Process for extracting magnesium from a gray-brown salt lake clay containing magnesium in multiple occurrence states

Abstract

This invention relates to the field of metal extraction technology, and more particularly to a process for extracting magnesium from grayish-brown salt lake clay containing magnesium in multiple states. The process for extracting magnesium from grayish-brown salt lake clay containing magnesium in multiple states is characterized by the following steps: crushing and sieving the salt lake clay, then impregnating the fine particles in a leaching agent, and filtering to obtain a magnesium-containing leachate; wherein the leaching agent is prepared from concentrated hydrochloric acid, concentrated sulfuric acid, and low-mineralized water, with a volume ratio of concentrated hydrochloric acid, concentrated sulfuric acid, and low-mineralized water of 0.05-0.15:0.05-0.15:0.8; the low-mineralized water is natural water from the Mahai Basin. This invention uses low-mineralized water and a mixed acid (sulfuric acid + hydrochloric acid) to prepare a composite leaching agent, which is then extracted using Cl... ‑ The multiple synergistic mechanisms of competitive adsorption-displacement, sulfate complexation and dissolution, and ultrasonic cavitation effect achieve a high leaching rate, significantly improving leaching capacity compared to single-body water processes, while reducing acidic wastewater discharge.

Description

Technical Field

[0001] This invention relates to the field of metal extraction technology, and in particular to a magnesium extraction process from gray-brown salt lake clay containing magnesium in multiple occurrence states. Background Technology

[0002] Sedimentary saline lake clays are mainly distributed in arid to semi-arid closed basins, such as the Qaidam Basin in China (Mahai and Qarhan Salt Lakes), the Great Salt Lake in the United States, and the Salar de Uyuni in Bolivia. Their formation is controlled by geological processes, such as source input: weathering products from surrounding mountains (feldspar, mica, etc.) are carried to the saline lake by surface runoff; and evaporation and concentration: intense evaporation leads to a decrease in the amount of Ca²⁺ in the brine. + Mg² + K + Plasma supersaturation leads to co-precipitation with clay minerals; sedimentary diagenesis: under burial and compaction, layered silicate minerals such as montmorillonite and illite are interlayered with evaporates (gypsum, halite), forming a porous media structure.

[0003] The Balunmahai area is located in the northwestern part of the Qaidam Basin in Qinghai Province. Its salt lake clay minerals mainly include kaolinite, illite, montmorillonite, and chlorite. The enclosed topography of the Qaidam Basin causes clay minerals weathered from the surrounding areas to be transported here by water and wind. Extreme drought leads to strong evaporation that far exceeds precipitation, resulting in continuous concentration of lake water and extremely high salinity. This high-salinity, still water environment inhibits hydrodynamics, facilitating the settling of even the finest clay particles. Furthermore, the abundant electrolytes in the water neutralize the surface charge of the clay particles through flocculation, causing them to rapidly aggregate and accelerate deposition. This ultimately forms a sedimentary saline clay layer at the bottom of the lake basin. Through long-term sedimentation and diagenesis, this clay layer often appears in specific strata within the saline lake sedimentary sequence: the upper layer is an evaporite layer, which can be divided into clay with high halite content (referred to as halite clay) and clay with high silt content (referred to as silt clay); the lower layer consists of grayish-brown clay (shallow strata, oxidizing environment, containing brown minerals such as hematite) and grayish-green clay (deep strata, reducing environment, containing grayish-green minerals such as siderite), rich in illite and chlorite. The magnesium in the grayish-brown saline lake clay exhibits significant polymorphism and strong solidification characteristics, and its complex existence directly restricts the efficiency of traditional extraction methods. First, magnesium is enriched in the interlayer regions or particle surfaces of clay minerals such as montmorillonite and illite in a surface-adsorbed state, forming exchangeable magnesium (Mg²⁺) through electrostatic interactions. + However, in high-salinity environments, Na... + Ca² + Competitive cations form a dynamic adsorption equilibrium with magnesium, especially during evaporation and concentration when the ionic strength increases, triggering an "ion-locking" effect that significantly enhances the binding energy of magnesium. Conventional ion exchange methods achieve desorption rates of less than 30%. Secondly, chemically bound magnesium undergoes isomorphic substitution (e.g., substituting Al³⁺ in aluminum-oxygen octahedra).+ Magnesium in the silicate tetrahedral framework is embedded in the silicate lattice or forms a co-precipitation structure with secondary minerals (magnesite, magnesia) – strong acids are needed to break down the mineral lattice (H). + The energy consumption is 2-3 times the theoretical value, and the dense layered structure of magnesite (MgCO3) requires high-temperature calcination above 700℃ to decompose, leading to a surge in energy costs. Furthermore, in organic-rich salt lake environments, magnesium forms organic complexes with humic acid and microbial extracellular polymeric substances (EPS). These complexes not only shield the active sites of magnesium ions but also transform into biomineral phases (such as magnesium-organic films) through microbial metabolism. These complexes can exist stably for hundreds of years under natural conditions, making it difficult for traditional leaching agents to penetrate their molecular barriers. The coupling of these three existing states forms a triple consolidation mechanism of "adsorption-lattice-biology," which becomes the core challenge for the efficient extraction of magnesium resources from salt lakes.

