Silicon-molybdenum-containing tailing-dolomite mineral-based soil conditioner as well as preparation method and application thereof

Abstract

The invention relates to the technical field of soil improvement. Specifically, the invention provides a silicon-molybdenum-containing tailing-dolomite mineral-based soil conditioner and a preparation method thereof. The invention further provides application of the soil conditioner to soil improvement. The soil conditioner is obtained by calcining silicon-molybdenum-containing tailings and dolomite, and the mass fraction of effective silicon contained in the soil conditioner is at least 3.5 times that of effective silicon contained in silicon-molybdenum-containing tailing raw ore used for preparing the soil conditioner. On one hand, the soil conditioner can significantly increase the pH value of soil and passivate heavy metals in the soil, and has huge potential in the aspects of acidified soil improvement and heavy metal stabilization; on the other hand, the effective silicon content of the silicon-containing molybdenum tailings is remarkably increased, the silicon fertilizer effect can be achieved when the silicon-containing molybdenum tailings are applied to soil, and effective microelement silicon is provided for plant growth.

Description

Technical Field

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

[0002] In China, farmland soil acidification is serious in some areas, of which about 40% of cultivated land is acidified. Compared with the 1980s, the average soil pH value has dropped by about 0.5 units. Soil acidification is more prominent in southern China, and the soil pH value has even dropped by about 1 unit (see: Luo Deying, A Preliminary Study on the Improvement Effect of Different Soil Conditioners on Acidified Cultivated Land, World Tropical Agriculture Information, 2023, No. 6, pp. 36-37). For example, in Hubei Province alone, China, the acidified soil covers more than 17 million mu of land, accounting for more than one-third (about 36.13%) of the total cultivated land area in the province, of which the area with soil pH below about 6.50 is as high as about 15.768 million mu, and the extremely acidified soil (pH value not exceeding about 4.50) is about 1.2432 million mu.

[0003] In recent years, a variety of soil conditioners have been widely used to improve acidified soils, 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 has shown that the use of soil remediation agents can also lead to other soil problems. For example, although lime-based soil conditioners can quickly increase the calcium and magnesium content in the soil and alleviate the problem of soil acidification, excessive use may lead to soil hardening. Although organic soil conditioners can significantly increase soil organic matter and microbial activity and improve the physical properties of the soil, they may increase greenhouse gas emissions and nutrient loss during use.

[0004] In addition, soil conditioners are also one of the ways to comprehensively utilize many solid wastes. As one of the countries with the largest molybdenum reserves in the world, China has a total molybdenum reserve of about 5.9005 million tons. With the mining and beneficiation of molybdenum ore, more than 95% of the raw ore is converted into molybdenum tailings after beneficiation operations and discharged in the form of waste slag. 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 poses 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 aggregates, some people have used molybdenum tailings to produce molybdenum tailings structural concrete that meets China's national standards and is used in the construction industry. However, the application of molybdenum tailings is limited by the transportation radius and is easily replaced by other waste slags. In addition, the building materials industry is saturated, resulting in a reduction in the utilization space of molybdenum tailings.

[0005] As an industrial byproduct, molybdenum tailings contain a large amount of silicate minerals and aluminum and iron oxides, which give molybdenum tailings excellent complexation, adsorption and ion exchange capabilities. At the same time, molybdenum tailings contain a large amount of silicon (Si), calcium (Ca), magnesium (Mg) and potassium (K) and other elements, which are also nutrients required for plant growth, making it a candidate material for soil conditioners. Molybdenum can also promote the increase of yields of various crops, improve quality (degrade carcinogens such as nitrates and nitrites in plants) and improve nitrogen fertilizer utilization. Therefore, the use of molybdenum tailings as soil conditioners has become a new high-value and sustainable new utilization method, with obvious environmental, economic and social benefits, as well as broad application prospects, especially the remediation of acidic heavy metal contaminated soils.

[0006] Existing studies have shown that through specific modification methods, effective components such as silicon, aluminum and iron in molybdenum tailings can be converted into efficient passivators for repairing heavy metal pollution in acidified soils. For example, Hu Zheng successfully developed new Na-type and K-type passivators using molybdenum tailings as raw materials in his paper "Research and Development of Silica Passivators Based on Molybdenum Tailings and Their Application in Acidic Soils". At a cadmium (Cd) ion concentration of about 100 mg / L, they have removal rates of about 99.76% and about 98.64%, respectively. However, in the synthesis stage of the passivator, the experiment can also consider the optimization of more reaction parameters, such as the optimization of auxiliary agent ratio, reaction temperature and other parameters.

