Method for preparing heavy metal contaminated soil remediation fertilizer by using coal gangue, heavy metal contaminated soil remediation fertilizer and application

Abstract

The present disclosure provides a method for preparing heavy metal contaminated soil remediation fertilizer from coal gangue, heavy metal contaminated soil remediation fertilizer and application, belonging to the technical field of waste resource utilization. The method comprises the following steps: mixing sulfur-calcium material, red mud and coal gangue, grinding and treating to obtain calcium-iron doped coal gangue powder; calcining the calcium-iron doped coal gangue powder to obtain calcined silicon-calcium-iron-aluminum active material, and cooling, dedusting and mixing the flue gas generated during calcination with ammonia water to obtain flue gas purification liquid; mixing straw extract, flue gas purification liquid and landfill leachate, stirring uniformly to obtain fermentation liquid; mixing the fermentation liquid with the calcined silicon-calcium-iron-aluminum active material, stirring, closed anaerobic fermentation and aeration aerobic fermentation treatment to obtain heavy metal contaminated soil remediation fertilizer, realizing effective utilization and resource conversion of coal gangue, which can not only effectively inhibit the environmental migration activity of heavy metals in soil, but also be used for repairing four kinds of heavy metal contaminated soil.

Description

Technical Field

[0001] This disclosure belongs to the field of solid waste resource utilization technology, specifically relating to a method for preparing heavy metal contaminated soil remediation fertilizer using coal gangue, the heavy metal contaminated soil remediation fertilizer and its application. Background Technology

[0002] Coal gangue, a solid waste generated during coal mining and processing, has seen its production increase year by year, causing serious environmental pollution. It mainly consists of organic matter, minerals, and a small amount of inorganic matter from coal seams, and its generation is primarily related to factors such as mining methods, geological conditions, and coal seam quality. Resource-based treatment of coal gangue can improve the utilization rate of coal resources and reduce waste. It is commonly used as an industrial raw material in building materials and ceramics, achieving resource reuse. Through resource-based treatment of coal gangue, environmental pollution can be reduced, resources can be conserved, a circular economy can be promoted, economic efficiency can be improved, and it can play a positive role in addressing the energy crisis. Therefore, given the large output and low utilization rate of coal gangue, with large amounts piled up without effective utilization, this not only wastes land resources but also potentially causes serious environmental pollution problems. It is necessary to transform coal gangue into a valuable resource through appropriate treatment and improvement, promoting its widespread application and contributing to environmental protection and sustainable development.

[0003] In addition, heavy metal pollution is mainly caused by factors such as mining, exhaust gas emissions, wastewater irrigation, and the use of products containing excessive levels of heavy metals. For humans, heavy metal pollutants can enter the body through the digestive tract, respiratory tract, and skin, binding to human proteins and affecting their structure and function, thus impacting human health. Heavy metal pollutants can also be directly absorbed by plants and enter the human body through the food chain, harming the biosphere. Soil heavy metal pollution is one of the most prominent environmental pollution problems in my country today.

[0004] Therefore, it is necessary to develop a method that can utilize coal gangue while simultaneously treating metal pollution in soil, achieving the synergistic utilization of solid waste resources. Currently, soil remediation materials are produced using coal gangue and red mud as raw materials through methods such as hydrogen peroxide oxidation. However, these materials are only suitable for remediating one or two heavy metals, such as cadmium or arsenic contaminated soil, or soil contaminated with a combination of cadmium and arsenic. They cannot simultaneously remediate three or more heavy metals. When remediation of multiple heavy metals is required, multiple remediation agents need to be added, resulting in high costs. Furthermore, current soil remediation agents only reduce the concentration of heavy metals, making their function relatively limited. Summary of the Invention

[0005] This disclosure aims to at least solve one of the technical problems existing in the prior art, and to provide a method for preparing heavy metal contaminated soil remediation fertilizer using coal gangue, the heavy metal contaminated soil remediation fertilizer, and its application.

[0006] One aspect of this disclosure provides a method for preparing fertilizer for remediating heavy metal contaminated soil using coal gangue, the method comprising: Sulfur-calcium materials, red mud, and coal gangue are mixed and ground to obtain calcium-iron coal gangue powder. The calcium-iron-coal gangue powder is calcined to obtain calcined silicon-calcium-iron-aluminum active material, and the flue gas generated by calcination is cooled, dusted, and mixed with ammonia water to obtain flue gas purification liquid. The straw extract, the flue gas purification liquid, and the landfill leachate are mixed and stirred evenly to obtain the fermentation starter liquid; The fermentation initiator is mixed with the calcined silicon-calcium-iron-aluminum active material, and then subjected to stirring, closed anaerobic fermentation, and aerated aerobic fermentation to obtain a fertilizer for remediating heavy metal contaminated soil.

