A modified Fenton sludge and biomass composite passivator and its preparation method

Abstract

The present invention discloses a modified Fenton sludge and biomass composite passivator and a preparation method thereof, belonging to the technical field of soil remediation; the passivator proposed by the present invention is composed of 90-100 parts of modified Fenton sludge and 1-10 parts of biomass material; wherein, the modified Fenton sludge is prepared by mixing and modifying Fenton sludge and ferrous sulfate particles through strong stirring; the composite passivator prepared by the present invention can simultaneously achieve arsenic-contaminated soil remediation, solid waste comprehensive utilization and soil quality improvement; the Fenton sludge in the composite passivator can replace common goethite and achieve better soil remediation effect, greatly reducing the cost, and the raw materials are easy to obtain, and it can be widely applied to the remediation of arsenic-contaminated soil in mining areas; the amorphous iron oxyhydroxide in the modified Fenton sludge can achieve the adsorption, complexation and precipitation of soil arsenic; while broadening the selection source of soil passivators, it provides a way for the resource utilization of Fenton sludge.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and particularly relates to a modified Fenton sludge and biomass composite passivator and a preparation method thereof. Background Art

[0002] At present, the treatment of arsenic-contaminated soil is an urgent problem to be solved. Arsenic is the world's number one teratogenic and carcinogenic toxin. When its content in the human body is higher than 60 mg, it will cause death. Arsenic in the soil is easily absorbed by various plants and then accumulates in the human body, causing serious harm to the human body.

[0003] Chinese invention patent CN 201910106943.5 discloses a method for repairing arsenic-contaminated farmland soil by using a compound passivator of dehydrated sludge and biochar. The passivator is prepared by compounding dehydrated sludge and biochar. However, the biochar needs to be pyrolyzed at 500 °C, which is not conducive to energy conservation. And it mainly uses the adsorption effect of dehydrated sludge and biochar on arsenic, and the effect is not stable enough. Chinese invention patent CN 201811446910.7 discloses a method for magnetic sludge carbon-enhanced electro-chemical oxidation to repair organic contaminated soil, including the following steps: S1, carbonizing sludge to obtain sludge carbon, and then modifying the sludge carbon with magnetite powder to prepare sludge magnetic carbon; S2, adding the sludge magnetic carbon to the soil to be repaired and stirring evenly to obtain a mixed soil; S3, adding an oxidant to the mixed soil by means of electro-diffusion, that is, adding an oxidant (sodium persulfate solution) to the repaired soil by means of electro-injection. This method needs to use an electric reactor to realize the diffusion of the passivator, and the process is relatively complex. Chinese invention patent CN 201710413193.7 invented a composite stabilizer for repairing lead, cadmium, and arsenic pollution in acidic soil, and its components include superphosphate, goethite, humic acid, quicklime, polyacrylamide and other components, and the components of the passivator are relatively complex.

[0004] In summary, the traditional sludge and biochar repair technology is not mature enough, and the goethite-based repair agent has a high cost. Therefore, inventing a low-carbon and high-efficiency arsenic-contaminated soil repair agent that can replace natural raw materials has become an urgent problem to be solved in engineering applications. Summary of the Invention

[0005] The purpose of the present invention is to provide a modified Fenton sludge and biomass composite passivator and a preparation method thereof, which are low-cost, simple in process, low-carbon and environmentally friendly, have a significant repair effect and can be widely applied, so as to solve the problems that the traditional sludge and biochar repair technology is not mature enough and the goethite-based repair agent has a high cost.

[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A modified Fenton sludge and biomass composite passivator, the passivator is composed of the following raw materials in parts by weight: 90-100 parts of modified Fenton sludge, 1-10 parts of biomass material; wherein, the modified Fenton sludge is prepared by mixing and modifying Fenton sludge and ferrous sulfate particles through strong stirring.

[0008] Preferably, the weight fraction of the raw materials for preparing the passivator is: 95-99 parts of modified Fenton sludge, 1-5 parts of biomass material.

[0009] As a further scheme of the present invention: the Fenton sludge is the sludge produced after treating organic wastewater (such as pharmaceutical wastewater, brewing wastewater, etc.) by the Fenton oxidation method, the main component is amorphous iron hydroxyoxide, the mass fraction of Fe2O3 is 50-85%, and the mass fraction of CaO is 5-10%.

