Resource recycling method for iron and aluminum in red mud based on step-by-step acid leaching

Abstract

The invention belongs to the technical field of solid waste resource utilization, discloses a resource recycling method for iron and aluminum in red mud based on step-by-step acid leaching, and effectively solves the problems of complex process and high acid and alkali consumption still existing in synergistic efficient separation and recycling of iron and aluminum in current red mud. Comprising the steps of red mud pretreatment, step-by-step iron leaching through waste sulfuric acid, aluminum leaching through waste hydrochloric acid, iron recovery through sodium carbonate precipitation, and aluminum recovery through pH adjustment after alkali dissolution separation. According to the method, high-selectivity leaching of the iron and the aluminum is achieved through step-by-step acid leaching, the cost is reduced through industrial waste acid, high-purity separation and recovery of the iron and the aluminum are achieved through step-by-step precipitation, and the method is simple in process, high in resource recovery rate, environmentally friendly and suitable for large-scale resourceful treatment of the red mud.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization technology, and particularly relates to a method for the resource recovery of iron and aluminum from red mud based on stepwise acid leaching. Background Technology

[0002] Red mud is a solid waste generated during alumina production. It is highly alkaline and contains valuable components such as iron, aluminum, titanium, and sodium. Currently, most red mud is stockpiled, occupying land and posing environmental risks. Existing red mud resource utilization technologies include extracting valuable metals and preparing building materials, but these generally suffer from low recovery rates, high energy consumption, and secondary pollution. In particular, the synergistic and efficient separation and recovery of iron and aluminum still suffers from drawbacks such as complex processes and high acid and alkali consumption.

[0003] Therefore, it is of great significance to develop a red mud resource utilization process that is reasonable, low-cost, and capable of selectively extracting iron and aluminum. Summary of the Invention

[0004] The purpose of this invention is to provide a method for the resource recovery of iron and aluminum from red mud based on stepwise acid leaching, which effectively solves the problems of complex processes and high acid and alkali consumption in the current synergistic and efficient separation and recovery of iron and aluminum from red mud.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for resource recovery of iron and aluminum from red mud based on stepwise acid leaching, comprising the following steps: S1, crushing and grinding the red mud to D90 < 100 μm to obtain red mud powder.

[0006] S2. Mix red mud powder and waste sulfuric acid at a solid-liquid mass ratio of 1:4-6, stir and react at 90±5℃ for 3.5h, and separate the solid and liquid to obtain primary leachate and primary leaching residue.

[0007] S3. Mix the primary leaching residue with waste hydrochloric acid at a solid-liquid mass ratio of 1:2-4, stir and react at 85±5℃ for 3 hours, and separate the solid and liquid to obtain secondary leachate and secondary leaching residue.

[0008] S4. After diluting the first leachate, add sodium carbonate solution dropwise at 65°C until the pH reaches 3-3.2. After aging at this temperature, filter to obtain ferric hydroxide.

[0009] S5. After diluting the secondary leachate, add excess sodium hydroxide solution and react at 60-70℃ for 2 hours. Filter to obtain sodium aluminate solution and iron-containing filter residue. Then adjust the pH of the sodium aluminate solution to 7-8 to obtain aluminum hydroxide.

[0010] Furthermore, the mass concentration of waste sulfuric acid is 22%-24%, and the mass concentration of waste hydrochloric acid is 32.5%-36.6%.

[0011] Furthermore, the primary and secondary leaching residues are washed to a pH of 6, and the washed secondary leaching residue is used for soil amendment or refractory materials.

[0012] Furthermore, in step S4, the liquid used to dilute the primary leachate is either the primary leachate washing liquid or the circulating filtrate within the system; in step S5, the liquid used to dilute the secondary leachate is the secondary leachate washing liquid.

[0013] Furthermore, in step S5, the pH of the sodium aluminate solution is adjusted by aeration with dilute hydrochloric acid or carbon dioxide.

[0014] Furthermore, the iron-containing filter residue obtained in step S5 is combined with the ferric hydroxide obtained in step S4 and dried together to obtain the ferric hydroxide product.

