Method for co-disposal of magnesium slag and aluminum ash to recover valuable resources

Abstract

The application provides a method for cooperatively disposing magnesium slag and aluminum ash to recover valuable resources, belongs to the technical field of industrial solid waste utilization, and is based on analysis of typical phase components in the magnesium slag and the aluminum ash; the magnesium slag and the aluminum ash are used as raw materials; metallic aluminum and aluminum nitride in the aluminum ash have reducibility; silicon, iron and other oxides are reduced under high-temperature conditions to produce ferrosilicon alloy (silicon content is greater than or equal to 75 wt%) and calcium aluminate products. The obtained ferrosilicon alloy can be returned to a silicon thermal method magnesium smelting process as a magnesium smelting reducing agent, and the calcium aluminate can be used as premelted slag in the steel industry or as raw material for extracting aluminum oxide by a carbon-alkali dissolution method. Furthermore, the whole process basically does not produce waste gas / waste water / waste residue and other secondary pollution, and realizes resource utilization of Si, Fe, Al and Ca elements.

Description

Technical Field

[0001] This invention belongs to the field of industrial solid waste utilization technology, and in particular relates to a method for the co-processing and recycling of valuable resources from magnesium slag and aluminum ash. Background Technology

[0002] Magnesium and aluminum are typical light metal materials with very important applications in national defense and civilian sectors. my country's primary magnesium and aluminum smelting technology and annual output rank among the world's top, giving it a strong international competitive advantage. However, this also results in the annual discharge of large amounts of solid and hazardous waste. Due to the lack of effective industrial disposal technologies, these wastes remain stockpiled for extended periods, causing serious harm to the ecological environment and becoming a bottleneck restricting the industry's green and sustainable development.

[0003] Magnesium slag is a solid waste generated during the Pidgeon process of magnesium smelting, with an annual discharge of approximately 6.5 million tons in my country. The main components of magnesium slag are dicalcium silicate (2CaO·SiO2), iron oxide (Fe2O3), magnesium oxide (MgO), and fluorite (CaF2). Currently, magnesium slag is mainly used as a cement admixture or in the production of building bricks. However, due to the high content of free magnesium oxide and calcium oxide in magnesium slag, the resulting building materials suffer from serious problems such as poor volume stability and easy cracking, resulting in a utilization rate of less than 10%. A large amount of magnesium slag is still primarily stockpiled. Furthermore, existing disposal technologies do not effectively recover and utilize the valuable metal resources such as Si, Fe, and Ca from magnesium slag.

[0004] Meanwhile, my country generates approximately 5 million tons of aluminum ash annually during primary aluminum smelting, aluminum product processing, and aluminum alloy recycling. A large amount of aluminum ash is produced after aluminum extraction, and it was designated as hazardous waste in 2016. Aluminum ash mainly consists of metallic aluminum (Al), alumina (Al₂O₃), aluminum nitride (AlN), and small amounts of chloride salts, and is also a valuable resource that can be utilized. Currently, domestic aluminum ash is mainly used to prepare protective rings or covering materials for aluminum electrolysis anodes, raw materials for recycled alumina, and products such as calcium aluminate refining agents / refractory materials / accelerators. While some of these applications have been industrialized, the products face challenges such as sluggish sales and insufficient competitiveness compared to similar products.

