Metal tailing improved water-retaining agent for high-cold and high-altitude areas and preparation method of metal tailing improved water-retaining agent

Abstract

The invention discloses an improved water-retaining agent for metal tailings in high-cold and high-altitude areas and a preparation method of the improved water-retaining agent, and belongs to the technical field of ecological restoration of the metal tailings. The water-retaining agent comprises pretreated phosphogypsum, biochar, organic fertilizer, PNIPAM-based temperature-sensitive hydrogel microspheres and calcium lignosulphonate, the mass of the pretreated phosphogypsum accounts for 30%-40% of the mass of metal tailings to be improved, the mass of the biochar accounts for 5%-7% of the mass of the metal tailings to be improved, and the mass of the PNIPAM-based temperature-sensitive hydrogel microspheres accounts for 5%-10% of the mass of the metal tailings to be improved. The mass of the organic fertilizer is 10%-15% of the mass of the metal tailings to be improved, the mass of the calcium lignosulphonate is 2%-2.5% of the mass of the metal tailings to be improved, and the mass of the PNIPAM-based temperature-sensitive hydrogel microspheres is 2%-3% of the total mass of other components of the water-retaining agent. By optimizing the components of the metal tailing improved water-retaining agent and combining the scientific proportion, efficient synergy of the components is achieved, the metal tailing improved water-retaining agent has excellent adaptability to the severe environment of the high-cold and high-altitude area, and synergistic promotion of metal tailing structure improvement, nutrient circulation and ecological reconstruction in the high-cold and high-altitude area is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ecological restoration of metal tailings, and relates to a metal tailing improvement water-retaining agent in an alpine high-altitude region and a preparation method thereof. BACKGROUND

[0002] The alpine high-altitude region (above 3000m) has special climatic conditions, such as low temperature, strong radiation, large diurnal temperature difference, scarce precipitation and strong evaporation. The metal tailings widely distributed in this region generally have problems such as loose structure, weak water-holding capacity (natural water-holding rate is usually less than 15%), lack of organic matter (usually less than 0.8%) and high heavy metal content. These characteristics jointly limit the application effect of conventional ecological restoration materials and technologies in such regions.

[0003] At present, common metal tailing improvement mainly includes water-retaining agent restoration relying on microorganisms or chemical synthesis of high molecular materials and water-retaining agent restoration combined with soil covering method. However, on the one hand, the alpine high-altitude region is characterized by harsh climate and fragile ecosystem, and the medium to be restored, i.e. the metal tailings in this region, is mostly in loose sand particle structure, which not only has the problem of high heavy metal content, but also generally has defects such as poor water and soil conservation capacity and unstable physicochemical properties, so the restoration difficulty is significantly higher than that in conventional regions. On the other hand, the restoration effect of existing microbial restoration materials is highly dependent on environmental conditions such as temperature and humidity, and the activity of microorganisms is easily inhibited at extremely low temperature. The soil covering method requires a large amount of high-quality soil resources, and the arable land resources in the alpine high-altitude region are scarce, with a very low proportion of agricultural land, which cannot meet the large demand for high-quality soil resources in the soil covering method. At the same time, the cost of materials, transportation and construction required for large-scale soil covering is extremely high, resulting in high restoration cost of the soil covering method. In addition, the existing restoration materials have poor synergy and single functional properties. Therefore, the effect of the current metal tailing improvement in the alpine high-altitude region is greatly limited.

[0004] Therefore, it is necessary to provide a metal tailing improvement water-retaining agent in an alpine high-altitude region and a preparation method thereof, to improve the adaptability of the improvement water-retaining agent to the special climatic conditions in the alpine high-altitude region, enhance the multiple synergistic improvement functionality of the components of the improvement water-retaining agent, and realize efficient and sustainable ecological restoration of the metal tailings in such regions at a low cost. SUMMARY

