Method for preparing light magnesium oxide from serpentine tailings

Abstract

The invention belongs to the technical field of comprehensive utilization of serpentine tailings, and particularly discloses a method for preparing light magnesium oxide from serpentine tailings. The method provided by the invention comprises the following steps: pretreating the serpentine tailings to obtain serpentine tailing powder; adding an additive, mixing, roasting, and collecting tail gas; adding water to be mixed with the roasting slag, aging, introducing carbon dioxide to carry out carbonization reaction, and carrying out solid-liquid separation to obtain filtrate and filter residues; evaporating and crystallizing the filtrate to obtain light magnesium carbonate, and heating to obtain light magnesium oxide. According to the invention, the production of high-valued light magnesium oxide is realized by using proper additives under specific process parameters, the serpentine solid waste is effectively consumed, the output of waste residues is avoided, and the method has the advantages of environmental protection and industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization technology of serpentine tailings, and in particular to a method for preparing light magnesium oxide from serpentine tailings. Background Technology

[0002] Serpentine has physical and chemical properties such as corrosion resistance, heat resistance, wear resistance, and sound insulation. Currently, it is mainly used in the following fields: (1) fertilizer production; (2) refractory materials; (3) ceramics production; (4) building materials; and (5) carbon neutralization.

[0003] Serpentine has a high magnesium content, but because silicates are more difficult to process than carbonates, it has not been used as a raw material for magnesium smelting in the past. Noranda was the first company to experiment with acid leaching from serpentine to obtain magnesium chloride and put it into industrial production, marking the first application of serpentine in the magnesium industry. my country has large serpentine reserves, and how to produce high-value products from serpentine tailings is key to alleviating the environmental pressure on the ore industry, while avoiding the generation of harmful slag is also a challenging task.

[0004] Therefore, it is necessary to develop a completely new serpentine utilization process to transform serpentine tailings into high-value products, while achieving comprehensive utilization of serpentine and avoiding environmental pollution. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention provides a method for preparing lightweight magnesium oxide from serpentine tailings. The innovative research of this invention shows that, when calcium carbonate or calcium fluoride is used as an additive, heat treatment can expose the magnesium oxide encapsulated in silica, and this exposed magnesium oxide possesses high activity. Subsequent processes can not only produce high-value lightweight magnesium oxide but also convert the slag into industrial building materials, achieving comprehensive recycling of serpentine tailings.

[0006] This invention provides a method for preparing light magnesium oxide from serpentine tailings, comprising the following steps:

[0007] S1. Pre-treat the serpentine tailings to obtain serpentine tailings powder with a particle size of <120 mesh;

[0008] S2. Mix serpentine tailings powder with additives, roast the mixture, and collect the tail gas.

[0009] S3. Add water and roasting residue, mix, age, introduce carbon dioxide gas to carry out carbonization reaction, and separate solid and liquid to obtain filtrate and filter residue.

[0010] S4. The filtrate is evaporated and crystallized to obtain light magnesium carbonate, which is then heated to obtain light magnesium oxide.

[0011] According to some embodiments of the present invention, in step S1, the pretreatment is: crushing, grinding, washing, drying and screening the serpentine tailings.

[0012] According to some embodiments of the present invention, in step S2, the additive is selected from calcium carbonate or calcium fluoride.

[0013] This invention has explored and obtained two optimal additives suitable for the thermal treatment of serpentine tailings to recover magnesium resources. Their advantages and inventive concepts are as follows:

[0014] Calcium carbonate additive: The core principle lies in its role as a calcium mineralizer, reconstructing the mineral phase through a "solid-phase exchange" reaction. Calcium carbonate decomposes at high temperatures into highly active CaO and CO2. CaO reacts with SiO2 in the thermal decomposition products of serpentine, preferentially forming stable calcium silicate (such as Ca2SiO4, Ca3Si2O7, etc.). This reaction "displaces" magnesium from the solid magnesium silicate lattice, generating free, highly active MgO, while fixing silicon in the stable calcium silicate slag. Calcium carbonate, as an additive, has the advantage of inexpensive and readily available raw materials. Limestone is also the cheapest alkaline calcium source, and the generated calcium silicate is a major mineral component of cement, providing high-quality raw materials for by-product cement. This process has significant advantages in cost and economic benefits, while also exhibiting excellent environmental performance, producing no harmful gases.