[0005] Magnesia slag and aluminum ash both possess the dual attributes of being both resources and hazards. While existing technologies for disposing of magnesium slag and aluminum ash have partially reduced their environmental impact, they have not yet effectively recovered their valuable resources. For magnesium slag, the main existing engineering applications are: using it as an admixture in secondary calcination of cement clinker; or combining it with gypsum, lime, etc., as a cement admixture for producing low-grade masonry cement. Chinese patents CN101492260A and CN115532357A both disclose methods for producing silicate cement using magnesium slag, but the magnesium slag content is low, only 20-30%, which is very limited in terms of reducing magnesium slag volume and utilizing its resources. Chinese patent CN108342585B discloses a comprehensive utilization method for magnesium reduction slag, which involves smelting a mixture of magnesium slag, silica powder, carbonaceous reducing agent, and binder pellets in an electric arc furnace to produce a silicon-calcium-iron alloy; or distilling the silicon-calcium-iron alloy in a vacuum vessel to separate metallic calcium and the silicon-iron alloy. Both the silicon-calcium-iron alloy and the separated silicon-iron alloy can be returned to the Pidgeon process for magnesium smelting as reducing agents. This technology partially realizes the resource utilization of elements such as Si and Fe in magnesium slag, but it has problems such as high energy consumption of process equipment and large carbon emissions, and there are no reports of subsequent industrial applications.

[0006] For aluminum ash disposal, it is mainly used to prepare protective rings or covering materials for aluminum electrolysis anode steel claws, to prepare raw materials for recycled alumina, and to prepare products such as calcium aluminate refining agents / refractory materials / accelerators. Some technologies have been industrialized. Chinese patent CN104131314B discloses a method for preparing anode steel claw protective rings by using aluminum ash as raw material, mixing it with alumina, pulp, and water through pulping, mixing, molding, ammonia removal, shaping, and cooling processes. Chinese patent CN108239704A discloses a method for the secondary resource utilization of aluminum ash to produce alumina. This method involves mixing aluminum ash with sodium oxide and wet grinding, then diluting it with water, and then dissolving the diluted slurry under high pressure in a reactor. After solid-liquid separation, an aluminum-containing solution is obtained, and finally, alumina is obtained through seeding and drying. Because the alumina in aluminum ash is all α-alumina, it suffers from low solubility and many impurities. Chinese patent CN115947611B discloses a method for preparing refractory materials by one-step sintering of secondary aluminum ash. However, the composition of the aluminum ash fluctuates greatly, and impurities remain in the product, affecting the quality and performance of the refractory material. These technologies suffer from problems such as long processes, the need to add various auxiliary raw materials, and secondary pollution from waste gas, wastewater, and waste residue. Summary of the Invention

[0007] To address the aforementioned technical problems, and considering the compositional characteristics, reactivity, and complementarity of magnesium slag and aluminum ash, this invention proposes a method for the co-processing and recycling of valuable resources from magnesium slag and aluminum ash.

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

[0009] A method for co-processing and recovering valuable resources from magnesium slag and aluminum ash includes the following steps:

[0010] A calcium additive is added to a mixture of aluminum ash and magnesium slag, and then smelted. During the smelting process, ferrosilicon alloy and calcium aluminate are produced. The calcium aluminate is used directly as a pre-melted slag for steelmaking or for the preparation of sodium aluminate and calcium carbonate.

[0011] This invention proposes a method for the co-processing and recovery of valuable resources from magnesium slag and aluminum ash. Based on the analysis of typical phase compositions in magnesium slag and aluminum ash, this invention uses magnesium slag and aluminum ash as raw materials, utilizing the reducing properties of metallic aluminum and aluminum nitride in the aluminum ash to reduce oxides such as silicon and iron under high-temperature conditions, producing ferrosilicon alloy (silicon content ≥75wt%) and calcium aluminate. The resulting ferrosilicon alloy can be returned to the silicothermic magnesium smelting process as a reducing agent, and the calcium aluminate can be used as pre-melting slag in the steel industry or as a raw material for the extraction of alumina by the carbon-alkali leaching method. Furthermore, the entire process generates virtually no secondary pollution such as waste gas / wastewater / slag, while simultaneously achieving the resource utilization of elements such as Si, Fe, Al, and Ca.

[0012] Furthermore, the mass of the aluminum ash is 0.7 to 1.0 times the mass of the magnesium slag. This mass ratio is limited to ensure that the amount of reducing agent in the aluminum ash is sufficient to reduce the Si and Fe oxides in the magnesium slag. Furthermore, the mass of the calcium additive, based on the mass of calcium oxide, is 0 to 0.5 times the mass of the magnesium slag, and is not zero.

