Silicon-containing molybdenum tailings-dolomite mineral-based soil amendment, method of making and use thereof

Abstract

The present application relates to the technical field of soil improvement. Specifically, the present application provides a silicon-molybdenum tailings-dolomite mineral-based soil conditioner and a preparation method thereof. The present application also provides the use of the soil conditioner for improving soil. The soil conditioner of the present application is obtained by calcining silicon-molybdenum tailings and dolomite, and contains effective silicon in a mass fraction of at least 3.5 times that of the silicon-molybdenum tailings used for preparing the soil conditioner. The soil conditioner of the present application can significantly increase the pH value of soil and passivate heavy metals in soil, and has great potential in acidification soil improvement and heavy metal stabilization. In addition, the soil conditioner of the present application can significantly increase the effective silicon content of silicon-molybdenum tailings, and can play a role of silicon fertilizer when applied to soil, thereby providing effective trace element silicon for plant growth.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil improvement. Specifically, the present application relates to a silicon-molybdenum tailings-dolomite mineral-based soil improver and a preparation method thereof. The present application also relates to the use of the soil improver for improving soil. BACKGROUND

[0002] In China, the acidification of farmland soil is a serious problem in some regions, with about 40% of the cultivated land showing acidification. Compared with the 1980s, the average soil pH value has decreased by about 0.5 units. The acidification of soil is more prominent in southern China, with the soil pH value even decreasing by about 1 unit (see: Luo Deying, Preliminary Study on the Improvement Effect of Different Soil Conditioners on Acidified Farmland, World Tropical Agricultural Information, 2023, No. 6, pp. 36-37). For example, in Hubei Province alone, there are more than about 17 million mu of acidified soil, accounting for more than about one-third (about 36.13%) of the total cultivated land area in the province, of which the area with soil pH value less than about 6.50 is about 15,768,000 mu, and the extremely acidified soil (pH value not more than about 4.50) is about 1,243,200 mu.

[0003] In recent years, a variety of soil improvers have been widely used for the improvement of acidified soil, including lime-based substances, minerals and industrial by-products, organic materials, etc. Soil remediation agents can reduce soil acidity, increase soil nutrients, optimize soil structure and improve microbial activity. However, long-term practice shows that the use of soil remediation agents can also cause other soil problems. For example, lime-based soil improvers can quickly increase the content of calcium and magnesium in the soil and alleviate the problem of soil acidification, but excessive use can cause soil hardening. Organic soil improvers can significantly improve soil organic matter and microbial activity and improve the physical properties of the soil, but can increase greenhouse gas emissions and nutrient loss during use.

[0004] In addition, soil conditioner is also one of the comprehensive utilization ways of many solid wastes. China is one of the countries with large molybdenum reserves in the world, and the total reserves of molybdenum resources have reached about 5.9 million tons. With the exploitation and beneficiation of molybdenum ore, more than about 95% of the raw ore is converted into molybdenum tailings after beneficiation operation, and is discharged in the form of waste residue. The storage of these tailings not only increases the economic cost of tailings pond construction and maintenance, occupies a large amount of land resources, but also causes a certain potential pollution risk to the surrounding environment. A large number of studies have promoted the large-scale, harmless and sustainable comprehensive utilization of molybdenum tailings, such as the development of building materials such as cement, concrete and ceramics. By replacing traditional fine aggregate, there are currently people who use molybdenum tailings to produce molybdenum tailings structural concrete that meets the national standards of China, and apply it to the construction industry. However, the application of molybdenum tailings is limited by the transportation radius, is easily replaced by other waste residues, and the building materials industry is already saturated, resulting in a reduction in the utilization space of molybdenum tailings.

[0005] As an industrial by-product, molybdenum tailings contain a large amount of silicate minerals and aluminum and iron oxides, which give molybdenum tailings excellent complexation, adsorption and ion exchange capacity. At the same time, molybdenum tailings contain a large amount of elements such as silicon (Si), calcium (Ca), magnesium (Mg) and potassium (K), which are also essential nutrients for plant growth, making it a candidate material for soil conditioner. Molybdenum can also promote the yield of various crops, improve quality (degrade carcinogens such as nitrate and nitrite in plants), and improve the efficiency of nitrogen fertilizer utilization. Therefore, using molybdenum tailings as a soil conditioner has become a new high-value and sustainable utilization way, with obvious environmental, economic and social benefits, and broad application prospects, especially for the remediation of acid heavy metal contaminated soils.

[0006] Studies have shown that through specific modification methods, the effective components such as silicon, aluminum and iron in molybdenum tailings can be converted into high-efficiency passivation agents for remediation of heavy metal pollution in acidified soil. For example, in the paper "Research and Development of Siliceous Passivation Agent Based on Molybdenum Tailings and Its Application in Acidic Soil", Hu Zheng successfully developed a new type of Na and K passivation agent by using molybdenum tailings as raw material. Under a cadmium (Cd) ion concentration of about 100 mg / L, the removal rates were about 99.76% and about 98.64%, respectively. However, more reaction parameters can be considered for optimization in the synthesis stage of the passivation agent, such as the optimization of parameters such as the ratio of auxiliary agents and reaction temperature.

[0007] At present, how to fully and comprehensively utilize silicon-containing molybdenum tailings still needs further research and development in many aspects, and there is still a huge space for in-depth research. SUMMARY

[0008] Object of the invention

[0009] In view of the problems existing in the prior art described in the background section above, the purpose of the present application is to provide a silicon-containing molybdenum tailings-dolomite mineral-based soil amendment and a preparation method thereof. The purpose of the present application is also to provide the use of the soil amendment for improving soil.

[0010] Embodiments

[0011] To achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0012] Scheme 1: A silicon-containing molybdenum tailings-dolomite mineral-based soil amendment, wherein the soil amendment is obtained by calcining silicon-containing molybdenum tailings and dolomite, and contains an effective silicon mass fraction that is at least 3.5 times the effective silicon mass fraction contained in the silicon-containing molybdenum tail ore used to prepare the soil amendment.

