Hexavalent chromium polluted soil curing agent and preparation method thereof, and road subgrade filler and preparation method thereof

Abstract

The invention discloses a hexavalent chromium polluted soil curing agent and a preparation method thereof, and a road subgrade filler and a preparation method thereof, and belongs to the technical field of environmental geotechnical engineering materials. The hexavalent chromium polluted soil curing agent provided by the invention is prepared from the following raw materials in parts by weight: 20-40 parts of an alkali-activated component, 40-60 parts of a gelling-reducing component, 5-15 parts of cation exchange resin and 5-15 parts of an early strength component, wherein the alkali-activated component is selected from one or more of red mud, carbide slag or alkaline residue; the gelling-reducing component is selected from one or two of blast furnace slag or steel slag; the early strength component is selected from one or more of phosphogypsum or desulfurized gypsum. The hexavalent chromium polluted soil curing agent disclosed by the invention has good gelling property, reducibility and self-alkali excitation property, has relatively high curing efficiency and reduces the leaching toxicity of chromium, and the preparation method and the application method are simple to operate and short in treatment period.

Description

Technical Field

[0001] The invention relates to the technical field of environmental geotechnical engineering materials, and in particular to a hexavalent chromium contaminated soil solidifying agent and a preparation method and application thereof. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance the understanding of the overall background of the invention and should not be necessarily regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Chromium and its compounds are essential raw materials for industries such as metallurgy, electroplating, leather making, and printing and dyeing. Therefore, while chromium is widely used, it also causes a lot of soil pollution. Chromium exists in the soil mainly in the form of hexavalent chromium and trivalent chromium. Hexavalent chromium has extremely strong mobility and toxicity and is one of the internationally recognized carcinogens. Therefore, the treatment of hexavalent chromium-contaminated soil is imminent.

[0004] At present, the main treatment technologies for hexavalent chromium contaminated soil include solidification / stabilization method, leaching method, electric remediation method, etc., among which the solidification / stabilization method is widely used. This technology first reduces the hexavalent chromium in the soil to trivalent chromium through a reducing agent, and then adds cement, alkali-activated blast furnace slag and other cementitious materials to reduce the mobility of pollutants through solidification and adsorption, thereby forming a risk control for hexavalent chromium contaminated sites. However, the solidification / stabilization method still has disadvantages: the step-by-step addition of reducing agents and curing agents is relatively cumbersome, and the disposal cycle and remediation effect are difficult to control; the prices of reducing agents and alkali activators are high, which increases the cost of controlling contaminated sites; cement production consumes a large amount of non-renewable resources such as limestone and coal, and the emission of carbon dioxide exacerbates the greenhouse effect; for some contaminated sites that need to replace fill, the treatment method of contaminated soil is mainly landfill, which occupies a large amount of land. Current research shows that using it as roadbed fill after solidification and stabilization is a new method of resource utilization. The patent with the authorization announcement number CN108160684B discloses a combined repair method for chromium-contaminated soil, which adds a reducing agent, an adsorbent and a curing agent to the chromium-contaminated soil in sequence. Although it can achieve a good repair effect, the repair period is long and the repair method is cumbersome, making it difficult to apply in actual engineering. The patent with the authorization announcement number CN105499262B discloses a method for stabilizing and repairing alkaline chromium-contaminated soil, which uses calcium polysulfide and activated magnesium oxide as reducing agents and alkaline activators, has high costs and cannot be applied on a large scale. Therefore, it is an urgent problem to develop a green, low-carbon hexavalent chromium-contaminated soil curing agent based on simultaneous reduction-curing and enable it to be used to solidify hexavalent chromium-contaminated soil to prepare road subgrade fillers. Summary of the invention

[0005] In view of this, the present invention provides a hexavalent chromium contaminated soil solidifier and a preparation method and application thereof. The hexavalent chromium contaminated soil solidifier provided by the present invention is mainly composed of industrial solid waste, and not only has good gelling properties, but also has reducing and self-alkali excitation properties. It can reduce highly toxic hexavalent chromium to low-toxic trivalent chromium without using external reducing agents and alkali exciters, and solidify / stabilize chromium to reduce the leaching toxicity of chromium. It can be used to solidify hexavalent chromium contaminated soil to prepare road subgrade fillers, which can improve the resource utilization rate of industrial solid waste, reduce the amount of traditional cement used, and reduce costs and carbon emissions.

