Passivator for repairing nickel-chromium pollution in soil as well as preparation method and application of passivator

Abstract

The invention provides a passivator for repairing nickel-chromium pollution in soil as well as a preparation method and application of the passivator. The passivating agent comprises at least one of cement and calcium hydroxide, and a calcium magnesium phosphate fertilizer; the mass ratios of the cement, the calcium magnesium phosphate fertilizer and the calcium hydroxide are 0-50%, 25-66.7% and 25-66.7% respectively. According to the passivator, nickel and chromium are passivated in the form of hydroxides through the comprehensive effects of precipitation, solidification, adsorption and the like, so that the content of nickel and chromium in soil is effectively reduced, and the passivator is low in cost, simple in preparation process and free of secondary pollution to the soil.

Description

Technical Field

[0001] The invention relates to the technical field of heavy metal contaminated soil remediation, and relates to a passivating agent for remediating nickel-chromium pollution in soil, a preparation method and an application thereof. Background Art

[0002] Nickel and chromium in the soil mainly come from rock weathering, atmospheric dust, industrial waste accumulation, sewage irrigation, fertilizer application, decaying plants and animal remains, etc. Nickel and chromium are environmental carcinogens. After being absorbed by plants, nickel and chromium in the soil eventually enter the human body through the food chain and accumulate. When the accumulation in the human body reaches a certain level, it will show pathogenicity, such as inducing lung cancer and nasopharyngeal cancer.

[0003] At present, the remediation technologies for heavy metal contaminated soil are divided into physical, biological and chemical remediation. Among them, solidification / stabilization in chemical remediation methods has developed rapidly in recent years due to its low cost and easy implementation. It is currently an important way to remediate heavy metal contaminated soil, especially for medium and light pollution (between 1 and 3 times the screening value of my country's soil environmental quality Class II land use (GB36600-2018) (inclusive), which is light pollution; between 3 and 5 times (inclusive), which is moderate pollution).

[0004] The toxicity of heavy metals in the soil is mainly affected by their effective content, so the main purpose of heavy metal contaminated soil remediation is to reduce the effective content of heavy metals in the soil. Solidification / stabilization methods can effectively reduce the effective content of heavy metals. The key to using solidification / stabilization methods to remediate heavy metal contaminated soil is passivation. At present, some studies have used mineral materials (sepiolite, artificial zeolite) and composite materials (anhydrous disodium hydrogen phosphate, quicklime) as a formula to prepare a nickel-contaminated soil remediation material; however, the mineral materials prepared by this method mainly fix heavy metal ions in the soil through physical adsorption and ion exchange adsorption. This adsorption is very unstable and can easily desorb and return to the solution and soil. There are also some studies that mix Mg(NO3)2·6H2O / Ca(NO3)2·6H2O with Al(NO3)3·9H2O and other materials to prepare layered double hydroxides (MgAl-LDH or CaAl-LDH), and then calcine at high temperature (300-900℃, 36-48h) to obtain mineral materials for in-situ remediation of heavy metal chromium contaminated soil. Although the above materials have improved adsorption stability, the preparation process of the remediation material is long, the ingredients are many, and the process is complicated, which is not conducive to large-scale promotion and application. Other methods mix and grind hypochlorite, reducing sulfide, and reducing iron salt in different proportions to obtain nickel-contaminated soil remediation agents. The process complexity has been improved, but hypochlorite is a strong oxidant and is prone to secondary pollution. In addition, the above methods of heavy metal contaminated soil remediation are difficult to effectively remediate sites with nickel and chromium composite pollution at the same time.

[0005] Therefore, there is an urgent need for a passivating agent that is environmentally friendly, inexpensive, has simple preparation steps, can effectively repair nickel and chromium contaminated soil, and has no secondary pollution. Summary of the invention

[0006] The invention provides a passivating agent for repairing nickel-chromium pollution in soil, which has a good repairing effect on soil with medium or light nickel-chromium pollution in industrial sites.

