Method for selectively extracting magnesium from serpentine

Abstract

The application belongs to the technical field of hydrometallurgy and mineral processing, and particularly discloses a method for selectively extracting magnesium from serpentine. The method comprises the following steps: crushing, ball milling and sieving serpentine raw ore to obtain serpentine powder; mixing the serpentine powder with a zinc sulfate solution, and performing leaching reaction by heating and stirring; after the reaction is completed, performing solid-liquid separation to obtain filtrate and filter residue; performing evaporation concentration and crystallization treatment on the filtrate to precipitate crystals, collecting the crystals and performing calcination treatment, mixing the obtained product with aluminum powder, performing vacuum aluminothermic reduction reaction, and performing condensation collection to obtain magnesium metal. The method can selectively extract magnesium from serpentine, and turns waste into treasure. Not only the problem of synchronous dissolution of impurities such as iron and nickel in the traditional acid leaching method is avoided, but also a high-value magnesium metal product is obtained.

Description

Technical Field

[0001] This invention relates to the fields of hydrometallurgy and mineral processing technology, and in particular to a method for selectively extracting magnesium from serpentine. Background Technology

[0002] Serpentine is a hydrous magnesium silicate mineral with the general chemical formula A6[Si4O]. 10 ](OH)8, where A is mainly Mg 2+ Fe 2+ Ni 2+ Elements such as magnesium can be isomorphously substituted for magnesium. The MgO content in serpentine can generally reach 43.6%, and my country has proven serpentine reserves of over 5 billion tons, which are widely distributed and represent a highly promising magnesium resource.

[0003] Currently, the mainstream method for extracting magnesium from serpentine is the direct sulfuric acid leaching method. This involves using high-concentration sulfuric acid to leach magnesium from serpentine under specific temperature conditions, followed by neutralization precipitation, evaporation crystallization, and calcination to obtain magnesium oxide. Studies have shown that under conditions of 5 mol / L sulfuric acid concentration, 4 mL / g liquid-to-solid ratio, and leaching temperature of 100 °C, the magnesium leaching rate can reach over 93.98%. However, existing methods have several drawbacks: firstly, high-concentration sulfuric acid severely corrodes equipment, resulting in high processing costs; secondly, during the acid leaching process, large amounts of impurities such as iron, aluminum, and nickel are simultaneously leached (iron leaching rate approximately 60%, aluminum approximately 82%, and nickel approximately 90%), leading to cumbersome subsequent separation and purification steps and difficulty in guaranteeing product purity; and thirdly, the acid leaching wastewater is difficult to treat and easily causes environmental pollution.

[0004] Therefore, developing a magnesium extraction method that can selectively extract magnesium from serpentine, avoid the simultaneous dissolution of impurities, and is environmentally friendly has significant industrial value and environmental implications. Summary of the Invention

[0005] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention provides a method for selectively extracting magnesium from serpentine. The method of this invention aims to efficiently and cleanly convert magnesium in serpentine into a high-purity metallic magnesium product, solving problems such as impurity co-dissolution, difficult separation, and serious environmental pollution in existing serpentine magnesium extraction processes.

[0006] This invention provides a method for selectively extracting magnesium from serpentine, comprising the following steps:

[0007] S1. The raw serpentine ore is crushed, ball-milled, and sieved to obtain serpentine powder with a particle size ≤200 mesh.

[0008] S2. Mix serpentine powder with zinc sulfate solution, heat and stir to carry out leaching reaction, and after the reaction is completed, separate solid and liquid to obtain filtrate and filter residue.

[0009] S3. The filtrate is evaporated and concentrated, crystallized to precipitate crystals, the crystals are collected and calcined, the obtained product is mixed with aluminum powder, vacuum aluminothermic reduction reaction is carried out, and magnesium metal is obtained by condensation and collection.

[0010] According to a specific embodiment of the present invention, the method of the present invention uses a zinc sulfate solution as a serpentine leaching solution to selectively leach magnesium from serpentine in the form of magnesium sulfate, while zinc reacts with silicon, hydroxyl groups, and sulfate ions to form Zn8(OH). 13 [SiO(OH)3SO4] precipitation fixes silicon in situ, avoiding the problems of silica gel blockage and simultaneous dissolution of impurities such as iron and aluminum in the traditional acid leaching method. The resulting magnesium sulfate solution is pure, and finally, metallic magnesium with a purity of over 99.5% is obtained.

[0011] According to some embodiments of the present invention, the serpentine ore contains 35% to 45% magnesium oxide and 38% to 45% silicon dioxide.

[0012] According to some embodiments of the present invention, in step S1, the ball milling uses a planetary ball mill with a ball milling speed of 400~800 rpm; preferably, the ball milling speed is 600~800 rpm; preferably, the sieving process is a 200-mesh sieve with a sieve residue of ≤5%.

[0013] According to some embodiments of the present invention, in step S2, the solid-liquid ratio of the serpentine powder and the zinc sulfate solution is 1:(5~20)g / mL; the concentration of the zinc sulfate solution is 0.5~2.0 mol / L.

[0014] According to some preferred embodiments of the present invention, in step S2, the solid-liquid ratio of the serpentine powder to the zinc sulfate solution is 1:(8~20)g / mL; the concentration of the zinc sulfate solution is 0.8~1.5 mol / L.

