A method for preparing heavy metal adsorbent materials by co-grinding and pyrolysis of petroleum-contaminated soil and iron oxides.

Abstract

This invention discloses a method for preparing heavy metal adsorbent materials (PCS) by co-milling and pyrolysis of petroleum-contaminated soil and iron oxides. First, iron oxides or their natural minerals are added to the petroleum-contaminated soil. Then, a high-energy ball milling process is used for mechanochemical activation. The milled mixture is then subjected to slow pyrolysis to form carbonized soil with a surface rich in carbonates and metal oxides. This carbonized soil can be used to adsorb heavy metals from wastewater, with a maximum adsorption capacity of over 300 mg / g for lead. This method simultaneously achieves efficient remediation and high-value resource utilization of PCS through the exploitation, value-added transformation, and "waste-to-waste" approach of the endogenous resources of petroleum-contaminated soil. It contributes to the innovation of petroleum-contaminated soil remediation models and the synergistic remediation of soil-water pollution.

Description

Technical Field

[0001] This invention relates to the field of soil pollution prevention and control and solid waste resource utilization technology, and in particular to a method for preparing heavy metal adsorbent materials by co-grinding and pyrolysis of petroleum-contaminated soil and iron oxides. Background Technology

[0002] Petrochemicals are a pillar industry of my country's national economy. Petroleum is primarily refined into finished oil products, while heavy oil is refined to produce paraffin wax, asphalt, coke, and other products. Some components are also used to produce resins, rubber, and fibers. During the extraction, refining, storage, and transportation of petroleum, leaks and spills frequently result in petroleum contaminated soil (PCS), leaving behind large amounts of PCS. There is an urgent need for green, efficient, and low-cost remediation technologies, especially value-added conversion and reuse technologies. Currently, widely used treatment technologies include thermal treatment, chemical oxidation, extraction / leaching, and microbial degradation, with the primary goal of achieving remediation standards. The main uses of the remediated soil are returning it to farmland, paving roads, or mixing it into building materials.

[0003] The remediation of oil-contaminated soil should first consider separating and recovering the oil from the soil, followed by harmless treatment and resource utilization of the soil. Pyrolysis is an important method to achieve these goals, as it can rapidly crack long-chain hydrocarbons into short-chain hydrocarbons, and high-calorific-value fuel oil can be recovered through volatilization-condensation. However, according to the "General Rules for Identification of Solid Waste" (GB34330—2017), all substances generated during environmental remediation and pollution restoration are classified as solid waste. Therefore, soil disposed of after oil-contaminated soil remediation (including pyrolysis) except for return to the field is considered solid waste and requires safe disposal or resource utilization.

[0004] Studies have found that because the organic carbon remaining in the soil after pyrolysis is usually converted into stable, non-toxic amorphous or graphitized solid carbon, it has no negative impact on plant seed germination and subsequent growth. Therefore, carbonized soil after PCS pyrolysis can be safely used for agricultural purposes. However, the economic value for agricultural use is relatively low, making it difficult to compensate for the high cost of PCS pyrolysis. Furthermore, the environmental functions and resource potential of carbonized soil have not been fully explored and utilized. A reasonable treatment and disposal strategy should not only improve the remediation efficiency of PCS but also consider the reuse value of PCS derivatives after remediation.

[0005] Therefore, the functional components and environmental performance of carbonized soil should be re-examined to seek resource recovery methods with higher economic value. Carbonized soil contains adsorbent functional components derived from conventional clean soil, such as carbonates, clay minerals, and metal oxides, as well as amorphous / graphitized solid carbon transformed from non-volatile organic compounds during pyrolysis. All of these components have a certain adsorption capacity for heavy metals and still have significant potential for enhancement. Mineral or carbonaceous adsorbent materials are typically modified using acid-base methods, loaded with metals, or doped with non-metallic elements. These methods are also valuable for the functional modification of carbonized soil. The applicant's previous research using liquid-solid impregnation or impregnation-calcination methods resulted in high energy consumption or large wastewater generation, increasing costs and the pressure of subsequent compliance treatment. Therefore, it is necessary to develop green, efficient, and low-cost treatment methods. Summary of the Invention

[0006] To address the aforementioned problems and technical analysis, one objective of this invention is to provide a method for preparing heavy metal adsorbent materials by co-grinding and pyrolysis of petroleum-contaminated soil and iron oxides. This method produces materials with numerous active sites and a large specific surface area. Another objective of this invention is to achieve the resource utilization of PCS (Polymerized Iron Oxide Scheme).

