CN113457620A - Method for preparing magnetic meat and bone biochar by modifying magnetic fluid - Google Patents

Abstract

The invention provides a method for preparing magnetic meat and bone biochar by modifying magnetic fluid, which comprises the following steps: preparing magnetic meat and bone biochar S1, characterizing biochar S2, adsorbing experiment S3, sequentially extracting experiment S4 and processing data S5; the preparation S1 of the magnetic meat and bone biochar comprises the preparation of the meat and bone biochar and the preparation of the magnetic meat and bone biochar; the preparation method of the meat and bone biochar comprises the following steps: the abnormal dead carps are collected from a certain fishing farm in Xinzhou city, and the carps are cut into blocks, washed and naturally dried in the air; pulverizing and sieving (0.83mm) to obtain carp meat and bone powder, placing the carp meat and bone powder into a corundum crucible, compacting, and carrying out anoxic pyrolysis for 7h (N) in a tubular furnace at 600 DEG C₂Atmosphere, heating rate 15 deg.C/min^‑1) Naturally cooling to room temperature, taking out, crushing and sieving by a 0.25mm sieve; the modification of the magnetic fluid can ensure that the surface of the CBC is more uniformly loaded with Fe3O₄Increase the specific surface area, total pore volume, average pore diameter and surface charge, and can also be used for Cd²⁺The adsorption efficiency is improved by 160%.

Description

Method for preparing magnetic meat and bone biochar by modifying magnetic fluid

Technical Field

The invention relates to Cd²⁺The technical field of pollution remediation, in particular to a method for preparing magnetic meat and bone biochar by modifying magnetic fluid.

Background

The biochar is a porous carbonaceous solid material prepared by pyrolyzing biomass at low temperature (less than 700 ℃) under the complete/partial anoxic condition, and has better adsorption and removal effects on pollutants such as heavy metals and the like due to the large specific surface area, more negative surface charges and rich oxygen-containing functional groups (including carboxyl, hydroxyl, anhydride and the like). However, since the biochar has a small particle size and a low density, separation and reuse after adsorption become one of the main problems to be solved. Magnetic media (Fe, Fe) are introduced into the biochar₂O₃Or Fe₃O₄) The magnetic biochar is formed, so that the adsorption capacity of the biochar on heavy metals can be improved, and efficient separation can be realized by means of an external magnetic field. The preparation method of the magnetic biochar mainly comprises a precursor mixed pyrolysis method, a chemical coprecipitation method, a ball milling method and the like. The precursor mixed pyrolysis method is characterized in that an iron oxide precursor and biochar are fully mixed and then subjected to anoxic pyrolysis for preparation, equipment is simple, and steps are simple and convenient, but the method is difficult to control the type and particle size of the loaded iron oxide and is not suitable for preparation of high-water-content biomass raw materials; the chemical coprecipitation method is to treat Fe by NaOH²⁺/Fe³⁺The iron oxide is loaded on the biochar by the aqueous solution, the method has higher operation requirement, and the precipitation type and the particle size of the iron oxide are difficult to control; the ball milling method is to prepare magnetic biochar by using mechanical force, but the method destroys the crystal structure of the material. The Magnetic fluid is a colloidal solution formed by dispersing a Magnetic medium (with the diameter of about 10nm) coated by a surfactant in a base liquid, wherein the Magnetic medium is Fe₃O₄The base liquid is generally water or kerosene and the like, the magnetic fluid prevents the nano particles from settling under the action of gravity due to the never-standing Brownian motion, and the surfactant is coated to provide short-distance steric hindrance and electrostatic repulsion among the particles, so that the nano particles are prevented from agglomerating and can stably exist for a long time; the magnetic fluid has liquid fluidity and solid material magnetism, so the magnetic fluid has wide application in the fields of biomedicine, environmental management, mineral separation and the like, and the research on preparing the magnetic biochar by using the magnetic fluid is rarely reported.

