Treatment method of crystallized oxalate in aluminum oxide production process

Abstract

The invention provides a treatment method of crystallized oxalate in an aluminum oxide production process, and belongs to the field of solid waste treatment in the aluminum industry. The method comprises the following steps: mixing crystallized oxalate with water to obtain a first mixed solution; oxalic acid is added into the first mixed solution, the pH value of the first mixed solution is adjusted to 5.5-7.0, sodium aluminate in the first mixed solution is leached, and a second mixed solution is obtained; carrying out solid-liquid separation on the second mixed solution to obtain a sodium oxalate-containing solution and solid-phase aluminum hydroxide; dropwise adding a calcium nitrate solution into the sodium oxalate-containing solution until no precipitate is generated in the sodium oxalate-containing solution to obtain a third mixed solution; carrying out solid-liquid separation on the third mixed solution to obtain calcium oxalate and a sodium nitrate-containing solution; the sodium nitrate-containing solution is circulated for mixing with the crystalline oxalate to form a closed cycle. By adopting the method provided by the invention, aluminum hydroxide in the crystallized oxalate can be recovered, and high-purity calcium oxalate can be obtained by reacting the crystallized oxalate with calcium nitrate.

Description

Technical Field

[0001] The present application relates to the technical field of solid waste treatment in the aluminum industry, and in particular to a method for treating crystalline oxalate in an alumina production process. Background Art

[0002] Crystalline oxalate is a major byproduct of alumina production. Its presence severely impacts decomposition efficiency and alumina quality. To control crystalline oxalate in alumina production, various technologies for its removal have been developed both domestically and internationally. Common methods for removing crystalline oxalate include solution combustion, adsorption, crystallization, and chemical precipitation. The solution combustion method has high energy consumption and production application costs; the adsorption method can only remove certain organic matter and reduce the critical concentration of sodium oxalate, but has no effect on sodium oxalate itself; and the chemical precipitation method typically results in alumina losses and is therefore less commonly used. The crystallization method has the advantages of low energy consumption, less equipment investment, and lower production application costs, and has therefore been widely used.

[0003] The main components of crystalline oxalate are aluminum hydroxide, sodium oxalate, sodium hydroxide, sodium aluminate, and sodium hydroxide. Crystalline oxalate is primarily processed through causticization. The principle of the causticization process is to dissolve sodium oxalate and aluminum hydroxide in a sodium aluminate solution, then causticize it with lime milk from production, producing non-degradable calcium oxalate and sodium hydroxide for the recovery of useful substances. However, the causticization reaction conditions of lime milk are relatively harsh, resulting in low causticization efficiency, aluminum loss, low production efficiency, complex production processes, and demanding reaction conditions. Summary of the Invention

[0004] The present application provides a method for treating crystalline oxalate in an alumina production process, thereby providing a new method for treating crystalline oxalate in an alumina production process.

[0005] The present invention provides a method for treating crystalline oxalate in an alumina production process, the method comprising:

[0006] mixing the crystalline oxalate with water to obtain a first mixed solution;

[0007] adding oxalic acid to the first mixed solution and adjusting the pH value of the first mixed solution to 5.5 to 7.0 to leach sodium aluminate from the first mixed solution to obtain a second mixed solution;

[0008] performing solid-liquid separation on the second mixed liquid to obtain a sodium oxalate solution and solid aluminum hydroxide;

[0009] adding a calcium nitrate solution dropwise to the sodium oxalate solution until no precipitate is generated in the sodium oxalate solution to obtain a third mixed solution;

[0010] performing solid-liquid separation on the third mixed liquid to obtain calcium oxalate and a sodium nitrate-containing solution;

[0011] The sodium nitrate-containing solution is circulated for mixing with the crystallized oxalate to form a closed cycle.

[0012] Optionally, the method further includes:

[0013] The sodium nitrate-containing solution after multiple cycles is used for desulfurization treatment in the alumina production process.

[0014] Optionally, the leaching temperature is 60° C. to 100° C., and the leaching time is 30 min to 120 min.

[0015] Optionally, the mass concentration of sodium oxalate in the sodium oxalate-containing solution is 50 g / L to 70 g / L.

[0016] Optionally, the molar concentration of the calcium nitrate solution is 1.0 mol / L to 2.2 mol / L.