[0010] Preferably, the mass fraction of Fe2O3 in the Fenton sludge is 70-85%, and the mass fraction of CaO is 6-8%.

[0011] As a further scheme of the present invention: the ferrous sulfate particles are an industrial by-product of preparing titanium dioxide by the sulfuric acid method, wherein the mass fraction of ferrous sulfate is 80-100%, the mass fraction of insoluble substances is less than 0.2%, and the mass fractions of heavy metals such as arsenic, lead, cadmium, mercury, chromium, etc. are all less than 0.00002%, and the quality meets the requirements of the national standard "Water treatment agent - Ferrous sulfate" GB / T 10531-2016, and it can be used as a fertilizer.

[0012] As a further scheme of the present invention: the mass ratio of Fenton sludge to ferrous sulfate particles in the modified Fenton sludge is 2-5:1.

[0013] Preferably, the mass ratio of Fenton sludge to ferrous sulfate particles in the modified Fenton sludge is 2-3:1

[0014] As a further scheme of the present invention: the biomass material is one or more of crop straws, bamboo powder, sawdust, etc., and is sieved through a 100-mesh sieve after being crushed.

[0015] Preferably, the biomass material is selected to be easily obtained according to the crops and native plants in the area where the arsenic-contaminated soil in the mining area is located.

[0016] A preparation method of a modified Fenton sludge and biomass composite passivator, comprising the following steps:

[0017] S1. Filter, dry and dehydrate the Fenton sludge, grind it and sieve it through a 0.1 mm sieve;

[0018] S2, modifying the Fenton sludge with a particle size of less than 0.1 mm prepared in S1 and ferrous sulfate particles by strong stirring to obtain modified Fenton sludge, so that its pH value is stabilized at 6-8;

[0019] S3. Fully mix the modified Fenton sludge prepared in S2 with the biomass material, so that the modified Fenton sludge adheres to the surface of the biomass material, thereby preparing a passivating agent.

[0020] The invention discloses an application of a modified Fenton sludge and a biomass composite passivator for repairing arsenic-contaminated soil in a mining area. Specifically, the modified Fenton sludge and the biomass composite passivator are added to the arsenic-contaminated soil at a ratio of 1-10% of the mass fraction of the soil dry basis, the soil moisture content is 10-30%, and the soil is passivated for 14-90 days to complete the soil repair.

[0021] Preferably, the passivating agent is added to the arsenic-contaminated soil at a ratio of 3-6% of the mass fraction of the soil dry basis, the soil moisture content is 15-25%, and the remediation time is 20-30 days.

[0022] Compared with the prior art, the present invention provides a sintering steel slag-based mine area arsenic contaminated soil passivator and a preparation method thereof, which has the following beneficial effects:

[0023] (1) The raw materials for preparing the passivating agent used in the present invention are modified Fenton sludge and biomass materials, wherein the modified Fenton sludge is prepared by modifying Fenton sludge and ferrous sulfate particles by strong stirring and mixing. Fenton sludge is sludge produced after organic wastewater such as pharmaceutical wastewater and brewing wastewater is treated by Fenton oxidation method, and has extremely low heavy metal content; ferrous sulfate particles are industrial by-products of preparing titanium dioxide by sulfuric acid method; biomass materials are agricultural solid waste; they are low in cost and widely available, and can complete the passivation of arsenic-contaminated soil while achieving waste treatment, which is green and environmentally friendly and has no secondary pollution to the soil.

[0024] (2) The modified Fenton sludge has high content of iron ions and organic matter and can be used as soil fertilizer. Biomass materials can increase the specific surface area of ​​the modified Fenton sludge, which is beneficial to the mixing uniformity of the modified Fenton sludge in the soil layer, improve the passivation effect, and provide some organic matter for the soil.

[0025] (3) Fenton sludge contains a high content of amorphous iron oxyhydroxide, which can replace common goethite materials in the preparation of arsenic-contaminated soil passivation agents and achieve the same remediation effect.

