Method for thermochemically converting red mud into low-iron red mud solid and ferric chloride product
Through the thermochemical conversion method, red mud is reacted with chlorine or hydrogen chloride in a thermochemical reactor to produce gaseous ferric chloride, which solves the problems of low iron recovery in red mud and complex iron chloride production, and achieves efficient resource utilization of red mud.
Patent Information
- Application Number
- CN202510525732.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-25
- Publication Date
- 2025-07-11
AI Technical Summary
The current iron recovery rate of red mud is low, the traditional iron chloride production methods are complex and costly, and the comprehensive utilization rate of red mud is low, making it difficult to achieve resource utilization.
Through the thermochemical conversion method, red mud is reacted with chlorine or hydrogen chloride gas in a thermochemical reactor to produce gaseous ferric chloride, and then condensed or evaporated to crystallize anhydrous ferric chloride or hexahydrate ferric chloride, control the reaction temperature and gas-solid contact efficiency to obtain low-iron red mud solids and high-purity ferric chloride products.
The efficient conversion of iron in red mud was achieved, and low-iron red mud solids were obtained for building materials, and iron chloride products were used for market demand, simplifying processes and improving resource utilization.
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Figure CN120288833A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method for recycling red mud resources, in particular to a method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products. Background Art
[0002] Red mud is a solid waste generated during the production of alumina by calcining bauxite in the aluminum industry. For every ton of aluminum produced, 1 - 1.5 tons of red mud will be generated. The overall comprehensive resource utilization rate is low, and most of the red mud is still disposed of by stacking, which not only occupies a large amount of land resources, but also damages the water supply, air and soil due to the alkalinity of the red mud, affecting the ecological balance of the entire region.
[0003] Red mud is a potential resource that can be used in fields such as road bases and subgrade materials, environmental and remediation materials, etc. At the same time, due to the large amount of metal elements contained in red mud itself, it is mainly used to extract valuable components therein for metal recycling, etc. The element with the highest content in red mud is iron. After efficiently recovering iron resources through processes such as magnetic separation and acid leaching, the tailings rich in silicon and aluminum components can be further used as a substitute for cement raw materials, reducing limestone consumption and calcination carbon emissions, forming a synergistic closed loop of "metal extraction - tailings resource utilization - carbon emission reduction", and promoting the full-chain transformation of industrial solid waste into low-carbon materials, which is a relatively excellent resource utilization path.
[0004] Currently, the methods for iron recovery from red mud are mainly divided into: physical recovery methods and chemical recovery methods. Physical recovery mainly separates according to the different physical properties of iron-containing minerals, including gravity separation, magnetic separation, and flotation. However, the recovery rate of physical recovery is not high and cannot meet industrial requirements. In addition, there is also chemical recovery, where the iron in the red mud is converted into other forms and then iron is extracted. Chemical recovery is mainly divided into two methods: wet extraction and pyrometallurgical extraction. Wet extraction mainly involves acid leaching and dissolving iron with various acids and then enrichment; among them, the type, concentration, leaching time, etc. of the acid will all affect the iron leaching rate. The wet method itself has the advantages of high recovery rate and low energy consumption, but due to the complex operation, it consumes a large amount of acid and generates a large amount of acid-containing waste, making it difficult to be industrially applied. Pyrometallurgical extraction is to change the existing form of iron at high temperature and then separate it. Most of the application methods use reducing agents such as carbon and hydrogen to reduce ferric oxide in the red mud into magnetic iron or magnetite, and then magnetic separation is carried out. Most of the whole process is carried out in a high-temperature environment (above 1000°C). The fluidized reduction process has a lower reaction temperature and shorter reaction time compared with the traditional pyrometallurgical smelting process, which has the effect of reducing energy consumption, but it is necessary to select concentrates with a higher iron content and then reduce them to magnetite for magnetic separation. Therefore, it is particularly important to develop a red mud resource recovery method that does not require high-quality iron ore, has a simple device, and is widely applicable.