[0015] According to some embodiments of the present invention, in step S2, the conditions for the leaching reaction are: stirring speed 200~600 rpm, temperature 65~95 ℃, and time 4~10 h.

[0016] According to some preferred embodiments of the present invention, the leaching reaction conditions are: stirring speed 300~500 rpm, temperature 75~95 ℃, and time 5~8 h.

[0017] According to some embodiments of the present invention, during the leaching reaction, the pH of the system is adjusted to 5.0±0.3 every 20 to 40 minutes using dilute sulfuric acid or ammonia.

[0018] According to some embodiments of the present invention, in step S2, the filter residue further undergoes the following treatment:

[0019] The filter residue is mixed with dilute sulfuric acid solution, stirred and heated to react, and then separated into solid and liquid to obtain a regenerated zinc sulfate solution.

[0020] In this invention, the regenerated zinc sulfate solution can be recycled for leaching reaction with serpentine powder, thereby realizing the recycling of zinc salts.

[0021] According to some embodiments of the present invention, in step S3, the temperature of evaporation and concentration is 80-105 °C; after collecting the crystals, they are further subjected to ice water washing and drying treatment.

[0022] According to some embodiments of the present invention, in step S3, the calcination treatment is carried out at a temperature of 700–1000 °C for 2–5 h.

[0023] According to some embodiments of the present invention, in step S3, the temperature of the aluminothermic reduction reaction is 1000~1250℃, the time is 1.5~4 h, and the excess coefficient of aluminum powder is 1.2~2 times the theoretical amount.

[0024] The beneficial effects of this invention are:

[0025] This invention utilizes zinc sulfate solution as the leaching solution for serpentine powder to achieve efficient and selective leaching of magnesium, while the Zn8(OH) generated during the reaction process... 13 [SiO(OH)3SO4] precipitation can fix silicon in situ, avoiding the problem of silica gel clogging the filter pores in the traditional acid leaching method; while the synergistic effect of sulfate and zinc ions can not only maintain the pH stability of the reaction system, but also significantly reduce the dissolution of impurity elements such as iron, aluminum, and nickel, thereby obtaining a high-purity magnesium sulfate solution, which is finally calcined and aluminothermicly reduced to obtain a metallic magnesium product with a purity ≥99.5%;

[0026] This invention also enables the recycling of zinc salts, Zn8(OH). 13 The zinc sulfate solution obtained by regenerating the zinc in the [SiO(OH)3SO4] precipitate can be well used for the leaching reaction of serpentine powder, and has good cycle stability, which can continuously obtain high-grade metallic magnesium products, with significant economic and environmental benefits.

[0027] In the technical solution of this invention, the leaching reaction of zinc sulfate solution is more favorable by utilizing the disruptive effect of mechanochemical activation on the serpentine lattice; furthermore, the lattice disruption mechanism driven by isomorphic substitution of zinc ions and Zn8(OH) are utilized. 13The formation and reaction-driven role of [SiO(OH)3SO4] precipitate, as well as the structural support and synergistic effect of sulfate ions, enable the efficient leaching of magnesium from serpentine, resulting in high-purity magnesium sulfate and subsequent metallic magnesium products.

[0028] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0030] Figure 1 Zn8(OH) in Example 1 of this invention 13 XRD pattern of [SiO(OH)3SO4] precipitate. Detailed Implementation

[0031] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0032] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0033] In this embodiment, the magnesium content in the magnesium product is calculated using the difference method, i.e., 100% minus the sum of the mass fractions of each impurity element. The determination of the impurity element content (including but not limited to iron, aluminum, nickel, zinc, silicon, etc.) is performed according to GB / T 13748.20-2024 "Chemical Analysis Methods for Magnesium and Magnesium Alloys Part 20: Determination of Elemental Content by Inductively Coupled Plasma Atomic Emission Spectrometry". The specific procedure is as follows: Accurately weigh approximately 0.5000 g of the magnesium sample and place it in a 100 mL beaker. Add 10 mL of analytical grade pure nitric acid (1+1), heat at low temperature until the sample is completely dissolved, cool, and then transfer to a 50 mL volumetric flask. Dilute to the mark with deionized water. Use an inductively coupled plasma atomic emission spectrometer (ICP-AES) to determine the working curve and the emission intensity of each impurity element in the sample solution at the selected analytical spectral wavelength. Calculate the content of each impurity element based on the working curve. The detection limits for each element are: Fe ≤ 0.001%, Al ≤ 0.001%, Ni ≤ 0.001%. For high-purity metallic magnesium samples with a magnesium content greater than 99.9%, trace impurities were determined according to GB / T 13748.24-2025 "Chemical Analysis Methods for Magnesium and Magnesium Alloys Part 24: Determination of Trace Impurity Elements by Glow Discharge Mass Spectrometry". The purity of metallic magnesium was calculated by the difference method.

