A method for treating acidic mine wastewater at its source

Abstract

This invention discloses a method for treating acidic mine wastewater at its source, belonging to the field of mine environmental remediation. The method includes biological leaching of pyrite-containing waste rock or flotation tailings. After biological leaching, more than 60% of the iron and sulfur in the waste rock or tailings can be removed. Simultaneously, functional microorganisms induce the generation of potassium ferroalloy, passivating residual pyrite in the waste rock or tailings, thereby inhibiting secondary dissolution of residual pyrite and greatly reducing the risk of subsequent acidic mine wastewater generation from stockpiling. Biological leaching is simple to operate, low in cost, and environmentally friendly. This invention can treat the pollution problem of acidic mine wastewater generated from pyrite-containing waste rock or tailings at its source, and is of great significance for the harmless disposal of pyrite-containing waste rock or flotation tailings and mine environmental remediation.

Description

Technical Field

[0001] This invention belongs to the field of mine environmental management, specifically relating to a method for treating acidic mine wastewater at its source. Background Technology

[0002] Pyrite is the most abundant and widely distributed sulfide mineral in the Earth's crust. High-purity pyrite can be used to produce sulfuric acid. Therefore, during pyrite mining, low-grade pyrite is often discarded, generating a large amount of pyrite-bearing waste rock. Furthermore, pyrite is often associated with copper, gold, zinc, and coal, but due to its relatively low economic value, it is often discarded as gangue during the mining and beneficiation of these mineral resources. Currently, there is no effective method for disposing of pyrite-bearing solid waste. Fine-particle tailings are discharged into tailings ponds, while large-particle waste rock is often simply piled up or landfilled. This massive amount of pyrite-bearing solid waste not only occupies a large amount of land, but the exposed pyrite, upon contact with water, oxygen, and microorganisms, will be oxidized, releasing ferrous and sulfuric acid into the surrounding environment. Under the action of oxygen, ferrous ions are oxidized to ferric ions, thus accelerating the dissolution of pyrite. Meanwhile, the leaching of iron from pyrite also leads to the leaching of other heavy metals from its associated minerals, generating acidic mine wastewater (AMD), which pollutes the environment and threatens the safety of surrounding drinking water sources. Therefore, controlling and managing AMD generated during mining is urgently needed.

[0003] Currently, the common method for treating AMD is to build wastewater treatment plants at the end of the treatment process, using alkaline substances to neutralize and precipitate AMD, thereby increasing the environmental pH and reducing heavy metal pollution. However, under natural conditions, Fe... 2+ To Fe 3+ The oxidation of pyrite is limited, and the overall oxidation process is relatively slow, leading to the continuous generation of AMD (maltose oxidase), a process that can last for decades or even centuries. To reduce treatment costs or even solve the AMD problem, it is necessary to address AMD at its source. The conventional approach to source control is to isolate the pollution source from oxygen, water, and microorganisms, but its stability is greatly affected by the environment and it is prone to failure.

[0004] Therefore, this invention takes a novel approach by enhancing the interaction between acidophilic microorganisms and pyrite, dissolving most of the pyrite in the waste rock in a short time and utilizing biological passivation to greatly reduce the risk of acidic mine wastewater generated from subsequent waste rock storage. It is low-cost, feasible, and of great significance for the harmless disposal of pyrite-containing waste rock and the source control of acidic mine wastewater. Summary of the Invention

[0005] The purpose of this invention is to decontaminate exposed pyrite-containing waste rock or flotation tailings, reducing the risk of acidic mine wastewater generated from their storage. A method for source control of acidic mine wastewater generated from pyrite-containing waste rock or flotation tailings has been developed. This method can harmlessly dispose of acidic mine wastewater pollution sources and reduce end-of-pipe treatment costs.

[0006] The objective of this invention is achieved through the following means:

[0007] A method for treating acidic mine wastewater at its source involves biological leaching of pyrite-containing waste rock or flotation tailings.

[0008] The method for treating acidic mine wastewater at its source stipulates that the sulfur content in the waste rock or flotation tailings containing pyrite is not less than 5%.

[0009] The method for treating acidic mine wastewater at its source involves adding acidophilic microorganisms to wash pyrite-containing waste rock or flotation tailings.

[0010] The method for treating acidic mine wastewater at its source includes adding at least one of the following acidophilic microorganisms: *Thiobacillus acidophilus*, *Thiobacillus acidophilus*, *Thiobacillus thermophilus*, and *Leptospira ferrooxidans*.

