A method for enhancing uranium ore bioleaching based on sulfur autotrophic denitrification pre-desulfurization
By removing the sulfide coating on the surface of uranium ore through sulfur autotrophic denitrification pretreatment, combined with bioleaching by Acidophilic Thiobacillus ferrooxidans, the problems of high mass transfer resistance and slow leaching rate of uranium ore were solved, achieving efficient extraction and low-cost pretreatment of uranium ore.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHONGHE FUZHOU JINAN URANIUM IND CO LTD
- Filing Date
- 2026-05-11
- Publication Date
- 2026-06-30
AI Technical Summary
When processing low-grade uranium ore, existing bioleaching technologies suffer from high energy consumption and large equipment investment due to the physical barrier formed by the sulfide inclusions in the uranium ore, which increases mass transfer resistance and slows reaction kinetics. This makes large-scale application difficult.
The sulfur autotrophic denitrification technology is adopted, which utilizes sulfur autotrophic denitrifying bacteria under anaerobic conditions to selectively oxidize and remove the sulfide coating layer on the surface of uranium ore using sulfide-iron compounds in uranium ore as electron donors and nitrates as electron acceptors. Subsequently, acidophilic ferrooxidizing thiobacillus is inoculated for bioleaching.
It significantly improved the exposure of uranium mineral surfaces, increased bioleaching efficiency, and raised the uranium leaching rate from 41.2% to 66.5%, a relative increase of 61%. Furthermore, the method has low operating costs and is easy to apply industrially.
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Figure CN122303585A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of uranium metallurgy technology, and in particular to a method for enhancing uranium ore bioleaching based on sulfur autotrophic denitrification pre-desulfurization. Background Technology
[0002] Uranium is a strategic and critical resource for the development of the nuclear industry. With the gradual depletion of easily processed uranium ore resources, the proportion of mining low-grade, complex associated uranium ore is increasing year by year, making the research on economical and efficient extraction technologies an important issue that urgently needs to be addressed in this field.
[0003] Bioleaching technology, utilizing the oxidation process of microorganisms such as *Acidithiobacillus ferrooxidans*, has become an important approach for processing low-grade uranium ore. The core mechanism of this technology lies in the fact that bacteria oxidize pyrite or Fe²⁺ in the solution. + Fe³ + , using Fe³ + The strong oxidizing properties of uranium oxidize the sparingly soluble tetravalent uranium [U(Ⅳ)] into soluble hexavalent uranium [U(Ⅵ)]. Compared with traditional acid leaching, bioleaching has significant advantages such as high leaching efficiency (1.5 to 2.3 times higher), low energy consumption (40% to 60% lower), and high leaching rate (uranium leaching rate can reach 92% to 97%).
[0004] However, existing bioleaching technologies still have limitations in practical applications. Studies have shown that uranium ores commonly contain a large amount of sulfide minerals such as pyrite. These sulfides often exist in the form of inclusions on the surface or within the fissures of uranium minerals, forming a dense physical barrier that hinders effective contact between the leaching agent and the uranium minerals. This results in increased mass transfer resistance, slow reaction kinetics, and prolonged leaching cycles during the leaching process, becoming a key technical bottleneck restricting further improvements in bioleaching efficiency. To address this problem, existing technologies use pretreatment methods such as microwaves and ultrasound to break down the sulfide inclusions, but these methods generally suffer from drawbacks such as high energy consumption, large equipment investment, and difficulty in large-scale application. Therefore, developing a pretreatment method that can selectively remove the sulfide inclusions from the surface of uranium ore and enhance the subsequent bioleaching effect has significant practical significance and industrial application value. Summary of the Invention
[0005] Sulfate autotrophic denitrification technology is widely used in water treatment. This technology utilizes bacteria to reduce nitrates using reduced sulfur such as pyrite as electron donors, without the need for an external organic carbon source. However, its application in uranium ore pretreatment desulfurization to enhance bioleaching has not been reported. To address the shortcomings of existing technologies, this invention provides a method for enhancing uranium ore bioleaching based on sulfur autotrophic denitrification pre-desulfurization. This method utilizes sulfur autotrophic denitrifying bacteria to selectively remove the sulfide coating layer from the ore surface, exposing the uranium mineral surface, followed by bioleaching using *Acidithiobacillus ferrooxidans*, achieving highly efficient uranium ore extraction.