[0007] The present invention also provides a preparation method and application of the passivating agent. The raw materials are cheap and readily available, the preparation process is simple, and there is no secondary pollution after application.

[0008] The first aspect of the present invention provides a passivating agent for remediation of nickel-chromium pollution in soil, which comprises at least one of cement and calcium hydroxide, and calcium magnesium phosphate;

[0009] The mass proportions of the cement, calcium magnesium phosphate fertilizer and calcium hydroxide are (0-50%), (25-66.7%) and (25-66.7%) respectively.

[0010] The passivator as described above, wherein the mass proportions of the cement, calcium magnesium phosphate fertilizer and calcium hydroxide are (33.3-50%), (25-66.7%) and (25-66.7%) respectively.

[0011] The passivating agent as described above, wherein in the calcium magnesium phosphate fertilizer, the mass content of P2O5 is ≥12%, the mass content of CaO is ≥20%, the mass content of SiO2 is ≥20%, and the mass content of MgO is ≥12%;

[0012] And / or, the cement is Portland cement.

[0013] A second aspect of the present invention provides a method for preparing the passivating agent as described above, comprising the following steps:

[0014] 1a) adding the calcium hydroxide into water and stirring until the calcium hydroxide is dispersed in the water to obtain a suspension;

[0015] 2a) adding calcium magnesium phosphate to the suspension and stirring, and then drying to obtain solid particles, wherein the solid particles are the passivating agent.

[0016] The preparation method as described above, wherein in step 1a), the ratio of the mass of calcium hydroxide to the volume of water is 0.2 to 1 g / 10 ml;

[0017] And / or, the mass ratio of calcium hydroxide to calcium magnesium phosphate is (1-2):1;

[0018] And / or, in step 2a), the stirring speed is 60-80 r / min, the time is 2-3 min, and the drying temperature is 40-60° C., and the time is 10-12 h.

[0019] The method for preparing the passivator as described above, wherein after step 2a), the method further comprises dispersing cement evenly in water, adding the solid particles in step 2a) and continuing to stir, and obtaining the passivator after secondary drying.

[0020] The method for preparing the passivating agent as described above, wherein the ratio of the mass of cement to the volume of water is 1:(3-5) g / ml;

[0021] And / or, the mass ratio of cement to calcium hydroxide is m:1, 0<m≤2;

[0022] And / or, the mass ratio of the cement to the calcium magnesium phosphate fertilizer is n:1, 0<n≤2;

[0023] And / or, the treatment temperature of the secondary drying treatment is 20-27° C., and the treatment time is 8-10 hours.

[0024] The third aspect of the present invention provides a method for remediating nickel-chromium pollution in soil, which comprises the following steps: mixing the above-mentioned passivating agent with soil.

[0025] The method for remediating nickel-chromium pollution in soil as described above, wherein the soil is industrial site soil left over from a relocated pickling plant, and the mass ratio of the above passivating agent to the soil is 1:(25-50).

[0026] The method for remediating nickel-chromium pollution in soil as described above, wherein the soil moisture content in the soil is 20-30%;

[0027] And / or, the particle size of the soil is 1 to 2 mm;

[0028] and or, in the soil, the concentration of nickel is 900-4500 mg / kg, and the concentration of chromium is 48-120 mg / kg;

[0029] The invention provides a passivator for repairing nickel-chromium pollution in soil. The passivator comprises at least one of cement and calcium hydroxide and calcium magnesium phosphate, and the mass ratio of cement, calcium hydroxide and calcium magnesium phosphate in the passivator is further controlled, so that the effective content of nickel-chromium in the soil can be effectively reduced. The raw materials of the passivator are inexpensive and easily available, the preparation process is simple, and there is no secondary pollution after application. In particular, the passivator has a good repairing effect on nickel-chromium pollution in industrial sites. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] In the soil of industrial sites with moderate to light nickel-chromium pollution, the passivators commonly used at present are difficult to apply on a large scale due to their complicated preparation process, poor effect of solidifying or stabilizing heavy metals in the soil, and easy secondary pollution. Therefore, there is a need for a passivator that can effectively solidify or stabilize the nickel-chromium heavy metals in the soil, and has low raw material prices, simple preparation process, and no secondary pollution, so as to effectively repair the soil of industrial sites on a large scale.

