Method for determining doping amount of remediation agent for heavy metal contaminated soil

Abstract

The invention belongs to the technical field of soil remediation, and particularly discloses a method for determining the doping amount of a remediation agent for heavy metal contaminated soil. The method comprises the following steps: preparing target heavy metal contaminated soil with different concentrations and passivating; mixing red mud, blast furnace slag and an alkali activator to obtain a repairing agent; adding different doping amounts of repairing agents into the heavy metal contaminated soil, mixing and solidifying to obtain different repaired soil; the target heavy metal leaching amount of different repaired soil is measured; fitting the leaching amounts of the heavy metal contaminated soil with the same concentration under different mixing amounts, solving the optimal mixing amount of the concentration, and then solving the optimal mixing amount of the remediation agent with other concentrations; fitting the optimal doping amounts of the remediation agents with different concentrations to obtain a function relationship between the heavy metal concentration and the doping amounts of the remediation agents, and then substituting the heavy metal concentration of the pre-remediation heavy metal contaminated soil into the function relationship to obtain the corresponding optimal doping amount of the remediation agents. The method has the characteristics of simplicity in operation, high utilization efficiency of the repairing agent, low repairing cost and no secondary pollution.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil remediation, and particularly relates to a method for determining the dosage of a remediation agent for heavy metal contaminated soil, which is simple to operate, has high utilization efficiency of the remediation agent, low remediation cost, and no secondary pollution. Background Technique

[0002] The heavy metal contaminated soil remediation technology aims to reduce the toxicity, mobility or bioavailability of heavy metals in soil through physical, chemical, biological and other means, so that it meets the environmental safety standards. With the development of industry and the improvement of environmental governance requirements, the remediation technology shows a diversified trend. At present, it is mainly divided into four categories: physical remediation, chemical remediation, biological remediation and combined remediation technology.

[0003] The solidification / stabilization technology of heavy metal contaminated soil is one of the physical remediation technologies. The solidification / stabilization technology is to add solidifying agents (such as cement, lime, clay) or stabilizing agents (such as phosphates, humic acids) to physically and chemically react with heavy metals in soil (such as adsorption, precipitation, ion exchange, complexation, etc.), so as to reduce the mobility and bioavailability of heavy metals, convert them into low-toxicity or inert forms, and ultimately reduce the risks to the environment and human health. Since the solidification / stabilization technology has the characteristics of relatively simple operation, low cost, short remediation cycle, etc., and is applicable to the treatment of various heavy metal composite contaminated soils, it has become the mainstream means for the remediation of industrial polluted sites.

[0004] In the prior art, for the solidification / stabilization technology of heavy metal contaminated soil, there is a cement-based solidification / stabilization technology that uses cement, fly ash, lime, etc. as solidifying agents. Through the hydration reaction of cement, the generated colloid wraps heavy metal ions, and at the same time, the alkaline environment promotes the formation of hydroxide precipitates of heavy metals. Although the aforementioned technology has a significant fixing effect on heavy metals (such as Pb, Cd, Cr, etc.) and good long-term stability, and the cost is low and the technology maturity is high; however, since it will significantly increase the pH value of the soil and cause soil compaction, it may damage the original ecological function of the soil. There is also a phosphate stabilization technology that uses phosphates (such as calcium dihydrogen phosphate, hydroxyapatite, etc.) to react with heavy metals to form insoluble phosphate minerals (such as Cd3(PO4)2, Pb5(PO4)3OH) to reduce the mobility of heavy metals. Although the aforementioned technology has excellent stabilization effects on heavy metals such as Pb, Cd, Zn, etc., and the reaction process is mild, with little impact on the pH of the soil, and the generated phosphate minerals have high chemical stability; but there are also problems such as the relatively high price of phosphate agents, the long reaction cycle resulting in low repair efficiency, and excessive phosphates may also cause eutrophication of the soil or water body. In addition, there is also an organic polymer stabilization technology that uses functional groups (such as -COOH, -NH2) of organic polymer materials (such as humic acid, chitosan, synthetic resin, etc.) to form complexes or chelates with heavy metal ions to reduce their mobility. Although the aforementioned technology is highly efficient and low-toxic, some organic materials (such as humic acid) can improve the soil structure and can be used under various soil conditions such as acidic, neutral, and alkaline; but there are also problems such as the organic complex may decompose under the action of microorganisms, resulting in insufficient long-term stability, and the cost of synthetic polymer agents is relatively high, and the residual agents may affect the soil ecology, and the environmental behavior and long-term toxicity of complex organic molecules are not fully clear, and there are uncertainties in environmental risks.

