Method for treating chromite alkaline leaching tailings through microorganism mineralization

Abstract

The invention provides a method for treating chromite alkaline leaching tailings by microbial mineralization, which comprises the following steps: improving the reduction efficiency of Cr (VI) by utilizing a specific mixed flora through synergistic metabolism, efficiently reducing hexavalent chromium into trivalent chromium under a mild condition, and promoting a reduction product to be further converted into a stable chromium-containing mineral phase by virtue of the induction effect of an iron source and a mineralizing agent, so that the chromite alkaline leaching tailings are subjected to microbial mineralization treatment. The long-term stable curing of Cr is realized, and the problems of Cr (VI) redissolution and secondary pollution which are easy to occur in a traditional chemical detoxification method are fundamentally solved. The technological process is easy to operate and low in energy consumption, high-temperature and high-pressure or complex equipment is not needed, the toxic leaching concentration of the treated chromite alkaline leaching tailings is remarkably lower than the hazardous waste identification standard, enrichment of valuable elements such as chromium and iron in a stable mineral form can be promoted, follow-up resource recycling is facilitated, and good environmental benefits and resource potential are achieved.

Description

Technical Field

[0001] This application relates to the field of heavy metal microbial detoxification technology, and more specifically, to a method for microbial mineralization treatment of chromite alkaline leaching tailings. Background Technology

[0002] Currently, the traditional high-temperature oxidative roasting process for producing chromium salts from chromite resources has long been used, resulting in problems such as low chromium recovery rates, large amounts of solid waste generation, difficulties in end-of-pipe treatment, and low levels of resource recycling. In recent years, the liquid-phase oxidation method for chromite, employing a high-concentration alkaline medium for full wet leaching, has effectively solved these problems, achieving efficient separation of chromium and iron and good chromium recovery. However, this process produces a large amount of chromium-containing alkaline leaching tailings, which, due to their high content of chromium, iron, and other elements, pose both potential environmental risks and significant economic value.

[0003] Currently, dry or wet chemical detoxification processes are mainly used to treat chromium-containing alkaline leaching tailings. However, due to changes in the external environment or incomplete treatment, large amounts of Cr(VI) in the treated chromium slag often "redissolve," and after long-term precipitation leaching, it enters the surrounding environment, causing serious secondary pollution. Therefore, there is an urgent need to provide a novel microbial detoxification method for chromium-containing tailings to overcome the poor adaptability of existing processes to chromite alkaline leaching tailings. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for microbial mineralization treatment of alkaline leaching tailings from chromite ore. This method utilizes a specific mixed microbial community to efficiently reduce hexavalent chromium to trivalent chromium under mild conditions, and forms a stable precipitate through mineralization. This fundamentally overcomes the problems of Cr(VI) redissolution and secondary pollution that easily occur in traditional chemical detoxification methods. The method provided by this invention has a simple process flow and low energy consumption. While achieving deep detoxification of the tailings and meeting leaching toxicity standards, it effectively promotes the stable solidification and resource recovery potential of valuable elements such as chromium and iron.

[0005] In a first aspect, the present invention provides a method for microbial mineralization treatment of chromite alkaline leaching tailings, the method comprising: S1. The chromite alkali leaching tailings are ground and then slurried to obtain a slurry, and the pH of the slurry is adjusted to 7-9. S2. The pH-adjusted slurry, mixed bacterial solution, iron source, and mineralizing agent are mixed and stirred so that the hexavalent chromium in the chromite alkaline leaching tailings undergoes a reduction reaction under the action of the mixed bacterial solution, and is reduced to trivalent chromium. The trivalent chromium then undergoes a mineralization reaction with the iron source and mineralizing agent to form a precipitate, thus obtaining a solid-liquid mixture. S3. After the solid product in the solid-liquid mixture meets the leaching toxicity standard requirements, the solid-liquid mixture is filtered and washed to obtain detoxification tailings. The microorganisms in the mixed bacterial solution are selected from at least two of Bacillus megaterium, Pseudomonas putida, Oligotrophosporium and Paleobacterium.

[0006] Optionally, in step S1, more than 50% of the chromite alkali leaching tailings after grinding have a particle size of no more than 0.15 mm.

