Treatment method of hexavalent chromium polluted solid material and application thereof

Abstract

The invention discloses a treatment method of a hexavalent chromium polluted solid material and application of the treatment method, and belongs to the technical field of environmental engineering. The method provides a green and efficient microwave enhanced repairing scheme. The method comprises the following steps: fully mixing the hexavalent chromium polluted soil with a reducing material and a low-molecular-weight organic acid solution to form a to-be-repaired mixture; and then the mixed material is subjected to microwave irradiation treatment, and rapid and deep repairing is completed. Release of indissolvable hexavalent chromium is promoted through protonation and complexation of the organic acid, meanwhile, by means of the local hot spot effect generated on the surface of the wave-absorbing reduction material through microwaves, the selectivity and reducing capacity of the reduction material on hexavalent chromium are remarkably improved, cooperation of the microwaves, the organic acid and the reduction material is achieved, and the reduction effect of hexavalent chromium is improved. The method has the remarkable advantages of being high in remediation speed, good in reduction effect and the like, and is particularly suitable for treatment of high-concentration contaminated soil containing insoluble hexavalent chromium compounds and industrial waste residues.

Description

Technical Field

[0001] This invention belongs to the field of environmental engineering technology, specifically relating to a method for treating hexavalent chromium contaminated solids and its application. Background Technology

[0002] Hexavalent chromium, as a class of heavy metal pollutants with strong oxidizing properties, high mobility, and high toxicity, poses a serious threat to human health and the ecological environment. Its contaminated soils are mostly alkaline, with pH values ​​generally between 8 and 11, and sometimes exceeding 12, increasing the complexity of remediation. The difficulty in remediation stems not only from its toxicity but also from the complexity and high heterogeneity of its existence forms in the soil medium. Hexavalent chromium in soil typically coexists in two forms: soluble hexavalent chromium, in ionic or adsorbed form, which is easily migrated and released, and relatively easy to contact and be reduced by remediation agents; and insoluble hexavalent chromium, in compound or precipitated form, such as… and The formed calcium chromate may enter the lattice of the layered double hydroxide structure.

[0003] For soil, waste residue, or sludge heavily contaminated with hexavalent chromium, the content of this type of bound, stable, and difficult-to-release insoluble hexavalent chromium can be as high as 10. 2 -10 3 mg / kg, far exceeding conventional risk control standards. This constitutes a "contact barrier" in the remediation process, meaning that traditional agents have difficulty effectively contacting and reducing this portion of hexavalent chromium fixed by the mineral phase, resulting in incomplete remediation and a risk of secondary release when environmental conditions change (such as a decrease in pH).

[0004] However, existing wet chemical reduction technologies generally suffer from several drawbacks when treating heavily contaminated soil, waste residue, or sludge with high concentrations and multiple forms of hexavalent chromium (e.g., total hexavalent chromium concentration not less than 3000 mg / kg, and insoluble hexavalent chromium concentration not less than 100 mg / kg). These drawbacks include insufficient remediation agent efficacy, difficulty in completely overcoming the "contact barrier," complex process flow, and secondary pollution. Therefore, developing a new technology that can overcome these shortcomings and achieve green, efficient, deep, and stable remediation has become an urgent need in the field of environmental engineering. Summary of the Invention

[0005] To address the technical problems of insufficient remediation agent efficacy, difficulty in completely overcoming the "contact barrier," complex processes, and secondary pollution associated with commonly used technologies, this invention provides a method for treating hexavalent chromium-contaminated solid materials, comprising the following steps: Mix hexavalent chromium contaminated solid material, reducing agent, and accelerator to obtain the mixture to be remediated; The mixture to be repaired is treated with microwave irradiation to obtain a microwave repair product.

[0006] Furthermore, the mass-volume ratio of hexavalent chromium contaminated solid material, reducing agent, and co-solvent in the mixture to be repaired is 1g:(0.01-0.05)g:(0.5-10)ml.

[0007] Furthermore, the mass-volume ratio of hexavalent chromium contaminated solid, reducing agent, and co-solvent in the mixture to be repaired is 1g:(0.01-0.05)g:(0.5-5)ml.

[0008] Furthermore, when the proportion of water-soluble hexavalent chromium in the hexavalent chromium contaminated solid is less than 90% of the total hexavalent chromium, the solubilizing agent is an organic acid, and the organic acid includes one or more of citric acid, tartaric acid and oxalic acid, and the concentration of the organic acid is not higher than 0.5 mol / L; In the case where the proportion of water-soluble hexavalent chromium in the hexavalent chromium contaminated solid exceeds 90% of the total hexavalent chromium, the solvent includes water.

[0009] Furthermore, the reducing agent is one or more of acid-activated montmorillonite supported on zero-valent iron sulfide, zero-valent iron sulfide, or other reducing agents containing iron and sulfur and possessing microwave absorption properties.

