Preparation method and application of mango seed biochar / sulfurized zero-valent iron composite material

Abstract

The invention provides a preparation method and application of a mango seed biochar / sulfurized zero-valent iron (BC / s-ZVI) composite material. The method comprises the following steps: carbonizing mango seeds to prepare biochar, putting the mango seed biochar, zero-valent iron and sodium dithionite into a ball milling tank according to a certain proportion through mechanical ball milling, then adding a morpholine ethanesulfonic acid sodium salt biological buffer solution (MES) into the ball milling tank as a grinding aid, then putting mechanical grinding balls with a certain size and mass, sealing, carrying out ball milling for 6 hours, and finally, carrying out ball milling for 2-3 hours. And centrifuging, freeze-drying, grinding and sieving to obtain the BC / s-ZVI. The maximum adsorption capacities of the BC / s-ZVI on Cd (II), Pb (II), As (III) and As (V) are respectively 31.16 mg / g, 332.2 mg / g, 109.74 mg / g and 74.68 mg / g; the BC / s-ZVI enables the effective state concentrations of As, Cd and Pb in the soil to be respectively reduced by 51.72%, 37.79% and 36.57%. The material is simple in process, can be widely applied to deep treatment of wastewater containing arsenic, lead and cadmium in industrial and mining enterprises and fixation of available arsenic, lead and cadmium in composite polluted soil, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to a method for preparing mango kernel biochar / zero valent iron sulfide composite material (BC / s-ZVI). Using mango kernels as the main material, mango kernel biochar BC / s-ZVI can be prepared by ball milling, which can be used to treat arsenic, cadmium and lead composite pollution in water and soil. Background Technology

[0002] Heavy metal pollution in water and soil contains metal elements such as Pb, Cd, As, Cu, and Cr. Pollutants Pb, Cd, and As are considered to be the most toxic elements. Heavy metals are non-biodegradable and can be utilized by organisms through the food chain. Even at very low concentrations, they are extremely toxic.

[0003] Pb, Cd, and As enter the human body through contaminated water, food, and air. Pb can damage the nervous, circulatory, and cardiovascular systems, and studies have shown that it may be a human carcinogen. Cd can adversely affect the nervous system, and long-term exposure can even lead to lung cancer, kidney cancer, and bone diseases. Arsenic compounds can cause kidney cancer, liver cancer, and skin cancer. Therefore, remediating arsenic, cadmium, and lead pollution in water bodies and soil is particularly important.

[0004] Remediation methods for heavy metal contaminated soil often include in-situ or non-in-situ methods, on-site or off-site methods, and include physical remediation, bioremediation, and chemical remediation. A combination of technologies is typically employed to achieve more economical and effective remediation of heavy metals in the soil. Solidification / stabilization remediation is considered an environmentally sustainable and cost-effective technology that can reduce the activity and availability of heavy metals. Stabilizing materials are added to the contaminated soil, and these materials react with the heavy metals in the soil, altering their physicochemical properties and thus reducing their migration into water, plants, and other environmental media.

[0005] Biochar possesses a highly aromatic structure, containing numerous phenolic hydroxyl, carboxyl, and carbonyl groups. These fundamental physicochemical properties endow biochar with excellent stability and adsorption characteristics. Its passivation mechanism for heavy metals mainly involves electrostatic adsorption, ion exchange, adsorption of surface mineral components, cation-π bond interactions, and complexation and precipitation of surface functional groups. Therefore, it can strongly adsorb heavy metals in water and soil and affect their migration, effectively reducing the bioavailability and toxicity of heavy metal pollutants. Mango is one of the main economic crops in Guangxi, and agricultural waste can be used as a biomass raw material for biochar production. Therefore, mango kernels can serve as an ideal precursor for the preparation of carbon-based materials.

