A porous nanosilica loaded dithiocarbamate soil heavy metal passivator, and a preparation method and application thereof
By using porous nano-silica loaded with dithiocarbamate passivating agents to fix heavy metals and release nutrients, the problems of low passivation efficiency and soil fertility decline in existing technologies are solved, achieving efficient passivation and soil improvement.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HENAN UNIVERSITY
- Filing Date
- 2023-04-10
- Publication Date
- 2026-06-26
Smart Images
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Figure FT_2 
Figure FT_3
Abstract
Description
Technical Field
[0001] This invention belongs to the field of soil heavy metal pollution remediation technology, specifically relating to a porous nano-silica supported dithiocarbamate soil heavy metal passivating agent, its preparation method, and its application. Background Technology
[0002] With the rapid development of my country's industry and economy, the problem of heavy metal pollution in soil has become increasingly prominent.
[0003] To address the aforementioned problems, this invention constructs a simple and easily repairable nano-passivation material that can efficiently passivate multiple heavy metals in soil at low addition levels, releasing K, Ca, Mg, and N without affecting the soil's physicochemical properties. It contains essential nutrients for plants and microorganisms, increases soil fertility, and the presence of silica can improve the soil environment and reduce its disturbance to soil organisms. It is expected to be applied to the chemical in-situ passivation remediation of farmland soil. Summary of the Invention
[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a porous nano-silica-supported dithiocarbamate soil heavy metal passivating agent. This agent, when used as a soil heavy metal passivating agent, can complex with heavy metal ions such as Pb, Cd, Cu, Zn, Ni, and Hg, fixing the heavy metals to its surface, reducing the leaching of heavy metals from the solid-liquid phase, and decreasing their migration. Simultaneously, the passivating agent can release K, Ca, and Mg. Porous silica contains essential nutrients such as nitrogen, phosphorus, and silicon, which are necessary for plants and microorganisms, and can increase soil fertility. It can also improve the soil environment.
[0005] This invention also provides a method for preparing the above-mentioned porous nano-silica supported dithiocarbamate soil heavy metal passivating agent and its application in the remediation of heavy metal contaminated soil.
[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0007] A method for preparing a porous nano-silica-supported alkyl dithiocarbamate soil heavy metal passivating agent includes the following steps:
[0008] 1) Add a soluble silicate aqueous solution as a substrate to the reactor, wherein the mass concentration of silica is 10-30%, and add an alkaline aqueous solution under stirring conditions, and stir and mix at 10-30℃;
[0009] 2) Add an organic amine solution and react at 10–30°C for 1–2 hours;
[0010] 3) Add the carbon disulfide-water mixture and stir at 10-30°C for 2-4 hours;
[0011] 4) Heat to 40℃~50℃, remove excess carbon disulfide by vacuum, and then react for 1~2 hours; the reaction solution is dried to obtain passivating agent powder.
[0012] Specifically, in step 1), the soluble silicate may include sodium silicate and / or potassium silicate, etc., with a silicate modulus of 1 to 3.5. Sodium silicate is preferred.
[0013] Furthermore, in step 1), the alkali may include sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, calcium oxide, magnesium oxide, or ammonia, etc. Calcium hydroxide is preferred.
[0014] Specifically, in step 2), the organic amine may include one or more of the following secondary amine organic amines: diethylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, polyethylenepolyamine, and piperazine. Diethylamine, polyethylenepolyamine, and piperazine are preferred.
[0015] Specifically, in step 4), the drying method can be baking, spray drying, or flash evaporation, etc.
[0016] Specifically, the mass ratio of alkyl dithiocarbamate to silicon dioxide contained in the passivating agent product can be 1:(0.2 to 0.8).
[0017] Furthermore, the molar ratio of organic amine to base is 1:(0.5 to 4.5), where the base is the sum of the basic oxide contained in the soluble silicate in step 1) and the alkali contained in the added alkaline aqueous solution; the molar ratio of organic amine to carbon disulfide can be 1:(1 to 7).
[0018] In this invention, sodium silicate serves as a precursor to silica and also provides alkaline conditions for the reaction system. While organic amines react with carbon disulfide, nano-silica undergoes hydrolysis as the pH value decreases, resulting in nano-silica with large pore volume. The reaction product, alkyl dithiocarbamate, is then introduced into the pore structure of the nanoparticles.
[0019] This invention provides a porous nano-silica supported alkyl dithiocarbamate soil heavy metal passivating agent prepared by the above preparation method.
