A method for preparing magnesium oxide by using phosphorus tailings medium temperature pyrolysis combined with water leaching carbonization
By subjecting phosphorus tailings to medium-temperature pyrolysis and water leaching carbonization under a steam atmosphere, the problems of incomplete calcination and impurity introduction in phosphorus tailings were solved, achieving efficient and high-purity magnesium oxide preparation and simplifying the process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GUIZHOU CHANHEN CHEM CO LTD
- Filing Date
- 2024-01-05
- Publication Date
- 2026-05-15
AI Technical Summary
Existing technologies for processing phosphate tailings suffer from incomplete reactions or product sintering due to high-temperature calcination, and wet processing may introduce new impurities, making it difficult to efficiently separate and extract high-purity magnesium oxide.
Magnesium oxide was prepared by calcining phosphorus tailings under a steam atmosphere, followed by hydration and carbonization. The method involved medium-temperature pyrolysis combined with water leaching carbonization.
This method enables efficient decomposition of phosphorus tailings and preparation of high-purity magnesium oxide, avoids the introduction of new impurities, simplifies the process, and improves extraction rate and product purity.
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Figure CN117800376B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of magnesium oxide preparation technology, and in particular to a method for preparing magnesium oxide using medium-temperature pyrolysis combined with water immersion carbonization. Background Technology
[0002] Currently, the utilization of phosphorus tailings includes phosphorus reprocessing, chemical recovery of calcium and magnesium, fertilizer production, filling of mining voids, and production of building and roadbed materials. In my country, phosphorus tailings are mainly reverse flotation tailings, with dolomite as the primary mineral phase, followed by apatite and a small amount of quartz. This is typical of high-magnesium phosphorus tailings. Therefore, separating and extracting elements such as calcium and magnesium from phosphorus tailings can more effectively promote the high-value resource utilization of phosphorus tailings and achieve green development.
[0003] Methods for separating and extracting calcium and magnesium from phosphate tailings are divided into dry and wet methods. Dry methods mainly include calcination-carbonization, calcination-leaching, and ammonia cycling; wet methods include extraction-back-extraction and nitric acid demagnesification. Wet methods typically require the use of hazardous reagents such as nitric acid and sulfuric acid, which can introduce new substances and generate new impurities such as calcium sulfate, making the process more complex and difficult to solve the problem of impurity removal and the preparation of high-purity products. Dry methods require the complete calcination of dolomite in the phosphate tailings, usually at temperatures exceeding 1000℃, followed by digestion, carbonization, or ammonium salt leaching to separate and extract calcium and magnesium. This method is relatively simple and has become the preferred method for many researchers. However, the first step of this method involves high-temperature calcination, which presents a key problem: if the calcination temperature is too low, the energy provided is insufficient to break the CO bonds in the dolomite, resulting in incomplete decomposition of the reactants and a slow reaction rate; if the temperature is too high, although the dolomite decomposes completely, it promotes the sintering process of the calcined products, leading to a decrease in reactivity. Therefore, when using dry processing to separate and extract calcium and magnesium from phosphate tailings, it is essential to track changes in the solid-phase reaction behavior during the initial calcination process.
[0004] Different atmospheres have vastly different effects on the decomposition of carbonates. Carbon dioxide causes dolomite to decompose in two stages: first, dolomite decomposes into calcite, periclase, and carbon dioxide; second, calcite decomposes into lime and carbon dioxide at a higher temperature. The activation energy for the first stage of dolomite decomposition in a carbon dioxide atmosphere is lower than in other atmospheres (such as air, nitrogen, and oxygen). Water vapor accelerates the decomposition of carbonate minerals. The presence of water vapor not only advances the onset temperature of carbonate mineral decomposition but also increases the overall decomposition reaction rate.
