Treatment method for chromium-containing contaminated soil by synergistic disposal of waste desulfurization slag and waste organic solvent

Abstract

The present application relates to waste disposal technical field, especially to a kind of processing method for treating chromium-containing contaminated soil by synergistically disposing waste desulfurization residue and waste organic solvent, comprising the following steps: step one, the chromium-containing contaminated soil is broken, after processing, spray a certain proportion of waste organic solvent and water, ensure that the moisture content is 30-50%, obtain mixture A;Step two, a certain amount of catalyst is added to mixture A to catalyze the reaction, stir evenly, obtain mixture B;Step three, waste desulfurization residue is added to mixture B, stir evenly, obtain mixture C.In the present application, a kind of harmless treatment method for chromium-containing contaminated soil is provided, realizes detoxification while chromium-containing contaminated soil is used as another detoxification agent, waste is turned into treasure, reaches the effect of waste pollution control, while simplifying operation process, reduces processing cost, improves economic benefit, meets landfill standard and becomes the problem that the present technical personnel in the field urgently need to solve.

Description

Technical Field

[0001] This invention relates to the field of waste disposal technology, and in particular to a method for co-treating chromium-contaminated soil with waste desulfurization slag and waste organic solvents. Background Technology

[0002] Chromium and its compounds are important inorganic chemical raw materials, widely used in metallurgy, chemical industry, machinery, electronics, and pharmaceuticals. Statistics show that nearly 10% of commodities in my country are related to chromium salts. Heavy metal chromium, especially hexavalent chromium, is highly mobile, easily diffused, and highly carcinogenic; it is one of the three globally recognized carcinogenic metals, and countries worldwide generally consider chromium pollution a key target for prevention and control.

[0003] Chromium-containing pollutants generated by industrial activities enter the environment through various pathways, some in the form of trivalent chromium and others in the more toxic and easily migrating hexavalent form. According to incomplete statistics, China discharges 320,000-400,000 tons of chromium-contaminated wastewater annually. The first national soil pollution survey report indicates that my country's soil contaminated with hexavalent chromium amounts to as much as 15 million tons. Currently, the main treatment method for chromium-contaminated soil is chemical treatment, which involves adding reducing agents to reduce hexavalent chromium to trivalent chromium. Other methods include ion exchange, membrane separation, and biological treatment.

[0004] The publicly disclosed methods for treating chromium-contaminated soil include the following:

[0005] First, there is a Chinese invention patent, CN2021107099412, entitled "A Stabilizing Agent for Chromium Slag or Chromium-Contaminated Soil and Its Application Method," filed on June 25, 2021. This patent discloses the use of 0.1-0.2% hydroquinone, 0.1-0.2% organic amine, 2.5-3.2% reducing agent, 0.1-0.5% precipitant, 1.5-2.5% clay mineral, 0.5-0.75% alkalinity regulator, and 0.5-0.75% flocculant to stabilize and solidify chromium-contaminated soil. However, this method involves many types of reagents, resulting in high costs and significant landfill volume increases.

[0006] Second, a Chinese invention patent entitled "A Method for the Harmless Treatment and Resource Utilization of Chromium Slag," with a patent application date of December 29, 2021, and patent number CN2021116364737, discloses the following steps: (1) Pre-treating and reducing chromium slag sequentially to obtain detoxified chromium slag; (2) Acid-washing the detoxified chromium slag obtained in step (1) to obtain acid-washed detoxified chromium slag; (3) Sulfidating the acid-washed detoxified chromium slag obtained in step (2) to obtain sulfidated detoxified chromium slag; (4) Using the detoxified chromium slag obtained in step (1), or the acid-washed detoxified chromium slag obtained in step (2), or the sulfidated detoxified chromium slag obtained in step (3) for the remediation of hexavalent chromium-polluted water bodies or soil. However, this method is complex to operate, and the resulting resource-utilized products are difficult to sell and difficult to industrialize.