[0020] This invention also provides the application of the above-mentioned porous nano-silica supported alkyl dithiocarbamate soil heavy metal passivating agent in the remediation of heavy metal contaminated soil. Specifically, the passivating agent can be directly added to the heavy metal contaminated soil at a ratio of 0.1-0.5% by soil weight, and then mixed evenly with the soil by rotary tillage, plowing, or other methods.
[0021] When the above-mentioned porous nano-silica supported alkyl dithiocarbamate soil heavy metal passivating agent is applied in the remediation of heavy metal contaminated soil, the passivating agent is added to the heavy metal contaminated soil at a ratio of 0.1 to 0.5% by weight of the soil. It can be used to passivate heavy metals such as Pb, Cd, and Cu. It is suitable for the treatment of heavy metal pollution in non-ferrous metal smelting sites, farmland and solid waste sites, and can also be used for the treatment of polluted wastewater.
[0022] This invention utilizes soluble silicates as silica precursors while simultaneously providing alkaline conditions for the reaction. The addition of organic amines alters the surface polarity of silica, resulting in macroporous nano-silica supports. The reaction product of the organic amine and carbon disulfide, alkyl dithiocarbamate, is simultaneously generated and in-situ adsorbed onto the nano-silica surface, representing an in-situ synthesis-adsorption loading method. Different metal bases can impart different alkyl dithiocarbamates to silica. The passivating agent of this invention, as a soil heavy metal passivating agent, can complex with heavy metal ions such as Pb, Cd, and Cu, fixing the heavy metals to their surface, reducing the leaching of heavy metals from the solid-liquid phase, and decreasing their migration. Simultaneously, the passivating agent can release K, Ca, and Mg. Porous silica contains essential nutrients such as nitrogen, silicon, and nitrogen (N), which are necessary for plants and microorganisms, and increases soil fertility. It can also improve the soil environment.
[0023] The porous nano-silica-supported alkylamine dithiocarbamate soil heavy metal passivating agent provided by this invention possesses a large specific surface area at the nanoscale, achieving a high passivation effect with a low addition amount. The passivating agent of this invention can efficiently passivate heavy metals such as Pb, Cd, and Cu at an addition amount of 0.1% to 0.5% of the soil mass, with minimal impact on the physicochemical properties of the soil. It is easy to use and has good prospects for industrial production. The heavy metal passivating agent carrier provided by this invention is porous nano-silica, which can improve the stability of the passivating agent. Since the silica component of the heavy metal passivating agent carrier provided by this invention is a component of soil, it has minimal impact on the physicochemical properties of the soil and can improve the soil environment. The heavy metal soil passivating agent provided by this invention can release nutrients such as K, Ca, Mg, N, and Si required by plants while passivating heavy metals, increasing soil fertility.
[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0025] 1) The soil heavy metal passivating agent provided by this invention has high passivation efficiency for heavy metals and can achieve good remediation effect with low addition amount;
[0026] 2) The soil heavy metal passivating agent carrier provided by the present invention is porous nano-silica, which can improve the stability of the passivating agent. At the same time, porous silica can improve the soil environment and reduce the disturbance of the passivating agent to the soil.
[0027] 3) The soil heavy metal passivating agent provided by this invention can prepare different metal salts. While passivating heavy metals, it can release nutrients such as K, Ca, Mg, N, and Si required by plants, thus increasing soil fertility. Attached Figure Description
[0028] Figure 1 Transmission electron microscopy image of the passivating agent prepared in Example 1;
[0029] Figure 2 Scanning electron microscope image of the passivating agent prepared in Example 2;
[0030] Figure 3 Fourier transform infrared spectrum of the passivating agent prepared in Example 2;
[0031] Figure 4 The decrease in heavy metal content in soil leachate after remediation with the passivating agent prepared in Example 1;
[0032] Figure 5 The passivation efficiency of the passivating agent prepared in Example 4 on Cu, Pb and Cd in soil. Detailed Implementation
[0033] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.
[0034] In the embodiments, any steps or processes not described in detail can be performed using conventional techniques in the art. All raw materials used are common commercially available products that can be directly purchased in the art.
[0035] According to the technical specification for soil environmental monitoring (HJ / T166-2004), the available Cu, Pb and Cd in the soil were extracted by DTPA extraction method, and the heavy metal content in the extract was analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES).