[0006] This invention provides a method for enhancing uranium ore bioleaching based on sulfur autotrophic denitrification pre-desulfurization, comprising the following steps: S1. Sulfur autotrophic denitrification pre-desulfurization: Uranium ore is placed in a reactor and inoculated with sulfur autotrophic denitrifying bacteria. Under anaerobic conditions, nitrate-containing influent is introduced. The sulfur autotrophic denitrifying bacteria use the sulfur-iron compounds in the uranium ore as electron donors and nitrates as electron acceptors to metabolize and selectively oxidize and remove sulfides from the surface of the uranium ore to obtain desulfurized uranium ore. S2. Bioleaching: The desulfurized uranium ore obtained in step S1 is placed in a leaching system, inoculated with acidophilic ferrooxidizobacillus, and subjected to bioleaching to achieve uranium extraction.
[0007] Furthermore, in step S1, the sulfur-autotrophic denitrifying bacteria are derived from the domestication and enrichment culture of activated sludge from urban sewage treatment plants.
[0008] Furthermore, in step S1, the reactor inlet water adopts a bottom-inlet and top-outlet continuous water inlet method, and the bottom support layer is filled with packing material for microbial attachment. The packing material is one or a combination of at least two of sponge, K3, and iron oxide K3.
[0009] Preferably, in step S1, the filler is a sponge.
[0010] Furthermore, in step S1, the nitrate concentration in the nitrate-containing influent is 25–150 mg / L.
[0011] Preferably, in step S1, the nitrate concentration in the nitrate-containing influent is 100 mg / L.
[0012] Furthermore, in step S1, the pH value of the nitrate-containing influent is 3 to 6.
[0013] Preferably, in step S1, the pH value of the nitrate-containing influent is 4.
[0014] Furthermore, in step S1, the hydraulic retention time for sulfur autotrophic denitrification under anoxic conditions is 7.5–32 h.
[0015] Preferably, in step S1, the hydraulic retention time for sulfur autotrophic denitrification under anoxic conditions is 16 hours.
[0016] Furthermore, in step S1, the degree of sulfur autotrophic denitrification pre-desulfurization is controlled by the amount of nitrate reduction; wherein, the amount of nitrate reduction corresponding to different degrees of desulfurization is 1000-4000 mg.
[0017] Preferably, in step S1, the degree of sulfur autotrophic denitrification pre-desulfurization is controlled by the amount of nitrate reduction; the amount of nitrate reduction corresponding to the optimal degree of desulfurization is 2000 mg.
[0018] Furthermore, the acidophilic ferrous thiobacillus described in step S2 is cultured in 9K medium, the composition of which includes: 3 g / L ammonium sulfate, 0.1 g / L potassium chloride, 0.5 g / L potassium dihydrogen phosphate, 0.5 g / L magnesium sulfate heptahydrate, 0.01 g / L calcium nitrate, and 5 g / L ferrous sulfate heptahydrate, with the pH adjusted to 1.8 using 20% dilute sulfuric acid.
[0019] Further, in step S2, the Fe³⁺ in the leaching system + The concentration was 3 g / L, the acidity of concentrated sulfuric acid was 6 g / L; the leaching temperature was 30℃, and the leaching process was carried out under oscillation conditions with an oscillation speed of 150 r / min.
[0020] Compared with the prior art, the present invention has the following beneficial effects: 1) This invention introduces sulfur autotrophic denitrification technology into the field of uranium ore pretreatment for the first time. It utilizes sulfur autotrophic denitrifying bacteria to selectively oxidize and remove the sulfide coating layer on the surface of uranium ore, thus solving the technical problems of high leaching mass transfer resistance and slow leaching rate caused by sulfide coating.
[0021] 2) The method of the present invention has a high degree of selectivity. The sulfur autotrophic denitrification treatment only acts on the sulfides in the ore and has no significant effect on gangue minerals, thus avoiding the waste of reagents and environmental impact caused by over-treatment.
[0022] 3) Through pre-desulfurization treatment using sulfur autotrophic denitrification, the surface of uranium minerals is fully exposed, significantly improving subsequent bioleaching efficiency. Experiments show that after treatment using the method of this invention, the uranium leaching rate can be increased from 41.2% in the untreated state to 66.5%, a relative increase of 61%.
[0023] 4) The method of the present invention has low operating cost, the sulfur autotrophic denitrification process does not require an external organic carbon source, and the sludge production is low; the pretreatment and bioleaching processes are well integrated and easy to apply industrially. Attached Figure Description
[0024] Figure 1 This diagram illustrates the variation in nitrate and nitrogen reduction in effluent from sulfur autotrophic denitrification under different inoculation packing conditions.
[0025] Figure 2 This diagram illustrates the variation in nitrate and nitrogen reduction in effluent from sulfur autotrophic denitrification under different influent pH conditions.