[0006] Zero-valent iron (ZVI) possesses high reducing power and is considered a promising material for heavy metal remediation. Supporting ZVI on biochar can prevent ZVI aggregation, thereby enhancing its reactivity and the heavy metal removal capacity of biochar. Currently, the most commonly used methods for preparing nano-zero-valent iron biochar (nZVI / BC) are liquid-phase reduction and carbothermal reduction. In nZVI / BC prepared by carbothermal reduction, the iron typically exists in the form of large nano-iron clusters, which shields the graphitized structure, leading to weakened electron transfer capabilities. Sulfide modification can give zero-valent iron a larger specific surface area and stronger reducing power. Dithionite (S₂O₄) is a common sulfur precursor. 2− Solutions stand out due to their ease of preparation and management. Ball milling is an environmentally friendly and low-cost method for modifying biochar, which can reduce particle size, increase specific surface area, overcome the blockage points of iron oxide layer, and promote functional group recombination, thereby improving the material's ability to remove pollutants.

[0007] This invention provides a method for preparing mango kernel biochar using mango kernels, an agricultural waste from Guangxi, as the main raw material. Micron-sized zero-valent iron (mZVI) is used. The mZVI is sulfided by mixing with a sulfur-containing reagent or by ball milling in a limited oxygen environment. The mZVI is then dispersed on porous biochar material through ball milling, thus preparing a ternary composite material—BC / s-ZVI—containing biochar, mZVI, and Na2S2O4. XRD, infrared, zeta potential, specific surface area, and pore size characterization analyses were performed on the material, indicating the successful synthesis of BC / s-ZVI. This material can effectively remove arsenic, lead, and cadmium metals from wastewater and soil, demonstrating promising development prospects and practical significance. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing mango pit biochar / zero-valent iron sulfide composite materials using mango pit waste as a biomass source under normal temperature and pressure via ball milling. This method is simple to operate, low in cost, and poses no risk of secondary pollution. It exhibits excellent adsorption and removal performance of heavy metals, and the composite material can be rapidly separated from the solution by an external magnetic field. The prepared composite material can be widely used in the deep treatment of arsenic, lead, and cadmium-containing wastewater in industrial and mining enterprises and in the remediation of arsenic, lead, and cadmium-contaminated soil.

[0009] The preparation method of the above-mentioned BC / s-ZVI material includes the following steps:

[0010] (1) Pretreatment of mango pits: Soak the mango pits in tap water and wash them repeatedly. After draining, sieve them and place them in an oven to dry at 60 °C~80 °C for 12 h~24 h. After cooling, crush them with a universal crusher, sieve them, and put the mango pit powder into a desiccator for later use.

[0011] (2) Preparation of mango kernel biochar: The mango kernel powder obtained in step (1) is placed in a ceramic boat, and the ceramic boat is placed in a tube furnace. The temperature is raised to 400 °C~600 °C at a heating rate of 5 °C / min and carbonized for 2 h~4 h. After cooling, the obtained biochar is crushed and passed through a 100-mesh sieve to obtain mango kernel biochar. It is then sealed and placed in a desiccator for later use.

[0012] (3) Place the carbon source material, iron source material and sodium dithionite material into the ball mill jar in a certain proportion. At the same time, add sodium morpholine ethanesulfonate biological buffer solution (MES) as a grinding aid to the ball mill jar. Place mechanical grinding balls of a certain size and mass into the jar and fix the sealing cap of the ball mill jar to the jar to ensure a tight seal.

[0013] (4) Place the ball mill jar containing the sample into the mechanical ball mill, fix it in the corresponding position, close the ball mill chamber cover, set the specific parameters of the mechanical ball mill, and then carry out mechanical ball milling;

[0014] (5) After mechanical ball milling is completed, remove the ball mill jar, open the ball mill jar, and use a syringe to draw the suspension into a centrifuge tube;

[0015] (6) Place the centrifuge tube from step (5) in a low-speed centrifuge and centrifuge at 4000 rpm / min for 10 min to 20 min. Filter the filter cake and wash it several times with deionized water until it is neutral. Then place the filter cake in a freeze dryer and freeze dry it for 24 h to 48 h. After taking it out, grind it, sieve it, and collect the black solid powder BC / s-ZVI material.