The adsorption/fixation mechanism of the biochar on the heavy metal mainly comprises physical adsorption, precipitation, surface oxygen-containing functional group complexation, ion exchange, electrostatic adsorption and the like, and the heavy metal adsorbed by different mechanisms has different environmental meanings. Heavy metals adsorbed by physical adsorption and ion exchange mechanisms are easily released in the environment, and can directly threaten plants and human beings; heavy metals which are complexed and adsorbed through oxygen-containing functional groups on the surface are not easy to release; whereas the risk of release of the heavy metals adsorbed by precipitation depends on the type of precipitation, the fraction dissolved in sodium acetate/acetic acid may constitute a potential threat, the remaining insoluble ones are considered to constitute no direct threat to plants and humans. When the biochar is applied to remediation of heavy metal contaminated soil, the environmental risk of heavy metals on the biochar can be reduced by taking surface complexation and precipitation as the dominant adsorption and fixation mechanism; when the biochar is applied to water treatment, the absorption mechanism of which the physical absorption and ion exchange are dominant is favorable for recycling the biochar. Therefore, the method has important guiding significance for evaluating the application of the biochar by finding out the quantitative adsorption mechanism of the biochar for adsorbing the heavy metal.

In view of the above, the research uses the abnormal dead carps as the biomass raw material, prepares the carp meat and bone biochar (CBC) at 600 ℃, adopts the magnetic fluid to modify the carp meat and bone biochar to obtain the magnetic meat and bone biochar (MCBC), and discusses the influence of the magnetic fluid modification on the physicochemical property of the CBC; with Cd²⁺For the pollutant representation, the MCBC pair Cd is explored²⁺The adsorption mechanism of (1) and the sequential extraction experiment analyze the Cd adsorbed on the MCBC²⁺The environmental risk of the MCBC is expected to provide a certain theoretical basis for the application of the MCBC in the water and soil heavy metal pollution remediation process.

In view of the above, the present problems are improved and researched, and a method for preparing magnetic meat and bone biochar by modifying magnetic fluid is provided, aiming at achieving the purposes of solving the problems and improving the practical value through the technology.

Disclosure of Invention

The invention aims to provide a method for preparing magnetic meat and bone biochar by modifying magnetic fluid, which aims to solve the problems and the defects in the background technology.

In order to realize the purpose, the invention provides a method for preparing magnetic meat and bone biochar by modifying magnetic fluid, which is achieved by the following specific technical means:

the method for preparing the magnetic meat and bone biochar by modifying the magnetic fluid comprises the following steps: preparing magnetic meat and bone biochar S1, characterizing biochar S2, adsorbing experiment S3, sequentially extracting experiment S4 and processing data S5; the preparation S1 of the magnetic meat and bone biochar comprises the preparation of the meat and bone biochar and the preparation of the magnetic meat and bone biochar; the preparation method of the meat and bone biochar comprises the following steps: the abnormal dead carps are collected from a certain fishing farm in Xinzhou city, and the carps are cut into blocks, washed and naturally dried in the air; pulverizing, sieving (0.83mm) to obtain carp meat and bone powder, placing the carp meat and bone powder into corundum crucible, compacting, and pyrolyzing in tubular furnace at 600 deg.C under oxygen deficiency for 7 hr (N₂Atmosphere, heating rate 15 deg.C/min^-1) Naturally cooling to room temperature, taking out, pulverizing, sieving with 0.25mm sieve, washing with cyclohexane solution and ethanol to remove the residual biological oil on the surface of the charcoal, and oven drying at 80 deg.C to obtain meat and bone charcoal labeled as CBC; the preparation method of the magnetic meat and bone biochar comprises the following steps: magnetic fluid: FeCl is added₃·6HO₂(1.35g) and 40mL of ethylene glycol are mixed and dissolved, 1g of polyethylene glycol (PEG-4000) and 3.6g of NaAc are added to carry out magnetic stirring for 30min, then the mixture is placed in a reaction kettle to react for 12h at the temperature of 200 ℃, the mixture is taken out to be filtered after being cooled to the room temperature, the filter cake is washed for 2 to 3 times by absolute ethyl alcohol, and the filter cake is placed at the temperature of 60 ℃ and dried for 6h to prepare the magnetofluid; magnetic meat and bone biochar: placing 1g of magnetofluid and 4g of meat and bone biochar in a 100mL triangular flask, adding 50mL of deionized water, and oscillating at room temperature for 8h (150 r.min)^-1) Then, carrying out suction filtration, washing the filtrate by using deionized water until the filtrate is colorless and transparent, and drying the filter cake for 6 hours at the temperature of 60 ℃ to obtain magnetic meat and bone biochar which is marked as MCBC;

