A material and treatment method for passivating sulfur-containing tailings and inhibiting the generation of acidic mine wastewater

Abstract

The present invention provides a material and treatment method for passivating sulfur-containing tailings and inhibiting the generation of acid mine drainage. The material is formed by burning agricultural byproducts. When applied to sulfur-containing tailings, the material can not only passivate the sulfur-containing tailings but also further inhibit the generation of acid mine drainage. Furthermore, the treatment method is low-cost and simple to operate, making it highly commercializable.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental engineering, and in particular to a material and a treatment method for passivating sulfur-containing tailings and inhibiting the generation of acidic mine wastewater. Background Art

[0002] During the mining and processing of sulfur-containing minerals, a large amount of low-grade sulfur-containing tailings will be produced. Most of them are piled in the open air or stored in underground tailings ponds. After long-term rainwater leaching or groundwater contact and air oxidation, they will form a leachate with low pH, high sulfate concentration and high heavy metal concentration under the action of microorganisms. It is called acid mine drainage (AMD).

[0003] To mitigate the negative environmental impacts of AMD on ecosystems and human health, treatment technologies such as neutralization, adsorption, ion exchange, membrane technology, bioremediation, and electrochemical methods have been applied to AMD remediation. However, these technologies treat a continuous supply of AMD, requiring expensive maintenance and labor costs, and may also generate secondary pollutants. Therefore, these methods cannot form a long-term, scalable, and sustainable approach to AMD treatment.

[0004] Since the oxidation of sulfur-containing tailings is driven by oxygen, water, and microorganisms (such as Thiobacillus), AMD formation can be limited by eliminating any of these three components. Based on this concept, inhibiting tailings oxidation to prevent AMD formation at the source is considered the most promising approach. Currently, the most common approach involves co-treating the tailings with alkaline materials with high neutralizing potential. The presence of these alkaline materials facilitates acid neutralization, raising the pH to cause coprecipitation of heavy metals and forming a coating of iron hydroxide on the pyrite surface, known as microencapsulation. Research has shown that some alkaline materials, due to their presence in silicate glasses such as SiO2 and Al2O3, further react with Ca(OH)2 to form gels such as hydrated calcium silicate (known as the pozzolanic effect). These reactions reduce contact between sulfide components and oxidants, inhibiting tailings oxidation. Currently, commonly used alkaline materials include limestone and fly ash. However, these materials also carry high economic costs, especially since limestone is considered a critical chemical resource. Furthermore, the use of these materials fails to fully consider the impact of microbial activity on the oxidation of sulfur-containing tailings. Research indicates that the rate of microbial sulfide oxidation can be six orders of magnitude higher than the equivalent abiotic reaction rate. Some microorganisms, such as Thiobacillus ferrooxidans, can accelerate the oxidation of ferrous iron to ferric iron, thereby increasing the rate of sulfide oxidation and ultimately promoting the formation of AMD. Other studies have shown that dissolved O₂ in water contributes significantly to sulfide oxidation. Therefore, if microbial action can be combined to inhibit the growth of Thiobacillus ferrooxidans and reduce dissolved oxygen in the water, the remediation effect of alkaline materials on sulfur-containing tailings will be further enhanced.

[0005] In summary, seeking an alkaline material that is economical and can achieve good repair effects is of great significance for the repair of slag. As we all know, wood ash is an alkaline material with a wide source, cheap and easy to obtain, which is mainly produced by the combustion of renewable resources such as agricultural residues. It is estimated that 476 million tons of wood ash may be produced each year worldwide. It is currently often used as a soil conditioner and adsorbent. In addition, studies have shown that wood ash is a complex inorganic-organic mixture with multiple components. It not only contains inorganic substances but also carbon and organic minerals. It can provide biological growth, nutrition and necessary elements such as C, N, P, K, etc., can enhance biological activity, and provide a better environment for some microorganisms. The research focus of the present invention is to apply wood ash to the passivation of sulfur-containing tailings and inhibit its production of acidic mine wastewater, in order to explore its potential in this regard. Summary of the Invention

[0006] In response to the problems and shortcomings of the existing technology, the present invention provides a material and treatment method for passivating sulfur-containing tailings and inhibiting the generation of acid mine drainage. The material is applied to sulfur-containing tailings and achieves the purpose of passivating sulfur-containing tailings and inhibiting the generation of AMD through the combined effects of physical, chemical and microbial processes. The technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a wood ash material, comprising: burning agricultural by-products to form the wood ash material.

