A tailings-based controlled release soil conditioner

Abstract

The application provides a tailing-based controlled release soil conditioner, and relates to the field of solid waste recycling.The tailing-based controlled release soil conditioner comprises a silico-calcium-magnesium alkaline core and a coating layer arranged on the surface of the silico-calcium-magnesium alkaline core, the coating layer comprises iron-aluminum controlled release layers and silico-calcium-magnesium alkaline layers arranged alternately in sequence, and the outermost layer of the coating layer is an iron-aluminum controlled release layer; the silico-calcium-magnesium alkaline core and the silico-calcium-magnesium alkaline layers both comprise silico-calcium-magnesium alkaline materials and first binders; the components of the silico-calcium-magnesium alkaline materials comprise calcium silicate, dicalcium silicate, tricalcium silicate, diopside, enstatine, montresorite, calcium-magnesium melilite and calcium-aluminum melilite; the iron-aluminum controlled release layers comprise iron-aluminum controlled release materials and second binders; the iron-aluminum controlled release materials comprise alpha-FeOOH and gamma-AlOOH; and the silico-calcium-magnesium alkaline materials and the iron-aluminum controlled release materials are both prepared from tailings.The tailing-based controlled release soil conditioner makes full use of valuable elements in tailings, and can realize controllable release of valuable components in different soil of different pH values.

Description

Technical Field

[0001] This application relates to the field of solid waste recycling, and in particular to a tailings-based controlled-release soil conditioner. Background Technology

[0002] Tailings are industrial solid waste generated during mineral processing. Although existing technologies such as underground backfilling, utilization in building materials, and road materials can partially utilize them, they generally suffer from low added value and weak market competitiveness. In contrast, using tailings to prepare soil conditioners, as a high-value-added resource utilization approach, shows promising application prospects.

[0003] Common acidic soil conditioners mainly include lime-based conditioners (CaO, CaCO3, etc.) and industrial solid waste-based conditioners (steel slag, phosphogypsum, etc.). However, these soil conditioners often release alkalinity too quickly and are difficult to control during application, easily causing a sharp rise in soil pH, leading to soil compaction, seedling burn, and other problems. Furthermore, the calcium and magnesium components are released rapidly, making them difficult for plants to fully absorb and easily lost through surface runoff, resulting in low utilization efficiency. The soil is also prone to acidification under subsequent environmental fluctuations, and the conditioning effect lacks durability, requiring repeated application and increasing labor and material costs.

[0004] Existing processes for preparing soil conditioners using tailings as raw materials mainly include roasting and hydrothermal methods. These methods primarily utilize elements such as silicon, calcium, potassium, magnesium, and phosphorus in the tailings to improve the soil, but the functional development of iron and aluminum components is relatively lacking, resulting in the ineffective utilization of these resources. Furthermore, existing technologies often require the addition of large amounts of exogenous alkaline substances (CaCO3, Na2CO3, NaOH, etc.), leading to excessively high alkalinity in the resulting tailings-based conditioners. These materials lack pH responsiveness and continue to release alkaline substances even under high pH conditions, easily causing over-improvement and soil structure deterioration.

[0005] Therefore, there is an urgent need to develop a new type of tailings-based controlled-release soil conditioner, which focuses on utilizing the underutilized components in tailings, such as iron and aluminum, to construct a controlled-release carrier, thereby effectively regulating alkaline release behavior and overcoming the problems of strong alkalinity, rapid release, and poor persistence of existing tailings-based conditioners, thus promoting breakthroughs and development in tailings resource utilization technology. Summary of the Invention

[0006] The purpose of this application is to provide a tailings-based controlled-release soil conditioner to solve the above-mentioned problems.

[0007] To achieve the above objectives, this application provides a tailings-based controlled-release soil conditioner, comprising a silicon-calcium-magnesium alkaline core and a coating layer disposed on the surface of the silicon-calcium-magnesium alkaline core. The coating layer comprises an iron-aluminum controlled-release layer and a silicon-calcium-magnesium alkaline layer that are alternately stacked in sequence, and the outermost layer of the coating layer is the iron-aluminum controlled-release layer.

[0008] The silicon-calcium-magnesium alkaline core and silicon-calcium-magnesium alkaline layer include silicon-calcium-magnesium alkaline material and a first binder;

[0009] The components of the silicon-calcium-magnesium alkaline material include: calcium silicate, dicalcium silicate, tricalcium silicate, diopside, enstatite, forsterite, calcium magnesium feldspar, and calcium aluminum feldspar.

[0010] The iron-aluminum controlled-release layer comprises an iron-aluminum controlled-release material and a second binder.

[0011] The iron-aluminum controlled-release material includes α-FeOOH and γ-AlOOH;

[0012] Both the silicon-calcium-magnesium alkaline material and the iron-aluminum controlled-release material are prepared from tailings;

[0013] The preparation method of the tailings-based controlled-release soil conditioner includes:

[0014] The tailings are mixed with acid and leached, and solid-liquid separation is performed to obtain an iron-aluminum-rich leachate and a silicon-rich leachate residue.

[0015] The leaching residue and activator are mixed, calcined, and ground to obtain a silicon-calcium-magnesium alkaline material;

[0016] Under heating and stirring conditions, the leachate and precipitant are mixed, and precipitation and solid-liquid separation are performed to obtain iron-aluminum colloid; the iron-aluminum colloid is mixed with deionized water, and hydrothermal reaction, solid-liquid separation, washing and drying are performed to obtain iron-aluminum controlled-release material;

[0017] The silicon-calcium-magnesium alkaline material and the first binder are mixed to obtain a homogenized raw material. A portion of the homogenized raw material is granulated to obtain a silicon-calcium-magnesium alkaline core. The iron-aluminum controlled-release material, the second binder, and deionized water are mixed to obtain an iron-aluminum slurry. The iron-aluminum slurry and the other portion of the homogenized raw material are alternately layered on the surface of the silicon-calcium-magnesium alkaline core to obtain a tailings-based controlled-release soil conditioner.

[0018] Optionally, the tailings-based controlled-release soil conditioner meets at least one of the following conditions:

[0019] A. The particle size of the tailings-based controlled-release soil conditioner is 2mm-5mm;

[0020] B. The particle size of the iron-aluminum controlled-release material is 30nm-100nm;

[0021] C. The tailings-based controlled-release soil conditioner contains ≥20% effective SiO2, ≥15% effective CaO, and ≥5% effective MgO.

[0022] D. When the soil conditioner is applied to acidic soils with pH ≤ 6, it can stabilize the soil pH at 7.0 ± 0.5 within 30 days.

[0023] Optionally, the tailings-based controlled-release soil conditioner meets the following conditions:

[0024] A. The first binder comprises one or more of sodium carboxymethyl cellulose, humic acid, bentonite, ammonium sulfate, and ammonium chloride;

[0025] B. The second binder comprises one or more of sodium carboxymethyl cellulose, sodium silicate, and acidified attapulgite.

