Magnesium oxide-based building material based on full recycling of seawater desalination brine resources and preparation method and application thereof

Abstract

The application provides a magnesium oxide-based building material based on full recycling of seawater desalination brine resources and a preparation method and application thereof, and relates to the technical fields of building materials and seawater resource recycling. The preparation method comprises the following steps: S1: pretreatment and fractional extraction of seawater desalination brine to obtain a magnesium resource solution and a calcium resource solution; S2: a part of the magnesium resource solution is precipitated into magnesium hydroxide, calcined to obtain light-burned magnesium oxide; the calcium resource solution is carbonized to obtain calcite; S3: another part of the magnesium resource solution is synthesized into a magnesium acetate solution; S4: the light-burned magnesium oxide, the calcite and the magnesium acetate solution are mixed to prepare a cement slurry; and S5: casting forming and carbonization curing to obtain the magnesium oxide-based building material. The pollutants in the brine are converted into raw materials for producing magnesium oxide cement, the problem of excessively high carbon emission is completely solved from the source, efficient recovery and high-value utilization of valuable resources are realized, and low-carbon and environment-friendly building materials are developed.

Description

Technical Field

[0001] This invention relates to the fields of building materials and seawater resource recycling technology. Specifically, it relates to a magnesium oxide-based building material based on the full recycling of seawater desalination brine resources, its preparation method, and its application. Background Technology

[0002] Seawater desalination is an important way to solve global water shortages, and its production capacity continues to grow. However, the high-salinity brine produced during the desalination process is rich in valuable metals such as magnesium, calcium, and lithium. Direct discharge of this brine not only wastes resources but also leads to increased salinity in nearshore waters and damages marine ecosystems.

[0003] Meanwhile, traditional magnesium oxide cement production faces problems such as high carbon emissions, resource dependence, and high energy consumption. Furthermore, pure magnesium oxide cement suffers from performance defects such as large shrinkage and insufficient long-term stability, limiting its widespread application.

[0004] Currently, the main methods for treating seawater desalination brine include direct discharge, deep well injection, and dilution discharge. However, these methods all suffer from high environmental risks and low resource utilization rates. Furthermore, research on the modification of magnesium oxide cement is largely limited to simple compounding with single additives, failing to fundamentally address the issues of resource consumption and carbon emissions.

[0005] Those skilled in the art generally agree that seawater desalination brine has a complex composition, making it difficult to extract high-purity chemical raw materials economically and efficiently. Furthermore, current methods for preparing magnesium oxide primarily employ traditional magnesite calcination or dolomite calcination, which have poor water resistance. The main hydration product, (5Mg(OH)2·MgCl2·8H2O), decomposes upon contact with water, leading to significant strength loss, deformation, and efflorescence. This process is also highly carbon-intensive. Modification of magnesium oxide cement often focuses on admixtures (such as phosphates, silica fume, fly ash, and slag), and its high carbon emissions and resource consumption are considered inherent challenges in the industry. CO2 mineralization and sequestration are also difficult to promote on a large scale due to cost issues. To date, no technological solution has been able to simultaneously address these three challenges and create a closed-loop system.

[0006] Therefore, how to achieve efficient recovery and high-value utilization of valuable resources in seawater desalination brine, while developing low-carbon and environmentally friendly building materials, has become an urgent technical problem to be solved. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for preparing magnesium oxide-based building materials based on the full recycling of seawater desalination brine resources. This method connects seawater brine treatment, magnesium and calcium resource separation, chlorine-free magnesium oxide cement synthesis, carbonization curing, and wastewater treatment in a series, thereby eliminating pollutants (Mg) in the brine. 2+ Ca 2+This process transforms resources into raw materials for producing magnesium oxide cement, thereby fundamentally solving the problem of excessive carbon emissions, achieving efficient recovery and high-value utilization of valuable resources in seawater desalination brine, and developing low-carbon and environmentally friendly building materials.

[0008] The first aspect of this invention provides a method for preparing magnesium oxide-based building materials based on the full recycling of seawater desalination brine resources, the method comprising the following steps:

[0009] S1: Pre-treatment and fractional extraction of seawater desalination brine to obtain magnesium resource solution and calcium resource solution respectively;

[0010] S2: A portion of the magnesium resource solution is precipitated into magnesium hydroxide, and then the magnesium hydroxide is calcined to obtain lightly calcined magnesium oxide; the calcium resource solution is carbonized to obtain calcite;

[0011] S3: Synthesize another portion of the magnesium resource solution into magnesium acetate solution;

[0012] S4: The prepared lightly calcined magnesium oxide, calcite and magnesium acetate solutions are mixed to prepare cement paste;

[0013] S5: Cement slurry is poured into a mold and then carbonized and cured to obtain magnesium oxide-based building materials.