[0007] At present, there is still a need for further research and development in many aspects on how to fully and comprehensively utilize silicon-molybdenum tailings, and there is still huge room for in-depth research. Summary of the invention

[0008] Purpose of the Invention

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

[0010] Implementation

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] Option 1: A silicon-molybdenum tailings-dolomite mineral-based soil conditioner, wherein the soil conditioner is obtained by calcining silicon-molybdenum tailings and dolomite, and the mass fraction of effective silicon contained in it is at least 3.5 times the mass fraction of effective silicon contained in the silicon-molybdenum tailings raw ore used to prepare the soil conditioner.

[0013] Option 2: The silicon-molybdenum tailings-dolomite mineral-based soil conditioner according to the above-mentioned Option 1, wherein the soil conditioner contains one or more of calcium aluminate minerals, calcium ferroaluminate minerals, sulfates, carbonates, and surface alkaline functional groups.

[0014] Scheme 3: A method for preparing the silicon-molybdenum tailings-dolomite mineral-based soil conditioner according to the above-mentioned Scheme 1 or 2, wherein the preparation method comprises uniformly mixing the silicon-molybdenum tailings powder and the 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-molybdenum tailings powder to the dolomite powder is about 1:1.4.

[0016] Scheme 5: The preparation method according to Scheme 3 or 4 above, 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: A preparation method according to any one of Schemes 3 to 5 above, wherein the silicon-molybdenum-containing tailings contains an effective silicon mass fraction of less than about 30 mg / g.

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

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

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

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

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

[0023] Scheme 12: A preparation method according to any one of Schemes 3 to 11 above, wherein the silicon-molybdenum tailings are obtained by: washing the molybdenum tailings ore with water once or multiple times, and then drying the washed tailings sand.

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

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

[0026] Option 15: The use according to Option 12 or 13 above, wherein the improved acidified soil comprises uniformly mixing the silicon-molybdenum tailings-dolomite mineral-based soil conditioner with the acidified soil in a ratio of about 0.5 weight % to about 5.0 weight %, preferably about 1.0 weight %.

[0027] Technical Effects

[0028] The composite mineral material formed by high-temperature pyrolysis of silicon-molybdenum tailings and dolomite has great potential as a soil conditioner in improving acidified soil and stabilizing heavy metals. Specifically, the soil conditioner of the present invention can be used to improve soil contaminated by acidified cadmium and stabilize and repair heavy metal cadmium.

[0029] The purpose of the silicon-molybdenum tailings-dolomite mineral-based soil conditioner of the present invention for improving soil is mainly to utilize the silicate minerals generated by the high-temperature reaction of molybdenum tailings and dolomite, which not only improves the pH value of the soil, but also has a passivation effect on heavy metals, while avoiding the defects of traditional repair materials, achieving high efficiency and environmental safety of soil repair.

[0030] The silicon-molybdenum tailings-dolomite mineral-based soil conditioner of the present invention can improve the soil pH value and passivate heavy metals on the one hand, and can also provide sufficient trace element silicon for plant growth on the other hand. The silicon-molybdenum tailings-dolomite mineral-based soil conditioner of the present invention has a significantly higher effective silicon content and can act as a silicon fertilizer when applied to the soil; in addition, the effective silicon can also change the state of heavy metals in the soil through permeable adsorption, complexation and other methods, reduce the biological effectiveness of heavy metals, and achieve the stability of heavy metals, thereby reducing the transfer and enrichment of heavy metals into plants.

[0031] The silicon-molybdenum tailings-dolomite mineral-based soil conditioner of the present invention avoids the soil hardening problem that may be caused by excessive use of lime substances and also reduces transportation costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the specific implementation modes of the present invention, the drawings required for use in the specific implementation modes will be briefly introduced below. Obviously, the drawings described below are some implementation modes of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 It is the X-ray diffraction pattern of the silicon-molybdenum tailings-dolomite mineral-based soil conditioner of Examples 7 and 8 of the present invention, wherein the lower spectrum line is the soil conditioner of Example 7 of the present invention; and the upper spectrum line is the soil conditioner of Example 8 of the present invention.

[0034] Figure 2 It is the infrared spectrum of the silicon-molybdenum tailings-dolomite mineral-based soil conditioner of Examples 7 and 8 of the present invention, wherein the lower spectrum line is the soil conditioner of Example 7 of the present invention; and the upper spectrum line is the soil conditioner of Example 8 of the present invention.

[0035] Figure 3 These are electron microscope photos of the silicon-molybdenum tailings-dolomite mineral-based soil conditioners of Examples 7 and 8 of the present invention, wherein a and c are the soil conditioners of Example 7 of the present invention; b and d are the soil conditioners of Example 8 of the present invention.

[0036] Figure 4The pseudo-first-order kinetic fitting curves of cadmium adsorption by the silicon-molybdenum tailings-dolomite mineral-based soil conditioners of Examples 7 and 8 of the present invention, wherein the left figure is the soil conditioner of Example 7 of the present invention; and the right figure is the soil conditioner of Example 8 of the present invention.