[0007] Optionally, in step S1, the slurry preparation agent is water, and the liquid-solid ratio of the water to the ground chromite alkali leaching tailings is 4:1-8:1.

[0008] Optionally, the method for culturing microorganisms in the mixed bacterial solution includes: At least two of the following bacteria—Bacillus megaterium, Pseudomonas putida, Oligotrophosporium, and Bacillus cereus—are inoculated into alkaline NB liquid medium containing hexavalent chromium and cultured at 30 ℃-35 ℃ for 7 days. Then transfer the inoculum at a 10% v / v rate and continue to acclimate the microorganisms for 2-4 cycles, with each cycle lasting 7 days. The domesticated strain was cultured in NB liquid medium at an inoculation rate of 10% v / v. The cultured bacterial solutions were then mixed in equal volume ratios to obtain the mixed bacterial solution.

[0009] Optionally, the content of hexavalent chromium in the alkaline NB liquid culture medium is 100 mg / L-200 mg / L.

[0010] Optionally, the volume-to-mass ratio of the mixed bacterial solution to the chromite alkali leaching tailings is 0.2 L:1 kg to 0.4 L:1 kg.

[0011] Optionally, the iron source is ferric chloride or ferric sulfate; The mineralizing agent is calcium hydrogen phosphate or calcium gluconate.

[0012] Optionally, in step S2, the concentration of iron ions in the iron source is not less than 0.05 mol / L, and the concentration of metal ions in the mineralizing agent is not less than 0.05 mol / L.

[0013] Optionally, in step S2, the temperature of the reduction reaction and the mineralization reaction is 30 ℃-35 ℃; The total time for the reduction reaction and the mineralization reaction is 3-7 days; The stirring speed is 90 r / min-150 r / min.

[0014] Optionally, in step S3, after the solid product in the solid-liquid mixture meets the leaching toxicity standard requirements, the total chromium content in the solid-liquid mixture is less than 1 mg / L.

[0015] In summary, the present invention has at least one of the following beneficial technical effects: 1. This invention provides a method for microbial mineralization treatment of alkaline leaching tailings of chromite ore. Through a specific mixed bacterial community, hexavalent chromium is efficiently reduced to trivalent chromium under mild conditions, and a stable precipitate is formed through mineralization. This fundamentally overcomes the problems of Cr(VI) redissolution and secondary pollution that easily occur in traditional chemical detoxification methods. The method provided by this invention has a simple process flow and low energy consumption. While achieving deep detoxification of the tailings and meeting leaching toxicity standards, it effectively promotes the stable solidification and resource potential of valuable elements such as chromium and iron. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A flowchart of a method for microbial mineralization treatment of chromite alkaline leaching tailings provided in an embodiment of the present invention is shown. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention. Furthermore, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of the present invention.

[0019] Specific experimental steps or conditions are not specified in the embodiments; they can be performed according to the conventional experimental steps or conditions described in the prior art. Reagents and other instruments used, unless otherwise specified, are all commercially available conventional reagent products. Furthermore, the accompanying drawings are merely illustrative diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore, repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0020] Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of this specification.

[0021] In the description of this invention, it should be understood that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0022] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] In related technologies, chromite resources have long relied on traditional high-temperature oxidative roasting processes to produce chromium salts, which suffers from problems such as low chromium recovery rates, large amounts of solid waste generation, high difficulty in end-of-pipe treatment, and insufficient resource recycling. In recent years, the liquid-phase oxidation process for chromite, using a high-concentration alkaline medium for full wet leaching, has effectively solved these problems, achieving the separation of chromium and iron and efficient chromium recovery. However, the large amount of chromium-containing alkaline leaching tailings generated during this process, due to its high content of chromium and iron, poses both potential environmental risks and significant economic value.

[0024] Currently, these chromium-containing alkaline leaching tailings can be treated using dry or wet chemical detoxification processes. Although this can temporarily alleviate the chromium pollution problem, due to changes in external conditions and incomplete treatment, the treated chromium slag is prone to a large amount of Cr(VI) "redissolution" phenomenon. After long-term precipitation leaching, it enters the surrounding environment, causing serious secondary pollution.