[0032] The first aspect of the present invention provides a passivating agent for remediation of nickel-chromium pollution in soil, which comprises at least one of cement and calcium hydroxide, and calcium magnesium phosphate;

[0033] The mass proportions of cement, calcium magnesium phosphate and calcium hydroxide are (0-50%), (25%-66.7%) and (25-66.7%) respectively.

[0034] According to the above, the components contained in the passivator of the present invention have two conditions:

[0035] (1) comprising calcium hydroxide and calcium magnesium phosphate, wherein the mass proportion of calcium hydroxide is C, 0<C≤66.7%, and the mass proportion of calcium magnesium phosphate is B, 33.3%≤B≤66.7%;

[0036] (2) It includes cement, calcium magnesium phosphate and calcium hydroxide, the mass proportion of cement is A, 0<A≤50%; the mass proportion of calcium magnesium phosphate is B, 25%≤B≤66.7%; the mass proportion of calcium hydroxide is C, 25≤C≤66.7%.

[0037] The passivator provided by the present invention for the restoration of soil in industrial sites polluted by nickel and chromium comprises at least one of cement and calcium hydroxide, and calcium magnesium phosphate, and the mass proportions of cement, calcium magnesium phosphate and calcium hydroxide are (0-50%), (25%-66.7%) and (25-66.7%) respectively. Nickel and chromium are passivated in the form of hydroxides through the comprehensive effects of precipitation, solidification, adsorption and the like, thereby effectively reducing the content of nickel and chromium in the soil. The passivator has low cost, simple preparation process and does not cause secondary pollution to the soil.

[0038] In a specific embodiment, the mass proportions of cement, calcium magnesium phosphate and calcium hydroxide are (33.3-50%), (25-66.7%) and (25-66.7%) respectively.

[0039] When the passivator contains cement, calcium magnesium phosphate and calcium hydroxide, and the mass proportion is within the above range, the passivator has a better repair effect on the soil of industrial sites contaminated by nickel and chromium.

[0040] In a specific embodiment, in the calcium magnesium phosphate fertilizer, the mass content of P2O5 is ≥12%, the mass content of CaO is ≥20%, the mass content of SiO2 is ≥20%, and the mass content of MgO is ≥12%.

[0041] In another specific embodiment, the cement is Portland cement.

[0042] The aqueous solution of calcium magnesium phosphate fertilizer that meets the above requirements is alkaline, which can improve acidic soil, increase soil fertility, and has adsorption and precipitation effects on heavy metals in the soil.

[0043] Portland cement can bond other components in the passivator and increase the hardness of the passivator, thereby effectively combining the various components in the passivator together to form an overall structure, ensuring that the components in the binder will not easily separate or flow away during use, and playing the role of solidifying heavy metals.

[0044] The second aspect of the present invention provides a method for preparing the above passivating agent, comprising the following steps:

[0045] 1a) adding calcium hydroxide to water and stirring until the calcium hydroxide is dispersed in the water to obtain a suspension;

[0046] 2a) adding calcium magnesium phosphate to the suspension and stirring, and then drying to obtain solid particles, which are the passivating agent.

[0047] Based on the above method, a passivating agent including calcium magnesium phosphate and calcium hydroxide can be prepared.

[0048] Specifically, in step 1a), the ratio of the mass of calcium hydroxide to the volume of water is 0.2 to 1 g / 10 ml.

[0049] In another specific embodiment, the mass ratio of calcium hydroxide to calcium magnesium phosphate is (1-2):1.

[0050] In another specific embodiment, in step 2a), the stirring speed is 60-80 r / min, the time is 2-3 min, and the drying temperature is 40-60° C., and the time is 10-12 h.