[0014] Optionally, the cement paste, by weight percentage, includes 85-100% light-burned magnesia and 0-15% calcite; the magnesium acetate solution accounts for 50-60% of the total weight of light-burned magnesia and calcite.

[0015] The magnesium acetate solution has a concentration of 0.05 mol / L. The magnesium oxide solution uses water as the solvent.

[0016] Lightly calcined magnesium oxide (MgO) is the main cementing component and the primary agent for subsequent carbonization with CO2 to form high-strength magnesium carbonate. A high proportion of MgO ensures sufficient reactants to form a dense microstructure, guaranteeing high compressive strength in the resulting magnesium oxide-based building materials. Calcite, with a particle size much smaller than MgO, fills the gaps between MgO particles, making the slurry denser, reducing porosity, thereby increasing strength, reducing permeability, and minimizing drying shrinkage. A low-concentration magnesium acetate solution ensures a relatively gradual carbonization rate, avoiding violent exothermic reactions and rapid shrinkage, reducing internal stress, preventing cracking, and allowing sufficient time for CO2 to diffuse into the material, resulting in deeper and more uniform carbonization. This avoids surface hardening without internal reaction, completely preventing efflorescence and corrosion.

[0017] Optionally, the composition is 90-95% light-burned magnesia and 5-10% calcite. Preferably, the composition is 95% light-burned magnesia and 5% calcite.

[0018] Optionally, the active magnesium oxide content in the lightly calcined magnesium oxide is above 85%.

[0019] Optionally, the specific surface area of ​​lightly calcined magnesium oxide is not less than 15 m². 2 / kg.

[0020] Optionally, the calcite particle size is not higher than 5µm.

[0021] Optionally, the specific surface area of ​​calcite is not less than 12m². 2 / kg.

[0022] Optionally, in step S1, the fractional extraction includes the following steps: adjusting the pH of the brine to 9.5-10.5, controlling the temperature at 40-60℃, stirring at 300-500 rpm, reacting for 30-60 minutes, and obtaining a magnesium resource solution.

[0023] After magnesium extraction, the pH of the solution is adjusted to 8-9, a carbonizing agent is added to precipitate calcium ions into calcium carbonate, and the solution is filtered to obtain a calcium resource solution.

[0024] Optionally, in step S1, the fractional extraction includes the following steps: adjusting the pH of the brine to 9.8, controlling the temperature at 50°C, stirring at 400 rpm, reacting for 45 minutes, and obtaining a magnesium resource solution.

[0025] Optionally, the concentration of the carbonizing agent is 1.0-1.5 mol / L, the temperature is controlled at 30-50℃, and the precipitation time is controlled at 60-120 minutes.

[0026] Optionally, the calcination of magnesium hydroxide includes the following steps: drying magnesium hydroxide at 100-120℃ to a moisture content of ≤1%, then preheating at 300-400℃ for 20-40 minutes, and then calcining at 700-900℃ for 50-70 minutes, with the heating rate controlled at 5-10℃ / minute.

[0027] Optionally, the calcination of magnesium hydroxide includes the following steps: drying magnesium hydroxide at 100-120℃ to a moisture content of ≤1%, then preheating at 300-400℃ for 20-40 minutes, and then calcining at 800℃ for 50-70 minutes, with the heating rate controlled at 7℃ / min.

[0028] Optionally, in step S2, carbonization includes the following steps: carbonization pressure 0.3-0.5 MPa, carbonization temperature 20-40℃, carbonization time 60-120 min, and calcium resource solution concentration 10-20 wt%.

[0029] Optionally, in step S2, carbonization includes the following steps: carbonization pressure 0.4 MPa, carbonization temperature 30°C, carbonization time 60-120 min, and calcium resource solution concentration 15 wt%.

[0030] Optionally, in step S3, the synthesis of magnesium acetate in the magnesium acetate solution includes the following steps:

[0031] Another portion of the magnesium resource solution was precipitated to obtain magnesium hydroxide, which was then added to an acetic acid solution for acidification to obtain magnesium acetate. The concentration of the acetic acid solution was 2.0-3.0 mol / L, the reaction temperature was 60-80℃, the reaction time was 30-60 min, and the pH value was controlled at 5.5-6.5.