[0007] Optionally, the mass ratio of the sulfur-calcium material, red mud, and coal gangue is in the range of (5~25):(5~25):100.

[0008] Optionally, the calcination temperature is 500~900℃ and the time is 1~5 hours.

[0009] Optionally, the straw extract is formed using the following method: Mix water and straw powder at a liquid-to-solid ratio of (10~20):1mL / g, boil for 0.5~2.5 hours, and then cool to obtain straw extract.

[0010] Optionally, the ratio of the straw extract, flue gas purification liquid, and landfill leachate is in the range of (2.5~7.5):(5~35):100.

[0011] Optionally, the liquid-to-solid ratio of the fermentation initiator and the calcined silicon-calcium-iron-aluminum active material is (0.5~1.5):1mL / g.

[0012] Optionally, the closed anaerobic fermentation treatment takes 5 to 10 days; The aerobic fermentation process takes 5 to 15 days.

[0013] Another aspect of this disclosure provides a fertilizer for remediating heavy metal contaminated soil, prepared according to the method described above.

[0014] Another aspect of this disclosure proposes the application of a fertilizer for remediating heavy metal contaminated soil, which uses the heavy metal contaminated soil remediation fertilizer described above in soil remediation.

[0015] Optionally, the application process includes: Mix the heavy metal contaminated soil remediation fertilizer with the contaminated soil at a mass ratio of (1-3):100, stir evenly, sprinkle with water, and let it age for 6-8 days to obtain the remediated soil.

[0016] This disclosure provides a fertilizer for remediating heavy metal contaminated soil prepared from coal gangue, along with its method and application. The method includes: mixing sulfur-calcium materials, red mud, and coal gangue, and grinding them to obtain calcium-iron-doped coal gangue powder; calcining the calcium-iron-doped coal gangue powder to obtain calcined silicon-calcium-iron-aluminum active material; cooling, removing dust from the flue gas generated during calcination, and mixing it with ammonia water to obtain flue gas purification liquid; mixing straw extract, the flue gas purification liquid, and landfill leachate, and stirring evenly to obtain fermentation initiator liquid; mixing the fermentation initiator liquid with the calcined silicon-calcium-iron-aluminum active material, and subjecting the mixture to stirring, closed anaerobic fermentation, and aerated aerobic fermentation to obtain the fertilizer for remediating heavy metal contaminated soil. This method achieves effective utilization and resource transformation of coal gangue. The obtained fertilizer for remediating heavy metal contaminated soil can not only effectively inhibit the environmental migration activity of heavy metals in the soil, but also be used to remediate soils contaminated with four types of heavy metals with good remediation effects. Furthermore, it can simultaneously promote plant production and increase the percentage of plant root growth, thus possessing multiple functions. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating a method for preparing heavy metal contaminated soil remediation fertilizer using coal gangue according to an embodiment of the present disclosure. Figure 2 This is a flowchart illustrating a method for preparing heavy metal contaminated soil remediation fertilizer using coal gangue, according to an embodiment of this disclosure. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solutions of this disclosure, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the protection scope of this disclosure.

[0019] like Figure 1 and Figure 2 As shown, one aspect of this disclosure provides a method S100 for preparing heavy metal contaminated soil remediation fertilizer using coal gangue, specifically including the following steps S110~S140: S110. Sulfur-calcium materials, red mud, and coal gangue are mixed and ground to obtain calcium-iron coal gangue powder.

[0020] Specifically, sulfur-calcium materials, red mud, and coal gangue are weighed out according to a mass ratio of 5~25:5~25:100, mixed, and then ground to obtain calcium-iron coal gangue powder.

[0021] In step S110, the sulfur-calcium material can preferably be either gypsum or phosphogypsum.

[0022] S120. Calcium iron mixed with coal gangue powder is calcined to obtain calcined silicon calcium iron aluminum active material. The flue gas generated by calcination is cooled, dust removed, and mixed with ammonia water to obtain flue gas purification liquid.

[0023] Specifically, calcium-iron mixed with coal gangue powder is calcined for 1 to 5 hours to obtain calcined silicon-calcium-iron-aluminum active material. The calcination temperature is 500 to 900°C. The flue gas generated during the calcination process is cooled and dust removed before being directly introduced into ammonia water to obtain flue gas purification liquid. The ammonia water concentration is 0.5 to 2.5 M.

