Method for rapidly soilizing electrolytic manganese residue using microbial method

Abstract

The application belongs to the technical field of organic waste treatment, and particularly relates to a method for rapidly soilizing electrolytic manganese residue by using a microbial method; the method comprises the following steps: (1) mixing cane pith powder, filter mud of a sugar mill and red mud according to a certain proportion, and adding the mixture into a reaction tank together with electrolytic manganese residue and water, and obtaining corresponding mixed waste residue after sufficient reaction for 6 hours; (2) mixing and stirring the mixed waste residue, biological organic fertilizer and No. 1 compound microbial agent, and then feeding the mixture into a tank-type fermentation tank to perform aerobic fermentation, and obtaining active waste residue with low heavy metal ion content after rapid fermentation for 144 hours, and the active waste residue is turned over 2-3 times during the fermentation; (3) adding sulfur powder and No. 2 compound microbial agent into the active waste residue, and obtaining regenerated soil after rapid fermentation for 48 hours, and the active waste residue is turned over 2-3 times during the fermentation; the method fundamentally solves the problems of long-term large storage, difficult treatment and high treatment cost of electrolytic manganese residue, and is capable of treating waste with waste, and has great significance for green development of the manganese industry.

Description

Technical Field

[0001] This invention belongs to the field of organic waste treatment technology, specifically a method for rapidly soil-electrolyzing manganese slag using a microbial method. Background Technology

[0002] 1. Electrolytic manganese slag

[0003] Manganese metal, known as a "strategic metal," is an extremely important industrial raw material and one of the fundamental raw materials for pillar industries such as aerospace, machinery, chemicals, and agriculture. Since the beginning of the 21st century, with the rapid development of clean energy, lithium-ion batteries using manganese compounds as cathode materials have also developed rapidly, leading to even faster development of electrolytic manganese metal. However, the electrolytic manganese industry is a traditional hydrometallurgical industry. While promoting rapid local economic development, it also generates a large amount of "three wastes"—wastewater, waste residue, and waste gas—significantly limiting the sustainable development of the electrolytic manganese industry. Of particular concern is the large amount of waste residue generated by the electrolytic manganese industry, namely the filtered acid residue produced during the electrolysis process, commonly known as electrolytic manganese residue (or simply "manganese slag"). Currently, the main method for electrolytic manganese enterprises to handle manganese slag is to transport it to dedicated sites for damming and stockpiling. Long-term stockpiling consumes large areas of land, resulting in resource waste, increasing environmental pressure, polluting groundwater, and even posing significant health risks. Therefore, the stockpiling of electrolytic manganese slag is currently the most prominent environmental problem in the entire electrolytic manganese industry.

[0004] Electrolytic manganese slag is a powdery solid waste, consisting of fine black particles with a high moisture content, averaging around 30%. The main phases contained in electrolytic manganese slag are quartz (SiO2), pyrite (FeS2), calcium sulfate (CaSO4), gypsum (CaSO4·2H2O), alumina, and manganese oxide. The particles in electrolytic manganese slag are fine and randomly distributed, consisting of columnar crystals interspersed with other substances, interspersed with some densely packed, fluffy particles.

[0005] 2. Red mud

[0006] As one of the major alumina producers, China produces approximately 70 million tons of red mud annually. It is estimated that China's current red mud reserves exceed 600 million tons, primarily disposed of in land-based stockpiles. Red mud, also known as red clay, is an industrial solid waste discharged after alumina extraction from bauxite. It generally contains a high amount of iron oxide and resembles reddish soil in appearance, hence its name. However, some varieties are brown or even grayish-white due to lower iron oxide content. Red mud is an insoluble residue and can be classified into sintering red mud, Bayer process red mud, and combined process red mud, with its main components being SiO2, Al2O3, CaO, and Fe2O3. Land-based stockpiling of red mud not only wastes land resources but also makes it susceptible to leaching by rainwater and erosion by wind, thus polluting the surrounding atmosphere, water, and soil systems, posing a significant negative impact on the ecological health of red mud stockpiles and their surrounding areas.

[0007] The lack of biological activity and strong alkalinity of the soil are the main problems to be addressed in the comprehensive utilization of red mud. On the one hand, red mud originates from the waste residue produced after alkaline washing and high-temperature treatment of bauxite. It has extremely low organic matter, nutrient content, and soil biological activity, making it almost "dead mud" and incapable of biological growth. On the other hand, the alkaline substances in red mud exist in two forms: free alkali and chemically bound alkali. Approximately 20%-25% of the alkaline substances exist as free alkali, while the remainder exists as chemically bound alkali within alkaline minerals. Free alkali mainly exists in the form of NaOH, Na₂CO₃, NaAl(OH)₄, and Na₂SiO₃, which readily dissolve to form alkaline anions, leading to an increase in the pH value of the red mud. Chemically bound alkali mainly includes sodalite, nepheline, hydrated garnet, calcite, and tricalcium aluminate, which are desilication products from the alumina production process. The dissolution reaction of chemically bound alkali results in the alkalinity of the red mud, forming a pH buffer zone. Domestic and international scholars have conducted extensive research on the safe disposal and storage of red mud. The ideal measure to address red mud stockpiling and reduce environmental pollution risks is its resource utilization, including the recovery of valuable metals such as Al, Fe, and rare earth metals; its use as an adsorbent in wastewater treatment; and as an additive in ceramics and building materials, roadbed materials, and soil remediation agents. However, to date, the global red mud reuse rate is less than 2%. According to the "2019-2020 China Bulk Industrial Solid Waste Comprehensive Utilization Industry Development Report," China's red mud comprehensive utilization rate in 2020 was 8%, with a utilization volume of only 8.49 million tons. Large-scale comprehensive utilization of red mud is difficult to achieve. Therefore, the ecological disposal of red mud, as a feasible measure for the harmless utilization of bulk waste, has attracted widespread attention. Adding regulators to reduce the alkalinity, increase nutrients, and improve the physical structure of red mud, thereby accelerating the soilification and vegetation restoration process, and ultimately achieving the ecological reconstruction of red mud stockpiles, is a highly promising and practically significant approach in the ecological disposal of red mud.