[0005] In order to overcome the problems in the background art, the application optimizes the composition of the metal tailing improvement water-retaining agent and combines scientific proportioning, improves the adaptability of the metal tailing improvement water-retaining agent to the special climatic conditions in the alpine high-altitude region, fully plays the mutual synergistic effect between the components, realizes multiple functions such as "adhesion and solidification-intelligent water retention and fertilizer locking-structure improvement-heavy metal stabilization", and ensures effective improvement and restoration of the metal tailings under the harsh environmental conditions in the alpine high-altitude region.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: This invention proposes a water-retaining agent for improving metal tailings in high-altitude and cold regions. The water-retaining agent comprises pretreated phosphogypsum, biochar, organic fertilizer, PNIPAM-based thermosensitive hydrogel microspheres, and calcium lignosulfonate. The mass of the pretreated phosphogypsum is 30%-40% of the mass of the metal tailings to be improved, the mass of the biochar is 5%-7% of the mass of the metal tailings to be improved, the mass of the organic fertilizer is 10%-15% of the mass of the metal tailings to be improved, the mass of the calcium lignosulfonate is 2%-2.5% of the mass of the metal tailings to be improved, and the mass of the PNIPAM-based thermosensitive hydrogel microspheres is 2%-3% of the total mass of the pretreated phosphogypsum, biochar, organic fertilizer, and calcium lignosulfonate.

[0007] The pretreated phosphogypsum has a pH of 7.0-8.5.

[0008] In another aspect, this invention provides a method for preparing the above-mentioned metal tailings improver and water-retaining agent, the preparation method comprising the following steps: (1) Pretreatment of phosphogypsum was carried out by adjusting its pH to 7.0-8.5 to obtain pretreated phosphogypsum.

[0009] (2) The pretreated phosphogypsum obtained in step (1) is mixed evenly with biochar, organic fertilizer, PNIPAM-based thermosensitive hydrogel microspheres and calcium lignosulfonate to obtain a metal tailings improved water retention agent.

[0010] Preferably, the specific steps for pretreating phosphogypsum in step (1) include: S1: Pulverize the phosphogypsum and then add lime milk solution to obtain the reaction system.

[0011] From the perspective of industrial production sources, the vast majority of newly produced, untreated phosphogypsum is acidic. Therefore, the pretreatment of phosphogypsum mainly involves using lime milk to increase its pH value.

[0012] S2: Heating the reaction system of step S1.

[0013] S3: After the reaction in step S2 is completed, the reaction product is filtered, and then the filtrate is washed until the pH is 7.0-8.5. The filtrate is then dried to obtain pretreated phosphogypsum.

[0014] During the reaction, the reaction system is continuously stirred at a speed of 300-400 r / min.

[0015] The filtrate was dried at 105-110℃ for 3-4 hours.

[0016] Preferably, in step S1, the phosphogypsum is pulverized to 100-115 mesh, the mass fraction of lime milk in the lime milk solution is 8%-15%, and the mass ratio of lime milk solution added to phosphogypsum is phosphogypsum: lime milk solution = (3-6):1.

[0017] Preferably, in step S2, the heating temperature is 65-70℃ and the reaction time is 1-1.5h.

[0018] Preferably, in step (2), the biochar is obtained by pyrolysis of barley straw under an inert atmosphere, and the biochar is a powder with a particle size of 80-100 mesh.

[0019] The specific preparation process of biochar is as follows: after removing impurities from barley straw, it is crushed to 2-5 cm and dried at 80-100℃ for 4-6 h; then, under nitrogen protection, the barley straw is heated to 450-550℃ at a heating rate of 5-8℃ / min and kept at this temperature for 2-3 h for pyrolysis. After pyrolysis, it is cooled to room temperature under nitrogen atmosphere, the product is taken out and crushed to 80-100 mesh to obtain barley straw biochar.

[0020] Preferably, in step (2), the organic fertilizer is obtained by composting barley lees.

[0021] The specific preparation process of organic fertilizer is as follows: Take fresh highland barley lees with a moisture content of 65%-75%, add 10%-15% of its mass of compound composting agent, which is composed of Bacillus subtilis, yeast and actinomycetes mixed in a mass ratio of 2:1:1, with a viable count ≥2×10⁻⁶. 8 CFU / g; Fresh barley lees and compound composting agent are mixed evenly and composted at a height of 1.2-1.5m and a temperature of 25-30℃. The pile is turned over every 2-3 days, and the composting cycle is 15-20 days to obtain the organic fertilizer.

[0022] Preferably, in step (2), the specific preparation method of the PNIPAM-based thermosensitive hydrogel microspheres includes: Q1: Dissolve N-isopropylacrylamide, acrylamide, polyethylene glycol diacrylate, and ammonium persulfate in water to obtain an aqueous phase substance.

[0023] Q2: Under nitrogen protection, the aqueous phase substance from step Q1 is added dropwise to the hot paraffin oil phase containing Span 80, and the mixture is stirred at a constant temperature to carry out the polymerization reaction.