[0015] Calcium fluoride additive: The core principle lies in its role as a fluoride mineralizer, achieving low-temperature, high-efficiency activation through a "gas-solid synergistic" reaction. Specifically, the catalytic and destructive effects of fluorine: When CaF2 comes into contact with SiO2 at high temperatures, it reacts to generate gaseous SiF4; the escape of SiF4 gas directly creates micropores and channels on the surface and inside of serpentine particles, greatly increasing the reaction interface and mass transfer rate. At the same time, this reaction generates highly active CaO in situ, which can immediately react with exposed, newly formed SiO2 and MgO, thus having a dual effect of physicochemical destruction and chemical activation; Phase reconstruction and magnesium release: CaO preferentially combines with residual SiO2 to form calcium silicate. Meanwhile, fluoride ions, as a strong mineralizer, can significantly reduce the eutectic point and reaction activation energy of the silicate system, promoting the separation and growth of MgO grains, allowing them to exist in a more active form.

[0016] The advantages of using calcium fluoride as an additive are: lower reaction temperature and faster reaction speed. The addition of calcium fluoride can significantly reduce the calcination temperature (potentially by 50-100°C), saving energy. Simultaneously, due to mineralization and porosity formation, the generated MgO has higher activity, resulting in a faster and more thorough reaction in subsequent digestion, potentially increasing the magnesium leaching rate and speed. Furthermore, due to the more complete reaction, the slag may have better grindability and activity, and its mineral composition is more conducive to cement grinding and early hydration activity.

[0017] According to some embodiments of the present invention, in step S2, the amount of the additive is 0.5% to 3% of the mass of the serpentine tailings.

[0018] According to some preferred embodiments of the present invention, the amount of the additive is 0.8% to 2% of the mass of the serpentine tailings.

[0019] In the process of comprehensively utilizing serpentine tailings in this invention, there are strict requirements on the amount of additives used. This ensures that the additives can activate the serpentine tailings while avoiding excessive additives from affecting subsequent processes, thereby improving product purity and value.

[0020] According to some embodiments of the present invention, in step S2, the calcination treatment is carried out at a temperature of 200~500℃ for a time of 1~4h.

[0021] According to some preferred embodiments of the present invention, in step S2, when calcium carbonate is used as an additive, the calcination temperature is 250~450°C; when calcium fluoride is used as an additive, the calcination temperature is 200~350°C.

[0022] The temperature of the heat treatment of the mixture of serpentine tailings powder and additives is also crucial to the present invention. Too low a temperature will not only make it difficult to ensure high reaction efficiency, but will also make it difficult to leach magnesium. On the other hand, too high a reaction temperature will promote the production of harmful byproducts, affecting the magnesium recovery rate and product purity.

[0023] According to some embodiments of the present invention, in step S3, the liquid-solid mass ratio of water to calcined slag is (4~10):1; and the aging time is 3~8h.

[0024] According to some embodiments of the present invention, in step S3, the volume fraction of CO2 in the carbon dioxide gas is >40%; the carbonization reaction time is 2~4h.

[0025] According to some embodiments of the present invention, when the additive in step 2 is calcium carbonate, the source of the carbon dioxide gas includes the exhaust gas collected in step S2.

[0026] According to some embodiments of the present invention, in step S4, the temperature of the heating reaction is 80~100°C.

[0027] According to some embodiments of the present invention, the method further includes the following steps:

[0028] The filter residue obtained in step S3 is calcined at 700~900℃ to obtain cement as a byproduct, while carbon dioxide tail gas is collected.

[0029] During the heating process in step S4, carbon dioxide exhaust gas is collected.

