Hexavalent chromium reduction-elution repair method based on micro-nano iron-based material and application

Abstract

The invention relates to a hexavalent chromium reduction-elution repair method based on a micro-nano iron-based material and application. According to the method, reduction stabilization treatment is conducted through a reduction material, elution treatment is conducted through elution water, and reduction stabilization treatment and elution treatment cooperate to complete hexavalent chromium removal; the method is applied to removal of hexavalent chromium in soil. According to the method, effective reaction removal of hexavalent chromium in the soil is achieved, the content of manganese oxide and hydrogen peroxide in the original soil is reduced to a certain extent in the treatment process, and the concentration of hexavalent chromium in the repaired soil can be kept at a low level for a long period; the exposure time of the micro-nano iron-based material in the air is shortened, the effectiveness of the reduction material in the reaction is guaranteed, the concentration of pollutants in a three-stage discharge mud cake is effectively reduced, and the treatment amount of the mud cake is reduced; the reaction effectiveness is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of restoration of contaminated soil, and in particular to a hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials and application thereof. Background Art

[0002] There are many chromium chemical companies with wide distribution. As an important chemical raw material, chromium salts are widely used in electroplating, mining, leather making, metal processing and manufacturing, cement, textiles, dye production, wood preservation and other industries. Due to the extensive production in the early years and the poor management of the corresponding raw materials, emissions or wastes, a large amount of chromium has entered the environment, resulting in potential ecological risks in the overall environment. Therefore, the remediation and risk control of chromium-contaminated soil are key issues that need to be solved urgently.

[0003] Chromium in soil exists mainly in two forms: Cr(III) and Cr(VI). Most of Cr(III) exists in the soil environment in a stable form, with relatively low risk, while Cr(VI) is highly toxic, easily mobile, and bioavailable, with greater risk. The main approach to controlling chromium pollution risks is to reduce highly toxic and easily mobile Cr(VI) into low-toxic and easily stable precipitated Cr(III), or to directly remove Cr from the soil.

[0004] Among the existing technologies, the most commonly used remediation technologies for chromium-contaminated sites are chemical reduction technology and leaching technology. However, due to the influence of manganese oxides, hydrogen peroxide and other substances in the soil, the Cr(VI) concentration in the soil after chemical reduction remediation usually rebounds, which to a certain extent limits the promotion and application of this technology. The leaching technology is used alone for the remediation of Cr(VI)-contaminated soil, but there are problems such as the soil is difficult to meet the standards after remediation and needs further reduction and stabilization disposal.

[0005] Therefore, developing a remediation process that can effectively repair hexavalent chromium-contaminated soil and maintain stable concentrations after remediation is an urgent need for chromium pollution risk remediation and control. Summary of the invention

[0006] The present invention solves the problems existing in the prior art and provides a hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials and its application.

[0007] The technical solution adopted by the present invention is a hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials. The method uses reducing materials for reduction and stabilization treatment and uses elution water for elution treatment. The reduction and stabilization treatment and the elution treatment work together to complete the removal of hexavalent chromium.

[0008] Preferably, the method comprises the following steps: S1 collects samples from the area to be repaired and analyzes them to obtain repair data; S2 excavates the area to be repaired and pre-processes the excavated materials; S3 homogenizes and mixes the treated material to be repaired, the reducing material and water; S4 performs reduction-elution co-processing to achieve remediation.

[0009] Preferably, in S1, the remediation data includes the total amount, leaching and occurrence form of the target heavy metal factor.

[0010] Preferably, in S2, the pretreatment includes crushing and screening the excavated material, and homogenizing the screened material to be repaired.

[0011] Preferably, in S3, the reducing material, water and the material to be repaired are added to the stirring and feeding unit, the mass ratio of water to the material to be repaired is 2~5:1, and the amount of reducing material added is 0.1~5% of the mass of the material to be repaired; the stirring and feeding unit is equipped with a spiral mixer; the large-size contaminated soil blocks are broken by the mixing and pushing of the stirring blades, and the reducing material, soil and water are fully homogenized and mixed.

[0012] Preferably, the reduced material is a micro-nano iron-based material prepared by primary reduced iron powder, sodium silicate, pyrite, ferrous sulfate and water ball milling.

