using a buffer solution (e.g., 1–3 mol·L⁻¹) that matches the ionic strength of the process brine. -1 The pH reading is obtained directly from an industrial online glass electrode calibrated with a NaCl-based buffer solution, under actual process conditions. real The complex measurement errors (such as liquid junction potential) caused by the high salt effect are successfully transformed into a stable systematic deviation, thereby ensuring that the specific pH is maintained under the process conditions of this invention. real The readings can accurately and one-to-one correspond to specific chemical equilibrium states, and are the core benchmark for achieving stable and repeatable control in high-salt systems in this invention.

[0060] Saturation Index

[0061] The saturation index (SI) is a quantitative thermodynamic indicator used to determine the precipitation or dissolution tendency of a target solid phase (mineral) in solution. It is defined as follows:

[0062] Wherein, IAP is the activity product of the ions constituting the solid phase in solution, and K_sp is the solubility product constant of the solid phase under the same conditions. In this invention, by calculating and controlling the saturation index SI (MgCO3) of magnesite online within a narrow range of mild supersaturation (+0.30 to +0.60), the thermodynamic driving force of the magnesium precipitation process is precisely controlled. The key technical effect of this approach is that it ensures a reasonable precipitation rate while effectively suppressing explosive nucleation that leads to fine particles, difficult filtration, and lithium entrainment loss, thereby promoting ordered crystal growth and obtaining magnesium salt precipitation with excellent physical properties.

[0063] Example 1

[0064] 1) Composition of raw material brine:

[0065]

[0066] 2) Operating steps and procedures:

[0067] (S1) After filtering the above brine, inject 25 wt% ammonia water at 25°C to adjust the pH. real Quickly adjust to 10.5.

[0068] (S2) Pump the slurry into the pressurized carbonization tower and react for 15 minutes at 30°C and pCO2=3.0 atm. The endpoint pH is determined. real It is 7.9.

[0069] (S3) The carbonized liquid is fed into a first-stage pyrolysis crystallizer, with the temperature controlled at T1=60℃, the top gas phase pCO2=0.25 atm, and the liquid phase stable pH. real =8.9. During this period, 0.5 wt% of MgCO3 seed crystals were added based on the final solid product, and the mixture was allowed to mature for 20 minutes.

[0070] (S4) Solid-liquid separation is performed using a combination of cyclone-sedimentation-thin-layer filtration, and the filter cake is washed once with saturated NaCl solution.

[0071] (S5a) Heat the resulting magnesium precipitate filtrate to 90°C, maintaining a top pCO2 < 0.05 atm, and add 25 g·L⁻¹ -1 Lithium was precipitated from sodium carbonate and crystallized for 45 minutes.

[0072] 3) Results: Analysis revealed that Mg in the magnesium precipitation filtrate was... 2+ The concentration is 0.015 g·L. -1 The Mg / Li mass ratio is 7.5 × 10⁻⁶. -3 The technical specifications were met. The final lithium carbonate product obtained had high purity, and the calculated total lithium recovery rate reached 91.5%. This embodiment demonstrates that, under typical parameters, the present invention has excellent separation effect on high-magnesium chloride brine.

[0073] Example 2

[0074] 1) Composition of raw material brine:

[0075]

[0076] 2) Operating steps and procedures:

[0077] It is basically the same as Example 1, with the following differences:

[0078] (S1) Ammonia decomposition to adjust pH real Up to 8.5.

[0079] (S2) Carbonization at pCO2=2.0 atm.

[0080] (S3) At T1=55℃, pCO2=0.15 atm, pH real A pyrolysis was performed at 8.7°C. 0.1 wt% seed crystals were added.

[0081] (S4) Solid-liquid separation.

[0082] (S5b) The magnesium precipitate filtrate was concentrated and pyrolyzed by evaporation at 85°C by 1.5 times.

[0083] 3) Results: Mg in the magnesium precipitation filtrate2+ The concentration is 0.028 g·L. -1 The Mg / Li mass ratio is 1.87 × 10⁻⁶. -2 All of these are within the target scope defined in the claims. The total lithium recovery rate is 88.2%. This embodiment demonstrates that even under the most stringent boundary conditions, the present invention can still achieve effective separation, and the process window is robust and reliable.