[0024] Q3: After the polymerization reaction in step Q2 is completed, the reaction product is centrifuged, and then the reaction product obtained from the polymerization reaction in step Q2 is washed with an ethanol-acetone mixture. The washed material is purified with deionized water, and then sieved and vacuum dried to obtain PNIPAM-based thermosensitive hydrogel microspheres.

[0025] The reaction product was transferred to a centrifuge tube, and excess ethanol was added to demulsify and allow it to settle. The supernatant was removed by centrifugation, and then the product was repeatedly washed with a mixture of ethanol and propanol in a 1:1 volume ratio to remove unreacted monomers, initiators, oil phase and other impurities. Finally, it was washed with deionized water.

[0026] Preferably, in step Q1, the molar ratio of N-isopropylacrylamide to acrylamide is N-isopropylacrylamide:acrylamide = 9:1, the amount of polyethylene glycol diacrylate is 7%-8% of the total mass of N-isopropylacrylamide and acrylamide, and the amount of ammonium persulfate is 2%-3% of the total mass of N-isopropylacrylamide and acrylamide. The amount of water is sufficient to fully dissolve N-isopropylacrylamide, acrylamide, polyethylene glycol diacrylate, and ammonium persulfate; preferably, the solid-liquid ratio of the total mass of N-isopropylacrylamide and acrylamide to water is 1-3 g: 10 ml.

[0027] In step Q3, microspheres with a particle size of 150-300 μm are obtained by sieving.

[0028] Preferably, in step Q2, the temperature of the paraffin oil phase is 60-65℃, and the polymerization reaction time is 4-6h.

[0029] During the polymerization reaction, the mixture is stirred at a speed of 400-600 rpm.

[0030] In the paraffin oil phase, the volume ratio of paraffin oil to Span 80 is paraffin oil: Span 80 = (40-50):1.

[0031] The volume ratio of the aqueous phase to the paraffin oil phase is water phase: oil phase = 1: (3-6).

[0032] Calcium lignosulfonate can be obtained by direct purchase or by using sulfite pulp waste liquor as raw material and extracting it through conventional pretreatment, concentration, purification and drying processes.

[0033] In the metal tailings remediation and water-retaining agent of this invention, phosphogypsum serves as a structural modifier and pH adjuster, and its particles can effectively fill the pores of the tailings, enhancing the matrix's ability to retain water. Biochar has abundant microporous and mesoporous structures, mainly playing the roles of water retention, heat preservation, and heavy metal adsorption and fixation. Organic fertilizer replenishes the tailings with organic matter and nutrients, and its humic components have the functions of water retention and slow nutrient release. The PNIPAM-based thermosensitive hydrogel microspheres prepared by this invention can be naturally degraded after participating in remediation. Compared with traditional BIS cross-linked hydrogels, it fundamentally avoids the risk of "permanent" synthetic polymers accumulating in the environment and forming microplastic pollution, exhibiting excellent environmental friendliness and meeting the requirements of green and sustainable development. Furthermore, the low critical dissolution temperature of the PNIPAM-based thermosensitive hydrogel microspheres prepared by this invention is controlled to around 15°C. In high-altitude and cold regions, when nighttime temperatures drop (<10℃), the hydrogel swells significantly, maximizing the capture and storage of water. During the day, when temperatures rise (when the rhizosphere temperature exceeds 15℃), the hydrogel undergoes a phase transition, actively releasing water to the plant roots, thus achieving intelligent water regulation. Calcium lignosulfonate, through its hydrophilic groups such as sulfonic acid groups and phenolic hydroxyl groups, strongly adsorbs water molecules via hydrogen bonds, further enhancing the overall water-holding capacity of the system. Thanks to its anionic surface activity, calcium lignosulfonate can prevent particle aggregation through electrostatic repulsion and steric hindrance effects, thus dispersing tailings particles and improving water penetration and distribution.