[0017] Optionally, during the dropwise addition of the calcium nitrate solution, the temperature of the sodium oxalate solution is 40°C to 60°C.

[0018] Optionally, the purity of the solid-phase aluminum hydroxide is ≥98%.

[0019] Optionally, the purity of the calcium oxalate is ≥98%.

[0020] Optionally, the mass ratio of the crystalline oxalate to water is 1:(1.8-2.2).

[0021] Optionally, the crystalline oxalate includes one or more of aluminum hydroxide, sodium oxalate, sodium aluminate, sodium hydroxide and soluble organic matter.

[0022] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0023] An embodiment of the present application provides a method for treating crystalline oxalate in an alumina production process, the method comprising: mixing the crystalline oxalate with water to obtain a first mixed liquor; adding oxalic acid to the first mixed liquor, and adjusting the pH value of the first mixed liquor to 5.5-7.0 to leach sodium aluminate in the first mixed liquor to obtain a second mixed liquor; subjecting the second mixed liquor to solid-liquid separation to obtain a sodium oxalate solution and solid-phase aluminum hydroxide; adding a calcium nitrate solution dropwise to the sodium oxalate solution until no precipitate is produced in the sodium oxalate solution to obtain a third mixed liquor; subjecting the third mixed liquor to solid-liquid separation to obtain calcium oxalate and a sodium nitrate solution; and circulating the sodium nitrate solution for mixing with the crystalline oxalate to form a closed loop. First, by adjusting the pH of the first mixed solution to 5.5-7.0, oxalic acid is used to selectively neutralize sodium aluminate and sodium hydroxide, converting them into sodium oxalate and high-purity aluminum hydroxide, thereby preventing aluminum from being mixed into the subsequent calcium oxalate precipitation as an impurity. Secondly, after the second mixed solution is separated into solid and liquid, the liquid phase containing sodium oxalate further recovers oxalate and sodium resources, avoiding the problem of aluminum being directly discharged with oxalate waste in traditional processes. Thirdly, calcium nitrate is added to the sodium oxalate solution to generate high-purity calcium oxalate, which is used as a chemical raw material to realize the resource utilization of oxalate in oxalate instead of direct waste, thereby increasing the economic value of the by-product. Finally, the sodium nitrate solution (mainly composed of sodium nitrate and water) generated by the reaction can be directly recycled for leaching of crystallized oxalate. When the nitrate in the solution reaches a certain concentration, it can be used for desulfurization in alumina production, forming a closed loop for the entire system. This provides a new method for treating crystallized oxalate in the alumina production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0026] Figure 1 A first flow diagram of a method for treating crystalline oxalate in an alumina production process provided in an embodiment of the present application;

[0027] Figure 2 This is a second flow diagram of a method for treating crystalline oxalate in an alumina production process provided in an embodiment of the present application. DETAILED DESCRIPTION

[0028] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0029] The range descriptions described in this article, such as numerical ranges, ratio ranges, etc., include all possible sub-ranges and single numerical values ​​within the range. For example, the range description of "1 to 6" or "1~6" covers all sub-ranges from 1 to 6 (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6). Unless otherwise specified, the terms "including", "comprising", etc. used in this article mean "including but not limited to"; relational terms such as "first" and "second" are only used to distinguish different entities or operations, and do not imply an actual sequence or association relationship; "and / or" means that multiple situations can exist alone or at the same time; expressions such as "at least one", "multiple", and "at least one" refer to any combination of corresponding objects, including a combination of single or multiple objects. The proportional relationships involved in the article, such as mass ratios, molar ratios, etc., should be understood as the corresponding relationship between the first and second terms of the proportional formula in the order of description. The raw materials, reagents, instruments and equipment used in this article can be purchased on the market or prepared by existing methods.

[0030] Figure 1 A schematic flow chart of a method for treating crystalline oxalate in an alumina production process provided in an embodiment of the present application; Figure 2 This is a second flow diagram of a method for treating crystalline oxalate in an alumina production process provided in an embodiment of the present application.

[0031] like Figure 1 and Figure 2 As shown, the embodiment of the present application provides a method for treating crystalline oxalate in an alumina production process, the method comprising:

[0032] S1, mixing crystalline oxalate with water to obtain a first mixed solution;

[0033] In some embodiments, the mass ratio of the crystalline oxalate to water is 1:(1.8-2.2).