[0030] According to some embodiments of the present invention, the carbon dioxide tail gas is used for the carbon dioxide gas in step S3.

[0031] The closed-loop green chemical process of the present invention, which achieves "full utilization of resources," has the following beneficial effects:

[0032] 1) Turning waste into treasure, targeting bulk solid waste: This invention selects serpentine tailings (usually a huge amount of waste generated from mining nickel, asbestos, etc., which is highly alkaline and pollutes the environment when piled up) as raw material, which solves the environmental pain point and transforms negative-value waste into positive-value products.

[0033] 2) Chemical phase separation for selective extraction: This invention does not employ the traditional direct acid leaching method (which consumes acid and generates silicon-containing wastewater). Instead, it uses high-temperature solid-phase reconstruction. By adding a calcium agent (CaCO3 or CaF2), the "MgO-SiO2" system is reconstructed into a "MgO + CaO-SiO2" system at high temperature. This is a fundamental chemical design that achieves the selective separation of magnesium and silicon in the solid state. Magnesium is converted into easily leached active MgO, while silicon is converted into stable cement minerals.

[0034] 3) Optimization of the reaction pathway and introduction of mineralizing agents: The present invention (using CaCO3 as an additive) utilizes the classic concept of "solid-phase ion exchange" and utilizes CaCO3... 2+ For Mg 2+ The substitution has a strong thermodynamic driving force; a further optimized scheme (CaF2 as an additive): not only provides a calcium source, but more importantly, it utilizes the following chemical characteristics of fluorine: generating gas channels (SiF4), enhancing mass transfer, which belongs to process intensification; lowering the reaction energy barrier (mineralization), which belongs to reaction kinetic optimization; and possibly changing the reaction path by forming an intermediate fluoride phase, which belongs to reaction mechanism innovation.

[0035] 4) Material and energy closed loop: This invention realizes product closed loop, with main product (high-purity light magnesium oxide, high value-added chemical product) + by-product (cement clinker, bulk building materials), realizing full utilization of tailings without secondary solid waste; Medium closed loop: CO2 generated by roasting in this invention scheme (or CO2 required for carbonization can be considered to come from roasting flue gas) can be used in subsequent carbonization processes.

[0036] This invention not only proposes a method for extracting magnesium oxide from serpentine, but also highlights its systematic resource utilization concept and ingenious chemical reaction design. The use of calcium carbonate is an economical, stable, and reliable baseline solution, embodying the chemical wisdom of solid-phase substitution. The use of calcium fluoride, however, is a more advanced optimization solution. By introducing the "catalytic" and "pore-forming" functions of fluoride, it achieves a low-temperature, rapid, and efficient reaction, representing a creative improvement on the baseline solution. Both additives serve the same ultimate goal: to "decouple" magnesium and silicon at high temperatures and direct them to high-value product streams. This concept successfully transforms an environmental burden (tailings) into two valuable products (magnesium oxide and cement), achieving a high degree of unity between economic and environmental benefits.

[0037] In summary, this invention utilizes low-cost, small-volume additives to thermally treat serpentine tailings, combined with subsequent digestion and precipitation treatments, achieving comprehensive utilization of serpentine tailings. This invention focuses on improving the recovery rate of magnesium from serpentine tailings through the selection and optimization of key parameters in the process flow, and can produce high-purity, high-value light magnesium oxide products, realizing the high-value utilization of serpentine tailings solid waste. Simultaneously, this invention enables the complete recovery and utilization of by-products, achieving zero-slag production and harmless treatment of serpentine tailings by converting waste residue into industrial building materials and collecting and utilizing tail gas.

[0038] 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

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0040] Figure 1 This is a schematic diagram of the process flow for comprehensively utilizing serpentine in an embodiment of the present invention. Detailed Implementation

[0041] 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.

[0042] 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.