[0026] Figure 3 This diagram illustrates the variation in nitrate and nitrogen reduction in effluent from sulfur autotrophic denitrification under different influent nitrate and nitrogen conditions.
[0027] Figure 4 This diagram illustrates the variation in nitrate and nitrogen levels in the effluent from sulfur autotrophic denitrification under different hydraulic retention times.
[0028] Figure 5 This is a schematic diagram showing the change of pH value over time in uranium ore after desulfurization during the leaching process.
[0029] Figure 6 For uranium ore after desulfurization treatment, U 6+ A schematic diagram showing the change in concentration over time.
[0030] Figure 7 The images show a comparison of FT-IR spectra of uranium ore before and after desulfurization treatment; where (a) is uranium ore; (b) is uranium ore after desulfurization treatment; and (c) is desulfurized uranium ore after bioleaching.
[0031] Figure 8 XRD comparison images of uranium ore before and after autotrophic denitrification and leaching are shown; (a) is uranium ore before desulfurization; (b) is uranium ore before bioleaching after desulfurization; (c) is uranium ore after bioleaching. Detailed Implementation
[0032] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in 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 this specification, and not all embodiments. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this specification.
[0033] In this embodiment of the invention, the sulfur-autotrophic denitrifying bacteria source for desulfurization pretreatment is obtained from activated sludge from an urban wastewater treatment plant, specifically from an acclimatization and enrichment culture of activated sludge from an urban wastewater treatment plant in Guangchang County, Fuzhou City, Jiangxi Province. The acclimatization and enrichment process of the sulfur-autotrophic denitrifying bacteria is as follows: A portion of fresh activated sludge is placed in a closed reactor and acclimatized using sodium nitrate as the nitrogen source and sodium thiosulfate as the electron donor. The initial pH of the acclimatization culture medium is adjusted to 7.0±0.2, the temperature is controlled at 20±1℃, and the culture is continuously cultivated for 30 days under anoxic conditions, with the culture medium being replaced every 5 days, to obtain an enriched sulfur-autotrophic denitrifying bacteria community.
[0034] The present invention will be described in detail below through specific embodiments.
[0035] Example 1 Optimization of sulfur autotrophic denitrification pre-desulfurization process parameters The uranium ore used in this embodiment was obtained from a uranium mine in Fuzhou City, Jiangxi Province. The ore contained associated sulfide minerals such as pyrite. The uranium ore was crushed and screened to a particle size of 5-10 mm, then washed and dried for later use. The experimental reactor was a 1L effective volume plexiglass column. The bottom of the reactor was filled with a packing support layer, on which 1 kg of pretreated uranium ore was placed. Water was continuously fed in via a peristaltic pump, using a bottom-in, top-out method. The water inlet container was a 20L plastic drum.
[0036] Four single-factor experiments were conducted, with four variable gradients for each factor, to investigate the effects of inoculum packing, influent pH, influent nitrate concentration, and hydraulic retention time (HRT) on the sulfur autotrophic denitrification effect. Furthermore, before the batch experiments on influent nitrate concentration, influent pH, and hydraulic retention time (HRT), all four sulfur autotrophic denitrification columns were operated under the same control conditions (NO3). - (N=50mg / L, pH=5, HRT=12h, T=20±1℃) were continuously cultured for 7 days to obtain the same active state. The specific control conditions for each group of single-factor experiments are shown in Table 1.
[0037] Table 1 Control conditions for sulfur autotrophic denitrification experiments of uranium ore The specific implementation process of a single-factor experiment is as follows: (1) Determination of the optimal inoculum for sulfur autotrophic denitrification To determine the optimal packing material for the sulfur autotrophic denitrification process, this embodiment sets up four reactor groups: a blank group (no packing), a sponge packing group, a K3 packing group, and an iron oxide K3 packing group. The influent NO3 in each reactor is... - The reactors were operated continuously for 7 days at a nitrogen concentration of 20.79 mg / L, pH of 7, hydraulic retention time of 32 h, and a temperature of 20 ± 1 °C. Daily measurements of nitrate concentration (using the thymol spectrophotometric method) and pH (using the electrode method) were taken. The decrease in nitrate and nitrogen concentrations in the influent and effluent of the four reactors was as follows: Figure 1 As shown.
