Composite modified pig manure sludge biochar and preparation method thereof

Abstract

The invention discloses composite modified pig manure and sludge biochar, relates to the technical field of modified biochar, and mainly comprises pig manure and sludge. The invention also provides a preparation method of the compound modified pig manure and sludge biochar, pig manure and sludge are mixed and pyrolyzed to prepare the pig manure and sludge biochar, and the pig manure and sludge biochar is modified by sulfuric acid and a magnesium chloride solution to prepare the compound modified pig manure and sludge biochar. According to the composite modified pig manure and sludge biochar provided by the invention, pig manure and sludge are subjected to carbonization modification through a composite modification technology, so that heavy metal cadmium pollution is efficiently removed, and meanwhile, a new way is provided for resource utilization of organic wastes.

Description

Technical Field

[0001] The present invention relates to the technical field of modified biochar, and particularly to a composite modified pig manure sludge biochar and a preparation method thereof. Background Art

[0002] Heavy metal cadmium (Cd) pollution has become an increasingly serious environmental problem worldwide. Due to its non-degradability, cadmium can accumulate in human adipose tissue, muscles, and bones for a long time, thereby significantly increasing health risks such as anorexia, nausea, mental and nervous system diseases, heart diseases, skin cancer, and lung cancer. Therefore, developing an efficient, economical, and sustainable technical means to remove cadmium pollution in water environment has become an urgent need in the field of environmental protection.

[0003] Biochar adsorption technology has become one of the mainstream methods for treating heavy metal pollution in water due to its advantages such as simple operation, low cost, and short treatment time. However, unmodified biochar has significant deficiencies in morphology, porosity, and functional group distribution, resulting in weak catalytic ability and limited adsorption capacity, making it difficult to meet the high-efficiency treatment requirements in practical applications.

[0004] In recent years, composite modification technology has been widely studied as an innovative method. By combining two or more modifiers and utilizing their synergistic effects, this technology breaks through the limitations of single modification methods. Composite modification not only significantly improves the adsorption performance of adsorbents but also expands their application potential in fields such as environmental remediation and resource recovery, providing an important direction for the research and development of new adsorption materials.

[0005] At the same time, a large amount of organic waste in rural areas (such as livestock and poultry manure, sewage sludge, and green waste) has become an important source of non-point source pollution. In addition, the heavy metals contained in municipal sludge cannot be degraded during treatment and disposal, and only solid-liquid migration and chemical form transformation occur, further exacerbating the environmental pollution risk.

[0006] The above problems need to be solved urgently. Therefore, the present invention provides a composite modified pig manure sludge biochar and a preparation method thereof. Summary of the Invention

[0007] The technical problem to be solved by the present invention is: to provide a composite modified pig manure sludge biochar, which improves the adsorption performance of pig manure sludge biochar through composite modification technology, thereby achieving efficient removal of heavy metal cadmium pollution and providing a new way for the resource utilization of organic waste at the same time.

[0008] The technical solution adopted by the present invention to solve its technical problems is as follows: On the one hand, the present invention provides a composite modified pig manure sludge biochar, which is mainly prepared by pyrolyzing a mixture of pig manure and sludge to obtain pig manure sludge biochar (BC), and the pig manure sludge biochar (BC) is prepared by modification with sulfuric acid and magnesium chloride solution. The mass ratio of pig manure in the powder of pig manure and sludge of the composite modified pig manure sludge biochar (SMgBM-BC) is 10% - 90%.

[0009] Preferably, the adsorption capacity of the composite modified pig manure sludge biochar is 13.5339 - 20.0696 mg·g -1 .

[0012] On the other hand, the present invention provides a preparation method of a composite modified pig manure sludge biochar, comprising the following steps:

[0013] S1: Rinse the collected pig manure and sludge with distilled water to remove the dust particles adhering to the surface, then place them in an oven to dry until a constant weight is obtained, and then crush and sieve them to obtain pig manure and sludge powder.

[0014] S2: Take the mixed powder of pig manure and sludge and mix and stir it with sulfuric acid (H2SO4);

[0015] S3: After the stirring is completed, wash the carbonized material with distilled water to remove the excessive sulfuric acid until the pH value of the washing liquid is neutral to obtain a precipitate;

[0016] S4: Put the precipitate into a drying oven to dry, pour the dried precipitate into an agate jar, and ball-mill it to obtain biochar;

[0017] S5: Immerse the biochar in magnesium chloride solution and stir, separate the solid from the mixture, and dry it overnight in an oven;

[0018] S6: Pyrolyze the dried solid in a nitrogen atmosphere in a tube furnace;

[0019] S7: After the carbonization is completed, cool it to room temperature, wash it with deionized water until it is neutral, filter and dry it to a constant weight, grind the dried product, and sieve it to obtain the composite modified pig manure sludge biochar (SMgBM-BC).