[0043] Example 1

[0044] This embodiment provides a method for preparing lightweight magnesium oxide by comprehensively utilizing serpentine tailings. The specific steps are as follows:

[0045] 1) After crushing, grinding, washing, drying and sieving the serpentine tailings, serpentine tailings powder with a particle size of -120 mesh is obtained.

[0046] 2) Place the serpentine tailings powder in a muffle furnace, add calcium carbonate powder accounting for 1% of the mass of the serpentine tailings as an additive, mix well, heat to 300℃, and keep warm for 2 hours.

[0047] 3) Collect the carbon dioxide tail gas generated in step 2); after heating, the residue obtained is crushed and mixed with water at a liquid-solid mass ratio of 5:1, aged for 5 hours, and then the collected carbon dioxide tail gas is introduced (ensuring that the CO2 volume fraction is >40%) for carbonization reaction for 3 hours. After carbonization, the residue is filtered to obtain filtrate and filter residue.

[0048] 4) The filter residue is roasted at 800℃ to obtain cement as a byproduct, while carbon dioxide tail gas is collected at the same time; the filtrate is evaporated and crystallized to obtain light magnesium carbonate, which is then heated at 90℃ to obtain light magnesium oxide product, while carbon dioxide tail gas is collected at the same time.

[0049] Testing showed that this embodiment achieved a magnesium recovery rate of 98.5% from serpentine tailings, and the purity of the obtained light magnesium oxide product was 98.5%. The carbon dioxide tail gas in this embodiment was used for the carbonization process, and the by-product cement could be further used as industrial building material, thus achieving zero slag production and harmless treatment of serpentine tailings.

[0050] Example 2

[0051] This embodiment provides a method for preparing lightweight magnesium oxide by comprehensively utilizing serpentine tailings. The specific steps are as follows:

[0052] 1) After crushing, grinding, washing, drying and sieving the serpentine tailings, serpentine tailings powder with a particle size of -120 mesh is obtained.

[0053] 2) Place the serpentine tailings powder in a muffle furnace, add calcium carbonate powder accounting for 1% of the mass of the serpentine tailings as an additive, mix well, heat to 400℃, and keep warm for 2 hours.

[0054] 3) Collect the carbon dioxide tail gas generated in step 2); after heating, the residue obtained is crushed and mixed with water at a liquid-solid mass ratio of 5:1, aged for 5 hours, and then the collected carbon dioxide tail gas is introduced (ensuring that the CO2 volume fraction is >40%) for carbonization reaction for 3 hours. After carbonization, the residue is filtered to obtain filtrate and filter residue.

[0055] 4) The filter residue is roasted at 800℃ to obtain cement as a byproduct, while carbon dioxide tail gas is collected at the same time; the filtrate is evaporated and crystallized to obtain light magnesium carbonate, which is then heated at 90℃ to obtain light magnesium oxide product, while carbon dioxide tail gas is collected at the same time.

[0056] Testing showed that this embodiment achieved a magnesium recovery rate of 98.9% in serpentine tailings, and the purity of the obtained light magnesium oxide product was 98.8%.

[0057] Example 3

[0058] This embodiment provides a method for preparing lightweight magnesium oxide by comprehensively utilizing serpentine tailings. The specific steps are as follows:

[0059] 1) After crushing, grinding, washing, drying and sieving the serpentine tailings, serpentine tailings powder with a particle size of -120 mesh is obtained.

[0060] 2) Place the serpentine tailings powder in a muffle furnace, add calcium fluoride powder accounting for 1% of the mass of the serpentine tailings as an additive, mix well, heat to 300℃, and keep warm for 2 hours.

[0061] 3) Collect the silicon tetrafluoride tail gas generated in step 2); after heating, the slag obtained is crushed and mixed with water at a liquid-solid mass ratio of 5:1, aged for 5 hours, and carbon dioxide (CO2 volume fraction > 40%) is introduced for carbonization reaction for 3 hours. After carbonization, the filtrate and filter residue are obtained by filtration.

