CN110465544B - Method for repairing hexavalent chromium polluted farmland soil - Google Patents
Method for repairing hexavalent chromium polluted farmland soil Download PDFInfo
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Abstract
The invention discloses a method for repairing hexavalent chromium polluted farmland soil, which comprises the following steps: weighing oxalic acid, dissolving in water to prepare an oxalic acid solution; soaking activated carbon powder in an oxalic acid solution to obtain activated carbon powder slurry; g to C3N4/PDI@MMixing the OF powder with soil OF the hexavalent chromium polluted farmland, and uniformly stirring to obtain photocatalytic pre-doped soil; respectively weighing photocatalytic pre-doped soil, humus soil and activated carbon powder slurry, mixing, adding water, and stirring to obtain farmland soil to be restored; and irradiating the farmland soil to be restored by using a xenon lamp, turning the soil 1 time every 1 hour in the period, and restoring the soil of the farmland polluted by hexavalent chromium within 4-6 hours. The method has the advantages of simple process, strong operability, wide sources of related oxalic acid, active carbon, humus and the like, short restoration time, good restoration effect, energy conservation, no secondary pollution, and improvement of the original fertility of the cultivated land soil while eliminating the harm of hexavalent chromium.
Description
Technical Field
The invention relates to the field of treatment and restoration of soil in polluted agricultural land, in particular to a method for restoring soil in hexavalent chromium-polluted cultivated land.
Background
The safety of the quality of the cultivated land environment not only directly affects the quality of agricultural products but also affects the health of the personnel involved in the cultivation activities. At present, the heavy metal pollution situation of cultivated land in China is severe, and malignant pollution events frequently occur. The ministry of environmental protection and the national soil resources department release "national soil pollution condition survey bulletin" point out that the overproof rate of soil environmental pollution points in cultivated land in China is close to 20%. Industrial waste liquid produced in leather, electroplating, pharmaceutical, printing and dyeing and other industries usually contains a large amount of heavy metal chromium. The illegal discharge of these industrial waste liquids can cause severe hexavalent chromium pollution to the cultivated land soil around the factory building. Hexavalent chromium has the characteristics of high toxicity, easy migration, high teratogenicity and the like. The treatment and restoration of hexavalent chromium polluted farmland soil have important significance for guaranteeing grain safety and maintaining good ecological environment.
Currently, the remediation of chromium-contaminated soil is mainly achieved by two ways of reducing high-valence chromium in soil or removing chromium from contaminated soil, specifically including technologies such as solidification, stabilization, chemical leaching, electric remediation, biological remediation, and the like. For the restoration of the heavy metal polluted farmland, the curing and leaching technologies can obviously reduce the tiltability of the farmland and the original soil fertility of the farmland. The stabilization technology not only enhances the adsorption effect of the polluted soil on chromium, but also does not essentially realize the price reduction and detoxification of chromium, and chromium pollutants are easily transferred from the soil to crops.
The electric repair technology has the problems of large energy consumption, deep treatment of a chromium enrichment area and the like. The bioremediation technology has the problems of long restoration period and poor restoration effect. In summary, the research and development of a technology which has low energy consumption and short restoration period, can effectively realize the reduction and detoxification of hexavalent chromium and can effectively prevent the hexavalent chromium from migrating into crops is the key to solve the problem of soil treatment and restoration of the current hexavalent chromium cultivated land.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to solve the technical problem of providing a method for repairing hexavalent chromium polluted farmland soil.
The technical scheme is as follows: in order to solve the technical problems, the invention adopts the following technical scheme: a method for remediating hexavalent chromium-contaminated arable land soil, the remediation method comprising the steps of:
1) weighing oxalic acid, dissolving the oxalic acid in water, and stirring until the oxalic acid is completely dissolved to prepare an oxalic acid solution;
2) soaking activated carbon powder in an oxalic acid solution for 2-4 hours to obtain activated carbon powder slurry;
3) g to C3N4Mixing the PDI @ MOF powder with hexavalent chromium polluted farmland soil, and uniformly stirring to obtain photocatalytic pre-doped soil;
4) respectively weighing photocatalytic pre-doped soil, humus soil and activated carbon powder slurry, mixing the photocatalytic pre-doped soil, humus soil and activated carbon powder slurry, adding water, and stirring for 10-30 minutes at 20-60 rpm to obtain farmland soil to be restored;
5) and irradiating the farmland soil to be restored by using a xenon lamp, turning the soil 1 time every 1 hour in the period, and restoring the soil of the farmland polluted by hexavalent chromium within 4-6 hours.
