Experimental study on bacterial leaching and microbial metabolites of bauxite

It is reported that different types of silicate bacteria can separate from the low-grade silicon as an impurity bauxite containing aluminum silicate out, compared with the conventional method, bauxite Processing of this method is aluminum The silicon ratio is higher, which is suitable for separating aluminum by the Bayer process.

The characteristic of silicate bacteria is that they require silicon during their growth. It has been reported that the action of these bacteria on aluminosilicates is characterized by enzymes that utilize bacteria to break down the energy released by silicon in minerals. Silicate bacteria are typical abnormal bacteria. The classification of these bacteria is also fixed. Different researchers have isolated a large number of such bacteria, which belong to different kinds of bacilli. The internationally recognized silicate bacteria are ring-shaped. Bacillus, Chinese and former Soviet scholars believe that Bacillus licheniformis should also be attributed to silicate bacteria.

The mechanism by which silicate bacteria decompose aluminosilicate minerals is currently different, and there are few studies on this aspect. The purpose of this study is to demonstrate that the decomposition of aluminosilicate minerals by "silicate bacteria" is largely related to the treatment method; another main purpose of this paper is to illustrate that "silicate bacteria" decompose aluminosilicate minerals very large. The degree is closely related to the treatment method; another main purpose of this paper is to explain the different culture environments of bacteria, and their ability to decompose metabolites is different, which may be one of the reasons that affect the effect of bacteria leaching silicate minerals.

I. Materials and methods

(1) Materials

Five kinds of silicate ore samples were used in the experiment: No. 1 ore sample (bauxite ore sample, provided by Beijing Research Institute of Mining and Metallurgy); No. 2, No. 3, No. 4 and No. 5 were respectively - hydraulic diaspore The artificial mixed ore samples prepared in a ratio of 5:1 with kaolinite, feldspar , chlorite and quartz are shown in Table 1 for the content of alumina and silica in each sample.

Five kinds of silicate strains from different sources were used in the experiment. Three of the silicate bacteria (JXF-1, JXF-2, JXF-3) were purchased from the silicate fertilizer (Jiangxi Academy of Agricultural Sciences). Separated and screened by the Institute of Microbiology, both of which are related to Bacillus licheniformis; one of the other two is the genus Bacillus circulans BC, and the other is the model G. oxysporum BM, which is purchased from the Institute of Microbiology of the Chinese Academy of Sciences. It is cultivated and preserved by the author's laboratory.

Table 1 Contents of Al ₂ O ₃ and SiO ₂ before leaching of five test ore samples (mass fraction)

Table 2 Main mineral types and composition in five test ore samples

All of the above species are preserved in a matrix mineral salt medium containing 2% sucrose as a source of bacteria-producing carbon and energy. The medium composition was: sucrose 10g, K ₂ HPO ₄ 0.2g, MgSO ₄ ·7H ₂ O 0.2g, FeCl ₃ 0.005g, CaCO ₃ 0.1g, bauxite 0.2g, agar 0.1g, water 1000ml, pH 7.2 Sterilize at 121 ° C for 2 h. Live bacteria counts were determined by plate counting.

(two) method

1. Silicate mineral bacteria leaching method

The leaching of silicon from the test ore sample by using these strains in five different ways: (1) cultivating the strain in a sucrose medium containing the previously immersed ore, and leaching the silicon in the sugar medium; (2) Using a pre-selected strain cultured in a sucrose medium without an aluminosilicate mineral, and leaching the silicon in a sugar-free medium; (3) cultivating the strain in a sucrose medium previously containing the leached ore, Silicon leaching in a sugar-free medium; (4) leaching of silicon in a sugar medium using a strain previously cultured in a sucrose medium without aluminate minerals; (5) Control inactivation Leaching of the strain (sucrose in the leaching medium).

The leaching test was carried out in a 1 L conical flask containing 250 ml of Ashine matrix mineral salt medium, 30 g of aluminosilicate mineral sample (-38 μm) and 30 ml of active bacterial culture solution per ml. Contains 4.5 × 10 ⁸ cells.

The leaching form of the control inactivated species was the same as above, except that the bacterial liquid containing the live bacteria was sterilized at a high temperature of 120 ° C for 1.5 h. The leaching conditions of the above five kinds of bacteria were as follows: the pH of the leaching suspension was 7.5, the shaking speed of the shake flask was 240 r/min, and the culture was continued for 7 days at a culture temperature of 35 °C.

In all tests, after the leaching was completed, the solid leaching residue was separated from the liquid phase and rinsed with a weak alkaline solution at 70 ° C, the liquid phase was filtered, and the solid leaching slag was added to the initial slag to the total slag mineral powder. The content analysis of silicon and aluminum was carried out. After the sample is first dissolved alkali fusion, the content of silicon was measured using the molybdate blue colorimetry spectrometer aluminum atomic absorption method for measuring a silicon leachate samples performed by methods in the literature.