[0008] 3. Sugar factory filter mud (sulfurization process)

[0009] Sugar mill filter mud primarily originates from the clarification process in sugar production. During sugar refining, after the sugarcane juice undergoes clarification, residue is discharged through a filter press or vacuum filter; this residue is known as filter mud. Filter mud is divided into two types: sulfite filter mud and carbonate filter mud. Sulfite filter mud is produced by treating sugarcane juice with lime and sulfur dioxide as clarifying agents, while carbonate filter mud is produced by treating sugarcane juice with lime and carbon dioxide as clarifying agents.

[0010] The main components of filter mud from sugar mills using the sulfite process are: approximately 69.55% moisture, 58.66% organic matter, 1.19% nitrogen, 1.24% phosphorus (P₂O₅), 0.52% potassium (K₂O), 5.59% calcium (CaO), and 1.07% magnesium (MgO). Due to its low ash content, sulfite process filter mud has a low calcium salt content and a high organic matter content. It contains nitrogen, phosphorus, potassium, and trace elements required by sugarcane, and has a pH of approximately 6.0, making it slightly acidic. Improperly stored untreated sugar mill filter mud occupies land resources and, due to its high content of organic matter and sugars, is highly susceptible to mold, foul odors, and fly infestations, leading to environmental problems. Therefore, the comprehensive utilization of filter mud is a crucial link in the sugar industry's development of a circular economy, improvement of economic efficiency, and achievement of sustainable development.

[0011] 4. Sugarcane pith

[0012] Sugarcane pith is the internal part of the sugarcane plant, the residue left after pressing the juice during the sugar production process, and is usually removed from the bagasse. The main components of sugarcane pith include cellulose, hemicellulose, and lignin, which, like starch or sucrose, are carbohydrates composed of monosaccharides. Because sugarcane pith has a low calorific value, burning it in boilers may cause operational problems, environmental pollution, and health hazards, thus requiring proper handling.

[0013] Sugarcane pith can be used as roughage for ruminants, replacing some of the green grass. To improve its nutritional value as feed, its digestibility, palatability, and nutritional value can be enhanced through physical, chemical, and microbiological methods. For example, its nutritional value can be improved through pretreatment methods such as alkali treatment, acid treatment, or physical methods such as grinding, heating, and cooking. Summary of the Invention

[0014] The purpose of this invention is to provide a method for the rapid soil electrolysis of manganese slag using a microbial method, in order to solve the technical problems mentioned in the background art.

[0015] The present invention solves the above-mentioned technical problems with the following technical solution: a method for rapid soil electrolysis of manganese slag using a microbial method, comprising the following steps:

[0016] (1) Mix sugarcane pulp powder, sugar mill filter mud and red mud in a certain proportion, and add them together with electrolytic manganese slag and water into a reaction tank. After 6 hours of full reaction, the corresponding mixed waste residue is obtained.

[0017] (2) Mix the mixed waste residue, bio-organic fertilizer and No. 1 compound microbial agent and then put them into a trough fermentation tank for aerobic fermentation. After 144 hours of rapid fermentation, the pile is turned over 2 to 3 times during the process, and active waste residue with low heavy metal ion content can be obtained.

[0018] (3) Add sulfur powder and No. 2 compound microbial agent to the active waste residue. After 48 hours of rapid fermentation, the pile is turned over 2 to 3 times during the process to obtain regenerated soil.

[0019] Furthermore, the sugarcane pith powder consists of particles of approximately 2 mm, and the sugar mill filter mud has been pressure filtered. The mass ratio of the sugarcane pith powder, sugar mill filter mud, and red mud is 0.8–1.5:0.5–1.5:1. When the sugarcane pith powder, sugar mill filter mud, and strongly alkaline red mud are mixed, the lignin in the sugarcane pith can dissolve into small molecules under the action of strong alkali, promoting the separation of lignin and cellulose, which is beneficial for subsequent rapid fermentation. The organic matter and various inorganic elements such as N, P, K, and Ca abundant in the sugar mill filter mud can also promote subsequent fermentation.