Wherein the concentration of the oxalic acid solution in the step 1) is 0.5-2.5M.
Wherein the solid-to-liquid ratio of the activated carbon powder and the oxalic acid solution in the step 2) is 1-5: 10 mg/mL.
Wherein g-C of said step 3)3N4The mass ratio of the/PDI @ MOF powder to the soil of the hexavalent chromium-polluted cultivated land is 1-5: 100.
Wherein the mass ratio of the photocatalytic pre-doped soil, the humus soil and the activated carbon powder slurry in the step 4) is 100: 5-15.
Wherein the water content of the farmland to be restored in the step 4) is 25-35%.
Wherein the input power of the xenon lamp light source in the step 5) is 150-300W.
The working principle of the invention is as follows: g-C can be induced by sunlight irradiation3N4The catalysis of/PDI @ MOF occurs such that g-C3N4the/PDI @ MOF surface generates a large number of photogenerated holes and photogenerated electrons. The photoproduced electrons can directly reduce hexavalent chromium and convert the hexavalent chromium into trivalent chromium. And the photoproduction holes can oxidize organic matters in the humus soil to generate carbonate radicals. The carbonate radical can effectively reduce hexavalent chromium to trivalent chromium and carbon dioxide. During the soaking process, oxalic acid molecules are loaded on the surfaces and the inner parts of pores of the active carbon particles through electrostatic adsorption and capillary action. The oxalic acid is loaded to make the surface of the activated carbon electronegative, so that trivalent chromium ions can be effectively adsorbed. After being electrostatically adsorbed on the surface of the activated carbon, trivalent chromium ions are further stabilized on the activated carbon particles through chelation with oxalate, so that the trivalent chromium ions are prevented from being transferred into crops. The humus contains a large amount of reducing substances, which can prevent trivalent chromium from being oxidized again and avoid oxygen free radicals from damaging original nutrient substances in the farmland soil. Meanwhile, carbon dioxide generated in the hexavalent chromium reduction process can improve the content of inorganic carbon in the farmland soil, humus soil can improve the content of humus in the farmland soil, and active carbon can effectively improve the air permeability and water storage property of the farmland soil, which are beneficial to improving the fertility of the farmland soil。
Has the advantages that: the method has the advantages of simple process and strong operability, and the related additives such as oxalic acid, active carbon, humus soil and the like have wide sources. The invention has short treatment and repair time and good repair effect. The invention uses sunlight to excite catalytic reaction, thereby saving energy and generating no secondary pollution. The invention can eliminate the harm of hexavalent chromium and improve the original fertility of the cultivated land soil to a certain extent. The invention opens up a new way for repairing hexavalent chromium polluted farmland soil.
Drawings
FIG. 1 is a flow chart of the method for repairing hexavalent chromium-contaminated farmland soil.
Detailed Description
The invention is further described below with reference to the figures and examples.