[0020] Preferably, in step S2, the mass ratio of pig manure in the mixed powder of pig manure and sludge is 10% - 90%.

[0021] Preferably, in step S4, the ball-milling speed is 200 rmp - 600 rmp, and the ball-milling time is 1 h - 13 h.

[0022] Preferably, in step S4, the agate jar is filled with agate balls, and the mass ratio of the agate balls to the pig manure sludge mixed powder is 50:1. The diameters of the agate balls are 5, 8, and 15 mm, and the mass ratio of the 5-mm agate balls: 8-mm agate balls: 15-mm agate balls is 3:5:2.

[0023] Preferably, in step S5, 2 g of biochar is immersed in 25 mL of 1 mol / L magnesium chloride solution.

[0024] Preferably, the prepared composite modified pig manure sludge biochar (SMgBM-BC) is taken for adsorption experiments respectively. The experimental data is optimized by the response surface method to obtain the optimized conditions for the adsorption reaction of the composite modified pig manure sludge biochar (SMgBM-BC). The proportion of pig manure is 62.2%, the ball milling speed is 543.887 rpm, and the ball milling time is 13 h. Under these conditions, the adsorption capacity of the composite modified pig manure sludge biochar (SMgBM-BC) is 23.376 mg·g -1 。

[0025] The beneficial effects of the invention are as follows: The composite modified pig manure sludge biochar is mainly prepared by pyrolyzing the mixture of pig manure and sludge to obtain pig manure sludge biochar (BC), and the pig manure sludge biochar (BC) is prepared by modification with sulfuric acid and magnesium chloride solution. The invention carbonizes and modifies pig manure and sludge through the composite modification technology, thereby realizing the efficient removal of heavy metal cadmium pollution and providing a new way for the resource utilization of organic waste. Brief Description of the Drawings

[0026] The following is a preferred description of the present invention in conjunction with the drawings and embodiments.

[0027] In the figure: Figure 1 It is a diagram showing the influence of the mass ratio of pig manure and ball milling time on the adsorption capacity of the adsorbent;

[0028] Figure 2 It is a diagram showing the influence of ball milling speed and ball milling time on the adsorption capacity of the adsorbent;

[0029] Figure 3 It is a diagram showing the influence of ball milling ratio and ball milling time on the adsorption capacity of the adsorbent;

[0030] Figure 4 It is a TGA curve diagram of the thermogravimetric analysis experiment of biomass, pig manure sludge biochar (BC), and composite modified pig manure sludge biochar (SMgBM-BC);

[0031] Figure 5 It is a DTG curve diagram of biomass, pig manure sludge biochar (BC), and composite modified pig manure sludge biochar (SMgBM-BC);

[0032] Figure 6Adsorption efficiency and adsorption capacity of pig manure sludge biochar (BC) and composite modified pig manure sludge biochar (SMgBM-BC) for Cd 2+ Line graph of adsorption efficiency

[0033] Figure 7 Adsorption efficiency histogram of composite modified pig manure sludge biochar (SMgBM-BC) for Cd with the number of cycles 2+ Specific implementation manners

[0034] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] In the present invention, the pig manure and sludge are respectively collected from Wunan Second Sewage Treatment Plant in Changzhou City, Jiangsu Province and Lijia Breeding Pig Farm of Changzhou Xinghua Animal Husbandry.

[0036] The materials and instruments used in the following embodiments are all commercially available.

[0037] The present invention provides a composite modified pig manure sludge biochar (SMgBM-BC), which is mainly prepared by pyrolyzing a mixture of pig manure and sludge to obtain pig manure sludge biochar (BC), and the pig manure sludge biochar (BC) is modified by sulfuric acid and magnesium chloride solution. The mass ratio of pig manure in the powder of pig manure and sludge of the composite modified pig manure sludge biochar (SMgBM-BC) is 10% - 90%.

[0038] The present invention provides a preparation method for preparing composite modified pig manure sludge biochar (SMgBM-BC), comprising the following steps:

[0039] S1: Rinse the collected pig manure and sludge with distilled water to remove the dust particles adhering to the surface, then place them in an oven to dry until a constant weight is obtained, and then crush and sieve to obtain pig manure and sludge powder.