[0008] Furthermore, the agricultural by-products include rice straw, stalks, vines, and branches, preferably corn stalks and rice straw are compounded in a mass ratio of 1:1.

[0009] Furthermore, the preparation method comprises the following steps:

[0010] Step 1: Dry the agricultural by-products and burn them in an incinerator. The hot flue gas generated during the combustion process is used to recover heat and dust.

[0011] Step 2: Mix the combustion products and the recovered dust, grind them together, and pass them through a 2 mm sieve to obtain the wood ash material.

[0012] In a second aspect, the present invention provides a wood ash material obtained by the above-mentioned preparation method, wherein the particle size of the wood ash material is not higher than 2 mm.

[0013] In a third aspect, the present invention provides the use of the above-mentioned wood ash material in passivating sulfur-containing tailings.

[0014] Furthermore, the wood ash material is added in an amount of 10%-50% of the mass of the sulfur-containing tailings.

[0015] In a fourth aspect, the present invention provides a method for inhibiting the generation of acid mine drainage, comprising:

[0016] (1) Evenly mixing the wood ash material and the sulfur-containing tailings slag, the mass ratio of which is 10% to 50% of the sulfur-containing tailings;

[0017] (2) leaching the mixture of wood ash material and sulfur-containing tailings;

[0018] (3) Covering the sulfur-containing tailings after passivation treatment.

[0019] Furthermore, the control parameters of the leaching in step (2) are as follows: the volume of the leaching agent is calculated according to the liquid-solid ratio of 10:1 (L / Kg), pure water leaching agent is added, the mixture is horizontally oscillated at room temperature, the oscillation frequency is 110 to 120 times / min, after oscillating for 8 to 10 hours, it is allowed to stand for 14 to 16 hours, and the leachate is obtained after passing through a 0.45um filter membrane; the pH of the first leachate is controlled to be above 9.

[0020] The present invention converts agricultural byproducts into plant ash, which is then uniformly mixed with sulfur-containing tailings. This not only passivates the sulfur-containing tailings but also further inhibits the generation of acidic mine wastewater from the tailings. This is presumably because, on the one hand, the addition of plant ash creates an alkaline environment within the tailings, allowing heavy metals to precipitate as hydroxides on the pyrite surface. Over time, the precipitate completely encapsulates the pyrite particles, preventing any contact between the tailings and the oxidant, thereby halting the oxidation process. On the other hand, plant ash has a large specific surface area and contains oxygen-containing functional groups that may support metal adsorption, such as silanols, hydroxyls, carboxylic acids, and phenols, which also help remove heavy metals from the leachate. Finally, the addition of plant ash significantly increases the richness and diversity of the microbial community, reducing the dissolved oxygen content in the water surrounding the tailings through its metabolic activities. It also introduces competition with AMD-catalyzing microorganisms (Thiobacillus), increasing the growth of some reducing bacteria and further inhibiting the oxidation process. In summary, the wood ash material and the method for treating sulfur-containing tailings provided by the present invention are low-cost and simple to operate, can effectively passivate sulfur-containing tailings and inhibit the generation of AMD, and have strong promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the change of Fe concentration in the leachate of the group with added wood ash material and the control group over time in Example 1 of the present invention.

[0022] Figure 2 Schematic diagram of the change of Mn concentration over time in the leachate of the group with added wood ash material and the control group in Example 1 of the present invention.

[0023] Figure 3 Schematic diagram of the change of Zn concentration over time in the leachate of the group with added wood ash material and the control group in Example 1 of the present invention.

[0024] Figure 4 Schematic diagram of the change of Pb concentration over time in the leachate of the group with added wood ash material and the control group in Example 1 of the present invention.

[0025] Figure 5 Schematic diagram of the change of As concentration over time in the leachate of the group with added wood ash material and the control group in Example 1 of the present invention.

[0026] Figure 6 Schematic diagram of the change of Cd concentration over time in the leachate of the group with added wood ash material and the control group in Example 1 of the present invention.

[0027] Figure 7 This is a graph of the relative abundance of filler bacteria (genus level) in the group with added wood ash material and the control group in Example 1 of the present invention.

[0028] Figure 8This is a heat map of the functional abundance of filler bacteria in the group with added wood ash material and the control group in Example 1 of the present invention.