[0025] For example, CN116219176A discloses a method for smelting chromium-containing pig iron from vanadium-chromium slag tailings using a vanadium-chromium slag calcification process. This method involves stepwise smelting and casting of the chromium-containing tailings to obtain chromium-containing pig iron, achieving resource recovery of chromium. However, this method is mainly for vanadium-containing tailings from chromium extraction, and the reaction needs to be carried out at high temperatures, resulting in high energy consumption.

[0026] CN117551868A proposes a method for preparing chromium-silicon-ferroalloy by co-reduction of hazardous waste chromium slag and siderite using magnetic field enhancement. This method involves grinding chromium slag and siderite into pellets, followed by reduction roasting to obtain chromium-silicon-ferroalloy and high-MgO tailings, achieving the co-utilization of industrial solid waste, low-grade iron ore, and crop straw. However, this process also has high energy consumption and a long workflow.

[0027] CN120169785A discloses a method for co-treating chromium-containing sludge using waste dust collector bags and blast furnace dust. The method involves mixing the ash obtained from roasting the waste dust collector bags with blast furnace dust and then adding the mixture to the chromium-containing sludge. After filtration, drying, roasting, water cooling, grinding, and magnetic separation, chromium-containing iron spinel concentrate and low-chromium tailings are obtained, thus solidifying hexavalent chromium and achieving the harmless treatment of the chromium-containing sludge. Furthermore, existing literature has proposed new technologies for detoxifying chromium slag using yellow phosphorus tail gas, waste polyethylene plastics, and biomass waste. Through the coupled utilization of solid waste across industries, the potential of solid waste is fully explored, achieving "waste treatment with waste" to a certain extent. However, these methods generally suffer from high energy consumption, low efficiency, and harsh reaction conditions, posing a significant risk of secondary pollution, and have not yet been widely applied in industry.

[0028] Compared with the aforementioned detoxification processes, microbial detoxification technology has significant advantages in terms of greenness and environmental friendliness, and has become an important development direction in the field of chromite resource recycling. Therefore, it is urgent to propose a novel microbial detoxification method for chromium-containing tailings to solve the problem that existing processes are difficult to apply to chromite alkaline leaching tailings.

[0029] Based on this, embodiments of the present invention provide a method for microbial mineralization treatment of chromite alkaline leaching tailings. Figure 1 A flowchart of a method for microbial mineralization treatment of chromite alkaline leaching tailings provided in an embodiment of the present invention is shown, as follows: Figure 1 As shown, the method includes: Step S1: The chromite alkali leaching tailings are ground and then slurried to obtain a slurry, and the pH of the slurry is adjusted to 7-9. In some embodiments, the alkali leaching tailings of chromite can be crushed first and then ground. In some embodiments, in step S1, more than 50% of the chromite alkali leaching tailings after grinding have a particle size of no more than 0.15 mm. In this embodiment of the invention, by controlling the fineness of the alkaline leaching tailings particles after grinding, more than half of the particles are no larger than 0.15 mm in size, thereby increasing the specific surface area of ​​the alkaline leaching tailings, enhancing the contact efficiency between microorganisms and alkaline leaching tailings particles, and promoting the full progress of the reduction reaction of hexavalent chromium and subsequent mineralization processes.

[0030] In some embodiments, in step S1, the slurry preparation agent is water, and the liquid-solid ratio of the water to the ground chromite alkali leaching tailings is 4:1-8:1.

[0031] For example, the liquid-to-solid ratio of water to the ground chromite leaching tailings is 4:1, 5:1, 6:1, 7:1, or 8:1. In this embodiment of the invention, by controlling the liquid-to-solid ratio of the slurry within the range of 4:1 to 8:1, the slurry is ensured to have suitable fluidity, providing sufficient conditions for mass transfer and mixing reaction of microorganisms, leaching tailings particles, and reaction reagents (iron source and mineralizer), while avoiding increased load on subsequent processing and waste of resources due to excessive water.