[0034] Meanwhile, in the composite improvement system constructed in this invention, PNIPAM thermosensitive hydrogel, calcium lignosulfonate, phosphogypsum, biochar, and organic fertilizer form a synergistic network through multi-pathway interactions: PNIPAM thermosensitive hydrogel, as an intelligent moisture regulation unit, combines its water storage and release behavior with the porous structure of biochar to construct a dual "macro-micro" water retention mechanism; the hydrophobic framework (phenylpropane unit) of calcium lignosulfonate can be firmly adsorbed onto the surface of biochar through strong π-π interactions and hydrophobic interactions, and the sulfonic acid groups (-SO3) on the calcium lignosulfonate molecular chain... - ) and carboxyl group (-COO) - ) on the Ca in phosphogypsum 2+ It possesses extremely strong complexing ability, directly binding to the surface of phosphogypsum particles through ionic and coordinate bonds. The long molecular chains of calcium lignosulfonate interweave between biochar, phosphogypsum, and tailings particles, forming a flexible, viscoelastic three-dimensional network structure. This acts as a natural polymeric binder, bridging biochar particles and phosphogypsum to enhance aggregate stability. The addition of phosphogypsum not only rapidly neutralizes alkalinity, but also releases Ca... 2+It also interacts with calcium lignosulfonate and organic matter components, promoting the formation of aggregate structures. Biochar, as a functional carrier, has a large specific surface area to load hydrogels and adsorb and fix nutrients released from the decomposition of organic fertilizer, forming a slow-release reservoir while providing a habitat for microorganisms. The organic acids produced during the decomposition of organic fertilizer synergistically regulate pH with phosphogypsum, and the introduced microbial communities rapidly colonize using the habitat of biochar and the moisture environment provided by the hydrogel, driving the ecological restoration process of the entire system. This multi-component system, through deep coupling of physical, chemical, and biological processes, achieves synergistic promotion of structural improvement, nutrient cycling, and ecological reconstruction of the tailings environment.

[0035] The beneficial effects of this invention are: 1. The metal tailings water-retaining agent of this invention achieves deep coupling of physical, chemical and biological processes by optimizing the composition of the metal tailings water-retaining agent and combining it with scientific ratio. As a result, it has excellent adaptability to the harsh environment of high-altitude and cold regions, and effectively promotes the synergistic improvement of metal tailings structure, nutrient cycling and ecological reconstruction in high-altitude and cold regions.

[0036] 2. This invention uses common solid wastes from high-altitude and cold regions, such as phosphogypsum, barley straw, and barley distiller's grains, as the main raw materials, fully implementing the "waste-to-waste" approach, significantly reducing raw material costs and alleviating the environmental pressure of solid waste generation.

[0037] 3. When the water-retaining agent of this invention is applied in high-altitude and cold environments, the water holding capacity of metal tailings can be increased by more than 20%, the content of available heavy metals can be reduced by more than 50%, and the organic matter content can be significantly increased, creating favorable conditions for vegetation restoration.

[0038] 4. By controlling the molar ratio of N-isopropylacrylamide to acrylamide to 9:1, the low critical dissolution temperature of PNIPAM-based thermosensitive hydrogel microspheres is adjusted to about 15°C, which is beneficial to further enhance the environmental adaptability of the water-retaining agent. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0040] In the embodiments and comparative examples of this invention, unless otherwise specified, all chemical reagents used in the experiments were commercially available analytical grade.

[0041] Example 1 The metal tailings to be improved in this embodiment are located in a lead-zinc tailings pond in Yushu, Qinghai Province, at an altitude of 3800m, with an average annual temperature of -2.5℃, an annual precipitation of 320mm, a natural water holding capacity of 12%, an organic matter content of 0.6%, an available Pb content of 85mg / kg, and a Zn content of 120mg / kg.

[0042] This embodiment prepares the water-retaining agent using the following method: (1) Pretreatment of phosphogypsum: Take local phosphogypsum, crush it to 110 mesh, mix it with 10% lime milk solution at a mass ratio of phosphogypsum: lime milk solution = 5:1, stir at 350 r / min and react at 65℃ for 1.2 h; after the reaction is completed, filter to obtain filtrate, then wash it 4 times with deionized water until the pH of the filtrate is 7.0, and dry it at 108℃ for 3.5 h.

[0043] (2) Preparation of barley straw biochar: Collect local barley straw, remove impurities and crush to 3cm, dry at 90℃ for 5h; place in a tube furnace, introduce nitrogen gas with a purity of 99.9%, heat to 500℃ at a rate of 6℃ / min, and pyrolyze at a constant temperature for 2.5h. After cooling in a nitrogen atmosphere, pulverize to 90 mesh.

[0044] (3) Preparation of organic fertilizer: Take fresh barley lees with a moisture content of 70% and add 12% of its mass of compound composting agent (Bacillus subtilis: yeast: actinomycetes = 2:1:1, viable count 2.5×10⁻⁶). 8 Mix (CFU / g) for 18 minutes; pile in a temperature-controlled fermentation shed, 1.3m high, at a temperature of 28℃, turn over every 2.5 days, and allow to decompose for 18 days.