[0005] Therefore, this invention has conducted extensive research on the calcination of phosphorus tailings in the presence of steam. Under the steam atmosphere, the phase transformation, microstructure changes, and occurrence and distribution of major elements during the pyrolysis of phosphorus tailings were studied, providing a new method for the dry treatment of phosphorus tailings and realizing the research on the preparation of magnesium oxide from phosphorus tailings by medium-temperature pyrolysis-water leaching carbonization. Summary of the Invention
[0006] In view of this, the present invention provides a method for preparing magnesium oxide using medium-temperature pyrolysis combined with water leaching carbonization of phosphate tailings. The present invention is achieved using the following technical solution:
[0007] A method for preparing magnesium oxide using medium-temperature pyrolysis combined with water leaching carbonization of phosphate tailings includes the following steps:
[0008] (1) High-temperature complete calcination: The high magnesium phosphorus tailings are heated to 1200℃, kept at that temperature for 60 min, and then cooled to room temperature to obtain the high-temperature calcined product;
[0009] (2) Medium-temperature calcination with steam: The high magnesium and phosphorus tailings are heated to 600℃-800℃ in a steam atmosphere and kept at that temperature for 10min-90min. After cooling to room temperature, the product of medium-temperature calcination with steam is obtained.
[0010] (3) The concentrations of calcium oxide and magnesium oxide in the high-temperature calcination product and the medium-temperature calcination product in steam were determined respectively;
[0011] (4) Hydration treatment: The product of medium-temperature calcination with steam and water are mixed at a solid-liquid ratio of 1:10 g / mL and placed at a temperature of 20℃±2℃ and a relative humidity of 75%±5% for 24 hours to carry out the hydration reaction. After the reaction is completed, the product is dried to obtain the hydration product.
[0012] (5) Water immersion treatment: Mix the hydration product and water at a solid-liquid ratio of 1:15~100g / mL, and immerse at room temperature for 30min;
[0013] (6) Carbonization treatment: Carbon dioxide is introduced into the water-immersed material in step (5) and the carbonization reaction is stirred. The carbonization temperature is controlled at 20℃~60℃ and the carbonization time is 10min-60min. After solid-liquid separation, the filtrate and calcium carbonate precipitate are collected.
[0014] (7) The filtrate is evaporated and crystallized, cooled to room temperature, and then basic magnesium carbonate solid is obtained. Finally, it is calcined to obtain magnesium oxide.
[0015] Preferably, the heating rate in step (1) is 10℃ / min.
[0016] Preferably, the partial pressure of water vapor in step (2) is 0.00MPa-0.04MPa.
[0017] Preferably, the heating rate in step (2) is 5℃ / min-20℃ / min.
[0018] Preferably, step (3) involves placing the high-temperature calcined product and the medium-temperature calcined product with steam into separate three-necked flasks, adding deionized water and stirring until homogeneous. While stirring, the temperature is raised to 80°C, and ammonium chloride is added to react for 30 minutes. After the reaction is complete, the mixture is filtered and washed to obtain the filtrate and residue. The Ca concentration in the filtrate is then detected using an atomic absorption spectrometer. 2+ Mg 2+ The concentration was determined, and the mass of the corresponding oxide was calculated.
[0019] Preferably, the drying in step (4) involves placing the hydrated material in a drying oven at 100℃~110℃ to near dryness, then heating it to 150℃±5℃ to dry it to constant weight, and then cooling it to room temperature.
[0020] Preferably, the flow rate of carbon dioxide in step (6) is 200 mL / min to 800 mL / min.
[0021] Compared with the prior art, the present invention has the following beneficial effects:
[0022] (1) This invention performs medium-temperature calcination treatment on phosphorus tailings under a steam atmosphere, studies the solid-phase reaction behavior during the pyrolysis of phosphorus tailings, solves the problem of no new impurities being introduced, and the high temperature and long time required for complete calcination, and provides a new method for dry treatment of phosphorus tailings.
[0023] (2) The degree of decomposition of phosphorus tailings was characterized by the extraction rate of calcium and magnesium. It was found that when the partial pressure of water vapor was 0.02 MPa, the heating rate was 10 °C / min, the calcination temperature was 758 °C, and the holding time was 1.08 h, the dolomite in the phosphorus tailings was completely decomposed.
[0024] (3) The process of this invention is simple and realizes the high-value utilization of phosphorus tailings. Attached Figure Description
[0025] Figure 1 This is a process flow diagram for preparing magnesium oxide by combining thermal pyrolysis and water leaching carbonization in phosphate tailings.
