Method for treating acid mine drainage with red mud residue

Abstract

The application relates to the field of waste treatment, in particular to a method for treating acid mine drainage by using red mud residue, which comprises the steps of hydrothermal treatment, joint calcination, wastewater treatment, phosphatization and fixation. The method is characterized in that a composite adsorption system is formed by hydrothermal treatment of organic adsorption materials containing fibers and red mud residue, and the composite adsorption system is further fixed by phosphoric acid after calcination. The method can achieve better heavy metal fixation effect after preparation of geopolymer or other concrete systems.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment, and in particular to a method for treating acidic mine water with red mud residue. Background Technology

[0002] Red mud slag is a highly alkaline solid waste generated during the alumina production process. Its main components are iron oxide, aluminum oxide, and silicon dioxide, and it also contains alkaline substances such as sodium carbonate and potassium hydroxide. Using red mud slag to treat acidic wastewater is a waste-to-waste approach. By using red mud slag to adsorb, neutralize, and precipitate acidic wastewater, it has low operating costs, simple maintenance, low energy consumption, mild conditions, and extremely low equipment requirements, thus having broad application prospects.

[0003] Acid mine drainage (AMD) is a major environmental problem arising from mining activities. It typically refers to highly acidic wastewater with high heavy metal content generated when sulfide minerals (mainly pyrite FeS2) are exposed to air and water and undergo oxidation reactions. Currently, over 20,000 kilometers of freshwater rivers worldwide are polluted by acid mine drainage, threatening aquatic ecosystems and biodiversity. Using red mud slag to treat AMD utilizes its alkalinity to neutralize acidic substances in the water, while simultaneously adsorbing heavy metal ions from the AMD, thus achieving purification.

[0004] After the above treatment, the wastewater has been initially purified. However, the sludge system formed by the red mud residue still requires further treatment. Since the red mud residue itself has a weak adsorption capacity for heavy metal ions through alkaline environment and its own adsorption properties, and heavy metal ions are more easily released under acidic conditions (such as acid rain and other natural environmental influences), there is a significant need to improve its adsorption and fixation performance for heavy metals. Summary of the Invention

[0005] Based on the above problems, this application provides a method for treating acidic mine water with red mud residue, which has extremely strong adsorption performance for heavy metal ions. At the same time, even in an acidic environment, there will be no large amount of heavy metal leaching after treatment, thus providing good heavy metal adsorption and fixation performance.

[0006] First, this application provides a method for treating acidic mine water with red mud residue, comprising the following steps: S1. Red mud slag and fiber-containing organic adsorbent material are hydrothermally treated to form a composite adsorption system, wherein the mass ratio of the fiber-containing organic adsorbent material to the red mud slag is 0.1 to 0.3:1. S2. The composite adsorption system obtained in step S1 is calcined at a temperature not exceeding 800℃ to obtain a composite treatment agent. S3. Adsorbent is obtained by treating acidic mine water with a composite treatment agent; S4. Treat the adsorbent with phosphate solution; S5. Prepare geopolymers by using the impregnated adsorbent as a gel material or as part of a gel material.

[0007] In the above scheme, a bifunctional adsorption system is formed by hydrothermally combining red mud slag (rich in iron and aluminum oxides) with fibrous organic adsorbent materials. Calcination then creates a stable composite adsorption system. Finally, phosphate treatment achieves chemical fixation of heavy metal ions, providing excellent heavy metal ion adsorption and fixation effects. Specifically, in steps S1 and S2, hydrothermal treatment causes a hydrothermal reaction in the red mud, forming crystalline structures such as sodalite and zeolite. During this process, the organic adsorbent material undergoes physical adsorption, forming a composite functional adsorption structure. Subsequent calcination fixes the two materials together, providing excellent initial adsorption performance. In step S4, phosphate treatment converts heavy metals into heavy metal phosphates, achieving better fixation of heavy metals and reducing leaching even in acidic environments.

[0008] Preferably, in step S4, the mass of phosphorus in the phosphate solution is 0.005 to 0.02 times the mass of the composite treatment agent, and / or, In step S4, the solid-liquid ratio of phosphoric acid impregnation is 3–10:1, and / or, The temperature in step S4 shall not exceed 40°C.