[0007] High-energy ball milling is an economical, environmentally friendly, and solvent-free method for preparing environmentally functional materials. The mechanical energy generated during the milling process can effectively reduce the particle size of the adsorbent and increase its specific surface area. Furthermore, it generates more types of oxygen functional groups on the surface and edges of the material to enhance adsorbent activity and increase reaction sites. The ball milling process produces no waste gas or wastewater, offering significant green and environmental advantages. However, high-energy ball milling typically requires a long processing time. Selecting widely available, low-cost additives with no subsequent leaching risk for co-milling followed by pyrolysis is expected to provide a green and efficient way to improve the environmental function of pyrolysis derivatives of petroleum-contaminated soil, thereby enhancing their resource value. The resulting functional materials, when applied to wastewater treatment, can form a new "waste-to-waste" model for the synergistic treatment of contaminated soil and wastewater, achieving high-quality utilization of PCS and promoting the shift from harmless treatment to resource utilization in the remediation of petroleum-contaminated soil.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for preparing heavy metal adsorbent materials by co-grinding and pyrolysis of petroleum-contaminated soil with iron oxides includes the following steps:

[0010] Step 1: Add iron oxide to petroleum-contaminated soil and grind, mix, and mechanically and chemically activate it using a ball mill; the mass ratio of iron oxide to petroleum-contaminated soil is 1:4 to 19, and the ball milling time is 0.5 to 2 hours;

[0011] Step 2: Transfer the mixture obtained in Step 1 to a tube furnace and carry out slow pyrolysis under nitrogen protection, then cool to room temperature to obtain carbonized soil; the slow pyrolysis is carried out by heating to 400-600℃ at a rate of 5-20℃ / min and holding for 0.5-2h, then cooling to room temperature.

[0012] Step 3: Use the carbonized soil obtained as a heavy metal adsorbent to efficiently adsorb heavy metals in wastewater.

[0013] As a preferred embodiment of the method for preparing heavy metal adsorbent materials by co-grinding and pyrolysis of petroleum-contaminated soil and iron oxides according to the present invention, wherein the petroleum-contaminated soil is removed from impurities, dried, and then passed through a 2mm fine sieve.

[0014] As a preferred embodiment of the method for preparing heavy metal adsorbent materials by co-grinding and pyrolysis of petroleum-contaminated soil and iron oxides according to the present invention, the grinding balls are made of stainless steel or zirconium oxide, and large, medium and small grinding balls are combined with a ball-to-material ratio of 20 to 50:1 and a rotation speed of 500 rpm / min.

[0015] As a preferred embodiment of the method for preparing heavy metal adsorbent materials by co-grinding and pyrolysis of petroleum-contaminated soil and iron oxides according to the present invention, the heavy metals include lead, copper, zinc, cadmium, nickel, and manganese.

[0016] In a preferred embodiment of the method for preparing heavy metal adsorbent materials by co-grinding and pyrolysis of petroleum-contaminated soil and iron oxides according to the present invention, the amount of carbonized soil added is 0.5-2 g / L.

[0017] The method of this invention can achieve a total petroleum hydrocarbon removal rate of over 99% when treating petroleum-contaminated soil, and the maximum adsorption capacity for heavy metals can reach over 300 mg / g.

[0018] The beneficial effects achieved by this invention are:

[0019] (1) The present invention uses the method of doping iron oxides to change the composition of petroleum-contaminated soil, which can increase the content of metal oxides in the soil that have strong surface complexation or co-precipitation for most heavy metals, and improve the adsorption performance for common heavy metal cations.

[0020] (2) The present invention uses ball milling to dope iron oxides into petroleum-contaminated soil. On the one hand, it can mix more evenly with soil particles. On the other hand, iron oxides themselves are also highly efficient grinding aids, which can enhance the effect of mechanical and chemical treatment, convert mechanical energy into the chemical energy of soil minerals, reduce crystallinity, and improve reaction activity.

[0021] (3) The present invention alters the characteristics of functional components in the soil by co-grinding petroleum-contaminated soil with iron oxides. The surface is rich in carbonates and metal oxides, which enhances the precipitation and surface complexation capacity of carbonized soil and significantly improves the saturated adsorption capacity of heavy metals in wastewater. Attached Figure Description

[0022] Figure 1 The adsorption capacity of the material for lead, copper, zinc and cadmium in wastewater is shown in Example 1 of this invention when the amount of Fe3O4 added is different.

[0023] Figure 2 The residual TPH content and TOC content of the extract of different materials in Example 1 of this invention are given.

[0024] Figure 3 These are the XRD patterns of different materials in Example 1 of the present invention.