[0016] In step (3) of the above preparation method, the carbon source material can be one or more of mango kernel biochar, sugarcane bagasse biochar, and mulberry stalk; the iron source material can be one or more of commercial iron powder and metallic iron powder obtained by hydrogen reduction of iron oxide.

[0017] In step (3) of the above preparation method, the molar ratio of iron to sulfur in the iron source material and the sulfur source material is 0~0.5, preferably 0, 0.5, 0.1, 0.2, 0.3, 0.5, and more preferably 0.1. The mass ratio of iron to carbon in the iron source material and the carbon source material is 1:1~10:1, preferably 1:1, 3:1, 5:1, 10:1, and more preferably 3:1. The volume of the MES solution is 60 mL~180 mL, preferably 60 mL, 90 mL, 120 mL, 150 mL, 180 mL, and more preferably 120 mL.

[0018] In step (3) of the above preparation method, the composition of the grinding jar and the balls is zirconium oxide, the volume of the grinding jar is 500 ml, the diameter of the balls is 5 mm, and the mass ratio of the grinding balls to the raw materials (referred to as the ball-to-material ratio) is 15.

[0019] In step (4) of the above preparation method, the grinding jar and planetary disk in the ball mill rotate in opposite directions, and the transmission ratio of planetary disk / grinding jar is I = 1:2; the ball mill setting parameters are: planetary disk speed is 300 r / min; grinding jar speed is 600 r / min; one cycle of ball milling is 25 min; pause for 5 min between each cycle; ball milling cycle is 12; total ball milling time is 6 h; ball milling mode is reverse.

[0020] The present invention has the following advantages:

[0021] (1) Guangxi produces a large number of mango kernels every year. How to make efficient use of these agricultural and forestry wastes has always been a research challenge. By using mango kernels to make BC / s-ZVI material, the high-value utilization of mango kernels has been realized. At the same time, it has a good treatment effect on wastewater and soil containing heavy metals.

[0022] (2) The prepared BC / s-ZVI material has strong magnetic properties and can be separated from the solution under the action of an external magnetic field. The prepared composite material has a good passivation effect on heavy metals arsenic, lead and cadmium in aqueous solution and soil.

[0023] (3) The present invention directly synthesizes carbon source, iron source and sodium dithionite into BC / s-ZVI material, avoiding the incorporation of other elemental impurities in the intermediate process.

[0024] (4) The present invention uses mechanical ball milling to prepare materials, which can prepare a large number of BC / s-ZVI materials at one time. The preparation scheme is simple and highly reproducible. Attached Figure Description

[0025] Figure 1 The XRD pattern is for BC / s-ZVI.

[0026] Figure 2 The image shows the infrared spectrum of BC / s-ZVI.

[0027] Figure 3 This is the Zeta plot for BC / s-ZVI.

[0028] Figure 4 This is a specific surface area analysis chart for BC / s-ZVI.

[0029] Figure 5 The adsorption isotherm of arsenic, lead, and cadmium by BC / s-ZVI is shown.

[0030] Figure 6 Graph showing the passivation effect of BC / s-ZVI in soil for fixing arsenic, lead, and cadmium. Detailed Implementation

[0031] (1) Pretreatment of mango pits: Soak the mango pits and wash them 5 times with tap water, then wash them once with deionized water. After draining, crush them with a universal grinder, pass them through a 20-mesh sieve, place them in an oven and dry them at 65 °C for 24 h, and put them in a desiccator for later use.

[0032] (2) Preparation of mango kernel biochar: The mango kernel powder obtained in step (1) is placed in a ceramic boat, the ceramic boat is placed in a tube furnace, the temperature is increased at a rate of 5 °C / min, and carbonized at 500 °C for 2 h. After cooling, the obtained biochar is crushed and passed through a 100-mesh sieve to obtain mango kernel biochar. It is then sealed and placed in a desiccator for later use.

[0033] (3) Weigh 450 g of grinding balls (zirconia material, 5 mm in diameter) using an electronic balance and put them into a 500 mL ball mill jar lined with zirconia.