[0036] The contaminated soil used in the following examples came from the vicinity of a farmland in Jiyuan City. The pollution values of Cu, Pb, and Cd in the soil are shown in Table 1.
[0037] Table 1. Range of Cu, Pb, and Cd contamination values in the contaminated soil used in the examples;
[0038]
[0039] Example 1
[0040] A method for preparing a porous nano-silica-supported alkyl dithiocarbamate soil heavy metal passivating agent includes the following steps:
[0041] 1) Weigh 143.16 g (silicon dioxide concentration 23.47%, sodium oxide concentration 8.17%) of sodium silicate aqueous solution (modulus 2.87) into the reactor, and add 5.92 g (0.08 mol) of calcium hydroxide (purity 95%) dispersed in 100 mL of deionized water into the reactor. Control the temperature at 20℃ and stir to mix.
[0042] 2) Dissolve 29.59 g (0.40 mol) of diethylamine (99% purity) in 80 mL of deionized water, add it to the reactor, control the temperature at 20℃, and stir the reaction for 1 h;
[0043] 3) Place 32.08 g (0.42 mol) of carbon disulfide (purity 99.5%) in a constant pressure dropping funnel, add 25 mL of deionized water and mix, then slowly add it dropwise into the reactor, control the temperature at 20℃, and stir the reaction for 2 h;
[0044] 4) Heat to 40℃, vacuum to recover excess carbon disulfide, stir and react for 2 h to obtain a reaction solution, and obtain a powder passivating agent after flash evaporation, wherein the mass ratio of alkyl dithiocarboxylate to silicon dioxide is 1:0.49.
[0045] The microstructure of the prepared passivating agent was analyzed using transmission electron microscopy. For example... Figure 1 As shown, the primary particles of the prepared passivating agent have a spherical structure with a primary particle size of 10-20 nm. After stacking and assembly, they form a network aggregate structure.
[0046] The passivating agent prepared in this embodiment was applied at 0.1% to 0.5% of the soil mass (soil bulk density was 1.4 g / cm³). 3 The effect of adding it to the collected contaminated soil on the passivation of available Cu, Pb, and Cd in the soil leachate is as follows: Figure 4 As shown:
[0047] When the remediation agent was added at a concentration of 0.1%, the available Cu in the soil decreased from 7.28 mg / kg to 0.07 mg / kg, and the passivation efficiency reached 99%.
[0048] When the remediation agent was added at a concentration of 0.3%, the available Pb in the soil decreased from 272 mg / kg to 24 mg / kg, and the passivation efficiency reached 91%.
[0049] When the amount of remediation agent added was 0.4%, the available Cd in the soil decreased from 5.76 mg / kg to 0.42 mg / kg, the passivation efficiency reached 93%, and the remediation effect was obvious.
[0050] Example 2
[0051] A method for preparing a porous nano-silica-supported alkyl dithiocarbamate soil heavy metal passivating agent includes the following steps:
[0052] 1) Weigh 177.18 g of sodium silicate aqueous solution (modulus 3.50) (silica concentration 28.22%, sodium oxide concentration 8.07%) into the reactor, dissolve 0.81 g (0.02 mol) of sodium hydroxide (purity 99%) in 60 mL of deionized water and add it to the reactor, and stir to mix at 30℃.
[0053] 2) Dissolve 19.97 g (0.23 mol) piperazine (99% purity) in 200 mL of deionized water, add it to the reactor, control the temperature at 30℃, and stir the reaction for 1 h;
[0054] 3) Place 36.66 g (0.48 mol) of carbon disulfide (purity 99.5%) in a constant pressure dropping funnel, add 30 mL of deionized water and mix, then slowly add it dropwise into the reactor, control the temperature at 30℃, and stir the reaction for 3 h.
[0055] 4) Heat to 50℃, vacuum to recover excess carbon disulfide, stir and react for 1 h to obtain a reaction solution, and spray dry to obtain a powder passivating agent, wherein the mass ratio of alkyl dithiocarboxylate to silicon dioxide is 1:0.77.
[0056] The microstructure of the prepared passivating agent was characterized using scanning electron microscopy, such as... Figure 2 As shown, after spray drying and granulation, the nanoparticles formed near-spherical particles with a diameter of 3-8 μm. Magnification reveals that the assembled spheres exhibit a non-rigid aggregate structure, readily disintegrating into smaller particles with numerous pores and a larger specific surface area. Spray drying and granulation can increase the particle size of the passivating agent, reducing dust generation during construction. It also facilitates the disintegration and pulverization of the passivating agent, promoting its natural decomposition into smaller particles upon introduction into the soil, thus aiding in its dispersion. Furthermore, the abundant pore structure on the sample surface effectively enhances the reaction efficiency of the passivating agent.