[0032] Step S2: The pH-adjusted slurry, mixed bacterial solution, iron source, and mineralizer are mixed and stirred so that the hexavalent chromium in the chromite alkaline leaching tailings undergoes a reduction reaction under the action of the mixed bacterial solution, reducing it to trivalent chromium. The trivalent chromium then reacts with the iron source and the mineralizer to form a precipitate, thus obtaining a solid-liquid mixture. In some embodiments, the reagent for adjusting the pH of the slurry is sulfuric acid or calcium hydroxide; In some embodiments, the microorganisms in the mixed bacterial solution are selected from at least two of Bacillus megaterium, Pseudomonas putida, Oligotrophosporium and Paleobacterium.

[0033] This invention constructs a synergistic composite microbial community system by combining at least two functionally complementary microbial species from Bacillus megaterium, Pseudomonas putida, Oligotrophosporium, and Bacillus cereus. This mixed microbial community enhances the reduction efficiency and stability of hexavalent chromium under high alkalinity and high chromium stress through the synergistic effect of multiple metabolic pathways, avoiding the limitations of insufficient functionality or poor environmental adaptability of single microbial species, thereby improving the detoxification of alkaline leaching tailings and the reliability of the process.

[0034] In some embodiments, the method for culturing microorganisms in the mixed bacterial solution includes: Step S11: Inoculate at least two of the following: Bacillus megaterium, Pseudomonas putida, Oligotrophosporium and Bacillus cereus into alkaline NB liquid medium containing hexavalent chromium, and culture at 30 ℃-35 ℃ for 7 days. It should be noted that NB liquid medium is a nutrient broth medium, the main components of which are peptone, beef extract (or beef extract powder) and sodium chloride. The preparation steps are as follows: Weigh 18 g of culture medium powder, add 1 liter of distilled water or deionized water, stir and heat until completely dissolved; dispense into Erlenmeyer flasks, autoclave at 121 ℃ for 15 min, and let cool to room temperature for later use; The pH of NB liquid medium is 8-9; In some embodiments, the content of hexavalent chromium in the alkaline NB liquid culture medium is 100 mg / L-200 mg / L.

[0035] Step S12: Transfer the inoculum at a rate of 10% v / v and continue to acclimate the microorganisms for 2-4 cycles, with each cycle lasting 7 days. It should be noted that a 10% v / v inoculum volume means that the volume of the inoculated bacterial solution accounts for 10% of the total volume of the culture system; for example, 10 mL of bacterial solution is added to 100 mL of culture medium.

[0036] Step S13: The domesticated strain is cultured in NB liquid medium at an inoculation rate of 10% v / v. The cultured bacterial solutions are then mixed in equal volume ratios to obtain the mixed bacterial solution.

[0037] This invention employs a phased chromium tolerance acclimatization and expansion method. First, multiple functional strains are subjected to multi-cycle progressive adaptive culture in a chromium-containing alkaline medium to effectively screen out dominant strains that maintain high activity in a high-chromium alkaline environment. Subsequently, a mixed bacterial solution is prepared by expanding the culture and mixing in equal volumes to ensure the rapid adaptability and efficient reduction capacity of the mixed bacterial community to the actual alkaline leaching tailings environment, significantly improving the bioreduction efficiency and mineralization stability of hexavalent chromium.

[0038] In some embodiments, the volume-to-mass ratio of the mixed bacterial solution to the chromite alkali leaching tailings is 0.2 L:1 kg to 0.4 L:1 kg.

[0039] For example, the volume-to-mass ratio of the mixed bacterial solution to the chromite alkali leaching tailings is 0.2 L:1 kg, 0.25 L:1 kg, 0.3 L:1 kg, 0.35 L:1 kg, and 0.4 L:1 kg. In this embodiment of the invention, by controlling the volume-to-mass ratio of the mixed bacterial solution to the chromite alkali leaching tailings within the range of (0.2-0.4) L:1 kg, it ensures that the functional microorganisms have sufficient biomass and activity concentration in the slurry system to efficiently initiate and complete the reduction and mineralization process of hexavalent chromium, while avoiding the increase in subsequent solid-liquid separation load and treatment cost caused by excessive addition of bacterial solution.

[0040] In some embodiments, the iron source is ferric chloride or ferric sulfate; The mineralizing agent is calcium hydrogen phosphate or calcium gluconate.