[0013] Scheme 2: The silicon-containing molybdenum tailings-dolomite mineral-based soil amendment according to the above-mentioned scheme 1, wherein the soil amendment contains one or more of calcium aluminate minerals, calcium-iron-aluminate minerals, sulfates, carbonates, and surface basic functional groups.

[0014] Scheme 3: A method for preparing the silicon-containing molybdenum tailings-dolomite mineral-based soil amendment according to the above-mentioned scheme 1 or 2, wherein the preparation method comprises uniformly mixing silicon-containing molybdenum tailings powder and dolomite powder in a weight ratio of about 1:(1.2-1.6); and then calcining the obtained mixture at a temperature of up to 1100°C, for example, at a temperature of about 1000°C to about 1100°C.

[0015] Scheme 4: The preparation method according to the above-mentioned scheme 3, wherein the weight ratio of the silicon-containing molybdenum tailings powder and the dolomite powder is about 1:1.4.

[0016] Scheme 5: The preparation method according to the above-mentioned scheme 3 or 4, wherein the calcination time is at least about 0.8 hours, preferably in the range of about 0.9 to about 1.1 hours, and more preferably about 1.0 hour.

[0017] Scheme 6: The preparation method according to any one of the above-mentioned schemes 3 to 5, wherein the silicon-containing molybdenum tailings contain an effective silicon mass fraction of less than about 30 mg / g.

[0018] Scheme 7: The preparation method according to any one of the above-mentioned schemes 3 to 6, wherein the particle size of the silicon-containing molybdenum tailings powder is less than about 0.150 mm.

[0019] Scheme 8: The preparation method according to any one of the above-mentioned schemes 3 to 7, wherein the particle size of the dolomite powder is less than about 0.075 mm.

[0020] Scheme 9: The method of preparation according to any one of the preceding Schemes 3 to 8, wherein the moisture content of the silicon-bearing molybdenum tailings is less than about 5 wt. %.

[0021] Scheme 10: The method of preparation according to any one of the preceding Schemes 3 to 9, wherein the moisture content of the dolomite is less than about 5 wt. %.

[0022] Scheme 11 : The method of preparation according to any one of the preceding Schemes 3 to 10, wherein the dolomite comprises at least about 28 wt. % calcium oxide, at most about 5 wt. % silicon oxide, at most about 1.2 wt. % iron oxide, at least about 18 wt. % magnesium oxide, at most about 0.85 wt. % aluminum oxide, and at most about 1 wt. % alkali metal oxide, for example, about 0.03 to about 0.05 wt. % potassium oxide and about 0.04 to about 0.06 wt. % sodium oxide.

[0023] Scheme 12: The method of preparation according to any one of the preceding Schemes 3 to 11, wherein the silicon-bearing molybdenum tailings are obtained by subjecting molybdenum tail ore to one or more washings with water, and then drying the washed tailings sand.

[0024] Scheme 13: Use of the silicon-bearing molybdenum tailings-dolomite mineral-based soil amendment according to the preceding Scheme 1 or 2 or prepared by the method of preparation according to any one of the preceding Schemes 3 to 12 for ameliorating acidified soil.

[0025] Scheme 14: The use according to the preceding Scheme 13, wherein the acidified soil is an acidified cadmium-contaminated soil.

[0026] Scheme 15: The use according to the preceding Scheme 12 or 13, wherein the ameliorating the acidified soil comprises mixing the silicon-bearing molybdenum tailings-dolomite mineral-based soil amendment uniformly with the acidified soil at a ratio of about 0.5 wt. % to about 5.0 wt. %, preferably about 1.0 wt. %.

[0027] Technical effects

[0028] The composite mineral material formed from the high-temperature pyrolysis of silicon-bearing molybdenum tailings and dolomite of the present invention has great potential as a soil amendment in acidified soil amelioration and heavy metal stabilization. In particular, the soil amendment of the present invention can be used to ameliorate acidified cadmium-contaminated soil and to stabilize and remediate the heavy metal cadmium thereof.

[0029] The application of the silicon-containing molybdenum tailings-dolomite mineral-based soil improver of the application to improve soil mainly utilizes the silicate mineral generated by the high-temperature reaction of molybdenum tailings and dolomite, which not only increases the pH value of soil, but also has the passivation effect on heavy metals, and meanwhile avoids the defects of traditional repair materials, realizing the efficiency and environmental safety of soil repair.

[0030] The silicon-containing molybdenum tailings-dolomite mineral-based soil improver of the application can not only increase the pH value of soil and passivate heavy metals, but also provide sufficient trace element silicon for plant growth. The silicon-containing molybdenum tailings-dolomite mineral-based soil improver of the application has a significantly higher effective silicon content, which can play the role of silicon fertilizer when applied to soil; in addition, the effective silicon can change the state of heavy metals in soil through penetration adsorption, complexation and other ways, reduce the biological availability of heavy metals, realize the stability of heavy metals, and thus reduce the transfer and enrichment of heavy metals to plants.

[0031] The silicon-containing molybdenum tailings-dolomite mineral-based soil improver of the application avoids the soil hardening problem that may be caused by excessive use of lime substances, and also reduces the transportation cost. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the specific embodiments of the application, the drawings needed in the specific embodiments will be briefly introduced as follows. Obviously, the drawings described in the following are some embodiments of the application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0033] Figure 1 The X-ray diffraction pattern of the silicon-containing molybdenum tailings-dolomite mineral-based soil improver of the application is shown in the figure, wherein the lower spectrum line is the soil improver of the application example 7; the upper spectrum line is the soil improver of the application example 8.

[0034] Figure 2 The infrared spectrum of the silicon-containing molybdenum tailings-dolomite mineral-based soil improver of the application is shown in the figure, wherein the lower spectrum line is the soil improver of the application example 7; the upper spectrum line is the soil improver of the application example 8.

[0035] Figure 3 The electron microscope photos of the silicon-containing molybdenum tailings-dolomite mineral-based soil improver of the application are shown in the figure, wherein a and c are the soil improver of the application example 7; b and d are the soil improver of the application example 8.