[0006] In a first aspect, the present invention provides a hexavalent chromium contaminated soil solidifying agent, which is prepared from the following raw materials in parts by weight:

[0007] 20-40 parts of alkali-activated component, 40-60 parts of gelling-reducing component, 5-15 parts of cation exchange resin and 5-15 parts of early strength component;

[0008] Among them, the alkali-activated component is selected from one or more of red mud, carbide slag or alkali slag; the gelling-reducing component is selected from one or two of blast furnace slag or steel slag; the early strength component is selected from one or more of phosphogypsum or desulfurized gypsum.

[0009] In a second aspect, the present invention provides a method for preparing the above-mentioned hexavalent chromium contaminated soil solidifying agent, comprising the following steps:

[0010] Drying and sieving the alkali-activated component, the gelling-reducing component, the cation exchange resin and the early-strengthening component;

[0011] The dried and sieved alkali-activated component, gelling-reducing component, cation exchange resin and early strength component are mixed in proportion, and then dry-mixed and stirred to obtain a dry mixed powder curing agent;

[0012] The dry mixed powder curing agent is ball-milled to obtain the hexavalent chromium contaminated soil curing agent.

[0013] In a third aspect, the present invention provides a road subgrade filler prepared from the following raw materials in parts by weight: 100 parts of hexavalent chromium-contaminated soil and 6 to 15 parts of the above-mentioned hexavalent chromium-contaminated soil curing agent.

[0014] In a fourth aspect, the present invention provides a method for preparing the above-mentioned roadbed filler, comprising the following steps:

[0015] S1. Dry the hexavalent chromium contaminated soil, add the hexavalent chromium contaminated soil curing agent in proportion, and dry-mix and stir to obtain a mixture;

[0016] S2. Conducting an indoor compaction test on the mixture to determine the optimum moisture content;

[0017] S3, adding water to the mixture of step S1 to an optimum moisture content, and mixing evenly to obtain.

[0018] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0019] (1) The hexavalent chromium contaminated soil solidifier provided by the present invention is mainly composed of industrial solid waste, is low in cost and environmentally friendly, and is a green hexavalent chromium contaminated soil solidifier; it not only has good gelling properties, but also has reducing and self-alkali excitation properties. The alkali excitation component can activate the active silica-alumina raw material, and the ferrous iron and low-valent sulfide in the gelling-reducing component can reduce the hexavalent chromium in the hexavalent chromium contaminated soil to low-toxic trivalent chromium. At the same time, under the action of the cation exchange resin, the trivalent chromium is captured, which helps to improve the curing efficiency of the curing agent and reduce the leaching toxicity of chromium.

[0020] (2) The preparation method of the hexavalent chromium contaminated soil solidifying agent provided by the present invention is simple, and the obtained hexavalent chromium contaminated soil solidifying agent can effectively solidify hexavalent chromium contaminated soil. Compared with the step of adding the reducing agent and the curing agent step by step in the traditional solidification / stabilization treatment, the treatment efficiency is greatly improved, the treatment cycle is shortened, and it can also improve the resource utilization rate of industrial solid waste, reduce the amount of traditional cement used, and reduce costs and carbon emissions. DETAILED DESCRIPTION

[0021] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0022] The present invention provides a hexavalent chromium contaminated soil solidifying agent, which is prepared from the following raw materials in parts by weight:

[0023] 20-40 parts of alkali-activated component, 40-60 parts of gelling-reducing component, 5-15 parts of cation exchange resin and 5-15 parts of early strength component;

[0024] Among them, the alkali-activated component is selected from one or more of red mud, carbide slag or alkali slag; the gelling-reducing component is selected from one or two of blast furnace slag or steel slag; the early strength component is selected from one or more of phosphogypsum or desulfurized gypsum.