[0005] The traditional production methods of ferric chloride mainly involve the reaction of chlorine with iron under high-temperature conditions, or the production of ferrous chloride by acid leaching of iron with hydrochloric acid, followed by oxidation with strong oxidants such as chlorine and oxygen to form ferric chloride. These methods generally have complex processes and high costs. Therefore, it is necessary to study a production method of ferric chloride with low operation difficulty, safety, and low cost.
[0006] The above-mentioned comprehensive utilization of red mud has problems such as low existence rate, low reduction rate in the iron recovery process, the need to select higher-quality iron ores, complex devices, and many processes. Summary of the Invention
[0007] The purpose of the present invention is to propose a method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products. This method has a simple process, high iron conversion rate, does not require higher-purity concentrates, can convert the iron resources in red mud, obtain low-iron red mud solid products for use in building materials and other fields, and at the same time, the gas products are evaporated and crystallized to obtain ferric chloride products, making the red mud more resourcefully utilized and achieving the technical goal of turning waste into treasure.
[0008] The present invention is achieved through the following technical solutions:
[0009] A method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products, the method comprising the following steps:
[0010] 1) The red mud is first dried and dehydrated, and then enters a thermal chemical reactor to undergo a chlorination reaction with chlorine or hydrogen chloride gas that also enters the reactor. The iron oxides in the red mud are discharged from the reactor in the form of gaseous ferric chloride, obtaining a low-iron-content red mud solid product;
[0011] 2) The gas containing gaseous ferric chloride discharged from the reactor is directly condensed into anhydrous ferric chloride, or first becomes a ferric chloride solution through water cooling, and then the solution is evaporated and crystallized to obtain ferric chloride hexahydrate;
[0012] 3) The obtained anhydrous ferric chloride or ferric chloride hexahydrate is subjected to a pulverization operation to form the final product, and the tail gas generated by the system is discharged after being absorbed and purified by a lime milk alkaline solution.
[0013] In the method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products, the red mud is a solid waste rich in iron elements, with an iron content > 5%, preferably > 10%, and more preferably > 20%.
[0014] In the method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products, the thermal chemical reactor is a gas-solid reaction device, such as but not limited to a fixed-bed reactor, preferably a fluidized-bed reactor.
[0015] The described method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products. The gaseous products of the thermochemical reactor are directly condensed to obtain anhydrous ferric chloride or cooled by water to obtain an aqueous solution of ferric chloride, and this aqueous solution is further evaporated and crystallized to obtain a solid product of ferric chloride hexahydrate.
[0016] The described method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products. During the condensation and evaporation crystallization processes, the tail gas containing chlorine gas is introduced for protection, so that the forward reaction of the reversible reaction of ferric chloride hydrolysis does not occur, reducing the hydrolysis reaction of the target product ferric chloride and avoiding the formation of iron hydroxide.
[0017] The described method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products. This method obtains three products: red mud with low iron content, anhydrous ferric chloride, and ferric chloride hexahydrate. Among them, the iron content of the red mud solid product is <5%, preferably <3%, and more preferably <1%; the purity of the anhydrous ferric chloride or ferric chloride hexahydrate product is >90%, preferably >95%, and more preferably >98%.
[0018] The described method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products. This method systematically analyzes the thermodynamic temperature required for the chlorination reaction of the components in the red mud with chlorine or hydrogen chloride and the melting and boiling points of the chlorination products, and finally determines that the operating temperature of the thermochemical reactor is controlled as follows:
[0019] 1) When using hydrogen chloride to treat red mud, it is 315 - 772 °C, preferably 400 - 750 °C, and more preferably 500 - 700 °C;
[0020] 2) When using chlorine to treat red mud, it is 558 - 772 °C, preferably 600 - 750 °C, and more preferably 650 - 700 °C.
[0021] The above method is based on the scientific regulation of the temperature required for the chlorination reaction of each component in the red mud and the melting and boiling points of each chlorination product. The purpose is to only turn the iron element in the red mud into gaseous chloride and discharge it from the red mud for resource utilization, and the common components in the remaining red mud do not undergo chlorination reactions or the chlorination products are still solids and exist in the solid products, which will not affect the purity of the target products.