[0009] In the above scheme, the quality of phosphorus has a certain impact on the final pollution fixation effect. Excessive phosphorus content will lead to a certain amount of phosphoric acid leaching in the system, which will have a significant impact on the curing process when preparing geopolymer materials.

[0010] Preferably, the fiber-containing organic adsorbent material is distiller's grains, and the distiller's grains are dried before use so that their moisture content is not higher than 60%.

[0011] Distillers' grains contain a significant amount of cellulose, as well as certain amounts of highly active substances such as protein and lignin. After drying, hydrothermal treatment generates more active groups in the grains, allowing them to better adhere to red mud slag. Calcination then forms a biochar framework, maintaining good porosity and specific surface area while improving the absorption and fixation of organic matter and heavy metals. Furthermore, the derivative system derived from distillers' grains can provide better strength support in the subsequent preparation of geopolymer systems.

[0012] Additionally, it should be noted that the solid-liquid ratio in this article refers to the mass ratio.

[0013] Preferably, in step S1, 0.1 to 0.5% of citric acid or a water-soluble salt of citric acid is also added, accounting for 0.1 to 0.5% of the mass of the red mud residue.

[0014] Citric acid can form complexes with iron and aluminum ions in red mud, promoting the uniform distribution of active sites during hydrothermal processes. It also inhibits the excessive formation of hydration products such as ettringite in red mud, preventing pore blockage and maintaining the adsorbent's high specific surface area and high adsorption performance. After calcination, some carboxyl groups remain, enhancing the coordination adsorption performance for components such as copper and nickel, thereby improving the fixation effect on metal ions. However, it is important to note that excessive citric acid should not be added to the system, otherwise it may cause the active components in the red mud to dissolve, leading to a decrease in the adsorption effect of the adsorbent and a reduction in its strength support performance in the geopolymer.

[0015] Preferably, in step S1, a mixture of sodium carbonate and sodium bicarbonate is added to adjust the pH of the system to 9-11.

[0016] Overall, using an alkaline environment for hydrothermal treatment is the optimal range for the dissolution and reprecipitation of aluminosilicates in red mud, promoting the formation of zeolite-like minerals or hydrotalcite-like structures. These mineral structures have interlayer anion exchange capabilities, which can capture heavy metal oxygen-containing anions (such as lead oxide and chromate), while inhibiting the hydrolytic degradation of cellulose to maintain the integrity of the cellulose structure and provide a better carbon skeleton structure for subsequent calcination.

[0017] Preferably, in step S1, the liquid-to-solid ratio in the hydrothermal treatment process is 5–10:1, and / or, The temperature in step S1 is 100–150°C, and / or, The processing time for step S1 is 6 to 12 hours.

[0018] Overall, after the above hydrothermal treatment, the active components of the material are highly dispersed, and the adsorption of the fiber-containing adsorbent material in the red mud slag is also good. The overall adsorption performance and capacity of heavy metals and organic matter are significantly improved, and it has good stability.

[0019] Preferably, in step S2, a two-step calcination method is adopted: first, calcination is carried out at 150-200°C for 30-60 minutes, and then calcination is carried out at 400-600°C for 120-240 minutes.

[0020] In the above scheme, a two-step calcination method is adopted. The main purpose of low-temperature calcination is to remove water physically adsorbed in the system, avoid the explosion of water vapor caused by rapid high-temperature heating, maintain the mechanical strength of the material, and at the same time, cellulose undergoes preliminary pyrolysis in this temperature range to form a stable carbonaceous intermediate, avoiding pore collapse caused by subsequent rapid high-temperature carbonization. The high-temperature short-term calcination, using a shorter time and lower temperature, avoids the decrease in specific surface area caused by long-term high-temperature sintering, which would affect the adsorption performance. On the other hand, it promotes the conversion of goethite (α-FeOOH) to hematite (α-Fe2O3) and gibbsite to active alumina, providing better chemical adsorption performance.

[0021] Preferably, in step S2, the heating rate during the process of calcining from low temperature to high temperature is 8-15℃ / min.

[0022] Within the above temperature range, the decrease in mechanical strength caused by excessively rapid heating can be avoided, and the ash content in the prepared adsorbent material can be reduced. However, excessively slow heating will not only reduce production efficiency, but also cause excessive oxidation of organic matter in the system, which will lead to a decrease in its adsorption performance for heavy metals and organic matter.