[0040] S2: Take the mixed powder of pig manure and sludge and mix and stir it with sulfuric acid (H2SO4);

[0041] S3: After stirring, wash the carbonized material with distilled water to remove the excessive sulfuric acid until the pH value of the washing solution is neutral to obtain a precipitate;

[0042] S4: Put the precipitate into an oven to dry, pour the dried precipitate into an agate pot, and ball mill to obtain biochar;

[0043] S5: Immerse the biochar in magnesium chloride solution and stir, separate the solid from the mixture, and dry it overnight in an oven;​

[0044] S6: Pyrolyze the dried solid in a nitrogen atmosphere in a tube furnace;

[0045] S7: After carbonization, cool to room temperature, wash with deionized water until neutral, filter and dry to constant weight, grind the dried product, sieve it, and obtain the composite modified pig manure sludge biochar (SMgBM-BC).

[0046] Preferably, in step S2, the mass ratio of pig manure in the pig manure and sludge mixed powder is 10% - 90%.

[0047] Preferably, in step S4, the ball milling speed is 200 rmp - 600 rmp, and the ball milling time is 1 h - 13 h.

[0048] Preferably, in step S4, the agate jar is filled with agate balls, the mass ratio of agate balls to the pig manure sludge mixed powder is 50:1, the diameters of the agate balls are 5, 8, and 15 mm, and the mass ratio of 5 mm agate balls: 8 mm agate balls: 15 mm agate balls is 3:5:2.

[0049] Example 1:

[0050] S1: Rinse the collected pig manure and sludge twice with distilled water to remove the dust particles adhering to the surface, then place them in an 85°C oven until a constant weight is obtained, and then crush and sieve through a 20-mesh sieve to obtain the pig manure and sludge powder.

[0051] S2: Take the pig manure and sludge mixed powder with a pig manure mass ratio of 10%, and add 2 ml (60% wt) sulfuric acid (H2SO4) per 1 g of the pig manure and sludge mixed powder and stir for 12 h;

[0052] S3: After stirring, wash the carbonized material with distilled water to remove the excess sulfuric acid until the pH value of the washing liquid is neutral to obtain a precipitate;

[0053] S4: Put the precipitate into a drying oven and dry for 12 h, pour the dried precipitate into an agate jar, and ball mill at a ball milling speed of 400 rmp for 7 h to obtain biochar;

[0054] S5: Immerse 2 g of biochar in 25 mL of 1 mol / L magnesium chloride solution and stir for 24 hours, separate the solid from the mixture, and dry it overnight in an oven;

[0055] S6: Pyrolyze the dried solid in a tube furnace (OTF-1200X, Kejing, China) in a nitrogen atmosphere at a gas flow rate of 60 mL / min, heat it to 700°C at a rate of 10°C / min, and pyrolyze and carbonize at 700°C for 2 h;

[0056] S7: After carbonization, it was cooled to room temperature, washed with deionized water until neutral, filtered and dried to constant weight at 85 °C, and the dried product was ground to pass through a 100-mesh sieve to obtain composite modified pig manure sludge biochar (SMgBM-BC).

[0057] Experimental Example 2:

[0058] S1: The collected pig manure and sludge were rinsed twice with distilled water to remove the dust particles adhering to the surface, then placed in an oven at 85 °C until a constant weight was obtained, and then crushed and passed through a 20-mesh sieve to obtain pig manure and sludge powder.

[0059] S2: Take a mixture of pig manure and sludge powder with 50% by mass of pig manure, and add 2 ml (60% wt) of sulfuric acid (H2SO4) per 1 g of the mixture of pig manure and sludge powder and stir for 12 h;

[0060] S3: After stirring, the carbonized material was washed with distilled water to remove the excess sulfuric acid until the pH value of the washing solution was neutral to obtain a precipitate;

[0061] S4: The precipitate was placed in a drying oven and dried for 12 h. The dried precipitate was poured into an agate pot and ball-milled at a ball-milling speed of 400 rmp for 7 h to obtain biochar;

[0062] S5: Soak 2 g of biochar in 25 mL of 1 mol / L magnesium chloride solution and stir for 24 hours. Separate the solid from the mixture and dry it overnight in an oven;

[0063] S6: The dried solid was pyrolyzed in a tube furnace (OTF-1200X, Kejing, China) at a gas flow rate of 60 mL / min in a nitrogen atmosphere, heated to 700 °C at a rate of 10 °C / min, and pyrolyzed and carbonized at 700 °C for 2 h;

[0064] S7: After carbonization, it was cooled to room temperature, washed with deionized water until neutral, filtered and dried to constant weight at 85 °C, and the dried product was ground to pass through a 100-mesh sieve to obtain composite modified pig manure sludge biochar (SMgBM-BC).

