Method and system for preparing magnesium oxide and light calcium carbonate by using calcium carbide purified ash

Abstract

The application discloses a method and system for preparing magnesium oxide and light calcium carbonate by using purified calcium carbide ash, and the purified calcium carbide ash is used as raw material, a mixed solution of an ammonium salt and a first acid is used as a dissolving solution to dissolve CaO in the raw material, filtration is performed, a solid phase is a magnesium-containing filter cake, a liquid phase is a calcium-containing solution, CO2 is introduced into the liquid phase, and light calcium carbonate is obtained; a mixed solution of an ammonium salt and a second acid is used to dissolve MgO in the magnesium-containing filter cake, an ammonia evaporation process is performed, filtration is performed, a liquid phase is a MgSO4 solution, the MgSO4 solution is subjected to ammonia and CO2 absorption, and filtration is performed to obtain a magnesium carbonate filter cake; and the magnesium carbonate filter cake is calcined to obtain magnesium oxide. In the application, by controlling the pH value of a leaching solution, coloring elements Fe, Ti and Mn in the raw material are basically not dissolved, a step of removing impurities can be directly omitted, a process is simplified, MgO and CaO components are fully utilized, high-value-added products are prepared, the whole process is simple, and industrial production is easy.

Description

Technical Field

[0001] This invention belongs to the field of resource utilization technology of calcium carbide furnace purification ash, specifically involving a method and system for preparing magnesium oxide and light calcium carbonate from calcium carbide purification ash residue. Background Technology

[0002] In the calcium carbide production process, the purification ash produced after the calcium carbide tail gas is incinerated in a fluidized bed furnace, resulting in gray spherical waste residue commonly known as purification ash. Currently, the common method for disposing of purification ash is to transport it off-site by truck and then landfill it. This not only occupies land and pollutes the environment during landfilling but also results in a significant waste of resources. The main components of this ash residue are magnesium oxide and calcium oxide, with magnesium oxide accounting for 30-50% by mass and calcium oxide accounting for 30-40% by mass. It can be used as a raw material for the production of magnesium oxide, thus turning waste into treasure and improving economic efficiency.

[0003] There are few research reports on the preparation of magnesium compounds from calcium carbide purification slag. The main process involves acid dissolution of the purification slag, followed by alkaline precipitation of the dissolved solution to prepare compounds such as magnesium hydroxide.

[0004] Patent (201811628620.4) discloses a system and method for producing magnesium hydroxide and light calcium carbonate from purified ash residue of a calcium carbide furnace. One method for producing magnesium hydroxide and light calcium carbonate from purified ash residue of a calcium carbide furnace includes the following steps: reacting acid (hydrochloric acid or nitric acid) with the purified ash residue; adding ammonia (ammonia gas or ammonia water, the same below) at 30–90°C to adjust the pH to 6–7; then adding an oxidant (hypochlorous acid, sodium hypochlorite, calcium hypochlorite); filtering to obtain a first mother liquor and waste residue; continuing to add ammonia to the first mother liquor at 30–90°C; filtering to obtain a second mother liquor and magnesium hydroxide product; adding a carbon source (CO2 or ammonium bicarbonate) to the second mother liquor at 30–90°C; filtering to obtain a third mother liquor and light calcium carbonate product; after distilling ammonia and crystallizing the third mother liquor, filtering and separating to obtain a fourth mother liquor and ammonium chloride product; the fourth mother liquor is returned to the acid dissolution step for recycling.

[0005] Patent (201811620503.3) discloses a method for preparing calcium sulfate and magnesium hydroxide from purified ash residue of a calcium carbide furnace. The method involves dissolving the purified ash residue in acid (hydrochloric acid or nitric acid) to obtain a mother liquor containing magnesium, calcium, manganese, and iron ions. The mother liquor is heated to 40–80°C, and an alkaline solution is added to adjust the pH to 6–7. Sodium hypochlorite or calcium hypochlorite is then added, and the reaction is carried out for 10–100 minutes. The residue is filtered and the filtrate is reserved. Sulfate is added to the filtrate, and the reaction is carried out for 1–3 hours. The mixture is then allowed to stand for 1–3 hours, filtered, and washed with water to obtain calcium sulfate, which is also reserved. The filtrate is then heated to 40–80°C, and an alkaline solution is added, and the reaction is carried out for 1–3 hours. The mixture is allowed to stand for 1–3 hours, filtered, and washed with water to obtain magnesium hydroxide, which is also reserved. Finally, the residue obtained after ammonia stripping and crystallization of the filtrate is added to the mother liquor.

[0006] It is evident that during the acid dissolution process, impurities such as manganese ions, iron ions, and aluminum ions enter the solution and must be removed through a purification process; at the same time, a large amount of acid and ammonia water or ammonia gas are consumed. Summary of the Invention

[0007] To overcome the problems in the prior art, the purpose of this invention is to provide a method and system for preparing magnesium oxide and light calcium carbonate using calcium carbide purification ash residue. This system can fully utilize the MgO and CaO components to prepare high value-added products. The process is simple and easy to implement, with no wastewater or waste gas emissions, and has high added value and good economic benefits.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing magnesium oxide and light calcium carbonate from calcium carbide purification ash residue includes the following steps:

[0010] Using calcium carbide purification ash as raw material, CaO in the raw material is dissolved in a mixed solution of ammonium salt and primary acid. After filtration, the solid phase is a magnesium-containing filter cake and the liquid phase is a calcium-containing solution. Then, CO2 is introduced into the liquid phase to obtain light calcium carbonate. MgO in the magnesium-containing filter cake is dissolved in a mixed solution of ammonium salt and secondary acid. After ammonia stripping, the solution is filtered to obtain a MgSO4 solution. The MgSO4 solution is then filtered to absorb ammonia and CO2, and finally, magnesium carbonate filter cake and filtrate are obtained. The magnesium carbonate filter cake is then calcined to prepare magnesium oxide.