[0034] Example 1

[0035] This embodiment provides a method for selectively extracting magnesium from serpentine, the specific steps of which are as follows:

[0036] 1) Ball milling pretreatment: The serpentine ore is crushed to a particle size of less than 5 mm by a jaw crusher, and then fed into a planetary ball mill for ball milling. The ball milling conditions are: the grinding media is zirconia balls, the ball-to-material mass ratio is 10:1, the ball milling speed is 600 rpm, and the ball milling time is 2 h. After ball milling, the ore is passed through a 200-mesh standard sieve, and the sieve residue is 4.5%, and serpentine powder is obtained for later use.

[0037] 2) Preparation of zinc sulfate leaching solution: Weigh 287.5 g of zinc sulfate heptahydrate (ZnSO4·7H2O, analytical grade), slowly add 1 L of deionized water, and stir thoroughly with a magnetic stirrer to dissolve, thus preparing the Zn... 2+ A zinc sulfate solution with a concentration of 1.0 mol / L.

[0038] 3) Leaching reaction: Take 100 g of serpentine powder obtained in step 1) and add it to 1000 mL of zinc sulfate solution prepared in step 2) to make the solid-liquid ratio 1:10 (g / mL); place the reaction mixture in a 2L three-necked round-bottom flask, place the flask in a constant temperature water bath, and install a mechanical stirrer and reflux condenser; turn on the stirrer, set the stirring speed to 400 rpm, raise the temperature to 85 ℃, and keep the temperature constant for 6 h; during the reaction, take a sample every 30 min to measure the pH value of the solution. If the pH deviates from the range of 5.0±0.3, adjust it slightly with dilute sulfuric acid or ammonia solution;

[0039] During the reaction, a white precipitate was gradually formed, and the solution color changed from colorless and clear to a milky white suspension. After the reaction was completed, a small amount of the reaction solution was filtered, and the filter residue was washed with deionized water, dried, and then subjected to X-ray diffraction analysis. The results are as follows. Figure 1 As shown, the precipitate is confirmed to be Zn8(OH). 13 [SiO(OH)3SO4] phase.

[0040] 4) Solid-liquid separation: The reaction mixture was vacuum filtered using a Buchner funnel with rapid qualitative filter paper (pore size 15-20 μm). The filter residue was collected and washed three times with 100 mL of deionized water. The washing liquid was combined with the filtrate. The filtrate (about 1050 mL) was colorless and transparent and was ready for use.

[0041] 5) Magnesium sulfate crystallization: The filtrate was placed in a rotary evaporator, with a water bath temperature of 90 ℃ and a vacuum degree of 0.08 MPa, and evaporated and concentrated to about 1 / 2 of the original volume (about 525 mL). The concentrated solution was transferred to a beaker, allowed to cool naturally to room temperature, and allowed to stand for 12 h. White needle-like magnesium sulfate crystals precipitated. The crystals were collected by suction filtration using a Buchner funnel, washed twice with a small amount of ice water, and dried in a vacuum drying oven at 50 ℃ for 6 h to obtain 137.6 g of magnesium sulfate heptahydrate crystals. The calculation showed that the magnesium leaching rate was 96.3%, and the purity of the magnesium sulfate product was 99.2% (excluding water).

[0042] 6) Calcination and decomposition to produce magnesium oxide: Place the magnesium sulfate heptahydrate crystals obtained in step 5) in a corundum crucible and put it into a muffle furnace; set the heating program: increase the temperature from room temperature to 850 ℃ at a rate of 5 ℃ / min, and hold for calcination for 4 h to completely decompose the magnesium sulfate heptahydrate into magnesium oxide; the reaction equation is:

[0043] MgSO4·7H2O → MgO + SO3↑ + 7H2O↑;

[0044] After calcination, the furnace was allowed to cool naturally to room temperature, yielding white magnesium oxide powder.

[0045] 7) Aluminothermic reduction: Weigh the magnesium oxide powder and aluminum powder (purity 99.5%, particle size 200 mesh) obtained in step 6), and mix them with an aluminum powder excess coefficient of 1.5. Mechanically mix the mixture in a ball mill jar for 30 min until homogeneous. Place the mixture into an aluminothermic reaction crucible, place it in a vacuum aluminothermic reaction furnace, evacuate to a vacuum degree ≤10 Pa, heat to 1150 ℃ at a rate of 10 ℃ / min, and hold for 2 h. After the reaction is completed, cool the furnace to room temperature and remove the reaction product from the magnesium collector to obtain high-purity metallic magnesium.

[0046] The product performance of Example 1 was tested and calculated: the final magnesium purity was 99.8%, with impurity elements including 0.04% iron, 0.03% aluminum, and 0.01% nickel.

[0047] The above product performance data shows that the method provided in this embodiment can efficiently and selectively extract magnesium from serpentine and obtain a high-purity final product.