[0032] Optionally, in step S3, the synthesis of magnesium acetate in the magnesium acetate solution includes the following steps:

[0033] Another portion of the magnesium resource solution was precipitated to obtain magnesium hydroxide, which was then acidified with acetic acid solution to obtain magnesium acetate. The concentration of acetic acid solution was 2.5 mol / L, the reaction temperature was 70℃, the reaction time was 30-60 min, and the pH value was controlled at 6.

[0034] Optionally, in step S4, the preparation process of the cement paste includes the following steps: first, dry-mix lightly calcined magnesium oxide and calcite for 2-3 minutes, then add magnesium acetate solution for wet mixing for 3-5 minutes, with a stirring speed of 800-1000 rpm.

[0035] Optionally, in step S4, the preparation process of the cement paste includes the following steps: first, dry-mixing lightly calcined magnesium oxide and calcite for 2.5 min, then adding magnesium acetate solution for wet mixing for 4 min, with a stirring speed of 900 rpm.

[0036] Optionally, in step S5, the carbonization curing includes the following steps: carbonization curing for 24-72 hours under conditions of CO2 concentration of 8-12%, relative humidity of 70±2%, and temperature of 25±1.5℃. Optionally, the carbonization curing time is 48 hours.

[0037] The second aspect of the present invention provides a method for preparing magnesium oxide-based building materials based on the full recycling of seawater desalination brine resources. The magnesium oxide-based building materials have a 28-day compressive strength ≥55MPa and a carbon sequestration efficiency of not less than 200 kgCO2 / ton of building materials.

[0038] Preferably, the magnesium oxide-based building material has a 28-day compressive strength ≥60 MPa and a carbon sequestration efficiency of 200-300 kg CO2 / ton of building material.

[0039] Optionally, a third aspect of the present invention provides a system for the full recycling of seawater desalination brine resources, comprising:

[0040] (1) Seawater desalination brine pretreatment unit to obtain pretreated brine; the seawater desalination brine pretreatment unit is used to pretreat and remove impurities from seawater desalination brine.

[0041] (2) A graded extraction unit is used to extract magnesium resource solution and calcium resource solution from the pretreated brine, respectively;

[0042] (3) Lightly calcined magnesium oxide and calcite preparation unit: a portion of the extracted magnesium resource solution is calcined to prepare lightly calcined magnesium oxide, and a calcium resource solution is carbonized to prepare calcite;

[0043] (4) Magnesium acetate synthesis unit, which synthesizes magnesium acetate solution from another part of the extracted magnesium resource solution;

[0044] (5) Cement preparation unit: lightly calcined magnesium oxide, calcite and magnesium acetate solution are mixed to prepare cement paste;

[0045] (6) Carbonation curing unit, which carbonizes and cures the cement paste;

[0046] (7) Wastewater treatment unit, which treats the remaining brine to achieve water resource recycling. For example, the wastewater can be recycled through membrane treatment technology.

[0047] Compared with the prior art, the present invention achieves at least one of the following beneficial effects:

[0048] (1) This invention relates to a method for preparing magnesium oxide-based building materials based on the full recycling of seawater desalination brine resources. This method connects seawater brine treatment, magnesium and calcium resource separation, chlorine-free magnesium oxide cement synthesis, carbonization curing, and wastewater treatment in a series, thereby removing pollutants (Mg) from the brine. 2+ Ca 2+ This process transforms resources into raw materials for producing magnesium oxide cement, thereby fundamentally solving the problem of excessive carbon emissions, achieving efficient recovery and high-value utilization of valuable resources in seawater desalination brine, and developing low-carbon and environmentally friendly building materials.

[0049] (2) The preparation method of the present invention can realize the full recycling of resources. Through the graded extraction process, it can realize the efficient recovery and high-value utilization of various valuable metals such as magnesium and calcium in seawater desalination brine. The recovery rate of magnesium resources reaches more than 85%, and the recovery rate of calcium resources reaches more than 80%.

[0050] (3) The preparation method of the present invention can achieve low-carbon or even negative carbon production. It utilizes the cement carbonization process to achieve CO2 mineralization and storage. Each ton of building materials can store no less than 200 kg of CO2. The carbon emissions during the production process are negative, thus achieving the dual goals of carbon reduction and carbon storage.

[0051] (4) The magnesium oxide-based building material prepared by the present invention has a compressive strength of ≥55MPa after 28 days, and a shrinkage rate of more than 50%, while significantly improving shrinkage performance and long-term stability.