[0011] Furthermore, the specific steps include:

[0012] (1) Grind the calcium carbide purification ash into calcium carbide purification ash powder;

[0013] (2) Prepare a mixed solution A with pH = 2 to 5 by mixing ammonium salt and primary acid. The mass fraction of mixed solution A is 15 to 40%. Dissolve the calcium carbide purification ash powder in step (1) with mixed solution A. After filtration, obtain a liquid phase and a solid phase. The liquid phase is a calcium-containing alkaline solution and the solid phase is a magnesium-containing filter cake.

[0014] (3) CO2 is introduced into the calcium-containing alkaline solution in step (2) to carry out carbonation reaction, and the solution is filtered to obtain filter cake. The filter cake is calcium carbonate precipitate, which is then washed and dried to obtain light calcium carbonate.

[0015] (4) Prepare a mixed solution B with pH = 1 to 4 by mixing ammonium salt and second acid. Take the magnesium-containing filter cake from step (2) and the mixed solution B for dissolution reaction and ammonia stripping process. Filter to obtain liquid phase and solid phase. The liquid phase is magnesium nitrate solution and the solid phase is acid leaching waste residue.

[0016] (5) In the magnesium nitrate solution in step (4), ammonia and CO2 gas are simultaneously introduced to carry out a precipitation reaction, and the solution is filtered to obtain magnesium carbonate filter cake.

[0017] (6) The magnesium carbonate filter cake obtained in step (5) is dried and calcined to obtain magnesium oxide.

[0018] Furthermore, in the calcium carbide purification ash residue, the mass fraction of CaO is 20-55 wt%, the mass fraction of MgO is 25-60 wt%, and the mass fraction of SiO2 is ≤20 wt%; the particle size of the calcium carbide purification ash residue powder is >95% 200 mesh.

[0019] Furthermore, the active calcium oxide content in the calcium carbide purification ash is calculated by subtracting the CaO contained in Ca2SiO4 from the total CaO content in the calcium carbide purification ash, and the Ca2SiO4 content is calculated by subtracting the SiO2 in K2MgSiO4 from the total SiO2 in the calcium carbide purification ash, leaving the remaining SiO2; the active magnesium oxide content is calculated by subtracting the MgO contained in K2MgSiO4 from the total MgO content in the calcium carbide purification ash, and the K2MgSiO4 content is calculated based on the K2O in the calcium carbide purification ash.

[0020] Furthermore, when CO2 is introduced into the calcium-containing alkaline solution in step (2), the CO2 gas flow rate is 0.5–1.2 L / min per liter of solution, the carbonization reaction temperature is 40–60 °C, and the carbonization reaction time is 30–90 min; in step (5), when ammonia and CO2 are simultaneously introduced into the magnesium nitrate solution in step (4) for precipitation reaction, the CO2 gas flow rate is 0.5–1.2 L / min per liter of solution, the ammonia gas flow rate is 1–2.4 L / min per liter of solution, the precipitation reaction temperature is 30–75 °C, and the precipitation reaction time is 30–120 min.

[0021] Furthermore, the magnesium carbonate filter cake obtained in step (5) is dried at a temperature of 95–120°C for 6–12 hours; and calcined at a temperature of 700–1000°C for 1–3 hours.

[0022] Furthermore, the first acid is one or more of acetic acid, hydrochloric acid, nitric acid, and formic acid; the second acid is one or more of sulfuric acid, phosphoric acid, citric acid, oxalic acid, and ammonium bisulfate; and the ammonium salt is one or more of ammonium acetate, ammonium nitrate, ammonium acetate, ammonium chloride, and ammonium sulfate.

[0023] Furthermore, in step (2), the dissolution reaction temperature is 25–60°C and the dissolution reaction time is 20–90 min; in step (4), the dissolution reaction temperature is 60–95°C and the dissolution reaction time is 30–180 min.

[0024] Furthermore, the mass fraction of mixed solution A is 15-40%, and the mass ratio of active calcium oxide in calcium carbide purification ash powder to mixed solution A is 1:(8-20).

[0025] The mass fraction of mixed solution B is 10-25%, and the mass ratio of active magnesium oxide to mixed solution B in the magnesium-containing filter cake is 1:(15-30).

[0026] A system for preparing magnesium oxide and light calcium carbonate using calcium carbide purification slag as described above includes a calcium leaching agent mixing tank, an ammonium acid tank for calcium, a calcium dissolving reactor, a first filter, a calcium precipitation reactor, a second filter, a magnesium dissolving reactor, a third filter, a magnesium precipitation reactor, a fourth filter, a calcination reactor, a magnesium leaching agent mixing tank, an ammonium acid tank for magnesium, and a carbon dioxide recovery tank.

[0027] The calcium dissolving reactor is connected to the first filter, the liquid outlet of the first filter is connected to the calcium precipitation reactor, the calcium precipitation reactor is connected to the second filter, the second filter is connected to the ammonium acid tank for calcium, the ammonium acid tank for calcium is connected to the mixing tank, and the mixing tank is connected to the calcium dissolving reactor.

[0028] The solid outlet of the first filter is connected to the magnesium dissolving reactor, which is connected to the inlet of the ammonia storage tank; the outlet of the ammonia storage tank is connected to the magnesium precipitation reactor.

[0029] The magnesium dissolving reactor is connected to the inlet of the third filter; the liquid phase outlet of the third filter is connected to the magnesium dissolving reactor; the magnesium precipitation reactor is also connected to the fourth filter.

[0030] The first outlet of the fourth filter is connected to the calcination reactor; the calcination reactor is connected to the carbon dioxide recovery tank; the gas outlet of the carbon dioxide recovery tank is connected to the magnesium precipitation reactor.

