A novel soil remediation agent and its preparation method and application

Abstract

The invention discloses a novel soil remediation agent and its preparation method and application, including the following raw materials by weight: 40-80 parts of activated carbon materials after regeneration, 14-70 parts of admixtures and 20-80 parts of sludge; wherein, each raw material is mixed and granulated, and carbonized under an inert gas environment, the temperature of the carbonization treatment is 200-800°C, and the treatment time is 1-2h; the sludge is non-hazardous waste sludge such as municipal sludge and papermaking sludge; the admixture is a mixture of one or more of tar, clay, asphalt, water glass, silica sol, sodium humate, CMC, polyethylene glycol, polyvinyl alcohol, phenolic resin, urea, polyphosphate sodium, P2O5, K2O, and nano-bentonite. It is prepared by the coordination of waste activated carbon and sludge, realizes the recycling of waste activated carbon materials and sludge materials, removes various heavy metal pollutants in the soil by adsorption and / or chemical reaction, and realizes the repair effect.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and in particular to a novel soil remediation agent and a preparation method and application thereof. Background Art

[0002] With the rapid growth of the national economy, the development of mineral resources has been accelerating, forming large areas of metal mines and abandoned land, and heavy metal pollution in the soil. In addition, with the optimization and layout adjustment of urban industrial structure, many enterprises or production and operation units have been relocated, and the original land use nature has been changed. Construction land and its surrounding areas have produced a certain degree of soil pollution. As the country attaches great importance to the construction of ecological civilization, the remediation of heavy metal contaminated soil is an unavoidable problem. Therefore, it is necessary to conduct in-depth research and strive to find the best solution.

[0003] In the existing technology, according to the principle of soil remediation, it can be divided into five types: physical, chemical, biological, electrical and thermal remediation. The specific methods are covering, encapsulation, landfill, soil flushing, electric extraction, stabilization / solidification, vitrification, phytoremediation and microbial remediation. These technologies have corresponding advantages and disadvantages and applicability. Covering, encapsulation and landfill are suitable for areas with serious pollution and small areas; soil flushing has a large amount of engineering work and requires chelating agents to be treated; electric extraction is suitable for shallow and low-concentration pollution sites and takes a long time to process; stabilization / solidification is widely used, but it cannot eradicate heavy metals from the soil; phytoremediation needs to improve efficiency. Therefore, suitable remediation technology and remediation agents are urgently needed for the reuse of heavy metal contaminated soil.

[0004] Most of the spent activated carbon after adsorption or decolorization in the chemical industry is treated as waste, which greatly increases the production cost. Many companies often do not seal the spent activated carbon for storage, which is naturally exposed to the air. The harmful substances adsorbed inside the activated carbon will be released again, causing secondary air pollution. If the storage conditions such as anti-seepage and anti-dispersion are not good, it is very easy to cause secondary pollution of water and soil, which greatly limits the application scale of activated carbon. In 2020, China's waste activated carbon production was more than 200,000 tons, and 70% of these activated carbons were incinerated or landfilled as waste. Therefore, the study of methods for the reuse or regeneration of waste activated carbon has attracted the attention of more and more scholars. The use of biomass waste materials to prepare activated carbon has become a research hotspot and has achieved relevant research results.

[0005] Patent CN107935784A discloses an activated carbon-based fertilizer soil remediation agent and a preparation method thereof, which is made of the following raw materials, calculated by the percentage of the total weight of the raw materials: 30-75% activated carbon powder, 0-40% humic acid, 20-30% wood vinegar, and 4-6% microbial agent. The activated carbon-based fertilizer soil remediation agent of this invention has the significant effects of repairing and improving soil, reducing environmental pollution, improving food safety, and increasing production and quality, but the microbial agent has high requirements for the environment and strict requirements for the pH of the soil itself, so the repair ability is limited.

[0006] Patent CN110304630B discloses a chicken manure / corn straw composite co-pyrolysis activated carbon soil remediation agent and its preparation method and application. The method comprises the following steps: (1) drying chicken manure and corn straw respectively, crushing and sieving to obtain chicken manure powder and corn straw powder; (2) mixing chicken manure powder and corn straw powder evenly, then adding a binder, heating and stirring evenly, granulating and drying to obtain composite spherical particles; (3) heating the composite spherical particles to 400-600°C for carbonization for 1-2h, then heating to 750-850°C and introducing water vapor for activation for 20-40min, and then cooling to room temperature to obtain a chicken manure / corn straw composite co-pyrolysis activated carbon soil remediation agent. The activated carbon soil remediation agent obtained by the invention has a high specific surface area and a rich pore structure, which is conducive to physical adsorption, but chicken manure as a raw material has high regional requirements and low yield. Summary of the invention