[0026] (4) The amorphous ferric hydroxide oxide in the modified Fenton sludge used in the present invention has fine particles and a large specific surface area, and has multiple effects on arsenic in contaminated soil, such as adsorption, complexation and precipitation. At the same time, the biomass material can expand the specific surface area of ​​the modified Fenton sludge, thereby achieving the purpose of efficient passivation of arsenic in the soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 XRD pattern of the Fenton sludge used in the present invention

[0028] Figure 2 Fourier transform infrared spectra of the soils repaired by the passivator under the conditions of each example and comparative example of the present invention. Among them, A is the soil repaired by the modified Fenton sludge and biomass composite passivator, B is the soil repaired by the unmodified Fenton sludge and biomass composite passivator, C is the soil repaired by the modified Fenton sludge passivator, and D is the control soil;

[0029] Figure 3 Contents of amorphous iron oxides in the soils repaired by the passivator under the conditions of Example 1 and Comparative Example 3 of the present invention. Among them, A1 is the control soil, B1 is the soil repaired by the modified Fenton sludge and biomass composite passivator, and C1 is the soil repaired by the goethite and biomass composite passivator;

[0030] Figure 4 SEM-EDS pattern of the soil repaired by the modified Fenton sludge and biomass composite passivator of the present invention Detailed implementation manners

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0032] Example 1:

[0033] Please refer to Figure 1 , Figure 1 XRD pattern of the Fenton sludge in the embodiment of the present invention. Its main components are goethite and calcite. Most of its peaks exist in a diffuse form, mainly amorphous iron oxides, which play a major role in the passivation process of arsenic.

[0034] The test soil in this experimental example was collected from the Lajiapo Mining Area, Chehe Town, Nandan County, Guangxi. The soil was naturally air-dried, ground and sieved through a 2 mm sieve. The modified Fenton sludge and biomass composite passivator was incorporated into the arsenic-contaminated soil at ratios of 1%, 3%, 5% and 7% of the dry basis mass fraction of the soil. After mixing evenly, it was passivated for 30 days under the conditions of a temperature of 25±1°C and a water content of 25%, thus completing the repair of the arsenic-contaminated mining area soil.

[0035] The modified Fenton sludge and biomass composite passivator used in this example was prepared by modifying the Fenton sludge with by-products of titanium dioxide industry, ferrous sulfate particles, and then strongly stirring and mixing with biomass bamboo powder. The mass percentage of the modified Fenton sludge to the biomass material was 90:10.

[0036] The Fenton sludge used in this example was taken from the sludge discharged after the Fenton oxidation process for water treatment in a brewery. Its mass fraction of Fe2O3 was 80%, and the mass fraction of CaO was 7%; the mass fraction of ferrous sulfate in the by - product of the titanium dioxide industry was 99%.

[0037] The mass ratio of the Fenton sludge to the ferrous sulfate, the by - product of industrial titanium dioxide, used in this example was 6:4. After strong stirring and mixing evenly, the modified Fenton sludge was obtained.

[0038] The Fenton sludge used in this example was prepared by the following method: the sludge discharged after treating brewery wastewater by the Fenton oxidation method was filtered and dehydrated, dried at 80 °C for 24 hours, and after grinding, the average particle size of the Fenton sludge was less than 0.1 mm.

[0039] The biomass material used in this example was bamboo powder, which was all passed through a 100 - mesh sieve after being crushed.

[0040] The original soil without adding a passivator was used as a blank control. In the control soil, the content of available arsenic was 12.15 mg / kg, and the TCLP leaching concentration of arsenic was 37.82 μg / L.

[0041] During the passivation process, soil samples were taken at 14, 30, 60, and 90 days. The content of available arsenic in the soil was determined by the method of extraction with NaHCO3 solution, and the leaching concentration of arsenic was determined by the TCLP leaching method. See Table 1 for details.

[0042] Please refer to Figure 4 , from Figure 4 it can be seen that the iron oxyhydroxide in the form of flakes or layers in the composite passivator is adsorbed on the surface of fibrous or rod - shaped biomass, completing the adsorption, complexation, and precipitation of arsenic in the contaminated soil.

[0043] Example 2:

[0044] A method for repairing arsenic - contaminated soil in mining areas with a modified Fenton sludge and biomass composite passivator, which is based on Example 1 but is different in that the mass percentage of the modified Fenton sludge to biomass is 95:5.