[0052] (5) This invention is based on a system for the full recycling of seawater desalination brine resources, which organically combines brine treatment, material preparation and carbon sequestration to form a complete industrial ecological chain, achieving a balance between economic and environmental benefits. Wastewater is recycled through membrane treatment technology, with a wastewater reuse rate of ≥70%, and the remaining wastewater is discharged in compliance with standards, thus solving the environmental problem of seawater desalination brine discharge. Attached Figure Description

[0053] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0054] Figure 1 An exemplary embodiment of the system flow diagram of the present invention based on the full recycling of seawater desalination brine resources is shown;

[0055] Figure 2 An exemplary embodiment is shown, illustrating a SEM image of the magnesium oxide-based building material of Example 3. Detailed Implementation

[0056] To more clearly illustrate the overall concept of the present invention, a detailed description will be provided below with reference to the accompanying drawings and examples.

[0057] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0058] Example 1

[0059] In an exemplary embodiment of the present invention, the system based on the full recycling of seawater desalination brine resources includes:

[0060] (1) Seawater desalination brine pretreatment unit: used for pretreatment and impurity removal of seawater desalination brine. The seawater desalination brine first enters the equalization tank, and then is pumped into the filter to remove most of the suspended solids and colloidal substances. After that, it is pumped into the ultrafiltration system to remove finer particles, colloids, large molecular organic matter and most bacteria.

[0061] (2) Fractional Extraction Unit: Magnesium and calcium resource solutions are extracted separately from the pretreated brine. The pretreated brine is pumped into the primary reaction vessel, and sodium hydroxide or lime slurry is precisely added through an automatic dosing system to adjust the pH of the brine to 9.5-10.5. The temperature is controlled at 40-60℃, the stirring speed is 300-500 rpm, and the reaction is carried out for 30-60 minutes. 2+ Almost all of the magnesium (OH)₂ precipitate was formed, yielding a magnesium resource solution. A portion of this solution was pumped into a plate and frame filter press for solid-liquid separation. The solid, a crude Mg(OH)₂ filter cake, was sent to prepare lightly calcined magnesium oxide. The filtrate (mainly containing Ca) 2+ Na + Cl - The solution then proceeds to the secondary precipitation stage. The filtrate from the primary magnesium extraction stage is pumped into the secondary reactor, the pH is adjusted to 8-9, and sodium carbonate solution is added to precipitate calcium ions as calcium carbonate. This is then separated again using a plate and frame filter press. The solid, a high-purity CaCO3 wet cake, is sent to prepare calcite. The filtrate, rich in NaCl, is the residual brine and is pumped into the wastewater treatment unit.

[0062] (3) Lightly calcined magnesium oxide and calcite preparation unit: a portion of the extracted magnesium resource solution is calcined to prepare lightly calcined magnesium oxide, and a calcium resource solution is carbonized to prepare calcite;

[0063] The magnesium hydroxide filter cake is first fed into a dryer and dried at 100-120℃ until the moisture content is ≤1%. Then it is fed into a calcination furnace and preheated at 300-400℃ for 20-40 minutes, and then calcined at 700-900℃ for 50-70 minutes. The heating rate is controlled at 5-10℃ / minute. Highly active lightly calcined magnesium oxide powder is obtained by rapid cooling.

[0064] The wet CaCO3 cake was re-pulped and the concentration was adjusted to 10-20%. It was then pumped into a carbonization reactor, carbon dioxide was introduced, the pressure was 0.3-0.5 MPa, the carbonization temperature was 20-40℃, and the carbonization time was 60-120 min. Finally, it was dried and ultra-finely ground to obtain calcite.

[0065] (4) Magnesium acetate synthesis unit: Another portion of the extracted magnesium resource solution is used to synthesize magnesium acetate solution; the remaining magnesium resource solution is pumped into a plate and frame filter press for solid-liquid separation. The solid is crude Mg(OH)₂ filter cake. The magnesium hydroxide filter cake is added to water for slurrying, and 2.0-3.0 mol / L acetic acid solution is added under stirring. The reaction temperature is 60-80℃, the reaction time is 30-60 min, and the pH value is controlled at 5.5-6.5 to generate magnesium acetate solution. The magnesium acetate solution is diluted with water to 0.05 mol / L for later use.

[0066] (5) Cement preparation unit: lightly calcined magnesium oxide, calcite and magnesium acetate solution are mixed to prepare cement paste; lightly calcined magnesium oxide and calcite powder are fed into a high-efficiency mixer for dry mixing for 2-3 minutes, and then magnesium acetate solution is added for wet mixing for 3-5 minutes, with a mixing speed of 800-1000 rpm. A uniform cement paste with good fluidity is obtained.