[0015] Compared with the prior art, the beneficial technical effects of the present invention are: (1) The present invention achieves high selective leaching of iron and aluminum by stepwise acid leaching, reduces costs by using industrial waste acid, and achieves high purity separation and recovery of iron and aluminum by segmented precipitation, achieving an iron leaching rate of >92% and an aluminum leaching rate of >88%, with the resulting iron hydroxide and aluminum hydroxide products having a purity of >95%.

[0016] (2) The process water and intermediate washing liquid of the present invention are recycled to reduce wastewater discharge; the final red mud leaching residue can be used for soil improvement, refractory materials, etc., to realize the utilization of all components. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the present invention. Detailed Implementation

[0018] Example 1: First, let me introduce some of the chemical raw materials used in this example: (1) Waste hydrochloric acid: industrial grade, mass concentration of about 34.6%, molar concentration of about 10.74 mol / L, determined by titration based on the sample. (2) Waste sulfuric acid: industrial grade, concentration of about 22.9%, molar concentration of about 3.07 mol / L, determined by titration based on the sample. If there are too many impurities such as iron, the sulfuric acid content may need to be determined by mass method. (3) Sodium hydroxide solution: industrial grade alkaline solution, mass fraction of about 33.25%, diluted to 6M by mass ratio of alkaline solution:water = 721.8:497.8. (4) Sodium carbonate: industrial grade of more than 98%, prepared into a 2.5 mol / L sodium carbonate solution.

[0019] This embodiment provides a method for the resource recovery of iron and aluminum from red mud based on stepwise acid leaching, such as... Figure 1As shown, the process includes the following steps: S1, take 6 kg of red mud (composition: Al2O3 22.9%, Fe2O3 21.83%, Na2O 10.77%, SiO2 17.02%, CaO 1.32%, TiO2 4.81%), and ball mill the red mud until D90 < 100 μm to obtain red mud powder.

[0020] S2. Add 30 kg of 22.9% industrial-grade waste sulfuric acid (total acidity approximately 6.14 mol / L) to the reactor, heat to 60°C, and then add red mud powder; raise the temperature to 90°C and stir the reaction for 3.5 h to fully dissolve the iron and free aluminum components in the red mud. Filter by pressure to obtain primary leaching solution and primary leaching residue; wash the primary leaching residue with hot water until the pH is close to 6, and use the washing solution for later use.

[0021] S3. Mix the primary leaching residue with 18 kg of 34.6% industrial-grade waste hydrochloric acid (total acidity approximately 10.74 mol / L), and stir at 85°C for 3 hours to fully dissolve the aluminum components in the red mud. The leaching solution will turn yellow, and the filter residue will be nearly white, indicating the end of the reaction. Filter by pressure to obtain secondary leaching solution and secondary leaching residue. Wash the secondary leaching residue with hot water until the pH is close to 6 (pH value in the drip tank). The washing solution of the secondary leaching residue is reserved for use. The washed secondary leaching residue can be used for soil amendment or refractory materials.

[0022] S4. Dilute the primary leachate with the primary leachate residue washing solution at a mass ratio of 2:1 until the pH is close to 2. Then, slowly add 2.5 mol / L sodium carbonate solution to the diluted primary leachate in a 65℃ water bath until the pH reaches 3.2. Keep warm and stir slowly for 1 hour, then filter to obtain ferric hydroxide residue and filtrate. Wash the ferric hydroxide residue with hot water at 60-80℃. Combine the washing solution and filtrate to dilute the primary leachate. Dry the ferric hydroxide residue at 100℃ to obtain the ferric hydroxide product.

[0023] After several reuses, the filtrate will be enriched with aluminum ions. At this point, it can be combined with the primary leachate and then evaporated and concentrated to prepare aluminum ferric sulfate.

[0024] S5. Dilute the secondary leachate with the secondary leachate washing solution at a mass ratio of 2:1, so that the pH after dilution is close to 2.