[0041] This invention effectively promotes the conversion of trivalent chromium into stable minerals by using ferric chloride or ferric sulfate as the iron source and calcium hydrogen phosphate or calcium gluconate as the mineralizing agent. The trivalent ferric ions provided by the iron source can co-precipitate and encapsulate the reduced trivalent chromium, while the calcium ions and anionic groups (such as phosphate) in the mineralizing agent further form stable, insoluble mineral phases (such as chromium phosphate and ferrochrome) with chromium and iron. This enhances the immobilization effect on the reduced chromium, fundamentally inhibiting the resolution and yellowing of Cr(VI), and improving the long-term environmental stability and resource utilization potential of the detoxification tailings.

[0042] In some embodiments, in step S2, the concentration of iron ions in the iron source is not less than 0.05 mol / L, and the concentration of metal ions in the mineralizing agent is not less than 0.05 mol / L.

[0043] In this embodiment of the invention, by controlling the concentrations of iron ions in the iron source and metal ions in the mineralizing agent to be no less than 0.05 mol / L, a sufficient supply of key ions required for the mineralization reaction is ensured. This provides sufficient thermodynamic driving force and reaction kinetic conditions for the co-precipitation of trivalent chromium with iron ions and mineralization components and the formation of stable mineral phases. This concentration range significantly enhances the immobilization efficiency and long-term stability of chromium while avoiding incomplete mineralization or loose structure caused by insufficient ion concentration. It achieves efficient in-situ sequestration of reduction products in complex systems and suppresses the risk of Cr(VI) re-dissolution.

[0044] In some embodiments, in step S2, the temperature of the reduction reaction and the mineralization reaction is 30 ℃-35 ℃; The total time for the reduction reaction and the mineralization reaction is 3-7 days; The stirring speed is 90 r / min-150 r / min.

[0045] It should be noted that the temperature during the mixing and stirring of the pH-adjusted slurry, mixed bacterial solution, iron source, and mineralizing agent is 30 ℃-35 ℃. During the stirring process, reduction reaction (microbial detoxification) and mineralization reaction occur. For example, the temperatures of the reduction and mineralization reactions are 30 ℃, 31 ℃, 32 ℃, 33 ℃, 34 ℃, and 35 ℃. In this embodiment of the invention, by controlling the reaction temperature within the range of 30 ℃–35 ℃, the optimal environmental conditions for the metabolism and reduction activity of functional microbial communities are provided, while promoting the thermodynamic process of chromite mineralization precipitation. The total time for the reduction and mineralization reactions is 3 days, 4 days, 5 days, 6 days, and 7 days. In this embodiment of the invention, a total reaction time of 3 to 7 days is set to ensure the full reduction of hexavalent chromium and the complete completion of subsequent mineral transformation, avoiding incomplete detoxification due to insufficient reaction time. The stirring speed is 90 r / min, 100 r / min, 110 r / min, 120 r / min, 130 r / min, 140 r / min, and 150 r / min. The embodiments of the present invention limit the stirring speed to 90–150 r / min, which enhances mass transfer efficiency, ensures sufficient contact and mixing of the inoculant, tailings, and reactant, and avoids damage to microbial activity caused by excessive shear force.

[0046] Step S3: After the solid product in the solid-liquid mixture meets the leaching toxicity standard requirements, the solid-liquid mixture is filtered and washed to obtain detoxification tailings. It should be noted that after detoxification, the solid-liquid mixture obtained (also known as detoxified tailings slurry) should have at least 500 g of detoxified tailings solid sample taken out, filtered, washed, and dried, and then subjected to toxicity leaching test. If the leaching toxicity does not meet the requirements of GB5085.3-2007, microbial detoxification should continue until the standard requirements are met. After that, it should be filtered and washed to obtain detoxified tailings, which can be used for further preparation of building materials or iron resource recovery. In some embodiments, the filtrate after filtration and the washing liquid after washing can be adsorbed using an ion exchange resin to recover a small amount of chromium. The adsorbed liquid is then returned to be used for slurry preparation of the alkaline leaching tailings of the ground chromite. Among them, ion exchange resins such as D301 and D201 can be selected.

[0047] In some embodiments, in step S3, after the solid product in the solid-liquid mixture meets the leaching toxicity standard requirements, the total chromium content in the solid-liquid mixture is less than 1 mg / L.