[0004] The physicochemical properties of salt lake clay significantly affect the occurrence and extraction efficiency of magnesium. Nitrogen adsorption-desorption (BET) analysis of salt lake clay containing grayish-brown magnesium in multiple occurrence states revealed that the clay exhibits typical mesoporous structure characteristics, with pore sizes concentrated in the range of 2-50 nm. Micropores of 2-10 nm dominate ion transport pathways, while mesopores of 10-50 nm provide diffusion channels. It also possesses a high specific surface area. This well-developed hierarchical pore structure not only provides ample active sites for magnesium ion adsorption and migration but also enhances the permeability of the solution within the mineral particles through capillary action. Regarding ion exchange characteristics, the clay exhibits a significant cation exchange capacity, mainly contributed by the interlayer negative charge of montmorillonite—specifically, the Al³⁺ in its aluminum-oxygen octahedrons. + Part of it was Mg² + Fe² + Equivalent state ion substitution results in a permanent negative charge per unit cell, thereby affecting Mg²⁺. + It exhibits specific adsorption capacity. Thermal stability studies show that the thermogravimetric-differential scanning calorimetry (TG-DSC) curve shows a significant endothermic valley in the 400-600℃ range, corresponding to the removal of interlayer bound water and hydroxyl groups. At this time, the interlayer spacing of montmorillonite shrinks, and some adsorbed magnesium is released. When the temperature rises above 800℃, the silicon-oxygen tetrahedron and aluminum-oxygen octahedron framework undergo reconstruction, resulting in an exothermic peak, marking the complete collapse of the mineral structure. Only at this stage is the lattice-bound magnesium fully released, but the energy consumption and equipment wear caused by the high temperature restrict its industrial application. The coupling effect of these physicochemical properties causes magnesium to form a dual "adsorption-lattice" solidification barrier in clay, which is the fundamental reason for the low efficiency of traditional extraction processes.

[0005] In summary, grayish-brown salt lake clays containing magnesium in various states are formed in unique salt lake sedimentary environments and possess many distinctive properties. In terms of mineral composition, they are rich in variety, containing not only common clay minerals such as montmorillonite and illite, but also salt minerals such as gypsum and mirabilite. Some magnesium-bearing minerals, such as magnesite and magnesia-montmorillonite, are also frequently present, representing potential magnesium resources. Structurally, they are mostly layered or platy, with well-developed intergranular pores, possessing a large specific surface area and ion exchange space. Chemically, they exhibit prominent characteristics, with strong ion exchange capacity; interlayer cations can exchange with external ions, and the surface carries a negative charge, adsorbing positively charged substances. Physically, they have extremely fine particle sizes, mostly in the micrometer or even nanometer range, are highly hygroscopic, swell upon contact with water, and their color varies depending on impurities. Furthermore, these minerals interact closely with the salt lake brine, forming as the salt lake evolves. Their formation and transformation are influenced by factors such as brine salinity and pH, and they also react upon the brine, significantly impacting the migration and enrichment of substances within it.

[0006] For magnesium-containing silicate minerals, strong alkaline solutions such as sodium hydroxide are commonly used for leaching. For example, serpentine reacts with sodium hydroxide, allowing magnesium to enter the solution in the form of magnesiumates. However, alkaline leaching requires high temperature and high pressure conditions, placing extremely high demands on equipment, making operation difficult and investment costs high. The large consumption of alkali solution and the difficulty in recovery lead to high production costs. Furthermore, the highly alkaline solution after leaching requires subsequent neutralization and other operations, making the process even more complex.

[0007] Water leaching is a method that uses water to dissolve water-soluble magnesium salts. For example, leaching magnesium from brine in a salt lake involves dissolving the magnesium salts in the brine. However, this method has low leaching efficiency, and sparingly soluble magnesium compounds are almost impossible to leach. The resulting solution has a low concentration of magnesium ions, requiring concentration and resulting in high energy consumption.