characterization of the biochar S2: c, H, N, O, S content was measured using an elemental analyzer (Elementar, Germany); observing the surface topography of the sample by adopting a scanning electron microscope (JEOL JSM-7800F, Japan); the specific surface area and pore size distribution of the sample were measured using a physical adsorption apparatus (Micromeritics ASAP2020C, USA); analyzing the crystal form of the sample by adopting an X-ray diffractometer (Haoyuan DX-2700BH, China); the surface functional groups were characterized using a Fourier transform infrared spectrometer (Bruker TENSOR27, Germany); measuring the surface charge condition of a sample (Hobriba sz-100, Japan) by adopting a Zeta potential analyzer; an X-ray photoelectron spectrometer (Thermo Fisher Scientific ESCALAB 250Xi, USA) is adopted to characterize the surface chemical characteristics of the sample; a hysteresis loop of the sample is characterized by adopting a vibrating sample magnetometer (LakeShore 7404, USA);

the flow of the adsorption experiment S3 is as follows: 20mL of Cd²⁺Solution (containing 0.01 mol. L)^-1NaNO of (2)₃As background electrolyte) and 0.0200g of adsorbent were added to a series of 50mL Erlenmeyer flasks and shaken at a constant temperature for adsorption (150 r. min)^-1) Adsorbing for a certain time, filtering with 0.45um filter membrane, and measuring Cd in the filtrate with flame atomic absorption spectrophotometer (AA-6300F, Shimadzu corporation)²⁺And (4) concentration. In kinetic experiments, Cd²⁺Initial concentrations were 50 and 100 mg.L, respectively^-1The adsorption time and the adsorption temperature are respectively 5-240min and 25 ℃; in isothermal adsorption experiments, Cd²⁺The initial concentration is 30-250 mg.L^-1The adsorption time was 240min, and the adsorption temperatures were 5, 25 and 45 ℃ respectively. Each set of experiments is performed in three parallels under the same condition;

the flow of the sequential extraction experiment S4 is as follows: 0.0200g of MCBC and 20mL of 100mg & L^-1Cd (2)²⁺Solution (containing 0.01 mol. L)^-1NaNO of (2)₃As background electrolyte) is added into a series of 50mL conical flasks, the mixture is vibrated and adsorbed for 240min at the temperature of 25 ℃, then the mixture passes through a 0.45um filter membrane, and Cd in the filtrate is measured by a flame atomic absorption spectrophotometer²⁺Concentration, collecting the loaded Cd²⁺CMBC (labeled as CMBC + Cd). The sequential extraction experimental procedure was as follows: in the first step, 0.1000g of MCBC + Cd and 10mL of deionized water were added to a 50mL Erlenmeyer flask and shaken at 25 deg.C (150 r.min)^-1) Filtering for 24h, and collecting filtrate; in the second step, 8 mL0.5mol.L is added to the residue of the previous step^-1MgCl₂The solution (adjusted to pH 7 with NaOH/HCl) was shaken at room temperature for 20min, filtered and the filtrate collected; thirdly, add 8mL of 1 mol. L to the residue of the previous step^-1NaOAc (pH adjusted to 5 with HOAc) and shaken at room temperature for 5h, filtered and the filtrate collected; the fourth step, at the topTo the residue of the first step was added 9mL of 36% HCl solution and 3mL of 70% HNO₃Standing the solution at room temperature for 16h, digesting at 95 deg.C for 2h, filtering, collecting filtrate, and measuring Cd in all collected filtrates with flame atomic absorption spectrophotometer²⁺The concentration of (3) is measured in three groups in parallel in the same experiment;

the data processing S5: equilibrium adsorption quantity q of Cd2+ by adsorbent_eCalculating according to the formula (1):

q_e＝V(c₀-c_e)/m (1)

Cd²⁺the removal rate η of (a) is calculated according to the formula (2):

η＝100％×(c₀-c_e)/c₀ (2)

the adsorption kinetic process is subjected to fitting analysis by adopting a quasi-first-order kinetic equation (3), a quasi-second-order kinetic equation (4), an Elovich equation (5), an intra-particle Diffusion equation (6) and a D-C (Diffusion-chemistry) equation (7), wherein the equations are respectively shown as follows:

q_t＝αlnt+β (5)

q_t＝k_dt^1/2+b (6)

t^1/2/q_t＝t^1/2/q_e+1/k_DC (7)

the isothermal adsorption process was fit analyzed using Langenuir equation (8), Freundlich equation (9) and Temkin equation (10), each as follows:

q_e＝q_mK_Lc_e/(1+q_mK_Lc_e) (8)

q_e＝AlnK_Tc_e (10)

the separation factor RL can be calculated according to equation (11):