[0010] Furthermore, during the microwave irradiation process, the microwave irradiation power is 0.28-0.56 kW, and the microwave time is 1-10 min.

[0011] Furthermore, it also includes: stabilizing the microwave repair product to obtain a cured product; The stabilization process includes landfilling.

[0012] Furthermore, the concentration of total hexavalent chromium in the hexavalent chromium contaminated solid material is not less than 1500 mg / kg, and the concentration of insoluble hexavalent chromium is not less than 100 mg / kg. The sources of the hexavalent chromium contaminated solid material include at least one of chromium salt industrial waste residue, electroplating chromium-containing sludge, and hexavalent chromium contaminated soil.

[0013] Furthermore, the leaching rate of hexavalent chromium is ≥99%, and the reduction rate of hexavalent chromium is ≥99%.

[0014] The present invention also provides an application of the treatment method for hexavalent chromium contaminated solids as described in any of the above claims in the remediation of hexavalent chromium contaminated soil.

[0015] Compared with the prior art, the present invention has at least the following advantages: This invention leverages the advantages of microwave remediation of hexavalent chromium contaminated solids, offering high efficiency and speed. Compared to traditional heating methods, microwaves generate heat instantaneously, significantly increasing the reaction temperature and accelerating the chemical reaction rate throughout the remediation process. Typically, microwave heating requires three orders of magnitude less time than traditional heating, solving the problems of slow reaction times and long cycles associated with traditional methods, thus enabling rapid treatment of hexavalent chromium contaminated soil.

[0016] In addition, microwaves not only heat the entire reaction system, but also generate local "hot spot effect" on the surface of the microwave-absorbing reducing material, thereby significantly improving the selectivity and reducing ability of the reducing material for hexavalent chromium, making the reduction reaction more efficient and complete.

[0017] The solubilizer in this invention has the following dual functions: when the solubilizer is an organic acid, on the one hand, the organic acid provides protons through dissociation to dissolve hexavalent chromium-containing minerals (such as hydrated calcium carbonate, calcium carbonate, etc.) in the soil, releasing the insoluble hexavalent chromium trapped within them; on the other hand, the carboxyl groups complex with the released calcium, aluminum, and other cations in the minerals, further disrupting the mineral structure and promoting the release of hexavalent chromium. In this way, even hexavalent chromium bound by the mineral lattice can be fully exposed, come into contact with reducing agents, and be reduced, thereby significantly improving the remediation effect.

[0018] Furthermore, it cannot be ignored that the protonation effect of organic acids is further enhanced under microwave irradiation, which not only promotes the complete release of the encapsulated insoluble hexavalent chromium, but also improves the electron transfer efficiency of the reducing material, thus significantly increasing the reduction rate of hexavalent chromium.

[0019] Microwaves, organic acids, and reducing agents work synergistically to form a "enhanced dissolution + deep reduction" linkage mechanism in the reaction system, thereby achieving the goal of deep remediation of hexavalent chromium contaminated soil.

[0020] Overall, this invention overcomes the technical bottleneck of slow release and reduction of insoluble hexavalent chromium by organically combining microwave and organic acid chemical functions, achieving rapid, deep, and efficient remediation. It provides a promising new technological path for the treatment of high-concentration, multi-form hexavalent chromium-contaminated soil, waste residue, or sludge. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0022] Figure 1The effect of organic acids on the dissolution of hexavalent chromium in soil with and without microwave treatment.

[0023] Figure 2 The effect of organic acid synergistic acid activation of montmorillonite-loaded sulfidated zero-valent iron on the reduction of hexavalent chromium in soil with and without microwave irradiation. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0026] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of the invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to the methods, devices, and materials in the embodiments of the present invention.

[0027] For soil, waste residue, or sludge contaminated with high concentrations of hexavalent chromium in multiple forms (for example, the total concentration of hexavalent chromium is not less than 3000 mg / kg, and the concentration of insoluble hexavalent chromium is not less than 100 mg / kg), the applicant previously attempted to use the same wet detoxification technology as for the treatment of hexavalent chromium-containing waste residue, namely, a combined treatment process using sulfuric acid and ferrous sulfate. Sulfuric acid can both promote the release of insoluble Cr(VI) and maintain the acidic environment required for the reduction of ferrous sulfate. However, this technical approach has revealed a series of insurmountable bottlenecks in engineering applications: The process involves huge reagent consumption and generates secondary solid waste: to completely release and reduce all forms of hexavalent chromium, an excess of acid and reducing agent far exceeding theoretical values ​​must be added. After the reaction is complete, a large amount of alkaline substances (such as lime) are needed to neutralize the treatment system. This process generates a large amount of chromium-containing gypsum and other precipitates, resulting in high treatment costs and the challenge of secondary solid waste disposal.