[0034] By mixing crystalline oxalate with water in a mass ratio of 1:(1.8-2.2), an initial suspension is formed to dissolve soluble sodium oxalate and other components. This also ensures that the solution has a moderate viscosity, which is beneficial for subsequent reactions and separation operations. For example, the mass ratio of crystalline oxalate to water can be 1:1.8, 1:1.9, 1:2.0, 1:2.1, 1:2.2, etc.

[0035] In some embodiments, the crystalline oxalate comprises one or more of aluminum hydroxide, sodium oxalate, sodium aluminate, sodium hydroxide, and soluble organic matter.

[0036] S2. adding oxalic acid to the first mixed solution and adjusting the pH value of the first mixed solution to 5.5 to 7.0 to leach sodium aluminate from the first mixed solution to obtain a second mixed solution;

[0037] Use oxalic acid to neutralize the sodium aluminate and sodium hydroxide in oxalate and convert them into sodium oxalate and aluminum hydroxide, which can prevent sodium aluminate and sodium hydroxide from entering the subsequent precipitation link. If not fully neutralized, the two will react with calcium nitrate to generate calcium hydroxide and aluminum hydroxide precipitates, thereby contaminating the calcium oxalate product and affecting its purity. If the pH is lower than 5.5, it is excessively neutralized by oxalic acid, resulting in waste of oxalic acid reagent. If the pH is higher than 7.0, it will cause incomplete neutralization, affecting the purity of calcium oxalate. Exemplary, oxalic acid is used to adjust the pH value of the first mixed solution to 5.5, 5.8, 6, 6.2, 6.5, 6.8, 7.0, etc.

[0038] In some embodiments, the leaching temperature is 60° C. to 100° C., and the leaching time is 30 min to 120 min.

[0039] The solubility of sodium oxalate increases with increasing temperature. Limiting the leaching temperature to 60°C to 100°C can allow more sodium oxalate to dissolve in hot water. Below 60°C, the solubility of sodium oxalate is less than 50g / L, which will result in a low solubility. Above 100°C, the solution boils, making it inconvenient to operate. Limiting the leaching time to 30min to 120min can ensure that sodium aluminate is fully converted into sodium oxalate while avoiding the increase in energy consumption caused by long-term high temperature. For example, the leaching temperature can be 60°C, 65°C, 70°C, 75°C, 80°C, 90°C, 100°C, etc., and the leaching time can be 30min, 40min, 60min, 80min, 100min, 120min, etc.

[0040] S3, performing solid-liquid separation on the second mixed liquid to obtain a sodium oxalate solution and solid aluminum hydroxide;

[0041] In some embodiments, the mass concentration of sodium oxalate in the sodium oxalate-containing solution is 50 g / L to 70 g / L.

[0042] The mass concentration of sodium oxalate in the sodium oxalate solution is 50 g / L to 70 g / L, corresponding to a solubility range of 60° C. to 100° C., to ensure that the solution is not oversaturated and impurities are precipitated. For example, the mass concentration of sodium oxalate in the sodium oxalate solution can be 50 g / L, 52 g / L, 55 g / L, 60 g / L, 65 g / L, 70 g / L, etc.

[0043] In some embodiments, the purity of the solid phase aluminum hydroxide is ≥98%.

[0044] In some embodiments, the solid aluminum hydroxide is washed with deionized water at 90-98°C.

[0045] S4, adding a calcium nitrate solution dropwise to the sodium oxalate solution until no precipitate is generated in the sodium oxalate solution, to obtain a third mixed solution;

[0046] In some embodiments, the molar concentration of the calcium nitrate solution is 1.0 mol / L to 2.2 mol / L.

[0047] The molar concentration of calcium nitrate solution is limited to 1.0 mol / L~2.2 mol / L. The low molar concentration will result in the concentration of Ca in unit volume of solution. 2+ The content is reduced, so the number of drops needs to be increased, which is not only inefficient but also increases the cost of reagents; on the contrary, if the molar concentration is too high, the viscosity of the solution will increase, and the titration end point will become difficult to observe clearly (for example, the turbidity change becomes less obvious), which is easy to cause Ca 2+ Excessive, thereby contaminating the solution containing sodium nitrate. Exemplary, the molar concentration of the calcium nitrate solution can be 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2.0 mol / L, 2.2 mol / L, etc.