[0045] (4) Preparation of PNIPAM-based thermosensitive hydrogel microspheres: Environmentally degradable PNIPAM-based thermosensitive hydrogel microspheres were prepared by reverse suspension polymerization: First, N-isopropylacrylamide and acrylamide (molar ratio 9:1), and the hydrolyzable crosslinking agent polyethylene glycol diacrylate (PEGDA) were mixed. PEGDA700 and ammonium persulfate initiator were dissolved in deionized water to form an aqueous phase (PEGDA700 was 7.5% of the total mass of N-isopropylacrylamide and acrylamide, and ammonium persulfate was 2% of the total mass of N-isopropylacrylamide and acrylamide). This aqueous phase was slowly added dropwise to a paraffin oil phase containing Span 80 at 65°C under nitrogen protection (paraffin oil: Span 80 = 50:1). The stirring speed was then increased to 500 rpm to form a stable water-in-oil emulsion, and polymerization was completed at a constant temperature for 5 hours. After the reaction, the reaction product was centrifuged and then washed with an ethanol-acetone mixture (ethanol-acetone volume ratio of 1:1) to remove impurities. After purification with deionized water and sieving, microspheres of 150-300 μm were obtained. Finally, the microspheres were vacuum dried at 40°C to obtain the PNIPAM-based thermosensitive hydrogel microspheres with temperature-responsive and biodegradable properties. This material can be controlled to degrade in soil environments through ester bond hydrolysis.

[0046] (5) Take 30% of the mass of the metal tailings to be improved, 6% of the mass of the metal tailings to be improved, 6% of the mass of the metal tailings to be improved, 2.2% of the mass of the metal tailings to be improved, 12% of the mass of the metal tailings to be improved, and 2% of the total mass of the pretreated phosphogypsum, biochar, organic fertilizer, and calcium lignosulfonate, and mix the above materials evenly. The metal tailings improver and water-retaining agent is thus obtained.

[0047] The water-retaining agent prepared in this embodiment was applied to the metal tailings to be improved in this embodiment, and the tailings were aged and cured under saturated water conditions for 12 days. After 30 days, the results showed that the moisture content of the metal tailings increased to 38%, the moisture release period was extended to 15 days, the available Pb and Zn contents decreased to 32 mg / kg and 58 mg / kg, respectively, and the organic matter content increased to 1.8%.

[0048] After sowing *Leymus chinensis* in the improved metal tailings area, the seedling survival rate reached 82%.

[0049] Example 2 The metal tailings to be improved in this embodiment are located in a copper mine tailings pond in Nagqu, Tibet, at an altitude of 4200m, with an average annual temperature of -4℃ and an annual precipitation of 320mm. The metal tailings are acidic (pH=4.0), with a water holding capacity of 9%, organic matter of 0.4%, and available Cu content of 92mg / kg.

[0050] This embodiment prepares the water-retaining agent using the following method: (1) Pretreatment of phosphogypsum: Take local phosphogypsum, crush it to 100 mesh, mix it with 15% lime milk solution at a mass ratio of phosphogypsum: lime milk solution = 3:1, stir at 400 r / min and react at 70℃ for 1 h; after the reaction is completed, filter to obtain filtrate, then wash it 4 times with deionized water until the pH of the filtrate is 8.2, and dry it at 110℃ for 3 h.

[0051] (2) Preparation of barley straw biochar: Collect local barley straw, remove impurities and crush to 2cm, dry at 80℃ for 5h; place in a tube furnace, introduce nitrogen gas with a purity of 99.9%, heat to 450℃ at a rate of 8℃ / min, and pyrolyze at a constant temperature for 3h. After cooling in a nitrogen atmosphere, pulverize to 80 mesh.

[0052] (3) Preparation of organic fertilizer: Take fresh barley lees with a moisture content of 65%, add 15% of its mass of compound composting agent, mix for 20 minutes; pile it in a temperature-controlled fermentation shed, pile height 1.5m, temperature controlled at 30℃, turn the pile once every 2 days, and compost for 15 days.