[0045] Example 3:

[0046] A method for repairing arsenic - contaminated soil in mining areas with a modified Fenton sludge and biomass composite passivator, which is based on Examples 1 - 2 but is different in that the mass fraction ratio of Fenton sludge to ferrous sulfate in the modified Fenton sludge is 7.5:2.5.

[0047] Comparative Example 1:

[0048] A method for repairing arsenic - contaminated soil in mining areas with a modified Fenton sludge and biomass composite passivator. Compared with Example 1, the difference in Comparative Example 1 is that only the modified Fenton sludge in Example 1 is used as the passivator without mixing in biomass. The passivation effect is shown in Table 1 in detail.

[0049] Comparative Example 2:

[0050] A method for repairing arsenic - contaminated soil in mining areas with a modified Fenton sludge and biomass composite passivator. Compared with Example 1, the difference in Comparative Example 2 is that only the unmodified Fenton sludge and biomass bamboo powder composite in Example 1 are used as the passivator. The passivation effect is shown in Table 1 in detail.

[0051] Please refer to Figure 2 , Figure 2 which is the Fourier transform infrared spectroscopy diagram of the soil after being repaired by the passivators in Example 1, Comparative Example 1 and 2 of the present invention. Among them, A is the soil repaired by the modified Fenton sludge and biomass composite passivator, B is the soil repaired by the unmodified sludge and biomass composite passivator, C is the soil repaired by the modified Fenton sludge passivator, and D is the control soil. As Figure 2 can be seen, the positions of each peak in the infrared spectrum of the soil after being treated with the passivator are basically the same, but the intensity of the peaks has changed. The vibration peak at 1036 cm -1 is the vibration peak of the hydroxyl group. After being modified with ferrous sulfate, the peak intensity of the hydroxyl group is significantly enhanced, indicating that the activity of amorphous iron oxyhydroxide after modification has increased.

[0052] Comparative Example 3:

[0053] A method for repairing arsenic - contaminated soil in mining areas with a modified Fenton sludge and biomass composite passivator. Compared with Example 1, the difference in Comparative Example 3 is that only the unmodified Fenton sludge in Example 1 is used as the passivator. The passivation effect is shown in Table 1 in detail.

[0054] Table 1. Composite ratio (%) of modified Fenton sludge and biomass and passivation effect

[0055]

[0056] Based on the above - mentioned examples and comparative examples, combined with Table 1, it can be known that: in Examples 1 - 3 and Comparative Examples 1 - 3 of the present invention, when the incorporation amount of the modified Fenton sludge and biomass composite passivator is 5% of the soil mass fraction, the best arsenic passivation effect is shown. And in Examples 1 - 3, effective passivation of arsenic in the mining area soil can be achieved. Especially in Example 1, when the ratio of Fenton sludge to ferrous sulfate is 6:4 and the mass percentage of the modified Fenton sludge to the biomass material is 90:10, the arsenic passivation effect is the best, and the content of available arsenic in the contaminated soil can be reduced from 12.15 mg / kg to 0.8 mg / kg, and the TCLP leaching concentration of arsenic can be reduced from 37.82 μg / L to 2.88 μg / L, with a significant passivation effect.

[0057] As Comparative Example 1, only modified Fenton sludge was used as the passivator. After passivation, the content of available arsenic in the soil was 3.51 mg / kg, and the TCLP leaching concentration of arsenic was 8.43 μg / L, which was much lower than the passivation effect of the composite with biomass bamboo powder. This indicates that the addition of biomass bamboo powder can increase the action area of modified Fenton sludge on arsenic and effectively improve the passivation effect of the passivator on soil arsenic.

[0058] As Comparative Example 2, only the passivator prepared by compounding unmodified Fenton sludge with biomass was used. Optimally, the content of available arsenic in the soil was 1.28 mg / kg, and the TCLP leaching concentration of arsenic was 13.31 μg / L. The passivator prepared by compounding unmodified Fenton sludge without ferrous sulfate modification with biomass had a poor TCLP leaching effect on arsenic, indicating that the amorphous iron oxide form of unmodified Fenton sludge without ferrous sulfate modification was not fully activated and the passivation effect was weak.