[0020] Furthermore, the mass ratio of the electrolytic manganese slag, red mud, sugar mill filter mud, sugarcane pith mixture, and water added to the reaction tank is adjusted according to actual conditions, and water is added in a timely manner during the reaction, preferably with water covering the solids, to ensure that the soluble substances in the red mud, sugar mill filter mud, and manganese slag dissolve and react fully. The reaction time is 6 hours, ensuring that the final substrate moisture content is between 60% and 70% and the pH value reaches between 6.0 and 7.5. Appropriate stirring should be carried out during the reaction. The electrolytic manganese slag and red mud undergo an acid-base neutralization reaction. The products of the neutralization reaction can solidify some of the heavy metal elements such as manganese (Mn), arsenic (As), lead (Pb), and chromium (Cr) in the waste residue mixture, thereby initially reducing the content of heavy metal ions. The lignin in sugarcane pith can dissolve under strongly alkaline conditions to form small molecules, which promotes the separation of lignin, cellulose, and hemicellulose. The three-dimensional network molecular structure of lignin is broken down in this process, forming multiple smaller molecules with straight-chain structures. This allows microorganisms to decompose and utilize lignin, cellulose, and hemicellulose more efficiently, thereby significantly improving the efficiency of fermentation degradation.

[0021] Furthermore, the mass ratio of the waste residue to the bio-organic fertilizer is 4:1 to 2, the amount of compound microbial agents No. 1 and No. 2 added is 3 to 5% of the total mass of the substrate, and the amount of sulfur powder added is 5 to 10% of the total mass of the substrate.

[0022] Furthermore, the No. 1 compound microbial agent contains one or more of Bacillus megaterium, Bacillus mucilaginosus, Bacillus subtilis, Bacillus laterosporus, Bacillus acidophilus, Bacillus thermophilus, Thiobacillus acidophilus, phosphate-solubilizing bacteria, and potassium-solubilizing bacteria. The main function of the No. 1 compound microbial agent is to reduce the content of heavy metal ions and salinity in the mixed waste residue, making it more suitable for microbial growth and facilitating further processing.

[0023] Furthermore, the sulfur powder is required to have a mesh size of 100-200. The sulfur powder can react chemically with heavy metals in the soil to form insoluble sulfides, thereby reducing the activity of heavy metals in the soil. The sulfur powder can also serve as a sulfur source, promoting the growth of specific microorganisms and helping to bioleach heavy metals from the soil.

[0024] Furthermore, the No. 2 compound microbial agent includes one or more of the following: silicate bacteria, phosphorus bacteria, potassium bacteria, yeast, nitrogen-fixing Rhodospirillum, lactobacillus, Bacillus subtilis, Rhodospirillum rubrum, Penicillium oxalate, Penicillium glabripennis, and Stratosporum. The No. 2 compound microbial agent can form chelates between nutrients and microbial metabolites, which can significantly improve the absorption and utilization rate of nutrients by plants. At the same time, it can bind fine particles of waste residue and improve the physical structure of waste residue through microorganisms and their metabolites. Before adding the No. 2 compound microbial agent, the moisture content of the substrate needs to be ensured to be above 50%.

[0025] Furthermore, the compound microbial agent is a high-performance strain screened by high-throughput screening technology, and the cells or particles are sorted by flow cytometry.

[0026] Specifically, the compound microbial agent is first activated by inoculating it onto a test tube slant at a temperature of 28–35°C and a pH of 6.0–7.5; then it is gradually scaled up through flat flasks or shake flasks and seed tanks to obtain a large number of highly active compound strains.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention, through the comprehensive utilization of microorganisms, presents a low-cost, large-scale, rapid, green, and pollution-free process for the soil-based treatment of electrolytic manganese slag. The process comprises three main steps: acid-base neutralization, quality improvement, and land reclamation. Currently, electrolytic manganese slag treatment and utilization processes suffer from numerous problems, including difficulty in large-scale disposal, unclear economic benefits, high energy consumption, and secondary pollution, preventing its industrialization in many fields. This invention is technologically advanced, innovatively combining the soil-based treatment of electrolytic manganese slag with red mud, agricultural and livestock waste, and microorganisms, achieving both good economic benefits and excellent environmental friendliness. On one hand, the method utilizes the acid-base neutralization reaction between red mud and electrolytic manganese slag to achieve low-cost, rapid, efficient, and pollution-free dealkalization of the slag. On the other hand, the rapid and efficient decomposition of agricultural waste by microorganisms can significantly increase the organic matter, nutrient content, and beneficial bacterial activity in the electrolytic manganese slag at low cost and high efficiency. In summary, this invention addresses the pain points of current electrolytic manganese slag treatment, fundamentally solving the problems of long-term large-scale stockpiling, difficulty in handling, and high treatment costs of electrolytic manganese slag. It treats waste with waste and is of great significance to the green development of the manganese industry. Attached Figure Description

[0029] Figure 1 This is a flowchart of a method for rapidly soil-electrolytic manganese slag treatment using a microbial approach, according to the present invention.

[0030] Figure 2 This is a flowchart illustrating the cultivation process of the compound formula microbial strains of the present invention. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this does not constitute a limitation on the scope of protection of the claims of the present invention.