[0084] Example 3

[0085] 1) Composition of raw material brine:

[0086]

[0087] 2) Operating steps and procedures:

[0088] It is basically the same as Example 1, with the following differences:

[0089] (S1) Ammonia decomposition to adjust pH real Up to version 11.0.

[0090] (S2) Carbonization at pCO2=5.0 atm.

[0091] (S3) At T1=65℃, pCO2=0.35 atm, pH real A pyrolysis step was performed at 9.1°C. 1.0 wt% of seed crystals were added.

[0092] (S4) Solid-liquid separation.

[0093] (S5a) Add 35 g·L at 100℃ -1 Lithium precipitate from sodium carbonate.

[0094] 3) Results: Mg in the magnesium precipitation filtrate 2+ The concentration was only 0.012 g·L. -1 The Mg / Li mass ratio is as low as 4.8 × 10⁻⁶. -3 The total lithium recovery rate is as high as 93.1%. This embodiment demonstrates that the present invention is fully applicable to high-concentration sulfate mixtures and exhibits excellent separation performance under the upper limit of process parameters.

[0095] Example 4

[0096] 1) Composition of raw material brine:

[0097]

[0098] 2) Operating steps and procedures:

[0099] It is basically the same as Example 1, with the following differences:

[0100] (S1) pH real Adjusted to 10.6.

[0101] (S2) pCO2=4.0 atm.

[0102] (S3) T1=62℃, pCO2=0.30 atm, pH real =9.0, add 0.6 wt% seed crystals.

[0103] (S4) Solid-liquid separation.

[0104] (S5b) The filtrate was evaporated and concentrated 3.0 times and then pyrolyzed at 95°C.

[0105] 3) Results: Mg in the magnesium precipitation filtrate 2+ The concentration is 0.021 g·L. -1 The Mg / Li mass ratio is 1.17 × 10⁻⁶. -2 The technical specifications are met. The total lithium recovery rate is 90.5%. This embodiment demonstrates that the present invention still has good processing capability for extreme brines with ionic strength and impurity ion concentrations far exceeding the conventional range.

[0106] Example 5

[0107] This embodiment aims to verify the process feasibility and robustness of the present invention when certain process parameters (especially ammonolysis and carbonization steps) are taken at boundary values.

[0108] 1) Raw material brine: The raw material brine used is exactly the same as that in Example 1, and is of the high magnesium chloride type. Its main ionic composition is:

[0109]

[0110] Its ionic strength I is approximately 10 mol·kg⁻¹ -1 .

[0111] 2) Operating steps and procedures:

[0112] It is basically the same as Example 1, with the following differences:

[0113] (S1) After filtering the above brine, ammonia water is added to adjust the pH. real Adjust to 8.5.

[0114] (S2) The slurry is pumped into a pressurized carbonization tower, where the carbonization reaction is carried out under relatively mild conditions, namely a temperature of 5°C and a carbon dioxide partial pressure pCO2 = 0.5 atm, until the reaction reaches its endpoint pH. real It reached 7.5.

[0115] (S3) The carbonized liquid is fed into a first-stage pyrolysis crystallizer, maintaining the process parameters within the core window: temperature T1 = 60℃, top gas phase pCO2 = 0.25 atm, and stable liquid phase pH. real =8.9, and a pyrolysis precipitation of magnesium is carried out.

[0116] (S4) Perform online solid-liquid separation on the generated slurry.

[0117] (S5) Heat the obtained magnesium precipitate filtrate to 90°C and maintain the top gas phase pCO2 < 0.05 atm to allow lithium carbonate to crystallize out.

[0118] Tests showed that the magnesium precipitation filtrate contained Mg. 2+ The concentration is 0.026 g·L. -1 The Mg / Li mass ratio is 1.7 × 10⁻⁶. -2 The technical specifications of this invention are met. The total lithium recovery rate is calculated to be ≥88%. This embodiment demonstrates that even when the front-end ammonolysis and carbonization steps are carried out under relatively mild or even boundary conditions deviating from the preferred range, the core S3 step (one-stage pressure-controlled pyrolysis) of this invention can still effectively separate magnesium and lithium, demonstrating the process's tolerance and strong correction capability.