[0028] The remediation effect is difficult to achieve and its stability is questionable: Due to limitations in mass transfer efficiency and reaction kinetics, the dissolution and reduction of sparingly soluble hexavalent chromium are difficult to complete, and the remediated soil often fails to meet increasingly stringent soil environmental quality standards. Furthermore, the introduction of excessive sulfate leads to soil salinization, damaging its ecological functions and hindering its safe subsequent utilization.

[0029] The process is lengthy and carries potential risks of secondary pollution: It involves multiple units including acidification, reduction, neutralization, and dehydration, resulting in complex operation and management and a long treatment cycle. The entire process carries risks of secondary pollution, such as the release of acidic gases and the leaching of wastewater containing heavy metals.

[0030] To address the shortcomings of existing technologies, this invention provides a method for enhancing the release and reduction of insoluble Cr(VI) in contaminated soil using microwaves. This method combines the dual functions of organic acid protonation effects to dissolve Cr(VI)-containing minerals (such as hydrated calcium carbonate, calcium carbonate, etc.) and the formation of soluble complexes with carboxyl-coordinated cations (such as calcium, aluminum, etc.), with the microwave's "localized high-temperature effect" enhancing the reduction capacity of the microwave-absorbing reducing material for hexavalent chromium, thereby achieving rapid, deep, and efficient remediation of Cr(VI) contaminated soil.

[0031] It should be noted that in the technical solution of this invention, the dissolution rate of hexavalent chromium under different treatment conditions can accurately characterize the solubilizing effect of organic acids. When organic acids are used alone, the dissolution rate of hexavalent chromium in the system is significantly increased, due to two factors: first, the protonation effect dissolves insoluble hexavalent chromium-containing minerals; second, the organic acid anions form complexes with other cations released from the minerals. Both factors work together to promote the dissolution of insoluble hexavalent chromium-containing minerals (such as...). Dissolution and release of hexavalent chromium in layered double hydroxides.

[0032] Microwave irradiation, through the synergistic effect of thermal and non-thermal effects, further enhances the dissolution effect of organic acids on insoluble hexavalent chromium-containing minerals, specifically in three aspects: First, it promotes the dissolution of H+ in organic acids. + Dissociation, enhancing system H + Concentration provides a sufficient basis for the protonation reaction; secondly, it lowers the H+ concentration. + The activation energy of the dissolution of minerals and the complexation reaction of organic acid ions significantly increases the overall reaction rate and substantially enhances the dissolution kinetics of hexavalent chromium; thirdly, it promotes the combination of organic acid ions and mineral cations to form complexes with higher solubility, further reducing... It hinders the reaction with minerals and enhances the release of hexavalent chromium from minerals.

[0033] In the reduction of hexavalent chromium, the core promoting effect of microwaves lies in zero-valent iron sulfide (the reducing material). As a microwave absorbing material, zero-valent iron sulfide can selectively absorb microwave energy, forming a local hotspot effect on its surface. By enhancing the electron selectivity for hexavalent chromium, it strengthens its own reduction ability and achieves efficient conversion of dissolved hexavalent chromium.

[0034] Meanwhile, by comprehensively evaluating the reduction efficiency of hexavalent chromium (i.e., the total hexavalent chromium removal rate), the enhancement of the selectivity and reducing capacity of the reduction process by microwaves can be verified: Zero-valent iron sulfide, as a reducing material with wave absorption characteristics, can form a "local hotspot effect" on its surface under microwave irradiation, improving the electron selectivity and electron transfer for hexavalent chromium. This allows the reducing capacity to concentrate on the target pollutant without being significantly consumed by other side reactions (such as hydrogen evolution), thereby enhancing the reduction capacity for hexavalent chromium. This indicates that this method achieves a synergistic unity of "promoting solubility" and "specific and efficient reduction."

[0035] Specifically, this invention provides a method for treating hexavalent chromium-contaminated solid materials, comprising the following steps: S1. Mix the hexavalent chromium contaminated solid material, reducing agent, and accelerator to obtain the mixture to be remediated.

[0036] In this invention, the concentration of total hexavalent chromium in the hexavalent chromium-contaminated solid material is not less than 1500 mg / kg, and the concentration of insoluble hexavalent chromium is not less than 100 mg / kg, including but not limited to at least one of chromium salt industrial waste residue, electroplating chromium-containing sludge, and hexavalent chromium-contaminated soil.

[0037] In some embodiments, the concentration of total hexavalent chromium can be between 1500 mg / kg and 5000 mg / kg.

[0038] In some embodiments, the concentration of total hexavalent chromium in the hexavalent chromium contaminated solid material may be not less than 2000 mg / kg. For example, the concentration of total hexavalent chromium in the hexavalent chromium contaminated solid material may be 2000-5000 mg / kg, such as 2000-4000 mg / kg, 2000-5000 mg / kg, or 2000-3000 mg / kg.