[0048] Example 2

[0049] This embodiment experimentally verifies the recycling of zinc salts, and the specific method is as follows:

[0050] 1) Zinc salt recovery:

[0051] The filter residue obtained in step 4 of Example 1 (wet weight approximately 185 g, dry weight approximately 162 g) was analyzed by XRF for its chemical composition (dry weight): ZnO 68.2%, SiO2 18.5%, SO3 8.1%, MgO 1.2%, H2O (loss on ignition) approximately 4.0%;

[0052] The filter residue was placed in a 2 L glass reactor, and 800 mL of 1.5 mol / L dilute sulfuric acid solution was added, maintaining a liquid-to-solid ratio of 5:1 (mL / g). Stirring was started (400 rpm), and the temperature was raised to 60 °C. The reaction was maintained at this temperature for 2 h. The reaction equation is as follows:

[0053] Zn8(OH) 13 [SiO(OH)3SO4] + 8H2SO4 → 8ZnSO4 + SiO2·nH2O↓ + 12H2O;

[0054] During the reaction, the precipitate gradually dissolves, releasing Zn. 2+ Silicon remained as amorphous silica hydrate (silica gel). After the reaction, the mixture was vacuum filtered while hot. The filter residue (mainly amorphous SiO2, containing a small amount of unreacted zinc precipitate) was washed three times with 100 mL of deionized water. The washing liquid and filtrate were combined. The total volume of the filtrate was approximately 950 mL. Zn was determined by ICP-OES. 2+The concentration was 1.04 mol / L, and the pH was approximately 3.5. The pH of the filtrate was adjusted to 5.0 ± 0.2 with dilute sodium hydroxide solution to obtain the regenerated zinc sulfate solution (Zn). 2+ Approximately 1.0 mol / L), while a small amount of Fe and Al hydroxide precipitates were formed, which were removed by filtration again; finally, approximately 900 mL of clear regenerated zinc sulfate solution was obtained, with a zinc recovery rate (based on zinc in the precipitate) of 93.7%.

[0055] 2) Circulating leaching experiment of regenerated zinc sulfate solution:

[0056] A second leaching experiment was conducted using 1000 mL of the above-mentioned regenerated zinc sulfate solution under the exact same conditions as in Example 1.

[0057] The product test results after one cycle were as follows: magnesium leaching rate was 95.8%, magnesium sulfate product purity was 99.1%, magnesium oxide purity was 99.4%; the final metallic magnesium purity was 99.7%, of which the impurity elements iron content was 0.05%, aluminum content was 0.03%, nickel content was 0.01%, and zinc residue content was 0.02%.

[0058] 3) Stability verification through multiple cycles:

[0059] To further investigate the cyclic stability of zinc salts, the zinc sulfate solution was regenerated and used for the leaching of the third batch of serpentine (i.e., the second cycle), under identical operating conditions. After the second cycle, the magnesium leaching rate was 95.3%, the magnesium sulfate product purity was 99.0%, and the metallic magnesium purity was 99.6%. After two consecutive cycles, the cumulative decrease in magnesium leaching rate was only 1.0 percentage point, and the product purity remained at the superior level.

[0060] To investigate the cumulative effect of trace impurities during the recycling process, ICP-OES analysis was performed on the regenerated zinc sulfate solution after the second cycle. The results showed that Fe in the solution... 3+ Al 3+ The concentrations were approximately 15 mg / L and 8 mg / L, respectively, Ni 2+ When the concentration is below 1 mg / L, most of these trace impurities will be filtered out during each regeneration process as hydroxide precipitates are generated by pH adjustment, and therefore will not cause significant interference to subsequent leaching.

[0061] Example 3

[0062] This embodiment provides a method for selectively extracting magnesium from serpentine. This embodiment is basically the same as that of Embodiment 1, except that in step 1) of this embodiment, the ball milling speed is 400 rpm; the other steps and conditions are the same as those of Embodiment 1.

[0063] The final product data of Example 3 was tested and calculated: the magnesium leaching rate was 91.7%, the purity of magnesium sulfate was 98.6%, and the purity of magnesium oxide was 98.9%; the final purity of metallic magnesium was 99.4%, of which the impurity elements iron content was 0.07%, aluminum content was 0.05%, and nickel content was 0.02%.

[0064] Example 4

[0065] This embodiment provides a method for selectively extracting magnesium from serpentine. This embodiment is basically the same as that of Example 1, except that in the leaching reaction of step 3) in this embodiment, the solid-liquid ratio is changed to 1:5, that is, 100 g of serpentine and 500 mL of zinc sulfate solution (concentration is still 1.0 mol / L); other steps and conditions are the same as those of Example 1.

[0066] The final product data of Example 4 was tested and calculated: the magnesium leaching rate was 91.8%, the purity of magnesium sulfate was 98.7%, and the purity of magnesium oxide was 99.0%; the final purity of metallic magnesium was 99.5%, of which the impurity elements iron content was 0.06%, aluminum content was 0.04%, and nickel content was 0.02%.

[0067] Example 5

[0068] This embodiment provides a method for selectively extracting magnesium from serpentine. This embodiment is basically the same as that of Example 1, except that in the leaching reaction of step 3), the solid-liquid ratio is changed to 1:20, that is, 100 g of serpentine and 2000 mL of zinc sulfate solution (concentration is still 1.0 mol / L); other steps and conditions are the same as those of Example 1.

[0069] The final product data of Example 5 was tested and calculated: the magnesium leaching rate was 97.5%, the purity of magnesium sulfate was 99.3%, and the purity of magnesium oxide was 99.6%; the final purity of metallic magnesium was 99.9%, of which the impurity elements iron content was 0.03%, aluminum content was 0.02%, and nickel content was 0.01%.

[0070] Example 6

[0071] This embodiment provides a method for selectively extracting magnesium from serpentine. This embodiment is basically the same as that of Example 1, except that the leaching reaction temperature in step 3) of this embodiment is 70 °C; the other steps and conditions are the same as those in Example 1.

