A steel slag-based slow-release compound fertilizer for heavy metal contaminated soil improvement and a preparation method thereof
By ball milling, magnetic separation, harmless treatment, calcination, and pressure differential structural modification of steel slag, a slow-release compound fertilizer suitable for heavy metal contaminated soil was prepared, solving the application problem of steel slag in weakly acidic or neutral soils and achieving long-term soil improvement and heavy metal solidification effects.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHENYANG JIANZHU UNIVERSITY
- Filing Date
- 2024-01-31
- Publication Date
- 2026-07-24
Smart Images
Figure CN118184440B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of soil remediation, specifically to the field of steel slag-based slow-release compound fertilizer technology for the improvement of heavy metal contaminated soil. Background Technology
[0002] Soil is the material basis for the survival of humans, animals, plants and microorganisms. The rapid development of industry has caused serious heavy metal pollution in soil. Heavy metals are easy to accumulate in the environment and are difficult to degrade, posing a major threat to human health. Due to the disadvantages of steel slag, such as low hydration activity, poor stability, high heavy metal content and high alkalinity, the utilization rate of steel slag is limited. Untreated steel slag will occupy land and pollute the environment. Therefore, it is urgent to explore new methods for the resource utilization of steel slag.
[0003] The application of domestic steel slag-based remediation materials for soil remediation and improvement is currently in the application and promotion stage, primarily used for the remediation and improvement of acidic soils. The mechanism of action of these materials involves initially providing a high-alkalinity environment to facilitate complexation ion exchange in the soil; in the middle stage, as alkalinity decreases, the ion exchange effect weakens while the gel solidification effect strengthens; and in the later stage, a large amount of C-S-H gel is formed, encapsulating the soil and further enhancing gel solidification. Due to the high alkalinity of steel slag, it is not suitable for weakly acidic or near-neutral soils, and the leaching rates of trace elements such as silicon, calcium, potassium, and phosphorus are also relatively low. Further mechanistic research is needed to gradually expand the application of this technology to other soil types. Summary of the Invention
[0004] To address the aforementioned problems, specifically those raised in the background section, this invention proposes a method for preparing a steel slag-based slow-release compound fertilizer for improving heavy metal contaminated soil, comprising the following steps: S1: Pre-treat the material by grinding the steel slag in a ball mill, and then storing the steel slag after passing it through a standard sieve and magnetic separation. S2: To harmlessly treat and carbonize the heavy metals in steel slag, take the ground steel slag and heat it in a reducing agent solution for 2 to 4 hours. The ratio of steel slag to reducing agent is (50 to 100): 1. The heating temperature is 45 to 85℃ and the stirring speed is 300 r / min. S3: Fertilizer modification, steel slag and potassium-containing compound mixture are roasted in an oxygen-containing atmosphere to obtain high-temperature modified steel slag, wherein the potassium-containing compound is 1 to 7 parts by weight (preferably 1 to 5 parts, more preferably 1 to 3 parts), and after roasting, it is ground twice and then sieved and stored.
[0005] S4: Pressure differential structural modification. The steel slag powder treated in S3 is placed in a high-pressure device for pressure differential structural modification. This high-pressure device has two inlets and a middle depressurization section. The pressurized gas is carbon dioxide. During gas flow, water vapor is first introduced at one end for wetting, then the flow is closed, and carbon dioxide is introduced at the other end to a predetermined pressure. Simultaneously, structural modification achieves carbonization to reduce alkalinity through wet carbonization.
[0006] S5: Add buffer and mix evenly to obtain the steel slag-based slow-release compound fertilizer for improving heavy metal contaminated soil. The ratio of steel slag mixture to buffer after S4 treatment is (50-200):1.
[0007] A further provision of the present invention is that the steel slag is blast furnace steel slag, converter steel slag, or electric furnace steel slag.
[0008] A further provision of the present invention is that the steel slag grinding time in the material pretreatment in step S1 is greater than 6 min and less than 20 min, and the standard range for steel slag sieving is 50 to 200 mesh.
[0009] A further provision of the present invention is that: the reducing agent for the harmless treatment of steel slag in step S2 is one or a combination of divalent ferrous salts and sulfites (more preferably one or more of ferrous sulfate, ferrous nitrate, ferrous carbonate, ferrous chloride, and sodium sulfite, such as ferrous sulfate). The weight parts of the steel slag are 60-160 parts (preferably 80-140 parts, more preferably 100-120 parts), the weight parts of the reducing agent are 0.5-5 parts (preferably 1-3 parts), and the weight parts of the water are 2500-5200 parts (preferably 3000-4700 parts, more preferably 3500-4200 parts). The heating temperature is preferably 55-80°C.