[0023] Preferably, in step S5, the geopolymer is configured to contain the following components in parts by mass: 50 portions of the dried product obtained in step S4 5-10 parts of metakaolin 5-10 parts of reinforcing material 15-30 parts of activator.

[0024] More preferably, in step S5, the water-to-binder ratio of the geopolymer is 0.3 to 0.4.

[0025] The above-mentioned formulation of the geopolymer has good overall mechanical properties. Furthermore, the use of metakaolin can further improve the fixation of heavy metal properties and enhance its resistance to acid rain erosion. The leaching under acidic conditions is further reduced, which also helps to control the casting and molding effect, thus balancing strength and fluidity.

[0026] In summary, this application employs a series of steps including hydrothermal treatment, co-calcination, wastewater treatment, phosphorylation, and fixation. A composite adsorption system is formed by hydrothermal treatment of fibrous organic adsorbent material and red mud slag. After calcination, phosphoric acid is used for further fixation. Subsequent preparation of geopolymers or other concrete systems can achieve better heavy metal fixation effects. Detailed Implementation

[0027] The technical solution of this application will be further described through the following specific embodiments.

[0028] The following embodiments provide a series of methods for treating acidic mine inrush water using red mud slag. To control the results of laboratory experiments, this application provides a solution for simulating acidic mine inrush water, and the specific preparation method is as follows: Weigh out lead nitrate, cadmium nitrate, copper nitrate, and zinc nitrate according to the following ion concentrations: Pb 2+ 80 mg / L; Zn 2+ 200 mg / L; Cu 2+ 150 mg / L; Cd 2+ 10 mg / L.

[0029] After the above system is prepared, make up the volume, add dilute nitric acid, adjust the pH to 3.0, mix well and set aside.

[0030] Example 1, the specific steps included in this application are as follows: S1. According to the mass fraction, 100 parts of dried red mud residue and 20 parts of dried distiller's grains were added to a stainless steel reactor, along with 0.3 parts by mass of sodium citrate. Then, water was added to bring the solid-liquid ratio to 8:1. The reactor was stirred at 200 rpm, and a mixed solution of sodium carbonate and sodium bicarbonate was added simultaneously until the pH reached 10.0 ± 0.2. The reactor was then sealed, the temperature was raised to 120°C, and the reaction was carried out for 8 hours. The mixture was then allowed to cool naturally to room temperature, filtered, and the filter cake was dried at a temperature not exceeding 40°C to obtain the composite adsorption system. The red mud residue was taken from an alumina manufacturer, and after natural air drying, it was passed through a 100-mesh sieve for later use. Its composition was determined as follows: Iron oxide 49.0% Alumina 18.1% 7.7% silicon dioxide Calcium oxide 5.7% Sodium oxide 4.5% Titanium dioxide 4.4% The balance consists of water and other metals, metal oxides, metal salts, or metal hydroxides comprising less than 2% by mass.

[0031] The lees were taken from a brewery, and after preliminary centrifugation and dehydration, they were naturally dried and pulverized to 100 mesh. According to the product's factory test, the cellulose content was 27.0%, crude protein 22.5%, crude fat 4.1%, hemicellulose 8.4%, lignin 24.1%, and the remainder was residual sugar, minerals, and other trace components.

[0032] S2. Add the composite adsorption system obtained in step S1 into a muffle furnace. First, heat the system to 180°C at 10°C / min and hold for 45 min. Then, heat the system to 500°C at 10°C / min and hold for 180 min. After that, allow it to cool naturally, grind it, and pass it through an 80-mesh sieve to obtain the composite treatment agent. S3. According to the ratio of 1L simulated mine inrush water to 20g composite treatment agent, add the composite treatment agent into the simulated mine inrush water, mechanically stir at 200rpm for 2h, then let it stand and settle for 30min, and obtain filter cake and supernatant by centrifugation.

[0033] S4. The solid-liquid mixture obtained in step S3 is added to water at a solid-liquid ratio of 1:5. After being fully dispersed, sodium dihydrogen phosphate is added at a mass ratio of 20g composite treatment agent to 0.77g sodium dihydrogen phosphate (i.e., phosphorus: composite treatment agent = 0.01:1). The mixture is then stirred and soaked at 40°C for 4 hours. After filtration, the mixture is rinsed with water until the supernatant is neutral. The filter cake is dried at 105°C until the temperature is constant, then ground and passed through a 100-mesh sieve.