[0005] In addition, current research on solidification / stabilization technologies for heavy metal-contaminated soils at home and abroad mostly focuses on the remediation effects under single heavy metal contamination or fixed dosages of remediation agents, lacking in-depth exploration of the dynamic response laws of the leaching characteristics of multiple heavy metals under different dosages of remediation agents. Moreover, due to the increasing demand for the remediation of high-concentration heavy metal-contaminated soils, but most related research is limited to low-concentration pollution simulation conditions, it is difficult to guide the treatment of complex pollution scenarios in actual engineering. For example, the literature "Li Yujiao, Wen Ya, Guo Qiannan, et al. Study on the remediation of Cd and Pb contaminated farmland soil by composite leaching with organic acids and FeCl3 [J]. Journal of Agro-Environment Science. 2014, 33(12): 2335-2342." shows that the influence of the dosage of the remediation agent on the leaching behavior of heavy metals may exhibit non-linear characteristics, and the interaction between heavy metals under composite pollution conditions may significantly change their leaching characteristics. Therefore, in the existing technology, for the dosage of the remediation agent during the remediation of heavy metal-contaminated soils, most of them are determined by empirical judgment. There are also cases where different proportions of the remediation agent are added, followed by heavy metal leaching tests, and then the optimal dosage of the remediation agent is obtained by comparing the heavy metal leaching amounts after different dosages. The latter method requires repeating the heavy metal leaching tests after adding different proportions of the remediation agent for the same heavy metal concentration in the same contaminated soil when the concentration of the same heavy metal changes, resulting in low remediation efficiency; and for contaminated soils with the same heavy metal concentration, the tested different proportion dosages are distributed in a point-like manner, so the obtained optimal dosage of the remediation agent often has a large deviation from the actual optimal dosage, resulting in deficiencies in the remediation effect and cost. Excessive dosage is also likely to cause secondary pollution.

[0006] Therefore, studying the leaching characteristics of different remediation agents and their different dosages for different heavy metal-contaminated soils, so as to effectively improve the utilization efficiency of the remediation agent and reduce the remediation cost, and avoid causing secondary pollution of the soil, has important practical significance. Summary of the Invention

[0007] To address the deficiencies in the existing technology, the present invention provides a method for determining the dosage of a remediation agent for heavy metal-contaminated soils, which is simple to operate, has a high utilization efficiency of the remediation agent, low remediation cost, and no secondary pollution.

[0008] The method for determining the dosage of the remediation agent for heavy metal-contaminated soils of the present invention is realized as follows: It includes steps of contaminated soil preparation, remediation agent preparation, soil remediation, toxicity leaching, dosage fitting, and optimal dosage determination. The specific content of each step is as follows: A. Contaminated soil preparation: Prepare target heavy metal-contaminated soils with different concentrations according to gradients and passivate them to obtain heavy metal-contaminated soils with different heavy metal concentrations; B. Remediation agent preparation: Mix red mud, blast furnace slag, and an alkali activator to obtain a remediation agent; C. Soil remediation: Different dosages of the aforementioned remediation agent were added to the heavy metal - contaminated soils with different heavy metal concentrations respectively, and after mixing, they were solidified to obtain different treated remediation soils. D. Toxicity leaching: The leaching amounts of the target heavy metals in the above - mentioned different remediation soils were measured respectively to obtain the heavy metal leaching amounts corresponding to different remediation soils. E. Dosage fitting: The leaching amounts of heavy metal - contaminated soils with the same concentration under different dosages of the remediation agent were fitted to obtain the optimal dosage of the remediation agent for the heavy metal - contaminated soil of this concentration. Then, by analogy as described above, the optimal dosages of the remediation agent for heavy metal - contaminated soils with other concentrations were obtained. F. Determination of the optimal dosage: The optimal dosages of the remediation agent for heavy metal - contaminated soils with different concentrations were fitted to obtain the functional relationship between the heavy metal concentration and the dosage of the remediation agent for the target heavy metal - contaminated soil. Then, the heavy metal concentration of the heavy metal - contaminated soil to be pre - remediated was substituted into the aforementioned functional relationship to obtain the corresponding optimal dosage of the remediation agent.

[0009] Further, the target heavy metal - contaminated soil in step A is a single - heavy - metal - contaminated soil, which is obtained by fully mixing an analytical - pure nitrate solution and soil in proportion and passivating for 15 days.

[0010] Further, the nitrate is any one of copper nitrate, lead nitrate, cadmium nitrate, chromium nitrate, and nickel nitrate. The target heavy metal - contaminated soil needs to be prepared into soils with 4 - 10 different concentrations of the target heavy metal.

[0011] Further, in step B, the mass ratio of red mud to blast furnace slag is 4:5 - 7, the mass ratio of the alkali activator to the sum of red mud and blast furnace slag is 1:4 - 6, and the alkali activator is water glass with a modulus of 1.5.

[0012] Further, the alkali activator is prepared by adding NaOH to adjust the modulus of water glass to 1.5. Both the red mud and the blast furnace slag have a particle size of 200 meshes, and the blast furnace slag is the waste slag discharged from the blast furnace during pig iron smelting.

[0013] Further, in step C, different dosages of the remediation agent were added to the heavy metal - contaminated soils with the same concentration respectively, and after mixing and solidifying, different treated remediation soils of this concentration were obtained. Then, by analogy as described above, the corresponding treated remediation soils of the remaining concentrations were obtained. Among them, the solidification time is 28 days.

[0014] Further, in step D, the toxicity characteristic leaching method was used to measure the leachable amounts of heavy metals in heavy metal - contaminated soils with different heavy metal concentrations under different dosages of the remediation agent after 28 days of remediation.