[0022] The described method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products. The selection principle of the thermochemical reactor should be that the temperature is controllable and the gas-solid contact efficiency is high; for example, but not limited to, when choosing a fluidized bed as the reactor, the gas velocity is increased, such as in addition to adding chlorine or hydrogen chloride into the reactor, an inert gas or lean oxygen air is additionally added; when choosing a fixed bed as the reactor, a dispersant is used to disperse the red mud, reduce the agglomeration of the red mud, and improve the contact efficiency between the chlorine-containing gas and the red mud.
[0023] The described method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products, where the dispersant is, for example but not limited to, inert wear-resistant particles such as quartz sand and corundum, and the particle size is slightly larger than the maximum particle size of the red mud for easy screening and reuse.
[0024] The advantages and effects of the present invention are as follows:
[0025] The method for resource utilization of red mud proposed by the present invention is based on scientific coordination of the reaction temperatures of various chemical reactions and the melting and boiling points of various products. By reasonably controlling the temperature range of each process, while removing iron from the red mud to ensure its usability in building materials such as cement, anhydrous ferric chloride or ferric chloride hexahydrate products can be selectively prepared according to market demand. This method has a simple, flexible process and a high iron conversion rate, which not only solves the problem of difficult solid waste treatment of red mud due to its high iron content, but also realizes the resource conversion of the rich iron elements in the red mud. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Figure 1 is the overall flowchart of the red mud resource treatment of the present invention;
[0027] Figure 2 is the XRD pattern of the iron-rich red mud used in the example of the present invention (the abscissa is the scanning angle / °, and the ordinate is the intensity / a.u.);
[0028] Figure 3 is the flowchart of the reaction involving hydrogen chloride in the present invention;
[0029] Figure 4 is the flowchart of the reaction involving chlorine gas in the present invention. DETAILED DESCRIPTION OF THE INVENTION
[0030] The present invention will be described in detail below with reference to the embodiments shown in the drawings.
[0031] A method for red mud resource utilization based on thermochemical conversion proposed by the present invention includes the following steps:
[0032] 1) The red mud is first dried and dehydrated, and then enters a thermal chemical reactor to undergo a chlorination reaction with chlorine gas or hydrogen chloride gas that also enters the reactor. The iron oxides in the red mud are discharged from the reactor in the form of gaseous ferric chloride, and a red mud solid product with a low iron content is obtained;
[0033] 2) The gas containing gaseous ferric chloride discharged from the reactor can be directly condensed into anhydrous ferric chloride, or can first be turned into a ferric chloride solution through water cooling and then the solution is evaporated and crystallized to obtain ferric chloride hexahydrate;
[0034] 3) Operations such as crushing are performed on the obtained anhydrous ferric chloride or ferric chloride hexahydrate to make the final product, and the tail gas generated by the system is discharged after being absorbed and purified by an alkaline solution such as lime milk.
[0035] Red mud is a solid waste rich in iron elements, with an iron content > 5%, preferably > 10%, and more preferably > 20%.
[0036] The thermal chemical reactor is a gas-solid reaction device, such as but not limited to a fixed bed reactor, preferably a fluidized bed reactor.
[0037] The gas product of the thermal chemical reactor is directly condensed to obtain anhydrous ferric chloride, or is water-cooled to obtain an aqueous solution of ferric chloride, and this aqueous solution is further evaporated and crystallized to obtain a solid product of ferric chloride hexahydrate.
[0038] This method is based on the scientific regulation of the temperature required for the chlorination reaction of each component in red mud and the melting and boiling points of each chlorination product, and determines the operating temperature of the thermal chemical reactor according to the relevant thermodynamic calculations of the reaction.