[0051] The present invention further limits the mass ratio of calcium magnesium phosphate fertilizer and calcium hydroxide, the stirring speed, the stirring time, and the temperature and time of the drying treatment in the process of preparing the passivator, which is beneficial to improving the effect of the passivator on repairing the soil.

[0052] In addition, in the above-mentioned preparation method of the passivator, after step 2a), the process further comprises: uniformly dispersing cement in water, adding the solid particles in step 2a), and performing secondary stirring, and obtaining the passivator after secondary drying.

[0053] Specifically, a passivating agent including cement, sodium hydroxide and calcium magnesium phosphate can be obtained by mixing cement with solid particles and stirring and secondary drying them in sequence.

[0054] Among them, the ratio of cement mass to water volume is 1: (3~5) g / ml.

[0055] In another specific embodiment, the mass ratio of cement to calcium hydroxide is m:1, 0<m≤2.

[0056] In another specific embodiment, the mass ratio of cement to calcium magnesium phosphate fertilizer is n:1, 0<n≤2.

[0057] The invention can further prepare a passivating agent with good effect of repairing nickel-chromium polluted soil in industrial sites by controlling the mass ratio of calcium hydroxide, cement and calcium-magnesium phosphate fertilizer in the passivating agent.

[0058] In another specific embodiment, the secondary drying temperature is 20-27° C., and the secondary drying time is 8-10 hours. The present invention can effectively improve the repair effect of the passivating agent on the soil of industrial sites with moderate to mild nickel-chromium pollution by further controlling the mass ratio of cement, calcium hydroxide, and calcium magnesium phosphate fertilizer in the passivating agent and the temperature and time of the secondary drying.

[0059] The third aspect of the present invention provides a method for remediating nickel-chromium pollution in soil, comprising the following steps: mixing a passivating agent with soil, wherein the soil includes nickel-chromium contaminated soil, especially nickel-chromium contaminated soil in industrial sites.

[0060] The present invention can effectively repair the soil of industrial sites polluted by nickel and chromium by using the above passivating agent.

[0061] In detail, when the mass ratio of the passivator to the soil is 1:(25-50), a relatively good nickel-chromium contaminated soil remediation effect can be obtained while taking into account the dosage of the passivator.

[0062] In another specific embodiment, the moisture content of the soil is 20% to 30%. By further limiting the moisture content of the soil during the repair process, the repair effect of the passivating agent is improved. Specifically, the above soil is the industrial site soil left behind by a relocated pickling plant.

[0063] In another specific embodiment, the particle size of the soil is 1 to 2 mm. The present invention limits the particle size of the soil to the above range, which is conducive to full contact between the soil and the passivator, thereby improving the repair effect of the passivator.

[0064] In another specific embodiment, the concentration of nickel in the soil is 900-4500 mg / kg, and the concentration of chromium is 48-120 mg / kg.

[0065] The passivating agent of the present invention can be used for remediation of nickel-chromium pollution in soil, and is particularly suitable for industrial site soil with light to moderate nickel-chromium pollution, where the nickel concentration is 900-4500 mg / kg and the chromium concentration is 48-120 mg / kg.

[0066] The solution provided by the present invention is further described below in conjunction with specific embodiments.

[0067] In the following examples and comparative examples, the cement used is ordinary Portland cement, model P·O32.5R; the calcium magnesium phosphate fertilizer used is purchased from Hubei Jinmingzhu Chemical Co., Ltd., and the main components include Ca3(PO4)2, CaSiO3, MgSiO3, wherein the P2O5 content is ≥12%, the CaO content is ≥20%, the SiO2 content is ≥20%, and the MgO content is ≥12%; the calcium hydroxide used is purchased from Xilong Chemical Co., Ltd., and the purity is ≥95.0%. The soil is the soil of the nickel-chromium contaminated industrial site left by a relocated pickling plant, wherein the leaching concentration of Ni is 11.502 mg / kg, the leaching concentration of Cr in the soil is 11.304 mg / kg, and the pH of the soil is 7.67.