[0062] 4) The filter residue is roasted at 800℃ to obtain cement as a byproduct, while carbon dioxide tail gas is collected at the same time; the filtrate is evaporated and crystallized to obtain light magnesium carbonate, which is then heated at 90℃ to obtain light magnesium oxide product, while carbon dioxide tail gas is collected at the same time.

[0063] Testing showed that this embodiment achieved a magnesium recovery rate of 99.3% in serpentine tailings, and the purity of the obtained light magnesium oxide product was 99.2%.

[0064] Example 4

[0065] This embodiment provides a method for preparing lightweight magnesium oxide by comprehensively utilizing serpentine tailings. The specific steps are as follows:

[0066] 1) After crushing, grinding, washing, drying and sieving the serpentine tailings, serpentine tailings powder with a particle size of -120 mesh is obtained.

[0067] 2) Place the serpentine tailings powder in a muffle furnace, add calcium carbonate powder accounting for 2% of the serpentine tailings mass as an additive, mix well, heat to 300℃, and keep warm for 2 hours.

[0068] 3) Collect the carbon dioxide tail gas generated in step 2); after heating, the residue obtained is crushed and mixed with water at a liquid-solid mass ratio of 5:1, aged for 5 hours, and then the collected carbon dioxide tail gas is introduced (ensuring that the CO2 volume fraction is >40%) for carbonization reaction for 3 hours. After carbonization, the residue is filtered to obtain filtrate and filter residue.

[0069] 4) The filter residue is roasted at 800℃ to obtain cement as a byproduct, while carbon dioxide tail gas is collected at the same time; the filtrate is evaporated and crystallized to obtain light magnesium carbonate, which is then heated at 90℃ to obtain light magnesium oxide product, while carbon dioxide tail gas is collected at the same time.

[0070] Testing showed that this embodiment achieved a magnesium recovery rate of 99.5% in serpentine tailings, and the purity of the obtained light magnesium oxide product was 99.3%.

[0071] Comparative Example 1

[0072] This comparative example provides a method for preparing lightweight magnesium oxide by comprehensively utilizing serpentine tailings.

[0073] This comparative example is basically the same as Example 1, except that in step 2) of this comparative example, sodium carbonate is used instead of calcium carbonate additive.

[0074] The final magnesium recovery rate in the serpentine tailings of this comparative example was 88.9%, and the purity of the obtained light magnesium oxide product was 84.3%.

[0075] Comparative Example 2

[0076] This comparative example provides a method for preparing lightweight magnesium oxide by comprehensively utilizing serpentine tailings.

[0077] This comparative example is basically the same as Example 1, except that no additives were used in step 2) of this comparative example.

[0078] In the end, the magnesium recovery rate in the serpentine tailings of this comparative example was 69.7%, and the purity of the obtained light magnesium oxide product was only 73.1%.

[0079] Comparative Example 3

[0080] This comparative example provides a method for preparing lightweight magnesium oxide by comprehensively utilizing serpentine tailings.

[0081] This comparative example is basically the same as Example 1, except that in step 2) of this comparative example, the temperature of the heating reaction is 100°C.

[0082] In the end, the magnesium recovery rate in the serpentine tailings of this comparative example was 65.1%, and the purity of the obtained light magnesium oxide product was only 62.1%.

[0083] Comparative Example 4

[0084] This comparative example provides a method for preparing lightweight magnesium oxide by comprehensively utilizing serpentine tailings.

[0085] This comparative example is basically the same as Example 1, except that in step 2) of this comparative example, the temperature of the heating reaction is 600°C.

[0086] In the end, the magnesium recovery rate in the serpentine tailings of this comparative example was 73.7%, and the purity of the obtained light magnesium oxide product was only 69.7%.

[0087] Comparative Example 5

[0088] This comparative example provides a method for preparing lightweight magnesium oxide by comprehensively utilizing serpentine tailings.

[0089] This comparative example is basically the same as Example 1, except that in step 2) of this comparative example, the amount of calcium carbonate additive is 5% of the mass of serpentine tailings.