[0031] The second outlet of the fourth filter is connected to the magnesium leaching agent mixing tank via the magnesium ammonium acid storage tank.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] This invention uses calcium carbide purification ash as the main raw material to produce calcium carbonate while preparing magnesium oxide. It makes full use of the MgO and CaO components to prepare high value-added products, which has good economic benefits. In this invention, by controlling the pH value of the leaching solution, the coloring elements such as Fe, Ti, and Mn in the raw materials are basically not dissolved, which can directly eliminate the impurity removal step, simplify the process, reduce equipment investment, and facilitate industrialization.

[0034] Furthermore, the present invention uses a mixed solution of ammonium acetate and acetic acid and ammonium nitrate and sulfuric acid as the dissolving medium. The leaching medium solution can be recycled in the process, which greatly reduces the consumption of raw materials and eliminates wastewater and waste gas emissions.

[0035] Furthermore, the dicalcium silicate phase contained in the calcium carbide purification ash can be slowly dissolved in acidic solutions. Therefore, calcium impurities will be dissolved during the magnesium dissolution process, affecting the purity of magnesium oxide. In this invention, the magnesium dissolution process uses a mixed solvent, in which sulfuric acid is added to accelerate the reaction rate and reduce the calcium content in the solution, thus preparing a higher quality magnesium oxide product. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the system for preparing magnesium oxide and calcium carbonate using calcium carbide-purified ash residue according to the present invention.

[0037] Figure 2 This is a process flow diagram of the present invention for preparing magnesium oxide and light calcium carbonate using calcium carbide-purified ash residue.

[0038] Figure 3 This is an X-ray powder diffraction pattern of magnesium oxide prepared according to the present invention.

[0039] Figure 4 This is a scanning electron microscope image of magnesium oxide produced according to the present invention.

[0040] Figure labels: 1-Acetic acid storage tank; 2-Calcium leaching agent mixing tank; 3-Ammonium sulfate tank for calcium; 4-Carbon dioxide tail gas storage tank; 5-Ball mill jar; 6-Calcium dissolving reactor; 7-First filter; 8-Calcium precipitation reactor; 9-Second filter; 10-Magnesium dissolving reactor; 11-Ammonia storage tank; 12-Third filter; 13-Magnesium precipitation reactor; 14-Fourth filter; 15-Calcination reactor; 16-Sulfuric acid storage tank; 17-Magnesium leaching agent mixing tank; 18-Ammonium sulfate tank for magnesium; 19-Carbon dioxide recovery tank; 31-First inlet of calcium leaching agent mixing tank; 32-Solid phase inlet of calcium dissolving reactor; 33-Liquid phase inlet of calcium dissolving reactor 34 - First feed inlet of the calcium precipitation reactor; 35 - Solid feed inlet of the magnesium dissolving reactor; 36 - First feed inlet of the second filter; 37 - Second feed inlet of the calcium precipitation reactor; 38 - First feed inlet of the magnesium leaching agent mixing tank; 39 - Liquid feed inlet of the magnesium dissolving reactor; 40 - Gas outlet of the magnesium dissolving reactor; 41 - Liquid outlet of the magnesium dissolving reactor; 42 - Liquid feed inlet of the magnesium precipitation reactor; 43 - Solid outlet; 44 - Liquid outlet; 45 - First outlet; 46 - Second gaseous feed inlet; 47 - First gaseous feed inlet; 48 - Second feed inlet of the calcium leaching agent mixing tank; 49 - Second feed inlet of the magnesium leaching agent mixing tank. Detailed Implementation

[0041] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0042] Furthermore, elements in this invention are referred to as being "fixed to" or "set on" another element, which may be directly on the other element or may also include an intervening element. When an element is considered to be "connected" to another element, it may be directly connected to the other element or may also include an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0043] This invention discloses a method for preparing magnesium oxide and light calcium carbonate from calcium carbide purification ash slag. Using calcium carbide purification ash slag as raw material, a mixed solution of ammonium acetate and acetic acid is used as the dissolving agent to dissolve CaO from the raw material. After filtration, the solid phase is a magnesium-containing filter cake, and the liquid phase is a calcium-containing solution. Then, CO2 is introduced into the liquid phase to prepare light calcium carbonate, and the filtrate is an ammonium acetate solution, which is returned to the dissolution process for recycling. A mixed solution of ammonium nitrate and sulfuric acid is used to dissolve MgO from the magnesium-containing filter cake. After an ammonia stripping process, filtration is performed, resulting in a dicalcium silicate slag as the solid phase and a MgSO4 solution as the liquid phase. The MgSO4 solution undergoes an ammonia and CO2 absorption process, followed by filtration to obtain a magnesium carbonate filter cake and filtrate. The magnesium carbonate filter cake is calcined to prepare magnesium oxide, and the filtrate is an ammonium nitrate solution, which is returned to the dissolution process for recycling. This method fully utilizes the MgO and CaO components to prepare high-value-added products, and the process is simple and easy to implement, making it suitable for industrial promotion.

[0044] See Figure 2 The specific steps of the method for preparing magnesium oxide and light calcium carbonate using calcium carbide purification ash residue are as follows:

[0045] (1) Raw material pretreatment process: The calcium carbide purification ash residue is transported to a ball mill and ground into powder;

[0046] (2) CaO leaching process: Ammonium acetate and acetic acid solution are prepared into a mixed solution A with pH = 2-5 in calcium leaching agent mixing tank 2. The mass fraction of mixed solution A is 15-40%. The calcium carbide purification ash powder in step (1) is leached in a calcium dissolving reactor at a mass ratio of active calcium oxide to mixed solution A of 1:(8-20). The reaction temperature is 25-60℃ and the reaction time is 20-90min. After filtration through the first filter, the liquid phase is a calcium-containing alkaline solution and the solid phase is a magnesium-containing filter cake.

[0047] (3) Light calcium carbonate preparation process: The calcium-containing alkaline solution in step (2) is transported to the calcium precipitation reactor, and CO2 is introduced to carry out the carbonation reaction. The filter cake after filtration by the second filter is calcium carbonate precipitate. After washing and drying, light calcium carbonate powder product is obtained. The filtrate is ammonium acetate aqueous solution, which is recycled to step (2) for use.