[0010] A further provision of the present invention is that the potassium-containing compound in step S3 is selected from one or a combination of potassium salts, potassium hydroxide, and organic potassium (preferably one or more of potassium carbonate, potassium bicarbonate, potassium hydroxide, and non-sulfur, nitrogen organic potassium, more preferably one or more of potassium carbonate, potassium bicarbonate, and potassium hydroxide, such as potassium carbonate and potassium bicarbonate), and the calcination temperature for the fertilizer modification is 1200-1400°C, and the holding time is 30-60 min.
[0011] A further provision of the present invention is that: in step S4, the pressure difference structure modification treatment involves introducing high-temperature steam to a pressure of 0.5–2 MPa (preferably 1–1.5 MPa), and pressurizing CO2 to 6–16 MPa (preferably 7–14 MPa, more preferably 8–12 MPa), with a pressure holding time of 18–30 h (preferably 20–28 h, more preferably 22–26 h), and the CO2 gas concentration is preferably 99%.
[0012] A further provision of the present invention is that the buffer added in step S5 is at least one of oxalic acid, malic acid, and citric acid, and its mass is 1 to 2% of the total mass.
[0013] A steel slag-based slow-release compound fertilizer for improving heavy metal contaminated soil is prepared by the method described in any one of claims 1 to 7, wherein the treated steel slag is 60 to 160 parts by weight and the buffer is 0.5 to 7 parts by weight.
[0014] A further provision of the present invention is that the steel slag is more preferably 100-120 parts by weight, and the buffer is more preferably 0.5-3 parts by weight.
[0015] An application of a steel slag-based slow-release compound fertilizer for the improvement of heavy metal contaminated soil, wherein the mass fraction of the fertilizer is 1-40 wt% (preferably 3-20 wt%, more preferably 5-10 wt%).
[0016] This invention offers the following advantages: It utilizes a steel slag system to adsorb and solidify heavy metals, significantly reducing the alkalinity of the steel slag through wet carbonization, thus broadening its applicability for soil improvement. High-temperature compounding enhances the nutrient content of the steel slag. Furthermore, by adding potassium salt particles to the molten slag, the silica, a major component of the molten slag, combines with the potassium salt to form potassium silicate. Combined with the phosphorus abundant in the steel slag, a phosphorus-potassium (P / K) compound fertilizer is prepared. Moreover, because potassium silicate releases more slowly than conventional fast-acting chemical fertilizers such as potassium chloride, potassium sulfate, and urea, this product can continuously improve soil quality. Soil environment; using pressure difference to modify the structure of steel slag mixture greatly improves the leaching capacity of nutrients. The preparation process is relatively simple and the effect is significant. Compared with the prior art, this invention can effectively solidify heavy metals in contaminated soil on the one hand, and adjust soil pH on the other hand. It can improve the physical and chemical properties of soil by utilizing elements such as P, K, and Mg that are beneficial to plant growth. It has a large specific surface area, suitable pore structure and surface structure, and has a strong adsorption capacity for heavy metals. At the same time, the beneficial elements and weak alkalinity in the fertilizer can regulate the physical and chemical properties of soil. It is a long-term slow-release fertilizer for continuous improvement. Attached Figure Description
[0017] Figure 1 This illustrates the Cr content after harmless treatment of steel slag in Experimental Example 1 of the present invention. 6+ Leaching diagram; Figure 2 The image shows V after the steel slag was treated to be harmless in Experiment Example 2. 5+ Leaching diagram; Figure 3 The changes in soil pH after the application of the soil conditioner in Experiment Example 3 are shown. Figure 4The changes in available phosphorus in the soil after the application of the amendment are shown in Experiment Example 3. Figure 5 The changes in available K in the soil after the application of the amendment are shown in Experiment Example 3; Figure 6 This shows the change in germination rate of *Boccoli florida* planted in soil after the application of the soil conditioner in Experiment Example 4; Figure 7 This shows the solidification of heavy metal Cu in the soil after the application of the amendment in Experiment Example 5. 2+ Condition; Figure 8 This shows the solidification of heavy metal Cr in the soil after the application of the soil conditioner in Experiment Example 5. 6+ Condition; Figure 9 This shows the solidification of heavy metal Cr in the soil after the application of the soil conditioner in Experiment Example 6. 6+ Condition; Figure 10 The images show the germination times of the Four Seasons Chinese cabbage seeds after 3 days and 7 days after the application of different amounts of the improver in Experiment Example 3. Detailed Implementation
[0018] The following is a reference to the appendix. Figure 1-10 The preferred embodiments of the present invention will be described below. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Example
[0019] (1) Put the steel slag into a ball mill and grind it for 10 minutes. After grinding, put the steel slag through a 50-mesh sieve and store it.