[0090] In the end, the magnesium recovery rate in the serpentine tailings of this comparative example was 63.7%, and the purity of the obtained light magnesium oxide product was only 60.2%.

[0091] In summary, the technical solution of this invention utilizes a small amount of additives and pre-treated serpentine tailings for mixed heat treatment, which can effectively expose the magnesium oxide encapsulated in silica within the serpentine and exhibit high activity. Through subsequent processes, high-purity, high-value-added lightweight magnesium oxide products can be produced, which, together with the waste residue, can be converted into industrial building materials, thus realizing the comprehensive recycling and utilization of serpentine tailings.

[0092] In Example 3, calcium fluoride was used as an additive to achieve excellent utilization of serpentine tailings. The silicon tetrafluoride gas collected in this process can be used as a silicon source or etching gas in chip manufacturing to deposit silicon thin films or silicon nitride insulating layers.

[0093] In Comparative Example 1, sodium carbonate was used as an additive. In this case, the roasting reaction tended to produce sodium metasilicate and magnesium oxide. Sodium metasilicate is highly water-soluble. During subsequent water digestion, a large amount of soluble sodium metasilicate would enter the solution, turning it into a strongly alkaline sodium silicate solution (water glass). The pH of this solution would become very high (>12), thus drastically reducing the solubility of the desired MgO / Mg(OH)2. Most of the magnesium would be trapped in the solid phase as the very stable Mg(OH)2, making it difficult to react effectively with the introduced CO2 to form soluble Mg(HCO3)2. The dissolved silicate ions (SiO3... 2-At high pH, ​​it forms a complex colloid with strong adsorption and encapsulation capabilities. It physically encapsulates unreacted Mg(OH)2 particles, preventing them from contacting CO2 and further reducing carbonization efficiency. Furthermore, a large number of sodium ions are present in the solution throughout the process. During the pyrolysis to produce basic magnesium carbonate, sodium salts (such as Na2CO3 and NaHCO3) may be encapsulated or adsorbed in the precipitate in the form of microcrystals, which are difficult to remove completely by washing. These sodium impurities will remain as Na2O after the final calcination into magnesium oxide, which seriously affects the purity of the product (for high-end applications such as electrical grade magnesium oxide, sodium content is a critical indicator).

[0094] In Comparative Example 3, the excessively low heat treatment temperature resulted in incomplete dehydroxylation of serpentine and decomposition of limestone, failing to generate sufficient active magnesium oxide. Simultaneously, silicon was not effectively fixed by calcium. The consequence was an extremely low magnesium leaching rate and the generation of large amounts of colloidal silicic acid during digestion, severely contaminating the product and causing a significant decrease in both magnesium oxide purity and yield, even rendering the entire process unusable.

[0095] In Comparative Example 4, the excessively high heat treatment temperature caused magnesium oxide particles to sinter, aggregate, and grow, resulting in a decrease in specific surface area and a significant drop in reactivity. The newly generated highly reactive magnesium oxide reacts with free or newly formed silica (from serpentine decomposition) in the system at high temperatures, forming stable, inert magnesium silicate minerals such as forsterite or enstatite. Once these stable magnesium silicate minerals are formed, the magnesium is re-locked within the silicate lattice. In subsequent digestion-carbonization processes, these minerals are extremely difficult to react with water and CO2, and are almost never converted into soluble Mg(HCO3)2, leading to a significant decrease in magnesium extraction rate. Furthermore, excessively high temperatures accelerate the localized direct bonding of MgO and SiO2 (especially at particle contact points), occurring before the complete reaction between CaO and SiO2. This "side reaction" directly reduces the amount of active MgO available for leaching. Meanwhile, if the temperature is too high or locally uneven, the crystal form of the generated calcium silicate mineral may change, and trace amounts of silicon may enter the solution in the form of colloidal silicic acid. During the subsequent carbonization and pyrolysis process, it may be mixed into the basic magnesium carbonate precipitate in the form of magnesium silicate impurities, ultimately contaminating the magnesium oxide product.