[0048] (4) MgO leaching process: Ammonium nitrate and sulfuric acid solution are mixed in a magnesium leaching agent mixing tank to prepare a mixed solution B with pH = 1-4. The mass fraction of mixed solution B is 10-25%. The magnesium-containing filter cake from step (2) is leached and ammonia stripping is carried out in a magnesium dissolving reactor at a mass ratio of active magnesium oxide to mixed solution A of 1:(15-30). The reaction temperature is 60-95℃ and the reaction time is 30-180min. After filtration through the third filter, the liquid phase is magnesium nitrate solution and the solid phase is used as acid leaching waste. The ammonia gas generated in the ammonia stripping process is recycled to step (5) for use.

[0049] (5) Magnesium carbonate preparation process: The magnesium nitrate solution obtained in step (4) is transported to the magnesium precipitation reactor, and ammonia and CO2 gas are introduced at the same time for precipitation. After filtration and washing separation by the fourth filter, magnesium carbonate filter cake is prepared; the obtained filtrate is an ammonium nitrate aqueous solution, which is recycled to step (4) for use.

[0050] (6) MgO product preparation process: The magnesium carbonate filter cake obtained in step (5) is dried and calcined in a calcination reactor to obtain magnesium oxide product.

[0051] Preferably, in step (1), the calcium carbide purification ash raw material has a CaO mass fraction of 20-55 wt%, a MgO mass fraction of 25-60 wt%, and a SiO2 mass fraction of ≤20 wt%; the particle size of the calcium carbide purification ash powder is ~200 mesh >95%.

[0052] The active calcium oxide content in step (2) can be calculated by subtracting the CaO contained in Ca2SiO4 from the total CaO content in the calcium carbide purification ash residue. The Ca2SiO4 content is calculated by subtracting the SiO2 in K2MgSiO4 from the total SiO2 in the calcium carbide purification ash residue, leaving the remaining SiO2.

[0053] The active magnesium oxide content in step (4) can be calculated by subtracting the MgO content in K2MgSiO4 from the total MgO content in the calcium carbide purification ash residue. The K2MgSiO4 content is calculated based on the K2O content in the calcium carbide purification ash residue.

[0054] In step (3), the carbonization reaction has a CO2 gas flow rate of 0.5–1.2 L / min per liter of solution, a carbonization temperature of 40–60 °C, and a carbonization time of 30–90 min. In step (5), the precipitation reaction conditions are a CO2 gas flow rate of 0.5–1.2 L / min per liter of solution, an ammonia gas flow rate of 1–2.4 L / min per liter of solution, a reaction temperature of 30–75 °C, and a reaction time of 30–120 min.

[0055] In step (6), the magnesium carbonate filter cake is dried at 95-120°C for 6-12 hours; the calcination temperature is 700-1000°C and the calcination time is 1-3 hours; the calcination tail gas is purified to obtain CO2, which is then recycled to step (5) or step (3) for use.

[0056] The chemical composition analysis results of the purified ash raw materials used in the following examples are shown in Table 1. The results show that the contents of MgO, CaO, SiO2, and K2O are 29.89%, 47.89%, 10.81%, and 4.39%, respectively. The main phase composition of the purified ash is calculated to be: magnesium oxide 28.0%, calcium hydroxide 5.9%, dicalcium silicate 22.9%, calcium oxide 28.5%, and K2MgSiO 49.1%. According to the method described in claim 3, the mass fraction of active magnesium oxide in the purified ash is 28.01%; the mass fraction of active calcium oxide is 32.94%.

[0057] Table 1. Chemical composition analysis results of purified ash (w B %)

[0058]

[0059] Example 1

[0060] The structure of the system used in this invention for preparing magnesium oxide and light calcium carbonate from calcium carbide-purified ash slag is as follows: Figure 1 As shown, it includes: acetic acid storage tank 1, calcium leaching agent mixing tank 2, calcium ammonium acid tank 3, carbon dioxide tail gas storage tank 4, ball mill tank 5, calcium dissolving reactor 6, first filter 7, calcium precipitation reactor 8, second filter 9, magnesium dissolving reactor 10, ammonia storage tank 11, third filter 12, magnesium precipitation reactor 13, fourth filter 14, calcination reactor 15, sulfuric acid storage tank 16, magnesium leaching agent mixing tank 17, magnesium ammonium acid tank 18, and carbon dioxide recovery tank 19;

[0061] The calcium dissolving reactor 6 is provided with a solid phase inlet 32 ​​and a liquid phase inlet 33, and the magnesium dissolving reactor 10 is provided with a solid phase inlet 35 and a liquid phase inlet 39.

[0062] The calcium dissolving reactor 6 is connected to the first filter 7, the liquid outlet of the first filter 7 is connected to the calcium precipitation reactor 8, the calcium precipitation reactor 8 is connected to the second filter 9, the second filter 9 is connected to the ammonium acid tank 3 for calcium, the ammonium acid tank 3 for calcium is connected to the mixing storage tank 2, and the mixing storage tank 2 is connected to the calcium dissolving reactor 6.

[0063] The solid outlet of the first filter 7 is connected to the magnesium dissolving reactor 10, the magnesium dissolving reactor gas outlet 40 of the magnesium dissolving reactor 10 is connected to the inlet of the ammonia storage tank 11; the outlet of the ammonia storage tank 11 is connected to the first gas phase inlet 47 of the magnesium precipitation reactor 13.

[0064] The magnesium dissolving reactor 10 has a liquid outlet 41 connected to the inlet of the third filter 12; the liquid outlet of the third filter 12 is connected to the liquid inlet 42 of the magnesium precipitation reactor of the magnesium dissolving reactor 10; the magnesium precipitation reactor 10 is also connected to the fourth filter 14.