[0053] (4) Preparation of PNIPAM-based thermosensitive hydrogel microspheres: Environmentally degradable PNIPAM-based thermosensitive hydrogel microspheres were prepared by reverse suspension polymerization: First, N-isopropylacrylamide and acrylamide (molar ratio 9:1), and the hydrolyzable crosslinking agent polyethylene glycol diacrylate (PEGDA) were mixed. PEGDA700 and ammonium persulfate initiator were dissolved in deionized water to form an aqueous phase (PEGDA700 was 7% of the total mass of N-isopropylacrylamide and acrylamide, and ammonium persulfate was 2.5% of the total mass of N-isopropylacrylamide and acrylamide). This aqueous phase was slowly added dropwise to a paraffin oil phase containing Span 80 at 63°C under nitrogen protection (paraffin oil: Span 80 = 45:1). The stirring speed was then increased to 400 rpm to form a stable water-in-oil emulsion, and polymerization was completed at a constant temperature for 6 hours. After the reaction, impurities were removed by washing with an ethanol-acetone mixture, and microspheres of 150-300 μm were obtained by purification with deionized water and sieving. Finally, the microspheres were vacuum dried at 40°C to obtain the final product, PNIPAM-based thermosensitive hydrogel microspheres with temperature-responsive and biodegradable properties. This material can be controlled to degrade in soil environments through ester bond hydrolysis.

[0054] (5) Take 40% of the mass of the metal tailings to be improved pretreated phosphogypsum, 5% of the mass of the metal tailings to be improved barley straw biochar, 2.5% of the mass of the metal tailings to be improved calcium lignosulfonate, 10% of the mass of the metal tailings to be improved organic fertilizer, and 3% of the total mass of the pretreated phosphogypsum, biochar, organic fertilizer, and calcium lignosulfonate PNIPAM-based thermosensitive hydrogel microspheres, and mix the above materials evenly. The metal tailings improver and water-retaining agent is thus obtained.

[0055] The water-retaining agent prepared in this embodiment was applied to the metal tailings to be improved in this embodiment, and the tailings were aged and cured under saturated water conditions for 15 days. After 45 days, the results showed that the pH of the metal tailings increased to 6.8, the water holding capacity increased to 35%, the available Cu content decreased to 35 mg / kg, and the organic matter content reached 1.6%.

[0056] When Kentucky bluegrass was sown in an improved metal tailings area, the survival rate was 78% after one month, and the plant height reached 12cm.

[0057] Example 3 The metal tailings to be improved in this embodiment are located in a gold mine tailings pond in Ali Prefecture, Tibet, at an altitude of 4,500 m, with an average annual temperature of -5°C and annual precipitation of less than 300 mm. The tailings matrix is ​​strongly alkaline (pH=9.2), extremely loose in structure, with a natural water holding capacity of only 8%, an organic matter content of less than 0.5%, and contains a variety of available heavy metals. In this embodiment, the water-retaining agent is prepared and applied using the following method: (1) Pretreated phosphogypsum: Industrial by-product phosphogypsum was pulverized to 115 mesh. It was mixed with 8% lime milk solution at a mass ratio of phosphogypsum: lime milk solution = 6:1 and reacted at 68℃ for 1.3 h with a stirring rate of 380 r / min. After the reaction was completed, the mixture was filtered, and the filter residue was repeatedly washed with deionized water until the pH of the filtrate was 8.0. Then it was dried at 106℃ for 4 h to obtain neutral pretreated phosphogypsum.

[0058] (2) Preparation of barley straw biochar: Local barley straw was collected, removed for impurities, and crushed to 4 cm. It was then dried at 95℃ for 4.5 h. The straw was placed in a tube furnace and heated to 550℃ at a rate of 7℃ / min under the protection of continuous high-purity nitrogen (purity ≥99.9%), and pyrolyzed at a constant temperature for 2.2 h. After pyrolysis, the straw was cooled to room temperature in a nitrogen atmosphere, the product was removed, and ground to 85 mesh to obtain porous barley straw biochar.

[0059] (3) Preparation of organic fertilizer: Take fresh barley lees with a moisture content of 68% and add 13% of its mass of compound composting agent (Bacillus subtilis: yeast: actinomycetes = 2:1:1, viable count ≥ 2.8 × 10⁻⁶). 8 Mix the mixture (CFU / g) mechanically for 15 minutes to ensure uniformity. Place the mixture (1.4m high) in a temperature-controlled fermentation facility, maintaining the pile temperature at 25℃, and turn the pile every 3 days. After 17 days of aerobic decomposition, fully decomposed organic fertilizer is obtained.