[0015] Further, in step E, first, according to the leachable amount of heavy metals, a scatter plot of the leachable amount of heavy metals - admixture amount of the remediation agent for heavy metal - contaminated soil with each heavy metal concentration at different admixture amounts of the remediation agent is plotted. Then, each scatter plot is fitted. Next, the function with the highest goodness of fit is selected. Subsequently, the intersection point of the fitted curve of the aforementioned function and the leaching toxicity identification standard value is obtained, and the abscissa of the aforementioned intersection point is taken as the optimal admixture amount of the remediation agent for the heavy metal - contaminated soil with this heavy metal concentration. Further, in step F, first, a scatter plot of the optimal admixture amount of the remediation agent - heavy metal concentration corresponding to heavy metal - contaminated soil with different heavy metal concentrations is plotted. Then, the scatter plot is fitted to obtain the functional relationship between different heavy metal concentrations of the heavy metal - contaminated soil and the optimal admixture amount of the remediation agent.

[0016] Further, in step F, first, the target heavy metal concentration in the pre - remediated heavy metal - contaminated soil is measured. Then, the measured target heavy metal concentration is substituted into the aforementioned corresponding functional relationship to obtain the corresponding optimal admixture amount of the remediation agent.

[0017] The reaction mechanism of the present invention is as follows:

[0018] The present invention has the following beneficial effects: 1. Through clear and standardized steps, the present invention constructs a systematic process for determining the admixture amount of the remediation agent: adding remediation agents with different admixture amounts to soils with different heavy metal concentrations, then performing toxicity leaching and fitting the optimal admixture amount of the remediation agent at different heavy metal concentrations. Then, based on the optimal remediation admixture amounts for different heavy metal concentrations, a quantitative model of the relationship between different heavy metal concentrations in heavy metal - contaminated soil and the optimal admixture amount of the remediation agent is fitted and established, breaking through the limitations of traditional point - like tests. Thus, the precise regulation of the dosage of the remediation agent for single - metal - contaminated soil at any heavy metal concentration can be quickly achieved. The process of the present invention is more scientific and standardized, reducing the blindness and repetition of operations, improving the efficiency of determining the admixture amount of the remediation agent, significantly reducing the deviation between the admixture amount of the remediation agent and the actual amount, solving the problem that in existing actual projects, the determination of the admixture amount of the remediation agent mostly relies on empirical formulas and lacks the support of a dosage - leaching toxicity quantitative model, resulting in insufficient remediation and resource waste in high - concentration pollution scenarios, improving the soil remediation effect and the utilization efficiency of the remediation agent, and also reducing and even avoiding secondary pollution problems such as soil or water eutrophication and decomposition of organic complexes caused by unreasonable admixture amounts.

[0019] 2. The repair agent of the present invention is composed of red mud, blast furnace slag and an alkali activator (sodium silicate and sodium hydroxide). Its solidification / stabilization mechanism is as follows: Under alkaline conditions, due to the rich content of silicate and alkaline components in red mud and blast furnace slag, geopolymers with a C-A-S-H gel network are generated through alkali activation reactions. This geopolymer takes silicon-aluminum tetrahedrons as basic units to form a zeolite-like structure with a three-dimensional network structure, which can not only physically encapsulate heavy metal ions in pores or lattices, but also stabilize heavy metals through chemical mechanisms such as ion exchange, complexation reactions and mineral phase formation, thus having a dual solidification mechanism of adsorption and mineral precipitation. Therefore, the repair agent of the present invention not only reduces the leaching toxicity of heavy metal-contaminated soil and realizes the repair of heavy metal-contaminated soil, but also overcomes the instability of the physical adsorption and fixation effect of existing repair agents, and the organic complexes formed by organic polymer materials are easily decomposed under the action of microorganisms, ultimately resulting in insufficient long-term stability after soil repair. It also avoids the problem of secondary pollution easily caused by chemical repair and organic polymer materials.

[0020] 3. The repair agent of the present invention composed of red mud, blast furnace slag and an alkali activator significantly reduces the risk of soil compaction compared with traditional cement-based materials (for example, the particle size of 200-mesh red mud and blast furnace slag improves the dispersibility), and the pH adjustment is milder (the natural alkalinity of red mud is lower than that of strong alkali curing agents), which is conducive to the restoration of soil ecological functions. Moreover, compared with the phosphate system, it avoids the risk of eutrophication and can significantly reduce the cost of the repair agent. It alleviates the problems of a large amount of industrial solid waste such as red mud and blast furnace slag occupying land and environmental pollution during stacking, realizes the resource utilization of industrial waste slag and reduces the cost of the repair agent.

[0021] 4. The target heavy metals of the present invention cover various common heavy metals such as copper, lead, cadmium, chromium, nickel, etc. It can not only quickly and accurately determine the dosage of the repair agent for single heavy metal-contaminated soil, but also, compared with the prior art that mostly focuses on the repair effect of single heavy metal pollution or under a fixed dosage of the repair agent, can be extended to complex scenarios of multiple heavy metal composite pollution in actual engineering.