[0024] It should be noted that, in this embodiment, the reaction mechanism of the calcination process is as follows: During calcination, sulfur and carbon in coal gangue are converted into carbon dioxide and sulfur dioxide gases. After cooling and dust removal in the flue gas, the carbon dioxide and sulfur dioxide gases are directly introduced into ammonia water and combine with ammonium to form sulfurous acid, ammonium sulfate, and ammonium carbonate. Simultaneously, during calcination, the coal-based materials in the coal gangue crack and release combustible gases. These combustible gases are then converted into carbon dioxide and water vapor. The high-temperature water vapor, combined with sodium salts in red mud (which act as fluxes), further enhances the activity of the silica-alumina minerals in the coal gangue, reduces crystallinity, and promotes the interaction between sulfur-calcium materials, red mud, and coal gangue. Secondly, during calcination, the aluminosilicate minerals in the red mud and coal gangue promote the decomposition of gypsum or phosphogypsum, forming sodium silicate-alumina-calcium minerals, calcium aluminate, calcium aluminoferrite, and other active mineral materials, as well as sulfur dioxide gas. The sulfur dioxide enters the flue gas and is subsequently absorbed by the ammonia water. In this way, the active mineral materials such as sodium silicate-aluminate-calcium-sodium minerals, calcium aluminate, and calcium iron-aluminate in the generated calcined material improve the ion exchange capacity and surface active sites of the original material, thereby facilitating the reproduction and function of microorganisms in subsequent steps.

[0025] S130. Mix the straw extract, flue gas purification liquid and landfill leachate, stir evenly, and obtain fermentation starter.

[0026] Specifically, straw extract, flue gas purification liquid, and landfill leachate are mixed in a volume ratio of 2.5~7.5:5~35:100 and stirred evenly to obtain fermentation starter.

[0027] In step S130, the straw is crushed, and water and straw powder are mixed at a liquid-solid ratio of 10~20:1mL / g, boiled for 0.5~2.5 hours, and cooled to obtain straw extract. The straw can be any one of corn straw, soybean straw and rice straw, and there is no specific limitation.

[0028] In this embodiment, by mixing the flue gas purification liquid generated in step S120 with straw extract and landfill leachate to form a fermentation initiator, microorganisms are provided. At the same time, some wastes (such as landfill leachate, flue gas, and straw) can be treated in a synergistic manner, which not only achieves comprehensive treatment of wastes, but also obtains a multifunctional soil remediation fertilizer.

[0029] S140. The fermentation initiator is mixed with calcined silicon-calcium-iron-aluminum active material, and then subjected to stirring, closed anaerobic fermentation, and aerated aerobic fermentation to obtain fertilizer for remediation of heavy metal contaminated soil.

[0030] Specifically, the fermentation initiator and calcined silicon-calcium-iron-aluminum active material are mixed at a liquid-to-solid ratio of 0.5~1.5:1mL / g, stirred evenly, and then sealed for anaerobic fermentation for 5~10 days, followed by aerobic fermentation for 5~15 days to obtain fertilizer for remediation of heavy metal contaminated soil.

[0031] It should be noted that in this embodiment, by mixing the fermentation initiation liquid and the calcined active material, the microorganisms in the fermentation initiation liquid can rapidly multiply on the surface and in the interlayer pores of the calcined active material using elements such as phosphorus, sodium, and iron. During the anaerobic fermentation stage, sulfate-reducing bacteria introduced from landfill leachate in the fermentation initiation liquid use organic matter from the landfill leachate and straw extract as electron donors to reduce sulfate and sulfite ions introduced from the flue gas purification liquid into hydrogen sulfide gas. The hydrogen sulfide then combines with elements such as calcium, sodium, iron, and magnesium in the calcined active material to form relatively stable sulfides. During the aerobic stage, aerobic bacteria fully utilize nutrients such as nitrogen, phosphorus, and potassium to rapidly multiply, achieving the aerobic fermentation process of the calcined active material.

[0032] In this embodiment, based on the component characteristics of landfill leachate, the components of solid minerals such as coal gangue, gypsum, and red mud are fully utilized. Through formulation, high-temperature activation, sulfur cycling, and alternating anaerobic and aerobic microbial processes, the effective utilization and resource transformation of coal gangue are achieved. The resulting fertilizer for remediating heavy metal-contaminated soil not only effectively inhibits the environmental migration activity of heavy metals in the soil, but can also be used to remediate soils contaminated with four types of heavy metals with good remediation effects. Furthermore, it can simultaneously promote plant production and increase the percentage of plant root growth, thus possessing diversified functions.

[0033] Another aspect of this disclosure is the provision of a fertilizer for remediating heavy metal contaminated soil, which is prepared according to the method described above. For details of the process, please refer to the above description, which will not be repeated here.

[0034] Another aspect of this disclosure proposes the application of a fertilizer for remediating heavy metal contaminated soil, which uses the heavy metal contaminated soil remediation fertilizer described above in soil remediation.

[0035] Specifically, the application process of fertilizers for remediating heavy metal contaminated soil includes: Mix the heavy metal contaminated soil remediation fertilizer with the contaminated soil at a mass ratio of (1-3):100, stir evenly, sprinkle with water, and let it age for 6-8 days to obtain the remediated soil.