Example 1 Effect of oxalic acid concentration on the Leaching Rate of hexavalent chromium in the soil for remediating cultivated land and the growth ratio of the relative root System of Rice
Weighing oxalic acid, dissolving in water, stirring until the oxalic acid is completely dissolved, and preparing oxalic acid solutions with different concentrations, wherein the concentrations of the oxalic acid solutions are 0.25M, 0.35M, 0.45M, 0.5M, 1.5M, 2.5M, 2.55M, 2.65M and 2.75M respectively. Respectively weighing activated carbon powder and an oxalic acid solution according to the solid-to-liquid ratio of 1: 10mg/mL, and soaking the activated carbon powder in the oxalic acid solution for 2 hours to obtain activated carbon powder slurry. g-C is weighed according to the mass ratio of 1: 100 respectively3N4(ii) PDI @ MOF powder and hexavalent chromium contaminating cultivated land soil and combining g-C3N4Mixing the/PDI @ MOF powder with soil of a hexavalent chromium polluted farmland, and uniformly stirring to obtain the photocatalytic pre-doped soil. Respectively weighing the photocatalytic pre-doped soil, the humus soil and the activated carbon powder slurry according to the mass ratio of 100:5, mixing the photocatalytic pre-doped soil, the humus soil and the activated carbon powder slurry, adding water, and stirring for 10 minutes at 20rpm to obtain the farmland soil to be restored, wherein the water content of the farmland soil to be restored is 25%. The soil of the farmland to be restored is irradiated by a xenon lamp (PL-X300D, Beijing Prinleiss technology limited), the soil is turned over for 1 time every 1 hour, the restoration of the soil of the farmland polluted by hexavalent chromium can be realized within 4 hours, and the input power of a xenon lamp light source is 150W.
Sampling and preparing chromium-contaminated soil, and basic properties: the soil adopted by the invention is directly taken from a chemical plant in Chongqing city. Sampling the chromium-contaminated soil according to the technical guidance for soil quality soil sampling (GB/T36197-2018). And drying the collected soil sample at the constant temperature of 105 ℃ for 24 hours, ball-milling for 6 hours, and sieving by a 200-mesh sieve. The soil particle size is concentrated between 1-100 μm, and the average particle size is 42.75 μm. The content of chromium element in the soil is 12.16 percent.
g-C3N4Preparation of/PDI @ MOF powder: g-C3N4the/PDI @ MOF powder is prepared with reference to the description of g-C3N4/PDI @ MOF heterologous junctions for the high level effective light-drive definition of pharmaceutical and phenolic micropollutants.
Hexavalent chromium toxicity leaching, concentration detection and leaching rate calculation for repairing farmland soil: toxicity leaching experiments leaching toxicity experiments were carried out on hexavalent chromium-contaminated farmland soil and detoxified soil according to the solid waste leaching toxicity leaching method-sulfuric acid-nitric acid method (HJ/T299-2007). The concentration of hexavalent chromium in the liquid is measured according to the diphenyl carbonyl dihydrazide spectrophotometry (GB7467-87) for measuring hexavalent chromium in water quality. The hexavalent chromium leaching efficiency of the cultivated land soil is measured according to the formula (1), wherein LCrIs the leaching rate of hexavalent chromium, c0For the hexavalent chromium leaching concentration of the chromium-contaminated farmland soil, ctIn order to restore the leaching concentration of hexavalent chromium in the cultivated land soil.
Detecting the root growth of the cultivated land restoration soil and calculating the relative root growth ratio of rice: the experiment of the root system growth of rice in the Soil for repairing cultivated land and the experiment of the root system growth of rice plants in the Soil of the adjacent uncontaminated cultivated land (as blank control) are carried out according to the international standard of Soil quality-Determination of the effects of pollutants on Soil flow-Part 1: method for the measurement of inhibition of root growth (ISO 11269-1-2012). And calculating the relative root system growth ratio of the rice according to the test result, wherein the relative root system growth ratio of the rice is the growth length of the root system of the rice plant in the soil of the restored cultivated land/the growth length of the root system of the rice plant in the soil adjacent to the uncontaminated cultivated land.
The test results of the leaching rate of hexavalent chromium in the soil for repairing the cultivated land and the relative root growth ratio of the rice are shown in table 1.