[0037] Figure 5 The quasi-second-order kinetic fitting curves of cadmium adsorption by the silicon-molybdenum tailings-dolomite mineral-based soil conditioners of Examples 7 and 8 of the present invention, wherein the left figure is the soil conditioner of Example 7 of the present invention; and the right figure is the soil conditioner of Example 8 of the present invention.

[0038] Figure 6 It is the isothermal adsorption model fitting curve of cadmium absorption by silicon-molybdenum tailings-dolomite mineral-based soil conditioner of Examples 7 and 8 of the present invention, which is the Langmuir equation fitting result.

[0039] Figure 7 The figures show the improvement effects of the silicon-molybdenum tailings-dolomite mineral-based soil conditioners of Examples 7 and 8 of the present invention on the pH of seven types of farmland soils when the exogenous cadmium addition amounts are about 0, 0.3, 1.5, and 3 mg / kg, wherein BK is the soil without the addition of the conditioner material under the same cadmium treatment conditions; in the figure, the letters a, b, and c represent the results of the significance analysis of the differences, compared with the control BK.

[0040] Figure 8 The morphological proportion distribution of Cd in the soil under different treatments in the high-tech area in the soil cadmium passivation experiment conducted using the silicon-molybdenum tailings-dolomite mineral-based soil conditioner of Examples 7 and 8 of the present invention.

[0041] Fig. 9 The morphological distribution of Cd in the soil under different treatments in the Danjiangkou area in the soil cadmium passivation experiment conducted using the silicon-molybdenum tailings-dolomite mineral-based soil conditioner of Examples 7 and 8 of the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without paying creative work belong to the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on normal conditions.

[0043] The endpoints and any values ​​of the scope disclosed in the present invention are not limited to the precise scope or value, and these scopes or values ​​should be understood to include values ​​close to these scopes or values. The term "about" used in the present invention means that the modified numeral can fluctuate within the range of ±20%, ±15%, ±10%, ±5% or ±2% of the numeral. For numerical ranges, the endpoint values ​​of each scope, the endpoint values ​​of each scope and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in the present invention.

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

[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 efficiency of plants' absorption and utilization of other nutrients, thereby reducing fertilization costs. Available silicon refers to the content of silicon in the soil that can be absorbed and utilized by plants, also known as bio-silicon. The content of available silicon has an important impact on plant growth, disease resistance, stress tolerance, etc. Available silicon can improve the disease resistance, stress tolerance and photosynthesis intensity of crops, thereby increasing yields.

[0046] When the content of available silicon in the soil is about <50 mg / kg, it means that the soil is severely deficient in silicon; when it is about 50 to about 100 mg / kg, it means that the soil is deficient in silicon; when it is about 100 to about 150 mg / kg, it means that the soil is potentially deficient in silicon; when it is about 150 to about 180 mg / kg, it means that the soil has a moderate level of silicon; and when it is about >180 mg / kg, it means that the soil is rich in silicon (see Zhang Zhantian et al., Research on the Effects of Silicon on Plant Growth and Development and Application, Yantai Fruit Trees, Issue 04, 2023).

[0047] For example, in China, effective silicon content below about 100 mg / kg is generally used as a critical indicator. However, many studies have shown that even if the effective silicon content is higher than about 100 mg / kg, the application of silicon fertilizer still has an effect of increasing yield. For example, Shang Quanyu et al. applied silicon fertilizer in rice fields with an effective silicon content of about 119.5 mg / kg, which increased rice yield and improved rice quality; Wu Ying et al. applied silicon fertilizer to paddy soil in Heilongjiang with an effective silicon content of about 200 to about 300 mg / kg, which still had a yield-increasing effect; Zhang Cuizhen et al.'s study on different soil types in Shandong Province (wet tidal soil, sandy black soil, salinized tidal soil, and brown soil) showed that when the effective silicon content was about 328.2, about 306.5, about 170.4, and about 110.9 mg / kg, respectively, the application of silicon fertilizer could have a positive effect on rice yield (see: Zhang Cuizhen et al., Study on the Effective Silicon Content and Silicon Fertilizer Effect of Paddy Soil in Shandong Province, Shandong Agricultural Science, 1999, 31(6), 10-12, 18; and Liu Lijun et al., Research Progress on Soil Silicon in Different Ecosystems 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. Even in soils with high effective silicon content, the rational application of silicon fertilizer can also bring about an increase in yield.