[0032] See Figure 1This invention provides a method for rapidly converting electrolytic manganese slag into soil using a microbial method. The process is as follows: First, sugarcane pith powder, red mud, and sugar mill filter mud are mixed in a certain proportion and added to a reaction tank along with electrolytic manganese slag and water. After 6 hours of full reaction, a neutral mixed waste residue is obtained. Then, the mixed waste residue, bio-organic fertilizer, and No. 1 compound microbial agent are mixed and stirred, and then sent to a bio-fermentation tank for aerobic fermentation. After 48 hours of rapid fermentation, during which the pile is turned 2-3 times, an active waste residue with low heavy metal ion content is obtained. Then, sulfur powder and No. 2 compound microbial agent are added to the active waste residue. After 144 hours of rapid fermentation, during which the pile is turned 2-3 times, regenerated soil is obtained. After all indicators are qualified, it can be used for planting economic forests. By combining fertigation technology (patents published under application numbers CN116195418A and CN116283372A) with phytoremediation, soil fertility and biological activity are further improved, ultimately resulting in regenerated soil free of heavy metal pollution and rich in organic matter, trace elements, and microorganisms beneficial to plant growth.

[0033] In this invention, the sugarcane pith powder consists of particles approximately 2 mm in size, and the mass ratio of the sugarcane pith powder, sugar mill filter mud, and red mud is 0.8–1.5:0.5–1.5:1. Mixing the sugarcane pith powder, sugar mill filter mud, and red mud optimizes the carbon-nitrogen ratio, improves the physical structure of the mixture, provides the trace elements necessary for plant growth, and promotes the decomposition of organic matter through microbial activity. This mixing also helps regulate the pH value, making it more suitable for microbial growth, reducing environmental pollution, and transforming waste into valuable resources, thereby accelerating the fermentation process and improving fermentation efficiency.

[0034] The mass ratio of the mixture of electrolytic manganese slag, red mud, sugarcane pith, and sugar mill filter mud added to the reaction vessel to water should be adjusted according to the actual situation. Water should be added in a timely manner during the reaction, ensuring that the water covers the solids, so as to ensure that the soluble substances in the red mud and manganese slag dissolve and react fully. The reaction time is about 6 hours. The reaction is considered complete when the final substrate moisture content is about 60% and the pH value reaches about 6.0-7.0. Appropriate stirring should be carried out during the reaction. The acidic electrolytic manganese slag and sugar mill filter mud can undergo an acid-base neutralization reaction with the red mud. The products of the neutralization reaction can solidify some of the heavy metal elements such as Mn, As, Pb, and Cr in the waste mixture, initially reducing the content of heavy metal ions. In addition, under the action of strong alkali, the lignin in sugarcane pith can be decomposed into small molecules, thereby promoting the separation of lignin, cellulose, and hemicellulose. The complex three-dimensional network structure of lignin is broken down, forming multiple smaller molecules with straight-chain structures. This is beneficial for microorganisms to decompose and utilize lignin, cellulose, and hemicellulose more efficiently, significantly improving the efficiency of fermentation degradation.

[0035] The mass ratio of the waste residue to the organic bio-fertilizer is 4:1 to 2. The amount of compound microbial agents No. 1 and No. 2 added is 3 to 5% of the total mass of the substrate, and the amount of sulfur powder added is 5 to 10% of the total mass of the substrate.

[0036] The No. 1 compound microbial agent contains one or more of the following: Bacillus megaterium, Bacillus mucilaginosus, Bacillus subtilis, Bacillus laterosporus, Bacillus acidophilus, Bacillus thermophilus, Thiobacillus acidophilus, phosphate-solubilizing bacteria, and potassium-solubilizing bacteria. The main function of the No. 1 compound microbial agent is to reduce the heavy metal ion content and salinity in the mixed waste residue, making it more suitable for microbial growth and facilitating further processing.

[0037] The sulfur powder must have a mesh size of 100-200. The main functions of the sulfur powder are twofold: firstly, it can react chemically with heavy metals in the soil to form insoluble sulfides, thereby further reducing the activity of heavy metals in the soil; secondly, sulfur powder can act as a sulfur source, promoting the growth of specific microorganisms and helping to bioleach heavy metals from the soil.

[0038] The No. 2 compound microbial agent includes one or more of the following: silicate bacteria, phosphorus bacteria, potassium bacteria, yeast, nitrogen-fixing Rhodospirillum, lactobacillus, Bacillus subtilis, Rhodospirillum rubrum, Penicillium oxalate, Penicillium glabripennis, and Stratosporum. The main functions of the No. 2 compound microbial agent are: firstly, to form chelates between nutrients (such as calcium and iron) and microbial metabolites (such as humic acid and amino acids), significantly improving the absorption and utilization rate of nutrients by plants; secondly, to bind fine particles of waste residue through microorganisms and their metabolites, improving the physical structure of the waste residue. Before adding the No. 2 compound microbial agent, the substrate moisture content must be above 50%.

[0039] The compound microbial agent is a high-performance strain screened by high-throughput screening technology. During the implementation process, flow cytometry (FCM) is used to sort the cells or particles.

[0040] like Figure 2 As shown, the compound microbial agent is first activated by inoculating it onto test tube slant agar at a temperature of 28–35°C and a pH of 7.0. It is then progressively scaled up through flat flasks, shake flasks, and seed tanks to obtain a large quantity of highly active compound microbial strains. The purpose of the primary seed culture is to propagate a large number of highly vigorous cells; the culture medium should be low in sugar and high in organic nitrogen, with culture conditions designed to promote bacterial growth. The secondary seed culture is to further expand the cell count to achieve a sufficient population of microorganisms required for fermentation.