[0025] Figure 4 These are the FTIR spectra of different materials in Example 1 of the present invention.

[0026] Figure 5 These are the O1s spectra of different materials in Example 1 of the present invention.

[0027] Figure 6 The adsorption capacity of Fe3O4@CS for different concentrations of lead, copper, zinc and cadmium in wastewater in Example 1 of this invention.

[0028] Figure 7 This invention presents the adsorption kinetics of Fe3O4@CS on wastewater with different concentrations of lead, copper, zinc, and cadmium in Example 1 of this invention.

[0029] Figure 8 This represents the chemical form of heavy metals adsorbed by RCS and Fe3O4@CS in Example 1 of this invention.

[0030] Figure 9 This is the VSM hysteresis loop of Fe3O4@CS in Embodiment 1 of the present invention. Detailed Implementation

[0031] To facilitate a clearer understanding of this technical solution by those skilled in the art, the technical solution of the present invention will be described in detail below with reference to embodiments:

[0032] Example 1

[0033] Petroleum-contaminated soil (total petroleum hydrocarbon content 156125 mg / kg) was mixed with iron(III) oxide (Fe3O4) by ball milling. The Fe3O4 addition was 10% of the material mass, the ball-to-material ratio was 40 / 1, the rotation speed was 500 r / min, and the treatment time was 1 h. After ball milling, the mixture was transferred to a tube furnace, N2 was introduced, and the temperature was increased to 500 °C at a rate of 10 °C / min. The temperature was maintained for 1 h, and after pyrolysis, the mixture was cooled and removed to obtain iron-loaded carbonized soil (Fe3O4@CS). Carbonized soil (BCS) obtained by ball milling and pyrolysis without the addition of iron(III) oxide and without ball milling, and carbonized soil (RCS) obtained by pyrolysis only without the addition of iron(III) oxide, were used as controls.

[0034] Figure 1 For Me 2+ Under the conditions of initial concentration of 100 mg / L, volume of 50 mL, and adsorbent dosages of 0.5 g / L, 2 g / L, 2 g / L, and 2 g / L for lead, copper, zinc, and cadmium solutions, respectively, the material's effect on Me was observed when the Fe3O4 addition amount (0%, 10%, and 20%) varied. 2+ The amount of adsorption.

[0035] like Figure 1 As shown, the material's effect on Pb 2+ Cu 2+ Zn 2+ and Cd 2+ The adsorption capacity of CS without the addition of iron oxides first increases and then decreases with increasing Fe3O4 dosage. 2+ Cu 2+ Zn 2+ and Cd 2+ The adsorption capacities were 74.12, 27.47, 18.64, and 10.74 mg / g, respectively. After adding 10% Fe3O4, the adsorbent for Pb... 2+ Cu 2+ Zn 2+ and Cd 2+ The adsorption capacity increased to 154.30, 45.22, 29.08, and 13.54 mg / g, but this increase was limited. When 20% Fe3O4 was added, the adsorbent's adsorption capacity for Me... 2+ The adsorption amounts of all metals decreased. The results show that appropriate addition of Fe3O4 can form more iron oxides on the soil surface, positively impacting heavy metal adsorption. Therefore, a dosage of 10% Fe3O4 is considered reasonable.

[0036] Figure 2The residual TPH levels in RCS and Fe3O4@CS are shown. The TPH content in PCS was 153,826 mg / kg. Through slow pyrolysis, the residual TPH content was significantly reduced, with TPH removal rates of 98.71% and 99.02% in RCS and Fe3O4@CS, respectively. The residual TPH contents in RCS and Fe3O4@CS were 1,982 and 1,507 mg / kg, respectively, which are far below the TPH content screening value (4,500 mg / kg) for Class II land use in the "Soil Environmental Quality Standard for Construction Land Soil Pollution Risk Control", achieving efficient and compliant remediation.

[0037] Figure 3 The XRD patterns of RCS, BCS, and Fe3O4@CS are shown. The characteristic peaks for carbon are at 2θ = 24.5°, 25.4°, and 26.6°, corresponding to the diffraction peaks of BCS and Fe3O4@CS at 2θ = 26.6°. This characteristic peak did not shift, indicating that ball milling and Fe3O4-assisted milling did not significantly affect the main crystal structure of RCS, but it does show changes in the structural composition of BCS and Fe3O4@CS compared to RCS. The Fe3O4@CS sample exhibits typical diffraction peaks of Fe3O4 at 2θ = 30° and 35.54°, indicating that Fe3O4 particles were successfully loaded onto RCS, and Fe3O4@CS was successfully prepared. Furthermore, typical diffraction peaks of Fe2O3 were detected at 2θ = 57.04° and 62.59°, which may be due to the formation of surface oxygen-containing complexes by functional oxygen-containing groups (such as carboxyl, hydroxyl, and aliphatic ethers) on the RCS surface through stable absorption configurations with Fe ions.