[0007] Third, a Chinese invention patent, patent number CN2019103596457, entitled "A Method for Detoxification and Stabilization Treatment of Heavy Metal Waste," was filed on April 30, 2019. It discloses the following: b) Adding iron-rich cutting mud and / or organic amine salt waste residue to solid chromium-containing waste and stirring until homogeneous to obtain mixture A; b) Adding acid to mixture A, stirring until homogeneous, and letting it stand for 1-3 days to obtain mixture B; c) Solidifying mixture B and landfilling it. While iron-rich cutting mud and organic amine salt waste residue can be used as reducing agents to reduce hexavalent chromium to trivalent chromium, achieving a detoxification effect, this method requires a large amount of organic ammonium salt to dispose of high-content hexavalent chromium. According to the latest landfill standards, the addition of large amounts of ammonium salt will cause water-soluble salts to fail to meet landfill standards, necessitating the addition of solidifying agents, resulting in a large increase in landfill volume. Furthermore, the addition of a large amount of sulfuric acid in this scheme makes the overall system highly acidic, requiring the addition of alkaline substances to adjust the pH later, increasing disposal costs. Summary of the Invention

[0008] The purpose of this invention is to provide a method for treating chromium-contaminated soil, which can detoxify the chromium-contaminated soil while also acting as a detoxifying agent to treat waste organic solvents and desulfurization slag, thus achieving the goal of treating waste with waste. The method is simple to operate, has low treatment costs, meets landfill standards, and improves economic efficiency. The proposed method is a co-treatment method for chromium-contaminated soil using waste desulfurization slag and waste organic solvents.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for co-treating chromium-contaminated soil with waste desulfurization slag and waste organic solvents includes the following steps:

[0011] Step 1: Crush the chromium-contaminated soil, and then spray it with a certain proportion of waste organic solvent and water to ensure that the moisture content is 30-50% to obtain mixture A.

[0012] Step 2: Add a certain amount of catalyst to mixture A to catalyze the reaction, stir evenly, and obtain mixture B;

[0013] Step 3: Add waste desulfurization residue to mixture B, stir evenly to obtain mixture C;

[0014] Step 4: Add a certain amount of cement to mixture C, the pH value rises to 7-8, and metal hydroxide precipitates are produced at the same time.

[0015] As a further description of the above technical solution:

[0016] In step one, the chromium-contaminated soil is crushed, and the diameter of the crushed chromium-contaminated soil is less than 1 cm.

[0017] As a further description of the above technical solution:

[0018] The waste organic solvent used in step one is a laboratory-generated solvent containing alcohols such as ethanol and dicarboxylic acids such as oxalic acid and citric acid. The content of alcohols and dicarboxylic acids is approximately 40%, and the waste organic solvent is weakly acidic. The alcohol reagents in the waste organic solvent can effectively reduce hexavalent chromium, as shown in the following reaction formula:

[0019] 3CH3CH2OH+4H2CrO4+6H2SO4=3CH3COOH+2Cr2(SO4)3+13H2O

[0020] The ethanol in the waste organic solvent and the iron and sulfur in the waste desulfurization slag can reduce hexavalent chromium, thereby detoxifying chromium-containing soil. The oxalic acid in the waste organic solvent can be catalytically reduced to hexavalent chromium by adding manganese ion catalyst.

[0021] As a further description of the above technical solution:

[0022] In step one, the ratio of hexavalent chromium content in the chromium-contaminated soil to alcohol and carboxylic acid content in the waste organic solvent is 1:1-2. If the moisture content is insufficient, a small amount of water is added to control the moisture content to 30-50%. If the pH value is alkaline, a small amount of waste acid is added to control the pH value of the system to around 5.0.

[0023] As a further description of the above technical solution:

[0024] The catalyst used in step two is divalent manganese ions such as manganese sulfate and manganese chloride, and the amount added is 1% of the carboxylic acid content in the waste organic solvent.

[0025] As a further description of the above technical solution:

[0026] The waste desulfurization slag used in step three refers to the waste slag generated during the pre-desulfurization treatment of molten iron before it enters the converter. The desulfurization slag generated during the pre-treatment of molten iron contains about 30%-40% iron and about 10-20% sulfur. The total iron and sulfur content of the waste desulfurization slag is 2-3 times that of hexavalent chromium in chromium-contaminated soil.