[0065] The solid phase outlet 43 of the fourth filter 14 is connected to the calcination reactor 15; the first outlet 45 of the calcination reactor 15 is connected to the carbon dioxide recovery tank 19; the gas outlet of the carbon dioxide recovery tank 19 is connected to the second gas phase inlet 46 of the magnesium precipitation reactor 13.

[0066] The liquid phase outlet 44 of the fourth filter 14 is connected to the inlet of the magnesium ammonium storage tank 18; the magnesium ammonium storage tank 18 is connected to the magnesium leaching agent mixing tank 17.

[0067] The calcium dissolving reactor 6 and the magnesium dissolving reactor 10 are each provided with two inlets. The calcium dissolving reactor 6 is provided with a solid phase inlet 32 ​​and a liquid phase inlet 33, and the magnesium dissolving reactor 10 is provided with a solid phase inlet 35 and a liquid phase inlet 39. The calcium leaching agent is added from the mixing tank 2 through the liquid phase inlet 33. The treated purified ash is added from the solid phase inlet 32. After complete dissolution, it is filtered by the first filter 7 and sent to the calcium precipitation reactor 8. After complete precipitation, it is filtered by the second filter 9 and the filtrate is sent to the calcium ammonium acid tank 3 for recycling. The liquid in the calcium ammonium acid tank 3 enters the mixing tank 2 through the second inlet 48 of the calcium leaching agent mixing tank.

[0068] The filter cake filtered by the first filter 7 is sent to the magnesium dissolving reactor 10 through the solid phase inlet 35 of the magnesium dissolving reactor. The gas from the magnesium dissolving reactor 10 is sent to the inlet of the ammonia storage tank 11 through the gas outlet 40 of the magnesium dissolving reactor. The gas from the outlet of the ammonia storage tank 11 is sent to the first gas phase inlet 47 of the magnesium precipitation reactor for recycling.

[0069] The liquid phase from the magnesium dissolving reactor 10 is fed into the inlet of the third filter 12 through the liquid outlet 41 of the magnesium dissolving reactor; the liquid phase from the third filter 12 is fed into the liquid inlet 42 of the magnesium precipitation reactor; the material from the magnesium precipitation reactor 10 is fed into the fourth filter 14.

[0070] The solid phase output of the fourth filter 14 is fed into the calcination reactor 15; the gas output from the calcination reactor 15 is fed into the carbon dioxide recovery tank 19 through the first outlet 45; the gas from the carbon dioxide recovery tank 19 is fed into the second gas phase inlet 46 of the magnesium precipitation reactor 13.

[0071] Finally, the liquid phase of the fourth filter 14 is fed into the inlet of the magnesium ammonium storage tank 18 through the liquid phase outlet 44; the material in the magnesium ammonium storage tank 18 is fed into the magnesium leaching agent mixing tank 17 through the second inlet 49 of the magnesium leaching agent mixing tank, mixed evenly, and then recycled.

[0072] This invention provides a method for preparing magnesium oxide and calcium carbonate from calcium carbide-purified ash residue, specifically comprising the following steps:

[0073] The calcium carbide purification ash was fed into a ball mill and ground into powder. 50.00g of the calcium carbide purification ash powder ground to 200 mesh was taken (the chemical composition analysis results are shown in Table 1). The active magnesium oxide content was calculated to be 14.01g and the active calcium oxide mass fraction was 16.47g. Ammonium acetate and acetic acid solution were prepared into a mixed solution A with pH=2 in a calcium leaching agent mixing tank 2. The mass fraction of mixed solution A was 40%. Calcium carbide purification ash powder was mixed with mixed solution A at a mass ratio of 1:8, i.e., 50.00g of calcium carbide purification ash powder and 131.76g of mixed solution A were carried out in a calcium dissolving reactor for dissolution reaction. The reaction temperature was 30℃ and the reaction time was 80min. After filtration, the liquid phase was a calcium-containing alkaline solution and the solid phase was a magnesium-containing filter cake. CO2 was introduced into the calcium-containing alkaline solution for carbonation reaction in a calcium precipitation reactor. The aeration rate was 0.8L / min per liter of solution, the carbonation temperature was 45℃, and the carbonation time was 50min. The filtered filter cake was calcium carbonate precipitate, which was then washed and dried to obtain 28.29g of light calcium carbonate powder product. Its chemical composition is shown in Table 2. The CaO content exceeded 54%, and other impurities were very few. The filtrate was an ammonium acetate aqueous solution, which was recycled to the calcium oxide dissolution step.

[0074] Table 2 Chemical analysis results of light calcium carbonate product (CC-1) (w B / %)

[0075]

[0076] Ammonium nitrate and sulfuric acid solutions were prepared into a mixed solution B with pH=1 in a magnesium leaching agent mixing tank. The mass fraction of mixed solution B was 25%. The magnesium-containing filter cake was then subjected to a leaching reaction and ammonia stripping process in a magnesium dissolving reactor at a mass ratio of active magnesium oxide to mixed solution A of 1:15, i.e., 210.15g of magnesium-containing filter cake to mixed solution B. The reaction temperature was 70℃ and the reaction time was 60min. The ammonia gas produced by the reaction was collected. After filtration, the liquid phase was a magnesium nitrate-containing solution, and the solid phase was used as acid leaching waste residue. The obtained magnesium nitrate solution was transferred to a magnesium precipitation reactor, where ammonia and CO2 were simultaneously introduced to carry out a precipitation reaction. The CO2 aeration rate was 0.9 L / min per liter of solution, and the ammonia aeration rate was 1.6 L / min per liter of solution. The reaction temperature was 45℃, and the reaction time was 60 min. After the reaction, the solution was filtered, washed, and separated to obtain a magnesium carbonate filter cake. The resulting filtrate was an ammonium nitrate aqueous solution, which was recycled to the magnesium oxide dissolution step. The magnesium carbonate filter cake was dried at 100℃ for 12 h and then placed in a calcination reactor for calcination at 800℃ for 3 h, yielding 13.75 g of magnesium oxide powder. Its chemical composition is shown in Table 3. Figure 3 and Figure 4 The purity of the magnesium oxide powder is approximately 99%.