[0048] In some embodiments, during the dropwise addition of the calcium nitrate solution, the temperature of the sodium oxalate solution is 40°C to 60°C.

[0049] The reaction temperature is limited to the range of 40°C to 60°C in order to balance the reaction rate and energy consumption, eliminate the cooling step, and effectively avoid the problem of increased solubility of calcium oxalate in a high temperature environment. And the temperature gradient design from leaching (60-100°C) to dropwise reaction (40-60°C) makes full use of thermal energy and avoids the energy consumption of repeated heating / cooling. Exemplarily, during the dropwise addition of calcium nitrate solution, the temperature of the sodium oxalate solution can be 40°C, 42°C, 45°C, 50°C, 55°C, 58°C, 60°C, etc.

[0050] S5, performing solid-liquid separation on the third mixed solution to obtain calcium oxalate and a sodium nitrate-containing solution;

[0051] In some embodiments, the purity of the calcium oxalate is ≥98%.

[0052] S6. Circulating the sodium nitrate-containing solution for mixing with the crystalline oxalate to form a closed loop.

[0053] It should be noted that the reasons why the aqueous solution containing sodium nitrate can be returned to the leaching process are as follows: (1) the solubility of sodium nitrate can reach 900 g / L at room temperature of 25°C; (2) the solubility of calcium oxalate generated by the reaction of calcium nitrate and sodium oxalate in water is extremely low, so the main components of the sodium nitrate solution are sodium nitrate and water, and the concentration is much lower than the solubility of sodium nitrate; (3) sodium nitrate does not react with sodium aluminate, sodium hydroxide, sodium oxalate and aluminum hydroxide in crystalline oxalate, so it can be used as a circulating solution to leach oxalate. When the sodium nitrate concentration reaches a certain range, it can be directly returned to the alumina production process for desulfurization.

[0054] In some embodiments, the method further comprises:

[0055] The sodium nitrate-containing solution after multiple cycles is used for desulfurization treatment in the alumina production process.

[0056] During the Bayer process of alumina production, low-cost sulfur, an impurity in the ore, can cause corrosion to equipment, reduce alumina quality, and decrease alumina decomposition efficiency, seriously impacting the safe and stable operation of the alumina production process. Currently, sodium nitrate is added to remove the impact of sulfur on the alumina process, but this method consumes a lot of nitric acid.

[0057] The sulfur element in the ore is mainly S 2- ions enter the sodium aluminate solution and react with iron to form compounds that are soluble in the sodium aluminate solution. During the high-temperature dissolution process, sodium nitrate gradually oxidizes low-valent sulfur into high-valent sulfur. Ultimately, these compounds are oxidized into sulfate ions. When a solution containing sodium nitrate is used to precipitate sulfate in the sodium aluminate solution, the sulfate combines with calcium ions to form calcium sulfate precipitate, which is discharged from the system with red mud. At the same time, some sodium hydroxide is also generated in the process, which not only facilitates the dissolution process but also effectively offsets some of the alkali consumption in the alumina production process.

[0058] Thus, the present invention can recover aluminum hydroxide from crystalline oxalate and utilize the crystalline oxalate to react with calcium nitrate to produce a desulfurizer for use in an alumina system, thereby reducing the cost of sodium nitrate. At the same time, calcium oxalate can be obtained, which is conducive to obtaining a chemical byproduct with high product quality.

[0059] The method for treating crystalline oxalate in the alumina production process provided in this application achieves efficient resource recovery, pollution reduction, and cost optimization through precise process design and parameter control. Its core advantages are summarized as follows:

[0060] 1. Efficient recovery and recycling of resources

[0061] (1) Closed-loop utilization of aluminum resources: The solid aluminum hydroxide (purity ≥98%) separated from the crystallized oxalate is directly returned to the alumina production process for roasting, avoiding the waste of aluminum elements and improving the utilization rate of raw materials. The sodium nitrate solution is circulated for oxalate leaching, and the Na + Replace part of caustic soda and reduce alkali consumption; NO3 - It can be recycled as a desulfurizing agent to reduce the input of external reagents.