[0011] The method for treating acidic mine wastewater at its source involves inoculating acidophilic microorganisms into a leaching system for waste rock or flotation tailings containing pyrite with a pulp concentration of 1–5%. The initial pH of the leaching system is 1.5–3.5, the temperature is 10–40°C, and the shaking speed of the leaching system is 100–200 r / min. The leaching time does not exceed 50 days.

[0012] The method for treating acidic mine wastewater at its source, further specifying an inoculation amount of 1×10⁻⁶. 7 ~9×10 7 Acidophilic microorganisms were introduced per mL into the washing system of pyrite-containing waste rock or flotation tailings.

[0013] The preferred method for treating acidic mine wastewater at its source involves crushing and screening pyrite-containing waste rock or flotation tailings to a particle size of less than 74 μm before rinsing.

[0014] A method for treating acidic mine wastewater generated from pyrite-containing waste rock or flotation tailings at its source, preferably comprising the following steps:

[0015] (1) After cleaning and air-drying the waste rock or flotation tailings containing pyrite, grind them to -74μm or more using a vibratory mill.

[0016] (2) First, the acidophilic microorganisms were inoculated into 9K medium containing 0.5% pyrite pulp at an inoculation rate of 5-20% for acclimatization culture. The initial pH was 1.5-3.5, the temperature was 10-45℃, and the shaking speed was 100-200 r / min. The number of viable cells was counted daily using a hemocytometer. When the bacterial concentration reached 10... 8 ~10 9 The bacteria were collected at a concentration of 1, 2, 3, 4, and 5% pyrite pulp to complete the first acclimatization. The bacteria were then collected, and the above steps were repeated. Acclimatization was carried out sequentially in pyrite pulp containing 1%, 2%, 3%, 4%, and 5% pyrite pulp concentrations until the acidophilic microorganisms could adapt to pyrite pulp concentrations of 0.5%–5%. After acclimatization and culture, the filter residue was removed, and the bacteria were collected by centrifugation.

[0017] (3) The acclimatized and cultured acidophilic microorganisms were inoculated at a rate of 1×10⁻⁶. 7 ~9×10 7 Inoculate at a concentration of 1 / mL into 9K medium containing pyrite-containing waste rock at a pulp concentration of 0.5–5% for expansion culture. Initial pH 1.5–3.5, temperature 10–45℃, and shaker speed 100–200 rpm. Count viable cells daily using a hemocytometer. When the bacterial concentration reaches 10-1... 8 ~10 9 The culture was expanded to a density of 100 cells / mL. The filter residue was removed, and the bacteria were collected by centrifugation.

[0018] (4) The cultured bacteria were inoculated at a rate of 1×10⁻⁶. 7 ~9×10 7 Bioleaching was carried out by inoculating 1 / mL of pyrite-containing waste rock with a slurry concentration of 1-5% and a pH of 1.5-3.0 into 9k medium and performing the bioleaching at a shaking speed of 100-200 r / min and a temperature of 10-40℃.

[0019] (5) The concentrations of ferric and ferrous ions in the solution were measured every 5 days using an enzyme-linked immunosorbent assay (ELISA) reader.

[0020] (6) After the biological rinsing is completed, the rinsing residue is collected by filtering with filter paper for surface morphology analysis, phase and elemental composition analysis.

[0021] The 9K culture medium formula of this invention is as follows: (NH4)2SO4 3.0 g / L, KCl 0.1 g / L, K2HPO4 0.5 g / L, MgSO4·7H2O 0.5 g / L, Ca(NO3)2 0.01 g / L, and the pH value is adjusted to 1.5-3.5 with 0.1 mol / L H2SO4.

[0022] This invention accelerates the dissolution of pyrite, removing most of it from waste rock in a short time. This reduces the risk of acidic mine wastewater generation from subsequent pyrite waste rock or tailings storage, lowers the maintenance costs of AMD end-of-pipe treatment systems, and offers significant environmental and social benefits. This invention is primarily applicable to the decontamination of pyrite solid waste, especially pyrite-containing waste rock or tailings. Attached Figure Description

[0023] Figure 1 This is the pyrite removal situation after rinsing pyrite waste rock with a sulfur content of 5% by *Thiobacillus ferrooxidans* in Example 1.

[0024] Figure 2 XRD pattern of slag sample from pyrite waste rock with 5% sulfur content after leaching with *Thiobacillus acidophilus* in Example 1;

[0025] Figure 3 This is a SEM image of the slag sample after rinsing pyrite waste rock with a sulfur content of 5% by *Thiobacillus acidophilus* in Example 1.