[0049] Therefore, the inclusion of an appropriate amount of effective silicon mass fraction in the soil conditioner can ensure that it can act as a silicon fertilizer when applied to the soil. In the present invention, it is required that the effective silicon mass fraction contained in the soil conditioner according to the first aspect of the present invention is at least 3.5 times the effective silicon mass fraction contained in the silicon-molybdenum tailings used to prepare the soil conditioner, that is, in the process of preparing the soil conditioner of the first aspect of the present invention, the dolomite increases the effective silicon mass fraction of the silicon-molybdenum tailings by at least 2.5 times. In some preferred embodiments, the soil conditioner of the present invention can, for example, contain an effective 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 invention preferably contains one or more of calcium aluminate minerals, calcium ferroaluminate minerals, sulfates, carbonates, and surface alkaline functional groups.

[0051] The calcium aluminate minerals and calcium ferroaluminate minerals contained in the composition open up new avenues for the diversified application of materials; the sulfate ions (SO4 2- ) and carbonate ions (CO3 2-) participates in promoting the precipitation of metal cations on the surface of the material, thereby significantly enhancing the material's ability to adsorb heavy metals; the presence of surface alkaline functional groups is due to the activation of silicon, calcium, magnesium and other ions by a large number of bases contained in dolomite and molybdenum tailings during the co-heating process. These activated ions can form stable complexes with heavy metal elements in contaminated soil, which is of great importance for the adsorption and fixation of heavy metal ions in the soil.

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

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

[0054] Generally, in order to improve the activity of silicon in the silicon-molybdenum tailings, a chemical activator can be used for activation, wherein the type and content of the alkaline oxide in the chemical activator are positively correlated with the activation rate of silicon dioxide. The chemical activator can be, for example, sodium hydroxide or dolomite. During the research process, the inventors of the present invention found that when sodium hydroxide is used as an auxiliary agent, it is possible to generate highly viscous sodium silicate, thereby causing product sintering. In the preparation method of the present invention, when dolomite is used as a chemical activator, an unexpected technical effect is achieved.

[0055] Dolomite can react and generate magnesium silicate with remarkable expansion characteristics during high temperature roasting, which is not only conducive to roasting, but also can effectively avoid the sintering problem of material. Dolomite can decompose and release alkaline substances during high temperature sintering, which is conducive to neutralizing the acidic substances in the soil, thereby improving the pH value of the soil. Meanwhile, 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 to heavy metal ions, but also provide essential nutrients for plant growth, promote the growth of plants. In addition, dolomite is abundant in reserves in my country, more than about 4 billion tons, widely distributed in various parts of China, for example, in Hubei, Hunan, Guangxi, Guizhou and other places, there are relatively large ore deposits. Therefore, dolomite is used as alkaline auxiliary agent (chemical activator) in the present invention.

[0056] In the preparation method of the second aspect of the present invention, the weight ratio of the silicon-molybdenum tailings powder to the dolomite powder is in the range of about 1:(1.2-1.6). Here, the weight of the dolomite powder should not be higher than about 1.6 times the weight of the silicon-molybdenum tailings powder, otherwise the dolomite content ratio is increased too much, thereby increasing the cost of material preparation. It should not be lower than about 1.2 times the weight of the silicon-molybdenum tailings powder, otherwise the effective silicon activation efficiency may be too low, and it may also affect the material's cadmium removal efficiency.

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

[0058] In the preparation method of the second aspect of the present invention, there is no special requirement for the dryness of the silicon-molybdenum tailings powder and the dolomite powder, as long as the moisture content does not adversely affect the two powders being fully mixed and can ensure that they are smoothly sintered into a soil conditioner. Normally, the obtained molybdenum tailings ore is relatively moist, and after washing, it is preferably naturally air-dried before subsequent crushing, mixing and sintering. Dolomite is generally a dry powder commodity. Preferably, in an exemplary embodiment, the moisture content of the silicon-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 preparation method of the second aspect of the present invention, there are no special requirements for the particle sizes of the silicon-molybdenum tailings powder and the dolomite powder, as long as they can ensure that the two powders can be fully mixed and can be smoothly sintered into a soil conditioner. However, in a preferred embodiment, the particle size of the silicon-molybdenum tailings powder is set to be less than about 0.150mm (-100 mesh); and / or the particle size of the dolomite powder is set to be less than about 0.075mm (-200 mesh). When the particle sizes of the silicon-molybdenum tailings powder and the dolomite powder both meet the above limits, the mass fraction of effective silicon in the fired soil conditioner material is higher.

[0060] In the preparation method of the second aspect of the present invention, the sintering time is also not particularly limited, as long as it can make the silicon-molybdenum tailings powder and the dolomite powder fully and smoothly sintered into the soil conditioner. For example, in an exemplary embodiment, the calcining time is at least about 0.8 hours. Preferably, the sintering time is in the range of about 0.9 to about 1.1 hours, more preferably about 1.0 hours.

