Ecological treatment method for acid waste rock storage yard or waste dump slope

Abstract

The method comprises the following steps: uniformly mixing residual sludge of a sewage plant, cow dung, agriculture and forestry solid wastes and kitchen waste hydrothermal carbon, adding silicate minerals and sulfur-containing minerals / waste rocks according to a ratio, and uniformly stirring, so as to obtain the ecological treatment method for the side slope of the acid waste rock storage yard or the waste dump. And adding a bacillus mucilaginosus and thiobacillus thiooxidans compound microbial agent into the mixture, carrying out compost main fermentation and post fermentation, spreading the obtained compost product to an acid waste rock storage yard or a waste dump slope, and planting local herbaceous plants. The compost product prepared by the method has the advantages of high mineral element and organic matter content, good heavy metal curing effect, strong site acidification buffer capability and the like, and can be widely applied to ecological management of acid waste rock storage yards or waste dump slopes, acid soil improvement and highway acid slope greening.

Description

Technical Field

[0001] The invention belongs to the technical fields of mine ecological environment treatment and acidic soil improvement, and particularly relates to a method for ecological treatment of slopes of acidic waste rock yards or spoil banks. Background Art

[0002] Mining usually forms waste rock yards or spoil bank slopes with huge areas. Affected by humid and hot climate conditions, sulfur-containing minerals or waste rocks generate acidic wastewater through long-term physical, chemical, and biological actions, which have obvious adverse effects on the surrounding water bodies, soil, and ecological environment, and urgent ecological treatment is needed. In addition, during the construction of expressways, many sections pass through complex rock areas with diverse geological conditions, and the problem of acidic slopes is also very prominent. Developing in-situ ecological restoration technologies for high and steep slopes of expressways according to local conditions is an urgent internal requirement for the construction of "beautiful highways".

[0003] Existing research has focused more on the formation mechanism, environmental hazards, and treatment technology development of mine acid wastewater, and mainly concentrated on source control such as mine water, pit water, tailings leachate, and leachate from biological heap leaching. The control methods mainly include alkali neutralization precipitation, sulfide precipitation, redox treatment, and microbial reduction to increase the pH value of the water body. However, the acid leaching process in waste rock dumps, open-pit slopes, etc. is slow, which belongs to a kind of invisible soil environmental damage. The research on ecological restoration and treatment technology for acid waste rock dumps or spoil bank slopes formed by mine exploitation is relatively weak. A small amount of research has reported the acid production process and control measures for acid slopes, and proposed measures such as soil spraying, fish-scale pits, stacking ecological bags, and ecological retaining walls. Some studies believe that laying inorganic mineral materials or industrial alkaline waste on the surface of waste rock or tailings can reduce the contact between sulfide minerals and water and oxygen, thus slowing down the generation of acid wastewater. Typical inorganic materials for acid soil improvement mainly include quicklime, slaked lime, limestone powder, geosynthetic clay, phosphogypsum, and fly ash, etc. The inorganic material covering technology has the advantages of a wide variety of materials, wide sources, and simple construction, but at the same time, there are deficiencies such as the large impact of the covering layer by rain erosion and the difficulty of plant growth due to the lack of soil matrix. When using simple artificial planting and soil spraying technology for ecological restoration of acid slopes, it is impossible to effectively control the acid water leaching formed after the oxidation of surrounding rock or ore body sulfides, which will continuously seep out and wash the slope, and affect the self-repair effect of the ecosystem. Xu Huibiao et al. (Research on the In-situ Solidification and Barrier Method for Acid Open-pit Slopes in Non-ferrous Metal Mines, China Mining Magazine, 2023, 32 (9)) combined the matrix characteristics of the acid open-pit slope of Zijinshan Gold-Copper Mine in Fujian to develop two oxygen barrier covering and acidification control methods. One is a thin-layer solidified isolation covering material composed of sand, calcium oxide, cement, potassium polyacrylate, and organic chelating agent, and the other is a thick-layer neutralization medium covering material prepared from 80 - 90% neutralization slag, 5 - 10% microbial bacterial fertilizer, and 1 - 5% organic fertilizer. The engineering application shows that the acidification of the surface soil in the typical restoration area is effectively controlled, and the average sulfur content drops by 70%, and the three-dimensional plant community gradually recovers. Patent CN202410233773.8 has announced a preparation method of a conditioner for barren soil in plateau mountainous areas. By mixing organic matter waste, silicate minerals, and a composite microbial agent composed of Bacillus and fungi for composting treatment, the prepared soil conditioner can effectively alleviate problems such as low organic matter content, soil compaction, and poor water storage and moisture retention effect in barren soil in plateau mountainous areas. However, this technology has no long-term stable operation effect on the ecological restoration of mine waste rock dumps or spoil bank slopes that are prone to acidification and have high heavy metal content.