[0013] Furthermore, the calcium additive is calcium oxide or limestone, which ensures the formation of a heptacalcium-aluminum product, facilitating the recovery of alumina resources in subsequent stages. Furthermore, the smelting temperature is 1400℃~1600℃, preferably 1500℃, and the holding time is 1~4h, preferably 2h. At this temperature, Si and Fe oxides can be reduced to a high degree, and the ferrosilicon and slag generated at this temperature are both liquid phases, allowing for effective separation. Extending the reaction time can improve the reduction rate and the separation effect between the metal and slag.

[0014] Furthermore, the method for preparing sodium aluminate and calcium carbonate from calcium aluminate is as follows: calcium aluminate is dissolved in an alkaline solution, and after the dissolution is completed, solid and liquid are separated. The resulting solution is a sodium aluminate solution, and the main component of the leaching residue is calcium carbonate (CaCO3).

[0015] Furthermore, the alkaline solution contains carbon alkali and caustic alkali, wherein the carbon alkali is Na2CO3 and the caustic alkali is NaOH.

[0016] Furthermore, the concentration of carbon alkali in the alkaline solution is 20–160 g / L, preferably 80 g / L; the concentration of caustic alkali is 0–20 g / L, preferably 5 g / L, and the concentration is not 0.

[0017] Furthermore, the ratio of the calcium aluminate to the alkaline solution is 1g:(5-10)mL.

[0018] Furthermore, the leaching temperature is 30–90°C, preferably 90°C, and the time is 0.5–3 h, preferably 0.5 h.

[0019] Furthermore, the composition range of magnesium slag is as follows: CaO 50-65wt%, SiO2 25-35wt%, MgO 4-10wt%, Fe2O3 2-5wt%, Al2O3 0.5-2.5wt%; the composition range of aluminum ash is as follows: Al 10-30wt%, AlN 10-30wt%, Al2O3 30-70wt%, CaO 0.2-0.8wt%, SiO2 2.5-3.5wt%, MgO 0.5-1.5wt%, Fe2O3 1-3wt%. Aluminum ash also contains a small amount of chloride salts (such as potassium chloride and sodium chloride).

[0020] Furthermore, the chloride salts in the raw materials physically volatilize under the high temperature of smelting, and are recovered after being cooled by a cooling device, and used as a refining agent for the purification of aluminum and magnesium.

[0021] Furthermore, the method for co-processing and recovering valuable resources from magnesium slag and aluminum ash specifically includes the following steps:

[0022] Step 1: Using aluminum ash and magnesium slag discharged from industrial production as raw materials, add industrial raw material calcium additives. Mix the aluminum ash, magnesium slag, and calcium additives evenly and pour them into a graphite crucible; the amount of aluminum ash is 0.7 to 1.0 times the mass of magnesium slag; the amount of calcium additive, based on the mass of calcium oxide, is 0 to 0.5 times the mass of magnesium slag.

[0023] Step 2: Place the graphite crucible in an electric heating furnace and melt (reduction) at 1400℃~1600℃ for 1~4 hours. During the melting process, ferrosilicon alloy and calcium aluminate are produced. The liquid ferrosilicon alloy formed during the melting process gradually gathers and deposits at the bottom of the graphite crucible, forming an alloy block.

[0024] Step 3: During the natural cooling process, the slag is pulverized and separated from the alloy block to obtain ferrosilicon alloy and materials mainly composed of calcium aluminate. The obtained ferrosilicon alloy can be returned to the silicothermic magnesium smelting process as a magnesium reducing agent. The obtained calcium aluminate can be directly used as pre-melted slag for steelmaking or as a raw material for extracting alumina by carbon-alkali leaching method in step 4.