[0077] Table 3. Chemical composition analysis results of magnesium oxide products (MG-1) (w B / %)

[0078]

[0079] Example 2

[0080] Unlike Example 1, this example provides a method for preparing magnesium oxide and calcium carbonate using calcium carbide-purified ash slag, comprising:

[0081] The calcium carbide purification ash was fed into a ball mill and ground into powder. 50.00g of the calcium carbide purification ash powder ground to 200 mesh was weighed (the chemical composition analysis results are shown in Table 1). The active magnesium oxide content was calculated to be 14.01g and the active calcium oxide mass fraction was 16.47g. Ammonium acetate and acetic acid solution were prepared into a mixed solution A with pH=5 in a calcium leaching agent mixing tank. The mass fraction of mixed solution A was 15%. Calcium carbide purification ash powder was mixed with mixed solution A at a mass ratio of 1:20, i.e., 50.00g of calcium carbide purification ash powder and 329.40g of mixed solution A were carried out in a calcium dissolving reactor for dissolution reaction. The reaction temperature was 40℃ and the reaction time was 60min. After filtration, the liquid phase was a calcium-containing alkaline solution and the solid phase was a magnesium-containing filter cake. CO2 was introduced into the calcium-containing alkaline solution to carry out a carbonation reaction in a calcium precipitation reactor. The aeration rate was 0.6L / min per liter of solution, the carbonation temperature was 60℃, and the carbonation time was 80min. The filtered filter cake was calcium carbonate precipitate, which was then washed and dried to obtain 28.13g of light calcium carbonate powder product. Its chemical composition is shown in Table 4, with a CaO content of 54.47% and very few other impurities. The filtrate was an ammonium acetate aqueous solution, which was recycled to the calcium oxide dissolution step.

[0082] Table 4 Chemical analysis results of light calcium carbonate product (CC-2) (w B / %)

[0083]

[0084] Ammonium nitrate and sulfuric acid solutions were prepared into a mixed solution B with pH=4 in a magnesium leaching agent mixing tank. The mass fraction of mixed solution B was 10%. The magnesium-containing filter cake was then subjected to a leaching reaction and ammonia stripping process in a magnesium dissolving reactor at a mass ratio of active magnesium oxide to mixed solution A of 1:30, i.e., 420.30 g of magnesium-containing filter cake to mixed solution B. The reaction temperature was 90℃ and the reaction time was 40 min. The ammonia gas produced by the reaction was collected. After filtration, the liquid phase was a magnesium nitrate-containing solution, and the solid phase was used as acid leaching waste residue. The obtained magnesium nitrate solution was transferred to a magnesium precipitation reactor, where ammonia and CO2 were simultaneously introduced to carry out a precipitation reaction. The CO2 aeration rate was 1.1 L / min per liter of solution, and the ammonia aeration rate was 2.2 L / min per liter of solution. The reaction temperature was 60℃, and the reaction time was 45 min. After the reaction, the solution was filtered and washed to prepare a magnesium carbonate filter cake. The resulting filtrate was an ammonium nitrate aqueous solution, which was recycled to the magnesium oxide dissolution step. The magnesium carbonate filter cake was dried at 105℃ for 8 h and then placed in a calcination reactor for calcination at 900℃ for 2 h, yielding 13.64 g of magnesium oxide powder. Its chemical composition is shown in Table 5, and its purity is approximately 99%.

[0085] Table 5. Chemical composition analysis results of magnesium oxide products (MG-2) (w B / %)

[0086]

[0087] Example 3

[0088] Unlike Example 2, this example provides a method for preparing magnesium oxide and calcium carbonate using calcium carbide-purified ash residue, which includes:

[0089] The calcium carbide purification ash was fed into a ball mill and ground into powder. 50.00g of the calcium carbide purification ash powder ground to 200 mesh was weighed (the chemical composition analysis results are shown in Table 1). The active magnesium oxide content was calculated to be 14.01g and the active calcium oxide mass fraction was 16.47g. Ammonium acetate and acetic acid solution were prepared into a mixed solution A with pH=3 in a calcium leaching agent mixing tank. The mass fraction of mixed solution A was 20%. Calcium carbide purification ash powder was mixed with mixed solution A at a mass ratio of 1:10, i.e., 50.00g of calcium carbide purification ash powder and 164.70g of mixed solution A were carried out in a calcium dissolving reactor for dissolution reaction. The reaction temperature was 60℃ and the reaction time was 40min. After filtration, the liquid phase was a calcium-containing alkaline solution and the solid phase was a magnesium-containing filter cake. CO2 was introduced into the calcium-containing alkaline solution for carbonation reaction in a calcium precipitation reactor. The aeration rate was 1.2L / min per liter of solution, the carbonation temperature was 40℃, and the carbonation time was 90min. The filtered filter cake was calcium carbonate precipitate, which was then washed and dried to obtain 28.37g of light calcium carbonate powder product. Its chemical composition is shown in Table 6, with a CaO content of 54.42% and very few other impurities. The filtrate was an ammonium acetate aqueous solution, which was recycled to the calcium oxide dissolution step.