[0039] The resource utilization method of the present invention can simultaneously obtain three products: red mud with a low iron content, anhydrous ferric chloride, and ferric chloride hexahydrate. Among them, the iron content of the red mud solid product < 5%, preferably < 3%, and more preferably < 1%; the purity of the anhydrous ferric chloride or ferric chloride hexahydrate product > 90%, preferably > 95%, and more preferably > 98%
[0040] The selection principle of the thermal chemical reactor is that the temperature is controllable and the gas-solid contact efficiency is high. For example, but not limited to, when a fluidized bed is selected as the reactor, the gas velocity is increased, such as in addition to adding chlorine or hydrogen chloride into the reactor, an inert gas or oxygen-deficient air is additionally added; when a fixed bed is selected as the reactor, a dispersant is used to disperse the red mud to reduce the agglomeration phenomenon of the red mud and improve the contact efficiency between the chlorine-containing gas and the red mud. The dispersant is, for example, but not limited to, inert wear-resistant particles such as quartz sand and corundum, and the particle size is slightly larger than the maximum particle size of the red mud to facilitate screening and reuse.
[0041] Basis for thermodynamic calculation
[0042] The main substances contained in red mud include iron oxide, aluminum oxide, silicon dioxide, sodium oxide, and a small amount of calcium oxide, etc. When chlorine-containing gas is introduced, each component will undergo corresponding chlorination reactions. According to each chlorination reaction and the melting and boiling point temperatures of the corresponding chlorination products, the temperature range of each process is regulated to achieve the goal of turning the iron element in red mud into gaseous chloride and discharging it from the red mud for resource utilization, while other common components do not undergo chemical reactions or the solid products generated do not discharge with the gas flow. The following are the relevant thermodynamic formulas for the reaction of the main substances in red mud with hydrogen chloride or chlorine:
[0043] Reactions occurring when hydrogen chloride gas is passed:
[0044]
[0045]
[0046] Based on the thermodynamic calculations of the reactions of the above components with hydrogen chloride, aluminum oxide, silicon dioxide, and titanium dioxide do not undergo chlorination reactions. The reaction to form gaseous iron chloride occurs when the temperature exceeds 315 °C. Sodium oxide and calcium oxide are thermodynamically feasible, but the melting point of sodium chloride is 801 °C and the melting point of calcium chloride is 772 °C. Therefore, as long as the temperature is controlled below 772 °C, gaseous sodium chloride or calcium chloride will not be produced, thus affecting the purity of the iron chloride product. Therefore, when using hydrogen chloride for red mud treatment, the operating temperature of the thermal chemical reactor needs to be controlled between 315 - 772 °C. To pursue a faster reaction rate and considering the temperature fluctuations during actual operation, the operating temperature is preferably controlled between 500 - 750 °C, more preferably 600 - 700 °C.
[0047] Reactions occurring with the introduction of chlorine gas:
[0048]
[0049] Based on the thermodynamic calculations of the reactions of the above components with chlorine gas, the formation temperature of iron chloride is above 558 °C. The remaining components, aluminum oxide and silicon dioxide, do not participate in the overall chlorination reaction. Although sodium oxide and calcium oxide can undergo chlorination reactions thermodynamically, due to the melting and boiling points of the resulting chlorination products, the corresponding gaseous-flowable chlorination product states need to be formed above 772 °C. Therefore, the operating temperature of the thermal chemical reactor with the introduction of chlorine gas needs to be controlled between 560 - 780 °C. To pursue a faster reaction rate and considering the temperature fluctuations during actual operation, the operating temperature is preferably controlled between 600 - 750 °C, more preferably 650 - 700 °C.
[0050] Based on the regulation of the thermodynamic temperatures of the reactions of the above components and the melting and boiling points of the chlorination products, the operating temperature of the thermal chemical reactor is finally determined as follows: 1) When using hydrogen chloride for red mud treatment, it is 315 - 772 °C, preferably 400 - 750 °C, more preferably 500 - 700 °C; 2) When using chlorine gas for red mud treatment, it is 558 - 772 °C, preferably 600 - 750 °C, more preferably 650 - 700 °C.