[0026] Figure 2 These are pyrolysis characteristics of phosphate tailings under different gas atmospheres;
[0027] Figure 3 It is the X-ray diffraction pattern of calcined phosphate tailings under a steam atmosphere;
[0028] Figure 4 This is a scanning electron microscope image of calcined phosphate tailings under a steam atmosphere;
[0029] Figure 5 This is the X-ray diffraction pattern of the magnesium oxide product prepared in Example 1. Detailed Implementation
[0030] In this embodiment, phosphorus tailings from Guizhou Chuanheng were selected as raw materials. The main components are shown in Table 1. The contents of CaO and MgO in the phosphorus tailings are 56.09% and 27.06%, respectively, the contents of P2O5 are 9.40%, and the contents of SiO2 are 3.84%. The mineral composition of the phosphorus tailings was analyzed by X-ray diffraction and it was found to be mainly composed of three minerals: dolomite, fluorapatite, and quartz.
[0031]
[0032] Example 1
[0033] like Figure 1 As shown, a method for preparing magnesium oxide from phosphate tailings by coupled thermal decomposition and water leaching carbonization under a steam atmosphere includes the following specific steps:
[0034] (1) Place the phosphate tailings in an oven at 80°C for 24 hours to dry, then grind them until the particle size is less than 300 mesh, and seal and store them for later use.
[0035] (2) Weigh 1.0000g of the prepared phosphorus tailings into a corundum crucible, place it in a high-temperature tube furnace and calcine it to 1200℃ at 10℃ / min, keep it at the temperature for 1h, cool it to room temperature after calcination, take out the calcined phosphorus tailings, weigh it to obtain 0.6197g of calcined product, with a loss on ignition rate of 38.03%.
[0036] (3) Place the calcined phosphate tailings into a 500ml three-necked flask, add 350ml of deionized water, and stir with a constant temperature magnetic stirrer at a speed of 400r / min. When the temperature reaches 80℃, add 1.00g of ammonium chloride and react for 30min. After the reaction is complete, cool to room temperature, filter and wash, and dilute the filtrate to a 500ml volumetric flask. Then dilute the filtrate 100 times to a 250ml volumetric flask and dilute to volume. Detect the Ca in the solution using a flame atomic absorption spectrometer. 2+ Mg 2+ The concentrations were calculated, and the corresponding masses of the oxides were: CaO: 0.3351g, MgO: 0.1615g.
[0037] (4) Weigh 1.0000g of the prepared phosphorus tailings into a corundum crucible, place it in a high-temperature tube furnace equipped with a steam generator, and calcine it to 758°C at a heating rate of 10°C / min. The partial pressure of water vapor is 0.02 MPa, and the holding time is 1.08h. After the reaction is completed, close the steam generator valve and the tube furnace, cool it to room temperature, take it out, weigh it to obtain 0.6671g of calcined product, and the loss on ignition is 33.29%.
[0038] The sample after step (4) was processed according to step (3) to obtain the mass of CaO: 0.3265g and the mass of MgO: 0.1573g. The extraction rate of calcium oxide was 97.43% and the extraction rate of magnesium oxide was 97.40%.
[0039] The composition of the sample obtained in step (4) was analyzed using an X-ray diffractometer. Figure 3 As shown, the phase composition at this stage is mainly calcium hydroxide, magnesium oxide, fluorapatite, and quartz. The microstructure is as follows: Figure 4 As shown, the calcined phosphorus tailings are mainly formed by spherical, flaky or blocky accumulations. There are many pores between the spherical particles, which increases the reactivity of the product. In addition, particle agglomeration was also found.
[0040] (5) Weigh 2.00g of the sample obtained in step (4) and put it into a small beaker. Add 20ml of deionized water, seal the beaker with a slit, and place it at a temperature of 20℃±2℃ and a relative humidity of 75%±5% for 24h to carry out the hydration reaction. After the reaction, place it in a drying oven at 100℃~110℃ to hydrate until it is nearly dry, then raise the temperature to 150℃±5℃ to dry, and dry it at this temperature until it reaches constant weight. Place it in a drying oven to cool to room temperature, weigh it to obtain 2.2847g of hydration product, and calculate that the active MgO content is 31.64%.
[0041] (6) Weigh 1.0000g of the sample obtained in step (5) into a three-necked flask, add 50ml of deionized water for digestion, pass in 250ml / min CO2, stir at 400r / min, carbonize at 50℃, and carbonize for 30min. After the reaction is complete, take out the sample, filter it for solid-liquid separation, and obtain magnesium bicarbonate solution. Evaporate and crystallize it, and calcine it to 900℃ to obtain magnesium oxide product. The purity of magnesium oxide is 97%, which meets the industrial light magnesium oxide standard HG / T2573-2006.