[0008] Bioleaching utilizes the interaction between microorganisms and their metabolites with magnesium-containing materials to dissolve magnesium; for example, organic acids produced by acidophilic microorganisms can react with magnesium compounds. However, microbial growth and metabolism are greatly affected by environmental factors such as temperature, pH, and nutrients, making the production process difficult to control and resulting in poor stability. Furthermore, the leaching speed is slow, and the production cycle is long, failing to meet the needs of large-scale industrial production. Currently, the technology is still immature, and further research is needed on the screening, cultivation, and application of microorganisms, leading to high technical costs. Summary of the Invention

[0009] The purpose of this invention is to address the aforementioned shortcomings of the prior art by proposing a magnesium extraction process from grayish-brown salt lake clay containing magnesium in multiple occurrence states.

[0010] The purpose of this invention is to provide a magnesium extraction process for gray-brown salt lake clay containing magnesium in multiple occurrence states, comprising the following steps: crushing and sieving the raw salt lake clay, then immersing the fine particles in a leaching agent, and filtering to obtain a leachate containing magnesium; wherein, the leaching agent is prepared by using concentrated hydrochloric acid, concentrated sulfuric acid, and low-mineralized water, with a volume ratio of concentrated hydrochloric acid, concentrated sulfuric acid, and low-mineralized water of 0.05-0.15:0.05-0.15:0.8; the low-mineralized water is natural water from the Mahai Basin.

[0011] Furthermore, the impregnation temperature is 25℃~45℃.

[0012] Furthermore, the impregnation temperature is 35°C.

[0013] Furthermore, the soaking time is 15-45 minutes.

[0014] Furthermore, the liquid-to-solid ratio of the leaching agent and the salt lake clay is 6 ml: 1 g.

[0015] Furthermore, ultrasonic-assisted leaching is employed.

[0016] Furthermore, the particle size of the fine particles is less than 16 mesh.

[0017] Furthermore, the volume ratio of concentrated hydrochloric acid, concentrated sulfuric acid, and low-mineralized water is 1:1:8.

[0018] This invention relates to a magnesium extraction process for salt lake clay containing magnesium in multiple occurrence states. Its core lies in the innovative use of a composite extractant prepared from low-mineralized water and mixed acids (sulfuric acid + hydrochloric acid), through Cl... - The multiple synergistic mechanisms of competitive adsorption-displacement, sulfate complexation and dissolution, and ultrasonic cavitation effect break through the bottlenecks of low efficiency, high energy consumption, and heavy pollution in magnesium extraction from salt lake clay using traditional methods. It achieves a high leaching rate, significantly improves leaching capacity compared to single-water-body processes, and reduces acidic wastewater discharge by more than 10%. This provides key technical support for the green development of magnesium resources in salt lakes and has important strategic significance for promoting the transformation of my country's salt lake industry towards high efficiency and low carbon emissions.

[0019] This invention, through systematic orthogonal experimental research, reveals the quantitative influence of process parameters such as temperature, time, and liquid-to-solid ratio on magnesium leaching rate, and achieves synergistic optimization of these parameters. For example, the magnesium leaching rate is significantly improved at a leaching temperature of 25℃; simultaneously, appropriate leaching time (e.g., 45 minutes) and liquid-to-solid ratio (6:1) can further optimize the leaching effect. The synergistic effect of these process parameters enables high-efficiency magnesium extraction with lower energy consumption and cost.

[0020] This invention introduces ultrasonic-assisted leaching technology, which enhances the mass transfer process through the cavitation effect of ultrasound, accelerating the desorption and dissolution of magnesium. During the leaching process, the microjets and shock waves generated by ultrasound can effectively disrupt the passivation layer on the surface of clay minerals, increasing the active sites at the reaction interface and thus improving the magnesium leaching rate. Furthermore, ultrasonic-assisted leaching can also promote the penetration and diffusion of the leaching agent within the mineral particles, further improving leaching efficiency. The introduction of this technology not only shortens the leaching time but also increases the magnesium leaching rate, providing strong support for the efficient extraction of magnesium resources.