[0034] (4) Weigh 20 g of reduced iron powder (average grain size 38 μm), 6.67 g of mango kernel biochar (average grain size 150 μm) (the mass ratio of iron to carbon is 3:1), 3.12 g of sodium dithionite (the molar ratio of sulfur to iron is 0.1), and 120 mL of MES solution. Put them into the ball mill jar (the ball-to-material ratio is 15) together with the grinding balls, seal the lid, and put the ball mill jar into the ball mill.

[0035] Set the ball milling parameters: planetary disk speed 300 r / min, ball milling jar speed 600 r / min, ball milling mode reverse, one cycle of ball milling 25 min, pause for 5 min between each cycle, for a total of 12 cycles of ball milling.

[0036] (5) After the ball milling is finished, remove the ball mill jar and let it cool naturally. Then, open the ball mill jar and use a syringe to draw the suspension into a centrifuge tube.

[0037] (6) Centrifuge the centrifuge tube from step (5) at 4000 rpm for 10 min in a low-speed centrifuge, filter, and wash the filter cake several times with deionized water until neutral; then place the filter cake in a freeze dryer and freeze dry for 24 h to 48 h; after removal, grind, sieve, and collect the black solid powder BC / s-ZVI material. Its X-ray diffraction analysis, infrared spectroscopy analysis, Zeta potential analysis, and specific surface area analysis results are as follows: Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown.

[0038] Applications of BC / s-ZVI materials:

[0039] Weigh 0.1 g of the mango kernel biochar MBC / s-ZVI composite material prepared in this example into a 100 mL plastic centrifuge tube. Add 50 mL of arsenic-containing solutions with concentrations of 10, 20, 50, 100, 200, and 500 mg / L; lead-containing solutions with concentrations of 100, 200, 500, 750, and 1000 mg / L; and cadmium-containing solutions with concentrations of 50, 100, 150, 300, and 600 mg / L (the pH of which has been adjusted to 6.0 with 0.1 mol / L sodium hydroxide or hydrochloric acid solution) to the above plastic centrifuge tubes. Place the plastic centrifuge tubes in a constant temperature water bath shaker and shake at 25 ± 1 °C and 180 rpm / min for 48 h. Then filter through a 0.22 μm filter membrane and store the filtrate in a polyethylene plastic centrifuge tube. The residual arsenic concentration in the solution was determined by atomic fluorescence spectrometry, and the residual lead and cadmium concentrations were determined by inductively coupled plasma atomic emission spectrometry. The results are as follows: Figure 5 As shown, the maximum adsorption capacities of BC / s-ZVI for Cd(II), Pb(II), As(III), and As(V) were 31.16 mg / g, 332.2 mg / g, 109.74 mg / g, and 74.68 mg / g, respectively.

[0040] 0.5 g of the mango kernel biochar / zero-valent iron sulfide composite material (BC / s-ZVI) prepared in this example and 50 g of arsenic-contaminated soil were weighed into 100 mL plastic centrifuge tubes. The tubes were sealed with perforated sealing film and placed in a constant temperature incubator at 25±1 °C for incubation. Every three days, the centrifuge tubes were weighed and the soil was replenished with water to maintain the soil moisture content at 70% field capacity. The incubation lasted for 10 days. After the 10th day, soil samples were collected, air-dried, and quartered. Available arsenic in the soil was extracted using the NaHCO3 extraction method, and the concentration of available arsenic in the soil leachate was analyzed by atomic fluorescence spectrometry. Available lead and cadmium in the soil were extracted using the triethanolamine-calcium chloride-diethylenetriaminepentaacetic acid extraction method, and the concentration of available lead and cadmium in the soil leachate was measured and analyzed by inductively coupled plasma atomic emission spectrometry. The results are as follows: Figure 6 As shown, BC / s-ZVI reduced the available concentrations of As, Cd, and Pb in the soil by 51.72%, 37.79%, and 36.57%, respectively.