[0041] A method for rapidly converting manganese slag into soil using biomass from sugarcane processing waste is characterized by the following detection indicators for the soil conversion of the electrolytic manganese slag: bulk density, pH, organic matter content, heavy metal ion content, and soil respiration intensity. These indicators should meet the following requirements: bulk density ≤ 1.8 g / cm³; pH between 6.5 and 7.5; total organic carbon (TOC) ≥ 10.0 g / kg; heavy metal ion content should not exceed the pollution risk screening value in the "Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control" (GB 15618—2018); and daily average soil respiration intensity ≥ 3.6 g / (m²·d).

[0042] A method for rapidly converting waste biomass from sugarcane production into manganese slag through soil electrolysis is characterized in that, after the regenerated soil is cultivated, a season of crops, preferably water spinach or sweet bamboo shoots, are planted. Combined with fertigation technology, the biological activity and fertility of the soil are further improved, and the quality of the cultivated land reaches a level higher than Grade 10 in the "Land Use Status Classification" (GB / T 21010-2017) standard or Grade 6 in the "Cultivated Land Quality Grade" (GB / T33469-2016) standard.

[0043] This invention mixes red mud, electrolytic manganese slag, and sugar factory filter mud (collectively referred to as waste residue). This mixing not only achieves acid-base neutralization but also provides exchangeable Ca2+, promoting the formation of aggregates and maintaining their structural stability. The Ca2+ dissolved in the manganese slag and sugar factory filter mud can replace Na+ and Mg2+ in the waste residue and directly participates in the construction of cation bridges between clay particles and organic matter. This promotes the formation of organic-inorganic complexes (C-P-OM) from clay particles (C), polyvalent cations (P), and organic molecules (OM). These complexes further combine to form large-particle aggregates, increasing the quantity and stability of the aggregates. Some heavy metal elements such as As, Pb, and Cr in the red mud are precipitated; some metal ions are preliminarily solidified.

[0044] Using biological methods to electrolyze manganese slag in soil: Microorganisms can promote the formation of soil aggregates. After adding organic materials, microorganisms produce biopolymers or organic cementing substances through metabolism or decomposition. The viscosity and cementing properties of these substances promote the formation of large-particle aggregates while reducing the content of small-particle aggregates in the soil. Biopolymers are natural polymers produced by living organisms. In other words, they are polymeric biomolecules derived from cells or extracellular substances. Biopolymers have covalent bonds and form relatively large monomer units. Based on the monomer units used and the structure of the formed biopolymers, biopolymers are divided into two main categories: polynucleotides, polypeptides, and polysaccharides. As natural polymers produced by living organisms, biopolymers added to soil show excellent potential in enhancing interparticle cohesion and reducing soil erodibility. Studies have found that the addition of biopolymers to soil can form surface adhesion, cell self-adhesive biofilms, and protective barriers, which can promote water retention and nutrient accumulation around plant roots, while effectively improving the stability of slope soils and enhancing the soil's resistance to erosion.

[0045] Microorganisms, through their own life activities and interactions with the surrounding environment, can enhance soil nutrient absorption, improve soil fertility, and promote plant growth and development. They also increase crop yields and control plant diseases and pests through various mechanisms, such as nitrogen fixation, potassium and phosphorus dissolution, plant hormone excretion, production of substances that inhibit plant pathogens, and protection of plants from abiotic and biotic stresses. Furthermore, microorganisms can adsorb heavy metal ions through their charged cell surfaces (especially cell walls), or use their metabolic products to bind with heavy metals to form precipitates. They can also directly absorb heavy metals as essential nutrients, accumulating them in different parts of the cell and reducing their mobility. For example, humic acid produced after sugarcane pith fermentation not only promotes the aggregation of dispersed waste particles into stable, larger aggregates, but also acts as a complexing agent for trace metal elements. Humic acid reduces the content of metal ions and trace elements in the soil, decreases mineralization, and thus affects the toxicity and bioavailability of metal ions.

[0046] Plant growth and development in the soil can improve soil structure: on the one hand, plant roots, as the part directly in contact with the soil, act as interpenetrators, increasing soil permeability and improving soil physicochemical properties; on the other hand, plant root, stem, and leaf residues can be decomposed by microorganisms and transformed into organic matter in the soil, thereby improving soil fertility. Plants and microorganisms form a symbiotic system in the soil. Plant growth and metabolism provide nutrients and necessary conditions for the survival and reproduction of microorganisms, while the reproduction of microorganisms creates more nutrients for plant growth. At the same time, the interaction of this symbiotic system improves the physicochemical properties of the soil and forms a soil nutrient cycling system, making long-term improvement of soil nutrients possible.

[0047] Soil, a region of the Earth's crust, is the meeting point of geography and biology, providing habitats for plants, animals, and microorganisms. Soil is the most suitable environment for microorganisms, possessing all the conditions necessary for their growth, reproduction, and life activities. Soil organic matter can be divided into three main categories: insoluble, soluble, and microbial. Soil organic matter has various sources, such as cellulose, lignin, plant remains, and polysaccharides (like pectin).

[0048] Soil biological activity refers to the sum of the vitality of various organisms in the soil. The activity of soil organisms largely depends on the physical and chemical properties of the soil, mainly involving factors such as soil temperature, humidity, aeration, gas composition, pH, and the content and composition of organic and inorganic matter. Soil respiration rate and fiber decomposition rate are important indicators of soil biological activity; they also reflect the rate and intensity of biological activity and the decomposition of organic residues in the soil.