[0026] Optionally, the tailings-based controlled-release soil conditioner satisfies at least one of the following conditions:

[0027] A. The tailings include one or more of the following: iron tailings, copper tailings, lead-zinc tailings, molybdenum tailings, gold tailings, tin tailings, and nickel tailings;

[0028] B. The tailings contain SiO2 with a mass content of ≥40%, Fe2O3 with a mass content of ≥8%, Al2O3 with a mass content of ≥8%, Cr with a mass content of ≤250 mg / kg, Cd with a mass content of ≤20 mg / kg, Pb with a mass content of ≤400 mg / kg, As with a mass content of ≤100 mg / kg, Hg with a mass content of ≤10 mg / kg, and Tl with a mass content of ≤5 mg / kg.

[0029] Optionally, the tailings-based controlled-release soil conditioner meets at least one of the following conditions:

[0030] A. The acid includes one or more of hydrochloric acid, sulfuric acid, and nitric acid;

[0031] B. The concentration of the acid is 1 mol / L-5 mol / L;

[0032] C. The solid-liquid mass ratio in the leaching process is 1:4-6;

[0033] D. The leaching process is carried out at a temperature of 50℃-80℃ for a duration of 1h-5h.

[0034] Optionally, the tailings-based controlled-release soil conditioner meets at least one of the following conditions:

[0035] A. The activator includes calcium-based activators and magnesium-based activators, wherein the calcium-based activator is one or more of calcium carbonate, calcium sulfate, calcium hydroxide, calcium nitrate, calcium phosphate, carbide slag and shell powder; the magnesium-based activator includes one or more of magnesium carbonate, magnesium sulfate, magnesium hydroxide, magnesium nitrate, magnesium phosphate, dolomite, serpentine, magnesite and sepiolite.

[0036] B. The mass ratio of Ca to Mg in the activator is 2-4:1.

[0037] C. The mass ratio of the leaching residue to the activator is 1-2:1;

[0038] D. The roasting process is carried out at a temperature of 1000℃-1200℃ for 30min-90min.

[0039] E. The particle size of the silicon-calcium-magnesium alkaline material is less than 200 mesh.

[0040] Optionally, the tailings-based controlled-release soil conditioner meets at least one of the following conditions:

[0041] A. The stirring speed during the process is 300 rpm-500 rpm;

[0042] B. The temperature of the precipitation process is 50℃-70℃;

[0043] C. The precipitant includes one or more of sodium hydroxide solution, potassium hydroxide solution, and ammonia solution;

[0044] D. The final pH value of the precipitation process is 3.5-4.5.

[0045] Optionally, the tailings-based controlled-release soil conditioner meets at least one of the following conditions:

[0046] A. In the hydrothermal reaction, the solid-liquid mass ratio of iron-aluminum colloid to deionized water is 1:4-6, the reaction temperature is 150℃-200℃, the reaction time is 6h-12h, and the saturated water vapor pressure is 1MPa-2MPa.

[0047] B. The pH value of the hydrothermal reaction is 4.0-5.0;

[0048] C. The specific surface area of ​​the iron-aluminum controlled-release material is ≥80m². 2 / g.

[0049] Optionally, the tailings-based controlled-release soil conditioner meets at least one of the following conditions:

[0050] A. The mass ratio of the iron-aluminum controlled-release material to the deionized water is 1:4-6;

[0051] B. The mass of the first binder is 0.5%-1.0% of the mass of the silicon-calcium-magnesium alkaline material mixed therewith;

[0052] C. The mass of the second binder is 0.5%-1.5% of the mass of the iron-aluminum controlled-release material mixed with it.

[0053] Compared with existing technologies, the beneficial effects of this application include: the tailings-based controlled-release soil conditioner provided in this application has an iron-aluminum controlled-release layer as the outermost layer. In acidic soil environments, this layer gradually dissolves, exposing the internal silicon-calcium-magnesium alkaline layer or silicon-calcium-magnesium alkaline core, thereby releasing valuable components and improving acidic soil; in alkaline soil environments, a dense isolation layer forms on the surface of the iron-aluminum controlled-release layer, coating and inhibiting the further release of the internal silicon-calcium-magnesium alkaline materials, avoiding over-improvement; at the same time, the nano-sized α-FeOOH and γ-AlOOH contained in the iron-aluminum controlled-release layer have a large number of active sites, which are effective against heavy metal Cd. 2+ and Pb 2+ This product possesses adsorption properties, enriching the functions of soil conditioners. With its multi-layered structure featuring alternating layers of silicon, calcium, and magnesium alkaline components and iron-aluminum controlled-release layers, it exhibits excellent pH responsiveness, enabling controlled release of valuable components from soils at varying pH levels. This allows for efficient remediation of acidic soils, providing both valuable silicon, calcium, and magnesium components and immobilizing heavy metals. It can be widely applied in agricultural production, soil remediation, landscaping, and urban greening. The innovative preparation method of this tailings-based controlled-release soil conditioner utilizes the iron-aluminum components in tailings, often overlooked in traditional techniques, to construct a controlled-release material and layer. This significantly enhances the added value and functionality of tailings resources. Under alkaline conditions, this controlled-release material forms a dense insulating layer that encapsulates the internal material, preventing further release of alkaline components. After the soil becomes acidic again, it continues to release alkaline substances, preventing over-modification and avoiding repeated applications that waste resources. This significantly improves the added value and functionality of tailings products. Attached Figure Description

[0054] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0055] Figure 1 A schematic diagram of the structure of a tailings-based controlled-release soil conditioner;

[0056] Figure 2 SEM image of the silicon-calcium-magnesium alkaline material provided in Example 1;

[0057] Figure 3 TEM image of the iron-aluminum controlled-release material provided in Example 1;

[0058] Figure 4 A photograph of the slurry of the iron-aluminum controlled-release material provided in Example 1;

[0059] Figure 5 This is a schematic diagram of the preparation method of the tailings-based controlled-release soil conditioner provided in Example 1. Detailed Implementation

[0060] As used in this article:

[0061] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0062] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0063] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0064] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0065] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0066] The first aspect of this application provides a tailings-based controlled-release soil conditioner, comprising a silicon-calcium-magnesium alkaline core and a coating layer disposed on the surface of the silicon-calcium-magnesium alkaline core. The coating layer comprises an iron-aluminum controlled-release layer and a silicon-calcium-magnesium alkaline layer that are alternately stacked in sequence, and the outermost layer of the coating layer is the iron-aluminum controlled-release layer.

[0067] In some embodiments, the tailings-based controlled-release soil conditioner includes a silicon-calcium-magnesium alkaline core, and a first iron-aluminum controlled-release layer, a silicon-calcium-magnesium alkaline layer, and a second iron-aluminum controlled-release layer sequentially and alternately disposed on the surface of the silicon-calcium-magnesium alkaline core, as shown in the specific structure. Figure 1 As shown.

[0068] It should be noted that under acidic soil conditions, the iron-aluminum controlled-release layer dissolves, exposing the internal silicon-calcium-magnesium alkaline layer, releasing valuable components and improving the acidic soil; under alkaline soil conditions, the surface of the iron-aluminum controlled-release layer undergoes hydroxylation to form a dense oxide layer that coats the internal material, preventing or delaying the release of the internal silicon-calcium-magnesium alkaline layer or silicon-calcium-magnesium alkaline core, thus avoiding over-improvement.