[0036] In this embodiment, only a small amount of soil remediation fertilizer is needed to remediate soil contaminated with lead, cadmium, mercury, and arsenic. The leaching concentrations of the four metals are all below 0.4 mg / L, while the relative root growth ratio of rice is greater than 110%.

[0037] The preparation method and specific applications of fertilizers for remediating heavy metal contaminated soil will be further illustrated below with several specific examples: It should be noted that the sources of the raw materials used in the following embodiments are explained as follows: The gypsum is all from Maclean, dihydrate, 99% content, CAS number 10101-41-4, MDL number MFCD00149625; Phosphogypsum: Taken from Longquan Phosphate Fertilizer Plant in Xifeng County, Guizhou Province. The phosphogypsum sample mainly contains 52.70% SO3, 37.01% CaO, 4.37% SiO2, 2.07% Al2O3, 1.63% P2O5 and other components (unavoidable impurities and loss on ignition). Red mud: The red mud comes from an alumina company in Shandong Province and mainly consists of 23.94% Al2O3, 21.65% Fe2O3, 16.74% SiO2, 14.13% CaO, 6.24% Na2O, 5.28% TiO2 and other components (unavoidable impurities and loss on ignition). Coal gangue: sourced from Shanxi Xishan Coal and Electricity Co., Ltd., mainly comprising 46.87% SiO2, 33.51% Al2O3, 12.04% Fe2O3, 2.72% CaO, 2.36% K2O, 1.37% TiO2 and other components (unavoidable impurities and loss on ignition); Landfill leachate: Landfill leachate was obtained by sampling from the Bai Mao Jian on-site collection pool in Zhuji, Shaoxing.

[0038] It should be further noted that, in the following embodiments, the heavy metal contaminated farmland soil was prepared using the following methods: Weigh 1 kg of uncontaminated farmland soil sample. Then, add 100 mg of lead, 100 mg of cadmium, 100 mg of mercury, and 100 mg of arsenic to the farmland soil sample. Add water to the soil containing lead, cadmium, mercury, and arsenic at a liquid-to-solid ratio of 1:1 ml / g, stir well, and allow to air dry naturally after 24 hours. The original leaching concentrations of lead, cadmium, mercury, and arsenic in the contaminated soil were 34 mg / L, 29 mg / L, 37 mg / L, and 22 mg / L, respectively.

[0039] It should be noted that when the soil remediation fertilizer prepared in each of the following embodiments is used to remediate agricultural land, the application process includes: mixing the soil remediation fertilizer prepared in each embodiment with the soil of agricultural land contaminated with heavy metals at a mass ratio of 2:100, stirring evenly, sprinkling water evenly, and aging for 7 days to obtain the remediated agricultural land soil.

[0040] It should be noted that in the following embodiments, the toxicity of the soil before and after remediation, as well as the root growth of the soil, were tested. The testing process is as follows: Toxicity leaching test: Toxicity leaching tests were conducted on samples of heavy metal contaminated farmland soil and remediated soil in accordance with the method of "Solid Waste Leaching Toxicity Leaching Method Sulfuric Acid Nitric Acid Method" (HJ / T 299-2007).

[0041] Detection of lead, cadmium, mercury, and arsenic ion concentrations: The concentrations of mercury and arsenic in the leachate were determined according to the standard "Determination of Mercury, Arsenic, Selenium, Bismuth and Antimony in Water - Atomic Fluorescence Spectrometry" (HJ 694-2014). The concentrations of lead and cadmium in the leachate were determined according to the standard "Determination of 32 Elements in Water - Inductively Coupled Plasma Atomic Emission Spectrometry" (HJ776-2015).

[0042] Root growth testing in remediated farmland soil: Root growth experiments of rice plants in uncontaminated farmland soil (control group) and root growth experiments of rice plants in remediated farmland soil (as blank control) were conducted according to the international standard "Soil quality - Determination of the effects of pollutants on soil flora - Part 1: Method for the measurement of inhibition of root growth" (ISO 11269-1-2012). The relative root growth ratio of rice was calculated based on the test results (Relative root growth ratio of rice = Root length of rice plants in remediated farmland soil / Root length of rice plants in uncontaminated farmland soil).

[0043] Example 1 This example illustrates the effect of different mass ratios of sulfur-calcium materials, red mud, and coal gangue on the performance of fertilizers prepared for remediating heavy metal-contaminated soil, and includes the following steps: S1. According to the mass ratios 2.5:5:100, 3:5:100, 4:5:100, 5:2.5:100, 5:3:100, 5:4:100, 5:5:100, 15:5:100, 25:5:100, 5:15:100, 15:15:100, 25:15:100, 5:25:100, 15: Weigh out sulfur-calcium materials, red mud, and coal gangue in ratios of 25:100, 25:25:100, 25:27.5:100, 25:30:100, 25:32.5:100, 27.5:25:100, 30:25:100, and 32.5:25:100 respectively. Mix them, grind them into powder, and obtain calcium-iron coal gangue powder. The sulfur-calcium materials can be gypsum.