[0038] from Figure 1 As can be seen, under the conditions of influent nitrate concentration of 20.79 mg / L, hydraulic retention time of 32 h, and temperature of 20 ± 1 ℃, after 7 days of continuous operation of reactors with four different inoculated packing materials, the average decrease in effluent nitrate in the sponge packing group was 5.69 mg / L, and the average nitrate reduction capacity reached 12.99 mg / L·d. - ¹; The average reduction in nitrate levels in the effluent from the K3 packing group was 3.83 mg / L, and the average nitrate reduction capacity was 8.76 mg / L·d. -¹; The average reduction in nitrate in the effluent from the K3 iron oxide packing group was 3.31 mg / L, and the average nitrate reduction capacity was 7.58 mg / L·d. - ¹; The average decrease in nitrate in the effluent of the control group (without filler) was 3.07 mg / L, and the average nitrate reduction capacity was 7.02 mg / L·d. - ¹.
[0039] The above data show that the sponge packing group has the strongest nitrate reduction capacity, averaging 12.99 mg / L·d. - ¹ The reason is that the sponge packing has a large specific surface area and good mass transfer performance, resulting in the highest biomass attachment and providing a stable growth and reproduction environment for microorganisms. The K3 packing group has relatively weak reduction ability because the rigid pore structure of K3 packing leads to poor mass transfer performance, and microorganisms only attach and grow on the surface. The iron oxide K3 packing group has even weaker reduction ability because the iron oxide alum attached to the surface of the iron oxide K3 packing group reduces the hydrophilicity of the packing, making it difficult for microorganisms to attach and grow, resulting in a smaller biomass. In addition, the experiment found that by the 7th day of operation, the difference in nitrate reduction ability among the four reactors had significantly narrowed compared to the initial stage, indicating that the influence of the inoculation packing on microbial activity decreases with the extension of the operating time, but still plays a key role in the reaction start-up stage. Considering both inoculation efficiency and reaction system stability, sponge packing was selected as the optimal inoculation packing for subsequent experiments.
[0040] (2) Determination of the optimal pH value for sulfur autotrophic denitrification To determine the optimal pH for sulfur autotrophic denitrification, this embodiment uses sponge packing material as the inoculum and sets up four reactors with influent pH values of 3, 4, 5, and 6. Each reactor is equipped with influent NO3... - The reactor operated continuously for 7 days under conditions of -N concentration of 50.17 mg / L, hydraulic retention time of 10.5 h, and temperature of 20 ± 1 °C. The influent and effluent nitrate concentrations and pH were measured daily. The decrease in nitrate and nitrogen concentrations in the influent and effluent of each reactor was as follows: Figure 2 As shown.
[0041] from Figure 2 As can be seen, different pH conditions have a significant impact on nitrate reduction capacity. When the influent pH is 4, the average decrease in nitrate in the reactor effluent reaches 5.77 mg / L, and the nitrate reduction capacity is 13.18 mg / L·d. -¹ The optimal pH level was observed, likely because a slightly acidic environment facilitates the exposure of sulfides in the ore, thereby enhancing the bacteria's sulfur utilization and improving denitrification. However, as the pH increased, the nitrate reduction capacity of the sulfur-autotrophic denitrifying bacteria decreased further. This is because the sulfur-autotrophic denitrification process itself produces alkali, causing a continuous rise in the pH of the reaction system, which inhibits the activity of nitrate reductases (Nar, Nir) in the denitrifying bacteria, hindering long-term stable denitrification. At pH 3, the sulfur-autotrophic denitrification activity was the worst, with an average decrease in effluent nitrate concentration of only 2.66 mg / L. This is because when the pH dropped to 3, the excessively acidic environment severely inhibited the normal metabolic activities of the bacteria, leading to a significant decrease in denitrification capacity. Considering both nitrate reduction capacity and the stability of the reaction system, an influent pH of 4 was determined to be the optimal parameter for subsequent experiments.
[0042] (3) Determination of the optimal influent nitrate concentration for sulfur autotrophic denitrification To determine the optimal influent nitrate concentration, this embodiment sets the influent NO3 concentration. - Four reactors with -N concentrations of 25 mg / L, 50 mg / L, 100 mg / L, and 150 mg / L were operated continuously for 7 days under conditions of pH=4, hydraulic retention time of 10.5 h, and temperature of 20±1℃. The influent and effluent nitrate concentrations and pH were measured daily. During the actual verification process, the influent nitrate concentrations of the four reactors were 24.73 mg / L, 49.19 mg / L, 100.33 mg / L, and 147.38 mg / L, respectively. The decrease in nitrate and nitrogen concentrations in the influent and effluent of each reactor was as follows: Figure 3 As shown.