[0049] Soil microorganisms are often likened to "converters" of soil nutrient cycling, "purifiers" of environmental pollutants, and "regulators" of terrestrial ecosystem stability. It can be said that without soil microorganisms, soil loses its biological activity and productivity. But how can the activity of soil microorganisms be improved? Soil biological activity is low when soil temperature is low, organic matter is lacking, and microbial populations are insufficient. Therefore, targeted treatment of red mud is necessary to restore its soil biological activity. Agricultural techniques (including tillage, cultivation, fertilization, irrigation, drainage, and pesticide application) can also affect soil biological activity. Under certain conditions, targeted inoculation measures can also purposefully increase the quantity and biochemical intensity of specific microorganisms.

[0050] Active organic matter is an important component of soil, mainly including dissolved organic carbon, microbial biomass, and light organic matter. In terms of soil nutrients, soil biological activity, and chemical properties: the content of dissolved organic carbon and microbial biomass carbon and nitrogen in the soil is positively correlated with the content of organic phosphorus, total nitrogen, and available nitrogen. Active organic matter is affected by soil texture, water content, humidity, and is also related to soil pH and cation exchange capacity. Soil microbial biomass carbon and the ratio of microbial biomass carbon to organic carbon are positively correlated with the content of soil clay and silt, and negatively correlated with sand content.

[0051] The meaning of arable land quality generally refers to the soil fertility and soil environmental quality that meet the needs of crop growth and safe production. Arable land is generally divided into commonly used arable land and temporary arable land. Commonly used arable land refers to land specifically used for growing crops, regularly cultivated, and capable of normal harvesting; while temporary arable land is land temporarily reclaimed outside of commonly used arable land for growing crops, and cannot be harvested normally. According to the national standard "Classification of Current Land Use" (GB / T 21010-2017), the classification of arable land grades is as follows: 1. There are 15 grades of arable land quality, with grade 1 being the best and grade 15 the worst. 2. Grades 1-4 are excellent, grades 5-8 are high, grades 9-12 are medium, and grades 13-15 are low. The "Arable Land Quality Grading" standard (GB / T 33469-2016) uses a comprehensive index method to evaluate the ability of arable land fertility, soil health status, and field infrastructure to meet the sustainable output and quality safety of agricultural products, resulting in grade classifications. Farmland quality is classified into 10 grades. The higher the comprehensive farmland quality index, the higher the farmland quality level. Grade 1 farmland has the highest quality, and Grade 10 farmland has the lowest quality. The testing indicators for electrolytic manganese slag soil conversion include: bulk density, pH, organic matter content, heavy metal ion content, and soil respiration intensity. These indicators should meet the following requirements: bulk density ≤ 1.8 g / cm³; pH between 6.5 and 7.5; total organic carbon (TOC) ≥ 10.0 g / kg; heavy metal ion content should not exceed the pollution risk screening value in the "Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control" (GB 15618—2018); daily average soil respiration intensity ≥ 3.6 g / (m²·d).

[0052] Microbial breeding and culture technology

[0053] Application of high-throughput screening of compound microbial agents (engineered strains). Traditional manual screening methods are inefficient, labor-intensive, and require significant human and material resources. Against this backdrop, high-throughput screening technology has emerged. Generally, high-throughput screening should meet two basic conditions:

[0054] 1. Develop a suitable screening model based on the characteristics of the target product (physicochemical properties, biological properties, etc.) to convert the characteristics of the sample into multiple signals that can be efficiently sensed and identified by cameras and high-speed computers.

[0055] 2. The relevant experimental processes are executed using an automated operating system controlled by artificial intelligence. This includes automatically completing steps such as pipetting, inoculation, and washing.

[0056] During the process, flow cytometry (FCM) is used to sort cells or particles. FCM is a novel analytical and screening technique that uses a flow cytometer to move cells or particles in a liquid stream, pass a beam of incident light through them, and use a highly sensitive detector to record the scattered light and different fluorescence signals, allowing for rapid measurement of cells or other particles in the liquid stream.

[0057] FCM mainly includes fluidized bed technology for samples, cell sorting and counting technology, and data acquisition and analysis technology. It features high measurement speed, numerous measurement parameters, large data acquisition volume, comprehensive analysis, flexible methods, and precise sorting of target cells.

[0058] FCM can be used not only for cell counting, characterization, cell cycle analysis, and chromosome sorting, but also for measuring genome size, flow cytometry karyotype analysis, and further for locating genes and constructing chromosome libraries.

[0059] Superior compound microbial strains are the foundation and key value of this technology; therefore, it is essential to have industrially viable strains that can improve performance. The purpose of breeding compound microbial strains is to improve their characteristics to meet the needs of practical implementation. Strain breeding includes two parts: selection and cultivation. During implementation, the requirements for compound microbial strains are: possessing a self-protection mechanism, rapid growth and reaction rates, ability to grow on culture media made from inexpensive raw materials, high yield of the target product, easy recovery, non-pathogenic bacteria, resistance to mutation and degeneration, genetic stability, mild and easily controllable culture conditions, and high yield.