[0039] In some embodiments, the concentration of total hexavalent chromium in the hexavalent chromium contaminated solid may be not less than 3000 mg / kg. For example, the concentration of total hexavalent chromium in the hexavalent chromium contaminated solid may be 3000-5000 mg / kg, such as 3000-4000 mg / kg or 3000-5000 mg / kg.

[0040] In some embodiments, the concentration of total hexavalent chromium in the hexavalent chromium contaminated solid may also be not less than 3500 mg / kg, such as 3500-4000 mg / kg or 3500-5000 mg / kg.

[0041] In some embodiments, the concentration of insoluble hexavalent chromium in the hexavalent chromium-contaminated solid material may be no less than 500 mg / kg, such as 500 mg / kg-3000 mg / kg, 500 mg / kg-3500 mg / kg, 500 mg / kg-4000 mg / kg, 500 mg / kg-2500 mg / kg, or 500 mg / kg-2000 mg / kg; for example, the concentration of insoluble hexavalent chromium in the hexavalent chromium-contaminated solid material may be no less than 1000 mg / kg, such as 1000 mg / kg-3000 mg / kg, 1000 mg / kg-3500 mg / kg, 1000 mg / kg-4000 mg / kg, 1000 mg / kg-2500 mg / kg, or 1000 mg / kg-2000 mg / kg; and for yet another example, the concentration of insoluble hexavalent chromium in the hexavalent chromium-contaminated solid material may be no less than 1500 mg / kg, such as 1500 mg / kg-3000 mg / kg, 500 mg / kg-3500 mg / kg, 500 mg / kg-4000 mg / kg, 1000 mg / kg-2500 mg / kg, or 1000 mg / kg-2000 mg / kg. mg / kg-3000 mg / kg or 1500 mg / kg-3500 mg / kg or 1500 mg / kg-4000 mg / kg or 1500 mg / kg-2500 mg / kg; and for example, the concentration of insoluble hexavalent chromium in the hexavalent chromium-contaminated solid material may also be not less than 2000 mg / kg, such as 2000 mg / kg-3000 mg / kg or 2000 mg / kg-3500 mg / kg or 2000 mg / kg-4000 mg / kg or 2000 mg / kg-2500 mg / kg; and for example, the concentration of insoluble hexavalent chromium in the hexavalent chromium-contaminated solid material may also be not less than 2500 mg / kg, such as 2500 mg / kg-3000 mg / kg or 2500 mg / kg-3500 mg / kg or 2500 mg / kg-4000 mg / kg.

[0042] In some embodiments, the mass-volume ratio of hexavalent chromium contaminated solid, reducing agent, and co-solvent in the mixture to be repaired is 1g:(0.01-0.05)g:(0.5-10)ml.

[0043] In some embodiments, the mass-volume ratio of hexavalent chromium contaminated solid, reducing agent, and co-solvent in the mixture to be repaired can also be 1g:(0.01-0.05)g:(0.5-5)ml.

[0044] In this invention, when the proportion of water-soluble hexavalent chromium in the hexavalent chromium contaminated solid material is less than 90% of the total hexavalent chromium, the co-solvent is an organic acid, and the organic acid includes one or more of citric acid, tartaric acid and oxalic acid, and the concentration of the organic acid is not higher than 0.5 mol / L. In the case where the proportion of water-soluble hexavalent chromium in the hexavalent chromium contaminated solid exceeds 90% of the total hexavalent chromium, the solvent includes water.

[0045] In this invention, the reducing agent is acid-activated montmorillonite supported on zero-valent iron sulfide, zero-valent iron sulfide, or other reducing agents containing iron and sulfur and possessing microwave absorption properties.

[0046] S2. The mixture to be repaired is treated with microwave irradiation to obtain a microwave repair product.

[0047] In this invention, during the microwave irradiation process, the microwave irradiation power is 0.28-0.56 kW, and the microwave time is 1-10 min.

[0048] S3. Stabilize the microwave repair product to obtain a cured product.

[0049] In this invention, the stabilization treatment includes landfilling.

[0050] In the method for treating hexavalent chromium contaminated solids provided by the present invention, the leaching rate of hexavalent chromium is ≥99%, and the reduction rate of hexavalent chromium is ≥99%.

[0051] The present invention also provides an application of the treatment method for hexavalent chromium contaminated solids as described in any of the above claims in the remediation of hexavalent chromium contaminated soil.

[0052] To facilitate a further understanding of the present invention by those skilled in the art, the following examples are provided: Example 1 S1. Weigh 10 g of naturally air-dried and sieved contaminated soil (total hexavalent chromium and water-soluble hexavalent chromium were measured to be 3828 mg / kg and 1225 mg / kg, respectively, so the proportion of water-soluble hexavalent chromium was 32%, and the proportion of sparingly soluble hexavalent chromium was 68%) into an Erlenmeyer flask. Then add 10 mL of 0.5 mol / L citric acid solution to the soil and stir well; then add 0.4 g of acid-activated montmorillonite-supported zero-valent iron sulfide composite material at 4% of the mass ratio of the contaminated soil, and continue stirring until well mixed to obtain the remediation mixture.