[0061] In the preparation method of the second aspect of the present invention, the dolomite used is a carbonate mineral known in the art, and its chemical composition is mainly CaMg(CO3)2. In a preferred embodiment, the dolomite used in the present invention comprises at least about 28% by weight of calcium oxide, up to about 5% by weight of silicon oxide, up to about 1.2% by weight of iron oxide, at least about 18% by weight of magnesium oxide, up to about 0.85% by weight of aluminum oxide, and up to 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 invention comprises 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 preparation method of the second aspect of the present invention, the silicon-molybdenum tailings used are obtained by: washing the molybdenum tailings with water once or multiple times to remove impurities therein, and then drying the washed tailings sand.

[0063] According to the third aspect of the present invention, the present invention provides the use of the silicon-molybdenum tailings-dolomite mineral-based soil conditioner according to the first aspect of the present invention or the silicon-molybdenum tailings-dolomite mineral-based soil conditioner prepared by the preparation method according to the second aspect of the present invention for improving acidified soil.

[0064] In the use described in the third aspect of the present invention, the acidified soil is acidified cadmium-contaminated soil.

[0065] In a preferred embodiment of the use of the third aspect of the present invention, the improved acidified soil includes mixing the silicon-molybdenum tailings-dolomite mineral-based soil conditioner with the acidified soil or the acidified cadmium-contaminated soil in a ratio of about 0.5 weight % to about 5.0 weight %, preferably about 0.8 weight % to about 3 weight %, for example about 1.0 weight % to about 2.0 weight %.

[0066] The present invention is further described in detail below with reference to specific embodiments.

[0067] raw material:

[0068] Two different silicon-containing molybdenum tailings (respectively marked as I and II) produced in Luanchuan County, Luoyang City, Henan Province are provided as raw materials for preparing the soil conditioner of the embodiment of the present invention. The silicon-containing molybdenum tailings are thoroughly rinsed three times with deionized water to remove impurities therein. Subsequently, the rinsed tailings sand is placed in a constant temperature drying oven for drying to ensure that its water content is less than about 5% by weight. After testing, the weight percentage content of the oxide components in the molybdenum tailings I and II is shown in Table 1 below:

[0069] Table 1

[0070] <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[K2O]]> <![CDATA[Fe2O3]]> <![CDATA[CO2]]> CaO MgO <![CDATA[Na2O]]> <![CDATA[SO3]]> <![CDATA[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 is provided as a raw material for preparing the soil conditioner of the present invention. The moisture content of the dolomite is less than about 5% by weight, and the oxide components contained therein are, by weight percentage: about 30.5% by weight of CaO, about 1.2% by weight of SiO2, about 0.1% by weight of Fe2O3, about 22.0% by weight of MgO, about 0.5% by weight of Al2O3, about 0.04% by weight of K2O and about 0.05% by weight of Na2O.

[0072] Determine the calcination raw material ratio and calcination temperature:

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

[0074] The silicon-molybdenum tailings obtained after washing and drying are calcined, and the calcination temperature is shown in Table 2. The effective silicon mass fraction contained in the uncalcined and calcined silicon-molybdenum tailings is measured, and the measurement results are also shown in Table 2. In the present invention, the method for determining the effective silicon mass fraction is similar to the provisions of the Agricultural Industry Standard of the People's Republic of China NY / T1121.15-2006.

[0075] Table 2

[0076] Molybdenum tailings Calcination temperature (℃) Effective silicon mass fraction mg / g Molybdenum tailings Ⅰ Uncalcined 14.5 Molybdenum tailings Ⅰ 800 22.22 Molybdenum tailings Ⅰ 900 24.35 Molybdenum tailings Ⅰ 1000 25.63 Molybdenum tailings Ⅰ 1100 27.3 Molybdenum tailings Ⅱ Uncalcined 10.72 Molybdenum tailings Ⅱ 800 14.98 Molybdenum tailings Ⅱ 900 17.98 Molybdenum tailings Ⅱ 1000 22.65 Molybdenum tailings Ⅱ 1100 25.2

[0077] From the results shown in Table 2 above, it can be seen that the higher the temperature at which the molybdenum tailings are calcined, the higher the effective silicon mass fraction in the ore will be; however, when the calcination temperature exceeds 1100°C, the calcined material shows a hardening phenomenon and is not easy to separate, and above this temperature, the increase in the effective silicon mass fraction has tended to be flat, or may even decrease. In addition, it can also be seen that even if the molybdenum tailings are calcined at the optimal temperature of 1100°C, the effective silicon mass fraction does not exceed about 30 mg / g.

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

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

[0080] Silicon-molybdenum tailings I and silicon-molybdenum tailings II are calcined and activated with dolomite to form silicon-molybdenum tailings-dolomite mineral-based soil conditioners, which are named MDSⅠ and MDSⅡ respectively, wherein MDS is the abbreviation of Molybdenum-Dolomite Silicate Hybrid.