[0038] Figure 4 Displaying FTIR spectra of RCS, BCS, and Fe3O4@CS. 3442 cm⁻¹ -1 The absorption peak at 2861 and 2926 cm⁻¹ is due to the stretching vibration of -OH, which is related to the formation of -O-Me groups on RCS. The stretching vibration of -OH is weakened in BCS and Fe₃O₄@CS, because Fe ions occupy adsorption sites (e.g., -OH) during ball milling, forming hydroxides. -1 The two absorption vibration peaks represent the symmetric and asymmetric CH stretching vibrations of trace residual petroleum hydrocarbons after pyrolysis. Compared to RCS, the Fe3O4@CS surface has an increased number of oxygen-containing functional groups, with -COOH (1630 cm⁻¹) being particularly prominent. -1 ) and CO3 2- (1440cm -1 The absorption peak intensity of CO3 increases, indicating that oxygen-containing functional groups can participate in the adsorption process by forming complexes with heavy metals through surface complexation. 2- It combines with heavy metals to form chemical precipitation, creating metal carbonate and phosphate precipitates, which facilitates adsorption. At 469 and 1028 cm⁻¹... -1The peaks at 590 and 788 cm⁻¹ represent the stretching vibrations of the Si-O bond, indicating that Si-O groups can form complexes with heavy metal ions. -1 The absorption peak at that point is the Fe-O peak. The Fe-O peak of Fe3O4@CS is slightly enhanced, indicating that the surface contains more iron oxides.

[0039] Figure 5 The O1s spectra of RCS, BCS, and Fe3O4@CS are shown. As can be seen from the figure, the O1s spectra of RCS, BCS, and Fe3O4@CS are split into three peaks at 531.70, 532.35, and 532.70 eV, which are attributed to CO32- and CO23-, respectively. 2- RCS contains a large amount of CO3 groups (34.56%), CO (40.65%), and C=O (24.79%). 2- The functional groups are generated by pyrolysis, which facilitates the adsorption of carbonate precipitation. (Fe3O4@CS contains CO3) 2- The contents of CO and C=O were 46.61%, 27.53%, and 25.86%, respectively. The significant decrease in CO group content indicates that the addition of Fe3O4 for co-pyrolysis converts CO into more CO3. 2- The presence of oxygen-containing groups helps Fe3O4@CS adsorb heavy metals.

[0040] Example 3

[0041] The Fe3O4@CS obtained in Example 1 was added to several 100ml portions of simulated wastewater containing lead, copper, zinc, and cadmium at concentrations of 10–200 mg / L. The Fe3O4@CS dosage in the wastewater containing lead, copper, zinc, and cadmium was 0.5, 2, 2, and 2 g / L, respectively, and the mixture was shaken for 6 hours. Figure 6 The adsorption results and isothermal adsorption curves for heavy metals by Fe3O4@CS are shown. The adsorption capacity of heavy metals increases with increasing heavy metal concentration and then gradually slows down until adsorption equilibrium is reached. The adsorption capacities of Fe3O4@CS for different concentrations of heavy metals are as follows: Pb 2+ >Cu 2+ >Zn 2+ >Cd 2+ The maximum adsorption capacity for lead can reach over 300 mg / g. These results are attributed to the increased oxygen-containing functional groups and specific surface area of ​​Fe3O4@CS, which promotes the adsorption of lead through surface complexation and adsorption. 2+ The removal of heavy metals was investigated. The Langmuir and Freundlich models were used to fit the heavy metal adsorption performance of Fe3O4@CS. The Langmuir model showed a better fit, indicating that heavy metals undergo monolayer adsorption at the active sites. The fitting results showed that Fe3O4@CS effectively removed Pb. 2+ Cu 2+ Cd 2+ and Zn 2+ The maximum adsorption capacities were 888.79, 69.34, 47.37 and 77.52 mg / kg, respectively.