[0069] The silicon-calcium-magnesium alkaline core and silicon-calcium-magnesium alkaline layer include silicon-calcium-magnesium alkaline material and a first binder;

[0070] The main components of the silicon-calcium-magnesium alkaline material include: calcium silicate (CaSiO3), dicalcium silicate (Ca2SiO4), tricalcium silicate (Ca3SiO5), diopside (CaMg2Si2O6), enstatite (MgSiO3), forsterite (Mg2SiO4), calcium magnesium feldspar (Ca2MgSi2O7), and calcium aluminum feldspar (Ca2Al2SiO7).

[0071] The iron-aluminum controlled-release layer comprises an iron-aluminum controlled-release material and a second binder.

[0072] The iron-aluminum controlled-release material includes α-FeOOH and γ-AlOOH;

[0073] Both the silicon-calcium-magnesium alkaline material and the iron-aluminum controlled-release material are prepared from tailings;

[0074] The preparation method of the tailings-based controlled-release soil conditioner includes:

[0075] The tailings are mixed with acid and leached, and solid-liquid separation is performed to obtain an iron-aluminum-rich leachate and a silicon-rich leachate residue.

[0076] The leaching residue and activator are mixed, calcined, and ground to obtain a silicon-calcium-magnesium alkaline material;

[0077] Under heating and stirring conditions, the leachate and precipitant are mixed, and precipitation and solid-liquid separation are performed to obtain iron-aluminum colloid; the iron-aluminum colloid is mixed with deionized water, and hydrothermal reaction, solid-liquid separation, washing and drying are performed to obtain iron-aluminum controlled-release material;

[0078] The silicon-calcium-magnesium alkaline material and the first binder are mixed to obtain a homogenized raw material. A portion of the homogenized raw material is granulated to obtain a silicon-calcium-magnesium alkaline core. The iron-aluminum controlled-release material, the second binder, and deionized water are mixed to obtain an iron-aluminum slurry. The iron-aluminum slurry and the other portion of the homogenized raw material are alternately layered on the surface of the silicon-calcium-magnesium alkaline core to obtain a tailings-based controlled-release soil conditioner.

[0079] It is important to note that tailings-based controlled-release soil conditioners can respond to soil pH levels. For example, their mechanism of action can be understood as follows: when the tailings-based controlled-release soil conditioner is initially applied to acidic soil, its outermost iron-aluminum controlled-release layer will slowly dissolve, and the more acidic the soil, the faster the iron-aluminum controlled-release layer will dissolve, releasing Fe... 3+ / Al 3+ The primary mechanism for adsorbing heavy metals involves the gradual exposure of the internal silicon-calcium-magnesium alkaline layer, releasing valuable components such as silicon, calcium, and magnesium, and raising the pH value to improve acidic soil. Simultaneously, as the first silicon-calcium-magnesium alkaline layer is fully released, a second iron-aluminum controlled-release layer is exposed. If the first layer fails to neutralize the soil, the second layer will continue to dissolve, releasing more silicon-calcium-magnesium alkaline material. If the soil has already been neutralized or slightly alkaline, the iron-aluminum controlled-release layer forms a dense barrier, preventing further release of the silicon-calcium-magnesium alkaline layer or its alkaline cores. The stronger the soil alkalinity, the more stable the barrier layer, and the less likely it is to release alkaline silicon-calcium-magnesium alkaline cores. When the soil pH decreases again over time, the iron-aluminum controlled-release layer will slowly dissolve once more, releasing the silicon-calcium-magnesium alkaline layer or its alkaline cores. This prevents the tailings soil conditioner from being too alkaline, which could easily lead to over-modification and soil salinization during application. At the same time, it also "stores" some of the soil conditioner in the soil, so that it can continue to release alkaline substances after the soil is re-acidified. This not only prevents over-modification but also avoids the waste of manpower and resources from multiple applications.

[0080] It should also be noted that the thickness of the silicon-calcium-magnesium alkaline core and coating layer in tailings-based controlled-release soil conditioners can be set according to the actual conditions such as the pH of the target soil, and the number of coating layers can be customized according to actual needs; the more coating layers there are, the less likely there will be over-improvement, and the better the control effect.

[0081] In some embodiments, the tailings-based controlled-release soil conditioner satisfies at least one of the following conditions:

[0082] A. The particle size of the tailings-based controlled-release soil conditioner is 2mm-5mm;

[0083] Optionally, the particle size of the tailings-based controlled-release soil conditioner can be any value between 2mm, 3mm, 4mm, 5mm or 2mm-5mm;

[0084] B. The particle size of the iron-aluminum controlled-release material is 30nm-100nm;

[0085] Optionally, the particle size of the iron-aluminum controlled-release material can be any value between 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm or 30nm-100nm.

[0086] It is important to note that when the particle size of α-FeOOH and γ-AlOOH is too coarse, it will severely impair the controlled-release function, mainly in the following aspects:

[0087] The controlled-release layer surface area decreased significantly, resulting in a reduction of surface active sites and the inability to form continuous Fe-O and Al-O passivation layers (key barriers to prevent internal alkaline materials from contacting the soil). This caused the silicon-calcium-magnesium alkaline materials in the soil conditioner to continue to function in the alkaline environment, resulting in over-modification. At the same time, the decrease in the specific surface area of ​​the controlled-release layer also led to a decrease in the adsorption capacity of the soil conditioner for Pb and Cd.

[0088] C. The effective SiO2 content of the tailings-based controlled-release soil conditioner is ≥20%, the effective CaO content is ≥15%, and the effective MgO content is ≥5%.

[0089] Optionally, the effective SiO2 content of the tailings-based controlled-release soil conditioner can be any value of 20%, 30%, 40%, 50% or ≥20%, the effective CaO content can be any value of 15%, 20%, 30%, 40%, 50% or ≥15%, and the effective MgO content can be any value of 5%, 6%, 7%, 8%, 9%, 10% or ≥5%.

[0090] D. When the soil conditioner is applied to acidic soils with pH ≤ 6, it can stabilize the soil pH at 7.0 ± 0.5 within 30 days.

[0091] Optionally, when applied to acidic soils with pH ≤ 6, the soil conditioner can stabilize the soil pH to any value between 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, or 6.5-7.5 within 30 days.

[0092] In some embodiments, the tailings-based controlled-release soil conditioner satisfies at least one of the following conditions:

[0093] A. The first binder comprises one or more of sodium carboxymethyl cellulose, humic acid, bentonite, ammonium sulfate, and ammonium chloride;

[0094] B. The second binder comprises one or more of sodium carboxymethyl cellulose, sodium silicate, and acidified attapulgite.