[0021] In summary, in this invention, the synergistic effect of low-mineralized water and mixed acids (sulfuric acid + hydrochloric acid) allows the low-mineralized water to act not only as a solvent but also through its unique ionic composition (such as high concentrations of Cl-). - The combined action of Cl in the mixed acid significantly improves the leaching efficiency of magnesium. Specifically, Cl in low-mineralized water... - By competitively adsorbing and displacing magnesium ions on the surface of clay minerals, the amount of Na is reduced. + Ca² + The interference of competing cations increases the desorption rate of magnesium; simultaneously, sulfuric acid reacts with magnesium ions to form highly soluble MgSO4, further shifting the reaction equilibrium towards magnesium dissolution. Hydrochloric acid provides additional H+. + The presence of ions helps to disrupt the structure of clay minerals, releasing more magnesium ions. The cavitation effect and microjets of ultrasound further enhance the mass transfer process, accelerating magnesium desorption and dissolution. This synergistic effect not only improves the magnesium desorption rate but also reduces external energy consumption and wastewater treatment pressure, achieving low-cost, green, and efficient extraction of magnesium resources. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of the present invention;

[0023] Figure 2 Linear fitting of Mg concentration in the compound solution. Detailed Implementation

[0024] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0025] All reagents used in this protocol are of analytical grade.

[0026] Technical routes such as Figure 1 As shown.

[0027] 1) Sample pretreatment and drying: The collected solid clay samples from various salt lakes were evenly spread in an electrically heated constant-temperature drying oven, set at 110℃, and dried until the samples were completely dehydrated. After drying, the equipment was allowed to cool to room temperature, and the dried samples were sealed and labeled with sample information.

[0028] Crushing and homogenization: The dry sample is mechanically crushed using a jaw crusher, and the crushing parameters are adjusted to the target particle size range (usually below 16 mesh). After crushing, the sample is thoroughly mixed to ensure uniform particle size distribution.

[0029] 2) Particle size classification and screening

[0030] The particle size distribution of the crushed samples was analyzed using a particle size analyzer, and a 16-mesh standard sieve was selected for sieving. Sample accumulation and clogging of the sieve openings were avoided during the sieving process, and the undersize material was collected as raw material for subsequent experiments.

[0031] 3) Construction of leaching system

[0032] Sample weighing: Use an electronic balance to accurately weigh a fixed weight of the screened clay sample and place it in a clean container.

[0033] Leaching agent addition: Based on the optimized conditions of orthogonal experiments (e.g., a mixed acid + low-mineralized water composite system from the mining area), slowly add the leaching agent according to the set liquid-to-solid ratio (e.g., 6:1), and simultaneously start the top-mounted mechanical stirrer (speed 200-300 rpm) to ensure full contact between the clay and the leaching agent. Specifically, setting the leaching temperature to 25℃, the leaching time to 45 minutes, and the liquid-to-solid ratio of the leaching system to 6:1 (e.g., 600ml:100g) will result in better extraction effects. The composition and content of the low-mineralized water from the mining area are shown in Table 1.

[0034] 4) Enhance the leaching reaction

[0035] Ultrasonic-assisted leaching: Transfer the beaker to a heated ultrasonic cleaner, set the temperature to 25-55℃ (depending on experimental conditions), and the time to 15-60 minutes. The ultrasonic cavitation effect enhances the mass transfer process, accelerating the desorption and dissolution of magnesium.

[0036] 5) Solid-liquid separation

[0037] After leaching, immediately use a circulating water vacuum pump to filter the suspension, controlling the filtration rate to prevent the filter paper from breaking. Collect the filtrate and label it; dry the filter residue and store it for later use.

[0038] The filtrate and filter residue can be further processed and analyzed. The magnesium ion concentration in the filtrate is determined by inductively coupled plasma optical emission spectrometry (ICP-OES) or mass spectrometry (ICP-MS), and the leaching rate is calculated. The mineral phase composition and morphological characteristics of the filter residue are analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM-EDS).

[0039] Conditions for leaching clay from salt lakes

[0040] This study conducted a systematic orthogonal experimental investigation on four key process parameters: leaching temperature, leaching time, acid concentration, and liquid-to-solid ratio. To deeply analyze the quantitative influence of each parameter on the target index, an L16(4^4) orthogonal experimental matrix was constructed based on the principle of four-factor, four-level orthogonal experimental design. This experimental design, through 16 sets of parameter combinations with significant differences, can efficiently achieve the decoupling analysis of the synergistic effect mechanism of multiple factors, while ensuring that the experimental schemes have good coverage and representativeness in the four-dimensional parameter space.

[0041] Specifically, the leaching temperatures were set at four different gradients: 25°C, 35°C, 45°C, and 55°C. These temperature gradients were designed to cover the possible operating temperature range so that we could observe the specific effect of temperature on the experimental results. The leaching times were also subdivided into four gradients: 15 minutes, 30 minutes, 45 minutes, and 60 minutes. This was to understand the extent to which the leaching process affected the sample at different time lengths. The liquid-to-solid ratios were also set at four different gradients: 3:1, 4:1, 5:1, and 6:1. These gradients reflect the different ratios between the solvent and the solid sample, helping to understand the specific impact of the liquid-to-solid ratio on the experimental results.