[0027] As a further description of the above technical solution:

[0028] The waste desulfurization residue in step three contains a large amount of sulfide ions and ferrous ions, which dissolve rapidly in acidic solutions. It also contains small amounts of barium ions, which can reduce hexavalent chromium, thus detoxifying the chromium-containing waste. The reaction formula is shown below:

[0029] Cr2O7 2- +6Fe 2+ +14H + →2Cr 3+ +6Fe 3+ +7H2O

[0030] Cr2O7 2- +3S 2- +14H + →2Cr 3+ +3S↓+7H2O

[0031] Fe 2+ +2Cr 3+ +8OH - →FeCr2O4↓+4H2O

[0032] Ba 2+ +CrO4 2- →BaCrO4↓

[0033] Cr 3+ +3OH - →Cr(OH)3↓

[0034] The iron and sulfur in the waste desulfurization slag can reduce hexavalent chromium, thereby detoxifying chromium-containing soil.

[0035] As a further description of the above technical solution:

[0036] The cement addition ratio in step four is 1:1-1.2 for chromium-contaminated soil.

[0037] As a further description of the above technical solution:

[0038] Both the waste organic solvent and the waste desulfurization residue can reduce hexavalent chromium individually, but using only one will lead to a significant increase in the amount added. Using only the waste organic solvent will lead to an increase in organic matter in the system, and using only the waste desulfurization residue will result in an excessive increase in landfill capacity and low economic benefits.

[0039] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0040] 1. In this invention, the goal of treating waste with waste is achieved by using ethanol in waste organic solvents in hazardous waste to reduce hexavalent chromium.

[0041] 2. In this invention, the addition of acidic organic solvents reduces the amount of water and waste acid added, and the pH value is controlled at a weakly acidic level, which reduces the amount of alkali added later and lowers the treatment cost of chromium-contaminated soil.

[0042] 3. In this invention, the reduction of hexavalent chromium from carboxylic acid compounds in waste organic solvents is completed by adding manganese ions as a catalyst, making full use of the effective components in the waste organic solvents, and providing a method for treating hexavalent chromium containing dicarboxylic acids.

[0043] 4. In this invention, oxalic acid / ethanol is used to synergistically reduce hexavalent chromium. After oxalic acid is combined with Cr(VI), the instability of the tetrahedral Cr(VI) species caused by the ligand field effect reduces the reaction barrier for the transformation of Cr(VI) to Cr(III), thereby facilitating electron transfer between Cr(VI) and ethanol and accelerating the reaction rate.

[0044] 5. The method for treating chromium-contaminated soil in this invention is simple in steps, has no requirements for temperature or pressure, is highly economical, and can be used for large-scale treatment of chromium-contaminated soil. Attached Figure Description

[0045] Figure 1 This is a data comparison table of six embodiments of the treatment method for the co-treatment of chromium-contaminated soil using waste desulfurization slag and waste organic solvents proposed in this invention. Detailed Implementation

[0046] 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 some embodiments of the present invention, and not all embodiments. 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.

[0047] Please see Figure 1 This invention provides a technical solution: a method for co-treating chromium-contaminated soil with waste desulfurization slag and waste organic solvents, comprising the following steps:

[0048] The first step is to crush the chromium-contaminated soil, ensuring that the diameter of the crushed soil is less than 1 cm. After crushing, spray a certain proportion of waste organic solvent and water to ensure a moisture content of 30-50%, resulting in mixture A. The ratio of hexavalent chromium in the chromium-contaminated soil to alcohols and carboxylic acids in the waste organic solvent is 1:1-2. If the moisture content is insufficient, add a small amount of water to control the moisture content to 30-50%. If the pH value is alkaline, add a small amount of waste acid to control the pH value of the system to around 5.0.

[0049] The waste organic solvents used were laboratory-generated solvents containing alcohols such as ethanol and dicarboxylic acids such as oxalic acid and citric acid. The content of alcohols and dicarboxylic acids was approximately 40%, and the waste organic solvents were weakly acidic. The alcohol reagents from the waste organic solvents can effectively reduce hexavalent chromium, as shown in the following reaction formula:

[0050] 3CH3CH2OH+4H2CrO4+6H2SO4=3CH3COOH+2Cr2(SO4)3+13H2O

[0051] Ethanol from waste organic solvents can reduce hexavalent chromium, thus detoxifying chromium-containing soil. Oxalic acid from waste organic solvents can be catalytically reduced to hexavalent chromium by adding manganese ion catalysts.