[0067] (6) Carbonation curing unit: The cement slurry is carbonized and cured. The cement slurry is injected into various molds through an automatic casting machine and left to stand for 24 hours at normal temperature and humidity to obtain preliminary demolding strength. The demolded green body is then placed in a kiln with a CO2 concentration of 8-12%, relative humidity of 70±2%, and temperature of 25±1.5℃ for carbonation curing for 24-72 hours. The gas in the kiln can be recycled to improve CO2 utilization. After carbonation, high-strength magnesium oxide-based building materials are obtained.

[0068] (7) Wastewater treatment unit, which treats the remaining brine to realize the recycling of water resources. The remaining brine is first treated with nanofiltration membrane to recover valuable elements, and then enters the reverse osmosis membrane system to remove most of the sodium chloride, producing high-quality recycled water that can be returned to the production system for preparing slurry or cleaning equipment.

[0069] Flowchart reference of the system Figure 1 As shown, the system has a processing capacity of 10,000 m 3 The plant produces seawater desalination brine daily, generates 50,000 tons of high-performance magnesium oxide-based building materials annually, processes 12,500 tons of CO2 annually, saves 65,000 tons of magnesite annually, and saves 18,000 tons of standard coal equivalent of energy annually.

[0070] Example 2

[0071] This embodiment relates to a method for preparing magnesium oxide-based building materials based on the full recycling of seawater desalination brine resources. The preparation method adopts the system and operating mode of Example 1, and includes the following steps:

[0072] S1: Take 10 cubic meters of seawater desalination brine (main component: Mg) 2+ 5.2 g / L, Ca 2+ 0.6 g / L, Na + 12.5 g / L, Cl - Pretreatment with 65.3 g / L of brine was performed to remove impurities, organic matter, and bacteria. The pretreated brine was then subjected to fractional extraction: sodium hydroxide was added to adjust the pH to 9.5, the temperature was controlled at 55℃, the stirring speed was 300 rpm, and the reaction was carried out for 30 minutes. Mg 2+Almost all of the magnesium (OH)₂ precipitate was formed, yielding a magnesium resource solution. A portion of the magnesium resource solution was subjected to solid-liquid separation to obtain a filtrate and a magnesium hydroxide filter cake, which was then set aside. The pH of the magnesium-extracted filtrate was adjusted to 8, and a 1.0 mol / L sodium carbonate solution was added to precipitate calcium ions into calcium carbonate. The temperature was controlled at 30°C, and precipitation was carried out for 80 minutes to obtain a calcium resource solution.

[0073] S2: Magnesium hydroxide was precipitated from half of the magnesium resource solution. First, it was dried at 100℃ to a moisture content of 1.0%, then preheated at 300℃ for 30 minutes, and finally calcined at 700℃ for 60 minutes (heating rate 6℃ / min) to prepare lightly calcined magnesium oxide with a specific surface area of ​​18.1 m². 2 / kg, with an active MgO content of 85%. The calcium resource solution was subjected to solid-liquid separation to obtain a wet calcium carbonate cake. Water was added to adjust the concentration to 15%, and the cake was carbonized at 0.4 MPa pressure and 30℃ for 90 min. After drying and ultrafine grinding, calcite was obtained with a particle size of 2 μm and a specific surface area of ​​13 m². 2 / kg, calcium carbonate purity is 97%.

[0074] S3: Perform solid-liquid separation on the other half of the magnesium resource solution to obtain magnesium hydroxide. Add water to the magnesium hydroxide filter cake and slurry it. Add 2.0 mol / L acetic acid solution while stirring and acidify at 60℃ for 45 min, controlling the pH value at 5.5, to generate magnesium acetate solution. Dilute the magnesium acetate solution with water to 0.05 mol / L for later use.

[0075] S4: By weight percentage, take 90% light-burned magnesia and 10% calcite and dry mix them in a mixer for 2.5 min. Then add magnesium acetate solution (the weight of magnesium acetate solution accounts for 50% of the total weight of light-burned magnesia and calcite) and wet mix for 4 min at a stirring speed of 900 rpm to obtain cement paste.

[0076] S5: Pour cement slurry into a 20×20×20mm cubic mold, compact it, level the surface, and demold it after curing under standard conditions for 24 hours. Then, carbonize and cure it for 48 hours under conditions of 10% CO2, relative humidity of 70±2%, and temperature of 25±1.5℃ to obtain magnesium oxide-based building materials.