[0051] Other possible reactions:
[0052]
[0053] During the collection of the product or the evaporation and crystallization of the product, hydrolysis reactions of ferric chloride and the reaction of chlorine with water in the above thermodynamic calculations will occur. To reduce the hydrolysis reaction of the target product ferric chloride and avoid the formation of iron oxide or iron hydroxide, a tail gas containing chlorine gas is introduced for protection during the evaporation and crystallization process, so that the forward reaction of the reversible reaction of ferric chloride hydrolysis does not occur. That is, by increasing the content of hydrogen chloride gas, the equilibrium constants of the first two chemical reactions in the above table are reduced, inhibiting the conversion of ferric chloride into iron oxide or iron hydroxide, and ensuring the output of ferric chloride.
[0054] Next, the method proposed in the present invention will be described. The experiment of the chlorination reaction of red mud with hydrogen chloride and chlorine will be carried out in the laboratory according to the established steps. The specific process and results are as Figure 3 、 4 shown.
[0055] Example 1: Introducing hydrogen chloride
[0056] The red mud (the raw material composition and components are shown in Table 1 and Figure 2 shown) was dried at a temperature of 105 °C for 24 h. 5 g of the dried raw material was weighed and mixed with 15 g of inert wear-resistant particles (quartz sand or corundum) as a dispersant, and then loaded into a thermal chemical reactor. Nitrogen was introduced to raise the temperature to 700 °C and kept constant. At this time, hydrogen chloride was introduced and reacted for 3 h. The solid product obtained was low-iron red mud and the gas product was ferric chloride. The low-iron red mud can be further processed and used as a building material to replace part of the cement. The discharged ferric chloride gas first becomes a ferric chloride solution through water cooling, and then the solution is evaporated and crystallized to obtain ferric chloride hexahydrate. The evaporation process can be protected by the tail gas containing hydrogen chloride to avoid the hydrolysis reaction of ferric chloride hexahydrate. The tail gas generated by the system is absorbed and purified by an alkaline solution such as lime milk and then discharged. After testing, the total remaining amount of the solid product red mud and the dispersant was 17.378 g, and the iron content was 1.428%. The specific composition parameters are shown in Table 1. The purity of the obtained ferric chloride hexahydrate product was 95.8%.
[0057] Example 2 of the present invention: Introducing chlorine
[0058] The red mud was dried at a temperature of 105 °C for 24 h. 5 g of the dried raw material was weighed and mixed with 15 g of inert wear-resistant particles (quartz sand or corundum) as a dispersant, and then loaded into a thermal chemical reactor. Nitrogen was introduced to raise the temperature to 700 °C and kept constant. At this time, chlorine was introduced and reacted for 3 h. The solid product obtained was low-iron red mud and the gas product was ferric chloride. The low-iron red mud can be further used as other raw materials in fields such as construction. The discharged ferric chloride gas can be directly condensed into anhydrous ferric chloride. The tail gas generated by the system is absorbed and purified by an alkaline solution such as lime milk and then discharged. After testing, the total remaining amount of the solid product red mud and the dispersant was 17.474 g, and the iron content was 0.861%. The specific composition parameters are shown in Table 1. The purity of the obtained ferric chloride hexahydrate product was 96%.
[0059] Table 1 Specific chemical components and contents in the Bayer red mud before and after aeration in the examples, wt%
[0060] Component <![CDATA[Na2O]]> <![CDATA[Fe2O3]]> <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[TiO2]]> CaO Cl Others Raw material red mud 11.487 42.919 12.724 23.167 5.819 1.972 0.058 1.854 Pass hydrogen chloride 7.054 1.428 15.285 58.612 6.273 1.153 8.682 1.513 Pass chlorine 8.090 0.861 16.732 55.473 6.712 1.166 9.764 1.202
[0061] It should be noted that the above two examples are only simple experimental methods and data carried out under laboratory conditions, and the time used is selected under the condition of ensuring laboratory safety. The time required for actual industrial operation is much less than this value.