[0052] The second step involves adding a certain amount of catalyst to mixture A to catalyze the reaction, stirring until homogeneous, and obtaining mixture B. The catalyst is divalent manganese ions such as manganese sulfate and manganese chloride, and the amount added is 1% of the carboxylic acid content in the waste organic solvent.

[0053] The third step is to add waste desulfurization slag to mixture B and stir it evenly to obtain mixture C. The waste desulfurization slag used refers to the waste slag generated during the pre-desulfurization treatment of molten iron before it enters the converter. The desulfurization slag generated during the pre-treatment of molten iron contains about 30%-40% iron and about 10-20% sulfur. The total iron and sulfur content of the waste desulfurization slag is 2-3 times that of hexavalent chromium in chromium-contaminated soil.

[0054] In addition, the waste desulfurization residue contains a large amount of sulfur ions and ferrous ions, which dissolve rapidly in acidic solutions. It also contains small amounts of barium ions, which can reduce hexavalent chromium, thus detoxifying chromium-containing waste. The reaction formula is shown below:

[0055] Cr2O7 2- +6Fe 2+ +14H + →2Cr 3+ +6Fe 3+ +7H2O

[0056] Cr2O7 2- +3S2- +14H + →2Cr 3+ +3S↓+7H2O

[0057] Fe 2+ +2Cr 3+ +8OH - →FeCr2O4↓+4H2O

[0058] Ba 2+ +CrO4 2- →BaCrO4↓

[0059] Cr 3+ +3OH - →Cr(OH)3↓

[0060] Iron and sulfur in waste desulfurization slag can reduce hexavalent chromium, thus detoxifying chromium-containing soil.

[0061] Step 4: Add a certain amount of cement to mixture C, and the pH value will rise to 7-8. At the same time, metal hydroxide precipitates will be produced. The ratio of cement added to chromium-contaminated soil is 1:1-1.2.

[0062] Specifically, both waste organic solvents and waste desulfurization slag can reduce hexavalent chromium individually, but using only one will lead to a significant increase in the amount added. Using only waste organic solvents will lead to an increase in organic matter in the system, and using only waste desulfurization slag will result in an excessive increase in landfill capacity and low economic benefits.

[0063] Specifically, dicarboxylic acids such as oxalic acid do not react with hexavalent chromium or react slowly. However, this invention accelerates the reduction reaction by adding a small amount of manganese ions as a catalyst, effectively utilizing carboxylic acid compounds from waste organic solvents. This catalytic effect may be due to the formation of a complex ion between Mn(II) and two carboxyl groups, leading to a further increase in the activity of α-OH, thereby facilitating the reaction between α-OH and CrO4. 2- It forms more complex complexes and accelerates the rate of organic acid reduction of hexavalent chromium.

[0064] Ethanol and oxalic acid in waste organic solvents can synergistically accelerate the transformation of hexavalent chromium to trivalent chromium. In the oxalic acid / ethanol reduction of Cr(VI), the activity of Cr in electron transfer to oxygen atoms or protonation reactions is further enhanced: according to frontier orbital theory, the smaller the band gap, the easier it is to be excited. The complex reduces the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, thereby increasing the driving force for electron transfer between the complex and the electron donor ethanol. The reduction of Cr(VI) to Cr(III) presents a significant barrier from tetrahedral configuration (Cr(VI) / Cr(V)) to octahedral configuration (Cr(IV) / Cr(III)). However, after oxalic acid is complexed with Cr(VI), the instability of the tetrahedral Cr(VI) species caused by the ligand field effect may lower the reaction barrier for the transformation of Cr(VI) to Cr(III), thus facilitating electron transfer between Cr(VI) and ethanol.

[0065] The solution of the present invention will be further described in detail below with reference to implementation examples.