[0025] In the present invention, the alkali-excited component has strong alkalinity, and after being mixed with the gelling-reducing component, it can provide an alkaline environment, accelerate the breaking of Si-O bonds and Al-O bonds in the gelling / reducing component, and promote the formation of hydrated gel; the gelling-reducing component contains reducing substances such as ferrous iron and low-valent sulfide, which play a continuous reducing role while the hydration reaction occurs, and can reduce the highly toxic hexavalent chromium to less toxic trivalent chromium. The trivalent chromium generates insoluble and stable Cr(OH)3, Ca2Cr(OH)7·3H2O precipitation and other substances in an alkaline environment. The gel produced by hydration can fill the pores of the soil, enhance the density of the soil, wrap the chromium ions, and reduce their mobility; wherein the active exchange groups in the cation exchange resin and Na + When in contact with trivalent chromium, trivalent chromium and Na + Ion exchange occurs, thereby capturing trivalent chromium, Na + It is released into the solution, thereby helping to improve the curing efficiency of the curing agent. After the early strength component comes into contact with water, it can react to form calcium vanadium, which can fill the soil pores and provide strength in the early stage of hydration of the cementitious material. Most of the above materials are industrial solid waste and are green environmentally low-impact materials.

[0026] In the present invention, the hexavalent chromium contaminated soil solidifying agent further comprises an adsorption component, and the adsorption component is selected from one or both of zeolite and activated carbon. The adsorption component can reduce the mobility of chromium ions by physical adsorption, and further assist in the solidification and stabilization of chromium. In the present invention, the cation exchange resin is further preferably 5 to 10 parts, and the adsorption component is preferably 2 to 6 parts.

[0027] In the present invention, the cation exchange resin is preferably an amino group-containing cation exchange resin.

[0028] The present invention also provides a method for preparing the above-mentioned hexavalent chromium contaminated soil solidifying agent, comprising the following steps:

[0029] Drying and sieving the alkali-activated component, the gelling-reducing component, the cation exchange resin and the early-strengthening component;

[0030] The dried and sieved alkali-activated component, gelling-reducing component, cation exchange resin and early strength component are mixed in proportion, and then dry-mixed and stirred to obtain a dry mixed powder curing agent;

[0031] The dry mixed powder curing agent is ball-milled to obtain the hexavalent chromium contaminated soil curing agent.

[0032] In the present invention, in the drying step, the drying temperature is 40-80° C. The present invention does not impose any special restrictions on the drying time, as long as the moisture content of each material after drying is less than 1%. In the screening step, the size of the sieve hole is 100 mesh or more, more preferably 200 mesh.

[0033] In the present invention, the dry mixing time is 10 to 60 minutes. The present invention does not impose any special restrictions on the equipment and rotation speed of the dry mixing, as long as the materials can be mixed evenly.

[0034] In the present invention, the ball milling adopts dry ball milling, and the ball milling time is 10 to 60 minutes. The present invention does not impose any special restrictions on the ball milling equipment, that is, the ball milling parameters, etc., as long as the specific surface area of ​​the material after ball milling can reach 400m 2 / kg or more, more preferably 400 to 500 m 2 / kg.

[0035] The present invention also provides a roadbed filler, which is prepared from the following raw materials in parts by weight: 100 parts of hexavalent chromium-contaminated soil and 6 to 15 parts of the above-mentioned hexavalent chromium-contaminated soil curing agent.