[0029] Figure 9 Schematic diagram of the change of Fe concentration in the leachate of the group with added wood ash material and the control group over time in Example 2 of the present invention.

[0030] Figure 10 Schematic diagram of the change of Mn concentration over time in the leachate of the group with added wood ash material and the control group in Example 2 of the present invention.

[0031] Figure 11 Schematic diagram of the change of Zn concentration over time in the leachate of the group with added wood ash material and the control group in Example 2 of the present invention.

[0032] Figure 12 Schematic diagram of the change of Pb concentration over time in the leachate of the group with added wood ash material and the control group in Example 2 of the present invention.

[0033] Figure 13 Schematic diagram of the change of As concentration over time in the leachate of the group with added wood ash material and the control group in Example 2 of the present invention.

[0034] Figure 14 Schematic diagram of the change of Cd concentration over time in the leachate of the group with added wood ash material and the control group in Example 2 of the present invention.

[0035] Figures 1 to 6 CONTROL: control group; PA: plant ash; VA: volcanic ash; LS: limestone; FA: fly ash.

[0036] Figures 9-14 CONTROL: control group; 10PA: 10% wood ash by mass; 20PA: 20% wood ash by mass; 30PA: 30% wood ash by mass; 40PA: 40% wood ash by mass; 50PA: 50% wood ash by mass. DETAILED DESCRIPTION

[0037] In the description of the present invention, it should be noted that if specific conditions are not specified in the examples, the experiments were carried out according to conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used, if the manufacturer is not specified, are all conventional products that can be purchased commercially.

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, which are intended to explain the present invention rather than to limit it.

[0039] Example 1

[0040] This example investigates a wood ash material and a method for passivating sulfur-containing tailings and inhibiting AMD production. The specific steps are as follows:

[0041] (1) Mix rice straw and corn stalks in a ratio of 1:1 and dry them naturally or at low temperature to obtain moisture;

[0042] (2) Burning the raw materials processed in step (1) under natural conditions to obtain wood ash material.

[0043] (3) Grind the wood ash obtained in step (2) evenly and pass it through a 2 mm sieve to obtain the product.

[0044] (4) Tailings were collected from the Shuilong Tailings area of Fogang County, Qingyuan City, Guangdong Province. They were pyrite associated with lead-zinc ore. Samples were collected at a depth of 15 cm or less and were taken at four different sampling points. They were air-dried, crushed, passed through a 2 mm sieve, and mixed evenly.

[0045] (5) A simulated column experiment was carried out in a plexiglass column, and the tailings obtained in step (4) and the wood ash material obtained in step (3) were uniformly mixed in a mass ratio of 10:3.

[0046] (6) A 7-day wet / dry cycle was applied to the column test. 280 ml of deionized water was manually injected weekly to simulate rainfall. This would result in an annual artificial irrigation of approximately 1,858 mm, which is consistent with the average annual rainfall in Qingyuan City (1,852 mm). The control parameters for leaching in the column test were: a liquid-to-solid ratio of 10:1 (L / Kg), horizontal oscillation of the column at a frequency of 110 times / min, oscillation for 9 hours, and then 16 hours of rest. After collecting the leachate on the second day and filtering it through a 0.45 μm filter membrane, the column was dried until the seventh day before starting the next cycle.

[0047] The leachate measurement results are as follows Figure 1-6 As shown in the figure, it can be seen that compared with the control group, the addition of wood ash effectively inhibits the generation of AMD in sulfur-containing tailings, with average removal rates of 99.9%, 94%, 99.7%, 98.5%, 92.4%, and 98.9% for Fe, Mn, Zn, Pb, As, and Cd, respectively. Wood ash is significantly more effective than volcanic ash, limestone, and fly ash in removing Fe, Mn, and Zn.

[0048] Microbial bacterial index results such as Figure 7-8 Table 1 shows the α-diversity analysis of the bacteria in the column packing. It is clear that the addition of wood ash significantly increased the richness and diversity of the microbial community. Furthermore, it introduced competition with the AMD-catalyzing microorganisms (Thiobacillus), significantly reducing the abundance of Sulfobacillus and promoting the growth of some reducing bacteria, such as Hydrogenophaga and Bacillus.