[0026] Figure 4 This is an example of secondary iron release from slag samples after rinsing pyrite waste rock with a sulfur content of 5% by *Thiobacillus ferrooxidans* in Example 1.

[0027] Figure 5 This is the pyrite removal situation after rinsing pyrite waste rock with a sulfur content of 12% by *Thiobacillus acidophilus* in Example 2.

[0028] Figure 6 The image shows the XRD pattern of the leaching residue sample after leaching pyrite waste rock with a sulfur content of 12% by *Thiobacillus acidophilus* in Example 2.

[0029] Figure 7 This is a SEM image of the leaching residue sample after rinsing pyrite waste rock with a sulfur content of 12% by *Thiobacillus acidophilus* in Example 2.

[0030] Figure 8 This is an example of secondary iron release from slag samples after rinsing pyrite waste rock with a sulfur content of 12% by *Thiobacillus ferrooxidans* in Example 2.

[0031] Figure 9 This is the pyrite removal situation after rinsing pyrite waste rock with a sulfur content of 23% by *Thiobacillus acidophilus* in Example 3.

[0032] Figure 10 XRD pattern of slag sample from pyrite waste rock with sulfur content of 23% after leaching with *Thiobacillus acidophilus* in Example 3;

[0033] Figure 11 SEM image of the slag sample after rinsing pyrite waste rock with a sulfur content of 23% by *Thiobacillus acidophilus* in Example 3;

[0034] Figure 12 This is an example of secondary iron release from slag samples after rinsing pyrite waste rock with a sulfur content of 23% by *Thiobacillus ferrooxidans* in Example 3.

[0035] Figure 13 This is the pyrite removal situation after biological leaching of pyrite waste rock with a sulfur content of 21% by Leptospira ferrous oxide in Example 4. Detailed Implementation

[0036] The following specific embodiments or implementation methods are intended to further illustrate the present invention, and are not intended to limit the present invention.

[0037] Example 1

[0038] The method described in this embodiment is mainly carried out according to the following steps:

[0039] (1) Waste rock samples collected from the site of acidic mine wastewater pollution were first cleaned to remove surface impurities, air-dried, crushed, and dry-ground. Then, they were sieved through a 200-mesh sieve to obtain powder samples with a particle size less than 74 μm. These samples were stored in a vacuum drying oven for later use. Before the experiment, powder X-ray diffraction analysis revealed that the main phases of the waste rock were quartz, muscovite, chlorite, gypsum, dolomite, and pyrite. XRF analysis showed that the mineral elemental composition was Fe: 4.68%, S: 4.56%, O: 45.30%, Si: 21.86%, Al: 10.21%, Ca: 6.82%, K: 4.42%, and other elements: 2.15%. Based on the XRD and XRF results, this portion of waste rock was named pyrite waste rock with a sulfur content of 5%.

[0040] (2) The pre-acclimatized acidophilic ferrous thiobacillus was prepared at 3×10 7 The inoculum was inoculated at a rate of 1 / mL into 9K medium containing 2% pyrite pulp for expansion culture. The culture conditions were: initial pH 2.0, temperature 30℃, and shaking speed 170r / min.

[0041] (3) Centrifuge to collect the *Acidithiobacillus ferrooxidans* cultured to mid-log phase in step (2), and then centrifuge them at a rate of 3 × 10⁻⁶. 7 The concentration of ferrous iron / mL was inoculated into 9k culture medium containing 2% slurry and 5% sulfur pyrite waste rock, and bioleached for 40 days. The initial conditions for bioleaching were pH 2.0, shaking speed 170 r / min, and temperature 30℃. (4) The concentrations of ferrous iron and total iron in the solution were measured every 5 days using an enzyme-linked immunosorbent assay (ELISA) reader.

[0042] (5) After the biological leaching is completed, the leaching residue is collected by filtering with filter paper for surface morphology analysis, phase and elemental composition analysis, and the leaching residue is subjected to secondary biological leaching to verify the stability of the leaching residue and evaluate the risk of acidic wastewater release.

[0043] Conclusion: Figure 1 As shown, after 40 days of bioleaching, less than 0.2% of the pyrite in the pyrite waste rock with a sulfur content of 5% dissolved, and the phase and morphology before and after leaching did not change significantly. Figure 2 and Figure 3 This indicates that the risk of acidic mine wastewater generation from waste rock with a sulfur content of this amount is very low. Therefore, the method of this invention is applicable to the treatment of pyrite waste rock with a sulfur content greater than 5%.