[0004] The soil in acid waste rock dumps or spoil grounds has poor structure, lacks organic matter content and nutrient elements essential for plants (especially nitrogen, phosphorus, and potassium), and has a relatively high heavy metal content, which is very unfavorable for plant growth and other biological activities. Therefore, vegetation and ecological restoration are often very difficult. Improving the planting substrate or establishing an artificial composite substrate layer, screening resistant varieties, and combining with the site factors of mining sites, and taking engineering and technical means for pollution control and near-natural ecological restoration are the urgent requirements for the construction of green mines. Summary of the Invention

[0005] The present invention provides a method for ecological treatment of slopes in acid waste rock dumps or spoil grounds. The excess sludge from the sewage treatment plant is mixed with cow dung, agricultural and forestry wastes, and hydrochar from food waste, and after adding silicate minerals and sulfur-containing minerals / waste rocks, it is mixed evenly again. A composite microbial agent with strong ability to decompose feldspar-like silicate minerals is inoculated into the mixed feedstock. The product obtained by co-composting maintains a moderately weak alkaline and can effectively lock heavy metals. It is spread on the slopes of acid waste rock dumps or spoil grounds, and native herbaceous plants are planted in the covering layer to achieve near-natural ecological restoration of the mine.

[0006] The implementation steps of the present invention are as follows: (1) The excess sludge from the sewage treatment plant is sequentially mixed with cow dung and agricultural and forestry solid wastes, and hydrochar from food waste is added as a conditioning agent to prepare a composting mixed substrate with a moisture content of 68-75%. (2) Silicate minerals, sulfur-containing minerals / waste rocks, and a composite microbial agent are sequentially added to the composting mixed substrate. After mixing evenly, the main fermentation of composting is carried out for 12-16 days, and the intensity of air supply and oxygenation is adjusted to maintain the temperature of the pile body at 50-62 °C. (3) The composting materials are subjected to post-fermentation treatment for 20-25 days. When the moisture content of the pile body is reduced to 35-40%, part of the composting product is added to the mixed feedstock in the main fermentation stage, composting microorganisms are inoculated, and the moisture content of the feedstock is adjusted to 60-65%. The remaining composting product is reserved for later use. (4) The obtained composting product is spread on the slopes of acid waste rock dumps or spoil grounds and native herbaceous plants are planted, and the thickness of the covering layer is 15-40 cm.

[0007] Further, the agricultural and forestry solid wastes in step (1) are any one or more of crop straws (such as soybeans, corn, sorghum straws), peanut shells, pinecones, and rice husks; the mass ratio of excess sludge in the composting mixed substrate is 60-70%, the mass ratio of cow dung is 20-30%, the mass ratio of agricultural and forestry solid wastes is 7-10%, and the mass ratio of hydrochar from food waste is 1.0-2.5%.

[0008] Further, the hydrothermal carbonization conditions for the food waste are as follows: the reaction temperature is 180-230 °C, the working pressure is 1.5-2.5 MPa, the hydrothermal treatment time is 1.2-2.0 h, the raw material of the hydrothermal carbon of the food waste is the mass ratio of food waste to dewatered sludge from the sewage treatment plant is (8-4):1, and the water content of the food waste is 88-94%.

[0009] Further, the silicate mineral in step (2) is any one or a combination of plagioclase, wollastonite, blast furnace slag, and phosphorus tailings. The mass proportion of plagioclase is 30-45%, and the addition amount of the silicate mineral is 6-10% of the mass of the compost mixed matrix.

[0010] Further, the sulfur-containing mineral / waste rock in step (2) includes pyrite, chalcopyrite, galena, sphalerite and other such minerals or their waste rock from open-pit slopes, and its addition amount is 6-12% of the mass of the compost mixed matrix.