[0053] S2. The mixture to be repaired is placed in a microwave oven for microwave irradiation treatment to obtain a microwave repair product. The microwave power is set to 560 W and the microwave time is set to 10 min to obtain the microwave repair product.

[0054] Results verification: The microwave remediation products were subjected to alkaline digestion, and the concentration of hexavalent chromium was determined by spectrophotometry. Analysis showed that the residual hexavalent chromium content in the soil after remediation was 3.23 mg / kg, with a hexavalent chromium reduction efficiency exceeding 99%.

[0055] Example 2 S1. Weigh 10 g of naturally air-dried and sieved contaminated soil (total hexavalent chromium and water-soluble hexavalent chromium were measured to be 3828 mg / kg and 1225 mg / kg, respectively, so the proportion of water-soluble hexavalent chromium was 32%, and the proportion of sparingly soluble hexavalent chromium was 68%) into an Erlenmeyer flask. Then add 20 mL of 0.3 mol / L citric acid solution to the soil and stir well; then add 0.4 g of acid-activated montmorillonite-supported zero-valent iron sulfide composite material at 4% of the mass ratio of the contaminated soil, and continue stirring until the remediation mixture is obtained.

[0056] S2. The mixture to be repaired is placed in a microwave oven for microwave irradiation treatment to obtain a microwave repair product. The microwave power is set to 560 W and the microwave time is set to 10 min.

[0057] Results Verification: After the reaction was completed, the microwave remediation products were subjected to alkaline digestion, and the concentration of hexavalent chromium was determined by spectrophotometry. Analysis showed that the residual hexavalent chromium content in the soil after remediation was 2.85 mg / kg, with a hexavalent chromium reduction efficiency exceeding 99%.

[0058] Example 3 S1. Weigh 10 g of naturally air-dried and sieved contaminated soil (total hexavalent chromium and water-soluble hexavalent chromium were measured to be 3828 mg / kg and 1225 mg / kg, respectively, so the proportion of water-soluble hexavalent chromium was 32%, and the proportion of sparingly soluble hexavalent chromium was 68%) into an Erlenmeyer flask. Then add 20 mL of 0.4 mol / L citric acid solution to the soil and stir well; then add 0.4 g of acid-activated montmorillonite-supported zero-valent iron sulfide composite material at a mass ratio of 4% of reducing material to contaminated soil, and continue stirring until well mixed to obtain the remediation mixture.

[0059] S2. The mixture to be repaired is placed in a microwave oven for microwave irradiation treatment to obtain a microwave repair product. The microwave power is set to 560 W and the microwave time is set to 7 min.

[0060] Results Verification: After the reaction was completed, the microwave remediation products were subjected to alkaline digestion, and the concentration of hexavalent chromium was determined by spectrophotometry. Analysis showed that the residual hexavalent chromium content in the soil after remediation was 2.69 mg / kg, with a reduction efficiency of over 99%.

[0061] Example 4 S1. Weigh 10 g of naturally air-dried and sieved contaminated soil (total hexavalent chromium and water-soluble hexavalent chromium were measured to be 1809 mg / kg and 633 mg / kg, respectively, so the proportion of water-soluble hexavalent chromium was 35% and the proportion of sparingly soluble hexavalent chromium was 65%) into an Erlenmeyer flask. Then add 10 mL of 0.5 mol / L citric acid solution to the soil and stir well; then add 0.2 g of acid-activated montmorillonite-supported zero-valent iron sulfide composite material at 2% of the mass ratio of the contaminated soil, and continue stirring until well mixed to obtain the remediation mixture.

[0062] S2. Place the mixture to be repaired in a microwave oven for microwave irradiation treatment to obtain the microwave repair product. The microwave power is set to 420 W and the microwave time is set to 10 min.

[0063] Results Verification: After the reaction was completed, the microwave remediation products were subjected to alkaline digestion, and the concentration of hexavalent chromium was determined by spectrophotometry. Analysis showed that the residual hexavalent chromium content in the soil after remediation was 2.47 mg / kg, with a hexavalent chromium reduction efficiency exceeding 99%.

[0064] Example 5 S1. Weigh 10 g of naturally air-dried and sieved contaminated soil (total hexavalent chromium and water-soluble hexavalent chromium were measured to be 4995 mg / kg and 3321 mg / kg, respectively, so the proportion of water-soluble hexavalent chromium was 66% and the proportion of sparingly soluble hexavalent chromium was 34%) into an Erlenmeyer flask. Then add 10 mL of 0.4 mol / L citric acid solution to the soil and stir well; then add 0.5 g of acid-activated montmorillonite-supported zero-valent iron sulfide composite material at 5% of the mass ratio of the contaminated soil, and continue stirring until well mixed to obtain the remediation mixture.

