Method for separating and recycling metal elements in red mud based on ammonium oxalate / oxalic acid solution system pretreatment

Abstract

The invention relates to the technical field of solid waste recovery, and particularly provides a method for separating and recovering metal elements in red mud based on ammonium oxalate / oxalic acid solution system pretreatment, which comprises the following steps: S1, taking red mud for pretreatment; s2, mixing the pretreated red mud with a mixed solution of oxalic acid and ammonium oxalate according to a specific liquid-solid ratio, wherein the pH value of the mixed solution is 2-4, and carrying out a leaching reaction; s3, after the leaching reaction is finished, a water-based filter membrane is adopted for filtering, and leaching residues enriched in iron, aluminum and titanium and leaching liquid containing aluminum, sodium and silicon are obtained; s4, mixing the leaching residues enriched with iron, aluminum and titanium with pulverized coal, roasting, and carrying out magnetic separation to obtain iron-rich concentrate and aluminum-titanium tailings; and S5, adjusting the pH value of the leachate containing aluminum, sodium and silicon, and filtering, washing and drying to obtain aluminum hydroxide. According to the method, enrichment of iron and titanium in the red mud and efficient separation of aluminum, sodium and silicon are achieved under the condition of low acid consumption, the technological process is simple, environment friendliness is achieved, and the metal recovery rate is high.

Description

Technical Field

[0001] This invention relates to the field of solid waste processing technology, and mainly to a method for separating and recovering metal elements from red mud based on a pretreatment system of ammonium oxalate / oxalic acid solution. Background Technology

[0002] Oxalate (C2O4) 2- Oxalic acid has been used to extract elements from certain soil-forming species for about a century. Under low pH conditions, oxalic acid can effectively dissolve poorly crystalline aluminum and iron minerals, but its leaching effect on well-crystalline iron oxides (such as hematite and goethite) and layered silicates is limited. Aluminum in oxalate leachates can originate from various occurrence forms, such as exchangeable aluminum, hydroxyl-intercalated aluminum, amorphous aluminum hydroxide, and aluminosilicate phases. Silicon in the leachate also mainly comes from the dissolution of these silicate structures. In existing technologies, aluminum in aluminum-containing oxalate leachates often exists stably in the form of complexes. Aluminum can be recovered through precipitation by adjusting the pH, or the leachate waste can be degraded using its complexing effect. The leachate residue, rich in iron and titanium, can be directly separated from aluminum and titanium through reduction roasting.

[0003] Currently, publicly available red mud recovery technologies often employ inorganic acid leaching, which suffers from problems such as high acid consumption, significant environmental pollution, and co-dissolution of impurities. Therefore, this invention proposes a direct leaching process using an ammonium oxalate / oxalic acid mixed solution to achieve the directional separation of multiple components in red mud. Summary of the Invention

[0004] To address the problems existing in the background technology, embodiments of the present invention provide a method for separating and recovering metal elements from red mud based on a pretreatment system of ammonium oxalate / oxalic acid solution. This method can achieve efficient separation of aluminum, sodium, silicon, iron, and titanium from red mud under low acid consumption conditions. Sodium, silicon, and some aluminum enter the leachate, while iron, titanium, and the remaining aluminum are enriched in the leaching residue. Iron in the leaching residue is separated by reduction roasting, and aluminum in the leachate is separated by adjusting the pH. The process of this invention is simple and has good prospects for industrial application.

[0005] Embodiments of the present invention provide a method for separating and recovering metal elements from red mud based on a pretreatment system of ammonium oxalate / oxalic acid solution, comprising the following steps: S1: Take red mud for pretreatment; S2: The pretreated red mud from step S1 is mixed with the leaching agent at a specific liquid-solid ratio, and stirred under light-proof, normal temperature and pressure conditions to carry out the leaching reaction; wherein, the leaching agent is a mixed solution of oxalic acid and ammonium oxalate with a pH value of 2~4. S3: After the leaching reaction is completed, the solution is filtered using a water-based filter membrane to obtain leaching residue enriched with iron, aluminum, and titanium, and leaching solution containing aluminum, sodium, and silicon. S4: The iron-aluminum-titanium enriched leaching residue is mixed with coal powder and roasted, and then separated by magnetic separation to obtain iron-rich concentrate and aluminum-titanium tailings. S5: Adjust the pH value of the leachate containing aluminum, sodium, and silicon, and after filtration, washing, and drying, obtain aluminum hydroxide.

