A remediation composition for hexavalent chromium-contaminated soil and a soil remediation method

Abstract

The present invention provides a remediation composition for soil contaminated with hexavalent chromium and a soil remediation method. The composition comprises catechin, flavonoid isorhamnetin and humic acid with a mass ratio of 1:1 - 3:0.1 - 1. The remediation composition for soil contaminated with hexavalent chromium according to the present invention can achieve a leaching rate of 93% for the hexavalent chromium contamination in the soil. At the same time, the composition can reduce more than 95% of the hexavalent chromium in the leaching solution to trivalent chromium with low toxicity, achieving the purpose of completely removing hexavalent chromium from the soil and greatly reducing the material cost of chemical leaching.

Description

Technical Field

[0001] The invention belongs to the field of soil remediation, and in particular relates to a remediation composition for soil hexavalent chromium pollution and a soil remediation method. Background Art

[0002] Heavy metal pollution in soil has a long cycle, is difficult to degrade, and is difficult to manage. Chromium is an important industrial metal that is widely used in many industries, but high concentrations of chromium emissions can cause harm to the environment and human health, and may lead to water pollution, soil deterioration, vegetation death, animal death, and increase the risk of human disease. In particular, hexavalent chromium (Cr(VI)) is particularly harmful to the environment. Chromium pollution exists in water, soil, and the atmosphere in some areas, mainly concentrated in industrial parks, mining areas, and abandoned sites.

[0003] Compared with Cr 3+ ,Cr 6+ It is highly toxic, about Cr 3+ Chromium also causes persistent pollution to the soil and its surrounding environment. High concentrations of chromium can damage the surrounding ecosystem and groundwater resources, leading to environmental degradation and harming human health. People who are exposed to chromium-containing soil for a long time are prone to symptoms such as skin itching, allergies, ulcers and dermatitis.

[0004] Chromium in the soil often seeps into groundwater and surface water with rainwater, causing water pollution. Hexavalent chromium (Cr(VI)) is highly toxic to aquatic organisms, and long-term drinking of contaminated water may cause harm to human health. High concentrations of chromium pollution will also affect the growth of microorganisms in the soil, destroy the ecological balance of microorganisms in the soil, destroy the activity of soil enzymes, inhibit plants from absorbing nutrients and water, lead to a decline in soil quality, affect the ecological function of the soil, cause poor growth, reduced yields, or even death of crops, affect the fertility of the soil, and its ability to retain water and fertilizer, damage soil biodiversity and ecosystem stability, and affect the balance of the ecosystem. High concentrations of chromium pollution can cause the soil structure to become loose or crusty, reduce soil aeration, permeability, and fertilizer retention, accelerate soil degradation, and damage the soil ecological environment.

[0005] A large number of scholars at home and abroad have conducted relevant research on the remediation of soil contaminated by heavy metals. Soil leaching is an effective and easy-to-control remediation method that can be used to remove a variety of pollutants. It uses water, redox agents, surfactants, chelating agents or acid solutions to remove pollutants from contaminated soil. Through ion exchange, precipitation, adsorption and chelation, heavy metals in the soil are transferred from the soil to the liquid phase, and then recovered or treated from the leachate for final disposal.

[0006] The Chinese invention patent with the application number CN201310493630.2 uses hydrochloric acid, reduced iron powder and sodium metabisulfite to leach hexavalent chromium contaminated soil, and the removal rate of hexavalent chromium can be close to 90%. However, hydrochloric acid and sodium metabisulfite have great destructive effects on the physical and chemical properties of the soil itself.

[0007] The Chinese invention patent with the application number CN202410316068.4 uses microorganisms to treat hexavalent chromium contaminated soil. The microbial culture time cycle is long, the relative cost is high, and the introduced microorganisms may also have a negative impact on the local ecology.