[0049] Table 1 Bacterial α diversity analysis index of the fillers in the group with added plant ash and the control group in Example 1

[0050]

[0051] Example 2

[0052] This example investigates the effect of applying wood ash materials with different mass percentages to the remediation of sulfur-containing tailings. The specific steps are as follows:

[0053] (1) Using rice straw or other plant stalks, vines, or branches as raw materials, drying naturally or drying at low temperature to obtain moisture;

[0054] (2) Burning the raw materials processed in step (1) under natural conditions to obtain wood ash material.

[0055] (3) Grind the wood ash obtained in step (2) evenly and pass it through a 2 mm sieve to obtain the product.

[0056] (4) Tailings were collected from the Shuilong Tailings area of Fogang County, Qingyuan City, Guangdong Province. They were pyrite associated with lead-zinc ore. Samples were collected at a depth of 15 cm or less and were taken at four different sampling points. They were air-dried, crushed, passed through a 2 mm sieve, and mixed evenly.

[0057] (5) A simulated column experiment is carried out in a plexiglass column, wherein the tailings obtained in step (4) and the wood ash material obtained in step (3) are uniformly mixed, and the weight proportion of the wood ash material in different reaction columns is 10%-50%.

[0058] (6) A 7-day wet / dry cycle was applied to the column test. 280 ml of deionized water was manually injected weekly to simulate rainfall. This would result in an annual artificial irrigation of approximately 1,858 mm, which is consistent with the average annual rainfall in Qingyuan City (1,852 mm). The control parameters for leaching in the column test were: a liquid-to-solid ratio of 10:1 (L / Kg), horizontal oscillation of the column at a frequency of 110 times / min, oscillation for 8 hours, and then 15 hours of rest. After collecting the leachate on the second day and filtering it through a 0.45 μm filter membrane, the column was air-dried until the seventh day before starting the next cycle.

[0059] The leachate measurement results are as follows Figure 9-14As shown. It can be concluded from the figure that: compared with the control group, the addition of wood ash material can effectively inhibit the generation of AMD in sulfur-containing tailings, and the final heavy metal removal rate varies depending on the addition ratio of wood ash material and the type of heavy metal. The average removal rate of each treatment column for Fe, Mn, and Zn reached the highest level in the 50PA column, which were 99.9%, 99.9%, and 99.9%, respectively. The average removal rate for As reached the highest level in the 10PA column, which was 99.8%. The average removal rates for Pb and Cd reached the highest level in the 10PA and 20PA columns, which were 98.5% and 99.8%, respectively.

[0060] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. The use of wood ash material in passivating sulfur-containing tailings of pyrite associated with lead-zinc mines, characterized in that: The plant ash material is obtained by mixing the combustion products generated by burning agricultural by-products with the dust generated during the recovery combustion process, wherein the agricultural by-products are corn stalks and rice straw in a mass ratio of 1:1; The passivation is to leach the mixture of the plant ash material and the sulfur-containing tailings slag, and the pH of the first leachate is controlled to be above 9; When the sulfur-containing tailings contain Fe, Mn and / or Zn, the wood ash material is added in an amount of 30%-50% of the mass of the sulfur-containing tailings.

2. The use according to claim 1, characterized in that: The preparation method of the plant ash material comprises the following steps: Step 1: Dry the agricultural by-products and burn them in an incinerator. The hot flue gas generated during the combustion process is used to recover heat and dust. Step 2: Mix the combustion products and the recovered dust, grind them together, and pass them through a 2 mm sieve to obtain the wood ash material.

3. A method for inhibiting the generation of acid mine drainage, characterized in that: include: (1) Using the wood ash material according to claim 1, when the sulfur-containing tailings contain Fe, Mn and / or Zn, the wood ash material and the sulfur-containing tailings are mixed evenly, the weight ratio of which is 30% to 50% of the sulfur-containing tailings; (2) leaching the mixture of the wood ash material and the sulfur-containing tailings, wherein the pH of the first leachate is controlled to be above 9; (3) Covering the sulfur-containing tailings after passivation treatment.

4. The method for suppressing the generation of acid mine drainage according to claim 3, characterized in that: The control parameters of the leaching in step (2) are as follows: the volume of the leaching agent is calculated based on a liquid-to-solid ratio of 10:1, wherein the liquid unit is liter and the solid unit is kilogram; pure water leaching agent is added, the mixture is horizontally oscillated at room temperature at an oscillation frequency of 110 to 120 times / min, oscillated for 8 to 10 hours, then allowed to stand for 14 to 16 hours, and filtered through a 0.45 μm filter membrane to obtain a leachate; and the pH of the initial leachate is controlled to be above 9.

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