[0044] Example 2

[0045] The method described in this embodiment is mainly carried out according to the following steps:

[0046] (1) First, the waste rock samples collected from the site of the acidic mine wastewater pollution were cleaned to remove surface impurities, air-dried, crushed, and dry-ground. Then, they were sieved through a 200-mesh sieve to obtain powder samples with a particle size of less than 74 μm. These samples were stored in a vacuum drying oven for later use. Before the experiment, powder X-ray diffraction analysis revealed that the main phases of the waste rock were quartz, muscovite, chlorite, gypsum, dolomite, and pyrite. XRF analysis showed that the mineral element composition was Fe: 13.68%, S: 12.12%, O: 35.10%, Si: 23.65%, Al: 6.40%, Ca: 0.26%, K: 2.23%, and other elements: 8.79%. Based on the XRD and XRF results, this part of the polluted waste rock was named pyrite waste rock with a sulfur content of 12%.

[0047] (2) The pre-acclimatized acidophilic ferrous thiobacillus was prepared at 3×10 7 The inoculum was inoculated at a rate of 1 / mL into 9K medium containing 2% pyrite pulp for expansion culture. The culture conditions were: initial pH 2.0, temperature 30℃, and shaking speed 170r / min.

[0048] (3) Centrifuge to collect the *Acidithiobacillus ferrooxidans* cultured to mid-log phase in step (2), and then centrifuge them at a rate of 3 × 10⁻⁶. 7 The concentration of ferrous iron / mL was inoculated into 9k culture medium containing 2% slurry and 12% sulfur pyrite waste rock, and bioleached for 40 days. The initial conditions for bioleaching were pH 2.0, shaking speed 170 r / min, and temperature 30℃. (4) The concentrations of ferrous iron and total iron in the solution were measured every 5 days using an enzyme-linked immunosorbent assay (ELISA) reader.

[0049] (5) After the biological leaching is completed, the leaching residue is collected by filtering with filter paper for surface morphology analysis, phase and elemental composition analysis, and the leaching residue is subjected to secondary biological leaching to verify the stability of the leaching residue and evaluate the risk of acidic wastewater release.

[0050] Conclusion: Figure 5As shown, after 40 days of bioleaching, the pyrite removal rate in pyrite waste rock with a sulfur content of 12% can reach 65%. XRD results confirmed that the pyrite phase was significantly reduced after leaching, and the formation of potassium ferrous sulfate was also detected. Figure 6 SEM results showed that the generated potassium ferrous sulfate would coat the surface of pyrite, thereby achieving passivation and hindering the secondary dissolution of residual pyrite. Figure 7 ).like Figure 8 As shown, after 60 days of secondary biological leaching of pyrite waste rock with a sulfur content of 12%, the total iron concentration in the solution was less than 8 mg / L, which proves the stability of the leaching residue and significantly reduces the risk of acidic mine wastewater generation.

[0051] Example 3

[0052] The method described in this embodiment is mainly carried out according to the following steps:

[0053] (1) First, the polluted samples collected from the acidic mine wastewater pollution site were cleaned to remove surface impurities, air-dried, crushed, and dry-ground. Then, they were sieved through a 200-mesh sieve to obtain powder samples with a particle size of less than 74 μm. These samples were stored in a vacuum drying oven for later use. Before the experiment, powder X-ray diffraction analysis revealed that the main phases of the waste rock were quartz, muscovite, chlorite, gypsum, dolomite, and pyrite. XRF analysis showed that the mineral element composition was Fe: 25.93%, S: 22.88%, O: 21.90%, Si: 12.06%, Al: 7.67%, Ca: 0.01%, K: 2.55%, and other elements: 7.00%. Based on the XRD and XRF results, this part of the polluted waste rock was named pyrite waste rock with a sulfur content of 23%.

[0054] (2) The pre-acclimatized acidophilic ferrous thiobacillus was prepared at 5×10 7 The inoculum was inoculated at a rate of 1 / mL into 9K medium containing 2% pyrite pulp for expansion culture. The culture conditions were: initial pH 2.0, temperature 30℃, and shaking speed 170r / min.

[0055] (3) Centrifuge to collect the *Acidithiobacillus ferrooxidans* cultured to mid-log phase in step (2), and then centrifuge them at a rate of 5 × 10⁻⁶ cm⁻¹. 7 The concentration of ferrous iron / mL was inoculated into 9k culture medium containing 3% pyrite slurry and 23% sulfur content, and bioleached for 40 days. The initial conditions for bioleaching were pH 2.0, shaking speed 170 r / min, and temperature 30℃. (4) The concentrations of ferrous iron and total iron in the solution were measured every 5 days using an enzyme-linked immunosorbent assay (ELISA) reader.