[0008] Traditional chemical leaching technology causes relatively serious secondary pollution to the soil. Biomass natural component extraction materials also have various functional groups such as hydroxyl and carboxyl that can chelate with heavy metal ions. Compared with traditional chemical leaching, while efficiently leaching soil heavy metals, it is environmentally friendly, has less interference with the soil, and has broad development prospects. Summary of the Invention

[0009] In view of this, the present invention aims to overcome the defects in the prior art and proposes a remediation composition for soil contaminated with hexavalent chromium and a soil remediation method.

[0010] To achieve the above object, the technical solution of the present invention is realized as follows:

[0011] The present invention provides a remediation composition for soil contaminated with hexavalent chromium, which comprises catechin, flavonoid isorhamnetin and humic acid in a mass ratio of 1:1 - 3:0.1 - 1.

[0012] Further, the mass ratio of catechin, flavonoid isorhamnetin and humic acid is 1:1.5 - 3:0.1 - 0.6.

[0013] Further, the molecular weight of the humic acid is 3000 - 5000. Within the above molecular weight range, the humic acid has the optimal "mediating effect" and the least interference with the soil.

[0014] The basic structure of the humic acid macromolecule is an aromatic ring and an aliphatic ring, with functional groups such as hydroxyl, carboxyl, carbonyl, and methoxy groups attached to the rings; there are also a certain amount of free radicals on the humic acid molecule. First, the carboxyl and phenolic hydroxyl groups in the humic acid can dissociate H + , react with hexavalent chromium ions to form soluble complexes. Secondly, after the phenolic hydroxyl group dissociates H + , it can also provide electron pairs, and the electron pairs have ion exchange ability, which can further exchange H in catechin and flavonoid isorhamnetin + , so as to promote the release of H in catechin and flavonoid isorhamnetin +The ability to enhance the ability of catechins and flavonoid isorhamnetin to react with hexavalent chromium ions to form soluble complexes; in addition, due to the strong adsorption of humic acid, it can promote the chelation of catechins and flavonoid isorhamnetin with hexavalent chromium heavy metal ions; finally, humic acid has amphiphilic properties, containing both hydrophobic groups such as C-H groups and aromatic structures, and hydrophilic groups such as carboxyl groups and hydroxyl groups, which enables humic acid to play a "mediating role" similar to that of dishwashing liquid in removing oil during the transfer of hexavalent chromium from soil to the aqueous phase, thus better washing out hexavalent chromium from the soil.

[0015] The present invention also provides a leaching solution for soil contaminated with hexavalent chromium, and the leaching solution contains the above-mentioned repair composition, and the percentage of the repair composition in the total weight of the leaching solution is 0.1 - 5%.

[0016] The present invention also provides a preparation method of a leaching solution for soil contaminated with hexavalent chromium, which includes the following steps:

[0017] Step 1 is to add catechins to deionized water, mix evenly to obtain a catechin solution, add flavonoid isorhamnetin to deionized water, mix evenly to obtain a flavonoid isorhamnetin solution, and add humic acid to deionized water, mix evenly to obtain a humic acid solution;

[0018] Step 2 is to mix and stir the catechin solution and the flavonoid isorhamnetin solution evenly, and then inject the humic acid solution into it under the conditions of heating and stirring. After completion, the above-mentioned leaching solution is obtained.

[0019] Further, the temperature of the heating step in Step 2 is 35 - 55°C; the flow rate of the injection step in Step 2 is 50 - 100 mL / min. Under this condition, humic acid can more fully exchange the H in catechins and flavonoid isorhamnetin + .

[0020] The present invention also provides a repair method for soil contaminated with hexavalent chromium, which includes the following steps: adding the hexavalent chromium contaminated soil to the above-mentioned leaching solution, performing oscillating leaching, and then performing centrifugation and filtration.

[0021] Further, the solid-liquid ratio of the hexavalent chromium contaminated soil to the leaching solution is 0.5 - 5 kg:20 L.

[0022] Further, the temperature of the oscillating leaching step is 25 - 50°C, and the rotation speed is 180 - 360 r / min; the time of the centrifugation step is 3 - 10 min, and the rotation speed is 3000 - 9000 r / min.