[0020] (2) Take 100 parts of finely ground steel slag and mix them evenly with 4000 parts of deionized water. Heat the mixture to 70 degrees Celsius and add 2 parts of FeSO4. Stir the mixture at 300 r / min and reduce it for 2 hours to obtain harmless steel slag. Steel slag produced by high-temperature metallurgy contains many high-valence heavy metal ions, such as Cr. 6+ V 5+ These high-valence heavy metal ions can cause serious environmental pollution, so it is necessary to use reducing agents to reduce these heavy metal ions into low-valence ions through reduction reactions.
[0021] During the reduction process, the higher the concentration of reducing ions per unit volume of solution, the higher the reduction efficiency of heavy metal ions in steel slag. Therefore, theoretically, the greater the amount of reducing agent and the smaller the amount of water, the better the reduction effect of heavy metals in steel slag. However, because the reducing agent has a limit to its solubility in water, using too little water will result in insufficient stirring and a decrease in reduction efficiency, while using too much reducing agent will lead to waste. Therefore, the amounts of reducing agent and water need to be within a reasonable range.
[0022] (3) The above-obtained harmless steel slag and 2 parts of potassium carbonate are mixed evenly and placed in a muffle furnace for high-temperature modification. High-temperature modification causes the silica-alumina glass in the harmless steel slag to remelt, absorb potassium-containing compounds, combine nutrients, and generate stable potassium silicide. This not only improves the nutrients in the steel slag, but also makes the steel slag more porous and improves its adsorption performance. The modification temperature is 1200℃ and the holding time is 30min to obtain high-temperature modified steel slag.
[0023] (4) The above-mentioned high-temperature modified steel slag is added to a high-pressure steam boiler for pressure differential structural modification. The high pressure differential can change the structure of the high-temperature modified steel slag, greatly improving the nutrient leaching capacity. Under sealed conditions, the pressure differential structural modification treatment in step S4 is to introduce high-temperature steam to 1 MPa and then pressurize it to 10 MPa. The CO2 concentration introduced in the steel slag carbonization treatment is 99%. After maintaining for 24 hours, the pressure is released instantaneously to obtain high-pressure modified steel slag. As an alkaline material, steel slag is directly used in the solidification and stabilization of heavy metal contaminated soil. At the same time, the hydroxyl groups formed by the hydration of steel slag will form a precipitation effect with heavy metal ions. However, the soil pH is high and it is not suitable for further recultivation. The steel slag carbonization provided by this invention, by introducing CO2 into the solution to react with CaO and MgO in the steel slag to form carbonates, greatly reduces the alkalinity of the steel slag and can significantly improve the applicable soil range of steel slag-based materials.
[0024] (5) Grind the obtained high-pressure modified steel slag and then pass it through 50 and 100 mesh sieves to obtain 100 parts of 50-100 mesh modified steel slag. Then add 3 parts of buffer oxalic acid to it, which can activate the activity of modified steel slag. Under the action of water in the soil, it promotes the hydration of modified steel slag, changes the surface structure of steel slag, increases the specific surface area, and forms hydrated calcium silicate (CSH), which can encapsulate and solidify heavy metal elements, improve the adsorption, solidification and remediation effect of heavy metal contaminated soil, and obtain steel slag-based heavy metal contaminated soil improvement slow-release compound fertilizer, which is denoted as fertilizer 1.
[0025] All the above quantities are by weight. Example
[0026] The heavy metal soil amendment slow-release fertilizer was prepared according to the method in Example 1 and is referred to as fertilizer 2. The only difference is that in step (2), the reduction time is 4 hours; in step (4), the carbonization is pressurized to 8 MPa. Example
[0027] The heavy metal soil amendment slow-release fertilizer was prepared according to the method in Example 1 and is referred to as fertilizer 3. The only difference is that in step (3), the modification temperature is 1000℃ and the heat preservation time is 20min; in step (5), after high pressure modified steel slag is ground, it is passed through 50 and 200 mesh sieves. Example
[0028] The heavy metal soil amendment slow-release fertilizer was prepared according to the method in Example 1 and is referred to as fertilizer 4. The only difference is that in step (4), carbonization is pressurized to 12 MPa; in step (5), after high-pressure modified steel slag is ground, it is passed through 50 and 200 mesh sieves. Example
[0029] The heavy metal soil amendment slow-release fertilizer was prepared according to the method in Example 1 and is referred to as fertilizer 5. The only difference is that in step (5), after high pressure modified steel slag is ground, it is passed through 50 and 200 mesh sieves and 1 part of buffer oxalic acid is added. Example
[0030] Heavy metal soil amendment slow-release fertilizer was prepared according to the method in Example 1, and is referred to as fertilizer. The only difference is that in step (2), the amount of FeSO4 added is 0.5 parts, 1 part, 1.5 parts, 3 parts, 4 parts, and 5 parts, respectively. Fertilizers 6, 7, 8, 9, 10, and 11 were obtained respectively.