[0036] Figure 4Adsorption pseudo-first order kinetics fitting curves of cadmium adsorption by the silicon-molybdenum tailings-dolomite mineral-based soil amendment of the present application embodiment 7 and 8, wherein the left graph is the soil amendment of the present application embodiment 7; the right graph is the soil amendment of the present application embodiment 8.

[0037] Figure 5 Adsorption pseudo-second order kinetics fitting curves of cadmium adsorption by the silicon-molybdenum tailings-dolomite mineral-based soil amendment of the present application embodiment 7 and 8, wherein the left graph is the soil amendment of the present application embodiment 7; the right graph is the soil amendment of the present application embodiment 8.

[0038] Figure 6 Isotherm adsorption model fitting curves of cadmium adsorption by the silicon-molybdenum tailings-dolomite mineral-based soil amendment of the present application embodiment 7 and 8, which are the results of Langmuir equation fitting.

[0039] Figure 7 Improvement effect of the silicon-molybdenum tailings-dolomite mineral-based soil amendment of the present application embodiment 7 and 8 on the pH of seven farmland soils under the condition of about 0, 0.3, 1.5, 3 mg / kg of exogenous cadmium addition, wherein BK is the soil without adding the amendment material under the same cadmium treatment condition; in the graph, letters a, b, c represent the results of significant difference analysis compared with the control BK.

[0040] Figure 8 Cd morphological proportion distribution in the soil under different treatments in the soil cadmium passivation experiment using the silicon-molybdenum tailings-dolomite mineral-based soil amendment of the present application embodiment 7 and 8 in the Gaoxin region.

[0041] Figure 9 Cd morphological proportion distribution in the soil under different treatments in the soil cadmium passivation experiment using the silicon-molybdenum tailings-dolomite mineral-based soil amendment of the present application embodiment 7 and 8 in the Danjiangkou region. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described clearly and completely below in combination with the embodiments of the present application. It should be understood by those skilled in the art that the embodiments are only for the purpose of helping to understand the present application, and should not be regarded as a specific limitation on the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application. The process parameters not specified in the following embodiments are usually in accordance with the conventional conditions.

[0043] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the invention. The endpoints of the ranges and any numerical values are to be understood as approximations. The terms "about" and "approximately" used herein when referring to a numerical value shall mean that the value is within ±20%, ±15%, ±10%, ±5%, or ±2% of the stated value. For numerical ranges recited herein, the endpoints of the ranges are included, the endpoints of the ranges are included, and individual points within the ranges are also included. The endpoints of the ranges and any individual points recited herein are to be understood as approximations.

[0044] According to a first aspect of the present invention, the present invention provides a silicon-containing molybdenum tailings-dolomite mineral-based soil amendment, wherein the soil amendment is obtained by calcining a silicon-containing molybdenum tailings with dolomite, and comprises an effective silicon mass fraction that is at least about 3.5 times, preferably at least about 4 times, and more preferably at least about 5 times the effective silicon mass fraction contained in the silicon-containing molybdenum tailings used to prepare the soil amendment.

[0045] Silicon is one of the essential elements for the growth and development of most plants. Silicon can promote the growth and development of plants, improve soil quality, and increase the absorption and utilization efficiency of other nutrients by plants, thereby reducing the cost of fertilization. Effective silicon refers to the content of silicon elements in soil that can be absorbed and utilized by plants, also known as biological silicon. The content of effective silicon has an important influence on the growth, disease resistance, and stress tolerance of plants. Effective silicon can improve the disease resistance, stress tolerance, and photosynthesis intensity of crops, thereby increasing the yield.

[0046] The content of soil effective silicon is about <50 mg / kg, indicating that the soil is severely silicon-deficient; about 50 to about 100 mg / kg, indicating that the soil is silicon-deficient; about 100 to about 150 mg / kg, indicating that the soil is potentially silicon-deficient; about 150 to about 180 mg / kg, indicating that the soil has a moderate degree of silicon; and about >180 mg / kg, indicating that the soil has abundant silicon (see Zhang Zhantian et al., Influence of Silicon on Plant Growth and Development and Application Research, Yantai Fruit Trees, 2023, No. 04).

[0047] For example in China, a critical indicator of less than about 100 mg / kg of available silicon content is generally accepted. However, a number of studies have shown that even if the available silicon content is higher than about 100 mg / kg, the application of silicon fertilizer still has a yield-increasing effect. For example, Shang Quanyu et al. applied silicon fertilizer in a rice field with an available silicon content of about 119.5 mg / kg, which increased the yield of rice and improved the quality of rice; Wu Ying et al. applied silicon fertilizer in a rice soil in Heilongjiang with an available silicon content of about 200 to about 300 mg / kg, which still had a yield-increasing effect; Zhang Cuizhen et al. studied different soil types (moisture meadow soil, sandy ginger black soil, salinized meadow soil, brown soil) in Shandong Province, and showed that when the available silicon content was about 328.2, about 306.5, about 170.4, and about 110.9 mg / kg, respectively, the application of silicon fertilizer had a positive effect on the yield of rice (see: Zhang Cuizhen et al., Study on Available Silicon Content and Silicon Fertilizer Effect of Rice Soil in Shandong Province, Shandong Agricultural Science, 1999, 31(6), 10-12, 18; and Liu Lijun et al., Research Progress of Soil Silicon in Different Ecological Systems in China, Acta Pedologica Sinica, 2021, 58(1), 31-41).

[0048] These research results show that the application of silicon fertilizer is not limited to silicon-deficient soils, and even in soils with a relatively high available silicon content, the reasonable application of silicon fertilizer can bring a yield-increasing effect.

