A method for rapid and stable leaching of rare earth elements from phosphate rock using *Thiobacillus ferrooxidans*

Abstract

This invention discloses a method for rapidly and stably leaching rare earth elements from phosphate rock using *Thiobacillus ferrooxidans*. The specific steps are as follows: (1) Activate and culture *Thiobacillus ferrooxidans* to obtain a bacterial suspension; (2) Use the activated bacterial suspension to leach rare earth elements from phosphate rock; (3) Conduct leaching experiments under different rotation speeds, aeration rates, and leaching methods, and select the optimal parameters for rapid and stable leaching of rare earth elements. The *Thiobacillus ferrooxidans* provided by this invention has acidophilic and aerobic properties and is widely present in acidic mine wastewater. Its own metabolic activities and metabolic products are conducive to the leaching of rare earth elements from phosphate rock, and it has the advantages of good leaching effect, low cost, and green environmental protection.

Description

Technical Field

[0001] This invention relates to the field of rare earth biological recycling technology, and provides a method for rapidly and stably bioleaching rare earth elements from phosphate rock using *Thiobacillus ferrooxidans*. Background Technology

[0002] my country is rich in phosphate rock resources, among which associated rare earth minerals have extremely high comprehensive utilization value. Although many studies have found that rare earth elements can be extracted from phosphate rock using hydrometallurgy and high-temperature hydrometallurgy, these technologies are cost-effective and environmentally unfriendly. In contrast, bioleaching technology for the recovery and utilization of rare earth elements has advantages such as being green, environmentally friendly, energy-efficient, and cost-effective. However, there is currently limited research on the extraction of rare earth elements using bioleaching technology, and bioleaching generally suffers from long reaction times, resulting in high time costs in industrial production. Therefore, this invention selects *Thiobacillus ferrooxidans* to leach rare earth elements from phosphate rock. *Thiobacillus ferrooxidans* can grow and metabolize normally under acidic conditions and has a strong tolerance to heavy metals. It is a widely used microorganism in industrial production. Therefore, exploring the leaching effect of *Thiobacillus ferrooxidans* on rare earth elements in phosphate rock and selecting appropriate process parameters and leaching methods for rapid and stable extraction of rare earth elements is of great significance for alleviating the rare earth market supply crisis and creating a green circular market. Summary of the Invention

[0003] Purpose of the invention: To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for rapidly and stably leaching rare earth elements from phosphate rock using *Thiobacillus ferrooxidans*.

[0004] Technical solution: A method for rapidly and stably leaching rare earth elements from phosphate rock using *Thiobacillus ferrooxidans*, characterized by the following steps:

[0005] (1) Collect associated rare earth phosphate rock and crush and grind it;

[0006] (2) Determine the rare earth content in phosphate rock;

[0007] (3) Prepare 9K medium, the components of which include: ammonium sulfate, potassium chloride, dipotassium hydrogen phosphate, calcium nitrate, magnesium sulfate, ferrous sulfate heptahydrate, distilled water, and adjust the pH to 2.0;

[0008] (4) Add lyophilized powder of ferrooxidizobacterium oxygenate to the 9K medium prepared in step (3) for activation. After repeating the activation several times, ferrooxidizobacterium oxygenate with good activity was obtained.

[0009] (5) Add the well-activated ferrooxidizing thiobacillus suspension from step (4) to the 9K medium prepared in step (3) and then perform bioleaching after adding the associated rare earth phosphate rock from step (1);

[0010] (6) After leaching is completed, the leachate containing rare earth elements is collected by centrifugation and filtration.

[0011] Specifically, the culture medium composition in step (3) includes: 3 g / L ammonium sulfate, 0.1 g / L potassium chloride, 0.5 g / L dipotassium hydrogen phosphate, 0.01 g / L calcium nitrate, 0.5 g / L magnesium sulfate, 44.2 g / L ferrous sulfate heptahydrate, and pH adjusted to 2.0;

[0012] Specifically, the concentration of *Thiobacillus ferrooxidans* in step (5) is greater than 1 × 10⁻⁶. 8 The inoculum size of the *Acidithiobacillus ferrooxidans* suspension in step (5) is 10%; the rotation speed of the bioleaching in step (5) is (0-150±5) rpm, (150±5-350±5) rpm, (350±5-550±5) rpm, and (550±5-750±5) rpm; the aeration rate of the bioleaching in step (5) is 0-0.5 L / min, 0.5-1 L / min, 1-1.5 L / min, and 1.5-2 L / min; the bioleaching method in step (5) is selected from any of the following:

[0013] Method 1 involves simultaneously adding associated rare earth phosphate rock and ferrooxidizing thiobacillus to a bioreactor.

[0014] Method 2: Pre-culture Acidobacterium ferrooxidans for 24 hours, and add associated rare earth phosphate rock after Acidobacterium ferrooxidans has grown to the logarithmic phase.