[0068] Example 1

[0069] The preparation method of the passivating agent of this embodiment comprises the following steps:

[0070] 1) Place 0.1 g of calcium hydroxide in a beaker, add 5 mL of water to dissolve, let stand, and discard the supernatant to obtain a suspension;

[0071] 2) Add 0.1 g of calcium magnesium phosphate (granules) to the suspension, set the vortex oscillator speed to 60 r / min, rotate for 3 min, stir, pour the mixed solution into a plate and spread it, dry it at 60°C for 12 h, crush it, and pass it through a 6 mm sieve to obtain solid particles.

[0072] 3) Add 0.8 ml of water to 0.2 g of cement, then add the solid particles in step 2), continue stirring, and air-dry naturally for 10 hours to obtain the passivating agent.

[0073] Example 2

[0074] This embodiment is basically consistent with Embodiment 1, except that the added amount of calcium hydroxide and calcium magnesium phosphate is 0.2g, and the added amount of cement is 0.4g.

[0075] Example 3

[0076] This embodiment is basically consistent with embodiment 2, except that the added amounts of calcium hydroxide, calcium magnesium phosphate fertilizer and cement are all 0.2 g.

[0077] Example 4

[0078] The preparation method of the passivating agent of this embodiment comprises the following steps:

[0079] 1) Place 0.2 g of calcium hydroxide in a beaker, add 5 mL of water to dissolve, let stand, and discard the supernatant to obtain a suspension;

[0080] 2) Add 0.2 g of calcium magnesium phosphate fertilizer (granules) to the suspension, set the vortex oscillator speed to 60 r / min, rotate for 2 min, stir, pour the mixed solution into a plate and spread it, dry it at 60°C for 10 h, crush it, and pass it through a 6 mm sieve to obtain a passivating agent.

[0081] Example 5

[0082] The preparation method of the passivating agent of this embodiment comprises the following steps:

[0083] 1) Place 0.2 g of calcium hydroxide in a beaker, add 10 mL of water to dissolve, let stand, and discard the supernatant to obtain a suspension;

[0084] 2) Add 0.4 g of calcium magnesium phosphate fertilizer (granules) to the suspension, set the vortex oscillator speed to 80 r / min, rotate for 3 min, stir, pour the mixed solution into a plate and spread it, dry it at 60° C. for 12 h, crush it, and pass it through a 6 mm sieve to obtain a passivating agent.

[0085] Example 6

[0086] This embodiment is basically consistent with Example 5, except that the addition amount of calcium magnesium phosphate is 0.4g and the addition amount of calcium hydroxide is 0.2g.

[0087] Comparative Example 1

[0088] This comparative example uses 0.6 g of cement as a passivating agent.

[0089] Comparative Example 2

[0090] This comparative example uses 0.6 g of calcium magnesium phosphate as a passivating agent.

[0091] Comparative Example 3

[0092] This comparative example uses 0.6 g of calcium hydroxide as a passivating agent.

[0093] Test example

[0094] The passivating agents in all the above embodiments and comparative examples are used for soil remediation in the following manner:

[0095] The passivating agent was mixed with 20 g of nickel-chromium contaminated industrial site soil passed through a 2 mm sieve, 4 ml of deionized water was added, and the mixture was shaken and mixed. After standing for one week, the sample was dried to obtain the repaired soil.

[0096] The leaching concentrations of nickel and chromium in the soil were determined according to the leaching method of solid waste toxicity, acetic acid solution buffer method (HJ / T 300-2007) and flame atomic absorption spectrophotometry.

[0097] The soil remediation effects of the passivators in the examples and comparative examples are shown in Table 1.

[0098] Table 1 Soil remediation effect of passivators in Examples and Comparative Examples

[0099]

[0100] It can be seen from Table 1 that, compared with Comparative Examples 1 to 3, the passivators provided by Examples 1 to 6 of the present invention have good soil remediation effects. The passivator obtained in Example 2 includes three components: cement, calcium magnesium phosphate fertilizer, and calcium hydroxide, and has a good remediation efficiency.