[0044] S2. Calcine calcium-iron mixed with coal gangue powder for 1 hour to obtain calcined silicon-calcium-iron-aluminum active material. The calcination temperature is 500℃. The flue gas generated during the calcination process is cooled and dust removed before being directly passed into ammonia water to obtain flue gas purification liquid. The ammonia water concentration is 0.5M.

[0045] S3. Crush the straw, mix water and straw powder at a liquid-solid ratio of 10:1 mL / g, boil for 0.5 hours, and cool to obtain straw extract, wherein the straw is corn straw.

[0046] Mix straw extract, flue gas purification liquid, and landfill leachate in a volume ratio of 2.5:5:100, stir well, and obtain fermentation starter.

[0047] S4. Mix the fermentation initiator and calcined silicon-calcium-iron-aluminum active material at a liquid-solid ratio of 0.5:1 mL / g, stir evenly, seal for anaerobic fermentation for 5 days, and then aerate for 5 days to obtain fertilizer for remediation of heavy metal contaminated soil.

[0048] Furthermore, the preparation of soil for remediated farmland, toxicity leaching tests, detection of lead, cadmium, mercury, and arsenic ion concentrations, and root growth tests of remediated arable land soil were all conducted in accordance with the previous descriptions, and the test results are shown in Table 1.

[0049] Table 1. Effects of the mass ratio of sulfur-calcium materials, red mud, and coal gangue on the performance of the prepared fertilizer for remediating heavy metal contaminated soil.

[0050] As shown in Table 1, when the mass ratio of sulfur-calcium material, red mud, and coal gangue is less than 5:5:100 (as shown in Table 1, the mass ratios of sulfur-calcium material, red mud, and coal gangue are 4:5:100, 3:5:100, 2.5:5:100, 5:4:100, 5:3:100, 5:2.5:100, and even lower ratios not listed in Table 1), the amount of sulfur-calcium material and red mud added is relatively small. During the calcination process, the amount of active mineral materials such as sodium silicate-aluminate-calcium-sodium minerals, calcium aluminate, and calcium iron-aluminate, as well as sulfur dioxide gas, is reduced. The ion exchange capacity and surface active site enhancement effect of the original materials are weakened, resulting in a significant increase in the leaching concentration of heavy metals in the remediated soil samples as the mass ratio of sulfur-calcium material, red mud, and coal gangue decreases. The relative root growth ratio of rice in the remediated soil samples decreases significantly as the mass ratio of sulfur-calcium material, red mud, and coal gangue decreases.

[0051] When the mass ratio of sulfur-calcium materials, red mud, and coal gangue is 5~25:5~25:100 (as shown in Table 1, where the mass ratios are 5:5:100, 15:5:100, 25:5:100, 5:15:100, 15:15:100, 25:15:100, 5:25:100, 15:25:100, and 25:25:100), during calcination, the aluminosilicate minerals in the red mud and coal gangue promote the decomposition of gypsum, forming sodium-based calcium-silica minerals, calcium aluminate, calcium aluminoferrite, and other active mineral materials, as well as sulfur dioxide gas. The sulfur dioxide enters the flue gas and is subsequently absorbed by ammonia water. The sodium-based calcium-silica minerals, calcium aluminate, and calcium aluminoferrite in the calcined material increase the ion exchange capacity and surface active sites of the original materials, thus facilitating subsequent microbial reproduction and activity. Ultimately, the heavy metal leaching concentrations in the remediated soil were all below 0.4 mg / L, and the relative root growth ratio of the rice plants was all above 110%.

[0052] When the mass ratio of sulfur-calcium material, red mud, and coal gangue is greater than 25:25:100 (as shown in Table 1, when the mass ratio of sulfur-calcium material, red mud, and coal gangue is 25:27.5:100, 25:30:100, 25:32.5:100, 27.5:25:100, 30:25:100, 32.5:25:100, and higher ratios not listed in Table 1), the amount of sulfur-calcium material and red mud added is excessive. During the calcination process, the reaction between materials becomes unbalanced, resulting in a significant increase in the leaching concentration of heavy metals in the remediated soil sample as the mass ratio of sulfur-calcium material, red mud, and coal gangue further increases. The relative root growth ratio of rice in the remediated soil sample significantly decreases as the mass ratio of sulfur-calcium material, red mud, and coal gangue further increases.

[0053] Therefore, considering both benefits and costs, the optimal ratio of sulfur-calcium materials, red mud, and coal gangue is 5-25:5-25:100, which is most conducive to improving the performance of the prepared soil remediation fertilizer. The concentration of heavy metal pollution in the soil after remediation is lower, and the roots exhibit good growth after treatment with the soil remediation fertilizer. This indicates that the soil remediation fertilizer in this embodiment not only removes heavy metals but also promotes plant root growth.