[0034] S5. Prepare the raw materials for preparing geopolymers according to the following proportions: 50 parts of the pulverized adsorbent obtained in step S4; Metakaolin, crushed to 300 mesh, 8 parts; Eight parts of reinforcing agent, including five parts of grade I fly ash and three parts of PVA fiber (average diameter 50μm, average length 10mm). The activator consists of 25 parts, including 15 parts water glass and 10 parts of a 50% sodium hydroxide aqueous solution.

[0035] Add the above components to water, control the water-to-binder ratio to 0.35 (including water in the activator), stir for 5 minutes, pour into the mold, then vibrate at a frequency of 50 Hz for 60 seconds, cure at 25°C and RH>95% for 24 hours, demold, and then cure for 28 days.

[0036] Example 2 differs from Example 1 in that the mass fraction of the distiller's grains is 30 parts.

[0037] Example 3 differs from Example 1 in that the mass fraction of the distiller's grains is 10 parts.

[0038] Example 4 differs from Example 1 in that the distiller's grains are replaced with an equal mass of straw powder, which is then pulverized to 100 mesh.

[0039] Example 5 differs from Example 1 in that the lees are replaced with an equal mass of vinegar lees (equal mass by dry weight), which are initially centrifuged and dehydrated, then naturally dried and pulverized to 100 mesh (long fermentation residue of a certain aged vinegar).

[0040] Example 6 differs from Example 1 in that sodium citrate is not added in step S1.

[0041] Example 7 differs from Example 1 in that, in step S1, the mass fraction of sodium citrate is 0.5 parts by mass.

[0042] Example 8 differs from Example 1 in that, in step S1, the mass fraction of sodium citrate is 0.1 parts by mass.

[0043] Example 9 differs from Example 1 in that, in step S1, the mass fraction of sodium citrate is 1 part by mass.

[0044] Example 10 differs from Example 1 in that, in step S2, it is directly calcined at 500°C for 210 minutes.

[0045] Meanwhile, the following comparative examples are designed to be compared with the implementation examples.

[0046] Compared with Example 1, the difference is that in step S1, no lees are added.

[0047] Compared with Example 1, Example 2 is different in that, in step S1, no hydrothermal reaction is carried out, and the same proportion as in Example 1 is used to directly impregnate the sample at 20°C for 8 hours.

[0048] Compared with Example 1, Example 3 differs in that the mass ratio of distiller's grains to red mud residue is 0.5:1.

[0049] Compared with Example 1, Example 4 does not involve phosphorylation. Instead, after adsorption in step S3, the residual solid is directly dried and added to the preparation of the geopolymer.

[0050] The effects of the above embodiments and comparative examples were verified by the following methods.

[0051] 1. Adsorption experiment: In step S4, the ion concentration in the residual clear liquid is measured to measure the removal effect of the adsorbents prepared in the above examples and control examples on various heavy metal ions.

[0052] 2. Simulated Acid Leaching Experiment: After curing the geopolymer obtained in step S5 for 28 days, an acid solution with a pH of 4 was prepared using nitric acid. The solution was leached at 20°C with a solid-liquid ratio of 1:20 for 28 days. The pH of the system was measured daily using a pH meter, and nitric acid was added to stabilize the pH at 4. After 28 days, the concentration of metal ions in the solution was measured, and the dissolution rate of heavy metal ions per unit volume of geopolymer was calculated. Based on the adsorption amount in Experiment 1, the dissolution ratio of heavy metal ions under the above conditions was calculated by the ratio of the total dissolved metal amount to the total adsorbed metal amount.

[0053] The concentration of metal ions was determined by atomic absorption spectrometry.

[0054] In addition, the 28-day flexural strength of the geopolymer obtained in step S5 of GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)" is determined.

[0055] The experimental results of Examples 1-10 and Control Examples 1-4 are shown in the table below.