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

[0082] Table 3

[0083]

[0084] As can be seen from the calcined performance data in Table 3 above, when the weight ratio of dolomite: silicon-containing molybdenum tailings is less than about 1.2, for example, the effective silicon content of the MDSII is not sufficiently improved (the multiple of the effective silicon relative to the molybdenum tailings is only about 3.26 times or less). When the weight ratio exceeds about 1.6, the improvement effect of the effective silicon mass fraction of the two silicon-containing molybdenum tailings has been flattened, or may even be reduced (for example, for MDSII, the effective silicon improvement multiple relative to the molybdenum tailings is reduced from the highest 5.79 times to 4.37 times). In addition, when the calcination temperature reaches about 1200°C, the improvement effect of the effective silicon mass fraction of the two silicon-containing molybdenum tailings is flattened, or may even be reduced (for example, for MDSII, the effective silicon improvement multiple relative to the molybdenum tailings is reduced from the highest 5.79 times to 5.62 times).

[0085] Taking into account multiple factors such as the effective silicon and cadmium removal rates measured in the context and cost-effectiveness, the silicon-molybdenum tailings-dolomite mineral-based soil conditioner prepared by Examples 7 and 8 using a silicon-molybdenum tailings:dolomite weight ratio of about 1.4 and a calcination temperature of about 1100°C achieved the best technical effect.

[0086] Material Characterization:

[0087] (1) X-ray diffraction analysis

[0088] X-ray diffraction analysis was performed on the silicon-molybdenum tailings-dolomite mineral-based soil conditioner according to the embodiment of the present invention. Figure 1 As exemplified, the X-ray diffraction patterns of Examples 7 and 8 of the present invention illustrate that: since the silicon-molybdenum-containing tailings and dolomite ore are rich in metal oxides, exhibiting a unique silicate structure and a high calcium oxide content, the silicon-molybdenum-containing tailings-dolomite mineral-based soil conditioner generated by high-temperature reaction is rich in silicate minerals, which can effectively fix heavy metals in the soil, reduce the migration and bioavailability of heavy metals, and reduce the potential risks of heavy metals to the environment and ecology.

[0089] In particular, the silicon-molybdenum tailings-dolomite mineral-based soil conditioner of Example 8 contains rich calcium aluminate minerals and calcium iron aluminate minerals, which open up new avenues for the diversified application of materials.

[0090] Sulfate ions (SO4 2- ) and carbonate ions (CO3 2- ), their presence will also promote the precipitation of metal cations on the surface of the material, thereby significantly enhancing the material's adsorption capacity for heavy metals.

[0091] (2) Infrared analysis

[0092] The silicon-molybdenum tailings-dolomite mineral-based soil conditioner obtained in Examples 7 and 8 was subjected to infrared spectroscopy analysis. Figure 2 The infrared spectra of Examples 7 and 8 of the present invention are shown as examples: alkaline functional groups exist on the surface of the silicon-molybdenum tailings-dolomite mineral-based soil conditioner of the present invention, which is due to the fact that dolomite and molybdenum tailings themselves contain a large number of bases, and at the same time, 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 are of great importance for adsorbing and fixing heavy metal ions in soil.

[0093] (3) Electron microscopy analysis

[0094] The silicon-molybdenum tailings-dolomite mineral-based soil conditioner obtained in the embodiment of the present invention was analyzed by electron microscope. Figure 3 The electron microscope photos of Examples 7 and 8 of the present invention shown exemplarily illustrate that the surface of the silicon-molybdenum tailings-dolomite mineral-based soil conditioner of the present invention is relatively flat and smooth, and its pore structure 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 materials was also found, which indicates that silicon-molybdenum tailings sand and dolomite coexist in the soil conditioner material of the present invention.

[0095] Performance Analysis

[0096] (1) Adsorption experiment

[0097] In order to study the passivation ability of the soil conditioner of the present invention, the following adsorption experiment was carried out to verify its effect: a Cd 2+ ion solution. Take about 25 mL of the above Cd 2+ The ion solution was added to a 50 mL centrifuge tube containing about 0.1 g of the soil conditioner of Examples 1 to 18 of the present invention. The centrifuge tube with the added sample was capped, shaken at about 220 rpm and 25±2°C for about 12 hours, then allowed to stand for about 24 hours, and then centrifuged at about 4000 rpm for about 30 minutes. After filtering, the Cd in the solution was determined by atomic absorption spectrophotometry (AAS). 2+ The concentration of ions was calculated and the metal cadmium removal rate of each example was calculated. Each example was repeated 3 times in parallel to take the average value. The experimental results are shown in Table 5 below.