TABLE 1 influence of oxalic acid concentration on hexavalent chromium leaching rate in soil for repairing cultivated land and relative root growth ratio of paddy rice
As can be seen from table 1, when the concentration of oxalic acid is less than 0.5M (as in table 1, when the concentration of oxalic acid is 0.45M, 0.35M, 0.25M and lower ratios not listed in table 1), the surface of activated carbon is loaded with fewer oxalate radicals, the surface of activated carbon is weak in electronegativity and poor in adsorption and chelation effects on chromium ions, so that the leaching rates of hexavalent chromium in the soil of the restored cultivated land are both higher than 24%, and as the concentration of oxalic acid is significantly increased, the relative root growth ratio of rice in the soil of the corresponding restored cultivated land is less than 1.13 and as the concentration of oxalic acid is significantly decreased; when the concentration of oxalic acid is equal to 0.5-2.5M (as shown in Table 1, when the concentration of oxalic acid is 0.5M, 1.5M and 2.5M), sufficient oxalic acid roots are loaded on the surface of the activated carbon, the surface of the activated carbon has strong electronegativity and good adsorption and chelation effects on chromium ions, so that the leaching rates of hexavalent chromium in the soil of the restored cultivated land are both lower than 17%, and the relative root growth ratio of paddy in the soil of the corresponding restored cultivated land is both greater than 1.18; when the concentration of oxalic acid is more than 2.5M (as shown in Table 1, when the concentration of oxalic acid is 2.55M, 2.65M and 2.75M and higher ratio not listed in Table 1), sufficient oxalic acid roots are loaded on the surface of the activated carbon, the surface of the activated carbon has strong electronegativity and good effects of adsorbing and chelating chromium ions, but the further increase of the concentration of oxalic acid has no significant influence on the leaching rate of hexavalent chromium in the soil for repairing cultivated land and the growth ratio of the rice relative to the root system. Therefore, comprehensively, the benefits and the cost are combined, and when the concentration of the oxalic acid is equal to 0.5-2.5M, the leaching rate of hexavalent chromium in the soil of the restored cultivated land and the relative root growth ratio of the rice are improved.
Example 2g-C3N4Comparison of quality of/PDI @ MOF powder and soil of hexavalent chromium-polluted farmland to restore influence of leaching rate of hexavalent chromium in farmland soil and growth ratio of rice relative to root system
Weighing oxalic acid, dissolving the oxalic acid in water, stirring until the oxalic acid is completely dissolved, and preparing an oxalic acid solution, wherein the concentration of the oxalic acid solution is 2.5M. Weighing activated carbon powder and oxalic acid solution according to the solid-to-liquid ratio of 3: 10mg/mL, and soaking the activated carbon powder in the oxalic acid solution for 3 hours to obtain activated carbon powder slurry. g-C is respectively weighed according to the mass ratio of 0.5: 100, 0.7: 100, 0.9: 100, 1: 100, 3: 100, 5:100, 5.1: 100, 5.3: 100 and 5.5: 1003N4(ii) PDI @ MOF powder and hexavalent chromium contaminating cultivated land soil and combining g-C3N4Mixing the/PDI @ MOF powder with soil of a corresponding hexavalent chromium-polluted farmland, and uniformly stirring to obtain the photocatalytic pre-doped soil. Respectively weighing the photocatalytic pre-doped soil, the humus soil and the activated carbon powder slurry according to the mass ratio of 100: 10, mixing the photocatalytic pre-doped soil, the humus soil and the activated carbon powder slurry, adding water, and stirring for 20 minutes at 40rpm to obtain the farmland soil to be restored, wherein the water content of the farmland soil to be restored is 30%. The soil to be repaired is irradiated by a xenon lamp (PL-X300D, Beijing Prinleis science and technology Limited company), the soil is turned over for 1 time every 1 hour, the soil in the hexavalent chromium polluted farmland can be repaired within 5 hours, and the input power of a xenon lamp light source is 225W.
The sampling, preparation and basic properties of the chromium-contaminated soil are the same as those of the example 1.
g-C3N4the/PDI @ MOF powder was prepared as in example 1.
The hexavalent chromium toxicity leaching, concentration detection and leaching rate calculation for repairing the farmland soil are the same as those in example 1.
The detection of root growth of the cultivated land restoration soil and the calculation of the relative root growth ratio of the rice are the same as those in example 1.