[0119] Example 6

[0120] This embodiment aims to verify the universality of the present invention for complex brine systems, as well as its excellent performance when some process parameters are taken at upper boundary values.

[0121] 1) Raw material brine: The same sulfate-chloride mixed concentrated brine as in Example 3 was used. Its main ionic composition is:

[0122]

[0123] Its ionic strength I is approximately 15 mol·kg⁻¹ -1 .

[0124] 2) Operating steps and procedures:

[0125] It is basically the same as Example 3, with the following differences:

[0126] (S1) After filtering the brine, ammonia water is added to adjust the pH. real Adjust to 11.0.

[0127] (S2) The slurry is pumped into a pressurized carbonization tower and carbonized under relatively harsh conditions, namely a temperature of 40°C and a carbon dioxide partial pressure of pCO2 = 4.8 atm, until the reaction endpoint pH is reached. real It reached 8.2.

[0128] (S3) The carbonized liquid is fed into a first-stage pyrolysis crystallizer, maintaining the temperature T1 = 62℃, the top gas phase pCO2 = 0.30 atm, and the liquid phase stable pH. real =9.0, selective magnesium precipitation was performed.

[0129] (S4) Perform solid-liquid separation on the generated slurry.

[0130] (S5a) The obtained magnesium precipitate filtrate was heated to 100°C, and 30 g·L⁻¹ was added using the co-ion effect method. -1 Sodium carbonate is used to precipitate lithium.

[0131] Mg in magnesium precipitation filtrate 2+ The concentration was only 0.014 g·L. -1 The Mg / Li mass ratio is as low as 6.0 × 10⁻⁶. -3 The separation effect is excellent. The total lithium recovery rate is calculated to be ≥92%. This embodiment demonstrates that the present invention is also applicable to complex brine systems with high ionic strength and high sulfate content, and exhibits excellent and stable separation performance under the upper limit of process parameters.

[0132] Example 7

[0133] This embodiment aims to verify the industrial application potential of the present invention for long-term continuous and stable operation under optimized median process parameters.

[0134] 1) Raw material brine: The same typical chloride-type high magnesium brine as in Example 1 is used.

[0135] 2) Operating steps and procedures:

[0136] It is basically the same as Example 1, with the following differences:

[0137] (S1) Continuous feeding, with online adjustment of ammonia flow rate to adjust pH. real The value was kept stable at 10.5.

[0138] (S2) The slurry continuously enters the pressurized carbonization tower, controlling the tower temperature at 30℃, the top gas phase pCO2 at 3.0 atm, and adjusting the brine to CO2 flow ratio to achieve the desired outlet pH. real It's stable at 8.0.

[0139] (S3) The carbonized liquid continuously enters the first-stage pyrolysis crystallizer, with the temperature controlled at T1=60℃ and the top gas phase pCO2=0.25atm. The ammonia replenishment is finely adjusted through a closed-loop control system to precisely stabilize the liquid phase pH at 8.9. 0.5 wt% MgCO3 seed crystals are continuously added. The entire system operates continuously and stably for 24 hours.

[0140] (S4) A belt filter is used to separate the solid and liquid components of the continuously produced slurry, and the thickness of the filter cake is controlled to be 5 mm.

[0141] (S5b) The magnesium filtrate is continuously fed into the two-stage pyrolysis system for concentration and lithium precipitation at 95°C.

[0142] During 24 hours of continuous operation, all system parameters remained stable, with no obvious scaling or clogging. Random sampling analysis showed that Mg in the magnesium precipitation filtrate... 2+ The concentration remained stable at 0.018 g·L⁻¹ -1 The Mg / Li mass ratio remained stable at 9.0 × 10⁻⁶. -3 The filtration flux of the belt filter remained consistently at ≥220 L·m. - 2·h -1 This indicates that the generated magnesium salt precipitate possesses excellent physical properties. This embodiment fully demonstrates the stability, reliability, and operability of the process of the present invention, and has the potential for large-scale industrial continuous production.