[0042] like Figure 5 As shown, the magnesium oxide product prepared by this invention has almost no other impurity peaks, indicating that it has high purity.
[0043] Example 2
[0044] The difference between Example 2 and Example 1 is that the calcination temperature is 750℃, the water vapor partial pressure is 0.00Mpa, the holding time is 60min, and other preparation conditions and methods remain unchanged.
[0045] Example 3
[0046] The difference between Example 3 and Example 1 is that the calcination temperature is 750℃, the water vapor partial pressure is 0.01 MPa, the holding time is 60 min, and other preparation conditions and methods remain unchanged.
[0047] Example 4
[0048] The difference between Example 4 and Example 1 is that the calcination temperature is 750℃, the water vapor partial pressure is 0.02 MPa, the holding time is 60 min, and other preparation conditions and methods remain unchanged.
[0049] Example 5
[0050] The difference between Example 5 and Example 1 is that the calcination temperature is 750℃, the water vapor partial pressure is 0.03 MPa, the holding time is 60 min, and other preparation conditions and methods remain unchanged.
[0051] Example 6
[0052] The difference between Example 6 and Example 1 is that the calcination temperature is 750℃, the water vapor partial pressure is 0.04 MPa, the holding time is 60 min, and other preparation conditions and methods remain unchanged.
[0053] Example 7
[0054] The difference between Example 7 and Example 1 is that the calcination temperature is 750℃, the heating rate is 5℃ / min, the holding time is 60min, and other preparation conditions and methods remain unchanged.
[0055] Example 8
[0056] The difference between Example 8 and Example 1 is that the calcination temperature is 750℃, the heating rate is 15℃ / min, the holding time is 60min, and other preparation conditions and methods remain unchanged.
[0057] Example 9
[0058] The difference between Example 9 and Example 1 is that the calcination temperature is 750℃, the heating rate is 20℃ / min, the holding time is 60min, and other preparation conditions and methods remain unchanged.
[0059] Example 10
[0060] The difference between Example 10 and Example 1 is that the calcination temperature is 650℃ and the holding time is 60min, while other preparation conditions and methods remain unchanged.
[0061] Example 11
[0062] The difference between Example 11 and Example 1 is that the calcination temperature is 700℃ and the holding time is 60min, while other preparation conditions and methods remain unchanged.
[0063] Example 12
[0064] The difference between Example 12 and Example 1 is that the calcination temperature is 725℃ and the holding time is 60min, while other preparation conditions and methods remain unchanged.
[0065] Example 13
[0066] The difference between Example 13 and Example 1 is that the calcination temperature is 775℃ and the holding time is 60min, while other preparation conditions and methods remain unchanged.
[0067] Example 14
[0068] The difference between Example 14 and Example 1 is that the calcination temperature is 800℃ and the holding time is 60min, while other preparation conditions and methods remain unchanged.
[0069] Example 15
[0070] The difference between Example 15 and Example 1 is that the calcination temperature is 750℃, the holding time is 10 min, and the holding time is 60 min, while other preparation conditions and methods remain unchanged.
[0071] Example 16
[0072] The difference between Example 16 and Example 1 is that the calcination temperature is 750℃, the holding time is 30 min, and the holding time is 60 min, while other preparation conditions and methods remain unchanged.
[0073] Example 17
[0074] The difference between Example 17 and Example 1 is that the calcination temperature is 750℃ and the holding time is 60min, while other preparation conditions and methods remain unchanged.
[0075] Example 18
[0076] The difference between Example 18 and Example 1 is that the calcination temperature is 750℃, the holding time is 90 min, and the holding time is 60 min, while other preparation conditions and methods remain unchanged.
[0077] Example 19
[0078] The difference between Example 19 and Example 1 is that the calcination temperature is 750℃, the holding time is 120 min, and the holding time is 60 min, while other preparation conditions and methods remain unchanged.
[0079] Example 20
[0080] The difference between Example 20 and Example 1 is that the liquid-to-solid ratio is 15:1, while other preparation conditions and methods remain unchanged.
[0081] Example 21
[0082] The difference between Example 21 and Example 1 is that the liquid-to-solid ratio is 20:1, while other preparation conditions and methods remain unchanged.
[0083] Example 22
[0084] The difference between Example 22 and Example 1 is that the liquid-to-solid ratio is 30:1, while other preparation conditions and methods remain unchanged.