[0095] In some embodiments, the tailings-based controlled-release soil conditioner satisfies at least one of the following conditions:

[0096] A. The tailings include one or more of the following: iron tailings, copper tailings, lead-zinc tailings, molybdenum tailings, gold tailings, tin tailings, and nickel tailings;

[0097] B. The tailings contain SiO2 with a mass content of ≥40%, Fe2O3 with a mass content of ≥8%, Al2O3 with a mass content of ≥8%, Cr with a mass content of ≤250 mg / kg, Cd with a mass content of ≤20 mg / kg, Pb with a mass content of ≤400 mg / kg, As with a mass content of ≤100 mg / kg, Hg with a mass content of ≤10 mg / kg, and Tl with a mass content of ≤5 mg / kg.

[0098] Optionally, the mass content of SiO2 in the tailings can be any value of 40%, 50%, 60%, 70%, or ≥40%; the mass content of Fe2O3 can be any value of 8%, 10%, 20%, 30%, or ≥8%; the mass content of Al2O3 can be any value of 8%, 10%, 20%, 30%, or ≥8%; the mass content of Cr can be any value of 250 mg / kg, 200 mg / kg, 150 mg / kg, 100 mg / kg, 50 mg / kg, 10 mg / kg, or ≤250 mg / kg; the mass content of Cd can be any value of 20 mg / kg, 10 mg / kg, 1 mg / kg, 0.1 mg / kg, or ≤20 mg / kg; and the mass content of Pb can be any value of 400 mg / kg, 350 mg / kg, 300 mg / kg, 250 mg / kg, 200 mg / kg, 150 mg / kg, 100 mg / kg, 50 mg / kg, 10 mg / kg, or ≤400 mg / kg. Any value of mg / kg, As can be any value of 100 mg / kg, 50 mg / kg, 10 mg / kg or ≤100 mg / kg, Hg can be any value of 10 mg / kg, 1 mg / kg, 0.1 mg / kg or ≤10 mg / kg, and Tl can be any value of 5 mg / kg, 1 mg / kg, 0.1 mg / kg or ≤5 mg / kg.

[0099] It should be noted that when the mass content of SiO2 in the tailings is ≥40%, the effective SiO2 content in the tailings-based controlled-release soil conditioner can ultimately meet the requirement of ≥20%.

[0100] Silicon plays a role in enhancing soil improvement in this soil conditioner, promoting soil particle aggregation to improve compaction, and helping to stabilize pH and reduce acidification rebound. In addition, it can promote the absorption and utilization of nutrients by crops, while supplementing crops with silicon nutrition to help them grow healthily. It can also enhance the crop's resistance to diseases and pests and its tolerance to adverse conditions such as drought and heavy metal toxicity by strengthening the siliceous layer of the crop epidermis.

[0101] When the mass content of Fe2O3 in the tailings is ≥8% and the mass content of Al2O3 is ≥8%, the yield of iron-aluminum controlled-release materials can be relatively high. When the content of heavy metals such as Cr, Cd, Pb, As, Hg, and Tl in the tailings meets the above requirements, the heavy metal content in the tailings-based controlled-release soil conditioner can be low, avoiding side effects during use.

[0102] In some embodiments, the tailings-based controlled-release soil conditioner satisfies at least one of the following conditions:

[0103] A. The acid includes one or more of hydrochloric acid, sulfuric acid, and nitric acid;

[0104] B. The concentration of the acid is 1 mol / L-5 mol / L;

[0105] Optionally, the concentration of the acid can be 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, or any value between 1 mol / L and 5 mol / L;

[0106] It is important to note that acid leaching can effectively separate silicon-containing and iron-aluminum-containing components in tailings. On the one hand, it reduces the impurity content in silicon-rich leaching residue and increases the silicon content, which helps to obtain more effective silicon in the subsequent roasting process. On the other hand, it increases the iron and aluminum content in the leachate, thereby increasing the yield of iron-aluminum controlled-release materials. Too low an acid concentration, leaching temperature, and reaction time will result in a low leaching rate of iron and aluminum components, while too high an acid concentration will lead to acid waste and increase the amount of wastewater to be treated. Too high a leaching temperature and reaction time will increase the cost of the process.

[0107] C. The solid-liquid mass ratio of the leaching is 1:4-6;

[0108] Optionally, the solid-liquid mass ratio of the leaching can be any value between 1:4, 1:5, 1:6, or 1:4-6;

[0109] D. The leaching temperature is 50℃-80℃, and the leaching time is 1h-5h.

[0110] Optionally, the leaching temperature can be any value between 50℃, 60℃, 70℃, 80℃ or 50℃-80℃, and the time can be any value between 1h, 2h, 3h, 4h, 5h or 1h-5h.

[0111] In some embodiments, the tailings-based controlled-release soil conditioner satisfies at least one of the following conditions:

[0112] A. The activator includes calcium-based activators and magnesium-based activators, wherein the calcium-based activator is one or more of calcium carbonate, calcium sulfate, calcium hydroxide, calcium nitrate, calcium phosphate, carbide slag, and shell powder;

[0113] Magnesium-based activators include one or more of magnesium carbonate, magnesium sulfate, magnesium hydroxide, magnesium nitrate, magnesium phosphate, dolomite, serpentine, magnesite, and sepiolite;

[0114] B. The mass ratio of Ca to Mg in the activator is 2-4:1;

[0115] Optionally, the mass ratio of Ca to Mg in the activator can be any value between 2:1, 3:1, 4:1, or 2-4:1;

[0116] It should be noted that the activator is mainly composed of calcium-based and magnesium-based activators. On the one hand, the activator provides the system with a large amount of alkaline calcium and magnesium components, which can not only supplement the soil with silicon and calcium elements, but also neutralize acidic soil.

[0117] On the other hand, under high temperature conditions, calcium-based and magnesium-based activators react with tailings, transforming quartz, potassium feldspar, and other phases in the tailings into silicates with similar compositions, such as calcium silicate and magnesium silicate. These silicates can further react in the soil to generate monosilicic acid, which can then be absorbed by plants. Therefore, silicates are effective silicon, and the activators activate the silicon in the tailings. At the same time, the occurrence state of calcium and magnesium changes from insoluble oxides, hydroxides, carbonates, etc., to silicate substances, which are more easily dissociated into calcium and magnesium ions in the soil environment, thereby achieving the effect of soil improvement and realizing the synchronous activation of calcium, magnesium, and silicon.

[0118] Taking calcium carbonate as a calcium-based activator and dolomite as a magnesium-based activator as an example, the following reaction occurs during calcination:

[0119] CaMg(CO3)2=CaCO3+MgCO3

[0120] CaCO3 = CaO + CO2(g)

[0121] MgCO3 = MgO + CO2(g)

[0122] CaO + SiO₂ = CaSiO₃

[0123] 2CaO + SiO2 = Ca2SiO4

[0124] 3CaO + SiO2 = Ca3SiO5

[0125] MgO + SiO2 = MgSiO3

[0126] 2MgO + SiO2 = Mg2SiO4

[0127] CaO + MgO + 2SiO₂ = CaMgSi₂O₆

[0128] 2CaO + MgO + 2SiO2 = Ca2MgSi2O7

[0129] 2CaO + Al₂O₃ + SiO₂ = Ca₂Al₂SiO₇

[0130] CaO + KAlSi₂O₈ = KAlSiO₄ + 2CaSiO₃

[0131] C. The mass ratio of the leaching residue to the activator is 1-2:1;

[0132] Optionally, the mass ratio of leaching residue to activator can be any value between 1:1, 1.5:1, 2:1, or 1-2:1;

[0133] It is important to note that the activation effect of silicon, calcium, and magnesium is controlled by limiting the ratio of activators, while the content of each component in the silicon-calcium-magnesium alkaline material is also controlled. If the activator content is too low, the content of unactivated phases such as quartz and potassium feldspar in the silicon-calcium-magnesium alkaline material will be high. If the content is too high, it will increase the cost and make the alkalinity too strong.