[0057] The prepared passivating agent was characterized and analyzed by Fourier transform infrared absorption spectroscopy. Figure 3 It can be seen that, compared with blank silica, the prepared silica-supported alkyl dithiocarbamates showed better performance at 2907, 1420, 1205, and 900 cm⁻¹. -1 A new absorption peak appeared. A database search revealed a peak at 2907 cm⁻¹. -1 1420 cm -1 The absorption peaks appearing at 1205 cm⁻¹ are the stretching vibration absorption peak and the shear vibration absorption peak of -CH₂-, respectively; -1The absorption peak at 900 cm⁻¹ is due to the stretching vibration of -C=S; the absorption peak at 900 cm⁻¹ is due to the shear vibration of -CSH. These results prove that a dithiocarboxyl group exists in the passivating agent.
[0058] The passivating agent prepared in this embodiment was added at 0.2% of the soil mass (soil bulk density was 1.4 g / cm³). 3 When the addition amount is 0.2%, the passivating agent dosage is 2.8 kg / m³. 3 When added to the collected contaminated soil, the passivation rates of available Cu, Pb, and Cd in the soil extract were 99%, 96%, and 85%, respectively, showing a significant remediation effect.
[0059] Example 3
[0060] A method for preparing a porous nano-silica-supported alkyl dithiocarbamate soil heavy metal passivating agent includes the following steps:
[0061] 1) Weigh 63.78 g of sodium silicate aqueous solution (modulus 3.50) (silica concentration 28.22%, sodium oxide concentration 8.07%) into the reactor, disperse 19.53 g (0.33 mol) magnesium hydroxide (purity 98%) in 180 mL of deionized water and add it to the reactor, control the temperature at 30℃ and stir to mix;
[0062] 2) Dissolve 27.78 g (0.10 mol) of polyethylene polyamine (99% purity) in 120 mL of deionized water, add it to the reactor, control the temperature at 30℃, and stir the reaction for 1 h;
[0063] 3) Place 50.41 g (0.66 mol) of carbon disulfide (purity 99.5%) in a constant pressure dropping funnel, add 40 mL of deionized water and mix, then slowly add it dropwise into the reactor, control the temperature at 30℃, and stir the reaction for 3 h.
[0064] 4) Heat to 50℃, vacuum to recover excess carbon disulfide, stir the reaction for 2 h to obtain a reaction solution, and spray dry to obtain a powder passivating agent, wherein the mass ratio of alkyl dithiocarboxylate to silicon dioxide is 1:0.23.
[0065] The passivating agent prepared in this embodiment was added at 0.1% of the soil mass (soil bulk density was 1.4 g / cm³). 3 When the addition amount is 0.1%, the passivating agent dosage is 1.4 kg / m³. 3 When added to the collected contaminated soil, the passivation rates of available Cu, Pb, and Cd in the soil extract were 99%, 99%, and 93%, respectively, showing a significant remediation effect.
[0066] Example 4
[0067] A method for preparing a porous nano-silica-supported alkyl dithiocarbamate soil heavy metal passivating agent includes the following steps:
[0068] 1) Weigh 70.87 g of sodium silicate aqueous solution (modulus 3.50) (silica concentration 28.22%, sodium oxide concentration 8.07%) into the reactor, dissolve 56.00 g (0.40 mol) ammonia water (purity 25%) in 80 mL of deionized water and add it to the reactor, and stir and mix at 20℃.
[0069] 2) Dissolve 12.12 g (0.20 mol) of ethylenediamine (99% purity) in 80 mL of deionized water, add it to the reactor, control the temperature at 20℃, and stir the reaction for 1 h;
[0070] 3) Place 33.61 g (0.44 mol) of carbon disulfide (purity 99.5%) in a constant pressure dropping funnel, add 30 mL of deionized water and mix, then slowly add it dropwise into the reactor, control the temperature at 20℃, and stir the reaction for 3 h.
[0071] 4) Heat to 50℃, vacuum to recover excess carbon disulfide, stir and react for 1 h to obtain a reaction solution, and obtain a powder passivating agent after flash evaporation, wherein the mass ratio of alkyl dithiocarboxylate to silicon dioxide is 1:0.48.