[0098] Table 5

[0099] Example No. Cadmium removal rate (100 mg / L of exogenous cadmium) 1MDSⅠ 0.874 3MDSⅠ 0.943 5MDSⅠ 0.969 7MDSⅠ 0.992 9MDSⅠ 0.928 11MDSⅠ 0.958 13MDSⅠ 0.961 15MDSⅠ 0.976 17MDSⅠ 0.989 2MDSⅡ 0.885 4MDSⅡ 0.946 6MDSⅡ 0.988 8MDSⅡ 0.994 10MDSⅡ 0.933 12MDSⅠI 0.944 14MDSⅠI 0.981 16MDSⅠI 0.991 18MDSⅠI 0.992

[0100] It can be seen from Table 5 above that the soil conditioner samples of Examples 7 and 8 of the present invention 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 conditioner of the present invention, the following kinetic analysis experiment was conducted: 2+ The initial concentration is about 100 mg / L, and the soil conditioner of Example 7 and Example 8 of the present invention is added to the solution at a dosage of about 1.0 g / L. Under a constant temperature of about 25°C, the solution is placed in an oscillator and oscillated at a rate of about 180 rpm. During the oscillation process, supernatant samples are taken at about 5, 10, 20, 30, 45, 60, 120, 240, 360 and 480 minutes. It is filtered through a water filter membrane with a pore size of 0.45 μm, and then diluted to a fixed volume with nitric acid at a concentration of about 2%. The Cd in the solution was determined using a flame atomic absorption spectrometer (AAS) with a model of Analytik Jena Novaa350 2+ Each set of experiments was carried out in triplicate.

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

[0104] Table 6

[0105]

[0106] The results showed that the correlation coefficient R 2 Greater than the correlation coefficient of the pseudo-first-order kinetic model; the adsorption capacity Q calculated by the pseudo-second-order kinetic equation e The Cd 2+ This shows that the material is very sensitive to Cd 2+ The adsorption is mainly chemical adsorption, and the adsorption process may be the formation of electronic force between metal ions and adsorbent materials by sharing electrons, indicating that chemical adsorption may be the main factor affecting the adsorption rate. This may be due to the heterogeneous physical structure and various chemical properties of the adsorbent surface, which may jointly contribute to this result.

[0107] (3) Isothermal adsorption analysis

[0108] Prepare Cd with deionized water 2+ The CdCl2 mother solution with a concentration of about 1000 mg / L is used as standby. A NaCl solution with a concentration of about 0.05 mol / L is used as the supporting electrolyte solution. 2+Cd concentrations of about 5, 10, 25, 50, 100, 150 mg / L 2+ ion solution. Take about 30mL of the above concentration of Cd 2+ The ion solution was added to a 50 mL centrifuge tube containing about 0.3 g of the soil conditioner of Examples 7 and 8 of the present invention. The centrifuge tube with the added sample was capped, shaken at about 180 rpm and 25±2° C. for about 24 hours, then centrifuged at about 6000 rpm for about 10 minutes, filtered, and the Cd in the equilibrated solution was determined by atomic absorption spectrophotometry (AAS). 2+ The Langmuir equation was used to fit the data to describe the relationship between the adsorbent material and Cd 2+ The adsorption equilibrium relationship between the three materials and the adsorption of Cd 2+ The initial concentration of the cadmium solution was used as the horizontal axis, and the equilibrium adsorption amount of the passivating agent was used as the vertical axis to draw the isothermal adsorption curve. Each group of experiments was carried out three times in parallel. The results are shown in Table 7 and the attached Figure 6 middle.

[0109] Table 7

[0110]

[0111] The Cd calculated by the Langmuir model 2+ The maximum adsorption capacity Q m About 130 mg / g and about 122 mg / g respectively.

[0112] (4) Soil improvement experiment

[0113] In order to evaluate the repair effect of the soil conditioner of the present invention on soils with different pollution levels, 7 representative acidified farmland soil samples (A-Gaoxin, B-Macheng, C-Huangshi, D-Xiaogan, E-Danjiangkou, F-Tongcheng and G-Tongshan) were selected according to the classification standard of effective silicon content and cadmium pollution status. With reference to the national "Standard for Risk Control of Soil Pollution in Agricultural Land of Soil Environmental Quality (Trial)" (GB 15618-2018), about 0, about 0.3, about 1.5, and about 3 mg / kg of exogenous cadmium (Cd(NO3)2·4H2O) were added to the 7 test soils to ensure that the soil was contaminated with Cd as the single pollution source. After stabilization at room temperature for 30 days, the soil conditioner samples of Examples 7 and 8 of the present invention were mixed with Cd-contaminated soil samples in an amount of about 1% by weight, and each treatment was repeated 3 times. The culture was carried out at room temperature, and deionized water was used to add appropriate moisture to the soil every 7 days. Soil samples were collected on the 30th day of the culture period, and the collected soil samples were naturally air-dried and then ground for measurement.

[0114] Soil pH measurement:

[0115] The soil pH value was measured by glass electrode method, using a mixture of soil and deionized water (1:2.5 weight ratio) for measurement. Each set of experiments was carried out in parallel three times. The experimental results are shown in Figure 7 middle.