[0062] (2) Oxalate and Calcium Resource Recovery: Sodium oxalate is converted into a soluble sodium oxalate solution through oxalic acid leaching, which then reacts with calcium nitrate to produce high-purity calcium oxalate (≥98%). This by-product in the chemical industry brings additional economic value to production. Calcium oxalate is highly pure and can be directly used in the chemical industry, building materials, and other fields, realizing waste resource recovery.

[0063] 2. Process parameter optimization and energy consumption control

[0064] (1) Precise pH control: Control the pH between 5.5 and 7.0 to ensure that sodium aluminate is completely converted into aluminum hydroxide precipitation and avoid residual OH - It reacts with calcium nitrate to generate impurities (such as Ca(OH)2), while preventing excessive consumption of oxalic acid and reducing reagent costs.

[0065] (2) Temperature gradient design: Leaching stage (60-100°C): High temperature (close to the boiling point of water) is used to increase the solubility of sodium oxalate (50-70 g / L), ensuring that oxalate can be fully dissolved, thereby avoiding the loss of aluminum caused by solid phase residue. The titration stage (40-60°C) takes over the temperature of the leachate after natural cooling (down 5-10°C), without the need for additional cooling, reducing energy consumption; at the same time, a high reaction rate is maintained to avoid slow reaction at low temperatures or increased solubility of calcium oxalate at high temperatures.

[0066] (3) Solution concentration matching: The sodium oxalate concentration (50-70 g / L) is strictly matched with the leaching temperature (60-100°C) to avoid oversaturation and precipitation of impurities while ensuring the efficiency of the subsequent calcium nitrate titration reaction. The calcium nitrate concentration (1.0-2.2 mol / L) balances titration efficiency and endpoint accuracy, avoiding excessively low concentrations that lead to increased reagent usage or excessively high concentrations that cause titration errors.

[0067] 3. Dual benefits of environmental protection and economy

[0068] (1) Closed-loop system reduces pollution: The closed circulation of sodium nitrate solution significantly reduces wastewater discharge; the high-purity separation of calcium oxalate and aluminum hydroxide prevents impurities from entering the environment, meeting clean production requirements. At the same time, it replaces the traditional sodium nitrate desulfurization process, reduces the use of external chemical agents, and reduces the risk of sulfur pollution.

[0069] (2) Significant cost reduction: The reaction product (sodium nitrate) from the neutralization of sodium aluminate with oxalic acid and the precipitation of sodium oxalate with calcium nitrate is recycled, reducing the consumption of purchased reagents such as caustic soda and sodium nitrate. The temperature gradient design (leaching → titration) reduces heating / cooling energy consumption; the solid-liquid separation step (centrifugation / filtration) is efficient and convenient, reducing equipment operating costs. High-purity calcium oxalate is sold as a chemical raw material, creating additional economic value.

[0070] 4. Process compatibility and stability

[0071] (1) Adapt to the mainstream alumina process: It is deeply compatible with the Bayer process and other alumina production processes. The separated aluminum hydroxide can be directly connected to the roasting process, and the sodium nitrate solution is used for desulfurization without the need for large-scale transformation of existing equipment.

[0072] (2) Strong resistance to impurities: Soluble organic matter and other impurities in the crystallized oxalate are effectively removed through the solid-liquid separation steps (S3 and S5), without affecting the aluminum recovery in the main process or the purity of the by-products. When the sodium nitrate solution is recycled, its high solubility (900g / L at 25°C) prevents crystallization from clogging the pipeline, ensuring long-term stable operation of the system.

[0073] 5. Desulfurization process innovation

[0074] (1) Treating waste with waste: Traditional alumina desulfurization requires additional sodium nitrate. This process uses oxalate to treat the by-product sodium nitrate solution, which is directly used for desulfurization, achieving the "recycling of desulfurizers" and thus reducing desulfurization costs.

[0075] (2) Efficient removal of sulfur: Sodium nitrate removes low-valent sulfur (S 2- ) is oxidized to sulfate (SO4 2- ), and is eventually discharged with red mud in the form of calcium sulfate, while generating NaOH to supplement alkali consumption and improve dissolution efficiency.