R_L＝1/(1+K_Lc₀) (11)

change of thermodynamic parameter Gibbs free energy of adsorption Delta G⁰Entropy change Δ S⁰And enthalpy change Δ H⁰Can be calculated according to equations (12) and (13):

ΔG⁰＝-RTlnK_L (12)

lnK_L＝-ΔH⁰/RT+ΔS⁰/R (13)

in the formulae (1) to (13), q_eAnd q is_tAre respectively Cd²⁺Equilibrium adsorption amount of (2) and adsorption amount at adsorption time t, mg.g^-1；c₀And c_eAre respectively Cd²⁺Initial concentration of (2) and concentration at adsorption equilibrium, mg.L^-1(ii) a V is the volume of the solution, L; m is the mass of the adsorbent, g; k is a radical of₁(min^-1)、k₂(g·mg^-1·min^-1)、k_d(g·mg^-1·min^-1/2)、k_DC(g·mg^-1·min^-1)、α(mg·g^-1·min^-1) And beta (g. mg)^-1) Constants of quasi-first order kinetics, quasi-second order kinetics, Elovich, intra-particle diffusion and D-C equation respectively; k_L(L·mg^-1)、K_F(L1/n·mg1^-1/n·g^-1) And K_T(L·mg^-1) Langmuir, Freundlich and Temkin model parameters; n is the Freundlic constant; a is a Temkin model parameter; q. q.s_mMg.g for maximum saturated adsorption^-1(ii) a R is gas constant, 8.314J (mol. K)^-1(ii) a T is the thermodynamic temperature, K.

Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages:

1. the modification of the magnetic fluid can ensure that the surface of the CBC is more uniformly loaded with Fe3O₄Increase of specific surface area, total pore volume, average pore diameter and surface bandElectric quantity, also can make it to Cd²⁺The adsorption efficiency is improved by 160%.

2. MCBC to Cd²⁺The adsorption process of (1) accords with quasi-second-order dynamics, D-C, Freundlich and a Temkin adsorption model, and the adsorption process is a spontaneous entropy-increasing endothermic process; the saturated adsorption capacity based on the Langnuir equation is 74.6-96.2mg g^-1。

3. MCBC adsorbing Cd²⁺The main mechanisms of (a) are ion exchange, precipitation and oxygen-containing functional group complexation; cd [ Cd ]²⁺The existing forms on MCBC include: exchangeable state (48.4%), acid extractable state (29.5%), stable state (21.8%) and aqueous state (0.3%). Therefore, MCBC is most suitable for Cd-containing applications²⁺Treating the wastewater; application to Cd²⁺When the polluted soil is repaired, the polluted soil needs to be separated from the soil in time so as to avoid Cd²⁺And released again when the soil environment changes.

Detailed Description

The invention provides a specific technical implementation scheme of a method for preparing magnetic meat and bone biochar by modifying magnetic fluid, which comprises the following steps:

the method for preparing the magnetic meat and bone biochar by modifying the magnetic fluid comprises the following steps: preparing magnetic meat and bone biochar S1, characterizing biochar S2, adsorbing experiment S3, sequentially extracting experiment S4 and processing data S5; the preparation of the magnetic meat and bone biochar S1 comprises the preparation of the meat and bone biochar and the preparation of the magnetic meat and bone biochar; the preparation method of the meat and bone biochar comprises the following steps: the abnormal dead carps are collected from a certain fishing farm in Xinzhou city, and the carps are cut into blocks, washed and naturally dried in the air; pulverizing, sieving (0.83mm) to obtain carp meat and bone powder, placing the carp meat and bone powder into corundum crucible, compacting, and pyrolyzing in tubular furnace at 600 deg.C under oxygen deficiency for 7 hr (N₂Atmosphere, heating rate 15 deg.C/min^-1) Naturally cooling to room temperature, taking out, pulverizing, sieving with 0.25mm sieve, washing with cyclohexane solution and ethanol to remove the residual biological oil on the surface of the charcoal, and oven drying at 80 deg.C to obtain meat and bone charcoal labeled as CBC; the preparation method of the magnetic meat and bone biochar comprises the following steps: magnetic fluid: FeCl is added₃·6HO₂(1.35g) and 40mL of glycol are mixed and dissolved, 1g of polyethylene glycol (PEG-4000) and 3.6g of NaAc are added for magnetic stirring for 30min and then are placed in a reaction kettle for reaction at 200 ℃ for 12h,cooling to room temperature, taking out, filtering, washing with anhydrous ethanol for 2-3 times, and drying the filter cake at 60 deg.C for 6 hr to obtain magnetic fluid; magnetic meat and bone biochar: placing 1g of magnetofluid and 4g of meat and bone biochar in a 100mL triangular flask, adding 50mL of deionized water, and oscillating at room temperature for 8h (150 r.min)^-1) Then, carrying out suction filtration, washing the filtrate by using deionized water until the filtrate is colorless and transparent, and drying the filter cake for 6 hours at the temperature of 60 ℃ to obtain magnetic meat and bone biochar which is marked as MCBC;

characterization of biochar S2: c, H, N, O, S content was measured using an elemental analyzer (Elementar, Germany); observing the surface topography of the sample by adopting a scanning electron microscope (JEOL JSM-7800F, Japan); the specific surface area and pore size distribution of the sample were measured using a physical adsorption apparatus (Micromeritics ASAP2020C, USA); analyzing the crystal form of the sample by adopting an X-ray diffractometer (Haoyuan DX-2700BH, China); the surface functional groups were characterized using a Fourier transform infrared spectrometer (Bruker TENSOR27, Germany); measuring the surface charge condition of a sample (Hobriba sz-100, Japan) by adopting a Zeta potential analyzer; an X-ray photoelectron spectrometer (Thermo Fisher Scientific ESCALAB 250Xi, USA) is adopted to characterize the surface chemical characteristics of the sample; a hysteresis loop of the sample is characterized by adopting a vibrating sample magnetometer (LakeShore 7404, USA);

the flow of adsorption experiment S3 is as follows: 20mL of Cd²⁺Solution (containing 0.01 mol. L)^-1NaNO of (2)₃As background electrolyte) and 0.0200g of adsorbent were added to a series of 50mL Erlenmeyer flasks and shaken at a constant temperature for adsorption (150 r. min)^-1) Adsorbing for a certain time, filtering with 0.45um filter membrane, and measuring Cd in the filtrate with flame atomic absorption spectrophotometer (AA-6300F, Shimadzu corporation)²⁺And (4) concentration. In kinetic experiments, Cd²⁺Initial concentrations were 50 and 100 mg.L, respectively^-1The adsorption time and the adsorption temperature are respectively 5-240min and 25 ℃; in isothermal adsorption experiments, Cd²⁺The initial concentration is 30-250 mg.L^-1The adsorption time was 240min, and the adsorption temperatures were 5, 25 and 45 ℃ respectively. Each set of experiments is performed in three parallels under the same condition;

the flow of the sequential extraction experiment S4 is as follows: 0.0200g of MCBC and 20mL of 100mg & L^-1Cd (2)²⁺Solution (containing 0.01 mol. L)^-1NaNO of (2)₃As background electrolyte) is added into a series of 50mL conical flasks, the mixture is vibrated and adsorbed for 240min at the temperature of 25 ℃, then the mixture passes through a 0.45um filter membrane, and Cd in the filtrate is measured by a flame atomic absorption spectrophotometer²⁺Concentration, collecting the loaded Cd²⁺CMBC (labeled as CMBC + Cd). The sequential extraction experimental procedure was as follows: in the first step, 0.1000g of MCBC + Cd and 10mL of deionized water were added to a 50mL Erlenmeyer flask and shaken at 25 deg.C (150 r.min)^-1) Filtering for 24h, and collecting filtrate; in the second step, 8 mL0.5mol.L is added to the residue of the previous step^-1MgCl₂The solution (adjusted to pH 7 with NaOH/HCl) was shaken at room temperature for 20min, filtered and the filtrate collected; thirdly, add 8mL of 1 mol. L to the residue of the previous step^-1NaOAc (pH adjusted to 5 with HOAc) and shaken at room temperature for 5h, filtered and the filtrate collected; the fourth step, 9mL of 36% HCl solution and 3mL of 70% HNO were added to the residue of the previous step₃Standing the solution at room temperature for 16h, digesting at 95 deg.C for 2h, filtering, collecting filtrate, and measuring Cd in all collected filtrates with flame atomic absorption spectrophotometer²⁺The concentration of (3) is measured in three groups in parallel in the same experiment;

data processing S5: equilibrium adsorption quantity q of Cd2+ by adsorbent_eCalculating according to the formula (1):

q_e＝V(c₀-c_e)/m (1)