[0085] Example 23
[0086] The difference between Example 23 and Example 1 is that the liquid-to-solid ratio is 100:1, while other preparation conditions and methods remain unchanged.
[0087] Example 24
[0088] The difference between Example 24 and Example 1 is that the CO2 flow rate is 200 ml / min, while other preparation conditions and methods remain unchanged.
[0089] Example 25
[0090] The difference between Example 25 and Example 1 is that the CO2 flow rate is 300 ml / min, while other preparation conditions and methods remain unchanged.
[0091] Example 26
[0092] The difference between Example 26 and Example 1 is that the CO2 flow rate is 500 ml / min, while other preparation conditions and methods remain unchanged.
[0093] Example 27
[0094] The difference between Example 27 and Example 1 is that the CO2 flow rate is 800 ml / min, while other preparation conditions and methods remain unchanged.
[0095] Example 28
[0096] The difference between Example 28 and Example 1 is that the carbonization temperature is 20°C, while other preparation conditions and methods remain unchanged.
[0097] Example 29
[0098] The difference between Example 29 and Example 1 is that the carbonization temperature is 30°C, while other preparation conditions and methods remain unchanged.
[0099] Example 30
[0100] The difference between Example 30 and Example 1 is that the carbonization temperature is 40°C, while other preparation conditions and methods remain unchanged.
[0101] Example 31
[0102] The difference between Example 31 and Example 1 is that the carbonization temperature is 60°C, while other preparation conditions and methods remain unchanged.
[0103] Example 32
[0104] The difference between Example 32 and Example 1 is that the carbonization time is 10 min, while other preparation conditions and methods remain unchanged.
[0105] Example 33
[0106] The difference between Example 33 and Example 1 is that the carbonization time is 15 min, while other preparation conditions and methods remain unchanged.
[0107] Example 34
[0108] The difference between Example 34 and Example 1 is that the carbonization time is 45 min, while other preparation conditions and methods remain unchanged.
[0109] Example 35
[0110] The difference between Example 35 and Example 1 is that the carbonization time is 60 min, while other preparation conditions and methods remain unchanged.
[0111] Example 36
[0112] The performance of the calcined phosphate tailings sample and the prepared magnesium oxide product obtained in Example 1 was tested.
[0113] 1) Test method for the decomposition rate of CaMg(CO3)2 in phosphate tailings: The calcined phosphate tailings were reacted with ammonium chloride, then filtered and washed. The concentration of calcium and magnesium ions in the filtrate was detected by flame atomic absorption spectrometry. The measured concentration of calcium and magnesium ions was converted into the corresponding mass m of oxides. i The mass of the corresponding oxide in the phosphate tailings obtained by calcination at 1200℃ is m. 1200i The ratio of the two represents the decomposition rate of CaMg(CO3)2, and is calculated using the following formula:
[0114] In the formula:
[0115] ω represents the decomposition rate of CaMg(CO3)2 in phosphate tailings, %
[0116] m i The mass (g) of CaO and MgO in pyrolyzed phosphorus tailings under different calcination conditions;
[0117] m 1200i The value is in grams (g) representing the mass of CaO and MgO in calcined phosphate tailings at 1200℃.
[0118] 2) Method for detecting MgO activity in calcined phosphate tailings: Weigh 2g of the calcined phosphate tailings and place it in a small beaker. Add 20ml of deionized water, seal the beaker with a small slit, and leave it at 20℃±2℃ and 75%±5% relative humidity for 24 hours. Then, place it in a drying oven at 100℃~110℃ to hydrate until nearly dry, then raise the temperature to 150℃±5℃ to dry, and dry it to constant weight at this temperature. Cool it to room temperature in a drying oven, weigh it, and calculate the MgO activity using the following formula:
[0119] In the formula:
[0120] ω1: Mass of the sample, g
[0121] ω2: Mass of the sample after hydration, in g
[0122] 0.45: The coefficient for converting the mass increase of active magnesium oxide after hydration into magnesium oxide.
[0123] 3) Determination of magnesium oxide content in products
[0124] The content of calcium oxide, magnesium oxide, and silicon dioxide in the product was determined with reference to the industrial light magnesium oxide standard HG / T2573-2006.
[0125] Examples 2-6 illustrate the effect of water vapor partial pressure on the pyrolysis performance of phosphate tailings in this invention.