[0043] from Figure 3 It was observed that as the influent nitrate concentration increased from 24.73 mg / L to 100.33 mg / L, the decrease in nitrate nitrogen concentration in both the influent and effluent gradually increased from 3.54 mg / L to 11.17 mg / L. The activity reached its optimal level at an influent nitrate concentration of 100.33 mg / L. This is because higher substrate concentrations allow microorganisms to more easily acquire the reaction substrate, thus promoting bacterial activity. When the influent nitrate concentration was further increased to 150 mg / L, the nitrate reduction capacity actually decreased compared to 100 mg / L. This may be because excessively high nitrate concentrations produce free nitrate and free nitrite, a denitrification intermediate. Both free nitrate and free nitrite inhibit bacterial activity, thereby reducing the denitrification reduction rate.
[0044] Considering both the nitrate reduction capacity and the stability of the reaction system, 100 mg / L was determined as the optimal influent nitrate concentration parameter for subsequent experiments.
[0045] (4) Determination of the optimal hydraulic retention time for sulfur autotrophic denitrification In sulfur autotrophic denitrification systems, the hydraulic retention time (HRT) significantly impacts the nitrate reduction capacity. A high or low HRT affects the growth and accumulation of sulfur autotrophic denitrifying bacteria, the substrate supply rate, and the discharge of reaction products. To determine the optimal HRT for sulfur autotrophic denitrification pretreatment, four reactors with HRTs of 7.5 h, 10.5 h, 16 h, and 32 h were established. (The last sentence appears to be incomplete and possibly refers to a separate, unrelated topic: "Influent NO3...") - The reactor operated continuously for 7 days under conditions of -N concentration of 100 mg / L, pH=4, and temperature of 20±1℃. The nitrate concentration and pH of the influent and effluent were measured daily. The decrease in nitrate and nitrogen concentrations in the influent and effluent of each reactor was recorded as follows: Figure 4 As shown.
[0046] from Figure 4 As can be seen, the average decreases in effluent nitrate concentration for HRTs of 32h, 16h, 10.5h, and 7.5h were 20.28 mg / L, 18.21 mg / L, 10.46 mg / L, and 6.01 mg / L, respectively, with corresponding average nitrate reduction capacities of 15.21 mg / L·d. -1 27.32 mg / L·d -1 23.91 mg / L·d -1 and 19.22 mg / L·d -1 It can be observed that as the hydraulic retention time increases from 7.5 h to 16 h, the average decrease in effluent nitrate concentration also increases from 6.01 mg / L to 18.21 mg / L, while the corresponding average nitrate reducing capacity increases from 19.22 mg / L·d. -1 Increased to 27.32 mg / L·d -1 Furthermore, the nitrate reduction capacity was strongest at a hydraulic retention time (HRT) of 16 h. This is because as the HRT increases, the flow velocity in the reactor gradually decreases, allowing microorganisms to come into contact with more reaction substrates. Simultaneously, the low flow velocity prevents the loss of attached microorganisms, thus promoting the reaction. While the average decrease in effluent nitrate concentration improved somewhat with a further increase in HRT to 16 h, the corresponding average nitrate reduction capacity actually decreased from 27.32 mg / L·d. -1 Decreased to 15.21 mg / L·d -1 The nitrate reduction capacity was inhibited, which may be due to insufficient substrate concentration supply caused by a longer HRT. Considering both the nitrate reduction capacity and the stability of the reaction system, 16 h was determined as the optimal hydraulic retention time parameter for subsequent experiments.
[0047] In summary, the optimal process parameters for sulfur autotrophic denitrification pre-desulfurization are: inoculated sponge packing, influent pH=4, and influent NO3. - -N concentration 100mg / L, hydraulic retention time 16h, temperature 20±1℃.
[0048] Example 2 Bioleaching test of desulfurized uranium ore To investigate the effect of sulfur autotrophic denitrification pre-desulfurization treatment on the bioleaching effect of uranium ore, this embodiment uses uranium ore with different desulfurization degrees as the research object and conducts a comparative bioleaching experiment.
[0049] (1) Culture of uranium leaching bacteria The uranium-leaching bacterial source used in this embodiment is *Acidithiobacillus ferrooxidans*, a bacterium that has been preserved and cultured by our research group for a long time. This bacterium is an obligate chemoautotrophic Gram-negative bacterium with aerobic and acidophilic characteristics, obtaining the energy required for growth and reproduction by oxidizing ferrous iron. The bacterial strain was expanded using 9K medium, which consists of the following components: ammonium sulfate 3 g / L, potassium chloride 0.1 g / L, potassium dihydrogen phosphate 0.5 g / L, magnesium sulfate heptahydrate 0.5 g / L, calcium nitrate 0.01 g / L, and ferrous sulfate heptahydrate 5 g / L. The pH was adjusted to 1.8 with 20% dilute sulfuric acid. *Acidithiobacillus ferrooxidans* was inoculated into 9K medium and cultured in a constant temperature shaker at 30°C and 150 rpm for 5-7 days to obtain a viable bacterial suspension for later use.