[0049] Therefore, the inclusion of an appropriate content of available silicon mass fraction in the soil conditioner can ensure that it can play the role of silicon fertilizer when applied to the soil. In the present application, the available silicon mass fraction included in the soil conditioner according to the first aspect of the present application is at least 3.5 times the available silicon mass fraction included in the silicon-containing molybdenum tailing ore used to prepare the soil conditioner, that is, the dolomite increases the available silicon mass fraction of the silicon-containing molybdenum tailing ore by at least 2.5 times during the preparation of the soil conditioner according to the first aspect of the present application. In some preferred embodiments, the soil conditioner of the present application may, for example, include an available silicon mass fraction of at least about 30 mg / g, preferably at least about 40 mg / g, more preferably at least about 50 mg / g, even more preferably at least about 60 mg / g, and most preferably at least about 70 mg / g.

[0050] The soil conditioner according to the first aspect of the present application preferably includes one or more of calcium aluminate minerals, calcium-iron-aluminate minerals, sulfates, carbonates, and surface basic functional groups.

[0051] The calcium aluminate minerals and calcium-iron-aluminate minerals included in the ingredients open up new ways for diversified applications of materials; the sulfate ions (SO4 2- ) and carbonate ions (CO3 2-) The participation promotes the precipitation of metal cations on the surface of the material, thereby significantly enhancing the adsorption capacity of the material for heavy metals; the presence of surface basic functional groups is due to the activation of a large amount of alkali bases contained in the dolomite and the molybdenum tailings themselves at the same time in the co-heating process. These activated ions can form stable complexes with heavy metal elements in contaminated soil, which is of great importance for adsorbing and fixing heavy metal ions in soil.

[0052] According to the second aspect of the present application, the present application provides a method for preparing the silicon-containing molybdenum tailings-dolomite mineral-based soil improver according to the first aspect of the present application described above, wherein the method comprises uniformly mixing silicon-containing molybdenum tailings powder with dolomite powder at a weight ratio of about 1:(1.2-1.6), for example, about 1:1.3, about 1:1.4, or about 1:1.5, and particularly preferably about 1:1.4; and then calcining the obtained mixture at a temperature of up to about 1100°C, for example, at a temperature of about 1000°C to about 1100°C, preferably 1100°C. In this process, the metal elements in the tailings sand react with calcium (Ca) and magnesium (Mg) and other elements in the dolomite to form stable silicate minerals. This change helps to increase the pH value and available silicon of the soil and enhance the adsorption capacity of the soil for heavy metals, thereby improving the soil environment.

[0053] In the preparation method of the second aspect of the present application, the silicon-containing molybdenum tailings used generally contain less than about 30 mg / g of available silicon mass fraction even after calcination.

[0054] Generally, in order to improve the activity of silicon in the silicon-containing molybdenum tailings, a chemical activator can be used for activation, wherein the type and content of alkaline oxides in the chemical activator are positively correlated with the activation rate of silicon dioxide. The chemical activator can be selected from sodium hydroxide or dolomite, etc. In the research process of the inventors of the present application, it is found that when sodium hydroxide is used as an additive, it is possible to cause the generation of viscous sodium silicate, thereby causing the sintering of the product. In the preparation method of the present application, when dolomite is used as a chemical activator, unexpected technical effects are achieved.

[0055] Dolomite can react to form magnesium silicate with significant expansion properties during high-temperature calcination, which is not only beneficial to calcination, but also effectively avoids the sintering problem of the material. Dolomite will decompose and release alkaline substances during high-temperature sintering, which is beneficial to neutralize the acidic substances in the soil, thereby increasing the pH value of the soil. At the same time, the calcium and magnesium ions produced by the decomposition of dolomite minerals can not only further enhance the adsorption and ion exchange capacity of dolomite for heavy metal ions, but also provide essential nutrients for plant growth, promoting plant growth. In addition, dolomite is abundant in China, with a reserve of more than 4 billion tons, widely distributed in China, such as large deposits in Hubei, Hunan, Guangxi, Guizhou and other places. Therefore, dolomite is used as an alkaline additive (chemical activator) in the present application.

[0056] In the preparation method of the second aspect of the present application, the weight ratio of the silicon-containing molybdenum tailings powder to the dolomite powder is in the range of about 1:(1.2-1.6), where the weight of the dolomite powder should not be more than about 1.6 times the weight of the silicon-containing molybdenum tailings powder, otherwise the content ratio of dolomite is increased too much, resulting in an increase in the cost of material preparation, and should not be less than about 1.2 times the weight of the silicon-containing molybdenum tailings powder, otherwise the effective silicon activation efficiency may be too low and may affect the removal efficiency of cadmium by the material.

[0057] In the preparation method of the second aspect of the present application, the calcination temperature is in the range of up to about 1100°C, where the calcination temperature should not be too high, for example, should not be higher than about 1100°C, otherwise more energy consumption and material sintering may occur, and above this temperature, the effective silicon mass fraction increases has become flat, or even may decrease; however, the calcination temperature should not be too low, for example, should not be lower than about 1000°C, otherwise the activation efficiency of effective silicon in molybdenum tailings may be low.

[0058] In the preparation method of the second aspect of the present application, the degree of drying of the silicon-containing molybdenum tailings powder and the dolomite powder is not particularly required, as long as the water content does not adversely affect the uniform mixing of the two powders and ensures their smooth sintering into soil conditioners. Generally, the obtained molybdenum tailings ore is relatively humid, and after washing, it is preferably first naturally air-dried, and then subjected to subsequent crushing, mixing and sintering. Dolomite is generally a dry powder commodity. Preferably, in an exemplary embodiment, the water content of the silicon-containing molybdenum tailings powder and the dolomite powder used in the preparation method can be set to less than about 5% by weight.

[0059] In the method of making of the second aspect of the present application, the particle size of the silicon-bearing molybdenum tailings powder and the dolomite powder is also not particularly limited, as long as it can ensure that the two powders can be mixed evenly and sintered smoothly into the soil amendment. However, in a preferred embodiment, the particle size of the silicon-bearing molybdenum tailings powder is set to be less than about 0.150 mm (-100 mesh); and / or the particle size of the dolomite powder is set to be less than about 0.075 mm (-200 mesh). When the particle size of both the silicon-bearing molybdenum tailings powder and the dolomite powder meets the above limit, the mass fraction of effective silicon in the sintered soil amendment material is higher.