[0066] The test sample was a chromium-contaminated soil (leaching solution Cr). 6+ The total chromium content in the leachate was 5000 mg / L (5000 mg / L for chromium, 8000 mg / L for total chromium). Cr (VI) was tested using the diphenylcarbazide spectrophotometric method (GB / T1555.5-1995). The chromium content in the leachate met the limit requirements in the <Standard for Pollution Control of Hazardous Waste Landfill> (GB 18597-2023), thus qualifying the leachate as qualified.

[0067] Implementation Case 1

[0068] Weigh 1 kg of chromium-contaminated soil, crush it using a crusher, and sieve it. Select chromium-contaminated soil particles with a diameter of less than 1 cm for further study. Add 125 mL of waste organic solvent (containing approximately 40% alcohols and dicarboxylic acids) and 0.5 g of manganese sulfate to the crushed chromium-contaminated soil. Then spray approximately 200 mL of water onto the soil to control the moisture content to approximately 40%. Next, add approximately 10 mL of inorganic waste sulfuric acid with an acidity of 0.1 mol / L to control the pH value to approximately 5.0. After mixing thoroughly, add 250 g of waste desulfurization slag (containing approximately 30% iron and 10% sulfur), stir well, let stand for 1 day, add 100 g of cement, stir and solidify. Perform leaching toxicity tests on the solidified product.

[0069] Implementation Case 2

[0070] Weigh 1 kg of chromium-contaminated soil, crush it using a crusher, and sieve it. Select chromium-contaminated soil particles with a diameter of less than 1 cm for further study. Add 140 mL of waste organic solvent (containing approximately 40% alcohols and dicarboxylic acids) and 0.56 g of manganese sulfate to the crushed chromium-contaminated soil. Then spray approximately 180 mL of water onto the soil to control the moisture content to approximately 40%. Next, add approximately 8 mL of inorganic waste sulfuric acid with an acidity of 0.1 mol / L to control the pH value to approximately 5.0. After mixing thoroughly, add 300 g of waste desulfurization slag (containing approximately 30% iron and 10% sulfur), stir well, let stand for 1 day, add 100 g of cement, stir and solidify. Perform leaching toxicity tests on the solidified product.

[0071] Implementation Case 3

[0072] The difference from Implementation Case 1 is that no waste desulfurization slag is added, while the other addition amounts and proportions are the same.

[0073] Implementation Case 4

[0074] The difference from Implementation Case 1 is that no waste organic solvent is added, the amount of recycled water added is 325 mL, and then about 15 mL of inorganic waste sulfuric acid with an acidity of 0.1 mol / L is added to control the pH value to about 5.0. The other added amounts and proportions are the same.

[0075] Implementation Case 5

[0076] The difference from Implementation Case 1 is that no catalyst manganese ions are added, while the other amounts and proportions are the same.

[0077] Implementation Case 6

[0078] The difference from Implementation Case 1 is that the carboxylic acid compounds in the added waste organic solvent are monocarboxylic acids, while the amount and proportion of the rest are the same.

[0079] In summary, please refer to Figure 1 The table below compares data from six embodiments. Results from embodiments 1-2 show that the method for co-treating chromium-contaminated soil using waste desulfurization slag and waste organic solvents provided by this invention has a large treatment capacity and a long-lasting solidification effect. Comparison with embodiments 3-4 shows that using waste organic solvents alone or waste desulfurization slag alone does not meet the control limits for hazardous waste landfill. Embodiment 5 shows that the catalyst has a significant catalytic effect; without the addition of a catalyst, the carboxylic acid compounds in the waste organic solvent cannot be fully utilized. Embodiment 6 shows that even with the addition of a manganese catalyst, monocarboxylic acids cannot effectively reduce hexavalent chromium. Organic acids containing only a single carboxyl group cannot form chelates with manganese ions; therefore, regardless of the presence or absence of manganese ions, they cannot undergo a redox reaction with hexavalent chromium.