[0060] Seed culture expansion involves activating a compound microbial strain by inoculating it onto test tube slant agar plates, followed by progressively scaled-up cultivation in flat flasks, shake flasks, and seed tanks to obtain a specific quantity and quality of the compound microbial strain. The expansion of compound microbial strains is of great significance, with fermenters producing tens of cubic meters of inoculum during large-scale implementation. The preparation of the compound microbial strain is divided into two stages: laboratory preparation and production workshop preparation.

[0061] Production workshop strain preparation: The liquid strain prepared in the laboratory is transferred to a seed tank for large-scale cultivation. The purpose of the seed tank is to allow the strain to grow rapidly after inoculation, reaching a certain cell mass to facilitate further product reactions. Inoculum age and inoculum size are two very important process conditions during the large-scale cultivation of the strain.

[0062] The purpose of primary seed culture is to propagate a large number of highly vigorous microorganisms. The culture medium should be low in sugar and high in organic nitrogen, and the culture conditions should be designed to favor microbial growth. Secondary seed culture is to further expand the number of microorganisms to achieve a sufficient population of microorganisms required for fermentation.

[0063] Example: A manganese company in Guangxi

[0064] The manganese slag was collected from the company's manganese slag stockpile, and the red mud was collected from a red mud stockpile of an aluminum company in Guangxi. The sampling method was implemented according to the sampling standards stipulated in the "Technical Specification for Soil Environmental Testing (HJ / T166-2004)". Five sampling points were set up using the quincunx sampling method, and approximately 1 ton of samples were collected from the surface layer at a depth of 0–20 cm. After mixing, the samples were transported back to the laboratory. The basic physicochemical properties and heavy metal content of the collected manganese slag and red mud are shown in the table below.

[0065] Table 1. Basic physicochemical properties of manganese slag

[0066]

[0067]

[0068] Table 2 Basic Physicochemical Properties of Red Mud

[0069] pH 10.62 Total organic carbon (TOC), g / kg 3.45 Available phosphorus, mg / kg 13.39 Available potassium, mg / kg 16.81 Total nitrogen, mg / kg 2.33 Bulk density, g / cm3 2.75 Average daily soil respiration intensity, g / (m2·d) ≤0.1

[0070] Table 3. Heavy metal ion content (mg / kg) of manganese slag and red mud.

[0071] Red mud 35.04 366.79 37.81 280.83 186.49 76.23 0.91 37.28 manganese slag - 91.86 - 90.37 33.82 44614 0.40 41.69

[0072] According to the "Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control" (GB 15618—2018), the Mn content in the manganese slag significantly exceeded the standard. Apart from this, the content of other heavy metals in the sample did not exceed the pollution risk control values, but some heavy metals exceeded the pollution risk screening values. This indicates a high pollution risk, requiring further control measures before crop planting can proceed.

[0073] Soil treatment of 1 ton of electrolytic manganese slag mainly involved neutralization, quality improvement, and phytoremediation. Neutralization: A mixture of 1.2 tonnes of red mud, sugar mill filter mud, and sugarcane pith (mass ratio of red mud, sugar mill filter mud, and sugarcane pith 1:1.2:1.2) and 1 tonne of electrolytic manganese slag underwent acid-base neutralization in a reaction tank, producing a slurry-like mixture which was then filtered. Quality Improvement: 200 kg of bio-organic fertilizer and 50 kg of compound microbial agent 1 were added to the neutralized mixture, and fermentation was carried out for 48 hours to passivate or solidify heavy metal ions. Then, 400 kg of bio-organic fertilizer, 100 kg of sulfur powder, and 50 kg of compound microbial agent 2 were added, and fermentation was carried out for 144 hours to increase its organic matter content and soil biological activity. Finally, the preliminary soil treatment of the electrolytic manganese slag was completed. After the preliminary soil treatment of the red mud was completed, a series of experiments and tests were conducted, and the results are as follows.

[0074] Table 4. Basic physicochemical properties of manganese slag after biological soil treatment.

[0075] pH 7.11 Total organic carbon (TOC), g / kg 10.94 Available phosphorus, mg / kg 28.89 Available potassium, mg / kg 28.14 Total nitrogen, mg / kg 845.26 Bulk density, g / cm3 1.66 Average daily soil respiration intensity, g / (m2·d) 5.7

[0076] Table 5. Heavy metal ion content (mg / kg) of manganese slag after biological soil treatment.

[0077] 17.87 101.13 5.28 60.77 79.36 773.18 0.09 13.51

[0078] Table 6 Germination rate of water spinach seeds

[0079] Untreated manganese slag 0％ Manganese slag after biological treatment 78％

[0080] The above data demonstrates that the daily average soil respiration intensity, organic matter, and nutrient element content of manganese slag significantly increased after biological soil treatment, while the bulk density decreased substantially, indicating a substantial improvement in the physical and chemical structure of the soil. Furthermore, the heavy metal content of the manganese slag treated by microbial methods was all below the pollution risk screening values ​​in the "Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control" (GB 15618—2018), meaning that the risk of heavy metals in the soil to agricultural product quality and safety, crop growth, or the soil ecological environment is low and generally negligible. Due to the improved extreme physical and chemical properties of the manganese slag, the germination rate of water spinach seeds increased from 0% to 78%, making it highly suitable for plant growth. This facilitates further phytoremediation of manganese slag (planting water spinach) to improve soil fertility and biological activity, and enhances the stability of soil aggregate structure. The quality of cultivated land reaches level 10 in the "Classification of Current Land Use" (GB / T21010-2017) standard or level 6 in the "Grade of Cultivated Land Quality" (GB / T 33469-2016) standard, ultimately achieving complete biological reclamation of manganese slag soil.