[0023] Further, the filtration step uses a microporous filter membrane for filtration, and the pore size of the microporous filter membrane is 0.22 - 0.45 μm.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] The remediation composition for soil chromium (VI) pollution of the present invention can achieve a leaching rate of 93% for chromium (VI) pollution in soil. At the same time, the composition can reduce more than 95% of the chromium (VI) in the leaching solution to low-toxic trivalent chromium, achieving the purpose of completely removing chromium (VI) from the soil, and greatly reducing the material cost of chemical leaching. Description of the Drawings

[0026] Figure 1 It is a bar chart of the leaching rate of chromium (VI) in soil according to the embodiment of the present invention;

[0027] Figure 2 It is a bar chart of the reduction rate of chromium (VI) in the leaching solution according to the embodiment of the present invention. Detailed Description of the Invention

[0028] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which the present invention belongs. The test reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0029] Preparation of the chromium (VI)-polluted soil described in each embodiment and comparative example of the present invention: The test soil is yellow soil, collected from the lakeside of Tianjin Polytechnic University in Xiqing District, Tianjin (39°03'N, 117°06'E). Larger gravels, weeds and other foreign matters are removed, air-dried naturally, passed through a 60-mesh nylon sieve, mixed evenly and then sealed for standby. Weigh 2.829 g of potassium dichromate (K2Cr2O7, analytical grade) dried at 110 °C for 2 h, dissolve it in water, transfer it to a 1000 ml volumetric flask, dilute it to the mark with distilled water, and shake well to prepare a 1 g / L chromium solution. Put the soil sample passed through a 60-mesh nylon sieve into a tray, pour 1 g / L chromium solution into it, and immerse the soil sample in the chromium solution. Air-dry and age it naturally for 90 days, stir it about every two days during this period, and ensure that the soil moisture content is about 50% by the gravimetric method to make the soil pollution uniform. After air-drying and aging, the soil is ground into powder by a high-speed grinder, dried, mixed evenly and stored in a plastic box in a cool place for standby.

[0030] The present invention will be described in detail below with reference to the embodiments.

[0031] Example 1

[0032] A remediation composition for soil chromium (VI) pollution, which comprises catechin, flavonoid isorhamnetin and humic acid in a mass ratio of 1:2:0.5.

[0033] A method for preparing a leaching solution for soil contaminated with hexavalent chromium, comprising the following steps:

[0034] Step 1: Add 10 g of catechin to 1000 mL of deionized water, mix evenly to obtain a catechin solution; add 20 g of flavonoid isorhamnetin to 1000 mL of deionized water, mix evenly to obtain a flavonoid isorhamnetin solution; add 5 g of humic acid to 1000 mL of deionized water, mix evenly to obtain a humic acid solution.

[0035] Step 2: Mix the catechin solution and the flavonoid isorhamnetin solution and stir evenly, then at a temperature of 40 °C, inject the humic acid solution into it at a flow rate of 50 mL / min. After completion, the leaching solution is obtained.

[0036] A method for repairing soil contaminated with hexavalent chromium, comprising the following steps: Add 0.1 kg of soil contaminated with hexavalent chromium to 2 L of the above leaching solution, carry out oscillating leaching, the temperature of the oscillating leaching is 30 °C, the rotation speed is 260 r / min, and then carry out centrifugation and filtration. The centrifugation time is 5 min, the rotation speed is 5000 r / min, and the pore size of the microporous filter membrane is 0.45 μm.

[0037] Example 2

[0038] The difference from Example 1 is only that: the repair composition comprises catechin, flavonoid isorhamnetin and humic acid with a mass ratio of 1:1:0.5.

[0039] Example 3

[0040] The difference from Example 1 is only that: the solid-liquid ratio of the soil contaminated with hexavalent chromium to the leaching solution is 2 kg / 20 L.

[0041] Comparative Example 1

[0042] The difference from Example 1 is only that: the repair composition comprises catechin, flavonoid isorhamnetin and humic acid with a mass ratio of 0.5:2:0.5.

[0043] Comparative Example 2

[0044] The difference from Example 1 is only that: the repair composition comprises catechin, flavonoid isorhamnetin and humic acid with a mass ratio of 1:0.5:0.5.