[0060] In the method of making of the second aspect of the present application, the sintering time is also not particularly limited, as long as it can enable the silicon-bearing molybdenum tailings powder and the dolomite powder to be sintered smoothly into the soil amendment. For example, in an exemplary embodiment, the sintering time is at least about 0.8 hour. Preferably, the sintering time is in the range of about 0.9 to about 1.1 hour, more preferably about 1.0 hour.

[0061] In the method of making of the second aspect of the present application, the dolomite used is a carbonate mineral known in the art, the chemical composition of which is mainly CaMg(C03)2. In a preferred embodiment, the dolomite used in the present application contains at least about 28% by weight of calcium oxide, at most about 5% by weight of silicon oxide, at most about 1.2% by weight of iron oxide, at least about 18% by weight of magnesium oxide, at most about 0.85% by weight of aluminum oxide, at most about 1% by weight of alkali metal oxide. The alkali metal oxide, for example, preferably includes about 0.03 to about 0.05% by weight of potassium oxide and about 0.04 to about 0.06% by weight of sodium oxide. In an exemplary embodiment, the dolomite used in the present application contains about 30.5% by weight of calcium oxide, 1.2% by weight of silicon oxide, 0.1% by weight of iron oxide, 22.0% by weight of magnesium oxide, 0.5% by weight of aluminum oxide, 0.04% by weight of potassium oxide and 0.05% by weight of sodium oxide.

[0062] In a preferred embodiment of the method of making of the second aspect of the present application, the silicon-bearing molybdenum tailings used is obtained by washing the molybdenum tail ore with water one or more times to remove impurities therein, and then drying the washed tailings sand.

[0063] According to a third aspect of the present application, the present application provides the use of a silicon-bearing molybdenum tailings-dolomite mineral-based soil amendment according to the first aspect of the present application as described above or a silicon-bearing molybdenum tailings-dolomite mineral-based soil amendment prepared by the method of making according to the second aspect of the present application as described above for improving acidified soil.

[0064] In the use of the third aspect of the present application, the acidified soil is an acidified cadmium-contaminated soil.

[0065] In a preferred embodiment of the use of the third aspect of the present application, the acidified soil is modified by mixing the silicon-containing molybdenum tailings-dolomite mineral-based soil amendment with the acidified soil or the acidified cadmium-contaminated soil uniformly at a ratio of about 0.5% to about 5.0% by weight, preferably about 0.8% to about 3% by weight, for example, about 1.0% to about 2.0% by weight.

[0066] The present application will be further described in detail with reference to the following specific examples.

[0067] Raw materials:

[0068] Two different silicon-containing molybdenum tailings raw ores (labeled as I and II, respectively) produced in Luanchuan County, Luoyang City, Henan Province were provided as raw materials for preparing the soil amendment of the present application. The silicon-containing molybdenum tailings raw ores were thoroughly washed with deionized water three times to remove impurities therein. Subsequently, the washed tailings sand was placed in a constant-temperature drying oven for drying treatment to ensure that the water content thereof was less than about 5% by weight. It was detected that the weight percentage content of oxide components in the molybdenum tailings raw ores I and II was as shown in Table 1 below:

[0069] Table 1

[0070] SiO2 Al2O3 K2O Fe2O3 CO2 CaO MgO Na2O SO3 [N2O5] I 64.6 11.3 5.3 3.8 3.8 3.4 2.7 1.9 1.8 - II 39.1 7.2 0.9 16.6 1.4 20.2 5.1 1.3 3.7 2.8

[0071] In addition, dolomite produced in Lingshou, Hebei Province was provided as a raw material for preparing the soil amendment of the present application, which had a water content of less than about 5% by weight and contained oxide components in a weight percentage of about 30.5% of CaO, about 1.2% of SiO2, about 0.1% of Fe2O3, about 22.0% of MgO, about 0.5% of Al2O3, about 0.04% of K2O, and about 0.05% of Na2O.

[0072] Determination of the ratio of calcined raw materials and calcination temperature:

[0073] (1) Calcination treatment of the silicon-containing molybdenum tailings:

[0074] The silicon-containing molybdenum tailings obtained after washing and drying were subjected to calcination treatment at the calcination temperatures shown in Table 2 below. The effective silicon mass fraction contained in the uncalcined and calcined silicon-containing molybdenum tailings was measured, and the measurement results are also shown in Table 2 below. In the present application, the determination method of the effective silicon mass fraction is similar to that specified in the Agricultural Industry Standard of the People's Republic of China NY / T1121.15-2006.

[0075] Table 2

[0076] Molybdenum tailings raw ore Calcination temperature (°C) Effective silicon mass fraction mg / g Molybdenum tailings raw ore I Un-calcined 14.5 Molybdenum tailings raw ore I 800 22.22 Molybdenum tailings raw ore I 900 24.35 Molybdenum tailings raw ore I 1000 25.63 Molybdenum tailings raw ore I 1100 27.3 Molybdenum tailings raw ore II Un-calcined 10.72 Molybdenum tailings raw ore II 800 14.98 Molybdenum tailings raw ore II 900 17.98 Molybdenum tailings raw ore II 1000 22.65 Molybdenum tailings raw ore II 1100 25.2

[0077] From the results shown in Table 2 above, it can be seen that the higher the calcination temperature for the molybdenum tailings raw ore, the higher the effective silicon mass fraction in the raw ore; however, above a calcination temperature of 1100°C, the calcined material presents a hardening phenomenon, which is not easy to separate, and above this temperature, the increase in the effective silicon mass fraction has tended to flatten, or even possibly decrease. In addition, it can also be seen that even if high-temperature calcination of the molybdenum tailings raw ore is carried out at the optimal temperature of 1100°C, the effective silicon mass fraction therein does not exceed about 30 mg / g.