The test results of the leaching rate of hexavalent chromium in the soil for repairing the cultivated land and the relative root growth ratio of the rice are shown in table 2.
TABLE 2g-C3N4Comparison of quality of/PDI @ MOF powder and soil of hexavalent chromium-polluted farmland to restore influence of leaching rate of hexavalent chromium in farmland soil and growth ratio of rice relative to root system
As can be seen from Table 2, when g-C3N4The mass ratio of the/PDI @ MOF powder to the soil of the hexavalent chromium-polluted cultivated land is less than 1: 100 (as shown in the table 2, g-C3N4The mass ratio of the/PDI @ MOF powder to the soil of the hexavalent chromium-polluted cultivated land is 0.9; 100. 0.7: 100, 0.5: 100 and lower ratios not listed in Table 2), g-C3N4The doping amount of the/PDI @ MOF powder is less, and the amount of photoproduction holes and photoproduction electrons generated by catalysis during sunlight irradiation is less, so that the efficiency of converting hexavalent chromium into trivalent chromium is low, the yield of carbon dioxide is low, and finally, the leaching rates of hexavalent chromium in the soil of the restored cultivated land are higher than 17 percent and are increased along with the g-C3N4The reduction of the mass ratio of the/PDI @ MOF powder to the soil of the hexavalent chromium-polluted cultivated land is obviously increased, the relative root growth ratios of the rice in the soil of the correspondingly repaired cultivated land are all less than 1.17 and are along with the g-C3N4The mass ratio of the PDI @ MOF powder to the hexavalent chromium-polluted cultivated land soil is reduced obviously; when g-C3N4The mass ratio of the/PDI @ MOF powder to the soil of the hexavalent chromium-polluted cultivated land is 1-5: 100 (as shown in the table 2, g-C3N4The mass ratio of the/PDI @ MOF powder to the soil in the hexavalent chromium polluted farmland is 1: 100, 3: 100 and 5: 100), g-C3N4Proper amount of/PDI @ MOF, and g-C can be induced by sunlight irradiation3N4the/PDI @ MOF surface generates a large number of photogenerated holes and photogenerated electrons. The photoproduced electrons can directly reduce hexavalent chromium and convert the hexavalent chromium into trivalent chromium. Organic matters in the humus soil can be oxidized by the photoproduction cavity to generate carbonate radicals. The carbonate radical can effectively reduce hexavalent chromium to trivalent chromium and carbon dioxide. The leaching rates of hexavalent chromium in the soil of the restored cultivated land are all lower than 13%, and the relative root growth ratios of paddy rice in the soil of the corresponding restored cultivated land are all larger than 1.27; when g-C3N4(PDI) MOF powder and hexavalent chromium contaminated cultivationThe soil mass ratio is more than 5:100 (as shown in Table 2, g-C3N4The mass ratio of the/PDI @ MOF powder to the soil in the hexavalent chromium-contaminated cultivated land is 5.1: 100, 5.3: 100, 5.5: 100 and higher ratios not listed in Table 2), g-C3N4Proper amount of/PDI @ MOF, and g-C can be induced by sunlight irradiation3N4the/PDI @ MOF surface generates a large number of photogenerated holes and photogenerated electrons. The photoproduced electrons can directly reduce hexavalent chromium and convert the hexavalent chromium into trivalent chromium. Organic matters in the humus soil can be oxidized by the photoproduction cavity to generate carbonate radicals. The carbonate radical can effectively reduce hexavalent chromium to trivalent chromium and carbon dioxide. However g-C3N4Further increasing the mass ratio of the PDI @ MOF powder to the soil of the farmland polluted by hexavalent chromium has no significant influence on the leaching rate of hexavalent chromium in the soil of the restored farmland and the relative root growth ratio of rice. Thus, in summary, combining benefits with costs when g-C3N4When the mass ratio of the/PDI @ MOF powder to the soil of the hexavalent chromium-polluted farmland is 1-5: 100, the leaching rate of hexavalent chromium in the soil of the restored farmland and the relative root growth ratio of rice are improved.