[0065] S2. Place the mixture to be repaired in a microwave oven for microwave irradiation treatment to obtain the microwave repair product. The microwave power is set to 560W and the microwave time is set to 10min.

[0066] Results Verification: After the reaction was completed, the microwave remediation products were subjected to alkaline digestion, and the concentration of hexavalent chromium was determined by spectrophotometry. Analysis showed that the residual hexavalent chromium content in the soil after remediation was 3.82 mg / kg, with a reduction efficiency of over 99%.

[0067] Example 6 S1. Weigh 10 g of naturally air-dried and sieved contaminated soil (total hexavalent chromium and water-soluble hexavalent chromium were measured to be 3455 mg / kg and 3316 mg / kg, respectively, so the proportion of water-soluble hexavalent chromium was as high as 96%) into an Erlenmeyer flask. Then add 5 mL of deionized water without organic acids to the soil and stir well; then add 0.4 g of acid-activated montmorillonite-supported zero-valent iron sulfide composite material at 4% of the mass ratio of the contaminated soil, and continue to stir well to obtain the remediation mixture.

[0068] S2. Place the mixture to be repaired in a microwave oven for microwave irradiation treatment to obtain the microwave repair product. The microwave power is set to 280W and the microwave time is set to 5 minutes.

[0069] Results Verification: After the reaction was completed, the microwave remediation products were subjected to alkaline digestion, and the concentration of hexavalent chromium was determined by spectrophotometry. Analysis showed that the residual hexavalent chromium content in the soil after remediation was 2.56 mg / kg, with a hexavalent chromium reduction efficiency exceeding 99%.

[0070] Example 7 S1. Weigh 10 g of naturally air-dried and sieved contaminated soil (total hexavalent chromium and water-soluble hexavalent chromium were measured to be 4828 mg / kg and 4533 mg / kg, respectively, so the proportion of water-soluble hexavalent chromium was as high as 94%) into an Erlenmeyer flask. Then add 5 mL of deionized water without organic acids to the soil and stir well; then add 0.5 g of acid-activated montmorillonite-supported zero-valent iron sulfide composite material at 5% of the mass ratio of the contaminated soil, and continue to stir well to obtain the remediation mixture.

[0071] S2. The mixture to be repaired is then placed in a microwave oven for microwave irradiation treatment to obtain the microwave repair product. The microwave power is set to 420W and the microwave time is set to 5 minutes.

[0072] Results Verification: After the reaction was completed, the microwave remediation products were subjected to alkaline digestion, and the concentration of hexavalent chromium was determined by spectrophotometry. Analysis showed that the residual hexavalent chromium content in the soil after remediation was 3.16 mg / kg, with a reduction efficiency of over 99%.

[0073] Comparative Example 1 Compared to Example 1, all other conditions in this comparative example remain unchanged, except that the microwave irradiation treatment in step S2 is omitted, and the reaction time is set to the time required for the system to reach the reaction plateau at room temperature and pressure: S1. Weigh 10 g of naturally air-dried and sieved contaminated soil (total hexavalent chromium and water-soluble hexavalent chromium were measured to be 3828 mg / kg and 1225 mg / kg, respectively, so the proportion of water-soluble hexavalent chromium was 32%, and the proportion of sparingly soluble hexavalent chromium was 68%) into an Erlenmeyer flask. Then add 10 mL of 0.5 mol / L citric acid solution to the soil and stir well; then add 0.4 g of acid-activated montmorillonite-supported zero-valent iron sulfide composite material at 4% of the mass ratio of the contaminated soil, and continue stirring until well mixed to obtain the remediation mixture.

[0074] S2. The mixture to be repaired is allowed to react at room temperature (25±2℃), with manual shaking and stirring for 1 minute every 1 hour to ensure homogeneity of the system. The reaction continues until the chemical reduction plateau is reached (72 hours as determined by preliminary experiments). After the reaction is completed, samples are taken for subsequent testing.

[0075] Results Verification: The above-mentioned remediation products were subjected to alkaline digestion, and the concentration of hexavalent chromium was determined by spectrophotometry. Analysis showed that the residual hexavalent chromium content in the soil after remediation was 1106 mg / kg, and the hexavalent chromium reduction efficiency was 71.1%.