[0022] In summary, the present invention has the characteristics of simple operation, high utilization efficiency of the repair agent, low repair cost and no secondary pollution. Description of the Drawings

[0023] Figure 1 is the flowchart of the method for determining the dosage of the repair agent for heavy metal-contaminated soil of the present invention; Figure 2 is the relationship diagram between different dosages of the repair agent and the toxicity leaching amount of 2000mg / kg Cu-contaminated soil in Example 1; Figure 3 is the relationship diagram between different dosages of the repair agent and the toxicity leaching amount of 4000mg / kg Cu-contaminated soil in Example 1; Figure 4 Relationship diagram between different dosages of the remediation agent and the toxicity leaching amount for Cu-contaminated soil at 6000 mg / kg in Example 1; Figure 5 Relationship diagram between different dosages of the remediation agent and the toxicity leaching amount for Cu-contaminated soil at 8000 mg / kg in Example 1; Figure 6 Relationship diagram between different dosages of the remediation agent and the toxicity leaching amount for Cu-contaminated soil at 10000 mg / kg in Example 1; Figure 7 Fitting diagram of different dosages of the remediation agent and the toxicity leaching amount for Cu-contaminated soil with different Cu concentrations in Example 1; Figure 8 Fitting diagram of Cu-contaminated soil with different Cu concentrations and different dosages of the remediation agent in Example 1; Figure 9 Relationship diagram between different dosages of the remediation agent and the toxicity leaching amount for Pb-contaminated soil at 500 mg / kg in Example 2; Figure 10 Relationship diagram between different dosages of the remediation agent and the toxicity leaching amount for Pb-contaminated soil at 4000 mg / kg in Example 2; Figure 11 Relationship diagram between different dosages of the remediation agent and the toxicity leaching amount for Pb-contaminated soil at 6000 mg / kg in Example 2; Figure 12 Relationship diagram between different dosages of the remediation agent and the toxicity leaching amount for Pb-contaminated soil at 8000 mg / kg in Example 2; Figure 13 Relationship diagram between different dosages of the remediation agent and the toxicity leaching amount for Pb-contaminated soil at 10000 mg / kg in Example 2; Figure 14 Fitting diagram of different dosages of the remediation agent and the toxicity leaching amount for Pb-contaminated soil with different Pb concentrations in Example 2; Figure 15 Fitting diagram of Pb-contaminated soil with different Pb concentrations and different dosages of the remediation agent in Example 2. Detailed implementation manners

[0024] The present invention will be further described below in conjunction with the accompanying drawings and examples, but the present invention is not limited in any way. Any changes or improvements made based on the teachings of the present invention fall within the protection scope of the present invention.

[0025] As Figure 1 shown, the method for determining the dosage of the remediation agent for heavy metal-contaminated soil of the present invention includes steps of contaminated soil preparation, remediation agent preparation, soil remediation, toxicity leaching, dosage fitting, and optimal dosage determination. The specific content of each step is as follows: A. Preparation of contaminated soil: Prepare target heavy metal - contaminated soil with different concentrations in gradients and passivate it to obtain heavy metal - contaminated soil with different heavy metal concentrations. B. Preparation of the repair agent: Mix red mud, blast furnace slag, and an alkali activator to obtain the repair agent. C. Soil remediation: Add different dosages of the aforementioned repair agent to the heavy metal - contaminated soil with different heavy metal concentrations respectively, mix them, and then solidify to obtain different treated repaired soils. D. Toxicity leaching: Measure the leaching amounts of the target heavy metals in the above - mentioned different repaired soils respectively to obtain the heavy metal leaching amounts corresponding to different repaired soils. E. Dosage fitting: Fit the leaching amounts of each heavy metal - contaminated soil with the same concentration under different dosages of the repair agent to obtain the optimal dosage of the repair agent for the heavy metal - contaminated soil at this concentration. Then, by analogy, obtain the optimal dosages of the repair agent for the heavy metal - contaminated soil with the remaining concentrations. F. Determination of the optimal dosage: Fit the optimal dosages of the repair agent for heavy metal - contaminated soil with different concentrations to obtain the functional relationship between the heavy metal concentration and the dosage of the repair agent for the target heavy metal - contaminated soil. Then, substitute the heavy metal concentration of the heavy metal - contaminated soil to be repaired into the aforementioned functional relationship to obtain the corresponding optimal dosage of the repair agent.

[0026] The target heavy metal - contaminated soil in step A is single - heavy - metal - contaminated soil, which is obtained by fully mixing an analytical - pure nitrate solution and soil in proportion and passivating for 15 days.

[0027] The nitrate is any one of copper nitrate, lead nitrate, cadmium nitrate, chromium nitrate, and nickel nitrate. The target heavy metal - contaminated soil needs to be prepared into soils with 4 - 10 different concentrations of the target heavy metal.

[0028] In step B, the mass ratio of red mud to blast furnace slag is 4:5 - 7, the mass ratio of the alkali activator to the sum of red mud and blast furnace slag is 1:4 - 6, and the alkali activator is water glass with a modulus of 1.5.

[0029] The alkali activator is prepared by adding NaOH to adjust the modulus of water glass to 1.5. Both the red mud and blast furnace slag have a particle size of 200 mesh, and the blast furnace slag is the waste slag discharged from the blast furnace during pig iron smelting.

[0030] In step B, the red mud, blast furnace slag, and alkali activator are mechanically stirred at a speed of 150 - 250 rpm for 5 - 8 minutes.