[0013] Preferably, in S4, the reduction-elution co-treatment comprises the following steps: S4.1 Through the friction and scrubbing action of the mud disintegrator, the materials to be repaired and the reduced materials are further homogenized, and the aggregates with an outer diameter greater than D1 are separated within time T1; S4.2 Soak the remaining material after separation in S4.1, and separate the material with an outer diameter greater than D2 within time T2, D2<D1; S4.3 Add flocculant to the screened rinse water of S4.2 and separate for time T3, and filter the precipitated material into a mud cake through a plate and frame filter press.

[0014] Preferably, in S4, the eluate is tested, the eluate is processed based on the test result, and the eluate is recycled as washing water.

[0015] Preferably, samples are collected from the effluent after S4 treatment to detect and analyze the total amount, leaching and occurrence form of the target heavy metal factors, and the remediation methods and optimization are evaluated based on the results, including but not limited to: The dosage of reducing materials is designed based on the total amount of hexavalent chromium in the soil and the reduction and removal capacity of micro-nano iron-based materials for hexavalent chromium (mg / g); Based on the occurrence of hexavalent chromium in the soil in extractable, reducible, oxidizable and residual states, the reaction pH is adjusted by adding citric acid and the like to promote the reduction effect of micro-nano iron-based materials on hexavalent chromium.

[0016] An application of the hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials is applied to the removal of hexavalent chromium in soil.

[0017] The invention relates to a hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials and an application thereof. The method uses a reducing material for reduction stabilization treatment and uses elution water for elution treatment. The reduction stabilization treatment and the elution treatment cooperate to complete the removal of hexavalent chromium. The method is applied to the removal of hexavalent chromium in soil.

[0018] The beneficial effects of the present invention are: (1) Based on the characteristics of small particle size, large specific surface area and strong reducing ability of micro-nano iron-based materials, combined with the efficient reduction-synchronous elution process that can achieve strong mixing of soil and reaction materials, the effective reaction and removal of hexavalent chromium in the soil is achieved. At the same time, the content of manganese oxides and hydrogen peroxide in the original soil is reduced to a certain extent during the treatment process, which is conducive to maintaining the hexavalent chromium concentration in the repaired soil at a low level for a long period of time; (2) Use the micro-nano iron-based material storage tank directly as the preparation tank for the micro-nano iron-based fluid material to reduce the exposure time of the micro-nano iron-based material in the air and ensure the effectiveness of the reducing material in the reaction; (3) Compared with conventional reducing agents, the application of micro-nano iron-based materials can effectively reduce the concentration of pollutants in the tertiary discharge mud cake and reduce the amount of mud cake treatment and disposal.

[0019] (4) The spiral stirring in the feeding stage initially achieves the homogenization of the soil and the reducing material, and then the homogenization of the reaction materials is further achieved through friction and scrubbing in the reduction-elution stage, which greatly improves the effectiveness of the reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the method of the present invention. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below in conjunction with embodiments, but the protection scope of the present invention is not limited thereto.

[0022] The invention relates to a hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials. The method uses a reducing material for reduction stabilization treatment and uses elution water for elution treatment. The reduction stabilization treatment and the elution treatment cooperate to complete the removal of hexavalent chromium.

[0023] The following is a specific implementation description combined with the steps. It should be noted that based on the application of this method to the removal of hexavalent chromium in soil, the following description is focused on soil remediation treatment.

[0024] S1 collects samples from the area to be repaired and analyzes them to obtain repair data; In S1, the remediation data include the total amount, leaching and occurrence forms of the target heavy metal factors.

[0025] In the present invention, soil samples are collected from the site to be disposed of, and the total amount, leaching and occurrence forms of risk heavy metal factors in the soil are analyzed to provide support for the design of process parameters such as the proportion of reducing material addition; Among them, the analysis of heavy metal occurrence forms mainly analyzes the proportion of weak acid extractable state, reducible state, oxidizable state and residual state of heavy metals.

[0026] S2 excavates the area to be repaired and pre-processes the excavated materials; In S2, the pretreatment includes crushing and screening the excavated materials, and homogenizing the screened materials to be repaired.

[0027] In the present invention, the polluted area to be repaired is excavated, and the excavated soil is crushed and screened using an ALLU sieve to pre-treat it, and construction waste, stones, etc. with a particle size greater than 100 mm after crushing are removed, and the remaining soil is homogenized to facilitate subsequent treatment and disposal.