[0080] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for co-treating chromium-contaminated soil with waste desulfurization slag and waste organic solvents, characterized in that, Includes the following steps: Step 1: Crush the chromium-contaminated soil, and then spray it with a certain proportion of waste organic solvent and water to ensure that the moisture content is 30-50% to obtain mixture A. Step 2: Add a certain amount of catalyst to mixture A to catalyze the reaction, stir evenly, and obtain mixture B; Step 3: Add waste desulfurization residue to mixture B, stir evenly to obtain mixture C; Step 4: Add a certain amount of cement to mixture C, the pH value rises to 7-8, and metal hydroxide precipitate is produced at the same time; The waste organic solvent used in step one is a laboratory-generated organic solvent containing ethanol, oxalic acid, and citric acid. The content of alcohols and dicarboxylic acids is 40%, and the pH value of the waste organic solvent is weakly acidic. In step one, the ratio of hexavalent chromium content in the chromium-contaminated soil to alcohol and carboxylic acid content in the waste organic solvent is 1:1-2. The catalyst used in step two is manganese sulfate and manganese chloride, and the amount added is 1% of the carboxylic acid content in the waste organic solvent. The waste desulfurization slag used in step three refers to the waste slag generated during the pre-desulfurization treatment of molten iron before it enters the converter. The desulfurization slag generated during the pre-treatment of molten iron contains 30%-40% iron and 10-20% sulfur. The total iron and sulfur content of the waste desulfurization slag is 2-3 times that of hexavalent chromium in chromium-contaminated soil. The waste desulfurization residue in step three contains a large amount of sulfur ions and ferrous ions, which dissolve quickly in acidic solutions. It also contains a small amount of barium ions, all of which can reduce hexavalent chromium and detoxify chromium-containing waste.

2. The treatment method for co-processing chromium-contaminated soil with waste desulfurization slag and waste organic solvents according to claim 1, characterized in that, In step one, the chromium-contaminated soil is crushed, and the diameter of the crushed chromium-contaminated soil is less than 1 cm.

3. The treatment method for co-processing chromium-contaminated soil with waste desulfurization slag and waste organic solvents according to claim 1, characterized in that, In step one, the alcohol-based reagents from the waste organic solvent can effectively reduce hexavalent chromium, as shown in the following reaction formula: 3CH3CH2OH+4H2CrO4+6H2SO4=3CH3COOH+2Cr2(SO4)3+13H2O The ethanol in the waste organic solvent can reduce hexavalent chromium, thereby detoxifying chromium-containing soil. The oxalic acid in the waste organic solvent can be catalytically reduced to hexavalent chromium by adding manganese ion catalyst.

4. The treatment method for co-processing chromium-contaminated soil with waste desulfurization slag and waste organic solvents according to claim 3, characterized in that, If the moisture content is insufficient in step one, add a small amount of water to control the moisture content to 30-50%. If the pH value is alkaline, add a small amount of waste acid to control the pH value of the system to 5.

0.

5. The treatment method for co-processing chromium-contaminated soil with waste desulfurization slag and waste organic solvents according to claim 1, characterized in that, The reaction formula in step three is as follows: Cr2O7 2- +6Fe 2+ +14H + →2Cr 3+ +6Fe 3+ +7H2O Cr2O7 2- +3S 2- +14H + →2Cr 3+ +3S↓+7H2O He 2+ +2Cr 3+ +8OH - →FeCr2O4↓+4H2O Not 2+ +CrO4 2- →BaCrO4↓ Cr 3+ +3OH - →Cr(OH)3↓ The iron and sulfur in the waste desulfurization slag can reduce hexavalent chromium, thereby detoxifying chromium-containing soil.

6. The treatment method for co-processing waste desulfurization slag and waste organic solvents in chromium-contaminated soil according to claim 1, characterized in that, The cement addition ratio in step four is 1:1-1.2 for chromium-contaminated soil.

7. The treatment method for co-processing chromium-contaminated soil with waste desulfurization slag and waste organic solvents according to claim 1, characterized in that, Both the waste organic solvent and the waste desulfurization residue can reduce hexavalent chromium individually, but using only one will lead to a significant increase in the amount added. Using only the waste organic solvent will lead to an increase in organic matter in the system, and using only the waste desulfurization residue will result in an excessive increase in landfill capacity and low economic benefits.

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