[0025] Step 4: Crush calcium aluminate and dissolve it in an alkaline solution. The ratio of calcium aluminate to alkaline solution is 1g:(5-10)mL. The dissolution temperature is 30-90℃ and the time is 0.5-3h. In the alkaline solution, the carbon-alkali concentration is 20-160g / L and the caustic alkali concentration is 0-20g / L. After dissolution, solid and liquid are separated to obtain sodium aluminate solution and leaching residue (mainly CaCO3). Sodium aluminate solution is used to prepare alumina, and leaching residue is used as cement raw material.

[0026] The principle of the reaction process in this invention is as follows:

[0027] This invention utilizes the reducing properties of metallic aluminum and aluminum nitride in aluminum ash to reduce silicon dioxide and ferric oxide in magnesium slag to elemental silicon and iron at high temperatures, forming a ferrosilicon alloy. Furthermore, the aluminum oxide naturally present in the aluminum ash raw material, as well as the aluminum oxide generated after the reduction of metallic aluminum and aluminum nitride, combines with calcium oxide in the magnesium slag to form calcium aluminate (mainly heptacalcium dodecyl). Calcium aluminate reacts with a carbonate solution to generate sodium aluminate solution and calcium carbonate precipitate, achieving the recycling of alumina resources. The specific reaction equations are as follows:

[0028] SiO2 + 2 / 3Al = Si + 1 / 3Al2O3

[0029] Fe₂O₃ + 2Al = 2Fe + Al₂O₃

[0030] Fe₂O₃ + 2AlN = 2Fe + Al₂O₃ + N₂

[0031] Si + Fe = FeSi (Alloy)

[0032] 12CaO + 7Al₂O₃ = Ca 12 Al 14 O 33

[0033] Ca 12 Al 14 O 33 +12Na2CO3+33H2O=14NaAl(OH)4+10NaOH+12CaCO3

[0034] Compared with the prior art, the present invention has the following advantages and technical effects:

[0035] (1) The method of the present invention uses metallic aluminum, aluminum nitride and other substances in aluminum ash as reducing agents to reduce silicon, iron and other oxides in magnesium slag and aluminum ash to produce ferrosilicon alloy and calcium aluminate products, realizing the co-processing of solid and hazardous waste in the magnesium and aluminum industry, and improving the utilization rate of magnesium slag and aluminum ash.

[0036] (2) The method of this invention produces ferrosilicon alloy and calcium aluminate. The resulting ferrosilicon alloy can be used directly as a reducing agent in the Pidgeon process for magnesium smelting. The calcium aluminate can be used directly as a raw material for producing calcium aluminate cement or as pre-melting slag in the steel industry. It can also be used to produce sodium aluminate solution through carbon-alkali leaching, and the leaching slag can be used as a raw material for silicate cement production. This method maximizes the recovery and utilization of valuable metals such as Si, Fe, Al, and Ca from magnesium slag and aluminum ash, resulting in significant economic benefits.

[0037] (3) The chloride salts in aluminum ash physically volatilize at high temperature, and the flue gas is cooled and then recovered for use as an aluminum and magnesium refining agent. At the same time, this method does not generate secondary pollution such as waste gas, wastewater and waste residue. Attached Figure Description

[0038] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0039] Figure 1 This is a process flow diagram of the method for co-processing and recovering valuable resources from magnesium slag and aluminum ash according to the present invention.

[0040] Figure 2 This is an X-ray diffraction (XRD) phase analysis diagram of the silicon-iron alloy obtained in Example 1 of the present invention. Detailed Implementation

[0041] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0042] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0043] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0044] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0045] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0046] In this embodiment of the invention, the raw materials are aluminum ash and magnesium slag discharged from industrial production. The magnesium slag composition range is as follows: CaO 50-65wt%, SiO2 25-35wt%, MgO 4-10wt%, Fe2O3 2-5wt%, Al2O3 0.5-2.5wt%. The aluminum ash composition range is as follows: Al 10-30wt%, AlN 10-30wt%, Al2O3 30-70wt%, CaO 0.2-0.8wt%, SiO2 2.5-3.5wt%, MgO 0.5-1.5wt%, Fe2O3 1-3wt%. In addition, the aluminum ash also contains a small amount of chloride salts (such as potassium chloride and sodium chloride).