[0036] The present invention also provides a method for preparing the roadbed filler, comprising the following steps:

[0037] S1. Dry the hexavalent chromium contaminated soil, add the hexavalent chromium contaminated soil curing agent in proportion, and dry-mix and stir to obtain a mixture;

[0038] S2. Conducting an indoor compaction test on the mixture to determine the optimum moisture content;

[0039] S3, adding water to the mixture of step S1 to an optimum moisture content, and mixing evenly to obtain.

[0040] The dry mixing time in step S1 of the present invention is preferably 10 to 60 minutes.

[0041] The present invention does not impose any special restrictions on the specific method for determining the optimal moisture content according to the indoor compaction test. Those skilled in the art can implement it according to conventional means. The compaction test refers to the standard "Highway Geotechnical Test Code" (JTG 3430-2020).

[0042] The technical solution of the present invention is further described below in conjunction with specific embodiments. In the following embodiments, the cation exchange resin is an amino-containing cation exchange resin. The parts involved in the following embodiments are all parts by weight.

[0043] Example 1

[0044] This embodiment provides a method for preparing a hexavalent chromium contaminated soil solidifying agent.

[0045] Carbide slag, blast furnace slag, cation exchange resin and desulfurized gypsum were dried at 60°C for 15 hours, then ground and sieved with a sieve size of 200 mesh. 30 parts of sieved carbide slag, 50 parts of blast furnace slag, 10 parts of cation exchange resin and 10 parts of desulfurized gypsum were added to a mixer and dry mixed for 20 minutes to obtain a mixed powder curing agent. The mixed powder curing agent was then added to a planetary ball mill and dry milled for 30 minutes to finally obtain a hexavalent chromium contaminated soil curing agent with a specific surface area of ​​450m 2 / kg.

[0046] Example 2

[0047] This embodiment provides a method for preparing a hexavalent chromium contaminated soil solidifying agent.

[0048] Carbide slag, blast furnace slag, cation exchange resin and phosphogypsum were dried at 60°C for 15 hours, then ground and sieved with a sieve size of 200 mesh. 30 parts of sieved carbide slag, 50 parts of blast furnace slag, 10 parts of cation exchange resin and 10 parts of phosphogypsum were added to a mixer and dry-mixed for 20 minutes to obtain a mixed powder curing agent. The mixed powder curing agent was then added to a planetary ball mill and dry-milled for 30 minutes to finally obtain a hexavalent chromium contaminated soil curing agent with a specific surface area of ​​420m 2 / kg.

[0049] Example 3

[0050] This embodiment provides a method for preparing a hexavalent chromium contaminated soil solidifying agent.

[0051] Carbide slag, blast furnace slag, cation exchange resin and desulfurized gypsum were dried at 60°C for 15 hours, then ground and sieved with a sieve size of 200 mesh. 30 parts of sieved carbide slag, 50 parts of blast furnace slag, 6 parts of cation exchange resin, 4 parts of zeolite and 10 parts of desulfurized gypsum were added to a mixer and dry mixed for 20 minutes to obtain a mixed powder curing agent. The mixed powder curing agent was then added to a planetary ball mill and dry milled for 30 minutes to finally obtain a hexavalent chromium contaminated soil curing agent with a specific surface area of ​​440m 2 / kg.

[0052] Example 4

[0053] This embodiment provides a method for preparing a hexavalent chromium contaminated soil solidifying agent.

[0054] Carbide slag, blast furnace slag, cation exchange resin and phosphogypsum were dried at 60°C for 15 hours, then ground and sieved with a sieve size of 200 mesh. 30 parts of sieved carbide slag, 50 parts of blast furnace slag, 6 parts of cation exchange resin, 4 parts of activated carbon and 10 parts of phosphogypsum were added to a mixer and dry mixed for 20 minutes to obtain a mixed powder curing agent. The mixed powder curing agent was then added to a planetary ball mill and dry milled for 30 minutes to finally obtain a hexavalent chromium contaminated soil curing agent with a specific surface area of ​​470m 2 / kg.