[0031] In step C, add different dosages of the repair agent to the heavy metal - contaminated soil with the same concentration respectively, mix them, and then solidify to obtain different treated repaired soils at this concentration. Then, by analogy, obtain the corresponding repaired soils after treatment with the remaining concentrations. Among them, the solidification time is 28 days.

[0032] In step B, different dosages of a remediation agent are added to each heavy metal - contaminated soil, and mechanical stirring is carried out at a speed of 300 - 500 rpm for 8 - 12 min.

[0033] In step D, the toxicity characteristic leaching procedure (TCLP) is adopted to measure the leachable amount of heavy metals in heavy metal - contaminated soils with different heavy metal concentrations after 28 - day remediation at different dosages of the remediation agent.

[0034] In step E, first, according to the leachable amount of heavy metals, a scatter plot of the leachable amount of heavy metals - remediation agent dosage is drawn for heavy metal - contaminated soils with each heavy metal concentration at different dosages of the remediation agent. Then, each scatter plot is fitted. Next, the function with the highest fitting degree is selected. Subsequently, the intersection point of the fitting curve of the aforementioned function and the leaching toxicity identification standard value (obtained according to GB 5085.3 - 2007 "Identification Standard for Hazardous Wastes - Identification for Leaching Toxicity") is found, and the abscissa of the aforementioned intersection point is used as the optimal dosage of the remediation agent for heavy metal - contaminated soils with this heavy metal concentration.

[0035] In step F, first, a scatter plot of the optimal dosage of the remediation agent - heavy metal concentration is drawn for heavy metal - contaminated soils with different heavy metal concentrations, and then the scatter plot is fitted to obtain the functional relationship between different heavy metal concentrations of heavy metal - contaminated soils and the optimal dosage of the remediation agent.

[0036] In step F, first, the concentration of the target heavy metal in the pre - remediated heavy metal - contaminated soil is measured, and then the measured concentration of the target heavy metal is substituted into the aforementioned corresponding functional relationship to obtain the corresponding optimal dosage of the remediation agent.

[0037] Example 1 A study is carried out on the relationship between the heavy metal concentration and the optimal dosage of the remediation agent in Cu - contaminated soil by using a remediation agent composed of red mud, blast furnace slag and an alkali activator.

[0038] S100: 2% copper nitrate solution (analytical pure) and standard soil are used to prepare 500 g of Cu - contaminated soil with concentrations of 2000 mg / kg, 4000 mg / kg, 6000 mg / kg, 8000 mg / kg, and 10000 mg / kg respectively, and then passivated for 15 d (passivated for 15 days according to the specification "ISO11268 (1993)" to stabilize heavy metals in the soil), obtaining 5 kinds of Cu - contaminated soil with different concentrations.

[0039] S200: First, crush and grind the red mud and blast furnace slag in Table 1 respectively and sieve them through a 200-mesh sieve. Then, fully mix the sieved red mud, blast furnace slag and alkali activator to obtain a repair agent. The mass ratio of red mud to blast furnace slag is 4:6, and the mass ratio of alkali activator to the sum of red mud and blast furnace slag is 1:5. The alkali activator is prepared by adding NaOH to water glass to adjust the modulus to 1.5.

[0040] Table 1 Components of Red Mud and Blast Furnace Slag

[0041] S300: Divide each of the purified Cu-contaminated soils at the aforementioned 5 concentrations into 5 equal parts, and respectively incorporate 0, 5%, 10%, 15% and 20% of the aforementioned repair agent and mix them. Then, let them stand and solidify for 28 days to obtain 25 portions of different repaired soils.

[0042] S400: Adopt the Toxicity Characteristic Leaching Procedure (TCLP) to respectively measure the Cu ion leaching amounts of the above 25 portions of different repaired soils, and obtain the Cu ion leaching amounts corresponding to the different repaired soils. S500: First, draw a scatter plot of the Cu-contaminated soil at a concentration of 2000 mg / kg with different dosages of the repair agent, and use Origin software for fitting. Select the function with the highest fitting degree, find the intersection point of the fitting curve and the Cu leaching toxicity identification standard value, and take the abscissa of this intersection point as the optimal dosage of the repair agent for the Cu-contaminated soil at a concentration of 2000 mg / kg. Then, by analogy as described above, respectively find the optimal dosages of the repair agent for the Cu-contaminated soils at concentrations of 4000 mg / kg, 6000 mg / kg, 8000 mg / kg and 10000 mg / kg (as Figures 2 to 7 shown).

[0043] S600: Fit the optimal dosages of the repair agent for the Cu-contaminated soils at 2000 mg / kg, 4000 mg / kg, 6000 mg / kg, 8000 mg / kg and 10000 mg / kg to obtain the functional relationship between the Cu ion concentration of the Cu-contaminated soil and the dosage of the repair agent (as Figure 8 shown). Then, in actual engineering applications, first analyze the Cu ion concentration of the pre-repaired Cu-contaminated soil, and then substitute the obtained Cu ion concentration into the aforementioned functional relationship to obtain the corresponding optimal dosage of the repair agent.