[0011] Further, the mass ratio of the silicate mineral to the sulfur-containing mineral / waste rock is 1:(1.0-1.2), and the particle size of the mineral or waste rock is 2000-150 μm.

[0012] Further, the addition amount of the composite microbial inoculant in step (2) is 0.6-1.0‰ of the mass of the compost mixed matrix, and it mainly includes Bacillus mucilaginosus ( Bacillus mucilaginosus ), Arthrobacter ( Arthrobacter ), Bacillus subtilis ( Bacillus subtilis ), Thiobacillus thiooxidans ( Thiobacillusthiooxidans ), Thiobacillus ferrooxidans ( ThiobacillusFerrooxidans ), wherein Bacillus mucilaginosus accounts for 25-40% of the total mass of the composite inoculant, and Thiobacillus thiooxidans accounts for 20-30% of the total mass of the composite inoculant.

[0013] Further, in step (3), in the main fermentation stage, the compost product is admixed at a mass ratio of 5-10% of the mixed feed, the compost microorganism is inoculated, and the water content of the compost feed is adjusted to 60-65%.

[0014] Further, in step (4), the covering thickness of the compost product on the acidic waste rock yard or the slope of the waste dump is 15-40 cm, and native herbaceous plants are planted according to the site conditions of the mining area. The typical herbaceous plants that can be selected include Digitaria sanguinalis, Hemarthria compressa, Cynodon dactylon, Neyraudia reynaudiana, Juncus przewalskii, Lolium perenne, etc.

[0015] Compared with the prior art, the present invention has the following technical effects: (1)Using the excess sludge from wastewater treatment plants as the main raw material to prepare a moderately weakly alkaline compost product that can effectively lock heavy metals, which can be widely applied to the ecological treatment of acidic waste rock dumps or spoil bank slopes, the improvement of acidic soils, and the greening of acidic slopes on highways, achieving multiple effects such as the coordinated disposal and resource utilization of organic solid wastes and the near-natural ecological restoration of mines.

[0016] (2)The prepared compost product is rich in organic matter and has a high content of mineral elements. It has good soil air permeability and aggregation properties, significantly improving the current problems such as poor soil structure, lack of organic matter content, and lack of nutrient elements essential for plants in mining areas; the compost product has a relatively high degree of humification, can effectively lock heavy metals, and is conducive to the ecological environment restoration of mining areas with high heavy metal content.

[0017] (3)By the metabolic action of microorganisms such as Thiobacillus thiooxidans and Acidithiobacillus ferrooxidans on sulfur-containing minerals / waste rocks, the acidity of the compost system is appropriately reduced, promoting better dissolution of silicate minerals by microorganisms such as Bacillus mucilaginosus in the compost system, thereby releasing mineral elements such as potassium, sodium, calcium, and magnesium and slowly increasing the alkalinity of the compost pile. While promoting growth, it effectively delays the acidification process of waste rock dumps or spoil bank slopes in mining areas.

[0018] (4)In this invention, hydrothermal carbon from food waste is added as a conditioner. Utilizing the rich carbohydrate substances in food waste and the high protein content in wastewater treatment plant sludge, humic substances are synthesized under hydrothermal conditions. After being added to the co-composting system, it helps to lock the heavy metals leached from waste rock dumps or spoil bank slopes, effectively reducing the heavy metal dissolution and its adverse effects during the weathering process of rock minerals / mine tailings. Detailed implementation mode

[0019] The following specific implementation examples further illustrate the present invention, giving detailed implementation methods and operation processes, but the protection scope of the present invention is not limited to the above content.