[0048] It should be noted that the total chromium content in the solid-liquid mixture after detoxification is less than 1 mg / L, indicating that the reduction of hexavalent chromium and the mineralization fixation of trivalent chromium are extremely thorough. Not only does the leaching toxicity of the solid product meet the hazardous waste identification standards, but the chromium residue in the liquid phase is also reduced to an extremely low level. This indicator fully demonstrates the high efficiency and integrity of the entire microbial mineralization and detoxification system provided in this embodiment of the invention.

[0049] To enable those skilled in the art to better understand this application, the following embodiments will be used to provide a detailed description of a method for microbial mineralization of chromite alkaline leaching tailings provided in this application.

[0050] Example 1 (1) The tailings from the alkali leaching of a chromite ore mine in Gansu were naturally dried and then ground until 70% of the particles were smaller than 0.15 mm. (2) Under the condition of a liquid-solid ratio of 5:1, deionized water and ground alkaline leaching tailings particles are mixed, and concentrated sulfuric acid is slowly added and stirred to adjust the slurry until the pH of the slurry reaches 8. (3) Four commercially available bacteria with chromium-reducing ability, namely Bacillus megaterium, Pseudomonas putida, Oligotrophosporium and Bacillus cereus, were inoculated into NB liquid medium containing 200 mg / L Cr(VI) and pH 8, and cultured at 30 °C for 7 days. Then, they were transferred at an inoculation rate of 10% v / v and the microbial domestication was carried out for 2 cycles with 7 days as one cycle. (4) The domesticated strains were cultured in NB liquid medium at an inoculation rate of 10% v / v. The obtained microbial liquids were prepared into mixed bacterial liquids in equal volumes. The liquid-solid ratio of the mixed bacterial liquid to the chromite leaching tailings was 0.4 L / kg. (5) Add the mixed bacterial solution of detoxifying microorganisms after domestication and expansion culture to the alkaline leaching tailings slurry, with ferric chloride as the iron source and calcium hydrogen phosphate as the mineralizing agent. After adding the alkaline leaching tailings slurry and stirring thoroughly, the concentrations of iron ions and calcium ions in the slurry are detected to ensure that they both reach 0.05 mol / L. (5) The slurry was subjected to microbial detoxification at a reaction temperature of 35 ℃ and a stirring speed of 100 r / min. After 7 days of detoxification, the detoxified tailings slurry was obtained.

[0051] (6) Take out about 650 g of solid sample of detoxification tailings from the detoxification tailings slurry, mix it with deionized water at a liquid-solid ratio of 10:1 and stir and wash it 3 times. After filtration and drying, conduct 16 toxicity leaching tests on the detoxification tailings in accordance with the requirements of GB 5085.3-2007. The test results are shown in Table 1. According to Table 1, the leaching toxicity of the detoxification tailings meets the requirements of GB 5085.3-2007. Table 1. Results of 16 toxicity leaching tests on detoxification tailings

[0052] (7) After filtering the detoxification tailings slurry, the filtrate is obtained. The filter residue is washed twice under the condition of liquid-solid ratio of 5:1 to obtain washing liquid and washed detoxification tailings. (8) After mixing the filtrate and washing liquid, the chromium in the filtrate was adsorbed and desorbed using macroporous anion exchange resin D301, and the chromium recovery rate reached 97.16%. The adsorbed liquid was returned to the slurry preparation stage to replace deionized water for slurry preparation.

[0053] The results of the analysis of the main elemental composition of the detoxified tailings after washing in step (7) are shown in Table 2. Among them, the iron content is 15.23%, and the detoxified tailings can be used for building material preparation.