[0047] The specific methods for preparing alumina from sodium aluminate solution are common knowledge in the field and are not the focus of this invention, so they will not be described in detail here.

[0048] Figure 1 This is a process flow diagram of the method for co-processing and recovering valuable resources from magnesium slag and aluminum ash according to the present invention.

[0049] All calcium additives used in the embodiments of this invention were purchased commercially.

[0050] The technical solution of the present invention will be further illustrated by the following embodiments.

[0051] Example 1

[0052] Step 1: Mix the powdered aluminum ash, magnesium slag, and calcium oxide additive evenly and pour them into a graphite crucible; the amount of aluminum ash is 0.7 times the mass of magnesium slag, and the amount of calcium oxide is 0.2 times the mass of magnesium slag.

[0053] Step 2: Place the crucible in an electric furnace and melt and reduce it at 1400℃ for 1 hour. The liquid ferrosilicon alloy formed during the melting process gathers together and deposits at the bottom of the crucible;

[0054] Step 3: During natural cooling, the slag pulverizes and separates from the alloy blocks, yielding ferrosilicon alloy and calcium aluminate. The ferrosilicon alloy can be returned to the silicothermic magnesium smelting process as a reducing agent. The calcium aluminate can be directly used as pre-melted slag for steelmaking or proceeded to Step 4. In this step, the ferrosilicon alloy contains 76 wt% silicon and 24 wt% iron. The main phase in the obtained calcium aluminate is heptaaluminum dodecacalcium (12CaO·7Al2O3, C...). 12 A7), and also contains a small amount of dicalcium silicate (2CaO·SiO2, C2S);

[0055] Step 4: Crush calcium aluminate and leach it using an alkaline solution. The ratio of calcium aluminate to alkaline solution is 1:6. The alkaline solution contains 60 g / L sodium carbonate and 5 g / L sodium hydroxide. The leaching reaction is carried out at 60°C for 0.5 hours. After leaching, solid-liquid separation is performed to obtain sodium aluminate solution and leaching residue (mainly CaCO3). The leaching residue is used as a cement raw material. Add 10 wt% ultrafine aluminum hydroxide seed crystals (particle size <320 mesh) to the sodium aluminate solution obtained after solid-liquid separation. The temperature is controlled at 50°C for 8 hours to decompose the seed crystals. Finally, the ultrafine aluminum hydroxide product is obtained through filtration, washing, and drying.

[0056] Figure 2 This is an X-ray diffraction (XRD) phase analysis diagram of the silicon-iron alloy obtained in Example 1 of this invention. Figure 2 It can be seen that the obtained ferrosilicon alloy phase conforms to the phase characteristics of high silicon and low iron alloys, and is almost identical to the phase of 75# ferrosilicon alloy purchased on the market, which confirms the feasibility of using it as a magnesium reducing agent to return to the Pidgeon process for magnesium smelting.

[0057] Example 2

[0058] Step 1: Mix the powdered aluminum ash, magnesium slag, and calcium oxide additive evenly and pour them into a graphite crucible; the amount of aluminum ash is 0.9 times the mass of magnesium slag; the amount of calcium oxide is 0.3 times the mass of magnesium slag.

[0059] Step 2: Place the crucible in an electric furnace and melt and reduce it at 1550℃ for 1.5 hours. The liquid ferrosilicon alloy formed during the melting process gathers together and deposits at the bottom of the crucible;

[0060] Step 3: During natural cooling, the slag pulverizes and separates from the alloy blocks, yielding ferrosilicon alloy and calcium aluminate. The ferrosilicon alloy contains 85 wt% silicon and 15 wt% iron. The calcium aluminate mainly consists of heptaaluminum dodecyl calcium (C). 12 A7 also contains a small amount of MgAl2O4. Ferrosilicon alloys can be returned to the silicothermic magnesium smelting process as a reducing agent, while calcium aluminate can be directly used as pre-melted slag for steelmaking.