[0062] Although the specific implementation of the present invention has been publicly disclosed as above, this method is not limited to using chlorine gas (or hydrogen chloride gas). The experimental examples only use two gases as examples to explore the effect of chlorination on iron removal from red mud. Combining with the realization of the current resource utilization goal, the chlorinated gas can be completely replaced by chlorine-containing waste gas, which can truly achieve the purpose of "treating waste with waste and comprehensive treatment".
Claims
1. A method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products, characterized in that, The method comprises the following steps: 1) The red mud is first dried and dehydrated, and then enters a thermal chemical reactor to undergo a chlorination reaction with chlorine or hydrogen chloride gas entering the reactor together. The iron oxide in the red mud is discharged from the reactor in the form of gaseous iron chloride, and a red mud solid product with a low iron content is obtained; 2) The gas containing gaseous iron chloride discharged from the reactor is directly condensed into anhydrous iron chloride, or first becomes an iron chloride solution through water cooling, and then the solution is evaporated and crystallized to obtain iron chloride hexahydrate; 3) The obtained anhydrous iron chloride or iron chloride hexahydrate is subjected to a crushing operation to produce the final product, and the tail gas generated by the system is discharged after being absorbed and purified by a lime milk alkaline solution.
2. The method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products according to claim 1, characterized in that, The red mud is a solid waste rich in iron elements, with an iron content > 5%, preferably > 10%, more preferably > 20%.
3. A method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products according to claim 1, characterized in that, The thermal chemical reactor is a gas-solid reaction device, such as but not limited to a fixed bed reactor, preferably a fluidized bed reactor.
4. A method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products according to claim 1, characterized in that, The gas product of the thermal chemical reactor is directly condensed to obtain anhydrous iron chloride, or is water-cooled to obtain an iron chloride aqueous solution, and the aqueous solution is further evaporated and crystallized to obtain an iron chloride hexahydrate solid product.
5. A method for thermochemically converting red mud into low-iron red mud solids and ferric chloride product according to claim 4, characterized in that, During the condensation and evaporation crystallization processes, the tail gas containing chlorine gas is introduced for protection, so that the forward reaction of the reversible reaction of iron chloride hydrolysis does not occur, reducing the hydrolysis reaction of the target product iron chloride and avoiding the formation of iron hydroxide.
6. The method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products according to claim 1, characterized in that, The method obtains three products: red mud with a low iron content, anhydrous iron chloride, and iron chloride hexahydrate. Among them, the iron content of the red mud solid product is < 5%, preferably < 3%, more preferably < 1%; the purity of the anhydrous iron chloride or iron chloride hexahydrate product is > 90%, preferably > 95%, more preferably > 98%.
7. A method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products according to claim 1, characterized in that, The method system analyzes the thermodynamic temperature required for the chlorination reaction of the components in the red mud with chlorine or hydrogen chloride and the melting and boiling points of the chlorination products, and finally determines that the operating temperature of the thermal chemical reactor is controlled as follows: 1) When using hydrogen chloride to treat red mud, it is 315 - 772 °C, preferably 400 - 750 °C, more preferably 500 - 700 °C; 2) When using chlorine to treat red mud, it is 558 - 772 °C, preferably 600 - 750 °C, more preferably 650 - 700 °C.
8. A method for thermochemically converting red mud into low-iron red mud solid and ferric chloride product according to claim 1, characterized in that, The selection principle of the thermal chemical reactor should be temperature controllability and high gas-solid contact efficiency; for example, but not limited to, when choosing a fluidized bed as the reactor, the gas velocity is increased, such as in addition to adding chlorine or hydrogen chloride into the reactor, an inert gas or lean oxygen air is additionally added; when choosing a fixed bed as the reactor, a dispersant is used to disperse the red mud, reduce the agglomeration of the red mud, and improve the contact efficiency between the chlorine-containing gas and the red mud.
9. A method for thermochemically converting red mud into low-iron red mud solids and ferric chloride products according to claim 7, characterized in that, The dispersant is, for example, but not limited to inert wear-resistant particles such as quartz sand and corundum, and the particle size is slightly larger than the maximum particle size of the red mud to facilitate screening and reuse.