[0076] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. The experimental methods in the following examples where specific conditions are not specified are generally measured according to industry standards. If there are no corresponding industry standards, then the methods are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0077] Example 1

[0078] This embodiment provides a method for treating crystalline oxalate in an alumina production process, which may include the following steps:

[0079] S11, mixing 50 g of crystalline oxalate with 100 mL of water to obtain a first mixed solution;

[0080] S21, adding oxalic acid to the first mixed solution and adjusting the pH value of the first mixed solution to 6.4 to leach sodium aluminate in the first mixed solution at a leaching temperature of 80° C. and a leaching time of 50 min to obtain a second mixed solution;

[0081] S31, performing solid-liquid separation on the second mixed liquid to obtain a sodium oxalate solution with a sodium oxalate concentration of 55 g / L, washing the solid aluminum hydroxide with 90°C water, and then drying it to a purity of 98.8%, and returning the solid aluminum hydroxide to the alumina production process for roasting;

[0082] S41, adding a 1.0 mol / L calcium nitrate solution dropwise to the sodium oxalate solution at a temperature of 40° C. until no precipitate is generated in the sodium oxalate solution, to obtain a third mixed solution;

[0083] S51, performing solid-liquid separation on the third mixed liquid to obtain calcium oxalate with a purity of 98.86% and a sodium nitrate-containing solution;

[0084] S61. Circulating the sodium nitrate-containing solution for mixing with crystalline oxalate to form a closed loop.

[0085] Example 2

[0086] This embodiment provides a method for treating crystalline oxalate in an alumina production process, which may include the following steps:

[0087] S11, mixing 50 g of crystalline oxalate with 100 mL of water to obtain a first mixed solution;

[0088] S21, adding oxalic acid to the first mixed solution and adjusting the pH value of the first mixed solution to 7.0 to leach sodium aluminate in the first mixed solution at a leaching temperature of 60° C. and a leaching time of 120 min to obtain a second mixed solution;

[0089] S31, performing solid-liquid separation on the second mixed liquid to obtain a sodium oxalate solution with a sodium oxalate concentration of 50 g / L, washing the solid aluminum hydroxide with 98°C water, and then drying it to a purity of 98.6%, and returning the solid aluminum hydroxide to the alumina production process for roasting;

[0090] S41, adding 1.2 mol / L calcium nitrate solution dropwise to the sodium oxalate solution at a temperature of 60° C. until no precipitate is generated in the sodium oxalate solution, to obtain a third mixed solution;

[0091] S51, performing solid-liquid separation on the third mixed liquid to obtain calcium oxalate with a purity of 98.06% and a sodium nitrate-containing solution;

[0092] S61. Circulating the sodium nitrate-containing solution for mixing with crystalline oxalate to form a closed loop.

[0093] Example 3

[0094] This embodiment provides a method for treating crystalline oxalate in an alumina production process, which may include the following steps:

[0095] S11, mixing 50 g of crystalline oxalate with 100 mL of water to obtain a first mixed solution;

[0096] S21, adding oxalic acid to the first mixed solution and adjusting the pH value of the first mixed solution to 5.5 to leach sodium aluminate in the first mixed solution at a leaching temperature of 100° C. and a leaching time of 30 minutes to obtain a second mixed solution;

[0097] S31, performing solid-liquid separation on the second mixed liquid to obtain a sodium oxalate solution with a sodium oxalate concentration of 70 g / L, washing the solid aluminum hydroxide with 94°C water, and then drying it to a purity of 98.6%, and returning the solid aluminum hydroxide to the alumina production process for roasting;

[0098] S41, adding a 2.2 mol / L calcium nitrate solution dropwise to the sodium oxalate solution at a temperature of 50° C. until no precipitate is generated in the sodium oxalate solution, to obtain a third mixed solution;

[0099] S51, performing solid-liquid separation on the third mixed liquid to obtain calcium oxalate and a sodium nitrate solution with a purity of 99.03%;

[0100] S61. Circulating the sodium nitrate-containing solution for mixing with crystalline oxalate to form a closed loop.