[0061] Example 3

[0062] Step 1: Mix the powdered aluminum ash, magnesium slag, and calcium oxide additive evenly and pour them into a graphite crucible; the amount of aluminum ash is 0.8 times the mass of magnesium slag, and the amount of calcium oxide is 0.25 times the mass of magnesium slag.

[0063] Step 2: Place the crucible in an electric furnace and melt and reduce it at 1500℃ for 2 hours. The liquid ferrosilicon alloy formed during the melting process gathers together and deposits at the bottom of the crucible;

[0064] Step 3: During natural cooling, the slag pulverizes and separates from the alloy blocks, yielding ferrosilicon alloy and calcium aluminate. The ferrosilicon alloy contains 82 wt% silicon and 18 wt% iron. The calcium aluminate mainly contains carbon. 12 A7 also contains a small amount of MgAl2O4; ferrosilicon alloy can be returned to the silicothermic magnesium smelting process as a reducing agent for magnesium smelting, and calcium aluminate can be directly used as pre-melted slag for steelmaking or proceeded to step 4.

[0065] Step 4: Crush the calcium aluminate obtained in Step 3, and dissolve the calcium aluminate using an alkaline solution. The alkaline solution has a carbon alkali concentration of 80 g / L and a caustic alkali concentration of 10 g / L. The ratio of calcium aluminate to alkaline solution is 1:8. The dissolution reaction is carried out at a temperature of 90℃ for 2 hours. After the dissolution is completed, solid-liquid separation is performed to obtain sodium aluminate solution and leaching residue (mainly composed of CaCO3).

[0066] Example 4

[0067] Step 1: Mix the powdered aluminum ash, magnesium slag, and calcium oxide additive evenly and pour them into a graphite crucible; the amount of aluminum ash is 0.9 times the mass of magnesium slag, and the amount of calcium oxide is 0.3 times the mass of magnesium slag.

[0068] Step 2: Place the crucible in an electric furnace and melt and reduce it at 1600℃ for 1.5 hours. The liquid ferrosilicon alloy formed during the melting process gathers together and deposits at the bottom of the crucible;

[0069] Step 3: During natural cooling, the slag pulverizes and separates from the alloy blocks, yielding ferrosilicon alloy and calcium aluminate. The ferrosilicon alloy contains 87 wt% silicon and 13 wt% iron. The calcium aluminate mainly contains carbon. 12 A7 also contains a small amount of MgAl2O4;

[0070] Step 4: Crush the calcium aluminate obtained in Step 3, and dissolve the calcium aluminate in an alkaline solution. The alkaline solution has a carbon alkali concentration of 90 g / L and a caustic alkali concentration of 20 g / L. The ratio of calcium aluminate to alkaline solution is 1:6. The dissolution reaction is carried out at a temperature of 80℃ for 2 hours. After the dissolution is completed, solid-liquid separation is performed to obtain sodium aluminate solution and leaching residue (mainly composed of CaCO3).

[0071] Example 5

[0072] Step 1: Mix the powdered aluminum ash, magnesium slag, and calcium additive limestone evenly and pour them into a graphite crucible; the amount of aluminum ash is 1.0 times the mass of magnesium slag, and the amount of limestone is 0.5 times the mass of magnesium slag.

[0073] Step 2: Place the crucible in an electric furnace and melt and reduce it at 1500℃ for 4 hours. The liquid ferrosilicon alloy formed during the melting process gathers together and deposits at the bottom of the crucible;

[0074] Step 3: During natural cooling, the slag pulverizes and separates from the alloy blocks, yielding ferrosilicon alloy and calcium aluminate. The ferrosilicon alloy contains 92 wt% silicon and 8 wt% iron. The calcium aluminate mainly contains carbon. 12 A7 also contains a small amount of CaO;

[0075] Step 4: Crush the calcium aluminate obtained in Step 3, and dissolve the calcium aluminate in an alkaline solution. The alkaline solution has a carbon alkali concentration of 20 g / L and a caustic alkali concentration of 10 g / L. The ratio of calcium aluminate to alkaline solution is 1:5. The dissolution reaction is carried out at a temperature of 30°C for 3 hours. After the dissolution is completed, solid-liquid separation is performed to obtain sodium aluminate solution and leaching residue (mainly composed of CaCO3).