Cd²⁺the removal rate η of (a) is calculated according to the formula (2):

η＝100％×(c₀-c_e)/c₀ (2)

the adsorption kinetic process is subjected to fitting analysis by adopting a quasi-first-order kinetic equation (3), a quasi-second-order kinetic equation (4), an Elovich equation (5), an intra-particle Diffusion equation (6) and a D-C (Diffusion-chemistry) equation (7), wherein the equations are respectively shown as follows:

q_t＝αlnt+β (5)

q_t＝k_dt^1/2+b (6)

t^1/2/q_t＝t^1/2/q_e+1/k_DC (7)

the isothermal adsorption process was fit analyzed using Langenuir equation (8), Freundlich equation (9) and Temkin equation (10), each as follows:

q_e＝q_mK_Lc_e/(1+q_mK_Lc_e) (8)

q_e＝AlnK_Tc_e (10)

the separation factor RL can be calculated according to equation (11):

R_L＝1/(1+K_Lc₀) (11)

change of thermodynamic parameter Gibbs free energy of adsorption Delta G⁰Entropy change Δ S⁰And enthalpy change Δ H⁰Can be calculated according to equations (12) and (13):

ΔG⁰＝-RTlnK_L (12)

lnK_L＝-ΔH⁰/RT+ΔS⁰/R (13)

in the formulae (1) to (13), q_eAnd q is_tAre respectively Cd²⁺Equilibrium adsorption amount of (2) and adsorption amount at adsorption time t, mg.g^-1；c₀And c_eAre respectively Cd²⁺Initial concentration of (2) and concentration at adsorption equilibrium, mg.L^-1(ii) a V is the volume of the solution, L; m is the mass of the adsorbent, g; k is a radical of₁(min^-1)、k₂(g·mg^-1·min^-1)、 k_d(g·mg^-1·min^-1/2)、k_DC(g·mg^-1·min^-1)、α(mg·g^-1·min^-1) And beta (g. mg)^-1) Constants of quasi-first order kinetics, quasi-second order kinetics, Elovich, intra-particle diffusion and D-C equation respectively; k_L(L·mg^-1)、K_F(L1/n·mg1^-1/n·g^-1) And K_T(L·mg^-1) Langmuir, Freundlich and Temkin model parameters; n is the Freundlic constant; a is a Temkin model parameter; q. q.s_mMg.g for maximum saturated adsorption^-1(ii) a R is gas constant, 8.314J (mol. K)^-1(ii) a T is the thermodynamic temperature, K.

In summary, the following steps: according to the method for preparing the magnetic meat and bone biochar by modifying the magnetic fluid, the magnetic fluid modification can ensure that the surface of the CBC is uniformly loaded with Fe3O₄Increase the specific surface area, total pore volume, average pore diameter and surface charge, and can also be used for Cd²⁺The adsorption efficiency is improved by 160%; MCBC to Cd²⁺The adsorption process of (1) accords with quasi-second-order dynamics, D-C, Freundlich and a Temkin adsorption model, and the adsorption process is a spontaneous entropy-increasing endothermic process; the saturated adsorption capacity based on the Langnuir equation is 74.6-96.2mg g^-1(ii) a MCBC adsorbing Cd²⁺The main mechanisms of (a) are ion exchange, precipitation and oxygen-containing functional group complexation; cd [ Cd ]²⁺The existing forms on MCBC include: exchangeable state (48.4%), acid extractable state (29.5%), stable state (21.8%) and aqueous state (0.3%). Therefore, MCBC is most suitable for Cd-containing applications²⁺Treating the wastewater; application to Cd²⁺When the polluted soil is repaired, the polluted soil needs to be separated from the soil in time so as to avoid Cd²⁺And released again when the soil environment changes.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (1)