[0072] The final product data of Example 6 was tested and calculated: the magnesium leaching rate was 88.6%, the purity of magnesium sulfate was 98.5%, and the purity of magnesium oxide was 98.8%; the final purity of metallic magnesium was 99.3%, of which the impurity elements iron content was 0.08%, aluminum content was 0.06%, and nickel content was 0.03%.

[0073] Comparative Example 1

[0074] This comparative example is basically the same as Example 1, except that in step 3) of this comparative example, the zinc sulfate solution is replaced with an equal volume of deionized water; the other steps and conditions are the same as in Example 1.

[0075] In this comparative example, the filtration rate after leaching was extremely fast, and the filtrate was colorless and transparent; almost no crystals were precipitated during evaporation and crystallization, with only a small amount of white fine precipitate observed; according to ICP-OES analysis, the magnesium content in the filtrate was only 0.08 g / L, which translates to a magnesium leaching rate of less than 1.0%.

[0076] Comparative Example 2

[0077] This comparative example is basically the same as Example 1, except that in step 3) of this comparative example, the zinc sulfate solution is replaced with an equal volume and concentration of dilute sulfuric acid solution; the other steps and conditions are the same as in Example 1.

[0078] In this comparative example, no obvious precipitation was observed during the leaching reaction; severe clogging occurred during filtration, and a gel-like silica gel layer formed on the surface of the filter paper. Even after multiple replacements of the filter paper, filtration was still difficult; after evaporation and crystallization of the filtrate, only a small amount of pale yellow magnesium sulfate crystals were obtained, and the magnesium leaching rate was only 19.6%.

[0079] The dilute sulfuric acid provided in this comparative example contains H+. + Concentration is only 10 -5 The concentration of magnesium in serpentine is far below that required by traditional acid leaching methods (usually 5 mol / L), insufficient to effectively dissolve magnesium; simultaneously, the dissolved silicate ions polymerize under acidic conditions to form silica gel, clogging the filter pores and making solid-liquid separation difficult; and the lack of Zn... 2+ The key reason for the failure of this method is the inability to form silicate precipitates to fix silicon.

[0080] Comparative Example 3

[0081] This comparative example is basically the same as Example 1, except that in step 3), the zinc sulfate solution is replaced with an equal volume, equimolar concentration, and pH=5.0 copper sulfate solution; the other steps and conditions are the same as in Example 1.

[0082] The final test and calculation of the product data for Comparative Example 3 showed that the magnesium leaching rate was 53.4%, the purity of magnesium sulfate was 92.3%, and the purity of magnesium oxide was 93.1%. The final purity of metallic magnesium was 97.2%, with impurity elements including iron (0.18%), aluminum (0.09%), nickel (0.04%), and copper residue (0.38%).

[0083] Comparative Example 4

[0084] This comparative example is basically the same as Example 1, except that in step 3) of this comparative example, the zinc sulfate solution is replaced with an equal volume of Zn 2+ A zinc chloride solution with a molar concentration and pH of 5.0; other steps and conditions are the same as in Example 1.

[0085] The final test and calculation of the product data for Comparative Example 4 showed that the magnesium leaching rate was 73.6%, the purity of magnesium sulfate was 95.2%, and the purity of magnesium oxide was 95.8%. The final purity of metallic magnesium was 98.1%, with impurities including 0.15% iron, 0.10% aluminum, and 0.04% nickel. Chlorine was found in the magnesium sulfate crystals (tested with silver nitrate, the chloride ion content was approximately 0.25%).

[0086] Analysis of the above embodiments and comparative examples:

[0087] In Example 1, the method of the present invention can efficiently and selectively extract magnesium from serpentine and obtain a high-purity final product, achieving a magnesium leaching rate of 96.3% and a final metallic magnesium purity of 99.8%. This superior technical effect is attributed to the synergistic effect of several key factors, the underlying mechanism of which is analyzed as follows:

[0088] (1) The lattice disruption effect of mechanochemical activation:

[0089] Serpentine (Mg3Si2O5(OH)4) has a typical layered silicate structure, Mg 2+ Located at octahedral coordination sites between the silicon-oxygen tetrahedral layer and the magnesium hydroxide layer, the serpentine particles are firmly bonded to the crystal lattice. Under high-energy ball milling conditions, the grinding balls exert strong impact, shearing, and friction on the serpentine particles, resulting in the following mechanochemical effects: ① Lattice distortion and amorphization: Ball milling causes severe distortion of the serpentine crystal structure, the disappearance of characteristic XRD diffraction peaks, and the formation of a highly active amorphous or nanocrystalline MgO·SiO2 phase. The lattice energy is significantly reduced, and the bond strength of the Mg-O bond is weakened, creating a thermodynamic prerequisite for subsequent chemical leaching. ② Particle refinement and increased specific surface area: After ball milling, the powder residue on a 200-mesh sieve is only 3.2%, and the specific surface area is increased from approximately 5.2 μm² of the original ore. 2 / g increased to approximately 86 m 2 / g; Particle refinement shortens the diffusion path of reactants and increases the solid-liquid reaction interface, allowing the zinc sulfate solution to fully contact the serpentine particles. ③ Formation of dangling bonds and defect sites on the surface: Mechanical force causes a large number of dangling bonds, lattice defects and microcracks to be generated on the surface of serpentine particles. These high-energy sites have higher reactivity, which is conducive to the adsorption of zinc ions and lattice erosion.