[0042] The adsorption kinetics of heavy metals by Fe3O4@CS are shown below. Figure 7 Fe3O4@CS for Pb 2+ Cu 2+ Zn 2+ and Cd 2+ The adsorption of Pb increases with time within the range of 0-60 min. As the adsorption process proceeds, the number of active sites decreases, and Pb... 2+ Cu 2+ Zn 2+ and Cd 2+ The adsorption rate slows down, and the adsorption capacity increases slowly for Cu. 2+ Zn 2+ and Cd 2+ The adsorption of Pb reached equilibrium after about 2 hours, while Pb... 2+ Adsorption equilibrium was reached after approximately 4 hours. The adsorption process was fitted using pseudo-first-order and pseudo-second-order kinetic models. The R² value of the pseudo-second-order kinetic model was... 2 R higher than that of the pseudo-first-order dynamics model 2 Therefore, chemisorption is the main adsorption mechanism for heavy metals by Fe3O4@CS, but both models have high R0 values. 2 This indicates that physical adsorption also occurs simultaneously.

[0043] Example 4

[0044] The Fe3O4@CS obtained in Example 1 was added to simulated wastewater containing lead, copper, zinc, and cadmium, respectively. The concentrations of lead and copper were 1000 mg / L, and the dosages of Fe3O4@CS were 2 g / L and 8.33 g / L, respectively; the concentrations of zinc and cadmium were both 500 mg / L, and the dosage of Fe3O4@CS was 5 g / L for both. After shaking for 6 hours, solid-liquid separation was performed, and the mixture was dried at 120℃ for 1 hour. The contents of exchangeable, carbonate-bound, metal oxide-bound, organically bound, and residual heavy metals in Fe3O4@CS were analyzed using the Tessel continuous extraction method. The results are shown in [Figure number missing]. Figure 8 .

[0045] The content of carbonate-bound heavy metals was significantly higher than that of other forms, indicating that carbonate binding is the main mechanism for heavy metal adsorption by Fe3O4@CS. Some heavy metals also exist in metal oxide-bound or organic-bound forms, with very few exchangeable forms. It is evident that the addition of Fe3O4 to assist pyrolysis increases the content of iron and manganese oxides, exposing them to the surface of soil particles and increasing the content of iron and manganese oxide-bound heavy metals. Furthermore, it converts some organic matter and petroleum hydrocarbons in PCS into amorphous carbon containing various organic complex groups, all of which are beneficial to Pb. 2+ Cu 2+ Cd 2+ and Zn 2+ Adsorption.

[0046] Example 5

[0047] To verify the magnetism of Fe3O4@CS in Example 1, the magnetization curve of Fe3O4@CS was measured as follows: Figure 9 As shown, the saturation magnetization is 18.31 emu / g, with no obvious hysteresis loop, and the magnetization curve is S-shaped, indicating that Fe3O4@CS has good magnetic properties and can achieve rapid solid-liquid separation under external magnetic force. Therefore, when using Fe3O4@CS as an adsorbent to treat wastewater containing heavy metals, magnetic separation can be used to recover residual Fe3O4@CS after the reaction. Compared with other methods, this significantly improves the solid-liquid separation efficiency, reduces wastewater treatment costs, and enhances its application value.

[0048] The above technical solutions only embody the preferred technical solutions of the present invention. Any modifications that may be made by those skilled in the art to certain parts thereof embody the principles of the present invention and fall within the protection scope of the present invention.

Claims

1. A method for adsorbing heavy metals in wastewater, characterized in that: Carbonized soil is added to wastewater containing heavy metals, with the dosage of carbonized soil being 0.5–2 g / L. The carbonized soil is a heavy metal adsorbent prepared by co-milling and pyrolysis of petroleum-contaminated soil and iron oxide Fe3O4, and the preparation method includes the following steps: Step 1: Add Fe3O4 to the petroleum-contaminated soil and mix and activate it mechanically and chemically by ball milling; the Fe3O4 is 10% of the total mass of the petroleum-contaminated soil and Fe3O4, the ball milling time is 1 hour, the ball-to-material ratio is 40:1, and the rotation speed is 500 rpm; Step 2: Transfer the mixture obtained in Step 1 to a tube furnace and perform slow pyrolysis under nitrogen protection, then cool to room temperature to obtain carbonized soil; the slow pyrolysis is to heat to 500℃ at a rate of 10℃ / min and hold for 1 hour, then cool to room temperature. Step 3: Use the carbonized soil obtained as a heavy metal adsorbent to efficiently adsorb heavy metals in wastewater. The heavy metal is Pb. 2+ .

2. The method for adsorbing heavy metals in wastewater according to claim 1, characterized in that: The petroleum-contaminated soil was cleaned, dried, and then passed through a 2mm fine sieve.

3. The method for adsorbing heavy metals in wastewater according to claim 1, characterized in that: The grinding balls are made of stainless steel or zirconium oxide, and come in large, medium, and small sizes.

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