[0059] As Comparative Example 3, only unmodified Fenton sludge was used as the passivator. The optimal available arsenic content and TCLP leaching concentration of arsenic were 4.21 mg / kg and 8.65 μg / L respectively, and the passivation effect on arsenic was much weaker than that of the passivator of ferrous sulfate-modified Fenton sludge composite with biomass.

[0060] Comparative Example 4:

[0061] On the premise of not adding by-product ferrous sulfate of industrial titanium dioxide and biomass, the passivation effects of different water treatment sludges on arsenic in soil were compared. The water treatment sludges from paper mills and smelters were respectively taken to passivate the soil according to the method in Example 1. The sludge was incorporated into arsenic-contaminated soil at a ratio of 5% of the dry basis mass of the soil, and the passivation effect of Fenton sludge on soil arsenic in Comparative Example 3 was compared. See Table 2 for details.

[0062] Table 2. Remediation effects of different water treatment sludges on arsenic-contaminated soil

[0063]

[0064] As shown in Table 2, after passivation with water treatment sludges from paper mills and smelters with different Fe2O3 contents and CaO contents alone, the contents of available arsenic in the soil were 8.01 and 6.24 mg / kg respectively, and the TCLP leaching concentrations of arsenic were 15.22 and 13.05 μg / L respectively. The passivation effects were much lower than those of the Fenton water treatment sludge from wineries. On the one hand, it was due to the iron content in different sludges, and on the other hand, mainly due to the existing form of iron. The iron in the Fenton water treatment sludge from wineries mainly existed in the form of amorphous goethite, which was very easy to complete the adsorption, complexation and coprecipitation of arsenic.

[0065] Comparative Example 5:

[0066] Compare the remediation effects of passivators prepared from different modified sludge composite biomasses on arsenic - contaminated soil. Prepare the passivator with the best composite ratio in Example 1, and respectively compare the passivation effects of passivators composed of modified sludge (paper mill water treatment sludge, smelter water treatment sludge, and winery Fenton water treatment sludge) and biomass bamboo powder on soil arsenic, as shown in Table 3.

[0067] Table 3. Passivation effects of different modified sludges and biomass bamboo powder composites on arsenic in soil

[0068]

[0069] As can be seen from Table 3, for the passivators prepared by respectively combining paper mill water treatment sludge and smelter water treatment sludge with ferrous sulfate and biomass bamboo powder, the content of soil available arsenic decreased to 3.33 and 2.41 mg / kg respectively, and the TCLP leaching concentration of arsenic was 8.26 and 6.88 μg / L. The passivation effect on arsenic was much lower than that of the composite passivator of modified Fenton sludge and biomass bamboo powder.

[0070] Comparative Example 6:

[0071] A method for remediating arsenic - contaminated soil in mining areas with a composite passivator of modified Fenton sludge and biomass. Compared with Example 1, the difference is that in Comparative Example 6, commercially purchased goethite is used to replace the Fenton sludge in Example 1 in equal amount. See Table 4.

[0072] Table 4. Composite passivator ratio (%) and passivation effect of replacing Fenton sludge with goethite in equal amount

[0073]

[0074] As can be seen from Table 4, for the passivator prepared by replacing Fenton sludge with an equal amount of goethite and combining it with biomass bamboo powder, after remediation, the available arsenic in the soil decreased to 1.50 mg / kg, and the TCLP leaching concentration of arsenic was 2.86 μg / L. Its passivation effect is similar to that of the composite passivator of modified Fenton sludge and biomass. Therefore, Fenton sludge in the composite passivator can be used to replace expensive goethite. Combining Figure 3 With Example 1 of the present invention, for the content of amorphous iron oxides in the soil after the passivator in Comparative Example 5 remediated the arsenic - contaminated soil, A1 is the control soil, B1 is the soil remediated by the composite passivator of modified Fenton sludge and biomass, and C1 is the soil remediated by the composite passivator of goethite and biomass. It can be seen that the content of amorphous iron oxides in the soil remediated by the composite passivator of modified Fenton sludge and biomass (14.9 g / kg) is higher than that in the soil remediated by the composite passivator of goethite and biomass (12.6 g / kg), and much higher than that of the control soil (6.09 g / kg). Amorphous iron oxides play a major role in the passivation process of arsenic, further confirming that modified Fenton sludge can be used to replace common goethite as a passivator material.