[0090] (2) The lattice disruption mechanism driven by isomorphic substitution of zinc ions:

[0091] Zn2+ The core role of Mg in this invention lies not only in the formation of precipitates, but also in its ability to enter the serpentine lattice through isomorphic substitution, thereby disrupting the mineral structure from within. This mechanism is the key innovation of this invention. Mg in the octahedral layer of serpentine 2+ The ionic radius is 0.072 nm, while Zn 2+ The ionic radii of Zn and Zn are both 0.074 nm, which is extremely close. According to Goldschmidt's law of isomorphic substitution, extensive isomorphic substitution can occur when the radius difference between the two ions is less than 15%. 2+ With Mg 2+ The radius difference is only about 2.8%, far below the 15% threshold, therefore Zn 2+ It can easily replace Mg 2+ Entering the octahedral sites of serpentine. In the initial stages of the reaction, Zn in the solution... 2+ Adsorbed onto the surface of serpentine particles, it gradually diffuses into the crystal lattice, replacing Mg in the octahedral layer. 2+ Because of Zn 2+ Its electronegativity (1.65) is higher than that of Mg. 2+ (1.31) The Zn-O bond has weak ionicity but strong covalentity. This substitution disrupts the stability of the serpentine lattice, leading to further weakening of the Si-O and Mg-O bonds and accelerating the release of magnesium from the lattice. This "inside-out" lattice disruption mechanism is far more efficient than simple external acid dissolution or coordination dissolution.

[0092] (3) Zn8(OH) 13 The formation and reaction-driving role of [SiO(OH)3SO4] precipitate:

[0093] With the destruction of the serpentine lattice, Mg 2+ SiO3 2- and OH - Zn is released from the solid phase into the solution. Under near-neutral conditions at pH ≈ 5.0, Zn... 2+ With SiO3 2- OH - and SO4 in the solution 2- A concerted coordination-precipitation reaction occurs, producing Zn8(OH). 13 [SiO(OH)3SO4] precipitate:

[0094] 8Zn 2+ + 13OH - + SiO3 2- + SO4 2- → Zn8(OH) 13 [SiO(OH)3SO4]↓

[0095] The formation of this precipitate plays several key roles: ① Extremely low solubility product: Zn₈(OH)₂ 13 The solubility product Ksp of [SiO(OH)3SO4] is approximately 10. -72 Orders of magnitude, meaning that once the precipitate forms, the Zn in the solution... 2+ SiO3 2- The OH- concentration will be maintained at an extremely low level. This continuous consumption of reaction products causes the dissolution equilibrium of serpentine to shift continuously to the right, promoting a more complete leaching reaction of magnesium. ② In-situ fixation of silicon: In traditional acid leaching methods, silicate ions dissolved from serpentine polymerize to form silica gel (mSiO2·nH2O), clogging the filter pores and encapsulating unreacted mineral particles, severely hindering the leaching reaction. In this invention, however, silicate ions are immediately fixed to Zn8(OH)2. 13 In the [SiO(OH)3SO4] precipitate, the formation of silica gel is avoided, ensuring smooth solid-liquid separation and eliminating the inhibitory effect of silicon on the leaching reaction. ③ The "in-situ exfoliation" effect of the precipitate: Zn8(OH) 13 After the [SiO(OH)3SO4] precipitate forms on the surface of serpentine particles, its loose and porous structure allows it to be easily peeled off from the particle surface under the mechanical action of stirring, exposing a fresh serpentine surface and enabling the reaction to continue. This "in-situ exfoliation" effect effectively avoids the product layer hindering the reaction kinetics.

[0096] (4) Structural support and synergistic effect of sulfate ions:

[0097] SO4 2- In this invention, it is a core component of the precipitation structure and plays an irreplaceable role. ① Structural template and spatial support: In Zn8(OH) 13 In the crystal structure of [SiO(OH)3SO4], SO4 2- As a bridging ligand, it connects adjacent zinc-hydroxy polynuclear complex units, forming a three-dimensional network structure. 2- The tetrahedral configuration provides a stable spatial framework, resulting in low solubility and high thermodynamic stability of the precipitate. The lack of SO4... 2- When (e.g., using ZnCl2, Comparative Example 4), Zn 2+ With silicate and OH - It can only form amorphous zinc silicate or basic zinc chloride. These precipitates have large solubility products and loose structures, making them unable to effectively fix silicon and drive the reaction. ② Charge compensation and interlayer stability: SO4 2- It carries two negative charges, which can effectively compensate for Zn8(OH) 13 3+Excess positive charge between positive charge layers maintains the overall electroneutrality of the precipitate and enhances its structural integrity. ③ pH buffering and reaction stability: SO4 2- / HSO 4- The system exhibits good buffering capacity around pH ≈ 5.0 (pKa2 = 1.99, its conjugate base SO42-). 2- (It can combine with H⁺ under weakly acidic conditions). This buffering effect allows the pH of the reaction system to be stably maintained within the range of 4.5–5.5, avoiding the reaction caused by Zn. 2+ Hydrolysis causes an excessive decrease in pH, which inhibits magnesium leaching, or due to OH... - Accumulation leads to an increase in pH, causing impurity ions to precipitate and contaminate the product. ④ Promotes the solvation and crystallization of magnesium: SO4 2- With Mg 2+ It has strong coordination properties, can form stable MgSO4 ion pairs, and reduce the amount of free Mg in the solution. 2+ The activity of MgSO4·7H2O indirectly promotes the dissolution of serpentine. Meanwhile, MgSO4·7H2O has excellent crystallization properties, making it easy to obtain high-purity magnesium sulfate products through evaporation crystallization.