[0044] It should be noted that in this embodiment, the dosage of the repair agent is the percentage of the mass of the repair agent in the mass of the heavy metal-contaminated soil. The positive effect of the repair agent dosage of 0-20% in this embodiment is that within this preset volume ratio range, it can effectively ensure that (AlO4) 5- and (SiO4) 4-, it reacts completely with Cu ions in the contaminated soil to ensure the formation of sufficient geopolymers. At the same time, it ensures that its three-dimensional network zeolite-like structure can encapsulate heavy metal ions in pores or lattices, and stabilize heavy metals through chemical mechanisms such as ion exchange, complexation reactions, and mineral phase formation.

[0045] It should be noted that the dosage of the repair agent in this embodiment is the percentage of the mass of the repair agent in the mass of the heavy metal contaminated soil. The positive effect of the repair agent dosage of 0-20% in this embodiment is that within this preset volume ratio range, it can effectively ensure that (AlO4) generated by red mud and blast furnace slag under the action of the alkali activator 5- and (SiO4) 4- , it reacts completely with Cu ions in the contaminated soil to ensure the formation of sufficient geopolymers. At the same time, it ensures that its three-dimensional network zeolite-like structure can encapsulate heavy metal ions in pores or lattices, and stabilize heavy metals through chemical mechanisms such as ion exchange, complexation reactions, and mineral phase formation.

[0046] Such as Figures 2 to 6 shown is a schematic diagram of the relationship between the Cu ion toxicity leaching amount of 5 kinds of Cu-contaminated soils with different dosages of the repair agent in this embodiment. From Figures 2 to 6 it can be seen that for the Cu-contaminated soil without adding the repair agent, as the initial concentration increases, the leaching amount (or leaching concentration) also increases, and increases regularly in a stepwise manner. For every additional 2000 mg / kg of Cu ion concentration, the leaching amount (or leaching concentration) increases by approximately 60 mg / L. After adding different dosages of the repair agent, under the action of the hydration reaction, the initial pollution concentration is no longer the only factor affecting the toxicity leaching, and the reduction amplitude of the toxicity leaching is significantly different. When the dosage of the repair agent exceeds 10%, the toxicity leaching of Cu ions tends to level off, indicating that the repair agent with a dosage of 10-20% is not efficient in solidifying Cu-contaminated soil and there is over-repair, and continued addition of the repair agent is more likely to cause secondary pollution.

[0047] Such as Figure 7 shown is the function fitting result of 5 kinds of Cu-contaminated soils with different dosages of the repair agent in this embodiment: as the dosage of the repair agent increases, the repair effect tends to be saturated, and there is a critical inflection point, indicating that the repair agent dosage has an S-shaped curve on the repair effect of Cu-contaminated soil. Therefore, the Boltzmann function model is used to fit the relationship between the repair agent dosage and the Cu ion toxicity leaching. The fitting results of Cu-contaminated soils with 2000 mg / kg, 4000 mg / kg, 6000 mg / kg, 8000 mg / kg, and 10000 mg / kg are shown in Table 2 (where x is the dosage of the repair agent, y is the toxicity leaching amount).

[0048] Table 2 Fitting results of Cu-contaminated soils with different concentrations

[0049] As Figure 8 shown, it is a graph of the variation of the optimal remediation admixture content of Cu-contaminated soil at 4 concentrations. It can be Figure 8 seen that for the intersection points of the concentration curves of 4000mg / kg, 6000mg / kg, 8000mg / kg, and 10000mg / kg with the Cu leaching toxicity identification standard value, using the three models of Boltzmann, ExpDec, and Logistic, the relationship between the optimal remediation admixture content and the Cu contamination concentration can be fitted as shown in Table 3 (where x is the remediation admixture content and Z is the heavy metal concentration): Table 3 Fitting results of the optimal remediation admixture content and its relationship with the Cu contamination concentration

[0050] According to the fitting results in Table 3, finally, the Logistic model is used to describe the relationship between the optimal remediation admixture content and the Cu-contaminated soil concentration as: .

[0051] Example 2

[0052] The relationship between the heavy metal concentration and the optimal remediation admixture content in Pb-contaminated soil is studied by using a remediation agent composed of red mud, blast furnace slag, and an alkali activator.

[0053] S100: 500g of Pb-contaminated soil with concentrations of 500mg / kg, 1000mg / kg, 1500mg / kg, 2000mg / kg, and 2500mg / kg are prepared by using a 2% lead nitrate solution (analytical pure) and standard soil, and then passivated for 15 days to obtain 5 kinds of Pb-contaminated soil with different concentrations.

[0054] S200: First, the red mud and blast furnace slag in Table 1 are respectively crushed, ground, and passed through a 200-mesh sieve, and then the sieved red mud, blast furnace slag, and alkali activator are fully mixed to obtain a remediation agent; the mass ratio of red mud to blast furnace slag is 4:6, and the mass ratio of the alkali activator to the sum of red mud and blast furnace slag is 1:5. The alkali activator is prepared by adding NaOH to water glass to adjust the modulus to 1.5.

[0055] S300: Each of the purified 5 kinds of Pb-contaminated soil with different concentrations is evenly divided into 5 parts, and the above-mentioned remediation agent is respectively incorporated at 0, 5%, 10%, 15%, and 20% and mixed, and then left to stand and solidify for 28 days to obtain 25 parts of treated different remediation soils.