[0056] (5) After the biological leaching is completed, the leaching residue is collected by filtering with filter paper for surface morphology analysis, phase and elemental composition analysis, and the leaching residue is subjected to secondary biological leaching to verify the stability of the leaching residue and evaluate the risk of acidic wastewater release.

[0057] Conclusion: Figure 9 As shown, after 40 days of bioleaching, the pyrite removal rate in pyrite waste rock with a sulfur content of 23% can reach 95%. XRD results confirmed that the intensity of the characteristic peak of pyrite was significantly reduced after leaching, and the formation of potassium ferrous sulfate was also detected. Figure 10 SEM results showed that the generated potassium ferrous sulfate would coat the surface of pyrite, thereby achieving passivation and hindering the secondary dissolution of residual pyrite. Figure 11 ).like Figure 12 As shown, after 60 days of secondary biological leaching of pyrite waste rock with a sulfur content of 23%, the total iron concentration in the solution was less than 8 mg / L, which proved the stability of the leaching residue and significantly reduced the risk of acidic mine wastewater generation.

[0058] Example 4

[0059] The method described in this embodiment is mainly carried out according to the following steps:

[0060] (1) First, the polluted samples collected from the acidic mine wastewater pollution site were cleaned to remove surface impurities, air-dried, crushed, and dry-ground. Then, they were sieved through a 200-mesh sieve to obtain powder samples with a particle size of less than 74 μm. These samples were stored in a vacuum drying oven for later use. Before the experiment, powder X-ray diffraction analysis revealed that the main phases of the waste rock were quartz, muscovite, chlorite, gypsum, dolomite, and pyrite. XRF analysis showed that the mineral element composition was Fe: 22.53%, S: 20.58%, O: 23.58%, Si: 17.66%, Al: 5.67%, Ca: 0.03%, K: 2.75%, and other elements: 7.20%. Based on the XRD and XRF results, this part of the polluted waste rock was named pyrite waste rock with a sulfur content of 21%.

[0061] (2) The pre-acclimatized ferrous leptospira were mixed at 5×10 7 Inoculation was carried out at a rate of 1 inoculum / mL in 9K medium containing 2% pyrite pulp for expansion culture. The culture conditions were: initial pH 1.8, temperature 45℃, and shaking speed 180r / min.

[0062] (3) Collect the Leptospira ferrous oxide bacteria cultured to the mid-log phase in step (2) by centrifugation, and then process them at a rate of 2 × 10⁻⁶. 7 The concentration of ferrous iron / mL was inoculated into a 9k culture medium containing 2% pyrite slurry and 21% sulfur content for 40 days of bioleaching. The initial conditions for bioleaching were pH 2.0, shaking speed 180 r / min, and temperature 45℃. (4) The concentrations of ferrous iron and total iron in the solution were measured every 5 days using an enzyme-linked immunosorbent assay (ELISA) reader.

[0063] (5) After the biological rinsing is completed, the rinsing residue is collected by filtering with filter paper for surface morphology analysis, phase and elemental composition analysis.

[0064] Conclusion: Figure 13 As shown, after 40 days of bioleaching, the pyrite removal rate in pyrite waste rock with a sulfur content of 21% can reach 98%, and the risk of acidic mine wastewater generation is significantly reduced.

Claims

1. A method for treating acidic mine wastewater at its source, characterized in that... Biological leaching of pyrite-containing waste rock or flotation tailings can accelerate the dissolution of pyrite and remove most of the pyrite from the waste rock in a short time. The biological leaching generates potassium ferrous sulfate, which passivates the residual pyrite and inhibits secondary dissolution. The pyrite-containing waste rock or flotation tailings are first crushed and screened to a particle size of less than 74 μm. Then, acidophilic microorganisms are inoculated into a leaching system of pyrite-containing waste rock or flotation tailings with a pulp concentration of 1-5%. The initial pH of the leaching system is 1.5-3.5, the temperature is 10-40℃, and the shaking speed of the leaching system is 100-200 r / min. The leaching time does not exceed 50 days. The sulfur content in the pyrite-containing waste rock or flotation tailings is not less than 5%.

2. The method according to claim 1, characterized in that... The acidophilic microorganisms include at least one of the following: acidophilic ferrooxidizing thiobacillus, acidophilic thiobacillus, thermophilic acidophilic thiobacillus, and ferrooxidizing Leptospira.

3. The method according to claim 1 or 2, characterized in that... According to the inoculation dose of 1x10 7 ~9x10 7 Acidophilic microorganisms were introduced per mL into the washing system of pyrite-containing waste rock or flotation tailings.

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