[0042] Throughout the orthogonal experiment, the experimental conditions were strictly adhered to, and the results of each group of experiments were recorded (as shown in Table 2). Subsequent data analysis will allow us to determine the degree of influence of each factor on the experimental results and the optimal combination of experimental conditions.

[0043] Table 1. Composition and content of low-mineralized water

[0044]

[0045] Table 2 Leaching Parameter Settings

[0046]

[0047] Leaching effect testing and leaching rate calculation

[0048] First, the magnesium content in the leachate and leaching residue was determined using inductively coupled plasma atomic emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS), respectively. Then, the leaching rate was calculated using the formula shown below.

[0049]

[0050] The principle of the calculation formula is: the percentage of the element content in the liquid relative to the total element content.

[0051] Examples and Comparative Examples

[0052] To illustrate the effect of low-mineralized water combined with mixed acid (98% sulfuric acid + 37% hydrochloric acid) as an extractant, the leaching effect of the extractant was compared with that of ordinary mixed acid (98% sulfuric acid + 37% hydrochloric acid + water) and fresh water as extractants under different leaching temperatures, leaching times, and liquid-solid ratios.

[0053] Table 3. Composition and content (volume fraction) of the solution after mixing the mixed acid with low-mineralized water.

[0054]

[0055] Based on the gradient compounding test results of mixed acid and low-mineralized water, the concentration curve of Mg ions in the composite extractant was fitted and used to calculate the initial values ​​in different leaching systems. After subtracting the blank value, the true leaching rate of Mg element in the experiment can be obtained. By comparing the true leaching rate, the residual mass ratio of Mg element in the leaching residue and the true leached magnesium ion concentration, the leaching effect of Mg ions can be compared.

[0056] The salt lake clay samples used in the examples were all collected from the Mahai Salt Lake mining area.

[0057] Example 1

[0058] Comparison of leaching effects under different component ratios in a low-mineralization water + mixed acid composite extractant system

[0059] Table 4 Comparison of leaching effects of extractants with different component ratios

[0060]

[0061] In experiments using a composite leaching agent consisting of low-mineralized water and mixed acids (sulfuric acid + hydrochloric acid) to extract magnesium from grayish-brown salt lake clay containing magnesium in multiple states, the volume fraction of different components significantly affected the leaching effect. Under conditions of 25℃, 45 minutes, and a liquid-to-solid ratio of 6:1, the highest magnesium concentration (13021 mg / L) and leaching rate (82.39%) were achieved when the volume fractions of sulfuric acid and hydrochloric acid were 0.1 and 0.1, respectively. Furthermore, the residual magnesium mass ratio in the leaching residue was only 1.67%, indicating that the composite leaching agent exhibited the best magnesium leaching effect under this ratio, significantly improving the magnesium extraction efficiency. While the leaching effects varied slightly under other ratios, a high leaching rate and magnesium concentration were maintained overall, further validating the effectiveness of the composite leaching agent.

[0062] In subsequent embodiments, unless otherwise specified, the ratio of components in the mixed extractant system is: sulfuric acid: hydrochloric acid: low-mineralization water = 1:1:8.

[0063] Example 2

[0064] Comparison of leaching effects of low-mineralized water + mixed acid composite extractant system under different process parameters

[0065] Table 5.1 Comparison of leaching effects under different temperature parameters

[0066]

[0067] In an experiment to extract magnesium from gray-brown salt lake clay containing magnesium in multiple states using a composite leaching agent composed of low-mineralized water and mixed acid (where sulfuric acid: hydrochloric acid: low-mineralized water = 1:1:8), different temperatures had a significant impact on the leaching effect under the conditions of a constant leaching time of 45 minutes and a constant liquid-to-solid ratio of 6:1. Data shows that at 25℃, the leached magnesium concentration reached 13021 mg / L, the magnesium leaching rate was 82.39%, and the residual magnesium mass ratio in the leaching residue was 1.67%. As the temperature rose to 35℃ and 55℃, the leached magnesium concentration increased, reaching 13928 mg / L and 14093 mg / L respectively, but the magnesium leaching rate fluctuated slightly, at 80.93% and 82.06% respectively. Simultaneously, the residual magnesium mass ratio in the leaching residue also increased slightly. This indicates that while high temperatures can increase the leached magnesium concentration, the increase in leaching rate is not significant and may increase the difficulty of subsequent processing. At 45℃, both the leached magnesium concentration and leaching rate were at a relatively intermediate level, at 11892 mg / L and 80.04% respectively. In summary, within the temperature range of 25℃ to 55℃, the effect of temperature on leaching efficiency is not linear. The optimal temperature needs to be determined by comprehensively considering factors such as leaching rate, leaching concentration, and residual leaching residue. The overall effect is best at 25℃.