[0031] Comparative Example Comparative Example 1 Comparative fertilizer A was prepared according to the method of Example 1, except that the reducing agent FeSO4 was not added.
[0032] Experimental Example Experimental Example 1 The Cr content of the harmless steel slag obtained in Example 1, Example 6 and Comparative Example 1 was tested. 6+ The changes in leaching amount are detailed in the attached figure. Figure 1 As shown. Cr 6+ The test method refers to the diphenylcarbazide spectrophotometric method specified in GB7647-87.
[0033] from Figure 1 As can be seen, with the increase of FeSO4 weight content, Cr 6+ The leaching amount of Cr initially decreased rapidly, and after the weight of FeSO4 reached 2 parts, the leaching amount of Cr... 6+ The leaching amount tends to reach equilibrium.
[0034] Experiment Example 2 V0 of the harmless steel slag obtained in Example 1, Example 6 and Comparative Example 1 was tested. 5+ The change in leaching amount, specifically as follows: Figure 2 As shown. V 5+ The test method refers to the inductively coupled plasma emission spectrometry method specified in HJ781-2016.
[0035] from Figure 2 As can be seen, with the increase of FeSO4 weight, V 5+The leaching amount first decreased slowly and then decreased rapidly. After the weight of FeSO4 reached 1.5 parts, the leaching amount tended to reach equilibrium.
[0036] Experimental Example 3 Fertilizer 1 prepared in Example 1 was added to soil contaminated with heavy metals. Changes in soil pH, available phosphorus (P), and available potassium (K) were tested; specific changes are shown in the attached figure. Figure 3 , 4 As shown in Figure 5. Soil pH was measured according to the method specified in NY / T1121.2-2006 standard; the measurement of available soil pH and K was mainly based on the ultraviolet spectrophotometry and atomic absorption spectrometry methods specified in "Soil Agrochemical Analysis" edited by Bao Shidan.
[0037] Fertilizer was mixed into the soil at concentrations of 0%, 3%, 5%, 10%, and 20% of the soil mass. The soil and fertilizer were then thoroughly mixed using a cylindrical mixer. The mixture was poured into an indoor incubator, and 100 seeds of *Bonito flakes* were planted evenly. After germination, the ratio of germinating seeds to the total number of seeds was calculated to determine the germination rate. A detailed experimental comparison chart is attached. Figure 10 As shown.
[0038] Experiment Example 4 Fertilizer 1 prepared in Example 1 was added to soil contaminated with heavy metals for improvement. The change in germination rate of *Phyllanthus edulis* planted in the improved soil was analyzed, as detailed in the attached figure. Figure 6 As shown.
[0039] The fertilizer application rate and planting method are the same as in Example 3. Heavy metal ions (Cr) in the soil... 6+ and Cu 2+ The initial concentrations were 133.35 mg / kg and 5.80 mg / kg.
[0040] Experimental Example 5 Fertilizer 1 prepared in Example 1 was added to heavy metal-contaminated soil for improvement. The soil heavy metal Cu content was measured after 28 days of improvement. 2+ Cr 6+ Concentration changes are detailed in the attached document. Figure 7 , 8 As shown.
[0041] The fertilizer application rate and planting method are the same as in Example 3. Heavy metal ions (Cr) in the soil... 6+ and Cu 2+ The initial concentrations were 133.35 mg / kg and 5.80 mg / kg.
[0042] Experimental Example 6 Fertilizers 1-5 prepared in Examples 1-5 were added to heavy metal-contaminated soil in the same dosage for soil improvement. The change in germination rate of *Pak Choy Sauerkraut* planted in the improved soil was analyzed, as detailed in the attached figure. Figure 9 As shown.
[0043] The fertilizer application rate is 5%, and the planting method is the same as in Example 3.