[0143] Comparative Example A (Deviating from the core process window)

[0144] 1) Use the same raw material brine as in Example 1;

[0145] 2) S1 and S2 are the same as in Example 1; S3 is set with T1 = 60℃, but the top gas phase pCO2 = 0.10 atm, at which point the liquid phase has a stable pH. real Only 8.6. Other conditions are the same as in Example 1.

[0146] Mg in magnesium precipitation filtrate 2+ Concentration as high as 0.054 g·L -1 The Mg / Li mass ratio deteriorated to 2.7 × 10⁻⁶. -2 This far exceeds the control target of this invention. Simultaneously, a 35% decrease in the filter's unit flux was observed, indicating that the generated precipitate particles are small, resulting in poor filtration performance and increased subsequent lithium loss.

[0147] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0148] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for separating magnesium and lithium in salt lake brine, characterized in that, Includes the following steps: Ammonolysis alkalization: Ammonia or ammonia water is added to the salt lake brine to adjust the alkalinity and obtain an alkalized slurry; Carbonization and dissolution: Carbon dioxide is introduced into the alkali slurry for pressurized carbonization, which causes magnesium and lithium in the salt lake brine to form magnesium bicarbonate and lithium bicarbonate, thus obtaining a carbonized liquid. Primary pyrolysis: control temperature, pressure, pH real , pyrolysis is carried out to decompose magnesium bicarbonate in the carbonization liquid into magnesium carbonate precipitation to obtain a slurry containing magnesium precipitation; in the primary pyrolysis step, the temperature T1 is controlled to be 55-65℃, the top gas phase carbon dioxide partial pressure pCO2 is 0.15-0.35 atm, and the liquid phase pH real is 8.7-9.1; Solid-liquid separation: The slurry containing magnesium precipitate is subjected to solid-liquid separation to obtain filtrate containing lithium bicarbonate and magnesium salt; Secondary pyrolysis: The filtrate containing lithium bicarbonate is pyrolyzed to decompose and crystallize lithium bicarbonate into lithium carbonate.

2. The separation method according to claim 1, characterized in that, The salt lake brine is a high-magnesium brine.

3. The separation method according to claim 1, characterized in that, In the ammonolysis basification step, the alkalinity is adjusted to a pH real = 8.5 - 11.

0.

4. The separation method according to claim 1, characterized in that, In the carbonization and dissolution step, pressurized carbonization is performed to pH [a specific pH value]. real It is 7.8–8.2; The conditions for pressurized carbonization include: temperature 5-40℃, carbon dioxide partial pressure pCO2 = 0.5–5.0 atm.

5. The separation method according to claim 1, characterized in that, The initial pyrolysis step also includes adding MgCO3 seed crystals to make the saturation index SI MgCO3 of magnesite in the carbonization solution range from +0.30 to +0.60; The amount of MgCO3 seed crystals added is 0.1–1.0 wt% of the magnesium carbonate precipitate.

6. The separation method according to claim 1, characterized in that, The magnesium concentration in the lithium bicarbonate-containing filtrate is ≤0.030 g·L⁻¹. -1 Mg / Li mass ratio ≤ 1.0 × 10 -2 .

7. The separation method according to claim 1, characterized in that, In the secondary pyrolysis step, the pyrolysis conditions include: temperature T2 = 85–100℃, and pCO2 in the top gas phase ≤ 0.10 atm.

8. The separation method according to claim 7, characterized in that, The decomposition and crystallization methods include the co-ion effect method or the concentrated pyrolysis method; When the decomposition and crystallization are achieved through the common ion effect method, it includes: adding a precipitant to the lithium bicarbonate-containing filtrate, wherein the precipitant includes sodium carbonate, and the amount of the precipitant is 15–35 g / L of lithium bicarbonate-containing filtrate. When the decomposition and crystallization are achieved by the concentration pyrolysis method, it includes: evaporating and concentrating the lithium bicarbonate-containing filtrate to a concentration ratio of 1.5-3.0 times, and then carrying out pyrolysis crystallization.

9. A method for preparing a magnesium salt and / or lithium salt, characterized in that, The salt lake brine is treated using the separation method described in any one of claims 1-8 to obtain magnesium salts and lithium carbonate.

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