[0068] Table 5.2 Comparison of leaching effects under different time parameters

[0069]

[0070] According to experimental data, under the conditions of 25℃ and a liquid-to-solid ratio of 6:1 (components: sulfuric acid: hydrochloric acid: low-mineralization water = 1:1:8), different leaching times significantly affected the magnesium extraction efficiency from grayish-brown salt lake clay containing magnesium in multiple states. Data showed that when the leaching time was 45 minutes, the leached magnesium concentration reached its highest value of 13021 mg / L, and the magnesium leaching rate also reached its highest level of 82.24%, with a residual magnesium mass ratio in the leaching residue of only 1.67%, indicating the optimal leaching effect at this time. In contrast, when the leaching time was 15 minutes and 30 minutes, the leached magnesium concentration and leaching rate were both lower, while the residual magnesium mass ratio in the leaching residue was higher. When the leaching time was extended to 60 minutes, although the leached magnesium concentration decreased slightly but remained at a high level (13064 mg / L), the leaching rate decreased slightly to 79.00%, and the residual magnesium mass ratio in the leaching residue increased to 2.01%. In summary, 45 minutes is a relatively ideal leaching time, which can effectively reduce the residual magnesium mass ratio in the leaching residue and improve magnesium extraction efficiency while ensuring a high leaching rate and magnesium concentration.

[0071] Table 5.3 Comparison of leaching effects under different liquid-solid ratio parameters

[0072]

[0073] According to experimental data, under the conditions of 25℃ and leaching time of 45 minutes (components: sulfuric acid: hydrochloric acid: low-mineralization water = 1:1:8), the liquid-to-solid ratio significantly affects the magnesium extraction effect from grayish-brown salt lake clay containing magnesium in multiple states. Data shows that as the liquid-to-solid ratio increases from 3:1 to 6:1, both the leached magnesium concentration and the magnesium leaching rate show an upward trend. Specifically, at a liquid-to-solid ratio of 6:1, the leached magnesium concentration reaches its highest value of 13021 mg / L, and the magnesium leaching rate also reaches its highest value of 82.39%. Although the residual magnesium mass ratio in the leaching residue (1.67%) is slightly higher than that at a liquid-to-solid ratio of 3:1 (1.49%), the overall leaching effect is significantly better than other liquid-to-solid ratio conditions. In contrast, at a liquid-to-solid ratio of 3:1, both the leached magnesium concentration and leaching rate are lower, at 8250 mg / L and 62.47%, respectively. Therefore, overall, a liquid-to-solid ratio of 6:1 ensures a high leaching rate and magnesium concentration, although the residual amount of leaching residue increases slightly, but the overall magnesium extraction effect is the best, making it a relatively ideal liquid-to-solid ratio condition.

[0074] Based on comprehensive experimental data and process optimization objectives, the optimal parameter combination for magnesium extraction from grayish-brown salt lake clay containing magnesium in multiple states is: temperature 25℃, time 45 minutes, and liquid-to-solid ratio 6:1. Under these conditions, the leaching rate reaches 82.39%, the leached magnesium concentration is as high as 13021 mg / L, and the residual amount of leaching residue is relatively low, ensuring efficient extraction while also considering low energy consumption and equipment stability. Compared to high temperature (55℃) or longer reaction time (60 minutes), the combination of 25℃ and 45 minutes significantly reduces energy consumption and operational complexity; while the liquid-to-solid ratio of 6:1 enhances the contact efficiency between the leaching agent and clay minerals, achieving dual optimization of leaching rate and economy. This parameter combination provides core technical support for the green development of salt lake magnesium resources, balancing efficiency, cost, and environmental protection.

[0075] Example 3

[0076] Comparison of low-mineralized water + mixed acid compound extractant system and low-mineralized water + single acid extractant system

[0077] Table 6 Comparison of leaching effects between compound mixed acid extractant and single acid extractant

[0078]