[0134] D. The calcination temperature is 1000℃-1200℃, and the time is 30min-90min;

[0135] Optionally, the calcination temperature can be any value between 1000℃, 1100℃, 1200℃ or 1000℃-1200℃, and the time can be any value between 30min, 40min, 50min, 60min, 70min, 80min, 90min or 30min-90min;

[0136] It should be noted that limiting the calcination temperature and time is to control the activation effect of silicon, calcium, and magnesium. Silicon has a good activation effect when the calcination temperature is between 1000℃ and 1200℃ and the time is between 30min and 90min. When the calcination temperature and time are below the above range, the activation effect of silicon, calcium, and magnesium becomes worse. When the calcination temperature and time are above the above range, the cost increases.

[0137] E. The particle size of the silicon-calcium-magnesium alkaline material is less than 200 mesh.

[0138] The particle size of the optional silicon-calcium-magnesium alkaline material can be any value of 200 mesh, 250 mesh, 300 mesh, 400 mesh or less than 200 mesh.

[0139] In some embodiments, the tailings-based controlled-release soil conditioner satisfies at least one of the following conditions:

[0140] A. The stirring speed during the process is 300 rpm-500 rpm;

[0141] Optionally, the stirring speed can be any value between 300 rpm, 400 rpm, 500 rpm, or 300 rpm and 500 rpm.

[0142] It should be noted that when the stirring speed is 300rpm-500rpm, the precipitant can be better dispersed, achieving rapid and uniform precipitation.

[0143] B. The temperature of the precipitation process is 50℃-70℃;

[0144] Optionally, the temperature of the precipitation process can be any value between 50℃, 60℃, 70℃, or 50℃-70℃;

[0145] It should be noted that when the temperature of the precipitation process is between 50℃ and 70℃, it can accelerate the precipitation process.

[0146] C. The precipitant includes one or more of sodium hydroxide solution, potassium hydroxide solution, and ammonia solution;

[0147] In some embodiments, the concentration of the precipitant is 1 mol / L-3 mol / L. When the concentration is below this level, the precipitation rate is too slow, and when the concentration is above this level, the precipitation rate is too fast, which can easily lead to the aggregation of the precipitate and an increase in particle size.

[0148] D. The final pH value of the precipitation is 3.5-4.5.

[0149] Optionally, the endpoint pH of precipitation can be 3.5, 4.0, 4.5, or any value between 3.5 and 4.5.

[0150] It is important to note that 3.5-4.5 is the suitable pH for the formation of iron-aluminum colloids. If the pH is too low, no precipitation will be formed or the amount of precipitation will be small. If the pH is too high, the precipitate may dissolve and impurities may be introduced.

[0151] In some embodiments, the tailings-based controlled-release soil conditioner satisfies at least one of the following conditions:

[0152] A. In the hydrothermal reaction, the solid-liquid mass ratio of iron-aluminum colloid to deionized water is 1:4-6, the reaction temperature is 150℃-200℃, the reaction time is 6h-12h, and the saturated water vapor pressure is 1MPa-2MPa.

[0153] Optionally, the solid-liquid mass ratio of the iron-aluminum colloid to deionized water can be any value between 1:4, 1:5, 1:6 or 1:4-6; the hydrothermal reaction temperature can be any value between 150℃, 160℃, 170℃, 180℃, 190℃, 200℃ or 150℃-200℃; and the reaction time can be any value between 6h, 8h, 10h, 12h or 6h-12h.

[0154] It is important to note that when the colloid content is too high, the system viscosity increases, leading to disordered aggregation of precursor particles rather than directional crystallization. The resulting product is a mixed aggregate with distorted morphology, and the encapsulation of unreacted colloidal nuclei results in a significant increase in acid-insoluble residues, causing the pH-responsive function of the coating layer to fail. When the colloid content is too low, insufficient nucleation driving force leads to abnormal crystal coarsening, a sharp reduction in specific surface area, and excessive interparticle spacing, resulting in a decrease in the bonding rate at the boehmite-goethite heterostructure interface. This prevents the formation of a continuous and dense isolation layer under alkaline conditions, thus losing the ability to control release.

[0155] It should be noted that when the hydrothermal reaction temperature is 150℃-200℃, it can promote the transformation of hydroxide colloids into a crystalline state; too low a temperature will affect the transformation effect. When the temperature is higher than 200℃, it will affect the particle size and specific surface area of ​​the material. In addition, when the reaction time is 6h-12h, the crystal growth is more complete; too low a time will result in incomplete growth, while too high a time may lead to a phase transition.

[0156] It is important to note that the hydrothermal reaction plays a crucial role: driving the amorphous ferric hydroxide and aluminum hydroxide colloids into crystalline boehmite (γ-AlOOH) and goethite (α-FeOOH) through a high-temperature, high-pressure liquid environment, while precisely controlling the crystal morphology (boehmite platy structure, goethite nanoneedle structure) and promoting the heterogeneous interfacial bonding between the two. This process significantly increases the density of active hydroxyl groups on the material surface, providing the necessary crystal structure and interfacial reactivity for the self-assembly of the coating layer to form a dense isolation membrane under alkaline conditions. This is a key preparation step for achieving pH-responsive controlled-release functionality.

[0157] B. The pH value of the hydrothermal reaction is 4.0-5.0;

[0158] Optionally, the pH value of the hydrothermal reaction can be 4.0, 4.5, 5.0, or any value between 4.0 and 5.0;

[0159] It is important to note that maintaining a slightly acidic environment of pH 4.0-5.0 in the hydrothermal system is crucial for achieving the directional transformation of the crystalline phase: under these conditions, the precursor iron-aluminum colloid surface undergoes moderate protonation to form active monomers with controllable positive charges. Too low a pH leads to uncontrolled colloidal dissolution, while too high a pH induces the precipitation of gibbsite and hematite impurities. Simultaneously, this pH window guides the [AlO] phase transformation through a hydrogen bonding network. 6 ] / [FeO 6 Octahedral units undergo dehydration condensation along specific crystal planes, promoting heteroepitaxial bonding between the boehmite {010} facet and the goethite {110} facet, forming a composite crystal structure with interfacial chemical bridging. If the pH deviates from this range, the pH-responsive function of the coating layer will be deactivated due to loss of phase purity, disordered crystal orientation, and weakened interfacial bonding.

[0160] C. The specific surface area of ​​the iron-aluminum controlled-release material is ≥80 m². 2 / g.