1. The method for preparing the magnetic meat and bone biochar by modifying the magnetic fluid comprises the following steps: preparing magnetic meat and bone biochar S1, characterizing biochar S2, adsorbing experiment S3, sequentially extracting experiment S4 and processing data S5; the method is characterized in that:

the preparation S1 of the magnetic meat and bone biochar comprises the preparation of the meat and bone biochar and the preparation of the magnetic meat and bone biochar; the preparation method of the meat and bone biochar comprises the following steps: the abnormal dead carps are collected from a certain fishing farm in Xinzhou city, and the carps are cut into blocks, washed and naturally dried in the air; pulverizing, sieving (0.83mm) to obtain carp meat and bone powder, placing the carp meat and bone powder into corundum crucible, compacting, and pyrolyzing in tubular furnace at 600 deg.C under oxygen deficiency for 7 hr (N₂Atmosphere, heating rate 15 deg.C/min^-1) Naturally cooling to room temperature, taking out, pulverizing, sieving with 0.25mm sieve, washing with cyclohexane solution and ethanol to remove the residual biological oil on the surface of the charcoal, and oven drying at 80 deg.C to obtain meat and bone charcoal labeled as CBC; the preparation method of the magnetic meat and bone biochar comprises the following steps: magnetic fluid: FeCl is added₃·6HO₂(1.35g) and 40mL of ethylene glycol are mixed and dissolved, 1g of polyethylene glycol (PEG-4000) and 3.6g of NaAc are added to carry out magnetic stirring for 30min, then the mixture is placed in a reaction kettle to react for 12h at the temperature of 200 ℃, the mixture is taken out to be filtered after being cooled to the room temperature, the filter cake is washed for 2 to 3 times by absolute ethyl alcohol, and the filter cake is placed at the temperature of 60 ℃ and dried for 6h to prepare the magnetofluid; magnetic meat and bone biochar: placing 1g of magnetofluid and 4g of meat and bone biochar in a 100mL triangular flask, adding 50mL of deionized water, and oscillating at room temperature for 8h (150 r.min)^-1) Then, carrying out suction filtration, washing the filtrate by using deionized water until the filtrate is colorless and transparent, and drying the filter cake for 6 hours at the temperature of 60 ℃ to obtain magnetic meat and bone biochar which is marked as MCBC;

characterization of the biochar S2: c, H, N, O, S content was measured using an elemental analyzer (Elementar, Germany); observing the surface topography of the sample by adopting a scanning electron microscope (JEOL JSM-7800F, Japan); the specific surface area and pore size distribution of the sample were measured using a physical adsorption apparatus (Micromeritics ASAP2020C, USA); analyzing the crystal form of the sample by adopting an X-ray diffractometer (Haoyuan DX-2700BH, China); the surface functional groups were characterized using a Fourier transform infrared spectrometer (Bruker TENSOR27, Germany); measuring the surface charge condition of a sample (Hobriba sz-100, Japan) by adopting a Zeta potential analyzer; an X-ray photoelectron spectrometer (Thermo Fisher Scientific ESCALAB 250Xi, USA) is adopted to characterize the surface chemical characteristics of the sample; a hysteresis loop of the sample is characterized by adopting a vibrating sample magnetometer (LakeShore 7404, USA);

the flow of the adsorption experiment S3 is as follows: 20mL of Cd²⁺Solution (containing 0.01 mol. L)^-1NaNO of (2)₃As background electrolyte) and 0.0200g of adsorbent were added to a series of 50mL Erlenmeyer flasks and shaken at a constant temperature for adsorption (150 r. min)^-1) Adsorbing for a certain time, filtering with 0.45um filter membrane, and measuring Cd in the filtrate with flame atomic absorption spectrophotometer (AA-6300F, Shimadzu corporation)²⁺And (4) concentration. In kinetic experiments, Cd²⁺Initial concentrations were 50 and 100 mg.L, respectively^-1The adsorption time and the adsorption temperature are respectively 5-240min and 25 ℃; in isothermal adsorption experiments, Cd²⁺The initial concentration is 30-250 mg.L^-1The adsorption time was 240min, and the adsorption temperatures were 5, 25 and 45 ℃ respectively. Each set of experiments is performed in three parallels under the same condition;