[0079] Under uniform conditions of 25℃, 45 minutes, and a liquid-to-solid ratio of 6:1, the type of leaching agent significantly affected the magnesium extraction efficiency from grayish-brown salt lake clay containing magnesium in multiple states. Three parallel experiments were conducted for comparison and verification of each leaching agent. When using a composite leaching agent of low-mineralized water and mixed acid (sulfuric acid + hydrochloric acid) (sulfuric acid: hydrochloric acid: low-mineralized water = 1:1:8), the highest leached magnesium concentration reached 14515 mg / L, with an average leaching rate of 82.34% and the lowest residual magnesium content in the leaching residue as low as 1.67%. However, when using low-mineralized water alone with sulfuric acid or hydrochloric acid, the leached magnesium concentration decreased significantly (highest in the sulfuric acid group: 8710 mg / L, highest in the hydrochloric acid group: 6930 mg / L), the leaching rates decreased to 68.94% and 65.81%, respectively, and the residual leaching residue was generally higher than that of the composite system (highest in the sulfuric acid group: 2.44%, highest in the hydrochloric acid group: 2.23%). This indicates that the mixed acid component, through Cl... - The synergistic effect of competitive adsorption and sulfate complexation significantly enhances the desorption and dissolution of magnesium, while the single acid extractant, lacking multiple mechanisms of action, results in a significant reduction in leaching efficiency.

[0080] Example 4

[0081] Comparison of low-mineralized water + mixed acid composite extractant system with fresh water + mixed acid extractant system

[0082] Table 7 Comparison of leaching effects between compound mixed acid extractant and fresh water mixed acid extractant

[0083]

[0084] Under conditions of 25℃, 45 minutes, and a liquid-to-solid ratio of 6:1, the composite leaching agent system (sulfuric acid: hydrochloric acid: low-mineralized water = 1:1:8) showed significantly better leaching performance for grayish-brown salt lake clay containing magnesium in multiple states than the fresh water + mixed acid system. The low-mineralized water + mixed acid combination resulted in a maximum leaching magnesium concentration of 14515 mg / L, an average leaching rate of 82.34%, and the lowest residual magnesium content in the leaching residue (1.67%). In contrast, the fresh water + mixed acid system resulted in a maximum leaching magnesium concentration of only 10800 mg / L, an average leaching rate of 73.12%, and a generally higher residual magnesium content in the leaching residue compared to the low-mineralized water system (maximum 2.56%). This indicates that ions in low-mineralized water (such as Ca²⁺)... + Mg² + The binding of magnesium to clay minerals may have been weakened through competitive adsorption or the salt effect, while the Cl in the mixed acid... - With SO4² - Synergistic effects promote magnesium dissolution, while the lack of these auxiliary mechanisms in freshwater systems leads to a significant decrease in leaching efficiency. Therefore, the composite system of low-mineralized water and mixed acid significantly improves magnesium leaching rate and resource utilization through the dual effects of ionic synergy and chemical complexation.

[0085] Example 5

[0086] Comparison of low-mineralized water + mixed acid composite extractant system with non-acidified extractant system

[0087] Table 8 Comparison of leaching effects between compound extractants and non-acid extractants

[0088]

[0089] Under the same experimental conditions of 25℃, 45 minutes, and a liquid-to-solid ratio of 6:1, the type of leaching agent had a significant effect on the magnesium extraction efficiency of gray-brown salt lake clay containing magnesium in multiple states: when using a composite leaching agent of low-mineralized water and mixed acid (sulfuric acid: hydrochloric acid: low-mineralized water = 1:1:8), the highest leached magnesium concentration reached 14515 mg / L, with an average leaching rate of 82.34%, and the residual magnesium mass ratio in the leaching residue was as low as 1.67%; while when using pure low-mineralized water or pure fresh water alone, the leached magnesium concentration plummeted to 1150-1620 mg / L, with an average leaching rate of less than 12%, and the residual leaching residue was as high as 5.73%-9.90%. This indicates that the mixed acid component, through Cl... - Competitive adsorption with SO4² - The complexation effect significantly enhances the desorption and dissolution of magnesium, while background ions in low-mineralized water (such as Ca²⁺) are reduced. + Mg² +The salt effect may further weaken the binding of magnesium by clay minerals; in contrast, the pure water system, lacking chemical activation and ionic synergy, results in extremely low magnesium leaching efficiency. Therefore, the composite extractant system achieves efficient extraction of magnesium resources through the synergistic effect of multiple mechanisms.

[0090] Example 6

[0091] The samples used in this method were all collected from the Mahai Salt Lake mining area. Besides the grayish-brown salt lake clay containing magnesium in multiple states, halite clay directly collected from the halite layer of the salt lake was also included. Its main components are a mixture of clay minerals and halite, reflecting the unique mineral assemblage of the salt lake sedimentary environment. In addition, silty clay samples were also included in the study. These samples, mainly composed of a mixture of clay minerals and silt, represent the characteristics of the salt lake's edge or shallow sedimentary environment. The selection of these samples not only considered the diversity of mineral composition but also the representativeness of different sedimentary layers in the salt lake, providing experimental support for a comprehensive evaluation of the effectiveness and applicability of the magnesium extraction process.