[0090] Table 6 Chemical analysis results of light calcium carbonate products (CC-3) (w B / %)

[0091]

[0092] Ammonium nitrate and sulfuric acid solutions were prepared into a mixed solution B with pH=2 in a magnesium leaching agent mixing tank. The mass fraction of mixed solution B was 15%. The magnesium-containing filter cake was then subjected to a leaching reaction and ammonia stripping process in a magnesium dissolving reactor at a mass ratio of active magnesium oxide to mixed solution A of 1:20, i.e., 280.20g of magnesium-containing filter cake to mixed solution B. The reaction temperature was 80℃ and the reaction time was 120min. The ammonia gas produced by the reaction was collected. After filtration, the liquid phase was a magnesium nitrate-containing solution, and the solid phase was used as acid leaching waste residue. The obtained magnesium nitrate solution was transferred to a magnesium precipitation reactor, where ammonia and CO2 were simultaneously introduced to carry out a precipitation reaction. The CO2 aeration rate was 1.0 L / min per liter of solution, and the ammonia aeration rate was 2.0 L / min per liter of solution. The reaction temperature was 50℃, and the reaction time was 100 min. After the reaction, the solution was filtered and washed to prepare a magnesium carbonate filter cake. The resulting filtrate was an ammonium nitrate aqueous solution, which was recycled to the magnesium oxide dissolution step. The magnesium carbonate filter cake was dried at 105℃ for 10 h and then placed in a calcination reactor for calcination at 950℃ for 1.5 h, yielding 13.44 g of magnesium oxide powder. Its chemical composition is shown in Table 7, and its purity is approximately 99%.

[0093] Table 7 Chemical composition analysis results of magnesium oxide products (MG-3) (w B / %)

[0094]

[0095] Example 4

[0096] Unlike Example 3, this example provides a method for preparing magnesium oxide and calcium carbonate using calcium carbide-purified ash residue, which includes:

[0097] The calcium carbide purification ash was fed into a ball mill and ground into powder. 50.00g of the calcium carbide purification ash powder ground to 200 mesh was weighed (the chemical composition analysis results are shown in Table 1). The active magnesium oxide content was calculated to be 14.01g and the active calcium oxide mass fraction was 16.47g. Ammonium acetate and acetic acid solution were prepared into a mixed solution A with pH=4 in a calcium leaching agent mixing tank. The mass fraction of mixed solution A was 30%. Calcium carbide purification ash powder was mixed with mixed solution A at a mass ratio of 1:15, i.e., 50.00g of calcium carbide purification ash powder and 247.05g of mixed solution A were carried out in a calcium dissolving reactor for dissolution reaction. The reaction temperature was 50℃ and the reaction time was 30min. After filtration, the liquid phase was a calcium-containing alkaline solution and the solid phase was a magnesium-containing filter cake. CO2 was introduced into the calcium-containing alkaline solution for carbonation reaction in a calcium precipitation reactor. The aeration rate was 1.0L / min per liter of solution, the carbonation temperature was 50℃, and the carbonation time was 75min. The filtered filter cake was calcium carbonate precipitate, which was then washed and dried to obtain 28.54g of light calcium carbonate powder product. Its chemical composition is shown in Table 8, with a CaO content of 54.49% and very few other impurities. The filtrate was an ammonium acetate aqueous solution, which was recycled to the calcium oxide dissolution step.

[0098] Table 8 Chemical analysis results of light calcium carbonate products (CC-4) (w B / %)

[0099]

[0100] Ammonium nitrate and sulfuric acid solutions were prepared into a mixed solution B with pH=3 in a magnesium leaching agent mixing tank. The mass fraction of mixed solution B was 20%. The magnesium-containing filter cake was then subjected to a leaching reaction and ammonia stripping process in a magnesium dissolving reactor at a mass ratio of active magnesium oxide to mixed solution A of 1:15, i.e., 210.15g of magnesium-containing filter cake to mixed solution B. The reaction temperature was 85℃ and the reaction time was 100min. The ammonia gas produced by the reaction was collected. After filtration, the liquid phase was a magnesium nitrate-containing solution, and the solid phase was used as acid leaching waste residue. The obtained magnesium nitrate solution was transferred to a magnesium precipitation reactor, where ammonia and CO2 were simultaneously introduced to carry out a precipitation reaction. The CO2 aeration rate was 1.0 L / min per liter of solution, and the ammonia aeration rate was 2.0 L / min per liter of solution. The reaction temperature was 50℃, and the reaction time was 90 min. After the reaction, the solution was filtered and washed to prepare a magnesium carbonate filter cake. The resulting filtrate was an ammonium nitrate aqueous solution, which was recycled to the magnesium oxide dissolution step. The magnesium carbonate filter cake was dried at 110℃ for 10 h and then placed in a calcination reactor for calcination at 850℃ for 2.5 h to obtain 13.58 g of magnesium oxide powder. Its chemical composition is shown in Table 9, and its purity is approximately 99%.

[0101] Table 9. Chemical composition analysis results of magnesium oxide products (MG-4) (w B / %)

[0102]

[0103] The technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only illustrate several implementation methods of the present invention. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent.