[0101] Practical application examples

[0102] The contaminated site was selected from a site left by a relocated stainless steel pickling plant in Taizhou City, Jiangsu Province, where the soil pH was 7.32, the average leaching concentration of heavy metal Cr was 10.47 mg / kg, and the average leaching concentration of Ni was 16.02 mg / kg. The passivating agent prepared in Example 3 was selected to repair the site. The repair area was 20 m long, 11.5 m wide, and 230 m in area. 2 . 0.5% passivator (about 600kg) was applied to the surface soil (0-20cm), mixed with a rotary tiller, sprayed with an appropriate amount of water, and sampled for testing after 15 days. The soil pH was 8.10, the average leaching concentration of Cr in the soil was 1.13mg / kg, the passivation efficiency was 89.25%, the average leaching concentration of Ni was 0.91mg / kg, and the passivation efficiency was 94.36%. Therefore, the passivator provided by the present invention can support the effective remediation of soil in industrial sites contaminated by large-scale heavy metal chromium and nickel.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A passivating agent for remediation of nickel-chromium pollution in soil, characterized in that: including at least one of cement and calcium hydroxide, and calcium magnesium phosphate; The mass proportions of the cement, calcium magnesium phosphate fertilizer and calcium hydroxide are (0-50%), (25-66.7%) and (25-66.7%) respectively.

2. The passivating agent according to claim 1, characterized in that The mass proportions of the cement, calcium magnesium phosphate fertilizer and calcium hydroxide are (33.3-50%), (25-66.7%) and (25-66.7%) respectively.

3. The passivating agent according to claim 1 or 2, characterized in that: In the calcium magnesium phosphate fertilizer, the mass content of P2O5 is ≥12%, the mass content of CaO is ≥20%, the mass content of SiO2 is ≥20%, and the mass content of MgO is ≥12%; And / or, the cement is Portland cement.

4. A method for preparing a passivating agent according to any one of claims 1 to 3, characterized in that: The following steps are involved: 1a) adding the calcium hydroxide into water and stirring until the calcium hydroxide is dispersed in the water to obtain a suspension; 2a) adding calcium magnesium phosphate to the suspension, stirring the mixture, and drying the mixture to obtain solid particles, wherein the solid particles are the passivating agent.

5. The method for preparing a passivating agent according to claim 4, characterized in that: In step 1a), the ratio of the mass of calcium hydroxide to the volume of water is 0.2-1 g / 10 ml; And / or, the mass ratio of calcium hydroxide to calcium magnesium phosphate is (1-2):1; And / or, in step 2a), the stirring speed is 60-80 r / min, the time is 2-3 min, and the temperature of the secondary drying treatment is 40-60° C., and the time is 10-12 h.

6. The method for preparing a passivating agent according to claim 4, characterized in that: After step 2a), the method further comprises dispersing cement uniformly in water, adding the solid particles in step 2a), stirring for a second time, and performing a second drying process to obtain the passivating agent.

7. The method for preparing a passivating agent according to claim 5, characterized in that: The ratio of cement mass to water volume is 1: (3-5) g / ml; And / or, the mass ratio of cement to calcium hydroxide is m:1, 0<m≤2; And / or, the mass ratio of the cement to the calcium magnesium phosphate fertilizer is n:1, 0<n≤2; And / or, the treatment temperature of the secondary drying treatment is 20-27° C., and the treatment time is 8-10 hours.

8. A method for remediating nickel-chromium pollution in soil, characterized in that: The method comprises the following steps: mixing the passivating agent according to any one of claims 1 to 3 with soil.

9. The method for remediating nickel-chromium pollution in soil according to claim 8, characterized in that: The mass ratio of the passivator to the soil is 1:(25-50).

10. The method for remediating nickel-chromium pollution in soil according to claim 8 or 9, characterized in that: The moisture content of the soil is 20-30%; And / or, the particle size of the soil is 1 to 2 mm; And / or, in the soil, the concentration of nickel is 900-4500 mg / kg, and the concentration of chromium is 48-120 mg / kg.

Images