[0101] Example 4

[0102] This embodiment provides a method for treating crystalline oxalate in an alumina production process, which may include the following steps:

[0103] S11, mixing 50 g of crystalline oxalate with 100 mL of water to obtain a first mixed solution;

[0104] S21, adding oxalic acid to the first mixed solution and adjusting the pH value of the first mixed solution to 6.8 to leach sodium aluminate in the first mixed solution at a leaching temperature of 90° C. and a leaching time of 50 min to obtain a second mixed solution;

[0105] S31, performing solid-liquid separation on the second mixed liquid to obtain a sodium oxalate solution with a sodium oxalate concentration of 65 g / L, washing the solid aluminum hydroxide with 93°C water, and then drying it to a purity of 98.4%, and returning the solid aluminum hydroxide to the alumina production process for roasting;

[0106] S41, adding 1.5 mol / L calcium nitrate solution dropwise to the sodium oxalate solution at a temperature of 50° C. until no precipitate is generated in the sodium oxalate solution, to obtain a third mixed solution;

[0107] S51, performing solid-liquid separation on the third mixed liquid to obtain calcium oxalate with a purity of 98.56% and a sodium nitrate-containing solution;

[0108] S61. Circulating the sodium nitrate-containing solution for mixing with crystalline oxalate to form a closed loop.

[0109] Example 5

[0110] This embodiment provides a method for treating crystalline oxalate in an alumina production process, which may include the following steps:

[0111] S11, mixing 50 g of crystalline oxalate with 100 mL of water to obtain a first mixed solution;

[0112] S21, adding oxalic acid to the first mixed solution and adjusting the pH value of the first mixed solution to 6.0 to leach sodium aluminate in the first mixed solution at a leaching temperature of 85° C. and a leaching time of 90 minutes to obtain a second mixed solution;

[0113] S31, performing solid-liquid separation on the second mixed liquid to obtain a sodium oxalate solution with a sodium oxalate concentration of 62 g / L, washing the solid aluminum hydroxide with 95°C water, and then drying it to a purity of 98.1%, and returning the solid aluminum hydroxide to the alumina production process for roasting;

[0114] S41, adding 1.8 mol / L calcium nitrate solution dropwise to the sodium oxalate solution at a temperature of 50° C. until no precipitate is generated in the sodium oxalate solution, to obtain a third mixed solution;

[0115] S51, performing solid-liquid separation on the third mixed liquid to obtain calcium oxalate with a purity of 98.55% and a sodium nitrate-containing solution;

[0116] S61. Circulating the sodium nitrate-containing solution for mixing with crystalline oxalate to form a closed loop.

[0117] Example 6

[0118] This embodiment provides a method for treating crystalline oxalate in an alumina production process, which may include the following steps:

[0119] S11, mixing 50 g of crystalline oxalate with 100 mL of water to obtain a first mixed solution;

[0120] S21, adding oxalic acid to the first mixed solution and adjusting the pH value of the first mixed solution to 6.8 to leach sodium aluminate in the first mixed solution at a leaching temperature of 90° C. and a leaching time of 50 min to obtain a second mixed solution;

[0121] S31, performing solid-liquid separation on the second mixed liquid to obtain a sodium oxalate solution with a sodium oxalate concentration of 65 g / L, washing the solid aluminum hydroxide with 90°C water, and then drying it to a purity of 98.5%, and returning the solid aluminum hydroxide to the alumina production process for roasting;

[0122] S41, adding 1.5 mol / L calcium nitrate solution dropwise to the sodium oxalate solution at a temperature of 50° C. until no precipitate is generated in the sodium oxalate solution, to obtain a third mixed solution;

[0123] S51, performing solid-liquid separation on the third mixed liquid to obtain calcium oxalate with a purity of 98.56% and a sodium nitrate-containing solution;

[0124] S61. The sodium nitrate-containing solution is recycled and mixed with 50 g of crystalline oxalate, and then steps S11 to S51 are repeated. The sodium nitrate concentration ratio of the sodium nitrate-containing solutions obtained twice is 1:1.4.

[0125] Comparative Example 1

[0126] This comparative example provides a method for treating crystalline oxalate in an alumina production process, which may include the following steps:

[0127] S11, mixing 50 g of crystalline oxalate with 100 mL of water to obtain a first mixed solution;

[0128] S21, leaching sodium aluminate from the first mixed solution at a leaching temperature of 80° C. and a leaching time of 50 min to obtain a second mixed solution;

[0129] S31, performing solid-liquid separation on the second mixed liquid to obtain a sodium oxalate solution with a sodium oxalate concentration of 53 g / L, washing the solid aluminum hydroxide with 90°C water, and then drying it to a purity of 98.2%, and returning the solid aluminum hydroxide to the alumina production process for roasting;

[0130] S41, adding a 1.0 mol / L calcium nitrate solution dropwise to the sodium oxalate solution at a temperature of 40° C. until no precipitate is generated in the sodium oxalate solution, to obtain a third mixed solution;

[0131] S51, performing solid-liquid separation on the third mixed liquid to obtain calcium oxalate with a purity of 84.66% and a sodium nitrate-containing solution;

[0132] S61. Circulating the sodium nitrate-containing solution for mixing with crystalline oxalate to form a closed loop.