[0098] In Example 2, the regenerated zinc sulfate solution was used to leach serpentine. The final indicators showed only a slight decrease compared to Example 1 (magnesium leaching rate 96.3%, metallic magnesium purity 99.8%), which used fresh zinc sulfate solution (magnesium leaching rate decreased by 0.5 percentage points, metallic magnesium purity decreased by 0.1 percentage points). This indicates that the regenerated zinc sulfate solution has leaching performance almost equivalent to that of the fresh solution.

[0099] Analysis of the economic and environmental benefits of zinc salt recycling in Example 2: The recycling in Example 2 demonstrates that zinc in the filter residue can be easily and efficiently recovered as a ZnSO4 solution through dilute sulfuric acid leaching, with a recovery rate of 93.7%. The recovered solution can be directly returned to the leaching process without further concentration. Based on an annual processing capacity of 1000 tons of serpentine, the initial addition of zinc sulfate is approximately 2875 kg. After recycling, only the zinc salt lost due to precipitation entrainment and washing (approximately 6%–10%) needs to be replenished annually, saving approximately 90% of the zinc salt cost. Simultaneously, the remaining silica-rich residue after zinc salt recovery (mainly composed of amorphous SiO2, with a content of approximately 85%–90%) can be sold as raw material for silica or silica gel, achieving secondary resource utilization. Therefore, the "zinc salt recycling" of this invention is entirely feasible and has significant economic and environmental benefits.

[0100] In Example 3, the ball milling speed was reduced from 600 rpm to 400 rpm, which weakened the mechanochemical activation effect. The overall particle size of the serpentine powder became coarser (approximately 8.5% residue on a 200-mesh sieve), resulting in a decrease in the powder's specific surface area. This led to insufficient contact between the zinc sulfate solution and the serpentine, causing the magnesium leaching rate to drop from 96.3% to 91.7%. Simultaneously, the insufficiently activated serpentine may release small amounts of iron and aluminum impurities during leaching, slightly reducing the purity of magnesium sulfate and the final metallic magnesium. This example demonstrates that the ball milling speed has a significant impact on the magnesium leaching effect. The present invention preferably uses a high-energy ball milling speed of 600 rpm to obtain the best activation effect.

[0101] In Example 4, when the liquid-to-solid ratio was reduced to 1:5, the volume of the zinc sulfate solution decreased, and the Zn concentration per unit volume of solution increased. 2+ The total amount decreased, and the pH buffering capacity of the reaction system also decreased. During the reaction, Zn... 2+ The consumption of these components leads to insufficient local concentrations, making it impossible to continuously and effectively form Zn8(OH). 13 The precipitation of [SiO(OH)3SO4] weakens the driving force for the magnesium leaching reaction, reducing the leaching rate to 91.8%. In addition, too small a solution volume may also lead to an increase in the viscosity of the reaction system, affecting the mass transfer efficiency.

[0102] In Example 5, when the liquid-to-solid ratio was increased to 1:20, the Zn in the reaction system... 2+ Ample supply and increased solution volume facilitate better contact and diffusion of reactants, and also improve pH stability. Zn8(OH) 13 The continuous formation of [SiO(OH)3SO4] precipitate is fully guaranteed, promoting a more complete magnesium leaching reaction and increasing the leaching rate to 97.5%. At the same time, the larger liquid-to-solid ratio helps to reduce the concentration of impurity ions in the reaction system, further improving the purity of magnesium sulfate and metallic magnesium.

[0103] In Example 6, lowering the leaching reaction temperature from 85 °C to 70 °C resulted in a significant decrease in the reaction rate. Since the dissolution of magnesium from serpentine is an endothermic process, the lower temperature makes it difficult to overcome the activation energy of the chemical reaction, reducing the rate of Mg-O bond breaking and slowing down the kinetics of magnesium release from the crystal lattice. Within a 6-hour reaction time, some magnesium failed to leach sufficiently, and the leaching rate dropped to 88.6%. Furthermore, at lower temperatures, Zn8(OH)... 13 The formation rate of [SiO(OH)3SO4] precipitate may also slow down, affecting its contribution to the reaction equilibrium.

[0104] Because serpentine is a highly stable layered silicate mineral, Mg 2+ It is firmly bonded to the crystal lattice. In the pure water system of Comparative Example 1, there is a lack of exogenous cations replacing Mg. 2+ There were also no anions or dissolved Mg.2+ When a soluble complex is formed and pH ≈ 7.0, H... + Extremely low concentration (10) -7 (mol / L) is insufficient to disrupt the serpentine lattice. Even with heating and stirring, the serpentine structure remains essentially unchanged, therefore pure water cannot effectively leach magnesium.