[0060] (4) Preparation of PNIPAM-based thermosensitive hydrogel microspheres: prepared by reverse suspension polymerization. First, N-isopropylacrylamide and acrylamide (molar ratio 9:1), hydrolyzable crosslinking agent polyethylene glycol diacrylate (PEGDA 700, accounting for 7% of the total monomer mass), and initiator ammonium persulfate (accounting for 2% of the total monomer mass) were dissolved in deionized water to form an aqueous phase (PEGDA 700 was used at 8% of the total mass of N-isopropylacrylamide and acrylamide, and ammonium persulfate was used at 3% of the total mass of N-isopropylacrylamide and acrylamide). Under nitrogen protection and stirring, the aqueous phase was added dropwise to a 60°C paraffin oil phase containing 2% Span 80 (paraffin oil: Span 80 = 40:1), and the stirring speed was increased to 600 rpm to form a stable emulsion. The polymerization was completed by reacting at 60°C for 4 hours. The reaction product was washed and purified with an ethanol-acetone mixture, then purified with deionized water, and sieved to obtain microspheres of 150-300 μm. Finally, it was vacuum dried at 40 °C to constant weight to obtain hydrogel microspheres with temperature response and degradability.

[0061] (5) Formulation and application of water-retaining agent: Based on the quality of the tailings to be improved, weigh 35% of pretreated phosphogypsum, 6.5% of highland barley straw biochar, 15% of organic fertilizer, and 2.3% of calcium lignosulfonate, and additionally add 2.5% of PNIPAM-based thermosensitive hydrogel microspheres by mass of the total mass of pretreated phosphogypsum, biochar, organic fertilizer, and calcium lignosulfonate. Place all the above components in a three-dimensional mixer and mix thoroughly to obtain the target water-retaining agent. Mix the water-retaining agent with the 0-20 cm substrate on the surface of the tailings by manual tillage according to the designed dosage, and age and cure under saturated water conditions for 15 days.

[0062] Evaluation of Improvement Effect: Sampling and testing were conducted 60 days after application. Results showed that the tailings pH significantly decreased from 9.2 to 7.5, and the water holding capacity increased to 33%. Available arsenic and lead contents decreased by 60% and 55%, respectively. Organic matter content increased to 1.5%. When Kobresia oleracea, adapted to the local environment, was sown in the remediation area, the average vegetation cover reached 35% after three months, and the plants were growing well, demonstrating that this water-retaining agent can effectively exert a synergistic improvement function even in the alkaline tailings environment at extremely high altitudes.

[0063] Comparative Example This comparative example uses the same method as Example 3 to prepare a metal tailings improved water-retaining agent, the difference being that sulfonated lignin is used instead of calcium lignin sulfonate in this comparative example.

[0064] Control setting: In an adjacent area of ​​the same tailings dam in Ali, Tibet, the water-retaining agent prepared in this comparative example was applied under the same environmental conditions and time points as in Example 3, and the same monitoring and evaluation methods were used.

[0065] Comparative effect evaluation: After 15 days of aging and curing under saturated water conditions and 60 days of application, the comparative monitoring data are as follows: Improved physical structure: In the area where sulfonated lignin was applied, the average weight diameter of the tailings agglomerates was approximately 18% lower than that in the area of ​​Example 3. This indicates that sulfonated lignin is less effective than calcium lignin sulfonate in promoting particle agglomeration and enhancing structural stability. This may be due to differences in their molecular structure and surface activity, leading to differences in Ca²⁺ content in phosphogypsum. + Its bridging effect and its ability to coat and adhere to biochar are relatively weak.

[0066] Moisture retention performance: The water retention rate of tailings in this area was 28%, lower than 33% in Example 3. This demonstrates that sulfonated lignin has slightly weaker immediate water absorption and retention capacity, and the strength of the hydrogen bond network formed by its hydrophilic groups (mainly sulfonic acid groups) and water molecules may not be as strong as that of the complex hydrophilic groups (sulfonic acid groups, phenolic hydroxyl groups, etc.) of calcium lignin sulfonate.

[0067] Chemical and biological activity: The pH adjustment effect (reduced to 7.8) and heavy metal fixation rate (As reduced by 52%, Pb reduced by 50%) were slightly lower than in Example 3, but the differences were relatively small. The organic matter content increased to 1.3%, indicating that its indirect influence on nutrient cycling still exists, but the microenvironment for microbial activity may be affected due to the weakened water retention and structural improvement effects.