[0075] Take the best proportion (5%) of the modified Fenton sludge and biomass composite passivator in the above examples and comparative examples and incorporate it into the contaminated soil. After the arsenic-contaminated soil is repaired for 14, 30, 60, and 90 days respectively, the passivation effect is detected, as shown in Table 5. When the passivation time is 30 days, both the content of available arsenic and the TCLP leaching concentration of arsenic are reduced by a large margin and gradually tend to be stable. Among them, the reduction rate of available arsenic reaches 90%. After 90 days of passivation, the reduction rate of the TCLP leaching concentration of arsenic reaches 96.46%.

[0076] Table 5. Content of available arsenic in soil and TCLP leaching concentration of arsenic at different repair times

[0077]

[0078] Comparing with the existing patent 1 (CN 201910106943.5, a method for repairing arsenic-contaminated farmland soil by using a composite passivator of dehydrated sludge and biochar), the passivator prepared by compounding 10% dried sludge + 1% biochar can reduce the content of available arsenic in the soil by 25.06% after 40 days of repair.

[0079] The existing patent 2 (CN202111352757.3, "A heavy metal stabilization preparation modified by iron and manganese sludge and its preparation and application") discloses that the reduction rate of available arsenic reaches 90.5% by means of technological means such as sulfuric acid acidolysis of water treatment sludge in a waterworks to adjust the Fe / Mn molar ratio. See Table 6 for details.

[0080] Table 6. Comparison of the effects of different sludge-based passivators on repairing arsenic-contaminated soil

[0081]

[0082] As mentioned above, the above is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered by the protection scope of the present invention.

Claims

1. A modified Fenton sludge and biomass composite passivator, characterized in that, The passivating agent is composed of the following raw materials in weight fractions: 90-100 parts of modified Fenton sludge and 1-10 parts of biomass material; wherein the modified Fenton sludge is prepared by mixing and modifying the Fenton sludge from a winery and ferrous sulfate particles through strong stirring; The winery Fenton sludge is sludge produced after organic wastewater is treated by Fenton oxidation method, and the mass fraction of Fe2O3 in the sludge is 50-85%, and the mass fraction of CaO is 5-10%; The mass ratio of brewery Fenton sludge to ferrous sulfate particles in the modified Fenton sludge is 2-5:

1.

2. The modified Fenton sludge and biomass composite passivator according to claim 1, wherein The ferrous sulfate particles are industrial by-products of preparing titanium dioxide by the sulfuric acid process, wherein the mass fraction of ferrous sulfate is 80-100%, the mass fraction of insoluble matter is less than 0.2%, and the mass fractions of heavy metals arsenic, lead, cadmium, mercury, and chromium are all less than 0.00002%.

3. A modified Fenton sludge and biomass composite passivator according to claim 1, characterized in that, The biomass material is one or more of crop straw, bamboo powder and sawdust, which are crushed and then passed through a 100-mesh sieve.

4. The preparation method of a modified Fenton sludge and biomass composite passivator according to any one of claims 1-3, characterized in that, The following steps are involved: S1. Filter, dry and dehydrate the Fenton sludge, grind it and pass it through a 0.1mm sieve; S2, modifying the Fenton sludge with a particle size of less than 0.1 mm prepared in S1 and ferrous sulfate particles by strong stirring to obtain modified Fenton sludge, so that its pH value is stabilized at 6-8; S3. Fully mix the modified Fenton sludge prepared in S2 with the biomass material, so that the modified Fenton sludge adheres to the surface of the biomass material, thereby preparing a passivating agent.

5. Use of a modified Fenton sludge and biomass composite passivator according to any one of claims 1-3, characterized in that, Used to repair arsenic-contaminated soil in mining areas, specifically: add modified Fenton sludge and biomass composite passivator into arsenic-contaminated soil at a ratio of 1-10% of the soil dry basis mass fraction, the soil moisture content is 10-30%, and the soil remediation is completed after passivation for 14-90 days.

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