[0096] Comparative Example 5 used an excessive amount of calcium carbonate additive for heat treatment. Therefore, after hydration, the excess CaO hydrates into Ca(OH)₂, resulting in an extremely high pH value (>12.5) in the slurry. In this strongly alkaline environment, the solubility of the target product Mg(OH)₂ is minimized. Although the purpose of introducing CO₂ is to carbonize Mg(OH)₂, the high concentration of CaO... 2+It will preferentially react with CO2 to form CaCO3 precipitate, competing for CO2 consumption, and may also encapsulate Mg(OH)2 particles, hindering their further carbonization and dissolution into soluble Mg(HCO3)2, thereby reducing the leaching rate and final yield of magnesium. Furthermore, during the carbonization-pyrolysis process, the Ca in the solution... 2+ Will with Mg 2+ Co-precipitation occurs, forming double salts (such as CaMg(CO3)2, dolomite) or calcium-doped basic magnesium carbonate. These calcium particles remain in the magnesium oxide product after subsequent calcination, forming calcium oxide (CaO) impurities. The large amount of CaCO3 precipitate particles generated are small and difficult to completely separate from the solution through filtration. They will be carried into subsequent processes and eventually mixed into the product. The "lightness" of light magnesium oxide comes from the specific loose structure of its precursor, basic magnesium carbonate. The introduction of calcium impurities will destroy the formation of this structure, resulting in an increase in the bulk density of the product and failure to meet physical indicators.

[0097] 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 preparing light magnesium oxide from serpentine tailings, characterized in that, Includes the following steps: S1. Pre-treat the serpentine tailings to obtain serpentine tailings powder with a particle size of <120 mesh; S2. Mix serpentine tailings powder with additives, roast the mixture, and collect the tail gas. S3. Add water and roasting residue, mix, age, introduce carbon dioxide gas to carry out carbonization reaction, and separate solid and liquid to obtain filtrate and filter residue. S4. The filtrate is evaporated and crystallized to obtain light magnesium carbonate, which is then heated to obtain light magnesium oxide.

2. The method for preparing light magnesium oxide from serpentine tailings according to claim 1, characterized in that, In step S1, the pretreatment is to crush, grind, wash, dry and screen the serpentine tailings.

3. The method for preparing light magnesium oxide from serpentine tailings according to claim 1, characterized in that, In step S2, the additive is selected from calcium carbonate or calcium fluoride.

4. The method for preparing light magnesium oxide from serpentine tailings according to claim 1, characterized in that, In step S2, the amount of the additive is 0.5% to 3% of the mass of the serpentine tailings.

5. The method for preparing light magnesium oxide from serpentine tailings according to claim 1, characterized in that, In step S2, the calcination treatment is carried out at a temperature of 200~500℃ for 1~4 hours.

6. The method for preparing light magnesium oxide from serpentine tailings according to claim 1, characterized in that, In step S3, the liquid-solid mass ratio of water to calcined slag is (4~10):1; the aging time is 3~8h.

7. The method for preparing light magnesium oxide from serpentine tailings according to claim 1, characterized in that, In step S3, the volume fraction of CO2 in the carbon dioxide gas is >40%; the carbonization reaction time is 2~4 hours.

8. The method for preparing light magnesium oxide from serpentine tailings according to claim 1, characterized in that, When the additive mentioned in step 2 is calcium carbonate, the source of the carbon dioxide gas mentioned in step S3 includes the exhaust gas collected in step S2.

9. The method for preparing light magnesium oxide from serpentine tailings according to claim 1, characterized in that, In step S4, the temperature of the heating reaction is 80~100℃.

10. The method for preparing light magnesium oxide from serpentine tailings according to claim 1, characterized in that, The method further includes the following steps: The filter residue obtained in step S3 is calcined at 700~900℃ to obtain cement as a byproduct, while carbon dioxide tail gas is collected. During the heating process in step S4, carbon dioxide exhaust gas is collected.

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