[0056] S400: Adopt the Toxicity Characteristic Leaching Procedure (TCLP) to measure the Pb ion leaching amounts of the above-mentioned 25 different repaired soils respectively, and obtain the Pb ion leaching amounts corresponding to different repaired soils. S500: First, plot the scatter diagram of Pb-contaminated soil with a concentration of 500 mg / kg at different dosages of the repair agent, and use Origin software for fitting. Select the function with the highest fitting degree, find the intersection point of the fitting curve and the Pb leaching toxicity discrimination standard value, and take the abscissa of this intersection point as the optimal dosage of the repair agent for Pb-contaminated soil with a concentration of 500 mg / kg. Then, by analogy as described above, find the optimal dosages of the repair agent for Pb-contaminated soil with concentrations of 1000 mg / kg, 1500 mg / kg, 2000 mg / kg, and 2500 mg / kg respectively (as Figures 9 to 13 shown).

[0057] S600: Fit the optimal dosages of the repair agent for Pb-contaminated soil with concentrations of 500 mg / kg, 1000 mg / kg, 1500 mg / kg, 2000 mg / kg, and 2500 mg / kg to obtain the functional relationship between the Pb ion concentration and the dosage of the repair agent for Pb-contaminated soil (as Figure 15 shown). Then, in actual engineering applications, first analyze the Pb ion concentration of the pre-repaired Pb-contaminated soil, and then substitute the obtained Pb ion concentration into the above functional relationship to obtain the corresponding optimal dosage of the repair agent.

[0058] It should be noted that in this embodiment, the dosage of the repair agent is the percentage of the mass of the repair agent in the mass of the heavy metal-contaminated soil. The positive effect of the repair agent dosage in this embodiment being 0 - 20% is that within this preset volume ratio range, it can effectively ensure that (AlO4) 5- and (SiO4) 4- generated by red mud and blast furnace slag under the action of the alkali activator react completely with the Pb ions in the contaminated soil, ensure the generation of sufficient geopolymers, and at the same time ensure that its three-dimensional network zeolite-like structure can wrap the heavy metal ions in the pores or lattice, and stabilize the heavy metals through chemical mechanisms such as ion exchange, complexation reaction, and mineral phase formation at the same time.

[0059] As Figures 9 to 13 shown is the schematic diagram of the relationship between the Pb ion toxicity leaching amounts of 5 kinds of Pb-contaminated soils with different dosages of the repair agent in this embodiment. From Figures 9 to 13As shown, experimental data show a significant downward trend in toxic leaching concentrations from Pb-contaminated soils with increasing remediation agent dosage. This phenomenon suggests that the remediation agent plays a significant role in reducing the bioavailability of lead in soil. The most significant decrease in toxic leaching concentrations was observed within the remediation agent dosage range of 0 to 5%, indicating the highest remediation efficiency within this dosage range. This finding may point to optimal chemical reaction conditions, where soil pH regulation promotes the conversion of lead to a less soluble form, thereby reducing its environmental mobility and bioavailability. Furthermore, the geopolymer in the remediation agent adsorbs and co-precipitates lead in the soil (e.g., Al₂O₃, Fe₂O₃, and alkaline substances can precipitate Pb), further reducing its activity. When the remediation agent dosage increases to 5% to 20%, the rate of decrease in toxic leaching concentrations slows significantly, indicating a saturation trend in the remediation effect.

[0060] like Figure 14 The following table shows the function fitting results of the five concentrations of Pb contaminated soil in this example at different dosages of the remediation agent: As the dosage of the remediation agent increases, the remediation effect tends to saturation, and there is a critical inflection point, indicating that the remediation effect of the remediation agent dosage on the Pb contaminated soil is an S-shaped curve. Therefore, the Boltzmann function model is used to fit the relationship between the dosage of the remediation agent and the toxic leaching of Pb ions. The fitting results of the Pb contaminated soil at 500mg / kg, 1000mg / kg, 1500mg / kg, 2000mg / kg and 2500mg / kg are shown in Table 4 (Formula type x is the dosage of repair agent, y is the toxic leaching amount).

[0061] Table 4 Fitting results of soil contaminated with different concentrations of Pb

[0062] like Figure 15 The figure shows the change of the optimal remediation dosage of Pb contaminated soil at four concentrations. Figure 15 It can be seen that the intersection of the concentration curves of 1000mg / kg, 1500mg / kg, 2000mg / kg and 2500mg / kg with the Pb leaching toxicity identification standard value, using the Boltzmann, ExpDec and Logistic models, can fit the optimal dosage of the repair agent and its relationship with the Cu pollution concentration as shown in Table 5 (Formula x is the optimal dosage of the repair agent, Z is the heavy metal concentration): Table 5 Optimal dosage of remediation agent and its fitting results with Pb pollution concentration

[0063] According to the fitting results in Table 5, the Boltzmann model was finally adopted to describe the relationship between the optimal dosage of the repair agent and the concentration of Pb-contaminated soil as follows: 。

[0064] The experiments in this embodiment show that the dosage prediction based on the Boltzmann model significantly improves the repair efficiency of high-concentration Pb-contaminated soil (500 - 2500 mg / kg), and the leaching toxicity decreases by more than 90%.