[0133] The purities of the solid-phase aluminum hydroxide and calcium oxalate obtained in Examples 1 to 6 and Comparative Example 1 were summarized, and the results are shown in Table 1.

[0134] Table 1 Purity of solid phase aluminum hydroxide and calcium oxalate in Examples and Comparative Examples

[0135] Group Purity of solid aluminum hydroxide, % Calcium oxalate purity, % Example 1 98.8 98.86 Example 2 98.6 98.06 Example 3 98.6 99.03 Example 4 98.4 98.56 Example 5 98.1 98.55 Example 6 98.5 98.56 Comparative Example 1 98.2 84.66

[0136] Comparison between Comparative Example 1 and Example 1 shows that failure to add oxalic acid to adjust the pH value results in a decrease in the purity of calcium oxalate. Comparison between Example 4 and Example 6 shows that returning the sodium nitrate-containing solution to the oxalate leaching system increases the sodium nitrate content in the solution. Once the sodium nitrate content reaches the set concentration, it can be directly used for desulfurization in the alumina production process.

[0137] In addition, one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages:

[0138] In the examples of this application, aluminum hydroxide can be recovered from the crystalline oxalate. Furthermore, the crystalline oxalate can be reacted with calcium nitrate to produce a desulfurizer for use in alumina systems, thereby reducing the cost of sodium nitrate. Furthermore, high-quality calcium oxalate can be produced, which is beneficial for obtaining high-quality chemical byproducts.

[0139] In the embodiments of the present application, the problems of low desulfurization efficiency in the prior art and high cost of using nitric acid for desulfurization in the alumina production process are solved. The characteristics of this technical solution are simple process flow, easy operation, cost-effectiveness, and significant economic benefits.

[0140] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A method for treating crystalline oxalate in an alumina production process, the method comprising: mixing the crystalline oxalate with water to obtain a first mixed solution; adding oxalic acid to the first mixed solution and adjusting the pH value of the first mixed solution to 5.5 to 7.0 to leach sodium aluminate from the first mixed solution to obtain a second mixed solution; performing solid-liquid separation on the second mixed liquid to obtain a sodium oxalate solution and solid aluminum hydroxide; adding a calcium nitrate solution dropwise to the sodium oxalate solution until no precipitate is generated in the sodium oxalate solution to obtain a third mixed solution; performing solid-liquid separation on the third mixed liquid to obtain calcium oxalate and a sodium nitrate-containing solution; The sodium nitrate-containing solution is circulated for mixing with the crystallized oxalate to form a closed cycle.

2. The method according to claim 1, characterized in that The method further comprises: The sodium nitrate-containing solution after multiple cycles is used for desulfurization treatment in the alumina production process.

3. The method according to claim 1, characterized in that The leaching temperature is 60° C. to 100° C., and the leaching time is 30 min to 120 min.

4. The method according to claim 1, wherein The mass concentration of sodium oxalate in the sodium oxalate-containing solution is 50 g / L to 70 g / L.

5. The method according to claim 1, wherein The molar concentration of the calcium nitrate solution is 1.0 mol / L to 2.2 mol / L.

6. The method according to claim 1, characterized in that During the dropwise addition of the calcium nitrate solution, the temperature of the sodium oxalate solution is 40°C to 60°C.

7. The method according to claim 1, characterized in that The purity of the solid phase aluminum hydroxide is ≥98%.

8. The method according to claim 1, characterized in that The purity of the calcium oxalate is ≥98%.

9. The method according to claim 1, characterized in that The mass ratio of the crystalline oxalate to water is 1:(1.8-2.2).

10. The method according to claim 9, characterized in that The crystalline oxalate comprises one or more of aluminum hydroxide, sodium oxalate, sodium aluminate, sodium hydroxide and soluble organic matter.

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