[0055] Comparative Example 1

[0056] The difference between this comparative example and Example 1 is that this comparative example does not contain a cation exchange resin.

[0057] Comparative Example 2

[0058] The difference between this comparative example and Example 1 is that in this comparative example, 10 parts of the cation exchange resin are replaced by 10 parts of zeolite.

[0059] Comparative Example 3

[0060] The difference between this comparative example and Example 2 is that in this comparative example, 10 parts of cation exchange resin are replaced by 10 parts of activated carbon.

[0061] Comparative Example 4

[0062] The hexavalent chromium contaminated soil solidifying agent of this comparative example is 42.5 grade silicate cement.

[0063] Test example

[0064] 1. Determination of hexavalent chromium contaminated soil parameters:

[0065] The surface soil around an abandoned tannery in Shandong Province was selected as the test soil. The soil sample was buried at a depth of about 0.1-0.5m. The test soil was yellow-brown in color. Its moisture content was 17%, its liquid limit was 35%, and its plastic limit was 13%. It was dried in a 60℃ forced air dryer and crushed to pass through a 2mm sieve.

[0066] The total amount and leaching toxicity of heavy metals in the contaminated soil were tested in accordance with the "Determination of Metal Elements in Solid Waste by Inductively Coupled Plasma Mass Spectrometry" (HJ 766-2015), "Determination of Hexavalent Chromium in Solid Waste by Alkaline Digestion / Flame Atomic Absorption Spectrophotometry" (HJ 687-2014) and "Solid Waste Leaching Toxicity Leaching Method Sulfuric Acid and Nitric Acid Method" (HJ / T 299-2007). The total amount and leaching concentration of total chromium and hexavalent chromium in the contaminated soil are shown in Table 1, among which the leaching concentration of hexavalent chromium exceeds the standard value of Class III water (≤0.05mg / L) and Class IV water (≤0.10mg / L) specified in the "Identification Standard for Hazardous Waste Leaching Toxicity Identification" (GB 5085.3-2007) and the "Groundwater Quality Standard" (GB / T14848-2017).

[0067] Table 1 Summary of determination parameters of hexavalent chromium contaminated soil

[0068]

[0069] 2. Solidification experiment of hexavalent chromium contaminated soil:

[0070] A specific number of portions of the hexavalent chromium-contaminated soil curing agent of Examples 1 to 4 and Comparative Examples 1 to 4 were dry-mixed with 100 portions of the above hexavalent chromium-contaminated soil and stirred for 20 minutes to obtain a mixture, and then the optimal moisture content was determined through an indoor compaction test. Water was added to the mixture to the optimal moisture content, and after mixing evenly, a cured soil specimen was prepared according to a compaction degree of 98%. After curing for 28 days, the unconfined compressive strength, total chromium and hexavalent chromium leaching concentrations, and CBR value (California bearing ratio) were tested. The curing experimental conditions and test results are summarized in Table 2.

[0071] Table 2 Solidification experimental conditions and test results of hexavalent chromium contaminated soil

[0072]

[0073]

[0074] It can be seen from Table 2 that the 28d unconfined compressive strength and CBR value of the soil after being cured by the hexavalent chromium curing agent meet the relevant requirements of the "Highway Roadbed Construction Specification" (JTG / T3610-2019); the total chromium and hexavalent chromium leaching toxicity of the cured soil are significantly reduced, meeting the relevant requirements of the "Hazardous Waste Identification Standard Leaching Toxicity Identification" (GB 5085.3-2007). The soil after being cured by the hexavalent chromium curing agent of the embodiment has a hexavalent chromium leaching concentration of less than 0.2 mg / L, and the lowest can be as low as less than 0.05 mg / L, which can meet the Class III water standard in the "Groundwater Quality Standard" (GB / T14848-2017), and can be used as road subgrade filler.