[0050] (2) Preparation of uranium ore with different desulfurization degrees Sulfate-autotrophic denitrifying bacteria can metabolize sulfides by using iron-sulfur compounds in uranium ore as electron donors and nitrates in water as electron acceptors, and achieve oxidative removal of sulfides through the following reaction pathways, as shown in equations (1) and (2): S 2- +1.6NO3 - +1.6H + 0.8N2 +SO4 2- +0.8H2O (1) S 2- +0.4NO3 - +2.4H + N2 +S+1.2H2O(2) Based on the above reaction principle, the amount of nitrate reduction can indirectly reflect the degree of sulfide oxidation. Therefore, this embodiment uses the amount of nitrate reduction as a quantitative indicator to characterize the degree of desulfurization of uranium ore. The optimal desulfurization pretreatment process parameters (sponge packing, influent pH=4, NO3) obtained in Example 1 are used. -Based on a nitrogen concentration of 100 mg / L, a hydraulic retention time of 16 h, and a temperature of 20 ± 1 °C, four groups of uranium ore with different desulfurization levels (A, B, C, and D) were prepared by controlling the operating time. These corresponded to nitrate reduction amounts of A = 0 mg, B = 1000 mg, C = 2000 mg, and D = 4000 mg, respectively. Group A served as a blank control group without sulfur autotrophic denitrification treatment. The nitrate reduction amount was calculated by multiplying the cumulative difference in nitrate concentration between the influent and effluent by the treated water volume.
[0051] (3) Biological leaching test In this embodiment, the bioleaching experiment used a 500ml Erlenmeyer flask as the reaction vessel, and a gas bath constant temperature shaker provided constant temperature and shaking conditions. 50g of uranium ore with different desulfurization levels (A=0mg, B=1000mg, C=2000mg, D=4000mg) were placed into four Erlenmeyer flasks respectively, and 200ml of *Thiobacillus ferrooxidans* bacterial solution was added to each flask. The Fe³⁺ content in the bacterial solution... + The concentration was 3 g / L, and concentrated sulfuric acid was added to bring the acidity of the system to 6 g / L. After sealing with sealing film, the conical flask was placed in a gas bath constant temperature shaker and leaching was carried out under shaking conditions of 150 r / min and 30℃ constant temperature.
[0052] The entire experiment was conducted at seven sampling points: t=0h, 1h, 2h, 4h, 8h, 12h, and 24h. The concentration of U in the solution was measured at each sampling point. 6+ Concentration, pH value, and Eh value. The pH value was determined using an electrode method. 6+ The concentration was determined by ammonium vanadate titration. The effect of sulfur autotrophic denitrification pre-desulfurization treatment on subsequent bioleaching was investigated by comparing the uranium leaching effects of uranium ores with different desulfurization levels. The changes in pH and uranium concentration during the bioleaching process of uranium ore under different desulfurization levels are shown in the figures below. Figure 5 , Figure 6 As shown.
[0053] from Figure 5 As can be seen, the pH change trends of uranium ores with different desulfurization levels during the leaching process are basically consistent, all showing a rapid decrease in the early stage followed by a steady increase. This is because in the initial stage of the reaction, sulfuric acid in the system continuously consumes carbonate minerals in the ore, leading to a rapid decrease in the pH of the leachate. As the acid-consuming substances are gradually depleted, the pH value in the later stage is mainly affected by Fe²⁺. + The oxidation process affects Fe² + It consumes H2O when reacting with oxygen in the air. + This causes the pH value to show a gradual upward trend. It is noteworthy that as the degree of desulfurization increases, the acidity of the solution at the end of the reaction becomes stronger, indicating that the desulfurization treatment promotes the dissociation of iron and sulfur compounds in the ore.
[0054] like Figure 6 As shown in the results of bioleaching experiments on uranium ore with different desulfurization levels, the pre-desulfurization treatment with sulfur autotrophic denitrification has a significant impact on the uranium ore leaching rate. The final leaching rate of the untreated uranium ore (Group A) was 41.2%; the leaching rate of Group B (with a nitrate reduction of 1000 mg) increased to 56.8%; the leaching rate of Group C (with a nitrate reduction of 2000 mg) reached the highest value of 66.5%, a relative increase of 61% compared to the untreated group; however, when the nitrate reduction increased to 4000 mg, the leaching rate of Group D actually decreased to 48.7%. Therefore, moderate pre-desulfurization treatment with sulfur autotrophic denitrification can significantly improve the bioleaching rate of uranium ore, but excessive desulfurization can have negative effects.