[0054] Table 2. Main elemental composition of the detoxified tailings after washing

[0055] Example 2 (1) The tailings from the alkali leaching of a chromite ore mine in Gansu were naturally dried and then ground until 80% of the particles were smaller than 0.15 mm. (2) Under the condition of a liquid-solid ratio of 4:1, deionized water and ground alkaline leaching tailings particles are mixed, and concentrated sulfuric acid is slowly added and stirred to adjust the slurry until the pH of the slurry reaches 8. (3) Four commercially available bacteria with chromium-reducing ability, namely Bacillus megaterium, Pseudomonas putida, Oligotrophosporium and Bacillus cereus, were inoculated into NB liquid medium containing 200 mg / L Cr(VI) and pH 8, and cultured at 30 °C for 7 days. Then, they were transferred at an inoculation rate of 10% v / v and the microbial domestication was carried out for 2 cycles with 7 days as one cycle. (4) The domesticated strains were cultured in NB liquid medium at an inoculation rate of 10% v / v. The obtained microbial liquids were prepared into mixed bacterial liquids in equal volumes. The liquid-solid ratio of the mixed bacterial liquid to the chromite leaching tailings was 0.2 L / kg. (5) Add the mixed bacterial solution of detoxifying microorganisms after domestication and expansion culture to the alkaline leaching tailings slurry, with ferric chloride as the iron source and calcium hydrogen phosphate as the mineralizing agent. After adding the alkaline leaching tailings slurry and stirring thoroughly, the concentrations of iron ions and calcium ions in the slurry are detected to ensure that they both reach 0.07 mol / L. (5) The slurry was subjected to microbial detoxification at a reaction temperature of 30 ℃ and a stirring speed of 90 r / min. After 7 days of detoxification, the detoxified tailings slurry was obtained. (6) The remaining steps are the same as in Example 1.

[0056] Example 3 (1) The tailings from the alkali leaching of a chromite ore mine in Gansu were naturally dried and then ground until 60% of the particles were smaller than 0.15 mm. (2) Under the condition of a liquid-to-solid ratio of 8:1, deionized water and ground alkaline leaching tailings particles are mixed, and calcium hydroxide is slowly added and stirred to adjust the slurry until the pH of the slurry reaches 9. (3) Four commercially available bacteria with chromium-reducing ability, namely Bacillus megaterium, Pseudomonas putida, Oligotrophosporium and Bacillus cereus, were inoculated into NB liquid medium containing 200 mg / L Cr(VI) and pH 8, and cultured at 30 °C for 7 days. Then, they were transferred at an inoculation rate of 10% v / v and the microbial domestication was carried out for 2 cycles with 7 days as one cycle. (4) The domesticated strains were cultured in NB liquid medium at an inoculation rate of 10% v / v. The obtained microbial liquids were prepared into mixed bacterial liquids in equal volumes. The liquid-solid ratio of the mixed bacterial liquid to the chromite leaching tailings was 0.3 L / kg. (5) Add the mixed bacterial solution of detoxifying microorganisms after domestication and expansion culture to the alkaline leaching tailings slurry, with ferric chloride as the iron source and calcium hydrogen phosphate as the mineralizing agent. After adding the alkaline leaching tailings slurry and stirring thoroughly, the concentrations of iron ions and calcium ions in the slurry are detected to ensure that they both reach 0.08 mol / L. (5) The slurry was subjected to microbial detoxification at a reaction temperature of 33 ℃ and a stirring speed of 150 r / min. After 7 days of detoxification, the detoxified tailings slurry was obtained. (6) The remaining steps are the same as in Example 1.

[0057] In summary, the microbial mineralization method for treating alkaline leaching tailings of chromite ore provided in this embodiment of the invention has advantages such as simple process flow, mild treatment conditions, and significantly reduced energy consumption. It effectively avoids the problems of high energy consumption and long process flow associated with traditional high-temperature roasting processes, achieving efficient detoxification in a short process, and ensuring that the leaching toxicity of the treated tailings stably meets national standards. This method also enables the full resource utilization of elements such as iron and chromium in the alkaline leaching tailings. The detoxified tailings can be used to prepare building materials or recover iron resources, and the washing liquid generated during the treatment process can also recover chromium through resin adsorption, effectively improving the level of resource recycling.

[0058] Furthermore, this method can significantly reduce the additional investment and operating costs for chromium salt production enterprises in the solid waste detoxification process, thereby reducing the unit production cost of basic chromium chemical products, enhancing the economic benefits of enterprises, and providing low-cost raw materials for downstream deep processing and resource utilization. More importantly, this technology can achieve long-term and stable remediation of difficult-to-treat chromium slag hazardous waste, sustainably solve the Cr(VI) redissolution and "yellowing" phenomenon after detoxification, and powerfully promote the green, low-carbon, and clean utilization of chromite resources.