[0006] Preferably, in step S1, the pretreatment includes grinding, crushing, and sieving.

[0007] More preferably, the sieving process uses a 200-mesh sieve to obtain red mud with a mesh size of less than 200 mesh.

[0008] Preferably, in step S1, the iron in the red mud is mainly in the form of hematite and goethite, and the aluminum is mainly in the form of gibbsite and aluminosilicate.

[0009] Preferably, in step S2, the concentration of ammonium oxalate in the mixed solution of oxalic acid and ammonium oxalate is 0.1M~0.3M, and the pH value is adjusted to 2~4 by adding oxalic acid. Ammonium oxalate acts as a complexing agent to provide oxalate ions, and oxalic acid acts as a pH adjuster to control the acidic environment.

[0010] Preferably, in step S2, the liquid-solid mixture is mixed at a ratio of 1g:30-100mL.

[0011] Preferably, in step S2, the leaching reaction time is not less than 1 hour; the leaching reaction temperature is 20℃-70℃.

[0012] Preferably, in step S3, the pore size of the water-based filter membrane is 25 mm.

[0013] More preferably, the filtration uses a sand core filter device.

[0014] Preferably, in step S4, the fixed carbon content of the pulverized coal is greater than 80 wt%, the particle size of the pulverized coal is 180-200 mesh, the mass of the pulverized coal is 5%-13% of the mass of the preheated dry red mud powder, and the mixing method is ball milling.

[0015] Preferably, in step S4, the calcination temperature is 750℃~1200℃ and the calcination time is 3 hours or more.

[0016] Preferably, in step S5, the pH value is adjusted to 6-8.

[0017] The above-described solution of the present invention has the following beneficial effects: (1) Compared with the existing red mud resource utilization technologies, which generally have problems such as large inorganic acid consumption, serious environmental pollution and co-dissolution of impurity ions, this invention uses a mixed solution of oxalic acid and ammonium oxalate with a pH of 2 to 4 as the leaching agent for red mud reduction roasting pretreatment. Under low acid consumption conditions, it realizes the enrichment of iron and titanium in red mud and the efficient separation of aluminum, sodium and silicon. The process is simple, environmentally friendly and has a high metal recovery rate.

[0018] (2) After reduction, roasting and magnetic separation, the iron, titanium and aluminum in the leaching residue obtained by this invention can be sold directly as iron ore or used directly. The aluminum in the leaching solution can be efficiently recovered after precipitation or the complexation of aluminum oxalate in the leaching solution can be used to degrade organic waste liquid. The overall process has good comprehensive resource recovery value and provides a feasible path for the large-scale resource utilization of red mud. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a process flow diagram of the method for pretreatment separation and recovery of metal elements in red mud based on the ammonium oxalate / oxalic acid solution system of the present invention; Figure 2 These are the XRD patterns and photographs of the original red mud used in Embodiment 1 of the present invention; Figure 3 These are the XRD pattern and photograph of the red mud leaching residue in Example 1 of the present invention; Figure 4 This is the XRD pattern of the iron-rich concentrate obtained by magnetic separation in Example 1 of the present invention. Detailed Implementation

[0021] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0022] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0023] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0024] This invention addresses existing problems by providing a method for separating and recovering metal elements from red mud based on a pretreatment system of ammonium oxalate / oxalic acid solution.

[0025] The red mud used in the following text comes from the residue obtained after aluminum extraction at the Shandong Aluminum Plant from Guinea bauxite mines, and belongs to the Bayer process red mud.