[0044] This invention demonstrates that it utilizes a steel slag system to adsorb and solidify heavy metals, significantly reduces the alkalinity of the steel slag through wet carbonization, thus expanding its applicability for soil improvement. High-temperature compounding enhances the nutrient content of the steel slag. Furthermore, in this process, adding potassium salt particles to the molten slag allows silicon dioxide, a major component of the molten slag, to combine with potassium salts to produce potassium silicate. Combined with the phosphorus abundant in the steel slag, a phosphorus-potassium (P / K) compound fertilizer is prepared. Since potassium silicate releases more slowly than conventional fast-acting chemical fertilizers such as potassium chloride, potassium sulfate, and urea, this product can continuously improve the soil environment. The use of pressure difference to modify the structure of steel slag mixtures greatly improves the leaching capacity of nutrients. The preparation process is relatively simple and the effect is significant. Compared with the prior art, this invention can effectively solidify heavy metals in contaminated soil and adjust soil pH. It can also improve the physical and chemical properties of soil by utilizing elements such as P, K, and Mg that are beneficial to plant growth. It has a large specific surface area, suitable pore structure and surface structure, and strong adsorption capacity for heavy metals. At the same time, the beneficial elements and weak alkalinity in the fertilizer can regulate the physical and chemical properties of soil. It is a long-term slow-release fertilizer that continuously improves soil quality.
[0045] Although the invention has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of the invention. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. The invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.
[0046] In the description of this invention, terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," which indicate direction or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. These are used merely for ease of description and do not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0047] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.
[0048] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to those processes, articles, or apparatus / devices.
[0049] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.
Claims
1. A method for preparing a steel slag-based slow-release compound fertilizer for improving heavy metal contaminated soil, characterized in that: Includes the following steps: S1: Pre-treat the material by grinding the steel slag in a ball mill, and then storing the steel slag after passing it through a standard sieve and magnetic separation. S2: Harmless treatment and carbonization of heavy metals in steel slag. Take the ground steel slag and heat it in a solution of ferrous salt and / or sulfite for 2-4 hours for reduction. The ratio of steel slag to ferrous salt and / or sulfite is (50-100):
1. The heating temperature is 45-85℃ and the stirring speed is 300r / min. S3: Fertilizer modification, steel slag and potassium-containing compound mixture are roasted in an oxygen-containing atmosphere to obtain high-temperature modified steel slag, wherein the potassium-containing compound is 1 to 7 parts by weight, and after roasting, it is ground twice and then sieved for storage. S4: The steel slag treated in S3 is placed into a high-pressure device. The high-pressure device has air intake at both ends and pressure release in the middle. First, water vapor is introduced into one end to wet the steel slag, then that end is closed, and carbon dioxide is introduced into the other end to a predetermined pressure. After maintaining the pressure, the pressure is released. S5: Add at least one of oxalic acid, malic acid or citric acid as a buffer, mix evenly to obtain the steel slag-based slow-release compound fertilizer for improving heavy metal contaminated soil. The ratio of steel slag mixture to buffer after S4 treatment is (50~200):
1.
2. The preparation method of a steel slag-based slow-release compound fertilizer for improving heavy metal contaminated soil as described in claim 1, characterized in that: The steel slag is blast furnace steel slag, converter steel slag, or electric furnace steel slag.
3. The method for preparing a steel slag-based slow-release compound fertilizer for improving heavy metal contaminated soil as described in claim 1, characterized in that: In step S1, the grinding time of the steel slag in the material pretreatment is greater than 6 minutes and less than 20 minutes, and the standard range of steel slag sieving is 50~200 mesh.
4. The preparation method of a steel slag-based slow-release compound fertilizer for improving heavy metal contaminated soil as described in claim 1, characterized in that: In step S3, the potassium-containing compound is selected from one or a combination of potassium salts, potassium hydroxide, and organic potassium. The calcination temperature for the fertilizer modification is 1200~1400℃, and the holding time is 30~60min.
5. The method for preparing a steel slag-based slow-release compound fertilizer for improving heavy metal contaminated soil as described in claim 1, characterized in that: In step S4, water vapor is first introduced to 0.5~2 MPa, and then CO2 is introduced to pressurize to 6~16 MPa. The pressure is maintained for 18~30 hours, and the CO2 gas concentration is 99%.
6. The method for preparing a steel slag-based slow-release compound fertilizer for improving heavy metal contaminated soil as described in claim 1, characterized in that: The buffer added in step S5 is at least one of oxalic acid, malic acid, and citric acid, and its mass is 1 to 2% of the total mass.
7. The method for preparing a steel slag-based slow-release compound fertilizer for improving heavy metal contaminated soil as described in claim 1, characterized in that: When used to improve soil contaminated with heavy metals, the compound fertilizer has a mass fraction of 1 to 40 wt%.