[0054] Example 2 This example illustrates the preparation method of heavy metal contaminated soil remediation fertilizer by taking the effect of different volume ratios of straw extract, flue gas purification liquid, and landfill leachate on the performance of the fertilizer. The method includes the following steps: S1. Weigh out the sulfur-calcium material, red mud, and coal gangue according to a mass ratio of 25:25:100, mix them, and grind them into powder to obtain calcium-iron coal gangue powder. The sulfur-calcium material can be any type of phosphogypsum.

[0055] S2. Calcine calcium-iron mixed with coal gangue powder for 3 hours to obtain calcined silicon-calcium-iron-aluminum active material. The calcination temperature is 700℃. The flue gas generated during the calcination process is cooled and dust removed before being directly passed into ammonia water to obtain flue gas purification liquid. The ammonia water concentration is 1.5M.

[0056] S3. Crush the straw, mix water and straw powder at a liquid-solid ratio of 15:1 mL / g, boil for 1.5 hours, and cool to obtain straw extract, wherein the straw is soybean straw.

[0057] Mix straw extract, flue gas purification liquid, and landfill leachate in volume ratios of 1:5:100, 1.5:5:100, 2:5:100, 2.5:2.5:100, 2.5:3:100, 2.5:4:100, 2.5:5:100, 5:5:100, 7.5:5:100, 2.5:20:100, 5:20:100, 7.5:20:100, 2.5:35:100, 5:35:100, 7.5:35:100, 7.5:37.5:100, 7.5:40:100, 7.5:42.5:100, 8:35:100, 8.5:35:100, and 9:35:100, and stir thoroughly to obtain fermentation starter.

[0058] S4. Mix the fermentation initiator and calcined silicon-calcium-iron-aluminum active material at a liquid-to-solid ratio of 1:1 mL / g, stir evenly, seal for anaerobic fermentation for 7.5 days, and then aerate for 10 days to obtain fertilizer for remediation of heavy metal contaminated soil.

[0059] Furthermore, the preparation of soil for remediated farmland, toxicity leaching tests, detection of lead, cadmium, mercury, and arsenic ion concentrations, and root growth tests of remediated arable land soil were all conducted in accordance with the previous descriptions, and the test results are shown in Table 2.

[0060] Table 2. Effects of the volume ratio of straw extract, flue gas purification liquid, and landfill leachate on the performance of the prepared heavy metal contaminated soil remediation fertilizer.

[0061] As shown in Table 2, when the volume ratio of straw extract, flue gas purification liquid, and landfill leachate is less than 2.5:5:100 (as shown in Table 2, when the volume ratios of straw extract, flue gas purification liquid, and landfill leachate are 2:5:100, 1.5:5:100, 1:5:100, 2.5:4:100, 2.5:3:100, 2.5:2.5:100, and even lower ratios not listed in Table 2), less straw extract and flue gas purification liquid are added, resulting in a reduction in the supply of electron donors, sulfate, sulfite, and related nutrients. Consequently, the leaching concentration of heavy metals in the remediated soil samples increases significantly as the volume ratio of straw extract, flue gas purification liquid, and landfill leachate decreases. The relative root growth ratio of rice in the remediated soil samples also decreases significantly as the volume ratio of straw extract, flue gas purification liquid, and landfill leachate decreases.

[0062] When the volume ratio of straw extract, flue gas purification liquid, and landfill leachate is equal to 2.5~7.5:5~35:100 (as shown in Table 2, where the volume ratios of straw extract, flue gas purification liquid, and landfill leachate are 2.5:5:100, 5:5:100, 7.5:5:100, 2.5:20:100, 5:20:100, 7.5:20:100, 2.5:35:100, 5:35:100, and 7.5:35:100), the mixed fermentation initiator and calcined active material allow microorganisms in the fermentation initiator to rapidly multiply on the surface and in the interlayer pores of the calcined active material using elements such as phosphorus, sodium, and iron. During the anaerobic fermentation stage, sulfate-reducing bacteria introduced from landfill leachate in the fermentation inlet use organic matter from the landfill leachate and straw extract as electron donors to reduce sulfate and sulfite ions introduced from the flue gas purification liquid into hydrogen sulfide gas. The hydrogen sulfide then combines with elements such as calcium, sodium, iron, and magnesium in the calcined active material to form relatively stable sulfides. In the aerobic stage, aerobic bacteria rapidly multiply by fully utilizing nutrients such as nitrogen, phosphorus, and potassium, achieving the aerobic fermentation process of the calcined active material. Ultimately, the heavy metal leaching concentration in the remediated soil was below 0.1 mg / L, and the relative root growth ratio of the rice was greater than 117%.