[0020] Example 1 The fresh dewatered excess sludge with a water content of 80% from a sewage treatment plant and the wet cow dung with a water content of 87% from a farm are dried in a greenhouse at 40°C for 10 h. Thereafter, the sludge, cow dung, peanut shells, and hydrothermal carbon from food waste are mixed to prepare a compost mixed matrix with a water content of nearly 72% according to a mass ratio of 70:20:8.5:1.5. Among them, the preparation conditions for the hydrothermal carbon from food waste are as follows: reaction temperature 220°C, working pressure 2.2 MPa, hydrothermal treatment time 1.3 h, and the wet basis mass ratio of food waste with a water content of 89% to excess sludge with a water content of 80% from the sewage treatment plant is 5:1. Take 100 kg of the compost mixed matrix, and add 2.8 kg of plagioclase, 5.2 kg of wollastonite, and 8.6 kg of pyrite in sequence. The particle size of the minerals is 150 μm; thereafter, add 0.1 kg of a composite microbial agent, which mainly includes Bacillus mucilaginosus, Bacillus subtilis, Arthrobacter, Thiobacillus thiooxidans, and Thiobacillus ferrooxidans. Among them, the proportions of Bacillus mucilaginosus and Thiobacillus thiooxidans in the total mass of the composite agent are 33 - 36% and 24 - 27% respectively; add 8 - 9 kg of the previously obtained compost product again, inoculate compost microorganisms and adjust the water content of the compost feed to 62 ± 1%. After mixing the above co-composting materials evenly, use a drum-type device to carry out the main fermentation of compost for 15 d, measure the heating rate at the center of the compost pile, and appropriately adjust the air supply and oxygenation intensity to maintain the compost fermentation temperature at 55 - 58°C; thereafter, transfer the compost pile materials to the post-fermentation, spread them into a 20 - 30 cm strip stack for curing treatment for 20 d, and turn the pile occasionally to slowly reduce the water content to 36 ± 2%.

[0021] The total nutrient content of the prepared compost product is 8.2%, the available nitrogen is 3.7 g / kg, and the bulk density is 1.31 g / cm 3 。This compost product is respectively spread on the waste rock yard with a pH value of 3.2 of a copper industry company, and the covering layer thicknesses are 2 cm and 30 cm respectively. Winter rye grass is planted in the covering layer, and the seed germination index GI values are 72% and 113% respectively; after 40 d, the average plant heights of the crops are 2.0 cm and 5.8 cm respectively, and the pH values of the soil leachate at a depth of 50 cm are 3.5 and 7.8 respectively.

[0022] Example 2 The dewatered sludge from the sewage treatment plant and the wet cow dung from the farm are sun-dried to appropriately reduce their moisture content. The sludge, cow dung, corn straw (0.8 - 1.5 cm), and hydrothermal carbon of food waste are mixed according to a mass ratio of 62:30:7:1 to prepare a compost mixed matrix with a moisture content of nearly 70%. Among them, the preparation conditions of the hydrothermal carbon of food waste are: reaction temperature 200 °C, working pressure 2.0 MPa, hydrothermal treatment time 1.6 h, and the wet-based mass ratio of food waste with a moisture content of 91% to the surplus sludge from the sewage treatment plant with a moisture content of 78% is 8:1. Take 100 kg of the compost mixed matrix, and sequentially add 2.5 kg of plagioclase, 2.0 kg of blast furnace slag, 2.0 kg of phosphate tailings, 1.5 kg of chalcopyrite, and 6.2 kg of waste rock from the open-pit slope of sphalerite. The particle size of the minerals is all 200 μm; then, add 0.09 kg of a composite microbial agent, which mainly includes Bacillus mucilaginosus, Bacillus subtilis, Arthrobacter, Thiobacillus thiooxidans, and Thiobacillus ferrooxidans. Among them, the proportions of Bacillus mucilaginosus and Thiobacillus thiooxidans in the total mass of the composite agent are 38 - 40% and 27 - 30% respectively; add 7 - 8 kg of the previously obtained compost product again, inoculate compost microorganisms and adjust the moisture content of the compost feed to 63 ± 1%. After the compost materials are mixed evenly, the main compost fermentation is carried out at a temperature of 56 - 60 °C for 13 d; then, the materials in the compost pile are post-fermented for 25 d. The other operating conditions not mentioned are the same as those in Example 1.

[0023] The total nutrient content of the prepared compost product is 8.4%, the available nitrogen is 3.3 g / kg, and the bulk density is 1.42 g / cm 3 . The compost product is respectively spread on the slopes of the acidic waste dump with a pH of 4.1 of a certain mining company, and the thickness of the covering layer is 2 cm and 30 cm respectively. The covering layer is planted with Setaria viridis, and the seed germination index GI values are 71% and 121% respectively; after 40 d, the average plant heights of the crops are 2.3 cm and 5.5 cm respectively, and the pH values of the soil leachate at a depth of 50 cm are 4.3 and 7.5 respectively.