[0077] Example 3

[0078] This embodiment relates to a method for preparing magnesium oxide-based building materials based on the full recycling of seawater desalination brine resources. The preparation method adopts the system and operating mode of Example 1, and includes the following steps:

[0079] S1: Take 10 cubic meters of seawater desalination brine (main component: Mg) 2+5.2 g / L, Ca 2+ 0.6 g / L, Na + 12.5 g / L, Cl - Pretreatment with 65.3 g / L of brine was performed to remove impurities, organic matter, and bacteria. The pretreated brine was then subjected to fractional extraction: sodium hydroxide was added to adjust the pH to 9.8, the temperature was controlled at 50℃, the stirring speed was 400 rpm, and the reaction time was 45 min. Mg 2+ Almost all of the magnesium (OH)₂ precipitate was formed, yielding a magnesium resource solution. A portion of the magnesium resource solution was subjected to solid-liquid separation to obtain a filtrate and a magnesium hydroxide filter cake, which was then set aside. The pH of the magnesium-extracted filtrate was adjusted to 8.5, and a 1.2 mol / L sodium carbonate solution was added to precipitate calcium ions into calcium carbonate. The temperature was controlled at 40℃, and precipitation was carried out for 90 minutes to obtain a calcium resource solution.

[0080] S2: Magnesium hydroxide was precipitated from half of the magnesium resource solution. First, it was dried at 110℃ to a moisture content of 0.8%, then preheated at 350℃ for 30 minutes, and finally calcined at 800℃ for 60 minutes (heating rate 7℃ / min) to prepare lightly calcined magnesium oxide with a specific surface area of ​​18.5 m². 2 / kg, with an active MgO content of 87%. The calcium resource solution was subjected to solid-liquid separation to obtain a wet calcium carbonate cake. Water was added to adjust the concentration to 15%, and the cake was carbonized at 0.4 MPa pressure and 30℃ for 90 min. After drying and ultrafine grinding, calcite was obtained with a particle size of 2 μm and a specific surface area of ​​15 m². 2 / kg, calcium carbonate purity is 97%.

[0081] S3: Perform solid-liquid separation on the other half of the magnesium resource solution to obtain magnesium hydroxide. Add water to the magnesium hydroxide filter cake and slurry it. Add 2.5 mol / L acetic acid solution while stirring and perform an acidification reaction at 70℃ for 45 min, controlling the pH value at 6.0, to generate magnesium acetate solution. Dilute the magnesium acetate solution with water to 0.05 mol / L for later use.

[0082] S4: By weight percentage, take 95% light-burned magnesia and 5% calcite and dry mix them in a mixer for 2.5 min. Then add magnesium acetate solution (the weight of magnesium acetate solution accounts for 55% of the total weight of light-burned magnesia and calcite) and wet mix for 4 min at a stirring speed of 900 rpm to obtain cement paste.

[0083] S5: Pour cement slurry into a 20×20×20mm cubic mold, compact it, level the surface, and demold it after curing under standard conditions for 24 hours. Then, carbonize and cure it for 72 hours under conditions of 10% CO2, relative humidity of 70±2%, and temperature of 25±1.5℃ to obtain magnesium oxide-based building materials.

[0084] Example 4

[0085] Based on Example 3, the main difference is that in step S4, 85% of lightly calcined magnesium oxide and 15% of calcite are dry-mixed in a mixer for 2.5 minutes by weight percentage, and then magnesium acetate solution (the weight of magnesium acetate solution accounts for 55% of the total weight of lightly calcined magnesium oxide and calcite) is added and wet-mixed for 4 minutes at a stirring speed of 900 rpm to obtain cement paste.

[0086] In step S5, the cement slurry is poured into a 20×20×20mm cubic mold, compacted, and the surface is leveled. After curing under standard conditions for 24 hours, the mold is removed, and then carbonized and cured for 24 hours under conditions of 10% CO2, relative humidity of 70±2%, and temperature of 25±1.5℃ to obtain magnesium oxide-based building materials.

[0087] Example 5

[0088] Based on Example 3, the main difference is that in step S4, 100% light-burned magnesia and 0% calcite are dry-mixed in a mixer for 2.5 minutes by weight percentage, and then magnesium acetate solution (the weight of magnesium acetate solution accounts for 55% of the total weight of light-burned magnesia and calcite) is added and wet-mixed for 4 minutes at a stirring speed of 900 rpm to obtain cement paste.