[0045] Comparative Example 3

[0046] The difference from Example 1 is only that: the repair composition comprises catechin, flavonoid isorhamnetin and humic acid with a mass ratio of 1:2:0.05.

[0047] Comparative Example 4

[0048] The difference from Example 1 is only that catechins are not added.

[0049] Comparative Example 5

[0050] The difference from Example 1 is only that isorhamnetin is not added.

[0051] Comparative Example 6

[0052] The difference from Example 1 is only that humic acid is not added.

[0053] Comparative Example 7

[0054] The difference from Example 1 is only that the solid-liquid ratio of hexavalent chromium-contaminated soil to the leaching solution is: 9 kg / 20 L.

[0055] The above Examples 1-3 and Comparative Examples 1-7 were tested for the chromium(VI) leaching rate in soil and the chromium(VI) reduction rate in the leaching solution. The results are as Figure 1 - Figure 2 shown. Catechins and isorhamnetin can promote each other to dissociate H + , react with chromium(VI) ions to form soluble complexes, and can promote each other's chelation of chromium(VI) heavy metal ions, so as to better wash out chromium(VI) from the soil. As can be seen from the role of the above humic acid in the leaching solution, in the case of inappropriate ratios of the three components or the absence of a certain component in the comparative example, the synergistic effect of the three components cannot be fully exerted, and the chromium(VI) leaching rate and the chromium(VI) reduction rate in the leaching solution are significantly inferior to those of the examples. Moreover, when the solid-liquid ratio of the contaminated soil to the leaching solution is too high, that is, when the leaching solution is insufficient, the chromium(VI) leaching rate and the chromium(VI) reduction rate in the leaching solution will also decrease significantly.

[0056] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A remediation composition for soil contaminated with hexavalent chromium, characterized in that: The composition comprises catechin, flavonoid isorhamnetin and humic acid with a mass ratio of 1: 1.5 - 3: 0.1 - 0.6; the molecular weight of the humic acid is 3000 - 5000.

2. A leaching solution for soil contaminated with hexavalent chromium, characterized in that: The eluent contains the repair composition described in claim 1, and the percentage of the repair composition in the total weight of the eluent is 0.1 - 5%.

3. The preparation method of the leaching solution for soil chromium(VI) pollution according to claim 2, characterized in that: It includes the following steps: Step 1 is to add catechin into deionized water, mix evenly to obtain a catechin solution, add flavonoid isorhamnetin into deionized water, mix evenly to obtain a flavonoid isorhamnetin solution, and add humic acid into deionized water, mix evenly to obtain a humic acid solution; Step 2 is to mix and stir the catechin solution and the flavonoid isorhamnetin solution evenly, and then inject the humic acid solution into it under the conditions of heating and stirring to obtain the eluent after completion.

4. The preparation method of the leaching solution for soil hexavalent chromium pollution according to claim 3, wherein: The temperature of the heating step in Step 2 is 35 - 55 °C; the flow rate of the injection step in Step 2 is 50 - 100 mL / min.

5. A method for repairing soil contaminated with hexavalent chromium, characterized in that: It includes the following steps: adding hexavalent chromium - contaminated soil into the eluent described in claim 2, performing oscillating elution, and then centrifuging and filtering.

6. The remediation method for soil chromium(VI) pollution according to claim 5, characterized in that: The solid - liquid ratio of the hexavalent chromium - contaminated soil to the eluent is 0.5 - 5 kg: 20 L.

7. The remediation method for hexavalent chromium pollution in soil according to claim 5, characterized in that: The temperature of the oscillating elution step is 25 - 50 °C, and the rotation speed is 180 - 360 r / min; the time of the centrifuging step is 3 - 10 min, and the rotation speed is 3000 - 9000 r / min.

8. The remediation method for soil contaminated with hexavalent chromium according to claim 5, characterized in that: The filtering step is carried out using a microporous membrane filter, and the pore size of the microporous membrane filter is 0.22 - 0.45 μm.

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