Example 3 influence of humus soil doping amount on hexavalent chromium leaching rate in soil for repairing cultivated land and relative root growth ratio of paddy rice
Weighing oxalic acid, dissolving the oxalic acid in water, stirring until the oxalic acid is completely dissolved, and preparing an oxalic acid solution, wherein the concentration of the oxalic acid solution is 2.5M. Weighing activated carbon powder and oxalic acid solution according to the solid-to-liquid ratio of 3: 10mg/mL, and soaking the activated carbon powder in the oxalic acid solution for 3 hours to obtain activated carbon powder slurry. Weighing g-C according to the mass ratio of 5:1003N4(ii) PDI @ MOF powder and hexavalent chromium contaminating cultivated land soil and combining g-C3N4Mixing the/PDI @ MOF powder with soil of a corresponding hexavalent chromium-polluted farmland, and uniformly stirring to obtain the photocatalytic pre-doped soil. Respectively weighing the photocatalytic pre-doped soil, the humus soil and the activated carbon powder slurry according to the mass ratio of 100: 2.5: 10, 100: 3.5: 10, 100: 4.5: 10, 100: 5:10, 100: 10, 100: 15: 10, 100: 15.5: 10, 100: 16.5: 10 and 100: 17.5: 10, mixing the photocatalytic pre-doped soil, the humus soil and the activated carbon powder slurry, adding water, stirring for 30 minutes under the condition of 60rpm, obtaining the farmland soil to be restored, wherein the farmland soil is obtainedThe water content of the farmland soil to be restored is 35 percent. The soil of the farmland to be restored is irradiated by a xenon lamp (PL-X300D, Beijing Prinleiss technology limited), the soil is turned over for 1 time every 1 hour in the period, the restoration of the soil of the farmland polluted by hexavalent chromium can be realized within 6 hours, and the input power of a xenon lamp light source is 300W.
The sampling, preparation and basic properties of the chromium-contaminated soil are the same as those of the example 1.
g-C3N4the/PDI @ MOF powder was prepared as in example 1.
The hexavalent chromium toxicity leaching, concentration detection and leaching rate calculation for repairing the farmland soil are the same as those in example 1.
The detection of root growth of the cultivated land restoration soil and the calculation of the relative root growth ratio of the rice are the same as those in example 1.
The test results of the leaching rate of hexavalent chromium in the soil for repairing the cultivated land and the relative root growth ratio of the rice are shown in table 3.
Table 3 influence of humus soil mixing amount on hexavalent chromium leaching rate in restored cultivated land soil and relative root growth ratio of paddy rice
As can be seen from table 3, when the mass ratio of the photocatalytic pre-doped soil, the humus soil and the activated carbon powder slurry is less than 100: 5:10 (for example, in table 3, when the concentration of oxalic acid is 100: 4.5: 10, 100: 3.5: 10, 100: 2.5: 10 and lower ratios not listed in table 3), the amount of humus soil is less, and the amount of the introduced organic reducing substance is less, so that the yield of carbon dioxide radicals is reduced, and the probability of trivalent chromium being oxidized into hexavalent chromium is increased, which finally results in that the leaching rate of hexavalent chromium in the soil of the restored cultivated land is higher than 16%, and is significantly increased along with the decrease of the amount of humus soil, and correspondingly, the growth ratio of rice relative to root systems in the soil of the restored cultivated land is less than 1.19, and is significantly decreased along with the decrease of the amount of humus soil; when the mass ratio of the photocatalytic pre-doped soil, the humus soil and the activated carbon powder slurry is equal to 100: 5-15: 10 (as shown in table 3, when the concentration of oxalic acid is 100: 5:10, 100: 10 and 100: 15: 10), the humus soil is proper, more organic reducing substances are introduced, the yield of carbon dioxide free radicals is high, and meanwhile, a large amount of reducing substances contained in the humus soil can prevent trivalent chromium