[0063] When the volume ratio of straw extract, flue gas purification liquid, and landfill leachate is greater than 7.5:35:100 (as shown in Table 2, the volume ratios of straw extract, flue gas purification liquid, and landfill leachate are 7.5:37.5:100, 7.5:40:100, 7.5:42.5:100, 8:35:100, 8.5:35:100, 9:35:100, and higher ratios not listed in Table 2), the addition of straw extract and flue gas purification liquid is excessive. This leads to an imbalance in the reaction between the fermentation initiator and the calcined active material during the anaerobic and aerobic fermentation process. Consequently, the leaching concentration of heavy metals in the remediated soil samples increases significantly with further increases in the volume ratio of straw extract, flue gas purification liquid, and landfill leachate. The relative root growth ratio of rice in the remediated soil samples decreases significantly with further increases in the volume ratio of straw extract, flue gas purification liquid, and landfill leachate.

[0064] Therefore, considering both benefits and costs, a volume ratio of straw extract, flue gas purification liquid, and landfill leachate of 2.5–7.5:5–35:100 is most conducive to improving the performance of the prepared soil remediation fertilizer. The concentration of heavy metal pollution in the remediated soil is lower, below 0.1 mg / L, and the root system exhibits good growth after treatment with this soil remediation fertilizer.

[0065] Example 3 This example uses the effect of the liquid-to-solid ratio of the mixed fermentation initiator and the calcined silicon-calcium-iron-aluminum active material on the performance of the prepared heavy metal contaminated soil remediation fertilizer to illustrate the preparation method of the heavy metal contaminated soil remediation fertilizer, including the following steps: S1. Weigh out sulfur-calcium material, red mud, and coal gangue according to a mass ratio of 25:25:100, mix them, and grind them into powder to obtain calcium-iron coal gangue powder. The sulfur-calcium material can be gypsum.

[0066] S2. Calcine calcium-iron mixed with coal gangue powder for 5 hours to obtain calcined silicon-calcium-iron-aluminum active material. The calcination temperature is 900℃. The flue gas generated during the calcination process is cooled and dust removed before being directly introduced into ammonia water to obtain flue gas purification liquid. The ammonia water concentration is 2.5M.

[0067] S3. Crush the straw, mix water and straw powder at a liquid-solid ratio of 20:1 mL / g, boil for 2.5 hours, and cool to obtain straw extract, wherein the straw is rice straw.

[0068] Mix straw extract, flue gas purification liquid, and landfill leachate in a volume ratio of 7.5:35:100, stir well, and obtain fermentation starter.

[0069] S4. Mix the fermentation initiator liquid and calcined silicon-calcium-iron-aluminum active material according to the liquid-solid ratios of 0.25:1mL / g, 0.3:1mL / g, 0.4:1mL / g, 0.5:1mL / g, 1.0:1mL / g, 1.5:1mL / g, 1.6:1mL / g, 1.7:1mL / g, and 1.75:1mL / g. Stir evenly, seal and anaerobic ferment for 10 days, then aerate and ferment for 15 days to obtain fertilizer for remediating heavy metal contaminated soil.

[0070] Furthermore, the preparation of soil for remediated farmland, toxicity leaching tests, detection of lead, cadmium, mercury, and arsenic ion concentrations, and root growth tests of remediated arable land soil were all conducted in accordance with the previous descriptions, and the test results are shown in Table 3.

[0071] Table 3. Effects of the liquid-to-solid ratio of the mixed fermentation initiator and calcined silicon-calcium-iron-aluminum active material on the performance of the prepared heavy metal contaminated soil remediation fertilizer.

[0072] As shown in Table 3, when the liquid-to-solid ratio of the mixed fermentation initiator to the calcined silicon-calcium-iron-aluminum active material is less than 0.5:1 mL / g (as shown in Table 3, when the liquid-to-solid ratio of the mixed fermentation initiator to the calcined silicon-calcium-iron-aluminum active material is 0.4:1 mL / g, 0.3:1 mL / g, 0.25:1 mL / g, and even lower ratios not listed in Table 2), less fermentation initiator is added, resulting in less supply of microorganisms and related nutrients. Consequently, the leaching concentration of heavy metals in the soil samples after remediation increases significantly as the liquid-to-solid ratio of the mixed fermentation initiator to the calcined silicon-calcium-iron-aluminum active material decreases, and the relative root growth ratio of rice in the soil samples after remediation decreases significantly as the liquid-to-solid ratio of the mixed fermentation initiator to the calcined silicon-calcium-iron-aluminum active material decreases.