[0076] Comparative Example 2 Compared to Example 1, all other conditions in this comparative example remain unchanged, except that the addition of organic acid in step S1 is omitted, and an equal volume of deionized water is used instead of citric acid solution: S1. Weigh 10 g of naturally air-dried and sieved contaminated soil (total hexavalent chromium and water-soluble hexavalent chromium were measured to be 3828 mg / kg and 1225 mg / kg, respectively, so the proportion of water-soluble hexavalent chromium was 32%, and the proportion of sparingly soluble hexavalent chromium was 68%) into an Erlenmeyer flask. Then add 10 mL of water to the soil and stir well; then add 0.4 g of acid-activated montmorillonite-supported zero-valent iron sulfide composite material at 4% of the mass ratio of the contaminated soil, and continue to stir well to obtain the remediation mixture.

[0077] S2. The mixture to be repaired is placed in a microwave oven for microwave irradiation treatment to obtain a microwave repair product. The microwave power is set to 560 W and the microwave time is set to 10 min to obtain the microwave repair product.

[0078] Results Verification: The remediation products were subjected to alkaline digestion, and the concentration of hexavalent chromium was determined spectrophotometrically. Analysis showed that the residual hexavalent chromium content in the soil after remediation was 2593 mg / kg, with a hexavalent chromium reduction efficiency of 32.7%.

[0079] Comparative Example 3 Compared to Example 1, all other conditions in this comparative example remain unchanged, except that the microwave irradiation treatment in step S2 is replaced with conventional heating treatment, with a heating temperature of 90°C and a heating time of 2 hours. S1. Weigh 10 g of naturally air-dried and sieved contaminated soil (total hexavalent chromium and water-soluble hexavalent chromium were measured to be 3828 mg / kg and 1225 mg / kg, respectively, so the proportion of water-soluble hexavalent chromium was 32%, and the proportion of sparingly soluble hexavalent chromium was 68%) into an Erlenmeyer flask. Then add 10 mL of 0.5 mol / L citric acid solution to the soil and stir well; then add 0.4 g of acid-activated montmorillonite-supported zero-valent iron sulfide composite material at 4% of the mass ratio of the contaminated soil, and continue stirring until well mixed to obtain the remediation mixture.

[0080] S2. The mixture to be repaired is heated to obtain the repair product.

[0081] Results verification: The remediation products were subjected to alkaline digestion, and the concentration of hexavalent chromium was determined spectrophotometrically. Analysis showed that the residual hexavalent chromium content in the soil after remediation was 548 mg / kg, with a hexavalent chromium reduction efficiency of 85.7%.

[0082] Comparative Example 4 Compared to Example 1, all other conditions remain unchanged in this comparative example, except that the microwave power in step S2 is set to be greater than 560W, specifically 600W: S1. Weigh 10 g of naturally air-dried and sieved contaminated soil (total hexavalent chromium and water-soluble hexavalent chromium were measured to be 3828 mg / kg and 1225 mg / kg, respectively, so the proportion of water-soluble hexavalent chromium was 32%, and the proportion of sparingly soluble hexavalent chromium was 68%) into an Erlenmeyer flask. Then add 10 mL of 0.5 mol / L citric acid solution to the soil and stir well; then add 0.4 g of acid-activated montmorillonite-supported zero-valent iron sulfide composite material at 4% of the mass ratio of the contaminated soil, and continue stirring until well mixed to obtain the remediation mixture.

[0083] S2. The mixture to be repaired is placed in a microwave oven for microwave irradiation treatment to obtain a microwave repair product. The microwave power is set to 600 W and the microwave time is set to 10 min to obtain the microwave repair product.

[0084] Results Verification: The microwave remediation products were subjected to alkaline digestion, and the concentration of hexavalent chromium was determined spectrophotometrically. Analysis showed that the residual hexavalent chromium content in the soil after remediation was 306 mg / kg, with a hexavalent chromium reduction efficiency of 92%.

[0085] Comparative Example 5 In this comparative example, all other conditions remain the same, except that the citric acid solution in step S1 is replaced with a sulfuric acid solution of the same concentration: S1. Weigh 10 g of naturally air-dried and sieved contaminated soil (total hexavalent chromium and water-soluble hexavalent chromium were measured to be 3828 mg / kg and 1225 mg / kg, respectively, so the proportion of water-soluble hexavalent chromium was 32%, and the proportion of sparingly soluble hexavalent chromium was 68%) into an Erlenmeyer flask. Then add 15 mL of 0.5 mol / L sulfuric acid solution to the soil and stir well; then add 0.4 g of acid-activated montmorillonite-supported zero-valent iron sulfide composite material at 4% of the mass ratio of the contaminated soil, and continue stirring until well mixed to obtain the remediation mixture.

[0086] S2. The mixture to be repaired is placed in a microwave oven for microwave irradiation treatment to obtain a microwave repair product. The microwave power is set to 560 W and the microwave time is set to 10 min to obtain the microwave repair product.

[0087] Results Verification: The microwave remediation products were subjected to alkaline digestion, and the concentration of hexavalent chromium was determined spectrophotometrically. Analysis showed that the residual hexavalent chromium content in the soil after remediation was 1286 mg / kg, with a hexavalent chromium reduction efficiency of 66.4%.