[0026] Example 1 This embodiment provides a method for separating and recovering metal elements from red mud based on a pretreatment system of ammonium oxalate / oxalic acid solution, such as... Figure 1 As shown, it includes the following steps: (1) Grind the red mud through a sieve to obtain solid powder with a particle size of less than 200 mesh; (2) Weigh 1g of red mud solid powder, put it into a 100mL single-necked flask, and put in a magnetic flask; (3) Measure 30 mL of 0.2 M ammonium oxalate solution and pour it into the single-necked flask in step (2), and adjust the pH to 3 by adding oxalic acid; (4) Place the single-necked flask from step (3) into a water bath, turn on the magnetic stirrer, set the stirring speed to 200 r / min, maintain the temperature at 30℃, and stir for 1 h; (5) The mixture stirred in step (4) is filtered through a low-pore water-based filter membrane to obtain iron- and titanium-rich red mud leaching residue and aluminum-sodium-silicon leaching solution. (6) Place the red mud leachate residue from step (5) into an oven to dry for 3 hours at a temperature of 60°C. (7) After mixing the coal powder with the red mud leaching residue from step (6) by ball milling at a mass fraction of 15%, it is placed in a muffle furnace for roasting at a roasting temperature of 1100℃ for 4 hours. The magnetic iron concentrate and tailings are separated by 1200 Gauss. (8) Place the aluminum sodium silicon leaching solution from step (5) into a beaker, add 1 mol / L sodium hydroxide solution to adjust the pH of the leaching solution to 6, and obtain aluminum hydroxide flocculent precipitate, then filter. (9) Place the aluminum hydroxide precipitate from step (8) into an oven to dry for 3 hours at a temperature of 60°C.

[0027] In this embodiment, the leaching rate of aluminum in step (5) is 35.2%, the leaching rate of sodium is 86.4%, the leaching rate of silicon is 83.6%, the leaching rate of iron is 1.3%, and the grade of iron concentrate in step (7) is 64.1%.

[0028] The XRD pattern and photograph of the red mud slag obtained in step (2) of this embodiment are as follows: Figure 3 As shown, compared with the original red mud (such as Figure 2Compared to the sample shown), the reddish color indicates that iron is enriched in the red mud leaching residue. The red mud residue obtained in step (2) was digested and tested to determine the leaching content of iron, aluminum, sodium, and silicon. The leaching rates of iron and aluminum are shown in Table 1. The XRD pattern and photographs of the red mud leaching residue used are shown in Table 1. Figure 3 As shown.

[0029] Example 2 This embodiment provides a method for separating and recovering metal elements from red mud based on a pretreatment system of ammonium oxalate / oxalic acid solution, such as... Figure 1 As shown, it includes the following steps: (1) Grind the red mud through a sieve to obtain solid powder with a particle size of less than 200 mesh; (2) Weigh 5g of red mud solid powder, put it into a 250mL single-necked flask, and put in a magnetic flask; (3) Measure 150 mL of 0.2 M ammonium oxalate solution and pour it into the single-necked flask in step (2), and adjust the pH to 3 by adding oxalic acid; (4) Place the single-necked flask from step (3) into a water bath, turn on the magnetic stirrer, set the stirring speed to 200 r / min, maintain the temperature at 30℃, and stir for 1 h; (5) The mixture stirred in step (4) is filtered through a low-pore water-based filter membrane to obtain red mud-rich leaching residue and aluminum-sodium-silicon leaching solution. (6) Place the red mud leachate residue from step (5) into an oven to dry for 3 hours at a temperature of 60°C. (7) The coal powder is mixed with the red mud leaching residue from step (6) by ball milling at a mass fraction of 15%, and then placed in a muffle furnace for roasting at a roasting temperature of 1100℃ for 4 hours. The magnetic iron concentrate and tailings are separated by 1200 Gauss. (8) Place the aluminum sodium silicon leaching solution from step (5) into a beaker, add 1 mol / L sodium hydroxide solution to adjust the pH of the leaching solution to 6, and obtain aluminum hydroxide flocculent precipitate, then filter. (9) Place the aluminum hydroxide precipitate from step (8) into an oven to dry for 3 hours at a temperature of 60°C.