[0161] Optionally, the specific surface area of ​​the iron-aluminum controlled-release material can be 80 m². 2 / g, 150 m 2 / g、200 m 2 / g、300 m 2 / g、400 m 2 / g or ≥80 m 2 / g can be any value.

[0162] It should be noted that when the specific surface area of ​​the iron-aluminum controlled-release material is ≥80 m² 2 At a specific surface area of ​​ / g, the controlled release effect of the iron-aluminum controlled-release material can be guaranteed. If the specific surface area is too low, a dense isolation layer cannot be formed in an alkaline soil environment, thus releasing the alkaline silicon-calcium-magnesium nuclei in the inner layer. In addition, a higher specific surface area can increase the active sites on the surface of the controlled-release material, promoting the adsorption of heavy metals such as Pb and Cd.

[0163] In some embodiments, the tailings-based controlled-release soil conditioner satisfies at least one of the following conditions:

[0164] A. The mass ratio of the iron-aluminum controlled-release material to the deionized water is 1:4-6;

[0165] Optionally, the mass ratio of the iron-aluminum controlled-release material to deionized water can be any value between 1:4, 1:5, 1:6, or 1:4-6.

[0166] B. The mass of the first binder is 0.5%-1.0% of the mass of the silicon-calcium-magnesium alkaline material mixed therewith;

[0167] Optionally, the mass of the first binder can be any value between 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or 0.5%-1.0% of the mass of the silicon-calcium-magnesium alkaline material mixed with it.

[0168] C. The mass of the second binder is 0.5%-1.5% of the mass of the iron-aluminum controlled-release material mixed with it.

[0169] Optionally, the mass of the second binder can be any value between 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or 0.5%-1.5% of the mass of the iron-aluminum controlled-release material mixed with it.

[0170] It is important to note that the binder is added to allow the slurry to better adhere to the surface of the alkaline silicon-calcium-magnesium core material during subsequent granulation, resulting in a denser particle structure. In addition, the binder ensures particle strength, preventing powdering or damage during transportation.

[0171] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0172] Example 1

[0173] This embodiment provides a tailings-based controlled-release soil conditioner and its preparation method. A schematic diagram of the soil conditioner's structure is shown below. Figure 1 As shown. The tailings used in the preparation process are iron tailings. The tailings contain 48.29% SiO2, 14.26% Fe2O3, 8.27% Al2O3, 27.19 mg / kg Cr, 1.44 mg / kg Cd, 39.10 mg / kg Pb, 23.08 mg / kg As, 1.27 mg / kg Hg, and 0.03 mg / kg Tl. The specific preparation steps are as follows:

[0174] S1: Iron tailings were acid leached using 3 mol / L hydrochloric acid. The solid-liquid mass ratio during acid leaching was 1:5, the leaching time was 3 hours, and the leaching temperature was 60℃. After leaching, the leachate and leaching residue were obtained by filtration.

[0175] S2: Weigh the leaching residue and activator at a mass ratio of 1.5:1. The calcium-based activator is calcium carbonate, and the magnesium-based activator is dolomite, with a calcium-to-magnesium element mass ratio of 2:1. Mix the weighed raw materials evenly and place them in a physicochemical ceramic crucible in a muffle furnace. Calcinate at 1200℃ for 60 minutes to obtain the calcined product. Ball mill the calcined product to a particle size below 200 mesh to obtain a silicon-calcium-magnesium alkaline material. The scanning electron microscope (SEM) image of the silicon-calcium-magnesium alkaline material is shown below. Figure 2 As shown, its composition includes 3.7% quartz (SiO2), 4.7% calcium silicate (CaSiO3), 17.1% dicalcium silicate (Ca2SiO4), 8.9% tricalcium silicate (Ca3SiO5), 1.1% forsterite (MgSiO3), 22.7% calcium aluminum feldspar (Ca2Al2SiO7), 15.2% calcium magnesium feldspar (Ca2MgSi2O7), 20.3% diopside (CaMg2Si2O6), and 6.3% enstatite (Mg2Si2O6).

[0176] S3: Under the conditions of stirring temperature 60℃ and stirring speed 400rpm, 1mol / L ammonia water was slowly added dropwise to the leachate to adjust the pH of the leachate to 4.0, causing the iron and aluminum components to form an amorphous colloid. After aging for 2 hours, the colloid was centrifuged and washed to obtain iron and aluminum colloids. The iron and aluminum colloids were dispersed in deionized water (the mass ratio of iron and aluminum colloids to deionized water was 1:5), and the pH of the system was adjusted to 4.0. The system was placed in a hydrothermal reactor for hydrothermal reaction, with the reaction temperature controlled at 150℃, the saturated water vapor pressure at 2MPa, and the reaction time at 12h. After the reaction, the colloids were centrifuged, washed, and dried to obtain the iron and aluminum controlled-release material, which has a specific surface area of ​​185m². 2 / g, transmission electron microscopy (TEM) image as follows Figure 3 As shown;

[0177] S4: Disperse the iron-aluminum controlled-release material in deionized water (the mass ratio of iron-aluminum controlled-release material to water is 1:5), and simultaneously add sodium carboxymethyl cellulose binder at a mass fraction of 1.0% of the iron-aluminum controlled-release material, and stir evenly to obtain an iron-aluminum slurry, such as... Figure 4 As shown, the main components of the iron-aluminum slurry are α-FeOOH and γ-AlOOH;

[0178] S5: Mix the silicon-calcium-magnesium alkaline material with the binder humic acid (the mass of the binder is 1.0% of the mass of the silicon-calcium-magnesium alkaline material), and spray water to form a silicon-calcium-magnesium alkaline core in a disc pelletizing machine. Then, spray the iron-aluminum slurry evenly, and simultaneously spray hot air to solidify the surface of the first iron-aluminum controlled-release layer. The mass of the iron-aluminum slurry is approximately 25% of the mass of the silicon-calcium-magnesium alkaline material.

[0179] S6: Add the same amount of silicon-calcium-magnesium alkaline material and binder humic acid as in step S5, and spray water to form a silicon-calcium-magnesium alkaline layer in a disc pelletizer. Then, spray the same amount of iron-aluminum slurry as in step S5 evenly, and spray hot air to solidify the surface of the second iron-aluminum controlled-release layer to obtain a tailings-based controlled-release soil conditioner with a particle size of 3mm.

[0180] The preparation method of this tailings-based controlled-release soil conditioner is illustrated in the following flowchart. Figure 5 As shown.

[0181] The prepared tailings-based controlled-release soil conditioner was used in a soil culture experiment. The initial pH of the soil was 5.65, and the amount of soil conditioner was 1% of the soil mass. The soil and soil conditioner were thoroughly mixed and placed in flower pots. Water was added to make the soil moisture content reach 20%. Water was added every three days according to the mass loss. The changes in the physicochemical properties of the soil are shown in Table 1.