[0076] Example 6

[0077] Step 1: Mix the powdered aluminum ash, magnesium slag, and calcium additive limestone evenly and pour them into a graphite crucible; the amount of aluminum ash is 0.7 times the mass of magnesium slag, and the amount of limestone is 0.1 times the mass of magnesium slag.

[0078] Step 2: Place the crucible in an electric furnace and melt and reduce it at 1400℃ for 2 hours. The liquid ferrosilicon alloy formed during the melting process gathers together and deposits at the bottom of the crucible;

[0079] Step 3: During natural cooling, the slag pulverizes and separates from the alloy blocks, yielding ferrosilicon alloy and calcium aluminate. The ferrosilicon alloy contains 78 wt% silicon and 22 wt% iron. The calcium aluminate mainly contains carbon. 12A7 also contains small amounts of C2S, CA and MgAl2O4;

[0080] Step 4: Crush the calcium aluminate obtained in Step 3, and dissolve the calcium aluminate in an alkaline solution. The alkaline solution has a carbon alkali concentration of 40 g / L and a caustic alkali concentration of 10 g / L. The ratio of calcium aluminate to alkaline solution is 1:10. The dissolution reaction is carried out at a temperature of 50°C for 1 hour. After the dissolution is completed, solid-liquid separation is performed to obtain sodium aluminate solution and leaching residue (mainly composed of CaCO3).

[0081] Comparative Example 1

[0082] Same as Example 4, except that the calcium additive is replaced with an equal amount of sodium chloride.

[0083] Replacing calcium oxide with sodium chloride does not yield the desired product because: 1. Sodium chloride almost completely volatilizes at the reaction temperature described in this invention; 2. The purpose of adding calcium oxide is to combine with the alumina contained in the aluminum ash to generate the product heptacalcium dodecyl heptaecalcium. If calcium oxide is replaced with other substances, the resulting product will change, making subsequent leaching and extraction of alumina difficult. This not only increases raw material costs but also creates difficulties in the production process.

[0084] Comparative Example 2

[0085] Step 1: Mix the powdered aluminum ash and magnesium slag evenly and pour them into a graphite crucible. The amount of aluminum ash is 0.7 times the mass of magnesium slag. Place the crucible in an electric furnace and calcine it at 1400℃ for 1 hour to obtain calcined clinker.

[0086] Step 2: Mix the roasted clinker obtained in Step 1 with water (liquid-to-solid ratio of 4 mL / g), then add acetic acid (volume fraction of 20%), and treat at 85°C for 3 hours to obtain the treated slurry;

[0087] Step 3: The slurry from Step 2 is subjected to solid-liquid separation and drying to obtain filter residue. The filter residue is mixed with calcium additive limestone and then subjected to grinding, molding (molding pressure of 20 MPa), drying and calcination (calcination temperature of 1500℃ and calcination time of 2 h). The amount of calcium oxide is 0.2 times the mass of magnesium slag in Step 1. The resulting ferrosilicon alloy has a silicon mass fraction of 95 wt% and an iron mass fraction of 5 wt%. The main phase in the calcium aluminate material is CA2, and it also contains a small amount of C2S and MgAl2O4.

[0088] The calcium aluminate (there are various types of calcium aluminate, and the calcium aluminate obtained in step 1 of this comparative example is not the heptacalcium-dodecyl calcium aluminate described in this invention) and the ferrosilicon alloy obtained in step 2 will react with the acid added in step 2, causing aluminum, calcium oxides, and metallic iron from the ferrosilicon alloy to enter the solution and be lost. Therefore, the target product described in this invention cannot be obtained after the reaction in step 3. This comparative example can achieve the recovery of silicon, but it cannot achieve the recovery of aluminum, calcium, and iron.