[0030] In this embodiment, the red mud slag obtained in step (2) was digested and tested to determine the leaching content of iron, aluminum, sodium and silicon. The leaching rate of iron and aluminum is shown in Table 1.

[0031] Example 3 This embodiment provides a method for separating and recovering metal elements from red mud based on a pretreatment system of ammonium oxalate / oxalic acid solution, such as... Figure 1 As shown, it includes the following steps: (1) Grind the red mud through a sieve to obtain solid powder with a particle size of less than 200 mesh; (2) Weigh 1g of red mud solid powder, put it into a 100mL single-necked flask, and put in a magnetic flask; (3) Measure 50 mL of 0.2 M ammonium oxalate solution and pour it into the single-necked flask in step (2), and adjust the pH to 3 by adding oxalic acid; (4) Place the single-necked flask from step (3) into a water bath, turn on the magnetic stirrer, set the stirring speed to 200 r / min, maintain the temperature at 30℃, and stir for 2 hours; (5) The mixture stirred in step (4) is filtered through a low-pore water-based filter membrane to obtain red mud-rich leaching residue and aluminum-sodium-silicon leaching solution. (6) Place the red mud leachate residue from step (5) into an oven to dry for 3 hours at a temperature of 60°C. (7) The coal powder is mixed with the red mud leaching residue from step (6) by ball milling at a mass fraction of 15%, and then placed in a muffle furnace for roasting at a roasting temperature of 1100℃ for 4 hours. The magnetic iron concentrate and tailings are separated by 1200 Gauss. (8) Place the aluminum sodium silicon leaching solution from step (5) into a beaker, add 1 mol / L sodium hydroxide solution to adjust the pH of the leaching solution to 6, and obtain aluminum hydroxide flocculent precipitate, then filter. (9) Place the aluminum hydroxide precipitate from step (8) into an oven to dry for 3 hours at a temperature of 60°C.

[0032] Example 4 This embodiment provides a method for separating and recovering metal elements from red mud based on a pretreatment system of ammonium oxalate / oxalic acid solution, such as... Figure 1 As shown, it includes the following steps: (1) Grind the red mud through a sieve to obtain solid powder with a particle size of less than 200 mesh; (2) Weigh 1g of red mud solid powder, put it into a 20mL single-necked flask, and put in a magnetic flask; (3) Measure 10 mL of 0.2 M ammonium oxalate solution and pour it into the single-necked flask in step (2), and adjust the pH to 3 by adding oxalic acid; (4) Place the single-necked flask from step (3) into a water bath, turn on the magnetic stirrer, set the stirring speed to 200 r / min, maintain the temperature at 50℃, and stir for 2 hours; (5) The mixture stirred in step (4) is filtered through a low-pore water-based filter membrane to obtain red mud-rich leaching residue and aluminum-sodium-silicon leaching solution. (6) Place the red mud leachate residue from step (5) into an oven to dry for 3 hours at a temperature of 60°C. (7) Mix the coal powder with the red mud leaching residue from step (6) by ball milling at a mass fraction of 10%~20%, and roast it in a muffle furnace at a roasting temperature of 1100℃ for 4 hours. Separate the magnetic iron concentrate and tailings by 1200 Gauss. (8) Place the aluminum sodium silicon leaching solution from step (5) into a beaker, add 1 mol / L sodium hydroxide solution to adjust the pH of the leaching solution to 6, and obtain aluminum hydroxide flocculent precipitate, then filter. (9) Place the aluminum hydroxide precipitate from step (8) into an oven to dry for 3 hours at a temperature of 60°C.