[0078] (2) General preparation method of the silicon-containing molybdenum tailings-dolomite mineral-based soil conditioner:

[0079] The dried silicon-containing molybdenum tailings and the dolomite as described above were crushed and passed through 100-mesh and 200-mesh sieves, respectively, and mixed uniformly according to the weight proportions shown in Table 3 to obtain Examples 1 to 18, and then the mixture obtained in each example was calcined at the temperature shown in Table 3 for about 1.0 hour. The obtained calcined material was ground to obtain the silicon-containing molybdenum tailings-dolomite mineral-based soil conditioner of the present application.

[0080] The silicon-containing molybdenum tailings I and the silicon-containing molybdenum tailings II were each calcined and activated with dolomite to form a silicon-containing molybdenum tailings-dolomite mineral-based soil conditioner, which were respectively named MDS I and MDS II, wherein MDS is the abbreviation of Molybdenum-Dolomite Silicate Hybrid.

[0081] The samples of Examples 1 to 18 were subjected to effective silicon mass fraction determination, and the results are also shown in Table 3.

[0082] Table 3

[0083]

[0084] As can be seen from the post-calcination performance data in Table 3 above, when the weight ratio of dolomite to silicon-containing molybdenum tailings is less than about 1.2, the effective silicon content of the MDSII is not sufficiently improved (the multiple of the effective silicon content relative to the original molybdenum tailings is only about 3.26 times or less). When the weight ratio exceeds about 1.6, the effective silicon content of the two silicon-containing molybdenum tailings is gradually improved, or even possibly reduced (for example, for the MDSII, the multiple of the effective silicon content relative to the original molybdenum tailings is reduced from a maximum of 5.79 times to 4.37 times). In addition, when the calcination temperature reaches about 1200°C, the effective silicon content of the two silicon-containing molybdenum tailings is gradually improved, or even possibly reduced (for example, for the MDSII, the multiple of the effective silicon content relative to the original molybdenum tailings is reduced from a maximum of 5.79 times to 5.62 times).

[0085] Taking into account the measured effective silicon and cadmium removal rates and cost-effectiveness in the above and below contexts, and other factors, the silicon-containing molybdenum tailings-dolomite mineral-based soil improver prepared in Examples 7 and 8, which have a weight ratio of silicon-containing molybdenum tailings to dolomite of about 1.4 and a calcination temperature of about 1100°C, achieve the best technical effect.

[0086] Material characterization:

[0087] (1) X-ray diffraction analysis

[0088] The silicon-containing molybdenum tailings-dolomite mineral-based soil improver of the present application was subjected to X-ray diffraction analysis. As shown in the exemplary display in FIG. 1, the X-ray diffraction pattern of the silicon-containing molybdenum tailings-dolomite mineral-based soil improver of the present application Examples 7 and 8 indicates that, due to the rich metal oxide content of the silicon-containing molybdenum tailings and dolomite ores, the unique silicate structure and high calcium oxide content, the silicon-containing molybdenum tailings-dolomite mineral-based soil improver generated by high-temperature reaction has rich silicate minerals, which can effectively immobilize heavy metals in the soil, reduce the migration and bioavailability of heavy metals, and reduce the potential risk of heavy metals to the environment and ecology. Figure 1

[0089] In particular, the silicon-containing molybdenum tailings-dolomite mineral-based soil improver of Example 8, which contains rich calcium aluminate minerals and calcium-iron-aluminate minerals in its composition, opens up new ways for the diversified application of the material.

[0090] In the silicon-containing molybdenum tailings-dolomite mineral-based soil improver of Examples 7 and 8, sulfate ions (SO42 2- ) and carbonate ions (CO32 2- ) were also detected, which also promote the precipitation of metal cations on the surface of the material, thereby significantly enhancing the adsorption capacity of the material for heavy metals.

[0091] (2) Infrared analysis​

[0092] The silicon-molybdenum tailings-dolomite mineral-based soil amendment obtained from Examples 7 and 8 was subjected to infrared spectroscopy analysis. As shown in the exemplary display of the infrared spectrogram of the silicon-molybdenum tailings-dolomite mineral-based soil amendment of Examples 7 and 8 of the present application, it is shown that there are basic functional groups on the surface of the soil amendment of the present application, which is due to the fact that dolomite itself contains a large amount of basic groups, and the activation of silicon, calcium, magnesium and other ions during the calcination process. These activated silicon, calcium, magnesium and other ions can form stable complexes with heavy metal elements in contaminated soil, which is of great importance for adsorbing and fixing heavy metal ions in soil. Figure 2

[0093] (3) Electron Microscope Analysis

[0094] The silicon-molybdenum tailings-dolomite mineral-based soil amendment obtained from Examples of the present application was subjected to electron microscope analysis. As shown in the exemplary display of the electron micrograph of the silicon-molybdenum tailings-dolomite mineral-based soil amendment of Examples 7 and 8 of the present application, it is shown that the surface of the soil amendment of the present application is relatively smooth, and the pore structure thereof presents a regular cylindrical shape, which is conducive to the flow and transmission of liquid or gas inside the material. In the observation of the surface and pore structure, the presence of blocky granular material was also found, which indicates that silicon-molybdenum tailings sand and dolomite coexist in the soil amendment material of the present application. Figure 3

[0095] Performance Analysis

[0096] (1) Adsorption Experiment

[0097] In order to study the passivation ability of the soil amendment of the present application, the following adsorption experiment was conducted to verify its effect: a Cd 2+ ion solution with a concentration of about 100 mg / L was prepared. About 25 mL of the above Cd 2+ ion solution was measured and added to a 50 mL centrifuge tube containing about 0.1 g of the soil amendment of Examples 1 to 18 of the present application. The centrifuge tube with the sample was covered and shaken at about 220 rpm, 25±2°C for about 12 hours, and then left to stand for about 24 hours. Then, the centrifuge tube was centrifuged at about 4000 rpm for about 30 minutes, and after filtration, the concentration of Cd 2+ ions in the solution was determined by atomic absorption spectrophotometry (AAS), and the removal rate of metal cadmium of each example was calculated. Each example was repeated in triplicate, and the average value was taken. The experimental results are shown in Table 5 below.