[0089] Comparative Example 3

[0090] Same as Example 4, except that the melting temperature is 1000°C.

[0091] The melting temperature in this comparative example was too low, so the reduction reaction could not proceed and the target product could not be obtained.

[0092] Because the smelting temperature is too low, the SiO2 in the magnesium slag cannot be reduced, so ferrosilicon alloy cannot be obtained in step 3. The main phases in the slag are C2S and CA6.

[0093] Comparative Example 4

[0094] Same as Example 4, except that the melting temperature is 2000℃.

[0095] The melting temperature in this comparative example is too high, which can yield the target product, but this temperature condition is difficult to achieve.

[0096] The silicon-iron alloy obtained in step 3 has a silicon mass fraction of 89 wt% and an iron mass fraction of 11 wt%, and the main phase in the obtained calcium aluminate is C. 12 A7 also contains a small amount of CA; after the dissolution in step 4, solid-liquid separation is performed to obtain sodium aluminate solution and leaching residue (the main component of which is CaCO3).

[0097] Comparative Example 5

[0098] Same as Example 4, except that the dissolution temperature is 100°C.

[0099] The dissolution temperature in this comparative example was too high, which was sufficient to obtain the target product, but such temperature conditions are difficult to achieve.

[0100] After the leaching process in step 4 is completed, solid-liquid separation is performed to obtain sodium aluminate solution and leaching residue (the main component of which is CaCO3).

[0101] Comparative Example 6

[0102] Same as Example 4, except that the dissolution temperature is 10°C.

[0103] The leaching temperature in this comparative example is too low. While the target product can be obtained at a low leaching temperature, the corresponding leaching efficiency is low, resulting in low aluminum resource recovery efficiency.

[0104] Step 4: After leaching, solid-liquid separation is performed to obtain sodium aluminate solution and leaching residue (mainly composed of C). 12 A7 and CaCO3).

[0105] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for the co-processing and recovery of valuable resources from magnesium slag and aluminum ash, characterized in that, Includes the following steps: A calcium additive is added to a mixture of aluminum ash and magnesium slag, and then smelted. During the smelting process, ferrosilicon alloy and calcium aluminate are produced. The calcium aluminate is used directly as a pre-melted slag for steelmaking or for the preparation of sodium aluminate and calcium carbonate. The mass of the aluminum ash is 0.7 to 1.0 times the mass of the magnesium slag; The calcium additive, based on the mass of calcium oxide, has a mass of 0 to 0.5 times that of magnesium slag, and its mass is not zero. The method for preparing sodium aluminate and calcium carbonate from calcium aluminate is as follows: calcium aluminate is dissolved in an alkaline solution, and after the dissolution is completed, solid and liquid are separated. The resulting solution is a sodium aluminate solution, and the main component of the leaching residue is calcium carbonate. The alkaline solution contains carbon alkali and caustic alkali.

2. The method for co-processing and recovering valuable resources from magnesium slag and aluminum ash according to claim 1, characterized in that, The calcium additive is calcium oxide or limestone.

3. The method for co-processing and recovering valuable resources from magnesium slag and aluminum ash according to claim 1, characterized in that, The melting temperature is 1400℃~1600℃, and the holding time is 1~4h.

4. The method for co-processing and recovering valuable resources from magnesium slag and aluminum ash according to claim 1, characterized in that, The alkaline solution contains carbon alkali with a concentration of 20-160 g / L and caustic alkali with a concentration of 0-20 g / L, and the concentration is not zero.

5. The method for co-processing and recovering valuable resources from magnesium slag and aluminum ash according to claim 1, characterized in that, The ratio of calcium aluminate to alkaline solution is 1g:(5~10)mL.

6. The method for co-processing and recovering valuable resources from magnesium slag and aluminum ash according to claim 1, characterized in that, The leaching temperature is 30~90℃, and the time is 0.5~3h.

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