from being oxidized again and can prevent oxygen free radicals from damaging original nutrient substances in the farmland soil. When the mass ratio of the photocatalytic pre-doped soil, the humus soil and the activated carbon powder slurry is more than 100: 15: 10 (for example, in the table 3, when the concentration of oxalic acid is 100: 15.5: 10, 100: 16.5: 10, 100: 17.5: 10 and the lower ratio which is not listed in the table 3), the humus soil is excessive, more organic reducing substances are introduced, the yield of carbon dioxide free radicals is high, and meanwhile, the humus soil contains a large amount of reducing substances, so that trivalent chromium can be prevented from being oxidized again, and the damage of oxygen free radicals to the original nutrient substances in the farmland soil can be avoided. However, the further increase of the mass ratio of the photocatalytic pre-doped soil, humus soil and activated carbon powder slurry has no significant influence on the leaching rate of hexavalent chromium in the soil for repairing cultivated land and the relative root growth ratio of rice. Therefore, comprehensively, the benefits and the cost are combined, and when the mass ratio of the photocatalytic pre-doped soil, the humus soil and the activated carbon powder slurry is equal to 100: 5-15: 10, the leaching rate of hexavalent chromium in the soil for repairing the cultivated land and the relative root growth ratio of rice are improved.
Comparative example
The method, the comparison treatment method 1, the comparison treatment method 2 and the comparison treatment method 3 have the influence on the hexavalent chromium leaching rate in the restored farmland soil and the relative root growth ratio of the rice
The method for treating the chromium-polluted soil comprises the following steps: weighing oxalic acid, dissolving the oxalic acid in water, stirring until the oxalic acid is completely dissolved, and preparing an oxalic acid solution, wherein the concentration of the oxalic acid solution is 2.5M. Weighing activated carbon powder and oxalic acid solution according to the solid-to-liquid ratio of 3: 10mg/mL, and soaking the activated carbon powder in the oxalic acid solution for 3 hours to obtain activated carbon powder slurry. Weighing g-C according to the mass ratio of 5:1003N4(ii) PDI @ MOF powder and hexavalent chromium contaminating cultivated land soil and combining g-C3N4Mixing the/PDI @ MOF powder with soil of a corresponding hexavalent chromium-polluted farmland, and uniformly stirring to obtain the photocatalytic pre-doped soil. According to the mass ratio of 100: 1Weighing the photocatalytic pre-doped soil, the humus soil and the activated carbon powder slurry at a ratio of 5:10, mixing the photocatalytic pre-doped soil, the humus soil and the activated carbon powder slurry, adding water, and stirring for 30 minutes at 60rpm to obtain the farmland soil to be restored, wherein the water content of the farmland soil to be restored is 35%. The soil of the farmland to be restored is irradiated by a xenon lamp (PL-X300D, Beijing Prinleiss technology limited), the soil is turned over for 1 time every 1 hour in the period, the restoration of the soil of the farmland polluted by hexavalent chromium can be realized within 6 hours, and the input power of a xenon lamp light source is 300W.
Comparative treatment method 1: weighing oxalic acid, dissolving the oxalic acid in water, stirring until the oxalic acid is completely dissolved, and preparing an oxalic acid solution, wherein the concentration of the oxalic acid solution is 2.5M. Weighing activated carbon powder and oxalic acid solution according to the solid-to-liquid ratio of 3: 10mg/mL, and soaking the activated carbon powder in the oxalic acid solution for 3 hours to obtain activated carbon powder slurry. Weighing hexavalent chromium-polluted farmland soil and the activated carbon powder slurry according to the mass ratio of 100: 10, mixing, adding water, stirring for 30 minutes at 60rpm to obtain the water content of the restored farmland soil of 35%, and aging for 6 hours to finish restoration of the hexavalent chromium-polluted farmland soil.