Claims

1. A method for ecological management of the slope of an acidic waste rock dump or spoil dump, characterized in that: The following steps are included: (1) Mix the wastewater treatment plant sludge with cow dung and agricultural and forestry solid waste, and add food waste hydrocharcoal as a conditioning agent to prepare a compost mixed matrix with a moisture content of 68-75%; (2) Add silicate minerals, sulfur-containing minerals / waste rock and composite microbial agents in order according to the weight ratio of the compost mixed matrix, mix them evenly, and then carry out the main compost fermentation for 12 to 16 days. Adjust the aeration intensity to maintain the temperature of the compost at 50 to 62 °C. (3) The compost material is subjected to post-fermentation treatment for 20 to 25 days. When the moisture content of the compost is reduced to 35 to 40%, part of the compost product is added to the mixed feed of the main fermentation stage to inoculate the composting microorganisms, and the rest of the compost product is retained for later use; (4) The resulting compost products are spread on the slopes of the acidic waste rock dump or spoil dump and native herbaceous plants are planted to achieve ecological management of the mine.

2. The method for ecological management of the slope of the acidic waste rock dump or spoil dump according to claim 1, characterized in that The agricultural and forestry solid waste in step (1) is any one or more of soybean straw, corn straw, sorghum straw, peanut shell, pine cone, and rice husk; the mass proportion of residual sludge in the compost mixed matrix is ​​60-70%, the mass proportion of cow dung is 20-30%, the mass proportion of agricultural and forestry solid waste is 7-10%, and the mass proportion of food waste hydrochar is 1.0-2.5%.

3. The method for ecological management of the slope of the acidic waste rock dump or spoil dump according to claim 1 or 2, characterized in that The preparation conditions of the food waste hydrothermal charcoal are: reaction temperature 180~230°C, working pressure 1.5~2.5MPa, hydrothermal treatment time 1.2~2.0h, the raw materials of the food waste hydrothermal charcoal are food waste and dewatered sludge from a sewage treatment plant in a mass ratio of (8~4):1, and the moisture content of the food waste is 88~94%.

4. The method for ecological management of the slope of the acidic waste rock dump or spoil dump according to claim 1, characterized in that The silicate mineral in step (2) is a combination of plagioclase and any one or more of wollastonite, blast furnace slag, and phosphate tailings, the mass proportion of plagioclase is 30-45%, and the amount of silicate mineral added is 6-10% of the mass of the compost mixed matrix.

5. The method for ecological management of the slope of the acidic waste rock dump or spoil dump according to claim 1, characterized in that The sulfur-containing minerals / waste rock in step (2) include pyrite, chalcopyrite, galena, sphalerite minerals or their open-pit slope waste rock, and the amount of sulfur-containing minerals / waste rock added is 6-12% of the mass of the compost mixed matrix.

6. The method for ecological management of the slope of an acidic waste rock dump or spoil dump according to claim 1, characterized in that In step (2), the mass ratio of the silicate mineral to the sulfur-containing mineral / waste rock is 1:(1.0-1.2), and the particle size of the mineral or waste rock is 2000-150 μm.

7. The method for ecological management of the slope of an acidic waste rock dump or spoil dump according to claim 1, characterized in that The amount of the composite microbial agent added in step (2) is 0.6-1.0‰ of the mass of the compost mixed matrix, which mainly includes Bacillus subtilis, Bacillus thiooxidans, Bacillus thiooxidans, and Bacillus ferrooxidans, wherein Bacillus subtilis accounts for 25-40% of the total mass of the composite agent, and Bacillus thiooxidans accounts for 20-30% of the total mass of the composite agent.

8. The method for ecological management of the slope of an acidic waste rock dump or spoil dump according to claim 1, characterized in that In the main fermentation stage of step (3), the compost product is mixed with the mixed feed at a mass ratio of 5-10%, the compost microorganisms are inoculated and the moisture content of the compost material is adjusted to 60-65%.

9. The method for ecological management of the slope of an acidic waste rock dump or spoil dump according to claim 1, characterized in that The thickness of the compost product covering the slope of the acidic waste rock dump or spoil dump in step (4) is 15 to 40 cm.