[0098] Table 5

[0099] Example number Cadmium removal rate (100 mg / L of exogenous cadmium) 1 MDS I 0.874 3 MDS I 0.943 5 MDS I 0.969 7 MDS I 0.992 9 MDS I 0.928 11 MDS I 0.958 13 MDS I 0.961 15 MDS I 0.976 17 MDS I 0.989 2 MDS II 0.885 4 MDS II 0.946 6 MDS II 0.988 8 MDS II 0.994 10 MDS II 0.933 12 MDS II 0.944 14 MDS II 0.981 16 MDS II 0.991 18 MDS II 0.992

[0100] ​​As can be seen from Table 5 above, the soil amendment samples of the present application embodiments 7 and 8 each achieved the maximum cadmium removal rate.

[0101] (2) Kinetic analysis experiment

[0102] In order to study the kinetics of cadmium absorption by the soil amendment of the present application, the following kinetic analysis experiment was conducted: the initial concentration of Cd 2+ was maintained at about 100 mg / L in the Cd-contaminated system, and the soil amendment of the present application embodiments 7 and 8 was added to the solution at a dosage of about 1.0 g / L. The solution was placed in a shaker under constant temperature conditions of about 25°C, and was shaken at a rate of about 180 revolutions per minute. During the shaking process, supernatant samples were taken at about 5, 10, 20, 30, 45, 60, 120, 240, 360 and 480 minutes, respectively. The samples were filtered through a water-based filter membrane with a pore size of about 0.45 μm, and then were diluted to volume using nitric acid with a concentration of about 2%. The concentration of Cd 2+ in the solution was determined using a flame atomic absorption spectrometer (AAS) with a model number of Analytik Jena Novaa350. Each set of experiments was determined in triplicate.

[0103] The experimental results are shown in Table 6 below and in the accompanying drawings of the specification. Figure 4 and 5

[0104] Table 6

[0105]

[0106] The results show that the correlation coefficient R 2 obtained by fitting the quasi-second-order kinetic model is greater than the correlation coefficient of the quasi-first-order kinetic model; the adsorption capacity Q e calculated from the quasi-second-order kinetic equation is also more consistent with the experimental value of Cd 2+ adsorption. This indicates that the adsorption of the material to Cd 2+ is mainly chemical adsorption, and the adsorption process may be the formation of electronic force between metal ions and adsorbent materials through sharing electrons, indicating that chemical adsorption may be the main factor affecting the adsorption rate. This may be the result of the heterogeneous physical structure and various chemical properties of the adsorbent surface.

[0107] (3) Isothermal adsorption analysis

[0108] A CdCl2mother liquor with a Cd 2+ concentration of about 1000 mg / L was prepared using deionized water. A NaCl solution with a concentration of about 0.05 mol / L was used as a supporting electrolyte solution, and Cd 2+ ​Cd at concentrations of approximately 5, 10, 25, 50, 100, and 150 mg / L 2+ Ionic solutions. Measure approximately 30 mL of Cd solutions of the above concentrations. 2+ The ion-containing solution was added to a 50 mL centrifuge tube containing approximately 0.3 g of the soil conditioner from Examples 7 and 8 of this invention. The centrifuge tube was capped and shaken at approximately 180 rpm and 25 ± 2 °C for approximately 24 hours. Then, it was centrifuged at approximately 6000 rpm for approximately 10 minutes, filtered, and the Cd concentration in the equilibrated solution was determined by atomic absorption spectrophotometry (AAS). 2+ Ion concentration. The data were fitted using the Langmuir equation to describe the relationship between the adsorbent material and Cd. 2+ The adsorption equilibrium relationship between the three materials was obtained through calculation, and the adsorption equilibrium relationship between the three materials and Cd was obtained. 2+ The saturated adsorption capacity was determined. Isothermal adsorption curves were plotted with the initial concentration of the cadmium solution on the x-axis and the equilibrium adsorption capacity of the passivating agent on the y-axis. Each experiment was performed in triplicate. The results are shown in Table 7 and Appendix. Figure 6 middle.

[0109] Table 7

[0110]

[0111] The Cd calculated using the Langmuir model 2+ Maximum adsorption capacity Q m They are approximately 130 mg / g and 122 mg / g, respectively.

[0112] (4) Soil improvement experiment

[0113] To evaluate the remediation effect of the soil conditioner of this invention on soils with different pollution levels, seven representative acidified farmland soil samples (A-Gaoxin, B-Macheng, C-Huangshi, D-Xiaogan, E-Danjiangkou, F-Tongcheng, and G-Tongshan) were selected based on the effective silicon content grading standard and cadmium pollution status. In accordance with the national standard "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard (Trial)" (GB 15618-2018), approximately 0, 0.3, 1.5, and 3 mg / kg of exogenous cadmium (Cd(NO3)2·4H2O) were added to the seven tested soil samples to ensure that Cd was the sole pollution source. After stabilization at room temperature for 30 days, the soil conditioner samples from Examples 7 and 8 of this invention were mixed with the Cd-contaminated soil samples at an addition amount of approximately 1% by weight, with each treatment repeated three times. The soil was cultured at room temperature, and deionized water was used to replenish the soil with appropriate moisture every 7 days. Soil samples were collected on the 30th day of the culture period, and the collected soil samples were air-dried and ground before being tested.

[0114] Soil pH measurement:

[0115] The pH value of the soil was determined by a glass electrode method, wherein a mixture of the soil and deionized water (1:2.5 by weight) was used for the determination. The determination was performed in triplicate for each group of experiments. The experimental results are shown in Table 6. Figure 7

[0116] The experimental results show that the soil improver of the present application, examples 7 and 8, can increase the pH value of the soil by about 1.05-2.45 and about 0.74-2.15 units, respectively. Moreover, from the results shown in Table 6, it can be seen that the soil improver of the present application can significantly increase the pH value of the soil in the presence of different concentrations of Cd pollution in the 7 soil samples. Figure 7

[0117] Soil cadmium passivation determination:

[0118] The soil samples from Gaoxin and Danjiangkou in the above soil improvement experiment were used for the soil cadmium passivation determination.