[0028] S3 homogenizes and mixes the treated material to be repaired, the reducing material and water; In S3, the reducing material, water and the material to be repaired are added to the stirring and feeding unit, the mass ratio of water to the material to be repaired is 2-5:1, and the amount of reducing material added is 0.1-5% of the mass of the material to be repaired; the stirring and feeding unit is equipped with a spiral mixer.

[0029] The reducing material is a micro-nano iron-based material prepared by primary reduced iron powder, sodium silicate, pyrite, ferrous sulfate and water ball milling; the configuration concentration is 2-15%.

[0030] In the present invention, the reducing material is added to the stirring and feeding unit in the form of a fluid. The stirring and feeding unit is provided with a spiral mixer, which can break up the large-size contaminated soil blocks and fully homogenize and mix the iron base, soil blocks and water.

[0031] In the present invention, specifically: The reducing material is prepared by ball milling process with primary reduced iron powder, sodium silicate, pyrite, ferrous sulfate and water in a certain proportion to obtain a micro-nano iron-based material with a D50 of about 300 nm. The reducing material is modified by oxygen-containing acid radicals to avoid oxidation and inactivation of the material in contact with oxygen and water in the environmental medium, thereby ensuring the long-term effectiveness of its repair application; the micro-nano iron-based material is added in the form of a fluid, and the concentration of the solution is preferably 5-10%; in order to reduce the exposure time of the micro-nano iron-based material in the air, a storage barrel of the micro-nano iron-based material is used as a preparation unit, and a vertical mechanical mixer is set at the opening of the barrel to achieve full mixing of the micro-nano iron-based material and water. The mixer is always in working state during the dosing period to avoid the sinking of the iron-based material during the output of the iron solution; The amount of micro-nano iron-based materials added is 0.5-2% of the mass of the contaminated soil; The amount of leaching water added is 3 to 4 times the mass of the contaminated soil, and comes from tap water or circulating water treated by water treatment facilities.

[0032] S4 performs reduction-elution co-processing to achieve remediation.

[0033] In S4, the reduction-elution co-treatment comprises the following steps: S4.1 Scrub mixing and primary separation; The materials to be repaired and the reducing materials are mixed evenly (further homogenized) and reduced in a mud dispersing machine (cylindrical soil scrubber) by lifting, rubbing, throwing, etc., and the aggregates with an outer diameter greater than D1 are separated within time T1; D1 is 2 mm here, which is used to separate aggregates larger than 2 mm, and T1 is 5-8 minutes; S4.2 Immersion separation and secondary separation; Soak the remaining material (fine aggregate) after separation in S4.1 to further separate the mud on the fine aggregate, and separate the material with an outer diameter greater than D2 within time T2, D2<D1; here D2 is 0.15mm, which is used to separate materials greater than 0.15 mm, and T2 is 7~10min; S4.3 Separation by precipitation and concentration by filtration; PAM flocculant is added to the sieved rinsing water of S4.2 to promote the precipitation and separation of free complexes in the water body, and the separation time is T3, where T3 is 20~25min, and the precipitated material is filtered into a mud cake through a plate and frame filter press.

[0034] In S4, the eluate is tested, the eluate is processed based on the test result, and the eluate is recycled as rinse water.

[0035] Samples are collected from the effluent after S4 treatment to detect and analyze the total amount, leaching and occurrence form of target heavy metal factors, and the remediation method and optimization are evaluated based on the results.

[0036] In the present invention, the eluent is treated by processes including but not limited to oxidation-reduction, flocculation precipitation, and high-efficiency adsorption.

[0037] The present invention also relates to an application of the hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials, which is applied to the removal of hexavalent chromium in soil.