[0126]
[0127] As shown in Table 2, the extraction rates of MgO and CaO, as well as the activity of MgO, are highest when the partial pressure of water vapor is 0.02 MPa. This is because as the partial pressure of water vapor increases, more water molecules enter the system, causing the calcined product magnesium oxide to react with it to form magnesium hydroxide, thus reducing the loss on ignition and decreasing the amount of active magnesium oxide. Furthermore, excessively high partial pressures of water vapor can also lead to interactions between the calcined products. For example, MgO, CaO, Mg(OH)₂, and Ca(OH)₂ react with SiO₂ to form CaSiO₃ and MgSiO₃, resulting in a decrease in the extraction rates of MgO and CaO from the calcined products.
[0128] Examples 7-9 illustrate the effect of heating rate on the pyrolysis performance of phosphate tailings in this invention.
[0129]
[0130] As shown in Table 3, the extraction rate and activity of MgO are highest at a heating rate of 10℃ / min, and the extraction rate of CaO is also relatively high. Excessively high heating rates lead to uneven heating of the substances in the system, resulting in incomplete decomposition and surface defects. At lower heating rates, the internal temperature gradient of each substance is smaller, and the reactants decompose fully. However, the calcined products have well-developed crystals and few lattice defects, resulting in lower activity and affecting subsequent leaching operations.
[0131] Examples 10-14 illustrate the effect of calcination temperature on the pyrolysis performance of phosphate tailings in this invention.
[0132]
[0133] As shown in Table 4, the extraction rates and activities of MgO and CaO were highest at a calcination temperature of 758℃. This indicates that increasing the calcination temperature is beneficial for the decomposition of the reactants, but excessively high temperatures will promote the sintering of the calcined products, leading to a decrease in their activity.
[0134] Examples 15-19 illustrate the effect of heat preservation time on the pyrolysis performance of phosphate tailings in this invention.
[0135]
[0136] As shown in Table 5, the extraction rates of CaO and MgO in the calcined product were highest when the holding time was 1.08 h, and the activity of MgO also had the highest value. This is because extending the holding time is beneficial to the further decomposition of reactants and reaction intermediates, but excessively long holding time will also promote the sintering process of the product and reduce the reactivity of the calcined product.
[0137] Examples 20-23 are studies on the effect of liquid-to-solid ratio on the preparation of magnesium oxide by water leaching carbonization of pyrolytic phosphorus tailings in this invention.
[0138]
[0139] As shown in Table 6, as the liquid-to-solid ratio increases, the MgO content decreases, while the contents of CaO and SiO2 increase relatively. This indicates that an excessively high liquid-to-solid ratio will cause some calcium carbonate precipitate to transfer to calcium bicarbonate and enter the liquid phase. Furthermore, due to the increase in solvent, some of the originally insoluble silicates will enter the liquid phase, resulting in a decrease in the MgO content of the obtained product.
[0140] Examples 24-27 are studies on the effect of CO2 flow rate on the preparation of magnesium oxide by water leaching carbonization of pyrolysis phosphate tailings in this invention.
[0141]
[0142] As shown in Table 7, increasing the CO2 flow rate leads to a decrease in MgO content and an increase in CaO and SiO2 content in the product. This indicates that an excessively high CO2 flow rate causes some of the calcium carbonate precipitate in the solution to react with carbon dioxide to form water-soluble calcium bicarbonate, resulting in a higher calcium oxide content in the prepared magnesium oxide product. In addition, an excessively high CO2 flow rate will relatively lower the pH of the solution, increase the solubility of calcium silicate in the calcined product, and allow some calcium silicate to enter the liquid phase, resulting in an increase in silicon content in the product.
[0143] Examples 28-31 are studies on the effect of carbonization temperature on the preparation of magnesium oxide by water leaching carbonization of pyrolytic phosphorus tailings in this invention.
[0144]
[0145] As shown in Table 8, increasing the carbonization temperature relatively increases the magnesium oxide content, while decreasing the content of calcium oxide and silicon dioxide. This is because calcium bicarbonate is unstable; with a moderate increase in temperature, calcium bicarbonate easily decomposes into calcium carbonate precipitate, achieving solid-liquid separation. However, excessively high carbonization temperatures reduce the reaction rate of magnesium oxide with carbon dioxide in aqueous solution, thus decreasing the magnesium oxide content.