[0119] The cadmium (Cd) in the soil was extracted by the BCR distribution extraction method according to the national standard GB / T 25282-2010 "Soil and sediment 13 trace element sequential extraction procedure". The acid extractable state, reducible state, oxidizable state, and residual state were extracted (1.000 g of soil sample was taken). The specific steps for the extraction of the Cd form in the soil are shown in Table 8.

[0120] Table 8:

[0121]

[0122] The solution samples in each step were extracted and the Cd concentration was determined by a flame atomic absorption spectrometer (AAS). The experimental results are shown in Tables 9 and 10. 2+ Figure 8 9

[0123] ​​​​​The experimental results show that after adding the MDSI and MDSII of the embodiments 7 and 8, the proportion of the oxidizable state and the acid extractable state of Cd in the soil is reduced, and the proportion of the residual state and the reducible state of Cd is increased. Under the treatment of the MDSI and MDSII, the proportion of the acid extractable state of Cd in the acidified soil of the Gaoxin area is reduced by about 16.54-24.43% and about 0.79-21.28% respectively. Under the treatment of the MDSI and MDSII, the proportion of the residual state of Cd is increased by about 5.21-29.58% and about 2.08-25.22% respectively. Under the treatment of the MDSI and MDSII, the proportion of the acid extractable state of Cd in the acidified soil of the Danjiangkou area is reduced by about 7.22-13.79% and about 6.53-16.49% respectively. Under the treatment of the MDSI and MDSII, the proportion of the residual state of Cd is increased by about 4.29-21.18% and about 1.90-13.73% respectively. Therefore, the soil improver of the application can effectively fix Cd and convert it into a more stable residual state.

[0124] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions claimed by the present application.

Claims

1. A silicon-molybdenum tailings-dolomite mineral-based soil conditioner, characterized in that, The soil conditioner is obtained by calcining silicon-containing molybdenum tailings and dolomite, and the effective silicon mass fraction it contains is at least 3.5 times that of the original silicon-containing molybdenum tailings used to prepare the soil conditioner. The preparation method of the soil conditioner includes calcining a mixture of silicon-containing molybdenum tailings powder and dolomite powder in a weight ratio of 1:(1.2-1.6) at a temperature of 1100°C. The weight percentage content of the oxide components in the molybdenum tailings is as follows: SiO2: 39.1% by weight Al2O3: 7.2% by weight K2O: 0.9% by weight Fe2O3: 16.6% by weight CO2: 1.4% by weight CaO: 20.2% by weight MgO: 5.1% by weight Na2O: 1.3% by weight SO3: 3.7% by weight; N2O5: 2.8% by weight.

2. The silicon-containing molybdenum tailings-dolomite mineral-based soil conditioner according to claim 1, characterized in that, The soil conditioner contains one or more of the following: calcium aluminate minerals, calcium iron aluminate minerals, sulfates, carbonates, and surface alkaline functional groups.

3. A method for preparing the silicon-containing molybdenum tailings-dolomite mineral-based soil conditioner according to claim 1 or 2, characterized in that, The preparation method includes calcining a mixture of silicon-containing molybdenum tailings powder and dolomite powder in a weight ratio of 1:(1.2-1.6) at 1100°C.

4. The preparation method according to claim 3, characterized in that, The preparation method includes calcining a mixture of silicon-containing molybdenum tailings powder and dolomite powder in a weight ratio of 1:1.4 at a temperature of 1100°C.

5. The preparation method according to claim 3, characterized in that, The silicon-containing molybdenum tailings contain less than 30 mg / g of effective silicon mass fraction.

6. The preparation method according to claim 3, characterized in that, The particle size of the silicon-containing molybdenum tailings powder is less than 0.150 mm.

7. The preparation method according to claim 3, characterized in that, The dolomite powder has a particle size of less than 0.075 mm.

8. The preparation method according to claim 3, characterized in that, The calcination time is at least 0.8 hours.

9. The preparation method according to claim 3, characterized in that, The calcination time is in the range of 0.9 to 1.1 hours.

10. The preparation method according to claim 3, characterized in that, The calcination time is 1.0 hour.

11. The preparation method according to any one of claims 3 to 10, characterized in that, The moisture content of the silicon-containing molybdenum tailings is less than 5% by weight.

12. The preparation method according to any one of claims 3 to 10, characterized in that, The dolomite has a moisture content of less than 5% by weight.

13. The preparation method according to any one of claims 3 to 10, characterized in that, The dolomite comprises ≥ 28% by weight of calcium oxide, ≤ 5% by weight of silicon oxide, ≤ 1.2% by weight of iron oxide, ≥ 18% by weight of magnesium oxide, ≤ 0.85% by weight of aluminum oxide and ≤ 1% by weight of alkali metal oxide.

14. The preparation method according to any one of claims 3 to 10, characterized in that, The silicon-containing molybdenum tailings are obtained by washing the raw molybdenum tailings with water once or multiple times, and then drying the washed tailings sand.

15. The use of the silicon-containing molybdenum tailings-dolomite mineral-based soil conditioner according to claim 1 or 2, or the silicon-containing molybdenum tailings-dolomite mineral-based soil conditioner prepared by the preparation method according to any one of claims 3 to 14, for the purpose of improving acidified soil.

16. The use according to claim 15, characterized in that, The acidified soil is cadmium-contaminated acidified soil.

17. The use according to claim 15 or 16, characterized in that, The improved acidified soil comprises mixing the silicon-molybdenum tailings-dolomite mineral-based soil conditioner with the acidified soil at a ratio of 0.5% to 5.0% by weight.

18. The use according to claim 17, characterized in that, The improved acidified soil comprises mixing the silicon-molybdenum tailings-dolomite mineral-based soil conditioner with the acidified soil at a ratio of 1.0% by weight.

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