[0075] The higher the proportion of hexavalent chromium curing agent, the better the curing effect on chromium. It can be seen from Table 2 that when the cation exchange resin is not contained, even if the curing agent reaches 10 parts, it cannot meet the Class IV water standard (i.e. ≤0.1 mg / L) in the "Groundwater Quality Standard" (GB / T 14848-2017). The cation exchange resin used in the above embodiment uses amino (-NH2, basic group) as the active exchange group, first with Na + When in contact with the reduced trivalent chromium, the trivalent chromium and Na + Ion exchange occurs, trivalent chromium is captured, and Na + The ion exchange mechanism is as follows:

[0076] Resin-NH2-Na +

[0077] 3Resin-NH2-Na + +Cr 3+ →(Resin-NH2)3-Cr 3+ +3Na + .

[0079] It can also be seen from Table 2 that Examples 3 and 4 containing both cation exchange resin and zeolite or activated carbon have lower hexavalent chromium leaching concentrations than Examples 1 and 2 containing only cation exchange resin. When cement is used as the hexavalent chromium curing agent (Comparative Example 4), it is difficult to effectively fix the hexavalent chromium and cannot be used in road subgrade materials.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. 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 contaminated soil solidifying agent, characterized in that: It is prepared from the following raw materials in parts by weight: 20-40 parts of alkali-activated component, 40-60 parts of gelling-reducing component, 5-15 parts of cation exchange resin and 5-15 parts of early strength component; Among them, the alkali-activated component is selected from one or more of red mud, carbide slag or alkali slag; the gelling-reducing component is selected from one or two of blast furnace slag or steel slag; the early strength component is selected from one or more of phosphogypsum or desulfurized gypsum.

2. The hexavalent chromium contaminated soil solidifying agent according to claim 1, characterized in that: The hexavalent chromium contaminated soil solidifying agent also includes an adsorption component, and the adsorption component is selected from one or both of zeolite and activated carbon.

3. The hexavalent chromium contaminated soil solidifying agent according to claim 2, characterized in that: The cation exchange resin is 5 to 10 parts, and the adsorption component is 2 to 6 parts.

4. The hexavalent chromium contaminated soil solidifying agent according to claim 1, characterized in that: The cation exchange resin is an amino-containing cation exchange resin.

5. The method for preparing the hexavalent chromium contaminated soil solidifying agent according to any one of claims 1 to 4, characterized in that: The steps include: Drying and sieving the alkali-activated component, the gelling-reducing component, the cation exchange resin and the early-strengthening component; The dried and sieved alkali-activated component, gelling-reducing component, cation exchange resin and early strength component are mixed in proportion, and then dry-mixed and stirred to obtain a dry mixed powder curing agent; The dry mixed powder curing agent is ball-milled to obtain the hexavalent chromium contaminated soil curing agent.

6. The preparation method according to claim 5, characterized in that: In the drying step, the drying temperature is 40-80° C.; in the screening step, the size of the sieve hole is greater than 100 meshes.

7. The preparation method according to claim 5, characterized in that: The dry mixing and stirring time is 10 to 60 minutes.

8. The preparation method according to claim 5, characterized in that: The ball milling adopts dry ball milling, and the ball milling time is 10 to 60 minutes.

9. A roadbed filler, characterized in that: The invention is prepared from the following raw materials in parts by weight: 100 parts of hexavalent chromium contaminated soil and 6 to 15 parts of the above hexavalent chromium contaminated soil curing agent.

10. The method for preparing a road subgrade filler according to claim 9, characterized in that: The steps include: S1. Dry the hexavalent chromium contaminated soil, add the hexavalent chromium contaminated soil curing agent in proportion, and dry-mix and stir to obtain a mixture; S2. Conducting an indoor compaction test on the mixture to determine the optimum moisture content; S3, adding water to the mixture of step S1 to an optimum moisture content, and mixing evenly to obtain.

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