[0059] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0060] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0061] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0062] The above provides a detailed description of a method for microbial mineralization treatment of chromite alkaline leaching tailings provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and its core ideas. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for microbial mineralization treatment of chromite alkaline leaching tailings, characterized in that, The method includes: S1. The chromite alkali leaching tailings are ground and then slurried to obtain a slurry, and the pH of the slurry is adjusted to 7-9. S2. The pH-adjusted slurry, mixed bacterial solution, iron source, and mineralizing agent are mixed and stirred so that the hexavalent chromium in the chromite alkaline leaching tailings undergoes a reduction reaction under the action of the mixed bacterial solution, and is reduced to trivalent chromium. The trivalent chromium then undergoes a mineralization reaction with the iron source and mineralizing agent to form a precipitate, thus obtaining a solid-liquid mixture. S3. After the solid product in the solid-liquid mixture meets the leaching toxicity standard requirements, the solid-liquid mixture is filtered and washed to obtain detoxification tailings. The microorganisms in the mixed bacterial solution are selected from at least two of Bacillus megaterium, Pseudomonas putida, Oligotrophosporium and Paleobacterium.

2. The method for microbial mineralization treatment of chromite alkaline leaching tailings according to claim 1, characterized in that, In step S1, more than 50% of the chromite alkali leaching tailings after grinding have a particle size of no more than 0.15 mm.

3. The method for microbial mineralization treatment of chromite alkaline leaching tailings according to claim 1, characterized in that, In step S1, the slurry preparation agent is water, and the liquid-solid ratio of the water to the ground chromite alkali leaching tailings is 4:1-8:

1.

4. The method for microbial mineralization treatment of chromite alkaline leaching tailings according to claim 1, characterized in that, The microbial culture method in the mixed bacterial solution includes: At least two of the following bacteria—Bacillus megaterium, Pseudomonas putida, Oligotrophosporium, and Bacillus cereus—are inoculated into alkaline NB liquid medium containing hexavalent chromium and cultured at 30 ℃-35 ℃ for 7 days. Then transfer the inoculum at a 10% v / v rate and continue to acclimate the microorganisms for 2-4 cycles, with each cycle lasting 7 days. The domesticated strain was cultured in NB liquid medium at an inoculation rate of 10% v / v. The cultured bacterial solutions were then mixed in equal volume ratios to obtain the mixed bacterial solution.

5. The method for microbial mineralization treatment of chromite alkaline leaching tailings according to claim 4, characterized in that, The content of hexavalent chromium in the alkaline NB liquid culture medium is 100 mg / L-200 mg / L.

6. The method for microbial mineralization treatment of chromite alkaline leaching tailings according to claim 1 or 4, characterized in that, The volume-to-mass ratio of the mixed bacterial solution to the chromite alkali leaching tailings is 0.2 L: 1 kg to 0.4 L: 1 kg.

7. The method for microbial mineralization treatment of chromite alkaline leaching tailings according to claim 1, characterized in that, The iron source is ferric chloride or ferric sulfate; The mineralizing agent is calcium hydrogen phosphate or calcium gluconate.

8. The method for microbial mineralization treatment of chromite alkaline leaching tailings according to claim 1 or 7, characterized in that, In step S2, the concentration of iron ions in the iron source is not less than 0.05 mol / L, and the concentration of metal ions in the mineralizing agent is not less than 0.05 mol / L.

9. The method for microbial mineralization treatment of chromite alkaline leaching tailings according to claim 1, characterized in that, In step S2, the temperature of the reduction reaction and the mineralization reaction is 30 ℃-35 ℃; The total time for the reduction reaction and the mineralization reaction is 3-7 days; The stirring speed is 90 r / min-150 r / min.

10. The method for microbial mineralization treatment of chromite alkaline leaching tailings according to claim 1, characterized in that, In step S3, after the solid product in the solid-liquid mixture meets the leaching toxicity standard requirements, the total chromium content in the solid-liquid mixture is less than 1 mg / L.

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