[0033] Example 5 This embodiment provides a method for separating and recovering metal elements from red mud based on a pretreatment system of ammonium oxalate / oxalic acid solution, such as... Figure 1 As shown, it includes the following steps: (1) Grind the red mud through a sieve to obtain solid powder with a particle size of less than 200 mesh; (2) Weigh 1g of red mud solid powder and put it into a 50mL centrifuge tube; (3) Measure 30 mL of 0.2 M ammonium oxalate solution and pour it into the centrifuge tube in step (2), and adjust the pH to 3 by adding oxalic acid; (4) Place the single-necked flask from step (3) into a constant temperature shaker, turn on the shaker reciprocating switch, set the stirring speed to 200 r / min, maintain the temperature at 30℃, and shake for 3 hours; (5) The mixture stirred in step (4) is filtered through a low-pore water-based filter membrane to obtain red mud-rich leaching residue and aluminum-sodium-silicon leaching solution. (6) Place the red mud leachate residue from step (5) into an oven to dry for 3 hours at a temperature of 60°C. (7) The coal powder is mixed with the red mud leaching residue from step (6) by ball milling at a mass fraction of 15%, and then placed in a muffle furnace for roasting at a roasting temperature of 1100℃ for 4 hours. The magnetic iron concentrate and tailings are separated by 1200 Gauss. (8) Place the aluminum sodium silicon leaching solution from step (5) into a beaker, add 1 mol / L sodium hydroxide solution to adjust the pH of the leaching solution to 6, and obtain aluminum hydroxide flocculent precipitate, then filter. (9) Place the aluminum hydroxide precipitate from step (8) into an oven to dry for 3 hours at a temperature of 60°C.

[0034] The photograph of the red mud residue obtained in step (2) of this embodiment is as follows: Figure 3 As shown, compared with the original red mud (such as Figure 2Compared to the sample shown below, the red mud leaching residue is reddish, indicating that iron is enriched in the residue. The iron and aluminum content of the red mud residue obtained in step (2) was tested by digestion, and the iron and aluminum recovery rates were obtained. The results are shown in Table 1 below. The XRD pattern of the red mud used is shown below. Figure 3 As shown, the aluminum hydroxide precipitate obtained in step (9) is a yellowish-white flocculent precipitate.

[0035] Comparative Example 1 The difference from Example 1 is that the leaching agent is replaced with 1M pure oxalic acid (pH value less than 1), while the other steps and parameters are the same as in Example 1.

[0036] Comparative Example 2 The difference from Example 1 is that the leaching agent is replaced with a mixed solution of sulfuric acid and ammonium sulfate, while the other steps and parameters are the same as in Example 1.

[0037] Comparative Example 3 The difference from Example 1 is that the leaching agent is replaced with a mixed solution of oxalic acid and sodium oxalate, while the other steps and parameters are the same as in Example 1.

[0038] Comparative Example 4 The difference from Example 1 is that it is roasted first and then leached, while the other steps and parameters are the same as in Example 1.

[0039] Table 1. Leaching rate results of Examples 1 to 5

[0040] As shown in Table 1 above, the red mud acid leaching recovery method of this invention has a high sodium and silicon recovery rate, and can also leach some aluminum into the solution, further enriching the iron in the slag. Furthermore, by reducing, roasting, and magnetically separating the leaching slag, the iron, aluminum, and titanium components in the leaching slag are separated, and the aluminum in the leachate can also be recovered as aluminum hydroxide precipitation, thus achieving the resource recovery of red mud. This invention features a short process, simple operation, and high recovery rate, providing a feasible solution for the resource utilization of red mud.

[0041] In Comparative Example 1, the excessive acidity caused most of the metals, including iron, to dissolve, resulting in a low iron leaching rate. Comparative Example 2, while disclosing an acidic environment, failed to achieve low aluminum and sodium leaching rates because ammonium sulfate could not complex with some of the sodium aluminosilicate in the red mud to separate aluminum and iron. Comparative Example 3, although disclosing sodium oxalate, could not adjust the pH to 3 by adding oxalic acid. If the acidity was too low, almost no reaction occurred. In Comparative Example 4, the initial roasting process involved numerous elements in the red mud, which would participate in the reaction during roasting, leading to the loss of some reactants. Subsequent leaching and separation, due to the complexity of the composition, would also increase the length of the separation process and operational costs.