[0055] Analysis of the overall leaching effect showed that the leaching rate was optimal when the nitrate reduction amount was 2000 mg. This phenomenon occurs because the sulfur autotrophic denitrification treatment selectively oxidizes and removes the insoluble sulfide coating on the ore surface, fully exposing the uranium minerals and thus facilitating the leaching action of *Acidithiobacillus ferrooxidans*. However, when desulfurization is excessive (nitrate reduction amount 4000 mg), most of the iron and sulfur compounds in the ore are excessively dissociated, leading to an imbalance of Fe²⁺ in the subsequent leaching process. + Insufficient supply affects the continued operation of the iron cycle, which in turn hinders further uranium leaching. Therefore, considering both leaching effectiveness and process economy, the optimal desulfurization level was determined to be 2000 mg of nitrate reduction.
[0056] Mineralogical mechanism analysis (1) Fourier transform infrared spectroscopy analysis Fourier transform infrared spectroscopy analysis was performed on uranium ore, uranium ore after desulfurization (nitrate reduction amount 2000 mg), and uranium ore after bioleaching of the desulfurized uranium ore. The analysis results are as follows: Figure 7 As shown. Figure 7 (a) is the Fourier transform infrared spectrum of uranium ore; (b) is the Fourier transform infrared spectrum of uranium ore after sulfur autotrophic denitrification (sulfur autotrophic denitrification conditions: influent pH = 4, influent nitrate concentration = 100 mg / L, HRT = 16 h, nitrate reduction corresponding to the degree of desulfurization = 2000 mg); (c) is the Fourier transform infrared spectrum of desulfurized uranium ore after bioleaching (bioleaching conditions: ore mass = 50 g, leaching solution volume = 200 ml, leaching solution Fe... 3+ Concentration = 3 g / L, acidity of concentrated sulfuric acid in the system = 6 g / L, shaking speed = 150 r / min, leaching temperature = 30℃).
[0057] from Figure 7 As can be seen in (a), the infrared spectrum of uranium ore shows that in the 400-700 cm⁻¹ range... - ¹ There are significant Fe-S bond vibration peaks in the region (e.g., 472 cm⁻¹).- ¹ and 530cm - ¹Double peaks), a typical characteristic of pyrite (FeS2). From Figure 7 As can be seen from (b) above, after sulfur autotrophic denitrification treatment, the intensity of the characteristic peaks of the above-mentioned sulfides decreased significantly, which confirms that the microbial-mediated sulfur oxidation reaction during the desulfurization process effectively acts on pyrite, causing the sulfur components to undergo oxidative transformation, and verifies the efficient desulfurization mechanism of the sulfur autotrophic denitrification system for sulfide minerals.
[0058] Desulfurized uranium ore ( Figure 7 In the infrared spectrum of (b) in the figure, except for the weakening of the characteristic peak of sulfides, there is a peak at 778 cm⁻¹. - ¹ and 960cm - UO characteristic peaks appear at ¹ (representing asymmetric and symmetric stretching vibrations, respectively), and at 1030 cm⁻¹ - A significant Si-O bond peak is present at position ¹, corresponding to a typical characteristic of silicate structures in uranium ore. After bioleaching ( Figure 7 In (c), the intensity of the UO characteristic peak is significantly weakened, indicating that uranium migrates from the solid phase to the liquid phase, the uranium oxide lattice is distorted, and U(Ⅳ) may be partially oxidized to U(Ⅵ) and form uranyl sulfate complexes that enter the leachate. This process is closely related to microbial-mediated electron transfer. Simultaneously, the Si-O bond peak is also significantly weakened, reflecting the destructive effect of acid on silicate minerals during leaching, and the dissociation of the silicon-oxygen tetrahedral structure. These mineral structure changes confirm that sulfur autotrophic denitrification pretreatment can selectively oxidize and remove the sulfide coating, opening a pathway for subsequent activation and migration of uranium. This also provides direct mineralogical evidence for the leaching experiment.
[0059] (2) X-ray diffraction analysis (XRD) To verify the impact of sulfur autotrophic denitrification pre-desulfurization and bioleaching processes on ore mineral composition at the crystal structure level, X-ray diffraction analysis was performed on uranium ore samples, uranium ore samples after desulfurization treatment, and ore samples after bioleaching. The analytical results are as follows: Figure 8 As shown, Figure 8 In the text, (a), (b), and (c) represent uranium ore, uranium ore treated by sulfur autotrophic denitrification, and uranium ore treated by bioleaching, respectively.