[0092] Table 9. Results of clay leaching from different layers in the Mahai area

[0093]

[0094] The differences in magnesium leaching effects among the three clay samples mainly stem from the differences in their total magnesium content and magnesium occurrence. The gray-brown clay had the highest total magnesium content (average 10028 mg / 100g), and it likely existed more in easily leached forms such as adsorbed and exchangeable forms. Therefore, the leaching concentration (average 13762 mg / L) and leaching rate (average 82.34%) of magnesium under the action of the composite extractant were significantly better than other samples. The total magnesium content of the silty clay (5336-5609 mg / 100g) was only 50%-60% of that of the gray-brown clay, and some magnesium may have been bound to silicate minerals, resulting in a moderate leaching rate (68.41%) and concentration (6090-6393 mg / L). The total magnesium content of the halite clay was the lowest (2525-2640 mg / 100g), and the high-salt environment inhibited magnesium dissolution through ion competitive adsorption and salting-out effects, further reducing the leaching efficiency (45%-57%), with a leached magnesium concentration of only 1983-2465 mg / L.

[0095] Under uniform experimental conditions, the leaching effect of the composite extractant on magnesium in the three clay samples varied due to the different characteristics of the samples. For the grayish-brown clay with the highest total magnesium content, the composite extractant achieved a leaching rate of over 80%, with an average magnesium concentration exceeding 10,000 mg / L, indicating its effective desorption of the adsorbed magnesium. For the silty clay layer, the magnesium content was lower than that of the grayish-brown clay (average 5,500 mg / 100g), and the quartz content was very high. Even with the composite extractant, only about 68% of the magnesium could be extracted, with a leaching concentration in the 6,000 mg / L range. For the halite clay layer, the magnesium content was much lower than that of the grayish-brown clay (average 2,585 mg / 100g), and it contained a large amount of quartz and feldspar components. The composite extractant could only leach out 45%-57% of the magnesium. The composite extractant, through the synergistic effect of complexation by mixed acids and salt effect by low-mineralized water, achieves highly efficient extraction of magnesium resources from gray-brown clay compared to silt and halite clay layers.

[0096] In summary, this method, through the selection of representative salt lake clay samples and the use of a composite extractant of low-mineralized water and mixed acid (sulfuric acid: hydrochloric acid: low-mineralized water = 1:1:8), conducted systematic extraction experiments under different conditions. The experimental results show that the sulfuric acid + hydrochloric acid + low-mineralized water composite extractant, through the synergistic effect of its components, exhibits excellent leaching effect on the grayish-brown clay of the Mahai region under suitable experimental conditions.

[0097] For any points not covered above, existing technologies shall apply.

[0098] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for extracting magnesium from grayish-brown salt lake clay containing magnesium in multiple occurrence states, characterized in that, The process includes the following steps: crushing and sieving the salt lake clay, then impregnating the fine particles in a leaching agent, using ultrasonic-assisted leaching, and filtering to obtain a leachate containing magnesium; wherein the leaching agent is prepared by using concentrated hydrochloric acid, concentrated sulfuric acid, and low-mineralized water, with a volume ratio of concentrated hydrochloric acid, concentrated sulfuric acid, and low-mineralized water of 0.05-0.15:0.05-0.15:0.8; the low-mineralized water is natural water from the Mahai Basin.

2. The magnesium extraction process from grayish-brown salt lake clay containing magnesium in multiple occurrence states as described in claim 1, characterized in that, Impregnation temperature: 25℃~45℃.

3. A process for the extraction of magnesium from a magnesian, limonitic, salt lake clay containing multiple occurrences of magnesium as claimed in claim 1, characterised in that, The impregnation temperature is 35℃.

4. The process for extracting magnesium from a magnesian gray-brown salt lake clay containing multiple occurrence states of magnesium according to claim 1, characterized in that, Soaking time: 15-45 minutes.

5. A process for the extraction of magnesium from a magnesian, limonitic, salt lake clay containing multiple occurrences of magnesium as claimed in claim 1, characterised in that, The liquid-to-solid ratio of the leaching agent to the salt lake clay is 6 ml: 1 g.

6. A process for the extraction of magnesium from a magnesian, limonitic, salt lake clay containing multiple occurrences of magnesium as claimed in claim 1, characterised in that, The particle size of the fine particles is less than 16 mesh.

7. The magnesium extraction process from grayish-brown salt lake clay containing magnesium in multiple occurrence states as described in claim 1, characterized in that, The volume ratio of concentrated hydrochloric acid, concentrated sulfuric acid, and low-mineralized water is 1:1:8.

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