[0007] In order to solve the problems existing in the above background technology, the present invention provides a new soil remediation agent, which is prepared by the synergistic use of waste activated carbon and sludge, realizing the recycling of waste activated carbon materials and sludge materials, and removing various heavy metal pollutants in the soil through adsorption and / or chemical reaction to achieve the remediation effect. To this end, the present invention also provides a preparation method and application of the above new soil remediation agent.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] The first aspect of the present invention provides a novel soil remediation agent, comprising the following raw materials in parts by weight:

[0010] 40-80 parts of regenerated activated carbon material, 14-70 parts of admixture and 20-80 parts of sludge;

[0011] After the raw materials are mixed, they are carbonized in an inert gas environment at a temperature of 200-800° C. for 1-2 hours.

[0012] Through experiments and verification, the carbonization treatment temperature is preferably 400-800°C. As the carbonization temperature increases, the pyrolysis components of the carbon material increase, the pyrolysis of the additive is more complete, and the final material generates more pores.

[0013] Specifically, the sludge is non-hazardous waste sludge such as municipal sludge and papermaking sludge.

[0014] Specifically, the sludge is pretreated in advance, and the moisture content of the pretreated sludge is ≤10%, the particle size is ≥200 mesh, the dry basis organic matter content is 20-60wt%, the dry basis ash content is 30-75wt%, and the dry basis fixed carbon content is 2-15wt%.

[0015] Specifically, the sludge pretreatment process includes but is not limited to one of aerobic fermentation treatment, anaerobic digestion treatment, thermal drying treatment and low-temperature belt drying treatment.

[0016] Specifically, the regenerated activated carbon material is obtained by subjecting waste activated carbon to desulfurization and / or denitrification treatment and then regenerating it with high-temperature steam. The particle size of the regenerated activated carbon material after crushing is ≤200 meshes.

[0017] Specifically, the high-temperature steam regeneration temperature is 400-700°C, the regeneration time is 1-4h, and the water-to-carbon ratio is 0.5-2.

[0018] Through experiments, it is verified that although the high-temperature steam regeneration process has a certain ability to restore the porosity of the material, the porosity of the material mainly depends on the subsequent carbonization process. Therefore, in order to achieve energy-saving effects, the high-temperature steam regeneration temperature is preferably 400-500°C.

[0019] Specifically, the admixture is a mixture of one or more of tar, clay, asphalt, water glass, silica sol, sodium humate, CMC, polyethylene glycol, polyvinyl alcohol, phenolic resin, urea, polysodium phosphate, P2O5, K2O, and nano-bentonite.

[0020] The second aspect of the present invention provides a method for preparing the novel soil remediation agent, comprising the following steps:

[0021] S1. After the waste activated carbon is subjected to desulfurization and / or denitrification treatment, it is regenerated by high-temperature steam, crushed and sieved to obtain a powdered regenerated activated carbon material;

[0022] S2, the pretreated sludge is then dried, dehydrated, crushed and sieved to obtain powdered sludge;

[0023] S3, mixing the regenerated activated carbon material obtained in step S1, the sludge obtained in step S2 and the admixture in proportion to obtain a dry mixture, the dry mixing time being 5-15 minutes;

[0024] S4, adding water to the dry mixture obtained in step S3 and mixing evenly to obtain a wet mixture, the wet mixing time is 5-15 min, and the amount of water added is 10-30wt% of the total amount of the wet mixture;

[0025] S5. Granulate the wet mixture obtained in step S4 and place it in an inert gas environment for carbonization treatment. The temperature of the carbonization treatment is 200-800° C. and the reaction time is 1-2 hours to obtain a new soil remediation agent.

[0026] Preferably, the inert gas atmosphere is one or more of nitrogen, argon, and helium, preferably nitrogen. The flow rate of the inert gas during the carbonization treatment is 6-15 L / min.

[0027] Specifically, in step S5, the diameter of the mixed particles obtained after granulating the wet mixture is 8-10 mm and the length is 4-20 mm.

[0028] The novel soil remediation agent prepared by the above preparation method contains the following water, volatile matter, ash and fixed carbon in percentage by mass, as shown in Table 1.

[0029] Table 1 Ingredients and contents of new soil remediation agents

[0030] Moisture Ash Volatile Matter Fixed Carbon 2-5.6wt% 16-69wt% 6-44wt% 2-21wt%

[0031] The specific surface area of ​​the new soil remediation agent prepared by the above preparation method is 200-1000m 2 / g, pore size is 2.3-10.3nm. The iodine adsorption value of the new soil remediation agent is 400-800mg / g, and the methylene blue adsorption value is 120-200mg / g.