[0015] Method 3: Pre-culture *Thiobacillus ferrooxidans* for 36 hours (*Thiobacillus ferrooxidans* will extract Fe from the leaching system). 2+ Completely converted to Fe 3+ Then add associated rare earth phosphate rock;

[0016] Specifically, the operating time is 40 to 54 days for speeds of (0 to 150±5) rpm, 28 to 32 days for speeds of (150±5 to 350±5) rpm, 10 to 14 days for speeds of (350±5 to 550±5) rpm, and 8 to 14 days for speeds of (550±5 to 750±5) rpm.

[0017] Specifically, the aeration time is 2-5 days for 0.5L / min aeration, 3-6 days for 1L / min aeration, 3-6 days for 1.5L / min aeration, and 5-7 days for 2L / min aeration.

[0018] Specifically, the leaching time is 2 to 6 days in Method 1, 2 days in Method 2, and 2 days in Method 3.

[0019] Specifically, the leaching temperature is 30±2℃.

[0020] Specifically, the bioleaching experiment was conducted in 4L of 9K medium.

[0021] Specifically, the dosage of associated rare earth phosphate rock is 10 g / L.

[0022] Specifically, the particle size of the associated rare earth phosphate rock in step (1) is 100 mesh. Beneficial effects

[0023] The advantages of this invention are:

[0024] (1) The present invention uses bioleaching technology, which is milder and produces less secondary pollution compared to chemical leaching.

[0025] (2) This invention utilizes ferrosulfobacterium ferrosulfide to leach rare earths. ferrosulfobacterium ferrosulfide is a microorganism widely used in industrial production. The leaching technology is relatively mature and has a wide range of applications. Therefore, bioleaching of rare earths has advantages in industrial applications.

[0026] (3) By continuously optimizing the process parameters under different rotation speeds, aeration rates, and leaching methods, the present invention reduces the leaching time from a maximum of 54 days to 2 days, resulting in rapid and stable leaching effects. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the bioreactor of the present invention;

[0028] Figure 2 A graph showing the trend of the effect of different rotation speeds on rare earth leaching amount;

[0029] Figure 3 This is a graph showing the changing trend of the effect of different aeration rates on rare earth leaching amount.

[0030] Figure 4 This is a graph showing the trend of the effect of different leaching methods on the amount of rare earth leached. Detailed Implementation

[0031] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0032] It should be noted that the descriptions of these embodiments are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] like Figure 1 As shown, unless otherwise specified, all reagents used in the examples can be purchased commercially. The bacterial strain used is *Thiobacillus oxidans*. The rare earth elements mentioned in the examples are Y, La, Ce, and Nd.

[0034] In the example, the particle size of the associated rare earth phosphate rock is 100 mesh;

[0035] In the examples, rare earth elements in the phosphate rock and leachate were determined using ICP-MS.

[0036] The culture medium in the example consisted of 3 g / L ammonium sulfate, 0.1 g / L potassium chloride, 0.5 g / L dipotassium hydrogen phosphate, 0.01 g / L calcium nitrate, 0.5 g / L magnesium sulfate, and 44.2 g / L ferrous sulfate heptahydrate.

[0037] The bioreactor in this embodiment includes: a 6L plexiglass reactor, a titanium alloy heating rod, a temperature controller, and an aeration device.

[0038] Figure 1 This is a schematic diagram of a bioreactor.

[0039] Example 1: Effect of different rotation speeds on rare earth leaching amount:

[0040] 1. Add 40.0g of associated rare earth phosphate rock to a 6L bioreactor;

[0041] 2. The activated *Thiobacillus ferrooxidans* was placed in 4L of 9K medium for leaching test;

[0042] 3. The inoculation amount is 10% (by volume);

[0043] 4. Adjust the initial pH value to 2 ± 0.2 using a 50% sulfuric acid solution;

[0044] 5. The leaching test temperature is (30±2)℃;

[0045] 6. The rotational speeds are (0—150±5) rpm, (150±5—350±5) rpm, (350±5—550±5) rpm, and (550±5—750±5) rpm;

[0046] 7. Samples were taken every two days and the rare earth leaching amount was determined using ICP-MS. The experiment was stopped when the leaching amount reached its maximum value, and the number of days of operation was recorded. Sterile water with pH=2 was used to replenish the evaporated water during the bioleaching process.

[0047] 8. After leaching is complete, collect the rare earth-containing leachate by centrifugation and filtration.

[0048] Figure 2 The graph shows the trend of the effect of different rotation speeds on the leaching amount of rare earth in Example 1. It can be seen that as the rotation speed increases and the running time decreases, the leaching amount of rare earth does not differ much. Considering time cost and industrial cost, 350±5-550±5 rpm was selected.

[0049] Example 2: Effect of different aeration rates on rare earth leaching amount:

[0050] 1. Add 40.0g of associated rare earth phosphate rock to a 6L bioreactor;

[0051] 2. The activated *Thiobacillus ferrooxidans* was placed in 4L of 9K medium for leaching test;

[0052] 3. The inoculation amount is 10% (by volume);

[0053] 4. Adjust the initial pH value to 2 ± 0.2 using a 50% sulfuric acid solution;

[0054] 5. The leaching test was conducted at a temperature of (30±2)℃ and a rotation speed of (550±5)rpm;

[0055] 6. Aeration rates are 0-0.5 L / min, 0.5-1 L / min, 1-1.5 L / min, and 1.5-2 L / min.