[0105] In Comparative Example 3, copper sulfate solution was used as the leaching solution, wherein Cu 2+ It possesses oxidizing properties and is partially reduced to metallic copper in the reaction system (purplish-red metallic copper particles are observed), consuming copper ions and preventing them from effectively participating in silicon fixation. The resulting precipitate is mainly basic copper sulfate (Cu4(OH)6SO4), which does not contain silicon. The unfixed silicate ions affect magnesium leaching. Simultaneously, copper ions enter the solution, contaminating magnesium sulfate and the final metallic magnesium product (copper content as high as 0.38%), severely reducing product quality. Therefore, Cu... 2+ Cannot replace Zn 2+ To achieve selective magnesium extraction.

[0106] In Comparative Example 4, zinc chloride was used as the leaching solution, although Zn 2+ It still exists, but SO4 is missing. 2- This leads to the following problems: (1) The precipitation structure is unstable and cannot effectively fix silicon: In the zinc sulfate system, Zn 2+ With OH - SiO3 2- and SO4 2- Together they form Zn8(OH) 13 [SiO(OH)3SO4] precipitate, SO4 2- It plays a role in structural stability by embedding itself between precipitate layers. However, in the zinc chloride system, Cl... - It is a monocharged anion with weak coordination ability and cannot coordinate like SO4. 2- In this way, they participate in the formation of stable polynuclear complexes. The precipitates generated are mainly amorphous zinc silicate (Zn2SiO4·xH2O) or basic zinc chloride (Zn5(OH)8Cl2·H2O). These precipitates have large solubility products and cannot continuously consume silicate ions in the solution, resulting in silicon not being completely fixed. Some silicate ions polymerize to form silica gel, affecting filtration and subsequent operations. (2) Magnesium leaching rate is significantly reduced: due to the lack of SO4 2- Synergistic effect of Zn 2+ The precipitates formed with silicate and hydroxyl groups are unstable and do not provide sufficient impetus for the leaching reaction. The leaching equilibrium of magnesium is difficult to shift to the right, resulting in a significant decrease in the leaching rate from 96.3% in Example 1 to 73.6%. (3) Chloride ion residual contamination products: Cl -It does not participate in the precipitation reaction and mostly remains in the solution. During the evaporation and crystallization process, some of it will be mixed into the magnesium sulfate crystals, resulting in a decrease in the purity of magnesium sulfate (95.2%), and may cause equipment corrosion in the subsequent aluminothermic reduction.

[0107] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for selectively extracting magnesium from serpentine, characterized in that, Includes the following steps: S1. The raw serpentine ore is crushed, ball-milled, and sieved to obtain serpentine powder with a particle size ≤200 mesh. S2. Mix serpentine powder with zinc sulfate solution, heat and stir to carry out leaching reaction, and after the reaction is completed, separate solid and liquid to obtain filtrate and filter residue. S3. The filtrate is evaporated and concentrated, crystallized to precipitate crystals, the crystals are collected and calcined, the obtained product is mixed with aluminum powder, vacuum aluminothermic reduction reaction is carried out, and magnesium metal is obtained by condensation and collection.

2. The method for selective magnesium extraction from serpentine according to claim 1, characterized in that, In step S1, a planetary ball mill is used for ball milling, and the ball milling speed is 400~800 rpm.

3. The method for selective magnesium extraction from serpentine according to claim 1, characterized in that, In step S2, the solid-liquid ratio of the serpentine powder to the zinc sulfate solution is 1:(5~20)g / mL; the concentration of the zinc sulfate solution is 0.5~2.0 mol / L.

4. The method for selective magnesium extraction from serpentine according to claim 1, characterized in that, In step S2, the leaching reaction conditions are: stirring speed 200~600 rpm, temperature 65~95 ℃, and time 4~10 h.

5. The method for selective magnesium extraction from serpentine according to claim 4, characterized in that, During the leaching reaction, the pH of the system is adjusted to 5.0±0.3 every 20~40 minutes using dilute sulfuric acid or ammonia.

6. The method for selective magnesium extraction from serpentine according to claim 1, characterized in that, In step S2, the filter residue also undergoes the following treatment: The filter residue is mixed with dilute sulfuric acid solution, stirred and heated to react, and then separated into solid and liquid to obtain a regenerated zinc sulfate solution. The regenerated zinc sulfate solution can be recycled for leaching reactions with serpentine powder.

7. The method for selective magnesium extraction from serpentine according to claim 1, characterized in that, In step S3, the evaporation and concentration temperature is 80–105 °C; after collecting the crystals, they are also washed with ice water and dried.

8. The method for selective magnesium extraction from serpentine according to claim 1, characterized in that, In step S3, the calcination treatment is carried out at a temperature of 700–1000 °C for 2–5 h.

9. The method for selective magnesium extraction from serpentine according to claim 1, characterized in that, In step S3, the temperature of the aluminothermic reduction reaction is 1000~1250 ℃, the time is 1.5~4 h, and the excess coefficient of aluminum powder is 1.2~2 times the theoretical amount.

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