[0032] In this application, sludge materials, additives and regenerated activated carbon materials are compounded, and the material obtained by the carbonization pyrolysis process is rationally utilized. The material has a rich internal void structure and rich surface functional groups. It exhibits excellent chemical adsorption and physical adsorption properties for heavy metal ions, and the metal oxides in the material also have certain catalytic properties, which is beneficial to the passivation of heavy metals after adsorption.

[0033] The third aspect of the present invention provides an application of the novel soil remediation agent, which is applied to the field of heavy metal contaminated soil treatment and / or soil improvement.

[0034] Specifically, the novel soil remediation agent has partial chemical reactions in the application of surface adsorption and decomposition of heavy metal contaminated soil.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] In the present invention, waste activated carbon and sludge are used as raw materials for recycling and resource utilization, thereby reducing the cost of soil adsorption treatment. The specific surface area of ​​waste activated carbon is increased through regeneration technology, and the regenerated activated carbon material, admixture and sludge are synergistically compounded. By controlling the addition of admixtures and the volume of sludge incorporated, and rationally utilizing the carbonization pyrolysis process to enrich the pore structure of the material, the purpose of adsorption and removal and / or chemical reaction removal of various heavy metal pollutants in the soil is achieved, thereby realizing the repair effect. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0038] The raw materials of the invention are waste activated carbon and papermaking sludge containing 60% water.

[0039] Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the present technology. Unless otherwise specified, the reagents and raw materials used in the present invention can be obtained from commercial sources.

[0040] Example 1

[0041] A method for preparing a novel soil remediation agent comprises the following steps:

[0042] (1) The waste activated carbon is treated with desulfurization and denitrification, and then the treated activated carbon is subjected to high-temperature steam regeneration for 2 hours at a temperature of 400°C and a water-carbon ratio of 1:1. After cooling, the activated carbon is crushed and passed through a 200-mesh sieve to obtain regenerated activated carbon powder.

[0043] (2) aerobic fermentation treatment was performed on papermaking sludge with a moisture content of 60% in advance, and then the sludge was dried and dehydrated at 105°C for 2 hours, and then crushed and passed through a 200-mesh sieve to obtain sludge powder;

[0044] (3) Dry-mixing the regenerated activated carbon powder with urea, nano-bentonite, and papermaking sludge powder for 10 minutes to obtain a dry mixture; then adding water and wet-mixing for 10 minutes to obtain a wet mixture; wherein the amount of regenerated activated carbon powder is 50 kg, the amount of papermaking sludge powder is 20 kg, the amount of urea is 5 kg, the amount of nano-bentonite is 10 kg, and the amount of water is 15 kg.

[0045] (4) The wet mixture was granulated to obtain mixed particles with a diameter of 8 mm and a length of 10 mm. The mixed particles were transported to a carbonization furnace and reacted in a nitrogen environment at 400°C for 2 h. The flow rate of the inert gas during the carbonization treatment was 9 L / min, thereby obtaining a new soil remediation agent.

[0046] Example 2

[0047] A method for preparing a novel soil remediation agent comprises the following steps:

[0048] (1) The waste activated carbon is treated with desulfurization and denitrification, and then the treated activated carbon is subjected to high-temperature steam regeneration for 1 hour at a temperature of 500°C and a water-carbon ratio of 2:1. After cooling, the activated carbon is crushed and passed through a 200-mesh sieve to obtain regenerated activated carbon powder.

[0049] (2) aerobic fermentation treatment was performed on papermaking sludge with a moisture content of 60% in advance, and then the sludge was dried and dehydrated at 105°C for 2 hours, and then crushed and passed through a 200-mesh sieve to obtain sludge powder;

[0050] (3) Dry-mixing the regenerated activated carbon powder with urea, nano-bentonite, and papermaking sludge powder for 15 minutes to obtain a dry mixture; then adding water and wet-mixing for 15 minutes to obtain a wet mixture; wherein the amount of regenerated activated carbon powder is 40 kg, the amount of papermaking sludge powder is 20 kg, the amount of urea is 5 kg, the amount of nano-bentonite is 10 kg, and the amount of water is 20 kg.

[0051] (4) The wet mixture was granulated to obtain mixed particles with a diameter of 8 mm and a length of 5 mm. The mixed particles were transported to a carbonization furnace and reacted in a nitrogen environment at 500°C for 2 h. The flow rate of the inert gas during the carbonization treatment was 6 L / min, thereby obtaining a new soil remediation agent.