[0104] It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of this invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing magnesium oxide and light calcium carbonate from calcium carbide-purified ash residue, characterized in that, Includes the following steps: Using calcium carbide purification ash as raw material, CaO in the raw material is dissolved in ammonium acetate and acetic acid as solvents. After filtration, the solid phase is a magnesium-containing filter cake and the liquid phase is a calcium-containing solution. Then, CO2 is introduced into the liquid phase to obtain light calcium carbonate. MgO in the magnesium-containing filter cake is dissolved in ammonium nitrate and sulfuric acid. After ammonia stripping, the mixture is filtered, and the liquid phase is a magnesium nitrate-containing solution. The magnesium nitrate-containing solution is then subjected to ammonia and CO2 absorption and filtered to obtain a magnesium carbonate filter cake and filtrate. The magnesium carbonate filter cake is then calcined to prepare magnesium oxide. Specifically, the following steps are included: (1) Grind the calcium carbide purification ash into calcium carbide purification ash powder; (2) Prepare a mixed solution A with pH=2~5 by ammonium acetate and acetic acid. Dissolve the calcium carbide purification ash powder in step (1) with the mixed solution A. After filtration, obtain a liquid phase and a solid phase. The liquid phase is a calcium-containing alkaline solution and the solid phase is a magnesium-containing filter cake. (3) CO2 is introduced into the calcium-containing alkaline solution in step (2) to carry out carbonation reaction, and the filter is filtered to obtain filter cake. The filter cake is calcium carbonate precipitate, which is then washed and dried to obtain light calcium carbonate. The filtrate is an aqueous solution of ammonium acetate, which is recycled to step (2) for use; (4) Prepare a mixed solution B with pH=1~4 using ammonium nitrate and sulfuric acid. Then, carry out a dissolution reaction and ammonia stripping process with the magnesium-containing filter cake from step (2) and the mixed solution B. Filter the solution to obtain a liquid phase and a solid phase. The liquid phase is a magnesium nitrate solution and the solid phase is acid leaching waste residue. The ammonia gas generated during the ammonia stripping process is recycled to step (5) for use. (5) In the magnesium nitrate solution in step (4), ammonia and CO2 gas are simultaneously introduced to carry out a precipitation reaction, and the solution is filtered to obtain magnesium carbonate filter cake; the resulting filtrate is an ammonium nitrate aqueous solution, which is recycled to step (4) for use; (6) The magnesium carbonate filter cake obtained in step (5) is dried and calcined to obtain magnesium oxide; the calcination tail gas is purified to obtain CO2, which is recycled to step (5) or step (3) for use; The particle size of calcium carbide purification ash powder is >95% (200 mesh). The chemical composition of the purified ash raw material is as follows: MgO, CaO, SiO2, and K2O contents are 29.89%, 47.89%, 10.81%, and 4.39%, respectively. The calculated main phase composition of the purified ash is: magnesium oxide 28.0%, calcium hydroxide 5.9%, dicalcium silicate 22.9%, calcium oxide 28.5%, and K2MgSiO 49.1%. The calculated mass fraction of active magnesium oxide in the purified ash is 28.01%, and the mass fraction of active calcium oxide is 32.94%. The mass fraction of mixed solution A is 15-40%, and the mass ratio of active calcium oxide in calcium carbide purification ash powder to mixed solution A is 1:(8-20). The mass fraction of mixed solution B is 10-25%, and the mass ratio of active magnesium oxide to mixed solution B in magnesium-containing filter cake is 1:(15-30). The active calcium oxide content in the calcium carbide purification ash is calculated by subtracting the CaO contained in Ca2SiO4 from the total CaO content in the calcium carbide purification ash. The Ca2SiO4 content is calculated by subtracting the SiO2 contained in K2MgSiO4 from the total SiO2 content in the calcium carbide purification ash, leaving the remaining SiO2. The active magnesium oxide content is calculated by subtracting the MgO contained in K2MgSiO4 from the total MgO content in the calcium carbide purification ash. The K2MgSiO4 content is calculated based on the K2O content in the calcium carbide purification ash.

2. The method for preparing magnesium oxide and light calcium carbonate from calcium carbide-purified ash slag according to claim 1, characterized in that, When CO2 is introduced into the calcium-containing alkaline solution in step (2), the CO2 gas flow rate is 0.5~1.2 L / min per liter of solution, the carbonization reaction temperature is 40~60℃, and the carbonization reaction time is 30~90 min. In step (5), when ammonia and CO2 are introduced into the magnesium nitrate-containing solution in step (4) for precipitation reaction, the CO2 gas flow rate is 0.5~1.2 L / min per liter of solution, the ammonia gas flow rate is 1~2.4 L / min per liter of solution, the precipitation reaction temperature is 30~75℃, and the precipitation reaction time is 30~120 min.

3. The method for preparing magnesium oxide and light calcium carbonate from calcium carbide-purified ash slag according to claim 1, characterized in that, The magnesium carbonate filter cake obtained in step (5) is dried at a temperature of 95~120℃ for 6~12h; and calcined at a temperature of 700~1000℃ for 1~3h.

4. The method for preparing magnesium oxide and light calcium carbonate from calcium carbide-purified ash slag according to claim 1, characterized in that, In step (2), the dissolution reaction temperature is 25~60℃ and the dissolution reaction time is 20~90min; in step (4), the dissolution reaction temperature is 60~95℃ and the dissolution reaction time is 30~180min.

5. A system for preparing magnesium oxide and light calcium carbonate from calcium carbide-purified ash slag using the method described in any one of claims 1-4, characterized in that, It includes a calcium leaching agent mixing tank (2), a calcium ammonium acid tank (3), a calcium dissolving reactor (6), a first filter (7), a calcium precipitation reactor (8), a second filter (9), a magnesium dissolving reactor (10), a third filter (12), a magnesium precipitation reactor (13), a fourth filter (14), a calcination reactor (15), a magnesium leaching agent mixing tank (17), a magnesium ammonium acid tank (18), and a carbon dioxide recovery tank (19). The calcium dissolving reactor (6) is connected to the first filter (7), the liquid outlet of the first filter (7) is connected to the calcium precipitation reactor (8), the calcium precipitation reactor (8) is connected to the second filter (9), the second filter (9) is connected to the ammonium acid tank (3) for calcium, the ammonium acid tank (3) for calcium is connected to the calcium leaching agent mixing tank (2), and the calcium leaching agent mixing tank (2) is connected to the calcium dissolving reactor (6). The solid outlet of the first filter (7) is connected to the magnesium dissolving reactor (10), which is connected to the inlet of the ammonia storage tank (11); the outlet of the ammonia storage tank (11) is connected to the magnesium precipitation reactor (13). The magnesium dissolving reactor (10) is connected to the inlet of the third filter (12); the liquid phase outlet of the third filter (12) is connected to the magnesium precipitation reactor (13); the magnesium precipitation reactor (13) is also connected to the fourth filter (14); The first outlet of the fourth filter (14) is connected to the calcination reactor (15); the calcination reactor (15) is connected to the carbon dioxide recovery tank (19); the gas outlet of the carbon dioxide recovery tank (19) is connected to the magnesium precipitation reactor (13); The second outlet of the fourth filter (14) is connected to the magnesium leaching agent mixing tank (17) via the magnesium ammonium acid tank (18).

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