Claims

1. A method for rapid soil electrolysis of manganese slag using microbial methods, characterized in that, Includes the following steps: (1) Mix sugarcane pulp powder, sugar mill filter mud and red mud in a certain proportion, and add them together with electrolytic manganese slag and water into a reaction tank. After 6 hours of full reaction, the corresponding mixed waste residue is obtained. (2) Mix the mixed waste residue, bio-organic fertilizer and No. 1 compound microbial agent and then put them into a trough fermentation tank for aerobic fermentation. After 144 hours of rapid fermentation, the pile is turned over 2 to 3 times during the process, and active waste residue with low heavy metal ion content can be obtained. (3) Add sulfur powder and No. 2 compound microbial agent to the active waste residue, and after 48 hours of rapid fermentation, turning the pile 2 to 3 times during the process, you can get regenerated soil. The sugarcane pith powder consists of particles of approximately 2 mm. The sugar mill filter mud has been pressure filtered. The mass ratio of sugarcane pith powder, sugar mill filter mud, and red mud is 0.8–1.5:0.5–1.5:

1. When sugarcane pith powder, sugar mill filter mud, and strongly alkaline red mud are mixed, the lignin in the sugarcane pith can dissolve into small molecules under the action of strong alkali, promoting the separation of lignin and cellulose, which is beneficial for subsequent rapid fermentation. The organic matter and various inorganic elements such as N, P, K, and Ca in the sugar mill filter mud can also promote subsequent fermentation. The mass ratio of the mixture of electrolytic manganese slag, red mud, sugar mill filter mud, sugarcane pith, and water added to the reaction tank should be adjusted according to the actual situation. Water should be added in a timely manner during the reaction, with the water level covering the solids. This ensures that the soluble substances in the red mud, sugar mill filter mud, and manganese slag dissolve and react fully. The reaction time is 6 hours, ensuring that the final substrate moisture content is between 60% and 70% and the pH value reaches between 6.0 and 7.

5. Appropriate stirring should be performed during the reaction. The electrolytic manganese slag and red mud undergo an acid-base neutralization reaction. The products of the neutralization reaction can solidify some of the heavy metal elements such as Mn, As, Pb, and Cr in the waste residue mixture, initially reducing the content of heavy metal ions. The lignin in the sugarcane pith can dissolve into small molecules under the action of strong alkali, promoting the separation of lignin, cellulose, and hemicellulose. The lignin breaks down from a complex three-dimensional network molecule into multiple smaller molecules with straight-chain structures, which is beneficial for microorganisms to decompose and utilize lignin, cellulose, and hemicellulose more efficiently, greatly improving the fermentation degradation efficiency. The mass ratio of the waste residue to the bio-organic fertilizer is 4:1-2, the amount of compound microbial agents No. 1 and No. 2 added is 3-5% of the total mass of the substrate, and the amount of sulfur powder added is 5-10% of the total mass of the substrate. The No. 1 compound microbial agent contains one or more of Bacillus megaterium, Bacillus mucilaginosus, Bacillus subtilis, Bacillus laterosporus, Bacillus acidophilus, Bacillus thermophilus, Thiobacillus acidophilus, phosphate-solubilizing bacteria, and potassium-solubilizing bacteria. The main function of the No. 1 compound microbial agent is to reduce the content of heavy metal ions and salinity in the mixed waste residue, making it more suitable for microbial growth and facilitating further processing. The sulfur powder is required to have a mesh size of 100-200. The sulfur powder can react chemically with heavy metals in the soil to form insoluble sulfides, thereby reducing the activity of heavy metals in the soil. The sulfur powder can also be used as a sulfur source to help bioleach heavy metals from the soil by promoting the growth of specific microorganisms. The No. 2 compound microbial agent includes one or more of the following: silicate bacteria, phosphorus bacteria, potassium bacteria, yeast, nitrogen-fixing Rhodospirillum, lactobacillus, Bacillus subtilis, Rhodospirillum rubrum, Penicillium oxalate, Penicillium glabripennis, and Stratosporum. The No. 2 compound microbial agent can form chelates between nutrients and microbial metabolites, which can significantly improve the absorption and utilization rate of nutrients by plants. At the same time, it can bind fine particles of waste residue and improve the physical structure of waste residue by microorganisms and their metabolites. Before adding the No. 2 compound microbial agent, the moisture content of the substrate needs to be ensured to be above 50%.

2. The method for rapid soil electrolysis of manganese slag using a microbial method according to claim 1, characterized in that, The compound microbial agent is a high-performance strain selected by high-throughput screening technology, and the cells or particles are sorted by flow cytometry.

3. A method for rapid soil electrolysis of manganese slag using a microbial method according to claim 2, characterized in that, The compound microbial agent is first activated by inoculating it onto test tube slant, with a culture temperature of 28–35°C and a pH of 6.0–7.5; then it is gradually scaled up through flat flasks or shake flasks and seed tanks to obtain a large number of highly active compound strains.

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