2. Analysis of organic acids, amino acids and polysaccharides

Four 500ml cone bottles were filled with 150ml medium I (Ashby matrix mineral salt medium containing bauxite powder 10g), II (Ashby matrix mineral salt medium without bauxite powder), III (Ashby matrix mineral salt medium containing 10 g of bauxite powder but no sucrose), IV (Ashby matrix mineral salt medium containing no bauxite or sucrose), sterilized at 120 °C for 2 h After cooling, the silicate bacterial suspension was transferred to a conical flask at a 2% inoculum and shaken at 36 ° C (200 r / min). The culture time was 0, 6, 12, 24, 36, 48, 72, 96 h. Post analysis.

Determination of organic acid: The organic acid in the fermentation broth is acid sulfuric acid extraction method, and the content of various organic acids is determined by high performance liquid chromatography. The specific measurement is carried out by a professional teacher in the laboratory.

Determination of amino acid: The fermentation broth was first treated with triammonium acetate, diluted with 0.015 mol/L hydrochloric acid, and then determined by an amino acid analyzer. Determination of polysaccharides in the fermentation broth of the three culture media: In the fermentation broth after extracting the organic acid, ethanol was added by centrifugation to obtain a crude polysaccharide, which was dried at 60 ° C, and the crude polysaccharide was weighed.

3. Analysis of silicate bacteria metabolites leaching kaolinite

Using a variety of silicate bacterial metabolites to leach silicate minerals - kaolinite (purity 86%, isolated and purified by this experiment, raw ore samples taken from Zhengzhou aluminum plant), using shake flask leaching method, the specific implementation in the results analysis They are described separately. Silicon in the leachate was determined by silicon molybdenum blue spectrophotometry.

Second, the results analysis

(1) Discussion on bacterial leaching results of mineral samples in five different bacterial leaching methods

The test strain was JXF-1. It was found in the experiment that the degree of leaching of silicon is closely related to the leaching method. The former is better than the leaching of the sucrose-cultured strains with the sucrose-like culture and the sucrose culture in the sucrose-free medium. It indicates that the strain cultured in the environment with the leached ore sample is highly adaptable, the stagnation period of the bacteria in the leaching process is short, and the bacteria reproduction speed is fast. The leaching results are shown in Table 3.

Table 3 Effect of leaching method on silicon removal effect of aluminosilicate ore sample (silicon leached in 7 days)/%

In a flask containing neither aluminosilicate ore and sucrose, that is, the leaching method (1), the bacterium was vigorously propagated at the start of leaching, and the number of bacteria exceeded 8 × 10 ⁸ /ml. However, at the end of the 7d leaching period, all bacterial species are either at rest or in a stage of growth and atrophy. However, the amount of viable bacteria is still higher than 10 ⁸ /ml, and the final pH of the culture solution is 5.5 ~ 6.5.

In the flask containing the ore sample but not containing sucrose, ie the leaching method (2), the leaching starts, the number of bacteria has an irregular decrease, and the bacterial reproduction has a stagnation period, eventually increasing from 4.5×10 ⁸ /ml to less than 8 ×10 ⁸ /ml. This initial stage of reproduction may utilize the stock of material and the material that is brought into the flask with the bacterial suspension. Subsequently, the bacteria appeared to dissolve and the amount decreased. At the end of the 7d leaching, there were less than 10 ⁷ bacteria per ml in the flask, and the final pH of the culture solution was between 6.8 and 7.3.

After the leaching, the mineral leaching of the solid leaching slag in the leaching method (1) was carried out, and the results are shown in Table 4. The results show that aluminosilicate minerals are the main target of bacterial action. Chlorite is easier to leaching than other minerals such as kaolinite, indicating that the leaching ability of bacteria to different structures of aluminosilicate minerals is different, which may be due to the difference in the state of occurrence of silicon in various minerals.

Table 4 Main mineral types and composition of bacterial leaching residue in five experimental ore samples

(II) Results of silicon immersion ability test of five different sources of silicate bacteria on mineral samples

The first bacterial leaching method was used to conduct bacterial immersion silicon research on No. 2 or No. 4 ore samples. The results are shown in Table 5. The results show that silicate bacteria from different sources can better leaching silicon from aluminosilicate minerals, but their leaching ability is significantly different. In general, the ability of Bacillus licheniformis to leach silicon is stronger than that of Bacillus circulans, which may be stronger than the ability of Bacillus licheniformis to decompose metabolites such as extracellular polysaccharides and organic acids. Related to Bacillus.

Table 5 Leaching results of silicon in mineral samples by various silicate bacteria (the amount of silicon leached in 7 days) /%

(3) Determination results of catabolic products of bacteria in different growth environments

Different bacterial leaching methods have different effects on the leaching of silicon from silicate minerals, and the main reason for this result may be closely related to the environment in which bacteria grow and reproduce. The difference between the first four leaching methods of the previous one (II) is essentially the production of four different leaching silicate bacteria in four different fermentation media. The content of organic acid and capsular polysaccharide in the fermentation broth after shaking culture for 48 hours in four different mediums I, II, III and IV was determined. The results are shown in Table 6.