[0060] from Figure 8As can be seen, compared with the raw uranium ore, after sulfur autotrophic denitrification desulfurization treatment, the SiO2 peak at 26.6°, the AlPO4 peak at 21°, the KAlSi3O8 peak at 68.2°, and the Fe3O4 peak at 54.8° showed almost no significant changes. This indicates that sulfur autotrophic denitrification treatment has high selectivity, reacting only with sulfides in the ore and having virtually no effect on gangue minerals (silicates, phosphates, iron oxides, etc.), verifying the precise targeting of this pretreatment process. After bioleaching, the characteristic peaks of the above minerals all showed a significant decrease, with the Fe3O4 peak at 54.8° showing a significant decrease in intensity, and the SiO2 peak at 26.6°, the AlPO4 peak at 21°, and the KAlSi3O8 peak at 68.2° also showing a significant weakening. This indicates that during bioleaching, sulfuric acid reacts with gangue minerals such as iron oxides and aluminosilicates in the ore, leading to a decrease in the content of these phases.
[0061] Comprehensive mineralogical analysis shows that the X-ray diffraction analysis results are highly consistent with the Fourier transform infrared spectroscopy analysis conclusions: sulfur autotrophic denitrification pretreatment can selectively act on the sulfide coating layer on the surface of uranium ore, achieving precise removal of the coating layer on the ore surface, while subsequent bioleaching dissolves uranium minerals and some gangue minerals in an acidic environment. Together, they constitute a complete uranium ore enhanced leaching process chain.
[0062] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions conceived without inventive effort should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims.
[0063] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.
Claims
1. A method for enhancing uranium ore bioleaching based on sulfur autotrophic denitrification pre-desulfurization, characterized in that, Includes the following steps: S1. Sulfur autotrophic denitrification pre-desulfurization: Uranium ore is placed in a reactor and inoculated with sulfur autotrophic denitrifying bacteria. Under anaerobic conditions, nitrate-containing influent is introduced. The sulfur autotrophic denitrifying bacteria use the sulfur-iron compounds in the uranium ore as electron donors and nitrates as electron acceptors to metabolize and selectively oxidize and remove sulfides from the surface of the uranium ore to obtain desulfurized uranium ore. S2. Bioleaching: The desulfurized uranium ore obtained in step S1 is placed in a leaching system, inoculated with acidophilic ferrooxidizobacillus, and subjected to bioleaching to achieve uranium extraction.
2. The method according to claim 1, characterized in that, In step S1, the sulfur-autotrophic denitrifying bacteria are derived from the domestication and enrichment culture of activated sludge from urban sewage treatment plants.
3. The method according to claim 1, characterized in that, In step S1, the reactor inlet water adopts a bottom-inlet and top-outlet continuous water inlet method, and the bottom support layer is filled with filler for microbial attachment. The filler is one or at least a combination of two of sponge, K3, and iron oxide K3.
4. The method according to claim 1, characterized in that, In step S1, the nitrate concentration in the nitrate-containing influent is 25–150 mg / L.
5. The method according to claim 1, characterized in that, In step S1, the pH value of the nitrate-containing influent is 3 to 6.
6. The method according to claim 1, characterized in that, In step S1, the hydraulic retention time for sulfur autotrophic denitrification under anoxic conditions is 7.5–32 h.
7. The method according to claim 1, characterized in that, In step S1, the degree of sulfur autotrophic denitrification pre-desulfurization is controlled by the amount of nitrate reduction; wherein, the amount of nitrate reduction corresponding to different degrees of desulfurization is 1000-4000 mg.
8. The method according to claim 1, characterized in that, The acidophilic ferrous thiobacillus described in step S2 is cultured in 9K medium, which consists of: 3 g / L ammonium sulfate, 0.1 g / L potassium chloride, 0.5 g / L potassium dihydrogen phosphate, 0.5 g / L magnesium sulfate heptahydrate, 0.01 g / L calcium nitrate, and 5 g / L ferrous sulfate heptahydrate. The pH is adjusted to 1.8 with 20% dilute sulfuric acid.
9. The method according to claim 1, characterized in that, In step S2, the Fe³⁺ concentration in the leaching system is 3 g / L, the concentrated sulfuric acid acidity is 6 g / L, the leaching temperature is 30℃, and the leaching process is carried out under oscillation conditions with an oscillation speed of 150 r / min.