[0038] The following are specific embodiments of the present invention: Under the condition of the same amount of micro-nano iron-based material added, conventional reaction processes such as reactors and reaction pools were used as comparative examples to compare the homogenization effect and the removal effect of hexavalent chromium in the soil with the present invention; The uniformity of the total iron content in the mixed soil was analyzed by XRF instrument, and the sufficiency of the mixing of micro-nano iron-based materials and soil in each process was analyzed; the removal effect of hexavalent chromium in the soil by each process was analyzed by analyzing the content of hexavalent chromium in the treated soil; The coefficient of variation of the iron content in the soil after the mixing treatment of the reactor process using the ALLu sieve for mechanical dry mixing and stirring is 22.3%; the coefficient of variation of the iron content in the soil after the mixing treatment of the reactor process using the excavator for mechanical wet mixing is 22.7%; the coefficient of variation of the iron content in the soil after the treatment using the process of the present invention is 12.6%, and the adequacy of mixing is better than that of the reactor and the reaction pool; The hexavalent chromium concentration of the soil treated by the reactor process decreased with the increase of time after the reaction. The removal rate of hexavalent chromium increased from 30.6% to 59.5% from 1d to 220d after the reaction. The hexavalent chromium concentration could not meet the screening value of Class II land use in GB36600-2018. The hexavalent chromium concentration of the soil treated by the reaction pool process decreased with the increase of time after the reaction. The removal rate of hexavalent chromium increased from 20.2% to 84.6% from 1d to 220d after the reaction. The hexavalent chromium concentration could not meet the screening value of Class II land use in GB36600-2018. -2018 Class II land use screening value; the soil treated by the process of the present invention can achieve a rapid decrease in the concentration of hexavalent chromium in the soil after a reaction of about 36 minutes, with a removal rate of >98.4%, and the hexavalent chromium concentrations of the second and third level discharges reach the screening value of Class II land use in GB36600-2018, and the hexavalent chromium leaching of the first level discharge is not detected; the soil test results 90 days after the reaction show that the hexavalent chromium concentrations of the second and third level discharges still reach the screening value of Class II land use in GB36600-2018, and the hexavalent chromium leaching of the first level discharge is not detected.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials, characterized in that: The method uses a reducing material for reduction stabilization treatment and uses elution water for elution treatment. The reduction stabilization treatment and the elution treatment cooperate to complete the removal of hexavalent chromium.

2. A hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials according to claim 1, characterized in that: The method comprises the following steps: S1 collects samples from the area to be repaired and analyzes them to obtain repair data; S2 excavates the area to be repaired and pre-processes the excavated materials; S3 homogenizes and mixes the treated material to be repaired, the reducing material and water; S4 performs reduction-elution co-processing to achieve remediation.

3. A hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials according to claim 2, characterized in that: In S1, the remediation data include the total amount, leaching and occurrence forms of the target heavy metal factors.

4. A hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials according to claim 2, characterized in that: In S2, the pretreatment includes crushing and screening the excavated materials, and homogenizing the screened materials to be repaired.

5. A hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials according to claim 2, characterized in that: In S3, the reducing material, water and the material to be repaired are added to the stirring and feeding unit, the mass ratio of water to the material to be repaired is 2-5:1, and the amount of reducing material added is 0.1-5% of the mass of the material to be repaired; the stirring and feeding unit is equipped with a spiral mixer.

6. A hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials according to claim 5, characterized in that: The reducing material is a micro-nano iron-based material prepared by primary reduced iron powder, sodium silicate, pyrite, ferrous sulfate and water ball milling.

7. A hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials according to claim 2, characterized in that: In S4, the reduction-elution co-treatment comprises the following steps: S4.1 Through the friction and scrubbing action of the mud disintegrator, the materials to be repaired and the reduced materials are further homogenized, and the aggregates with an outer diameter greater than D1 are separated within time T1; S4.2 Soak the remaining material after separation in S4.1, and separate the material with an outer diameter greater than D2 within time T2, D2<D1; S4.3 Add flocculant to the screened rinse water of S4.2 and separate for time T3, and filter the precipitated material into a mud cake through a plate and frame filter press.

8. The hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials according to claim 2, characterized in that: In S4, the eluate is tested, the eluate is processed based on the test result, and the eluate is recycled as rinse water.

9. The hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials according to claim 2, characterized in that: Samples are collected from the effluent after S4 treatment to detect and analyze the total amount, leaching and occurrence form of target heavy metal factors, and the remediation method and optimization are evaluated based on the results.

10. An application of the hexavalent chromium reduction-elution repair method based on micro-nano iron-based materials according to any one of claims 1 to 9, characterized in that: Applied to the removal of hexavalent chromium in soil.

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