[0068] In summary, this invention optimizes the composition of the water-retaining agent and combines it with a scientific ratio to fully leverage the synergistic effect of the components, effectively achieving deep coupling of physical, chemical, and biological processes. This, in turn, effectively improves the adaptability of the water-retaining agent to harsh environments at high altitudes and cold regions, as well as its remediation effect on metal tailings.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A water-retaining agent for improving metal tailings in high-altitude and cold regions, characterized in that: The water-retaining agent comprises pretreated phosphogypsum, biochar, organic fertilizer, PNIPAM-based thermosensitive hydrogel microspheres, and calcium lignosulfonate. The pretreated phosphogypsum accounts for 30%-40% of the mass of the metal tailings to be improved, the biochar accounts for 5%-7% of the mass, the organic fertilizer accounts for 10%-15% of the mass, the calcium lignosulfonate accounts for 2%-2.5% of the mass, and the PNIPAM-based thermosensitive hydrogel microspheres account for 2%-3% of the total mass of the pretreated phosphogypsum, biochar, organic fertilizer, and calcium lignosulfonate. The pretreated phosphogypsum has a pH of 7.0-8.

5.

2. The preparation method of the water-retaining agent for improving metal tailings in high-altitude and cold regions as described in claim 1, characterized in that: The preparation method includes the following steps: (1) Pretreatment of phosphogypsum was carried out by adjusting its pH to 7.0-8.5 to obtain pretreated phosphogypsum; (2) The pretreated phosphogypsum obtained in step (1) is mixed evenly with biochar, organic fertilizer, PNIPAM-based thermosensitive hydrogel microspheres and calcium lignosulfonate to obtain a metal tailings improved water retention agent.

3. The preparation method according to claim 2, characterized in that: In step (1), the specific steps for pretreating phosphogypsum include: S1: Pulverize the phosphogypsum and then add lime milk solution to obtain the reaction system; S2: Heating the reaction system of step S1; S3: After the reaction in step S2 is completed, the reaction product is filtered, and then the filtrate is washed until the pH is 7.0-8.

5. The filtrate is then dried to obtain pretreated phosphogypsum.

4. The preparation method according to claim 3, characterized in that: In step S1, the phosphogypsum is pulverized to 100-115 mesh, the mass fraction of lime milk in the lime milk solution is 8%-15%, and the mass ratio of lime milk solution added to phosphogypsum is phosphogypsum: lime milk solution = (3-6):

1.

5. The preparation method according to claim 3, characterized in that: In step S2, the heating temperature is 65-70℃ and the reaction time is 1-1.5h.

6. The preparation method according to claim 2, characterized in that: In step (2), the biochar is obtained by pyrolysis of barley straw under an inert atmosphere, and the biochar is a powder with a particle size of 80-100 mesh.

7. The preparation method according to claim 2, characterized in that: In step (2), the organic fertilizer is obtained by composting barley lees.

8. The preparation method according to claim 2, characterized in that: In step (2), the specific preparation method of PNIPAM-based thermosensitive hydrogel microspheres includes: Q1: Dissolve N-isopropylacrylamide, acrylamide, polyethylene glycol diacrylate, and ammonium persulfate in water to obtain an aqueous phase substance; Q2: Under nitrogen protection, the aqueous phase substance from step Q1 is added dropwise to the hot paraffin oil phase containing Span 80, and the mixture is stirred at a constant temperature to carry out the polymerization reaction; Q3: After the polymerization reaction in step Q2 is completed, the reaction product is centrifuged, and then the reaction product obtained from the polymerization reaction in step Q2 is washed with an ethanol-acetone mixture. The washed material is purified with deionized water, and then sieved and vacuum dried to obtain PNIPAM-based thermosensitive hydrogel microspheres.

9. The preparation method according to claim 8, characterized in that: In step Q1, the molar ratio of N-isopropylacrylamide to acrylamide is N-isopropylacrylamide:acrylamide = 9:1, the amount of polyethylene glycol diacrylate is 7%-8% of the total mass of N-isopropylacrylamide and acrylamide, and the amount of ammonium persulfate is 2%-3% of the total mass of N-isopropylacrylamide and acrylamide. In step Q3, microspheres with a particle size of 150-300 μm are obtained by sieving.

10. The preparation method according to claim 8, characterized in that: In step Q2, the temperature of the paraffin oil phase is 60-65℃, and the polymerization reaction time is 4-6h. In the paraffin oil phase, the volume ratio of paraffin oil to Span 80 is paraffin oil: Span 80 = (40-50):1; The volume ratio of the aqueous phase to the paraffin oil phase is water phase: oil phase = 1: (3-6).