[0056] 7. Samples were taken daily and the rare earth leaching amount was determined using ICP-MS. The experiment was stopped when the leaching amount reached its maximum value, and the number of days of operation was recorded. Sterile water with pH=2 was used to replenish the evaporated water during the bioleaching process.

[0057] Figure 3 The graph shows the trend of the effect of different aeration rates on the leaching amount of rare earth in Example 2. It can be seen that compared with the reactor without aeration, the reactor with aeration has a shorter running time. However, the running time increases with the increase of aeration rate. Furthermore, excessive aeration rate leads to a decrease in the leaching amount of rare earth. Therefore, the aeration rate was selected as 0-0.5 L / min.

[0058] Example 3: Effect of different leaching methods on rare earth leaching amount:

[0059] 1. Add 4L of 9K culture medium to a 6L bioreactor;

[0060] 2. An leaching test was conducted after adding activated *Thiobacillus ferrooxidans*.

[0061] 3. The inoculation amount is 10% (by volume);

[0062] 4. The initial pH value was 2 ± 0.2;

[0063] 5. The leaching test was conducted at a temperature of (30±2)℃, a rotation speed of (350±5—550±5)rpm, and an aeration rate of 0—0.5L / min;

[0064] 6. The leaching methods are a one-step method (adding 40.0g of associated rare earth phosphate rock and *Thiobacillus ferrooxidans* to the bioreactor simultaneously) and a two-step method (pre-culturing *Thiobacillus ferrooxidans* for a period of time before adding 40.0g of associated rare earth phosphate rock). The pre-culturing time for the two-step method is 24h (when *Thiobacillus ferrooxidans* reaches the logarithmic growth phase) and 36h (when *Thiobacillus ferrooxidans* extracts Fe from the leaching system). 2+ Completely converted to Fe 3+ hour);

[0065] 7. Samples were taken daily and the rare earth leaching amount was determined using ICP-MS. The experiment was stopped when the leaching amount reached its maximum value, and the number of days of operation was recorded. Sterile water with pH=2 was used to replenish the evaporated water during the bioleaching process.

[0066] 8. After leaching is complete, collect the rare earth-containing leachate by centrifugation and filtration.

[0067] Figure 4 The graph shows the trend of the effect of different leaching methods on the leaching amount of rare earth in Example 3. It can be seen that the two-step method has a more stable running time than the one-step method. However, the leaching amount of rare earth decreases rapidly in the two-step method (complete oxidation). Therefore, considering the optimal leaching amount and stability performance, the two-step method (logarithmic period) is selected.

[0068] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for rapidly and stably leaching rare earth elements from phosphate rock using *Thiobacillus ferrooxidans*, characterized in that, Includes the following steps: (1) Collect associated rare earth phosphate rock and crush and grind it; (2) Determine the rare earth content in phosphate rock; (3) Prepare 9K medium, the components of which include: ammonium sulfate, potassium chloride, dipotassium hydrogen phosphate, calcium nitrate, magnesium sulfate, ferrous sulfate, and distilled water, and adjust the pH to 2.0; (4) Add lyophilized powder of ferrooxidizobacterium oxygenate to the 9K medium prepared in step (3) for activation. After repeating the activation several times, ferrooxidizobacterium oxygenate with good activity was obtained. (5) Add the associated rare earth phosphate rock from step (1) to the well-activated ferrooxidizobacterium suspension in step (4) and then carry out bioleaching; (6) After leaching is completed, the leachate containing rare earth elements is collected by centrifugation and filtration; In step (5), the concentration of *Thiobacillus ferrooxidans* is greater than 1 × 10⁻⁶. 8 The inoculum amount of *Thiobacillus ferrooxidans* suspension in step (5) is 10% of the volume ratio; the rotation speed of bioleaching in step (5) is 345-555 rpm; the aeration rate of bioleaching in step (5) is 0-0.5 L / min; the bioleaching method in step (5) is to pre-culture *Thiobacillus ferrooxidans* for 24 h, and add associated rare earth phosphate rock after *Thiobacillus ferrooxidans* has grown to the logarithmic phase; the leaching temperature in step (5) is 28-32℃; the dosage of associated rare earth phosphate rock is 10 g / L; the particle size of associated rare earth phosphate rock in step (1) is 100 mesh.

2. The method for rapidly and stably leaching rare earth elements from phosphate rock using *Thiobacillus ferrooxidans* according to claim 1, characterized in that, The operating time is 28-32 days at a speed of 345 rpm and 10-14 days at a speed of 555 rpm.

3. The method for rapidly and stably leaching rare earth elements from phosphate rock using *Thiobacillus ferrooxidans* according to claim 1, characterized in that... The aeration rate of 0.5 L / min is maintained for 2-5 days.

4. The method for rapidly and stably leaching rare earth elements from phosphate rock using *Thiobacillus ferrooxidans* according to claim 1, characterized in that... The bioleaching time is 2 days.

5. The method for rapidly and stably leaching rare earth elements from phosphate rock using *Thiobacillus ferrooxidans* according to claim 1, characterized in that... Bioleaching was carried out in 4L of 9K medium.

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