Contrast treatment method 2: weighing g-C according to the mass ratio of 5:1003N4(ii) PDI @ MOF powder and hexavalent chromium contaminating cultivated land soil and combining g-C3N4Mixing the/PDI @ MOF powder with soil of a corresponding hexavalent chromium-polluted farmland, and uniformly stirring to obtain the photocatalytic pre-doped soil. And adding water into the photocatalytic pre-doped soil to enable the water content of the photocatalytic pre-doped soil to be 35%. The soil is pre-doped with photocatalysis by xenon lamp irradiation (PL-X300D, Beijing Prinleis science and technology Limited), the soil is turned over for 1 time every 1 hour in the period, the soil in the hexavalent chromium-polluted farmland can be repaired within 6 hours, and the input power of a xenon lamp light source is 300W.
Contrast treatment method 3: weighing hexavalent chromium-polluted farmland soil and humus soil according to the mass ratio of 100: 15, adding water, and stirring for 30 minutes at 60rpm to obtain the farmland soil to be restored, wherein the water content of the farmland soil to be restored is 35%. And aging for 6 hours to finish the restoration of the soil of the hexavalent chromium polluted farmland.
The sampling, preparation and basic properties of the chromium-contaminated soil are the same as those of the example 1.
g-C3N4the/PDI @ MOF powder was prepared as in example 1.
The hexavalent chromium toxicity leaching, concentration detection and leaching rate calculation for repairing the farmland soil are the same as those in example 1.
The detection of root growth of the cultivated land restoration soil and the calculation of the relative root growth ratio of the rice are the same as those in example 1.
The test results of the leaching rate of hexavalent chromium in the soil for repairing the cultivated land and the relative root growth ratio of the rice are shown in table 4.
TABLE 4 Effect of the inventive method, the comparative treatment method 1, the comparative treatment method 2 and the comparative treatment method 3 on the Leaching Rate of hexavalent chromium in the soil for remediating cultivated land and the relative root growth ratio of Rice
As can be seen from Table 4, the leaching rate of hexavalent chromium in the soil of the restored cultivated land after the treatment by the method of the invention is obviously lower than that of the comparative treatment method 1, the comparative treatment method 2 and the comparative treatment method 3. The relative root growth ratio of the paddy rice in the soil of the restored cultivated land after the treatment is far greater than that of the treatment method 1, the contrast treatment method 2 and the contrast treatment method 3.
Claims (3)
1. A method for remediating hexavalent chromium-contaminated farmland soil, characterized by comprising the steps of:
1) weighing oxalic acid, dissolving the oxalic acid in water, and stirring until the oxalic acid is completely dissolved to prepare an oxalic acid solution;
2) soaking activated carbon powder in an oxalic acid solution for 2-4 hours to obtain activated carbon powder slurry;
3) g to C3N4Mixing the PDI @ MOF powder with hexavalent chromium polluted farmland soil, and uniformly stirring to obtain photocatalytic pre-doped soil;
4) respectively weighing photocatalytic pre-doped soil, humus soil and activated carbon powder slurry, mixing the photocatalytic pre-doped soil, humus soil and activated carbon powder slurry, adding water, and stirring for 10-30 minutes at 20-60 rpm to obtain farmland soil to be restored;
5) irradiating the farmland soil to be restored by using a xenon lamp, turning the soil 1 time every 1 hour in the period, and restoring the soil of the farmland polluted by hexavalent chromium within 4-6 hours;
the concentration of the oxalic acid solution in the step 1) is 0.5-2.5M, the solid-to-liquid ratio of the activated carbon powder in the step 2) to the oxalic acid solution is 1-5: 10mg/mL, and g-C in the step 3)3N4The mass ratio of the/PDI @ MOF powder to the soil of the hexavalent chromium-polluted farmland is 1-5: 100, and the mass ratio of the photocatalytic pre-doped soil, the humus soil and the activated carbon powder slurry in the step 4) is 100: 5-15.
2. The method for remediating hexavalent chromium-contaminated farmland soil according to claim 1, wherein the soil moisture content of the farmland to be remediated of the step 4) is 25-35%.
3. The method for remediating hexavalent chromium-contaminated arable land soil according to claim 1, wherein the xenon lamp light source input power of the step 5) is 150-300W.
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