[0182] Table 1 Soil physicochemical properties

[0183]

[0184] As shown in Table 1, the soil environment was acidic in the early stage of cultivation. As the controlled-release layer dissolved, the soil conditioner released valuable components such as silicon, calcium, and magnesium and neutralized the acidic soil. After the soil was restored to neutral (pH=7), the second controlled-release layer effectively inhibited the further release of alkaline silicon, calcium, and magnesium alkaline cores, and the soil pH no longer changed significantly.

[0185] Example 2

[0186] The difference from Example 1 is that the mass ratio of leaching residue to activator is 1:1, the calcination temperature is 1100℃, and the time is 40min.

[0187] The tailings-based controlled-release soil conditioner was used to conduct a soil incubation experiment according to the method in Example 1. The changes in the physicochemical properties of the soil are shown in Table 2.

[0188] Table 2 Soil physicochemical properties

[0189]

[0190] As shown in Table 2, after adjusting the mass ratio of leaching residue to activator, calcination temperature, and calcination time within the specified range, the prepared soil conditioner still improves acidic soil and provides available silicon, calcium, and magnesium. Furthermore, through the use of iron-aluminum controlled-release materials and the layered structure, the soil conditioner exhibits excellent controlled-release properties. After the soil is remediated to neutral (pH=7), the second controlled-release layer effectively inhibits the further release of alkaline silicon, calcium, and magnesium nuclei, and the soil pH no longer changes significantly.

[0191] Example 3

[0192] The differences from Example 1 are: the hydrothermal reaction temperature was 200℃, the reaction time was 8 hours, the saturated water vapor pressure was 2 MPa, and the pH value of the hydrothermal reaction was 4.0. The prepared iron-aluminum controlled-release material had a specific surface area of ​​163 m². 2 / g.

[0193] The tailings-based controlled-release soil conditioner was used to conduct a soil incubation experiment according to the method in Example 1. The changes in the physicochemical properties of the soil are shown in Table 3.

[0194] Table 3 Soil physicochemical properties

[0195]

[0196] As shown in Table 3, after adjusting the temperature, reaction time, saturated water vapor pressure and reaction pH within the specified range, the prepared iron-aluminum controlled-release material still has a high specific surface area value, and the soil conditioner still has good controlled-release properties. After the soil is remediated to neutral (pH=7), the second controlled-release layer effectively inhibits the further release of alkaline silicon-calcium-magnesium alkaline cores, and the soil pH no longer changes significantly.

[0197] Comparative Example 1

[0198] The difference from Example 1 is that no iron-aluminum controlled-release layer is provided.

[0199] The tailings-based controlled-release soil conditioner was used to conduct a soil incubation experiment according to the method in Example 1. The changes in the physicochemical properties of the soil are shown in Table 4.

[0200] Table 4 Soil physicochemical properties

[0201]

[0202] As shown in Table 4, soil conditioners can provide available silicon, available calcium, available magnesium and other elements without the addition of an iron-aluminum controlled-release layer, but they do not have pH responsiveness. Under alkaline conditions, they still release a large amount of alkaline substances, resulting in over-remediation and soil salinization.

[0203] Comparative Example 2

[0204] The difference from Example 1 is that step S6 is not performed, and only a silicon-calcium-magnesium alkaline core and a layer of iron-aluminum controlled-release layer are set.

[0205] The tailings-based controlled-release soil conditioner was used to conduct a soil incubation experiment according to the method in Example 1. The changes in the physicochemical properties of the soil are shown in Table 5.

[0206] Table 5 Soil physicochemical properties

[0207]

[0208] As shown in Table 5, without performing step S6, simply retaining the silicon-calcium-magnesium alkaline core and the iron-aluminum controlled-release layer on the surface cannot achieve the controlled-release effect. This is because the controlled-release layer gradually decomposes under acidic conditions, exposing the silicon-calcium-magnesium alkaline core. Since there is no second controlled-release layer inside the silicon-calcium-magnesium alkaline core, the inert layer cannot be produced after the pH increases, thus hindering the release of alkaline substances.

[0209] It is proven that controlled-release soil conditioners must have a silicon-calcium-magnesium alkaline core and a coating layer set on the surface of the silicon-calcium-magnesium alkaline core. The coating layer includes iron-aluminum controlled-release layers and silicon-calcium-magnesium alkaline layers that are stacked alternately in sequence, with the outermost layer of the coating layer being the iron-aluminum controlled-release layer.

[0210] Comparative Example 3

[0211] The difference from Example 1 is that the leaching residue is mixed with the activator but not roasted; instead, it is directly ground to obtain a silicon-calcium-magnesium alkaline material.

[0212] The tailings-based controlled-release soil conditioner was used to conduct a soil incubation experiment according to the method in Example 1. The changes in the physicochemical properties of the soil are shown in Table 6.

[0213] Table 6 Soil physicochemical properties

[0214]

[0215] As shown in Table 6, compared with Example 1, the contents of available silicon, available calcium, and available magnesium in the soil decreased significantly, and the soil remediation effect was significantly reduced. This is because the leaching residue and the activator cannot undergo a chemical reaction without calcination, and the efficiency of the conversion of silicon, calcium, and magnesium in the leaching residue and the activator into available forms is greatly reduced.

[0216] Comparative Example 4

[0217] The difference from Example 1 is that the iron-aluminum colloid does not undergo the hydrothermal reaction in step S3.

[0218] The tailings-based controlled-release soil conditioner was used to conduct a soil incubation experiment according to the method in Example 1. The changes in the physicochemical properties of the soil are shown in Table 7.

[0219] Table 7 Soil physicochemical properties

[0220]

[0221] As shown in Table 7, the iron-aluminum controlled-release material does not have a controlled-release function without hydrothermal reaction. This is because aluminum hydroxide and iron hydroxide colloids can dissolve in both acidic and alkaline soil environments, while the α-FeOOH and γ-AlOOH generated after hydrothermal reaction can form a dense isolation layer under alkaline conditions, which can inhibit the release of internal alkaline raw materials.

[0222] Comparative Example 5

[0223] The difference from Example 1 is that all the raw materials used in S4, S5 and S6 are mixed together, and the mixture is formed by spraying water in a disc pelletizing machine while simultaneously being prepared by spraying hot air.

[0224] The tailings-based controlled-release soil conditioner was used to conduct a soil incubation experiment according to the method in Example 1. The changes in the physicochemical properties of the soil are shown in Table 8.

[0225] Table 8 Soil Physicochemical Properties

[0226]

[0227] As shown in Table 8, under the same conditions of raw materials and process parameters, it is still impossible to prepare a pH-responsive controlled-release soil conditioner without using the special structure proposed in this application.

[0228] The contents of available silicon, available calcium, and available magnesium in the soil conditioners prepared in the above examples and comparative examples were detected. The fixation rates of the soil conditioners for extractable Cd and Pb in the soil were also detected after 30 days (the initial extractable Pb content in the soil was 35.19 mg / kg, and the extractable Cd content was 1.98 mg / kg; the fixation rate was calculated by subtracting the content after cultivation from the initial content and then dividing by the initial content). The test results are shown in Table 9.