[0146] Examples 32-35 are studies on the effect of carbonization time on the preparation of magnesium oxide by water leaching carbonization of pyrolytic phosphorus tailings in this invention.
[0147]
[0148] As shown in Table 9, the magnesium oxide content is highest when the carbonization time is 30 min, while the calcium oxide and silicon dioxide contents are lowest. This is because extending the carbonization time facilitates the complete reaction of magnesium oxide with carbon dioxide in the aqueous solution to form magnesium bicarbonate solution. However, excessively long carbonization times also cause some calcium carbonate precipitate to enter the liquid phase and form calcium bicarbonate, leading to an increase in calcium oxide content and a decrease in product purity.
[0149] In summary, during the study of mesothermal pyrolysis of phosphate tailings under a steam atmosphere, when the steam partial pressure was 0.02 MPa, the heating rate was 10 °C / min, the calcination temperature was 758 °C, and the holding time was 1.08 h, the extraction rates of MgO and CaO in the calcined phosphate tailings were 97.40% and 97.43%, respectively, and the activity of MgO was 31.64%, indicating a high decomposition rate of calcium and magnesium carbonate in the phosphate tailings. The calcined phosphate tailings obtained under these calcination conditions were then subjected to water leaching carbonation treatment with a liquid-to-solid ratio of 50:1 ml / g, a CO2 flow rate of 250 ml / min, a reaction temperature of 50 min, and a reaction time of 30 min. Solid-liquid separation yielded a magnesium bicarbonate solution, which was then evaporated and crystallized to obtain basic magnesium carbonate solid. This solid was subsequently calcined to 900 °C to obtain magnesium oxide product. This product contained 97% MgO and 0.65% CaO, meeting the industrial light magnesium oxide standard HG / T2573-2006.
[0150] Therefore, this invention provides a method for medium-temperature pyrolysis of phosphate tailings under a steam atmosphere, combined with water leaching carbonization to prepare magnesium oxide products. This invention solves the key problems of introducing new impurities and high energy consumption and long time required for complete calcination of phosphate tailings, and produces relatively pure magnesium oxide, achieving efficient and comprehensive utilization of phosphate tailings.
Claims
1. A method for preparing magnesium oxide using medium-temperature pyrolysis combined with water leaching carbonization of phosphate tailings, characterized in that, Includes the following steps: (1) Medium-temperature calcination with steam: The high magnesium phosphorus tailings are heated to 600℃-800℃ in a steam atmosphere and held for 10min-90min. After cooling to room temperature, the product is obtained by medium-temperature calcination with steam; the partial pressure of steam is 0.01MPa-0.03MPa. (2) Hydration treatment: The product of medium-temperature calcination with steam and water are mixed at a solid-liquid ratio of 1:10 g / mL and placed at a temperature of 20℃±2℃ and a relative humidity of 75%±5% for 24 hours to carry out the hydration reaction. After the reaction is completed, the product is dried to obtain the hydration product. (3) Water immersion treatment: Mix the hydration product and water at a solid-liquid ratio of 1:15~100g / mL, and immerse at room temperature for 30min; (4) Carbonization treatment: Carbon dioxide is introduced into the water-immersed material in step (3) and the carbonization reaction is stirred. The carbonization temperature is controlled at 20℃~60℃ and the carbonization time is 10min-60min. After solid-liquid separation, the filtrate and calcium carbonate precipitate are collected. (5) Evaporation crystallization and calcination treatment: The filtrate is evaporated and crystallized, cooled to room temperature to obtain basic magnesium carbonate solid, and finally calcined to obtain magnesium oxide.
2. The method for preparing magnesium oxide using medium-temperature pyrolysis combined with water leaching carbonization of phosphate tailings as described in claim 1, characterized in that, The heating rate in step (1) is 5℃ / min-20℃ / min.
3. The method for preparing magnesium oxide using medium-temperature pyrolysis combined with water leaching carbonization of phosphate tailings as described in claim 1, characterized in that, The drying process in step (2) involves placing the hydrated material in a drying oven at 100℃~110℃ to near dryness, then heating it to 150℃±5℃ to dry it to constant weight, and then cooling it to room temperature.
4. The method for preparing magnesium oxide using medium-temperature pyrolysis combined with water leaching carbonization of phosphate tailings as described in claim 1, characterized in that, The flow rate of carbon dioxide in step (4) is 200 mL / min to 800 mL / min.