Claims

1. A method for preparing a mango kernel biochar / zero-valent iron sulfide composite material, characterized in that... The specific steps are as follows: (1) Mango pit pretreatment: Soak the mango pits in tap water and wash them repeatedly. After draining, sieve them and place them in an oven to dry at 60 °C~80 °C for 12 h~24 h. After cooling, crush them with a universal crusher, sieve them, and put the mango pit powder into a desiccator for later use. (2) Preparation of mango kernel biochar: The mango kernel powder obtained in step (1) is placed in a ceramic boat, and the ceramic boat is placed in a tube furnace. The temperature is increased to 400 °C~600 °C at a heating rate of 5 °C / min. The carbonization is carried out for 2 h~4 h. After cooling, the obtained biochar is crushed and passed through a 100-mesh sieve to obtain mango kernel biochar. It is sealed and placed in a desiccator for later use. (3) Place the carbon source material, iron source material and sodium dithionite material into the ball mill jar in a certain proportion. At the same time, add sodium morpholine ethanesulfonate biological buffer solution (MES) as a grinding aid to the ball mill jar. Place mechanical grinding balls of a certain size and mass into the jar and fix the sealing cap of the ball mill jar to the jar to ensure a tight seal. (4) Place the ball mill jar containing the sample into the mechanical ball mill, fix it in the corresponding position, close the ball mill chamber cover, set the specific parameters of the mechanical ball mill, and then carry out mechanical ball milling; (5) After mechanical ball milling is completed, remove the ball mill jar, open the ball mill jar, and use a syringe to draw the suspension into a centrifuge tube; (6) Place the centrifuge tube from step (5) in a low-speed centrifuge and centrifuge at 4000 rpm / min for 10 min to 20 min. Filter the mixture and wash the filter cake several times with deionized water until it is neutral. The filter cake is then placed in a freeze dryer and freeze-dried for 24 to 48 hours. After removal, it is ground, sieved, and the resulting black solid powder is BC / s-ZVI material.

2. The preparation method according to claim 1, characterized in that, In step (3) of the preparation method, the carbon source material can be one or more of mango kernel biochar, sugarcane bagasse biochar, and mulberry stalk biochar; the iron source material can be one or more of commercial iron powder and metallic iron powder obtained by hydrogen reduction of iron oxide.

3. The preparation method according to claim 1, characterized in that, In step (3) of the preparation method, the molar ratio of iron to sulfur in the iron source material and the sulfur source material is 0~0.5, preferably 0, 0.5, 0.1, 0.2, 0.3, 0.5, and more preferably 0.1; the mass ratio of iron to carbon in the iron source material and the carbon source material is 1:1~10:1, preferably 1:1, 3:1, 5:1, 10:1, and more preferably 3:1; the volume of the MES solution is 60 mL~180 mL, preferably 60 mL, 90 mL, 120 mL, 150 mL, 180 mL, and more preferably 120 mL.

4. The preparation method according to claim 1, characterized in that, In step (3) of the preparation method, the composition of the grinding jar and the balls is zirconium oxide, the volume of the grinding jar is 500 ml, the diameter of the balls is 5 mm, and the mass ratio of the grinding balls to the raw materials (referred to as the ball-to-material ratio) is 15.

5. The preparation method according to claim 1, characterized in that, In step (4) of the preparation method, the grinding jar and planetary disk in the ball mill rotate in opposite directions, and the transmission ratio of planetary disk / grinding jar is I = 1:2; the ball mill setting parameters are: planetary disk speed is 300 r / min; grinding jar speed is 600 r / min; one cycle of ball milling is 25 min; pause for 5 min between each cycle; the ball milling cycle is 12; the total ball milling time is 6 h; the ball milling mode is reverse.

6. The application of the mango kernel biochar BC / s-ZVI material prepared by the preparation method according to any one of claims 1-5, characterized in that... The mango kernel biochar BC / s-ZVI material has strong magnetic properties, which can separate the composite material from the solution under the action of an external magnetic field. The prepared composite material has a good removal effect on heavy metals arsenic, lead and cadmium in aqueous solution and soil.

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