[0229] Table 9. Content of valuable components and heavy metal fixation rate of soil conditioners

[0230]

[0231] Analysis: By comparing the valuable component content data in Table 9, it can be seen that the roasting process has a significant effect on increasing the content of available silicon, available calcium, and available magnesium in the soil conditioner (the content of available elements in Comparative Example 3 is extremely low); by comparing the Pb and Cd fixation rates, it can be seen that coating the surface of the silicon-calcium-magnesium alkaline core / silicon-calcium-magnesium alkaline layer with an iron-aluminum controlled-release layer prepared by hydrothermal reaction can effectively promote the reduction of extractable Pb and Cd content.

[0232] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0233] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A tailings-based controlled-release soil conditioner, characterized in that, It includes a silicon-calcium-magnesium alkaline core and a coating layer disposed on the surface of the silicon-calcium-magnesium alkaline core. The coating layer includes an iron-aluminum controlled-release layer and a silicon-calcium-magnesium alkaline layer that are alternately stacked in sequence. The outermost layer of the coating layer is the iron-aluminum controlled-release layer. The silicon-calcium-magnesium alkaline core and silicon-calcium-magnesium alkaline layer include silicon-calcium-magnesium alkaline material and a first binder; The components of the silicon-calcium-magnesium alkaline material include: calcium silicate, dicalcium silicate, tricalcium silicate, enstatite, diopside, forsterite, calcium magnesium feldspar, and calcium aluminum feldspar. The iron-aluminum controlled-release layer comprises an iron-aluminum controlled-release material and a second binder. The iron-aluminum controlled-release material includes α-FeOOH and γ-AlOOH; Both the silicon-calcium-magnesium alkaline material and the iron-aluminum controlled-release material are prepared from tailings; The preparation method of the tailings-based controlled-release soil conditioner includes: The tailings are mixed with acid and leached, and solid-liquid separation is performed to obtain an iron-aluminum-rich leachate and a silicon-rich leachate residue. The leaching residue and activator are mixed, calcined, and ground to obtain a silicon-calcium-magnesium alkaline material; Under heating and stirring conditions, the leachate and precipitant are mixed, and precipitation and solid-liquid separation are performed to obtain iron-aluminum colloid; the iron-aluminum colloid is mixed with deionized water, and hydrothermal reaction, solid-liquid separation, washing and drying are performed to obtain iron-aluminum controlled-release material; The silicon-calcium-magnesium alkaline material and the first binder are mixed to obtain a homogenized raw material. A portion of the homogenized raw material is granulated to obtain a silicon-calcium-magnesium alkaline core. The iron-aluminum controlled-release material, the second binder, and deionized water are mixed to obtain an iron-aluminum slurry. The iron-aluminum slurry and another portion of the homogenized raw material are alternately layered on the surface of the silicon-calcium-magnesium alkaline core to obtain a tailings-based controlled-release soil conditioner.

2. The tailings-based controlled-release soil conditioner according to claim 1, characterized in that, At least one of the following conditions must be met: A. The particle size of the tailings-based controlled-release soil conditioner is 2mm-5mm; B. The particle size of the iron-aluminum controlled-release material is 30nm-100nm; C. The tailings-based controlled-release soil conditioner contains ≥20% effective SiO2, ≥15% effective CaO, and ≥5% effective MgO by mass. D. When the soil conditioner is applied to acidic soils with pH ≤ 6, it can stabilize the soil pH at 7.0 ± 0.5 within 30 days.

3. The tailings-based controlled-release soil conditioner according to claim 1, characterized in that, At least one of the following conditions must be met: A. The first binder comprises one or more of sodium carboxymethyl cellulose, humic acid, bentonite, ammonium sulfate, and ammonium chloride; B. The second binder comprises one or more of sodium carboxymethyl cellulose, sodium silicate, and acidified attapulgite.

4. The tailings-based controlled-release soil conditioner according to claim 3, characterized in that, At least one of the following conditions must be met: A. The tailings include one or more of the following: iron tailings, copper tailings, lead-zinc tailings, molybdenum tailings, gold tailings, tin tailings, and nickel tailings; B. The tailings contain SiO2 with a mass content of ≥40%, Fe2O3 with a mass content of ≥8%, Al2O3 with a mass content of ≥8%, Cr with a mass content of ≤250 mg / kg, Cd with a mass content of ≤20 mg / kg, Pb with a mass content of ≤400 mg / kg, As with a mass content of ≤100 mg / kg, Hg with a mass content of ≤10 mg / kg, and Tl with a mass content of ≤5 mg / kg.

5. The tailings-based controlled-release soil conditioner according to claim 1, characterized in that, At least one of the following conditions must be met: A. The acid includes one or more of hydrochloric acid, sulfuric acid, and nitric acid; B. The concentration of the acid is 1 mol / L-5 mol / L; C. The solid-liquid mass ratio in the leaching process is 1:4-6; D. The leaching process is carried out at a temperature of 50℃-80℃ for a duration of 1h-5h.

6. The tailings-based controlled-release soil conditioner according to claim 1, characterized in that, At least one of the following conditions must be met: A. The activator includes calcium-based activators and magnesium-based activators, wherein the calcium-based activator includes one or more of calcium carbonate, calcium sulfate, calcium hydroxide, calcium nitrate, calcium phosphate, carbide slag, and shell powder; Magnesium-based activators include one or more of magnesium carbonate, magnesium sulfate, magnesium hydroxide, magnesium nitrate, magnesium phosphate, dolomite, serpentine, magnesite, and sepiolite; B. The mass ratio of Ca to Mg in the activator is 2-4:1; C. The mass ratio of the leaching residue to the activator is 1-2:1; D. The roasting process is carried out at a temperature of 1000℃-1200℃ for 30min-90min. E. The particle size of the silicon-calcium-magnesium alkaline material is less than 200 mesh.

7. The tailings-based controlled-release soil conditioner according to claim 1, characterized in that, At least one of the following conditions must be met: A. The stirring speed during the process is 300 rpm-500 rpm; B. The temperature of the precipitation process is 50℃-70℃; C. The precipitant includes one or more of sodium hydroxide solution, potassium hydroxide solution, and ammonia solution; D. The final pH value of the precipitation process is 3.5-4.

5.

8. The tailings-based controlled-release soil conditioner according to claim 1, characterized in that, At least one of the following conditions must be met: A. In the hydrothermal reaction, the solid-liquid mass ratio of iron-aluminum colloid to deionized water is 1:4-6, the reaction temperature is 150℃-200℃, the reaction time is 6h-12h, and the saturated water vapor pressure is 1MPa-2MPa. B. The pH value of the hydrothermal reaction system is 4.0-5.0; C. The specific surface area of ​​the iron-aluminum controlled-release material is ≥80 m². 2 / g.

9. The tailings-based controlled-release soil conditioner according to any one of claims 1-8, characterized in that, At least one of the following conditions must be met: A. The mass ratio of the iron-aluminum controlled-release material to the deionized water is 1:4-6; B. The mass of the first binder is 0.5%-1.0% of the mass of the silicon-calcium-magnesium alkaline material mixed therewith; C. The mass of the second binder is 0.5%-1.5% of the mass of the iron-aluminum controlled-release material mixed with it.

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