Table 6 Contents of metabolites synthesized by bacterial fermentation in different media for 48 hours

The amount of organic acid in Table 6 is the sum of the four organic acids (oxalic acid, tartaric acid, malic acid, citric acid) produced by the bacteria, and the amount of the amino acids is the sum of various amino acids produced by the bacteria. It can be seen from the results in Table 6 that the amount of organic acids, amino acids, and capsular polysaccharides produced by the bacteria in the fermentation medium I was the highest, and the effect of leaching the silicon in the ore samples was also the best. This can form complexes with organic acids, polysaccharide silicate minerals silicon and the like, to promote separation of the metal from the mineral lattice relevant. The amino acids in the bacterial fermentation broth were determined during the test.

(4) The synergistic effect of organic acids, amino acids and polysaccharides on the dissolution of kaolinite

The composition of each metabolite and test mineral in a 500 ml cone bottle in the test - the composition of the mixed organic acid: four organic acids (oxalic acid, tartaric acid, citric acid, malic acid) each having a concentration of 200 mg/L; The composition of the amino acid: the maximum concentration of each amino acid mixed composition; polysaccharide concentration of 8.5g / L; kaolinite 15g / L.

Organic acids, amino acids and polysaccharides have obvious effects on the ability to leach silicon and aluminum in silicate minerals. The test results are shown in Table 7. It can be seen from the results in Table 7 that the ability of each metabolite to decompose kaolinite is: mixed organic acid > mixed amino acid > polysaccharide. The ability of the mixture of amino acids, organic acids, and polysaccharides to dissolve kaolinite is greatly increased compared to the solubility of the individual metabolites. In addition, the ability of bacterial metabolites to leach the silicon and aluminum in kaolinite is related to its structure. The structure of metabolites is destroyed by hydrogen peroxide, and their ability to activate kaolinite is greatly reduced. At the same time, the metabolites of silicate bacteria activate the kaolinite through the complexation of organic substances with complexing groups, and each metabolite has a complex with various metals in the mineral, especially aluminum and silicon. The organic groups such as -COOH, -NH ₂ or -COO ^- , -NH ⁺ ₄ , all have a certain complexing ability for metal ions. From the results in the table, it can be ruled out that the ability of 0.001 mol of nitric acid to dissolve kaolinite in aluminum and silicon is much lower than the ability of various mixed metabolites to act on kaolinite, because various mixed metabolites have complex silicates. The ability of various metal ions in minerals to destroy the crystal lattice of minerals and release various metal elements.

Table 7 Leaching of silicon and aluminum of kaolinite by silicate bacterial metabolites

Third, the conclusion

(1) Tests have shown that the bacterial leaching effect of silicon in silicate minerals is closely related to the way of bacterial leaching. Different bacterium leaching forms have different abilities of bacteria to leaching silicon. The ability to leach silicon is the strongest when using a strain cultured in sucrose containing a leached ore sample in advance and leaching silicon in a medium having a sugar medium. The reason may be that the bacteria leaching silicon in this medium, because the bacteria have adapted to the leaching environment, the growth and reproduction do not go through the stagnation period; at the same time, the bacteria can use the sucrose in the medium as the nutrient for their own growth and reproduction. So that the bacteria will not be able to reduce the number of bacteria due to their own dissolution during the leaching process, thus ensuring the number of microorganisms necessary for the leaching of the ore sample.

(2) The lattice of different silicate minerals is different, and the ability of bacteria to leach out of silicon is different. The chlorite is a silicate mineral with a layered structure. The effect of bacteria leaching out silicon is most obvious, while the silicate minerals of quartz and feldspar are frame-like junctions. Stable, which is one of the possible reasons for the poor effect of bacteria leaching out of silicon.

(3) The test results show that the ability of bacteria to synthesize various metabolites in different media has certain differences. Silicate bacteria can synthesize oxalic acid, tartaric acid, citric acid, malic acid, etc. in various media. The main organic acids and various polysaccharides and various amino acids, in the mineral salt medium containing immersed ore and sucrose and various polysaccharides and various base acids in the Ashby matrix containing immersed ore and sucrose The amount and type produced are the most.

(4) The test showed that the final pH value of the culture solution decreased to some extent during the leaching process of the live bacteria of the ore sample, indicating that the bacteria could produce a certain amount of organic acid during the leaching and propagation process. The organic acid and the metal such as silicon or aluminum in the aluminosilicate mineral can form a complex, thereby causing it to dissolve into the leachate.

(5) The leaching test of silicate bacterial metabolites on the silicon and aluminum of kaolinite shows that the ability of the mixture of amino acid, organic acid and polysaccharide to dissolve kaolinite is greatly increased than that of the metabolite alone. In addition, the ability of bacterial metabolites to leach kaolinite from silicon and aluminum is related to its structure. The structure of metabolites is destroyed by hydrogen peroxide, and their ability to activate kaolinite is significantly reduced. The reason is that various mixed metabolites have the ability to complex various metal ions in silicate minerals, thereby destroying the lattice structure of minerals and releasing various metal elements.

Sun Desi, Zhang Qiang

(Beijing University of Science and Technology, North 100083; Jiujiang College, Jiangxi Jiujiang 332005)

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