[0116] The experimental results show that the soil conditioners of Examples 7 and 8 of the present invention increase the pH value of the soil by about 1.05-2.45 and about 0.74-2.15 units, respectively. Figure 7 It can be seen that in 7 soil samples, when Cd pollution is at different concentrations, the soil conditioner of the present invention can significantly increase the pH value of the soil.

[0117] Determination of soil cadmium passivation:

[0118] Soil cadmium passivation was determined using soil samples from Gaoxin and Danjiangkou in the above soil improvement experiment.

[0119] The form extraction method of cadmium (Cd) in soil refers to the National Standard of the People's Republic of China GB / T25282-2010 "Sequential Extraction Procedure for 13 Trace Elements in Soil and Sediment" and uses the BCR distribution extraction method to extract the acid extractable state, reducible state, oxidizable state, and residual state (weigh 1.000g soil sample). The specific form extraction steps of Cd in soil are shown in Table 8 below.

[0120] Table 8:

[0121]

[0122] The solution samples in each step were extracted and the Cd content was determined by flame atomic absorption spectrometry (AAS). 2+ The experimental results are shown in the attached Figure 8 and 9 middle.

[0123] The experimental results show that after adding MDSI and MDSII of Examples 7 and 8 of the present invention, the proportions of oxidizable and acid-extractable Cd in the soil are reduced, and the residual and reducible Cd are increased. In the acidified soil of the high-tech zone, the proportion of acid-extractable Cd is reduced by about 16.54-24.43% and about 0.79-21.28% respectively under the treatment of MDSI and MDSII. The proportion of residual Cd is increased by about 5.21-29.58 and about 2.08-25.22% respectively under the treatment of MDSI and MDSII. In the acidified soil of Danjiangkou, the proportion of acid-extractable Cd is reduced by about 7.22-13.79% and about 6.53-16.49% respectively under the treatment of MDSI and MDSII. The proportion of residual Cd is increased by about 4.29-21.18% and about 1.90-13.73% respectively under the treatment of MDSI and MDSII. Therefore, the soil conditioner of the present invention can effectively fix Cd and convert it into a more stable residual form.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions claimed to be protected by the present invention.

Claims

1. A silicon-molybdenum tailings-dolomite mineral-based soil conditioner, characterized in that: The soil conditioner is obtained by calcining silicon-molybdenum tailings and dolomite, and the mass fraction of effective silicon contained in the soil conditioner is at least 3.5 times the mass fraction of effective silicon contained in the silicon-molybdenum tailings used to prepare the soil conditioner.

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

3. A method for preparing the silicon-molybdenum tailings-dolomite mineral-based soil conditioner according to claim 1 or 2, characterized in that: The preparation method comprises calcining a mixture of silicon-molybdenum tailings powder and dolomite powder in a weight ratio of 1:(1.2-1.6), preferably 1:1.4, at a temperature ranging from 1000°C to 1100°C.

4. The preparation method according to claim 3, characterized in that: The silicon-molybdenum tailings contain an effective silicon mass fraction of less than 30 mg / g; and / or The particle size of the silicon-molybdenum tailings powder is less than 0.150 mm; and / or The particle size of the dolomite powder is less than 0.075 mm; and / or The calcination time is at least 0.8 hours, preferably in the range of 0.9 to 1.1 hours, and more preferably 1.0 hour.

5. The preparation method according to claim 3 or 4, characterized in that: The moisture content of the silicon-molybdenum tailings is less than 5% by weight; and / or The moisture content of the dolomite is less than 5% by weight.

6. The preparation method according to claim 3 or 4, characterized in that: The dolomite contains ≥28 wt % calcium oxide, ≤5 wt % silicon oxide, ≤1.2 wt % iron oxide, ≥18 wt % magnesium oxide, ≤0.85 wt % aluminum oxide and ≤1 wt % alkali metal oxide.

7. The preparation method according to claim 3 or 4, characterized in that: The silicon-molybdenum tailings are obtained by washing the molybdenum tailings with water once or multiple times, and then drying the washed tailings sand.

8. Use of the silicon-molybdenum tailings-dolomite mineral-based soil conditioner according to claim 1 or 2 or the silicon-molybdenum tailings-dolomite mineral-based soil conditioner prepared by the preparation method according to any one of claims 3 to 7 for improving acidified soil.

9. The use according to claim 8, characterized in that The acidified soil is acidified cadmium-contaminated soil.

10. The use according to claim 8 or 9, characterized in that The improved acidified soil comprises uniformly mixing the silicon-molybdenum tailings-dolomite mineral-based soil conditioner with the acidified soil in a ratio of 0.5 wt % to 5.0 wt %, preferably 1.0 wt %.

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