[0088] Analysis example 1 like Figure 1 As shown, the concentration of water-soluble hexavalent chromium in 10 g of naturally air-dried and sieved 20-mesh soil was 1225 mg / kg, with a hexavalent chromium leaching rate of 32.3%. 10 mL of 0.5 mol / L citric acid solution was added to the contaminated soil and stirred until homogeneous to obtain an acid-soluble system. The concentration of water-soluble hexavalent chromium in this acid-soluble system was 2703 mg / kg, with a hexavalent chromium leaching rate of 70.6%. The acid-soluble system was then placed in the microwave oven used in step S2 of Example 1 for microwave irradiation treatment. The microwave power was set to 560 W, and the microwave time was set to 10 min, resulting in a microwave irradiation system. The concentration of water-soluble hexavalent chromium in this microwave irradiation system was 3825 mg / kg, with a hexavalent chromium leaching rate of 99.9%.

[0089] like Figure 2 As shown, in step S1 of this invention, 0.4 g of acid-activated montmorillonite-supported sulfide zero-valent iron composite material was added at a mass ratio of 4% to 10 g of naturally air-dried and sieved contaminated soil to obtain a reduction system. The residual Cr(VI) (i.e., total hexavalent chromium) content was measured to be 2564.76 mg / kg, and the hexavalent chromium reduction rate was 33%. The total hexavalent chromium content in the raw material to be remediated in step S1 was 1081 mg / kg, and the hexavalent chromium reduction rate was 71.8%. The total hexavalent chromium content in the microwave remediation product in step S2 was 3.23 mg / kg, and the hexavalent chromium reduction rate was 99.9%.

[0090] It should be noted that "control" in the figure refers to the control experimental group, "Citrate" refers to the experimental group containing organic acids, and "MW-Citrate" refers to the microwave + organic acid experimental group.

[0091] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for treating hexavalent chromium contaminated solid materials, characterized in that, Including the following steps: Mix hexavalent chromium contaminated solid material, reducing agent, and accelerator to obtain the mixture to be remediated; The mixture to be repaired is treated with microwave irradiation to obtain a microwave repair product.

2. The method for treating hexavalent chromium contaminated solids according to claim 1, characterized in that, In the mixture to be repaired, the mass-volume ratio of hexavalent chromium contaminated solid, reducing agent, and co-solvent is 1g:(0.01-0.05)g:(0.5-10)ml.

3. The method for treating hexavalent chromium contaminated solids according to claim 2, characterized in that, In the mixture to be repaired, the mass-volume ratio of hexavalent chromium contaminated solid, reducing agent, and co-solvent is 1g:(0.01-0.05)g:(0.5-5)ml.

4. The method for treating hexavalent chromium contaminated solids according to claim 1, characterized in that, In the case where the proportion of water-soluble hexavalent chromium in the hexavalent chromium contaminated solid material is less than 90% of the total hexavalent chromium, the co-solvent is an organic acid, and the organic acid includes one or more of citric acid, tartaric acid and oxalic acid, and the concentration of the organic acid is not higher than 0.5 mol / L; In the case where water-soluble hexavalent chromium accounts for more than 90% of the total hexavalent chromium in the hexavalent chromium contaminated solid material, the solvent includes water.

5. The method for treating hexavalent chromium contaminated solids according to claim 1, characterized in that, The reducing agent is one or more of the following: acid-activated montmorillonite supported on zero-valent iron sulfide, zero-valent iron sulfide, or other reducing agents containing iron and sulfur and possessing microwave absorption properties.

6. The method for treating hexavalent chromium contaminated solids according to claim 1, characterized in that, During the microwave irradiation process, the microwave irradiation power is 0.28-0.56 kW, and the microwave duration is 1-10 min.

7. The method for treating hexavalent chromium contaminated solids according to claim 1, characterized in that, Also includes: The microwave repair product is stabilized to obtain a cured product; The stabilization process includes landfilling.

8. The method for treating hexavalent chromium contaminated solids according to claim 1, characterized in that, The concentration of total hexavalent chromium in the hexavalent chromium contaminated solid material is not less than 1500 mg / kg, and the concentration of insoluble hexavalent chromium is not less than 100 mg / kg. The sources of the hexavalent chromium contaminated solid material include at least one of chromium salt industrial waste residue, electroplating chromium-containing sludge, and hexavalent chromium contaminated soil.

9. The method for treating hexavalent chromium contaminated solids according to claim 1, characterized in that, The leaching rate of hexavalent chromium is ≥99%, and the reduction rate of hexavalent chromium is ≥99%.

10. The application of a method for treating hexavalent chromium contaminated solids as described in any one of claims 1-9 in the remediation of hexavalent chromium contaminated soil.

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