[0065] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for determining the dosage of a remediation agent for heavy metal contaminated soil, characterized in that: It includes the steps of contaminated soil preparation, remediation agent preparation, soil remediation, toxicity leaching, dosage fitting, and optimal dosage determination. The specific contents of each step are as follows: A. Preparation of contaminated soil: Prepare target heavy metal contaminated soil with different concentrations according to a gradient and passivate it to obtain heavy metal contaminated soil with different heavy metal concentrations; B. Preparation of repair agent: red mud, blast furnace slag and alkali activator are mixed to obtain a repair agent; C. Soil remediation: adding different amounts of the aforementioned remediation agent to the aforementioned heavy metal contaminated soils with different heavy metal concentrations, mixing and curing, to obtain different treated remediation soils; D. Toxicity leaching: Measure the target heavy metal leaching amount of the above different remediation soils respectively to obtain the heavy metal leaching amount corresponding to the different remediation soils; E. Dosage Fitting: Fit the leaching amount of each heavy metal contaminated soil with the same concentration at different dosages of the remediation agent to obtain the optimal dosage of the remediation agent for the heavy metal contaminated soil at that concentration. Then, the optimal dosage of the remediation agent for the remaining concentrations of heavy metal contaminated soil can be obtained by analogy. F. Determination of the optimal dosage: Fit the optimal dosage of the remediation agent for heavy metal contaminated soils with different concentrations to obtain the functional relationship between the heavy metal concentration of the target heavy metal contaminated soil and the dosage of the remediation agent. Then, bring the heavy metal concentration of the pre-remediation heavy metal contaminated soil into the aforementioned functional relationship to obtain the corresponding optimal dosage of the remediation agent.

2. The method for determining the dosage of the heavy metal contaminated soil remediation agent according to claim 1, characterized in that: The target heavy metal contaminated soil in step A is single heavy metal contaminated soil, which is obtained by fully mixing analytically pure nitrate solution with soil in proportion and passivating for 15 days.

3. The method for determining the dosage of the remediation agent for heavy metal contaminated soil according to claim 2, wherein: The nitrate is any one of copper nitrate, lead nitrate, cadmium nitrate, chromium nitrate, and nickel nitrate. The target heavy metal contaminated soil needs to be prepared to contain 4 to 10 different concentrations of the target heavy metal.

4. The method for determining the dosage of the remediation agent for heavy metal contaminated soil according to claim 1, characterized in that: The mass ratio of red mud to blast furnace slag in step B is 4:5-7, the mass ratio of the alkali activator to the red mud and blast furnace slag is 1:4-6, and the alkali activator is water glass with a modulus of 1.

5.

5. The method for determining the dosage of the remediation agent for heavy metal contaminated soil according to claim 4, wherein: The alkaline activator is prepared by adding NaOH to adjust the modulus of water glass to 1.

5. The red mud and blast furnace slag both have a particle size of 200 meshes. The blast furnace slag is waste slag discharged from smelting pig iron in a blast furnace.

6. The method for determining the dosage of the remediation agent for heavy metal contaminated soil according to claim 1, wherein: In step C, different amounts of remediation agents are added to each heavy metal contaminated soil of the same concentration, mixed and solidified to obtain different remediation soils treated with this concentration; then, according to the above, corresponding remediation soils treated with other concentrations are obtained; wherein, the solidification time is 28 days.

7. The method for determining the dosage of the remediation agent for heavy metal contaminated soil according to claim 1, wherein: In the step D, a toxicity characteristic leaching method is used to determine the amount of heavy metals that can be leached from heavy metal-contaminated soils with different heavy metal concentrations at different dosages of the remediation agent after 28 days of remediation.

8. The method for determining the dosage of the remediation agent for heavy metal contaminated soil according to claim 1, characterized in that: In the step E, first, according to the mobile leaching amount of heavy metals, a scatter plot of the mobile leaching amount of heavy metals-the remediation agent dosage for heavy metal-contaminated soil of each heavy metal concentration at different dosages of the remediation agent is drawn, and then each scatter plot is fitted, and then the function with the highest fitting degree is selected, and then the intersection of the fitting curve of the aforementioned function and the leaching toxicity identification standard value is calculated, and the abscissa of the aforementioned intersection is used as the optimal dosage of the heavy metal-contaminated soil remediation agent for the heavy metal concentration.

9. The method for determining the dosage of the remediation agent for heavy metal contaminated soil according to any one of claims 1 to 8, characterized in that: In the step F, first draw a scatter plot of the optimal dosage of the remediation agent corresponding to heavy metal - contaminated soils with different heavy metal concentrations, and then fit the scatter plot to obtain the functional relationship between different heavy metal concentrations and the optimal dosage of the remediation agent in the heavy metal - contaminated soil.

10. The method for determining the dosage of the heavy metal contaminated soil remediation agent according to claim 9, characterized in that: In the step F, first measure the target heavy metal concentration in the pre - remediated heavy metal - contaminated soil, and then substitute the measured target heavy metal concentration into the aforementioned corresponding functional relationship to obtain the corresponding optimal dosage of the remediation agent.

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