[0072] The passivating agent prepared in this embodiment was applied at 0.1% to 0.5% of the soil mass (soil bulk density was 1.4 g / cm³). 3 Adding it to the collected contaminated soil, the passivation rate of available Cu, Pb, and Cd in the soil leachate is as follows: Figure 5 As shown:
[0073] When the amount of repair agent added is 0.1%, the passivation efficiency for Cu can reach 99%.
[0074] When the amount of repair agent added is 0.3%, the passivation efficiency of Pb can reach 95%;
[0075] When the amount of repair agent added is 0.4%, the passivation efficiency of Cd can reach 99%; the repair effect is obvious.
[0076] Example 5
[0077] A method for preparing a porous nano-silica-supported alkyl dithiocarbamate soil heavy metal passivating agent includes the following steps:
[0078] 1) Weigh 51.98 g of potassium silicate aqueous solution (modulus 1.04) (silica concentration 30.78%, potassium oxide concentration 29.51%) into the reactor, dissolve 1.98 g (0.03 mol) of potassium hydroxide (purity 85%) in 130 mL of deionized water and add it to the reactor, and stir and mix at 10℃.
[0079] 2) Dissolve 22.12 g (0.30 mol) of diethylamine (99% purity) in 70 mL of deionized water, add it to the reactor, control the temperature at 10℃, and stir the reaction for 2 h;
[0080] 3) Place 26.73 g (0.35 mol) of carbon disulfide (purity 99.5%) in a constant pressure dropping funnel, add 20 mL of deionized water and mix, then slowly add it dropwise into the reactor, control the temperature at 10℃, and stir the reaction for 4 h.
[0081] 4) Heat to 40℃, vacuum to recover excess carbon disulfide, stir and react for 2 h to obtain a reaction solution, and obtain a powder passivating agent after flash evaporation, wherein the mass ratio of alkyl dithiocarboxylate to silicon dioxide is 1:0.28.
[0082] The passivating agent prepared in this embodiment was added at 0.3% of the soil mass (soil bulk density was 1.4 g / cm³). 3 When the addition amount is 0.3%, the passivating agent dosage is 4.2 kg / m³. 3 When added to the collected contaminated soil, the passivation rates of available Cu, Pb, and Cd in the soil extract were 99%, 90%, and 68%, respectively, showing a significant remediation effect.
Claims
1. A method for preparing a porous nano-silica-supported dithiocarbamate soil heavy metal passivating agent, characterized in that, Includes the following steps: 1) Add a soluble silicate aqueous solution as a substrate to the reactor, wherein the mass concentration of silica is 10-30%, and add an alkaline aqueous solution under stirring conditions, and stir and mix at 10-30℃; 2) Add an organic amine solution and react at 10–30°C for 1–2 hours; 3) Add the carbon disulfide-water mixture and stir at 10-30°C for 2-4 hours; 4) Heat to 40℃~50℃, remove excess carbon disulfide by vacuum, and then react for 1~2 hours; the reaction solution is then dried to obtain the final product. In step 2), the organic amine is one or more of diethylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, polyethylenepolyamine, and piperazine.
2. The preparation method according to claim 1, characterized in that, In step 1), the soluble silicate includes sodium silicate and / or potassium silicate, and the silicate modulus is 1 to 3.
5.
3. The preparation method according to claim 1, characterized in that, In step 1), the alkali includes sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, calcium oxide, magnesium oxide, or ammonia.
4. The preparation method according to claim 1, characterized in that, In step 4), the drying method is oven drying, spray drying, or flash evaporation.
5. The preparation method according to claim 1, characterized in that, The molar ratio of organic amine to base is 1:(0.5–4.5); the molar ratio of organic amine to carbon disulfide is 1:(1–7).
6. A porous nano-silica-supported dithiocarbamate soil heavy metal passivating agent prepared by any of the preparation methods described in claims 1 to 5.
7. The application of the porous nano-silica supported dithiocarbamate soil heavy metal passivating agent of claim 6 in the remediation of heavy metal contaminated soil; wherein the heavy metal is Pb, Cd or Cu.
8. The application as described in claim 7, characterized in that, The passivating agent is added to heavy metal contaminated soil at a ratio of 0.1% to 0.5% of the soil weight to passivate heavy metals Pb, Cd, and Cu.