the flow of the sequential extraction experiment S4 is as follows: 0.0200g of MCBC and 20mL of 100mg & L^-1Cd (2)²⁺Solution (containing 0.01 mol. L)^-1NaNO of (2)₃As background electrolyte) is added into a series of 50mL conical flasks, the mixture is vibrated and adsorbed for 240min at the temperature of 25 ℃, then the mixture passes through a 0.45um filter membrane, and Cd in the filtrate is measured by a flame atomic absorption spectrophotometer²⁺Concentration, collecting the loaded Cd²⁺CMBC (labeled as CMBC + Cd). The sequential extraction experimental procedure was as follows: in the first step, 0.1000g of MCBC + Cd and 10mL of deionized water were added to a 50mL Erlenmeyer flask and shaken at 25 deg.C (150 r.min)^-1) Filtering for 24h, and collecting filtrate; in the second step, 8 mL0.5mol.L is added to the residue of the previous step^-1MgCl₂The solution (adjusted to pH 7 with NaOH/HCl) was shaken at room temperature for 20min, filtered and the filtrate collected; thirdly, add 8mL of 1 mol. L to the residue of the previous step^-1NaOAc (pH adjusted to 5 with HOAc) and shaken at room temperature for 5h, filtered and the filtrate collected; the fourth step, 9mL of 36% HCl solution and 3mL of 70% HNO were added to the residue of the previous step₃Standing the solution at room temperature for 16h, digesting at 95 deg.C for 2h, filtering, collecting filtrate, and measuring Cd in all collected filtrates with flame atomic absorption spectrophotometer²⁺The concentration of (a) in (b),three groups of parallel experiments are carried out;

the data processing S5: equilibrium adsorption quantity q of Cd2+ by adsorbent_eCalculating according to the formula (1):

q_e＝V(c₀-c_e)/m (1)

Cd²⁺the removal rate η of (a) is calculated according to the formula (2):

η＝100％×(c₀-c_e)/c₀ (2)

the adsorption kinetic process is subjected to fitting analysis by adopting a quasi-first-order kinetic equation (3), a quasi-second-order kinetic equation (4), an Elovich equation (5), an intra-particle Diffusion equation (6) and a D-C (Diffusion-chemistry) equation (7), wherein the equations are respectively shown as follows:

q_t＝αlnt+β (5)

q_t＝k_dt^1/2+b (6)

t^1/2/q_t＝t^1/2/q_e+1/k_DC (7)

the isothermal adsorption process was fit analyzed using Langenuir equation (8), Freundlich equation (9) and Temkin equation (10), each as follows:

q_e＝q_mK_Lc_e/(1+q_mK_Lc_e) (8)

q_e＝AlnK_Tc_e (10)

the separation factor RL can be calculated according to equation (11):

R_L＝1/(1+K_Lc₀) (11)

change of thermodynamic parameter Gibbs free energy of adsorption Delta G⁰Entropy change Δ S⁰And enthalpy change Δ H⁰Can be calculated according to equations (12) and (13):

ΔG⁰＝-RTlnK_L (12)

lnK_L＝-ΔH⁰/RT+ΔS⁰/R (13)

in the formulae (1) to (13), q_eAnd q is_tAre respectively Cd²⁺Equilibrium adsorption amount of (2) and adsorption amount at adsorption time t, mg.g^-1；c₀And c_eAre respectively Cd²⁺Initial concentration of (2) and concentration at adsorption equilibrium, mg.L^-1(ii) a V is the volume of the solution, L; m is the mass of the adsorbent, g; k is a radical of₁(min^-1)、k₂(g·mg^-1·min^-1)、k_d(g·mg^-1·min^-1/2)、k_DC(g·mg^-1·min^-1)、α(mg·g^-1·min^-1) And beta (g. mg)^-1) Constants of quasi-first order kinetics, quasi-second order kinetics, Elovich, intra-particle diffusion and D-C equation respectively; k_L(L·mg^-1)、K_F(L1/n·mg1^-1/n·g^-1) And K_T(L·mg^-1) Langmuir, Freundlich and Temkin model parameters; n is the Freundlic constant; a is a Temkin model parameter; q. q.s_mMg.g for maximum saturated adsorption^-1(ii) a R is gas constant, 8.314J (mol. K)^-1(ii) a T is the thermodynamic temperature, K.