[0052] Example 3

[0053] A method for preparing a novel soil remediation agent comprises the following steps:

[0054] (1) The waste activated carbon is treated with desulfurization and denitrification, and then the treated activated carbon is subjected to high-temperature steam regeneration for 2 hours at a temperature of 400°C and a water-carbon ratio of 1:2. After cooling, the activated carbon is crushed and passed through a 200-mesh sieve to obtain regenerated activated carbon powder.

[0055] (2) aerobic fermentation treatment was performed on papermaking sludge with a moisture content of 60% in advance, and then the sludge was dried and dehydrated at 105°C for 2 hours, and then crushed and passed through a 200-mesh sieve to obtain sludge powder;

[0056] (3) Dry-mix the regenerated activated carbon powder with urea, nano-bentonite, and papermaking sludge powder for 15 minutes to obtain a dry mixture; then add water and wet-mix for 15 minutes to obtain a wet mixture; wherein the amount of regenerated activated carbon powder is 80 kg, the amount of papermaking sludge powder is 80 kg, the amount of urea is 15 kg, the amount of nano-bentonite is 30 kg, and the amount of water is 60 kg.

[0057] (4) The wet mixture was granulated to obtain mixed particles with a diameter of 10 mm and a length of 5 mm. The mixed particles were transported to a carbonization furnace and carbonized in a nitrogen environment at 800°C for 1 h. The flow rate of the inert gas during the carbonization treatment was 12 L / min, thereby obtaining a new soil remediation agent.

[0058] Comparative Example 1

[0059] This comparative example is a comparative experimental example of Example 1, the main difference being that:

[0060] During the carbonization treatment in step (4), the carbonization temperature is 700°C.

[0061] Comparative Example 2

[0062] This comparative example is a comparative experimental example of Example 1, the main difference being that:

[0063] The temperature during high temperature steam treatment in step (1) is 500° C.

[0064] During the carbonization treatment in step (4), the carbonization temperature is 700°C.

[0065] Experimental testing

[0066] 1. The component contents of the novel soil remediation agents prepared in Example 1, Comparative Example 1 and Comparative Example 2 were tested respectively, and the adsorption performance was tested according to GB / T7702.6-2008 "Test Method for Coal Granular Activated Carbon - Determination of Methylene Blue Adsorption Value" and GB / T7702.7-2008 "Test Method for Coal Granular Activated Carbon - Determination of Iodine Adsorption Value". The test results are shown in Table 2.

[0067] Table 2 Performance test results of new soil remediation agents

[0068] Iodine value Methylene blue Moisture Ash Volatile Matter Fixed Carbon Example 1 403mg / g 128mg / g 3.1％ 56％ 33％ 7.9％ Comparative Example 1 603mg / g 168mg / g 2.1％ 67％ 26％ 4.9％ Comparative Example 2 533mg / g 138mg / g 4.7％ 44.3％ 36.5％ 14.5％

[0069] It can be seen from the test results in Table 2 that the iodine adsorption value of the novel soil remediation agent prepared in the present invention is above 400 mg / g, and the methylene blue adsorption value is above 120 mg / g.

[0070] Compared with Example 1, the iodine value and methylene blue adsorption value of the new soil remediation agent of Comparative Example 1 are increased. The reason for this is that when preparing the new soil remediation in Comparative Example 1, the temperature of the carbonization treatment process is increased, the pyrolysis components of the carbon material are increased, the pyrolysis of the admixture is more complete, and more micropores and mesopores are generated. The pores become more complex and the effective adsorption pores are increased.

[0071] Compared with Example 1 and Comparative Example 1, the iodine value and methylene blue adsorption value of the new soil remediation agent of Comparative Example 2 did not show a significant increase or decrease, indicating that although the regeneration process will have a certain recovery ability on the pores of the material, the pore result of the material finally obtained still mainly depends on the subsequent carbonization treatment process.

[0072] 2. Application test of the new soil remediation agent prepared in Example 1, Comparative Example 1 and Comparative Example 2

[0073] The test site of the application test is the garden of the test park in Daxing District, Beijing. The new soil remediation agents obtained in Example 1, Comparative Example 1 and Comparative Example 2 are all cylindrical particles.

[0074] The test was conducted by outdoor cultivation. The new soil remediation agent prepared in Example 1, Comparative Example 1 and Comparative Example 2 was added to the test soil at 15% of the weight of the test soil, respectively, and recorded as Experimental Group 1, Experimental Group 2 and Experimental Group 3, respectively. Three parallel experiments were set up for each group, and a blank control group was set up at the same time (i.e., no soil remediation agent was added to the test soil of this group).