[0089] Example 6

[0090] Based on Example 3, the main difference is that in step S4, 70% light-burned magnesium oxide and 30% calcite are dry-mixed in a mixer for 2.5 minutes by weight percentage, and then magnesium acetate solution (the weight of magnesium acetate solution accounts for 55% of the total weight of light-burned magnesium oxide and calcite) is added and wet-mixed for 4 minutes at a stirring speed of 900 rpm to obtain cement paste.

[0091] Example 7

[0092] The main difference from Example 3 is that the concentration of the magnesium acetate solution is 0.1 mol / L.

[0093] Comparative Example 1

[0094] This comparative example relates to a method for preparing magnesium oxide-based building materials based on calcined magnesite, including the following steps:

[0095] (1) Lightly calcined magnesium oxide was obtained by calcining natural magnesite (MgCO3) at 800℃.

[0096] (2) By weight percentage, take 85% light-burned magnesium oxide and 15% commercially available calcite and dry mix them in a mixer for 2.5 min. Then add magnesium acetate solution (the weight of magnesium acetate solution accounts for 55% of the total weight of light-burned magnesium oxide and calcite) and wet mix for 4 min at a stirring speed of 900 rpm to obtain cement paste.

[0097] (3) Pour the cement slurry into a 20×20×20mm cubic mold, vibrate and level the surface, cure under standard conditions for 24 hours and then demold. Then carbonize and cure for 72 hours under conditions of 10% CO2, relative humidity of 70±2% and temperature of 25±1.5℃ to obtain magnesium oxide-based building materials.

[0098] Comparative Example 2

[0099] In a comparative example of the present invention, a method for preparing magnesium oxide-based building materials includes the following steps:

[0100] (1) After mixing magnesium chloride and water in a molar ratio of 1:13, hydrogen peroxide, triethoxy-1H,1H,2H,2H-tetrafluoron-octylsilane (FAS), and tetraethyl orthosilicate (TEOS) are added. The amount of hydrogen peroxide added is 10% of the mass of active magnesium oxide powder, the amount of triethoxy-1H,1H,2H,2H-tetrafluoron-octylsilane (FAS) added is 1% of the mass of active magnesium oxide powder, and tetraethyl orthosilicate (TEOS) is added at a molar ratio of 1:8. The mixture is stirred at 60°C and 600 r / min for 8 hours to obtain a treated magnesium chloride solution.

[0101] (2) Mix active magnesium oxide, magnesium chloride and water in a molar ratio of 6.5:1:13 to make magnesium oxychloride cement slurry. Pour the magnesium oxychloride cement slurry into a 20mm×20mm×20mm mold. Demold and cure after 1 day. Cure in air for 72 hours to obtain magnesium oxide-based building materials.

[0102] Test case

[0103] The performance of the magnesium oxide-based building materials prepared in the examples and comparative examples was tested, as shown in Table 1.

[0104] Table 1

[0105]

[0106] Referring to Table 1, the magnesium oxide-based building materials prepared in this application have a 28-day compressive strength of not less than 55 MPa and a shrinkage rate reduced by more than 50%. Thermogravimetric analysis (TG) and X-ray diffraction (XRD) analyses revealed that the main carbonization products are hydrated magnesia (Mg5(CO3)4(OH)2·4H2O) and magnesia (MgCO3·3H2O), with a carbon sequestration efficiency of not less than 200 kgCO2 / ton of building material. This achieves negative carbon emission production, demonstrating significant carbon reduction benefits. Furthermore, the carbonization products exhibit good stability and water resistance.

[0107] Figure 2 The scanning electron microscope (SEM) image of the magnesium oxide-based building material of Example 3 is shown. It can be seen that a large number of hydromagnesite (Mg5(CO3)4(OH)2·4H2O) crystals were formed in the sample of Example 1. These carbonate phases filled the pores, forming a dense microstructure. Simultaneously, the formation of magnesium carbonate crystals was observed on the calcite surface, confirming the synergistic effect between calcite and magnesium acetate.

[0108] Compared with Example 3, Example 3 (5% calcite addition) showed the highest compressive strength at 28 days, reaching 68.2 MPa, which is 16.60% higher than that of pure MgO cement Example 5 (without calcite).

[0109] In Example 2, the magnesium recovery rate reached 87% and the calcium recovery rate reached 82%, which is higher than the industry average.