[0073] When the liquid-to-solid ratio of the mixed fermentation initiator liquid to the calcined silicon-calcium-iron-aluminum active material is 0.5~1.5:1 mL / g (as shown in Table 3, where the liquid-to-solid ratio of the mixed fermentation initiator liquid to the calcined silicon-calcium-iron-aluminum active material is 0.5:1 mL / g, 1.0:1 mL / g, and 1.5:1 mL / g), the microorganisms in the mixed fermentation initiator liquid and the calcined active material can rapidly multiply using elements such as phosphorus, sodium, and iron in the active material on the surface and in the interlayer pores. During the anaerobic fermentation stage, sulfate-reducing bacteria introduced from landfill leachate in the fermentation initiator liquid use organic matter from the landfill leachate and straw extract as electron donors to reduce sulfate and sulfite ions introduced from the flue gas purification liquid into hydrogen sulfide gas. Hydrogen sulfide combines with elements such as calcium, sodium, iron, and magnesium in the calcined active material to form relatively stable sulfides. During the aerobic stage, aerobic bacteria fully utilize nutrients such as nitrogen, phosphorus, and potassium to rapidly multiply, achieving the aerobic fermentation process of the calcined active material. Ultimately, the heavy metal leaching concentrations in the remediated soil were all below 0.01 mg / L, and the relative root growth ratio of the rice plants was all greater than 123%.

[0074] When the liquid-to-solid ratio of the mixed fermentation initiator to the calcined silicon-calcium-iron-aluminum active material is greater than 1.5:1 mL / g (as shown in Table 3, when the liquid-to-solid ratio of the mixed fermentation initiator to the calcined silicon-calcium-iron-aluminum active material is 1.6:1 mL / g, 1.7:1 mL / g, 1.75:1 mL / g, and higher ratios not listed in Table 3), the amount of fermentation initiator added is excessive. During the anaerobic and aerobic fermentation process, the reaction between the fermentation initiator and the calcined active material becomes unbalanced. This leads to a significant increase in the leaching concentration of heavy metals in the remediated soil samples as the liquid-to-solid ratio of the mixed fermentation initiator to the calcined silicon-calcium-iron-aluminum active material further increases. The relative root growth ratio of rice in the remediated soil samples significantly decreases as the liquid-to-solid ratio of the mixed fermentation initiator to the calcined silicon-calcium-iron-aluminum active material further increases.

[0075] Therefore, considering both benefits and costs, a liquid-to-solid ratio of 0.5~1.5:1 mL / g for the mixed fermentation initiator and calcined silicon-calcium-iron-aluminum active material is most conducive to improving the performance of the prepared soil remediation fertilizer. The concentration of heavy metal pollution in the remediated soil is low, below 0.01 mg / L, and the roots exhibit good growth after treatment with this soil remediation fertilizer.

[0076] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

1. A method for preparing fertilizer for remediating heavy metal contaminated soil using coal gangue, characterized in that, The method includes: Sulfur-calcium material, red mud, and coal gangue are mixed and ground to obtain calcium-iron coal gangue powder; the mass ratio of the sulfur-calcium material, red mud, and coal gangue is (5~25):(5~25):100; the sulfur-calcium material is any one of gypsum or phosphogypsum; The calcium-iron-coal gangue powder is calcined to obtain calcined silicon-calcium-iron-aluminum active material. The flue gas generated during calcination is cooled, dusted, and mixed with ammonia water to obtain flue gas purification liquid. The calcination temperature is 500~900℃ and the time is 1~5 hours. The straw extract, the flue gas purification liquid, and the landfill leachate are mixed and stirred evenly to obtain the fermentation initiator liquid; the straw extract is formed by the following method: Mix water and straw powder at a liquid-to-solid ratio of (10~20):1mL / g, boil for 0.5~2.5 hours, and cool to obtain straw extract; the ratio of straw extract, flue gas purification liquid and landfill leachate is (2.5~7.5):(5~35):

100. The fermentation initiator is mixed with the calcined silicon-calcium-iron-aluminum active material, and then subjected to stirring, closed anaerobic fermentation, and aerated aerobic fermentation to obtain a fertilizer for remediating heavy metal contaminated soil; the liquid-solid ratio of the fermentation initiator and the calcined silicon-calcium-iron-aluminum active material is (0.5~1.5):1mL / g.

2. The method according to claim 1, characterized in that, The closed anaerobic fermentation process takes 5 to 10 days. The aerobic fermentation process takes 5 to 15 days.

3. A fertilizer for remediating heavy metal contaminated soil, characterized in that, Prepared by the method according to any one of claims 1 to 2.

4. The application of a fertilizer for remediating heavy metal contaminated soil, characterized in that, The heavy metal contaminated soil remediation fertilizer described in claim 3 is used in soil remediation.

5. The application according to claim 4, characterized in that, The application process includes: Mix the heavy metal contaminated soil remediation fertilizer with the contaminated soil at a mass ratio of (1-3):100, stir evenly, sprinkle with water, and let it age for 6-8 days to obtain the remediated soil.

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