[0056] The experimental results show that, compared to the simple red mud slag system in Control Example 1, the red mud slag system using distiller's grains composite material provides better heavy metal ion adsorption performance. The use of fibrous materials such as distiller's grains can effectively improve the adsorption and fixation performance of the treatment agent for heavy metals. It can be seen that, in addition to providing better adsorption, even after fixation with phosphoric acid, Control Example 1 also produced a greater heavy metal leaching effect during dissolution. This may be because, in Example 1, even when some metal ions were leached due to acidity, the coordination properties of residual carboxyl groups reduced the leaching effect. Comparing Examples 2-5 and Control Example 3, it can be seen that in Control Example 3, excessive addition of distiller's grains actually led to a decrease in overall adsorption performance. This may be because excessive ash was generated during calcination, resulting in a decrease in overall porosity. In Examples 4 and 5, straw powder and vinegar residue were used instead, and the overall effect was slightly worse than that of distiller's grains. In Control Example 2, due to the lack of hydrothermal treatment, the overall adsorption performance decreased significantly. In contrast, in Comparative Example 4, it can be seen that phosphorylation treatment has a significant effect on the fixation of metal ions.

[0057] In Examples 6-9, the addition of citric acid was adjusted. Citric acid not only provided better adsorption but also stronger immobilization performance for heavy metal ions. However, in Example 9, the excessive addition of citric acid led to the leaching of a small amount of citric acid during the preparation of the geopolymer, which may have interfered with the hydration reaction and negatively impacted the strength of the geopolymer. In Example 10, high-temperature calcination was directly employed. The most obvious problem was that it easily led to pore blockage. On the one hand, this affected the adsorption performance for heavy metal ions; on the other hand, it also affected the hydration reaction during the subsequent preparation of the geopolymer, resulting in a certain loss of overall strength.

[0058] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for treating acidic mine water with red mud residue, characterized in that, It includes the following steps: S1. Red mud slag and fiber-containing organic adsorbent material are hydrothermally treated to form a composite adsorption system, wherein the mass ratio of the fiber-containing organic adsorbent material to the red mud slag is 0.1 to 0.3:

1. S2. The composite adsorption system obtained in step S1 is calcined at a temperature not exceeding 800℃ to obtain a composite treatment agent. S3. Adsorbent is obtained by treating acidic mine water with a composite treatment agent; S4. Treat the adsorbent with phosphate solution; S5. Prepare geopolymers by using the impregnated adsorbent as a gel material or as part of a gel material.

2. The method for treating acidic mine water with red mud slag according to claim 1, characterized in that, In step S4, the mass of phosphorus in the phosphate solution is 0.005 to 0.02 times the mass of the composite treatment agent, and / or, In step S4, the solid-liquid ratio of phosphoric acid impregnation is 3–10:1, and / or, The temperature in step S4 shall not exceed 40°C.

3. The method for treating acidic mine water with red mud slag according to claim 1, characterized in that, The fiber-containing organic adsorbent material is distiller's grains, and the distiller's grains are dried before use so that their moisture content is not higher than 60%.

4. The method for treating acidic mine water with red mud slag according to claim 3, characterized in that, In step S1, 0.1 to 0.5% of citric acid or water-soluble citric acid salt by weight of red mud residue is also added.

5. The method for treating acidic mine water with red mud slag according to claim 3, characterized in that, In step S1, a mixture of sodium carbonate and sodium bicarbonate is added, and the pH of the system is adjusted to 9-11.

6. The method for treating acidic mine water with red mud slag according to claim 1, characterized in that, In step S1, the liquid-to-solid ratio in the hydrothermal treatment process is 5–10:1, and / or, The temperature in step S1 is 100–150°C, and / or, The processing time for step S1 is 6 to 12 hours.

7. The method for treating acidic mine water with red mud slag according to claim 1, characterized in that, In step S2, a two-step calcination method is adopted: first, calcination is carried out at 150-200℃ for 30-60 minutes, and then calcination is carried out at 400-600℃ for 120-240 minutes.

8. A method for treating acidic mine water with red mud slag according to claim 7, characterized in that, In step S2, during the process of calcining from low temperature to high temperature, the heating rate is 8-15℃ / min.

9. A method for treating acidic mine water with red mud slag according to claim 1, characterized in that, In step S5, the geopolymer is specifically configured to include the following components by mass: 50 portions of the dried product obtained in step S4 5-10 parts of metakaolin 5-10 parts of reinforcing material 15-30 parts of activator.

10. A method for treating acidic mine water with red mud slag according to claim 9, characterized in that, In step S5, the water-cement ratio of the geopolymer is configured to be 0.3 to 0.4.

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