[0110] Compared with Comparative Example 2, Example 2 showed a 32% increase in 28-day compressive strength. Compared with Comparative Example 2, the building material prepared in this application showed an increase of over 30% in 28-day compressive strength and a reduction of over 50% in shrinkage rate. Furthermore, Comparative Example 2 employed a composite modification of organic and inorganic materials, but it could not fundamentally solve the defect of instability of its hydration products upon contact with water, and the production process lacked any carbon sequestration capability.

[0111] In Comparative Example 1, although the final magnesium oxide-based building material has good compressive strength, the production of light-burned magnesium oxide by calcining magnesite produces a large amount of carbon dioxide, resulting in high carbon emissions in the overall production process. In contrast, this application achieves negative carbon emissions.

[0112] Based on Example 3, at 10,000 m 3 Based on the daily processing capacity, the annual sales revenue can reach 60-75 million yuan, the annual profit is 35-45 million yuan, and the investment payback period is 2-3 years. It reduces brine emissions by 3.65 million tons per year, seals 12,500 tons of CO2 per year, saves 65,000 tons of magnesite per year, and saves 18,000 tons of standard coal equivalent of energy per year.

[0113] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for preparing a magnesium oxide-based building material based on the full recycling of seawater desalination brine resources, characterized by, The preparation method comprises the following steps: S1: pretreating and fractionally extracting seawater desalination brine to obtain a magnesium resource solution and a calcium resource solution; in step S1, the fractionally extracting comprises the following steps: adjusting the pH value of the brine to 9.5-10.5, controlling the temperature at 40-60 ℃, stirring at a speed of 300-500 rpm, and reacting for 30-60 minutes to obtain the magnesium resource solution; In the solution after the magnesium resource extraction, the pH value is adjusted to 8-9, a carbonizing agent is added to precipitate calcium ions into calcium carbonate, and the calcium resource solution is obtained by filtering; S2: precipitating a part of the magnesium resource solution into magnesium hydroxide, and then calcining the magnesium hydroxide to obtain light-burned magnesium oxide; carbonizing the calcium resource solution to obtain calcite; in step S2, the calcining of the magnesium hydroxide comprises the following steps: drying the magnesium hydroxide at 100-120 ℃ to a water content of ≤1%, then preheating at 300-400 ℃ for 20-40 minutes, and then calcining at 700-900 ℃ for 50-70 minutes, with a temperature rising rate controlled at 5-10 ℃ / min; S3: synthesizing a magnesium acetate solution from another part of the magnesium resource solution; in step S3, the synthesis of the magnesium acetate in the magnesium acetate solution comprises the following steps: precipitating another part of the magnesium resource solution to obtain magnesium hydroxide, and then adding an acetic acid solution to perform acidification reaction to obtain magnesium acetate; wherein the concentration of the acetic acid solution is 2.0-3.0 mol / L, the reaction temperature is 60-80 ℃, the reaction time is 30-60 min, and the pH value is controlled at 5.5-6.5; S4: mixing the prepared light-burned magnesium oxide, calcite and magnesium acetate solution to prepare a cement slurry; S5: casting and forming the cement slurry, and then carbonizing and curing to obtain a magnesium oxide-based building material; In the cement slurry, by weight percentage, 85-95% of the light-burned magnesium oxide and 5-15% of the calcite are included; the magnesium acetate solution accounts for 50-60% of the total weight of the light-burned magnesium oxide and the calcite; The concentration of the magnesium acetate solution is 0.05 mol / L; The content of active magnesium oxide in the light-burned magnesium oxide is more than 85%; Light-burned magnesium oxide with specific surface area not less than 15 m 2 / kg; The particle size of the calcite is not higher than 5 µm; The calcite has a specific surface area of not less than 12 m 2 / kg.

2. The production method according to claim 1, characterized by, In step S2, the carbonizing comprises the following steps: a carbonizing pressure of 0.3-0.5 MPa, a carbonizing temperature of 20-40 ℃, a carbonizing time of 60-120 min, and a calcium resource solution concentration of 10-20 wt%.

3. The preparation method according to claim 1, characterized in that, In step S5, the carbonizing and curing comprises the following steps: carbonizing and curing for 24-72 h under the conditions of a CO2 concentration of 8-12%, a relative humidity of 70±2%, and a temperature of 25±1.5 ℃.

4. The magnesium oxide-based building material prepared according to the method of any one of claims 1-3, characterized in that, The 28-day compressive strength is ≥55 MPa, and the carbon sequestration efficiency is not less than 200 kgCO2 / ton of building materials.

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