[0042] In summary, the amorphous sodium aluminum silicate in red mud undergoes a coordination complexation reaction when leached with a mixed solution of ammonium oxalate and oxalic acid at a pH of 2-4, forming an aluminum oxalate complex. This allows the silicon and sodium to enter the solution, while the iron in the red mud remains in the filter residue and is enriched, resulting in high-purity iron during subsequent roasting.

[0043] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for separating and recovering metal elements from red mud based on a pretreatment system of ammonium oxalate / oxalic acid solution, characterized in that, Includes the following steps: S1: Take red mud for pretreatment; S2: The pretreated red mud from step S1 is mixed with the leaching agent at a specific liquid-solid ratio to carry out a leaching reaction; wherein, the leaching agent is a mixed solution of oxalic acid and ammonium oxalate with a pH value of 2~4. S3: After the leaching reaction is completed, the solution is filtered using a water-based filter membrane to obtain leaching residue enriched with iron, aluminum, and titanium, and leaching solution containing aluminum, sodium, and silicon. S4: The iron-aluminum-titanium enriched leaching residue is mixed with coal powder and roasted, and then separated by magnetic separation to obtain iron-rich concentrate and aluminum-titanium tailings. S5: Adjust the pH value of the leachate containing aluminum, sodium, and silicon, and after filtration, washing, and drying, obtain aluminum hydroxide.

2. The method for separating and recovering metal elements from red mud based on the ammonium oxalate / oxalic acid solution system pretreatment according to claim 1, characterized in that, In step S1, the pretreatment includes grinding, crushing, and sieving.

3. The method for separating and recovering metal elements from red mud based on the ammonium oxalate / oxalic acid solution system pretreatment according to claim 1, characterized in that, In step S1, the iron in the red mud is mainly in the form of hematite and goethite, while the aluminum is mainly in the form of gibbsite and aluminosilicate.

4. The method for separating and recovering metal elements in red mud based on the ammonium oxalate / oxalic acid solution system pretreatment according to claim 1, characterized in that, In step S2, the concentration of ammonium oxalate in the mixed solution of oxalic acid and ammonium oxalate is 0.1M~0.3M, and the pH value is adjusted to 2~4 by adding oxalic acid.

5. The method for separating and recovering metal elements in red mud based on the ammonium oxalate / oxalic acid solution system pretreatment according to claim 1, characterized in that, In step S2, the liquid-solid mixture is mixed at a ratio of 1g:30-100mL.

6. The method for separating and recovering metal elements in red mud based on the ammonium oxalate / oxalic acid solution system pretreatment according to claim 1, characterized in that, In step S2, the leaching reaction time is not less than 1 hour; the leaching reaction temperature is 20℃-70℃.

7. The method for separating and recovering metal elements from red mud based on the ammonium oxalate / oxalic acid solution system pretreatment according to claim 1, characterized in that, In step S3, the pore size of the water-based filter membrane is 25 mm.

8. The method for separating and recovering metal elements in red mud based on the ammonium oxalate / oxalic acid solution system pretreatment according to claim 1, characterized in that, In step S4, the fixed carbon content of the pulverized coal is greater than 80 wt%, the particle size of the pulverized coal is 180-200 mesh, the mass of the pulverized coal is 5%-13% of the mass of the preheated dry red mud powder, and the mixing method is ball milling.

9. The method for separating and recovering metal elements in red mud based on the ammonium oxalate / oxalic acid solution system pretreatment according to claim 1, characterized in that, In step S4, the calcination temperature is 750℃~1200℃, and the calcination time is more than 3 hours.

10. The method for separating and recovering metal elements in red mud based on the ammonium oxalate / oxalic acid solution system pretreatment according to claim 1, characterized in that, In step S5, the pH value is adjusted to 6-8.

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