[0025] Add an excess of no more than 20% of 6 mol / L sodium hydroxide solution (the amount is estimated based on the aluminum and iron composition) to the diluted secondary leachate, react at 65°C for 2 hours, and filter to obtain sodium aluminate solution and iron-containing filter residue (the iron-containing filter residue is combined with the iron hydroxide filter residue obtained in step S4 and dried together to obtain the iron hydroxide product). Then, slowly add 2 mol / L dilute hydrochloric acid dropwise to the sodium aluminate solution (pH around 13) until pH=7.5, causing aluminum hydroxide precipitate to form. After filtration, washing, and drying, obtain the aluminum hydroxide product.

[0026] In step S5, the filtrate after filtering aluminum hydroxide precipitate is concentrated into a saturated sodium chloride solution, and ammonium bicarbonate powder is added at 30-35℃. Sodium bicarbonate is precipitated due to the difference in solubility. The precipitated sodium bicarbonate is filtered and washed with cold water. Then, the sodium bicarbonate filter residue is calcined at 270-300℃ to decompose into sodium carbonate. The filtrate is evaporated, concentrated, cooled, and crystallized to precipitate ammonium chloride for use as nitrogen fertilizer.

[0027] This embodiment achieves highly selective leaching of iron and aluminum through stepwise acid leaching, reduces costs by utilizing industrial waste acid, and achieves high-purity separation and recovery of iron and aluminum through staged precipitation. Testing shows that the iron leaching rate is >92% and the aluminum leaching rate is >88% in this embodiment. The purity of the obtained iron hydroxide and aluminum hydroxide products is both >95%. This embodiment features a simple process, high resource recovery rate, and environmental friendliness, making it suitable for large-scale resource utilization of red mud.

[0028] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for the resource recovery of iron and aluminum from red mud based on stepwise acid leaching, characterized in that, Includes the following steps: S1. Crush and grind the red mud until D90 < 100 μm to obtain red mud powder; S2. Mix red mud powder and waste sulfuric acid at a solid-liquid mass ratio of 1:4-6, stir and react at 90±5℃, and separate the solid and liquid to obtain primary leachate and primary leaching residue. S3. Mix the primary leaching residue with waste hydrochloric acid at a solid-liquid mass ratio of 1:2-4, stir and react at 85±5℃, and separate the solid and liquid to obtain secondary leachate and secondary leaching residue. S4. After diluting the first leachate, add sodium carbonate solution dropwise at 65°C until the pH reaches 3-3.

2. After aging at this temperature, filter to obtain ferric hydroxide. S5. After diluting the secondary leachate, add excess sodium hydroxide solution and react at 60-70℃. Filter to obtain sodium aluminate solution and iron-containing filter residue. Then adjust the pH of the sodium aluminate solution to 7-8 to obtain aluminum hydroxide.

2. The method for resource recovery of iron and aluminum from red mud based on stepwise acid leaching according to claim 1, characterized in that, The mass concentration of waste sulfuric acid is 22%-24%, and the mass concentration of waste hydrochloric acid is 32.5%-36.6%.

3. The method for resource recovery of iron and aluminum from red mud based on stepwise acid leaching according to claim 1, characterized in that, The primary and secondary leaching residues were washed to a pH of 6. The washed secondary leaching residue was used for soil amendment or refractory materials.

4. The method for resource recovery of iron and aluminum from red mud based on stepwise acid leaching according to claim 3, characterized in that, In step S4, the liquid used to dilute the primary leachate is either the primary leachate washing liquid or the circulating filtrate within the system; in step S5, the liquid used to dilute the secondary leachate is the secondary leachate washing liquid.

5. The method for resource recovery of iron and aluminum from red mud based on stepwise acid leaching according to claim 1, characterized in that, In step S5, the pH of the sodium aluminate solution is adjusted by aeration with dilute hydrochloric acid or carbon dioxide.

6. The method for resource recovery of iron and aluminum from red mud based on stepwise acid leaching according to claim 5, characterized in that, The iron-containing filter residue obtained in step S5 is combined with the ferric hydroxide obtained in step S4 and dried together to obtain the ferric hydroxide product.

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