[0075] The quality of soil and repair agent in each experimental group 1-3 is the same. After mixing, the soil needs to be irrigated thoroughly for the first time. After the soil moisture is balanced, the soil solution extractor is inserted and cultured for 30 days. After the test time reaches 30 days, the soil solution is extracted to measure the changes in its pH value, EC (electrical conductivity) value, and P content.

[0076] After the test cultivation, the soil was naturally dried in the shade, and barley grass seeds were planted in the cultivated soil to measure the germination rate.

[0077] Soil pH was measured using a pH meter, EC was measured using electrical conductivity, and P content was measured using the molybdenum-antimony colorimetric method.

[0078] The germination rate was calculated by counting the number of barley grass seeds in each group.

[0079] After testing, the effects of the new soil remediation agents obtained in Example 1, Comparative Example 1 and Comparative Example 2 on the pH value, EC value, P content and germination rate in the soil are shown in Tables 3-6.

[0080] Table 3 Effect of new soil remediation agents on soil pH

[0081] Soil pH before treatment Soil pH after treatment Blank control group 7.3 7.8 Experimental Group 1 7.4 8.4 Experimental Group 2 7.2 8.3 Experimental Group 3 7.8 9.3

[0082] Table 4 Effect of new soil remediation agents on soil EC value

[0083] Soil EC value before treatment EC value of soil after treatment Blank control group 22.6 21.4 Experimental Group 1 22.5 11.2 Experimental Group 2 22.4 12.5 Experimental Group 3 22.6 10.3

[0084] Table 5 Effects of new soil remediation agents on soil P content

[0085] Soil P content before treatment Soil P content after treatment Blank control group 1.83 1.76 Experimental Group 1 1.94 1.22 Experimental Group 2 1.67 1.21 Experimental Group 3 1.78 1.12

[0086] Table 6 Effect of new soil remediation agent on germination rate of barley grass seeds

[0087] Barley grass germination rate Blank control group 78％ Experimental Group 1 89％ Experimental Group 2 90％ Experimental Group 3 96％

[0088] From the test results in Tables 3 to 6, it can be seen that after adding the new soil remediation agent obtained in Example 1, Comparative Example 1 and Comparative Example 2, the pH value of the test soil increased, the EC value decreased, and the P content decreased. Moreover, after adding the new soil remediation agent obtained in Example 1, Comparative Example 1 and Comparative Example 2, the germination rate of barley grass can be significantly improved after short-term cultivation. This proves that the new soil remediation agent of the present invention has the effect of repairing and improving soil and reducing environmental pollution.

[0089] In summary, in the present invention, waste activated carbon and sludge are used as raw materials for recycling and resource utilization, thereby reducing the cost of soil adsorption treatment, increasing the specific surface area of ​​waste activated carbon through regeneration technology, and synergistically compounding the regenerated activated carbon material, admixture and sludge. By controlling the addition of admixtures and the volume of sludge incorporated, and rationally utilizing the carbonization pyrolysis process to enrich the pore structure of the material, the purpose of adsorption and removal and / or chemical reaction removal of various heavy metal pollutants in the soil is achieved, thereby realizing the repair effect.

[0090] The above specific examples are used to illustrate the present invention, which is only used to help understand the present invention and is not intended to limit the present invention. For those skilled in the art, according to the concept of the present invention, some simple deductions, modifications or substitutions can be made.

Claims

1. A method for preparing a novel soil remediation agent, characterized in that: The steps include: (1) treating the waste activated carbon with desulfurization and denitrification, and then regenerating the treated activated carbon with high-temperature steam at a temperature of 500°C and a water-carbon ratio of 1:1 for 2 hours, cooling it, crushing it, and passing it through a 200-mesh sieve to obtain regenerated activated carbon powder; (2) aerobic fermentation treatment was performed on papermaking sludge with a moisture content of 60% in advance, and then the sludge was dried and dehydrated at 105°C for 2 hours, and then pulverized and passed through a 200-mesh sieve to obtain sludge powder; (3) 50 kg of regenerated activated carbon powder was dry-mixed with 5 kg of urea, 10 kg of sodium bentonite, and 20 kg of papermaking sludge powder for 10 min to obtain a dry mixture; and then 15 kg of water was added and wet-mixed for 10 min to obtain a wet mixture; (4) The wet mixture was granulated to obtain mixed particles with a diameter of 8 mm and a length of 10 mm. The mixed particles were transported to a carbonization furnace and reacted in a nitrogen environment at 700°C for 2 h. The flow rate of the inert gas during the carbonization treatment was 9 L / min, thereby obtaining a new soil remediation agent.