[0065] Experimental Example 3:

[0066] S1: The collected pig manure and sludge were rinsed twice with distilled water to remove the dust particles adhering to the surface, then placed in an oven at 85 °C until a constant weight was obtained, and then crushed and passed through a 20-mesh sieve to obtain pig manure and sludge powder.

[0067] S2: Take a mixture of pig manure and sludge powder with 90% by mass of pig manure, and add 2 ml (60% wt) of sulfuric acid (H2SO4) per 1 g of the mixture of pig manure and sludge powder and stir for 12 h;

[0068] S3: After the stirring is completed, wash the carbonized material with distilled water to remove the excessive sulfuric acid until the pH value of the washing liquid reaches neutrality to obtain a precipitate.

[0069] S4: Place the precipitate in an oven and dry it for 12 h. Pour the dried precipitate into an agate pot and ball-mill it at a ball-mill rotation speed of 400 rmp for 7 h to obtain biochar.

[0070] S5: Immerse 2 g of biochar in 25 mL of 1 mol / L magnesium chloride solution and stir for 24 h. Separate the solid from the mixture and dry it overnight in an oven.

[0071] S6: Pyrolyze the dried solid in a tube furnace (OTF-1200X, Kejing, China) at a gas flow rate of 60 mL / min in a nitrogen atmosphere. Heat it to 700 °C at a rate of 10 °C / min and pyrolyze and carbonize it at 700 °C for 2 h.

[0072] S7: After carbonization, cool it to room temperature, wash it with deionized water until neutrality, filter it and dry it to a constant weight at 85 °C. Grind the dried product to pass through a 100-mesh sieve to obtain composite modified pig manure sludge biochar (SMgBM-BC).

[0073] Example 4:

[0074] S1: Rinse the collected pig manure and sludge twice with distilled water to remove the dust particles adhering to the surface, then place them in an oven at 85 °C until a constant weight is obtained, and then crush them through a 20-mesh sieve to obtain pig manure and sludge powder.

[0075] S2: Take a mixture powder of pig manure and sludge with a pig manure mass ratio of 50%, and add 2 ml (60% wt) of sulfuric acid (H2SO4) to every 1 g of the mixture powder of pig manure and sludge and stir for 12 h.

[0076] S3: After the stirring is completed, wash the carbonized material with distilled water to remove the excessive sulfuric acid until the pH value of the washing liquid reaches neutrality to obtain a precipitate.

[0077] S4: Place the precipitate in an oven and dry it for 12 h. Pour the dried precipitate into an agate pot and ball-mill it at a ball-mill rotation speed of 400 rmp for 13 h to obtain biochar.

[0078] S5: Immerse 2 g of biochar in 25 mL of 1 mol / L magnesium chloride solution and stir for 24 h. Separate the solid from the mixture and dry it overnight in an oven.

[0079] S6: Pyrolyze the dried solid in a tube furnace (OTF-1200X, Kejing, China) at a gas flow rate of 60 mL / min in a nitrogen atmosphere, heat it to 700 °C at a rate of 10 °C / min, and pyrolyze and carbonize it at 700 °C for 2 h;

[0080] S7: After carbonization, cool it to room temperature, wash it with deionized water until neutral, filter it and dry it to a constant weight at 85 °C, grind the dried product, and pass it through a 100-mesh sieve to obtain composite modified pig manure sludge biochar (SMgBM-BC).

[0081] Example 5:

[0082] S1: Rinse the collected pig manure and sludge twice with distilled water to remove the dust particles adhering to the surface, then place them in an oven at 85 °C until a constant weight is obtained, and then crush them and pass them through a 20-mesh sieve to obtain pig manure and sludge powder.

[0083] S2: Take the pig manure and sludge mixed powder with 50% pig manure by mass, and add 2 ml (60% wt) sulfuric acid (H2SO4) to every 1 g of the pig manure and sludge mixed powder and stir for 12 h;

[0084] S3: After stirring, wash the carbonized material with distilled water to remove the excessive sulfuric acid until the pH value of the washing liquid is neutral to obtain a precipitate;

[0085] S4: Put the precipitate into a drying oven and dry it for 12 h, pour the dried precipitate into an agate pot, and ball mill it at a ball mill rotation speed of 400 rmp for 1 h to obtain biochar;

[0086] S5: Immerse 2 g of biochar in 25 mL of 1 mol / L magnesium chloride solution and stir for 24 hours, separate the solid from the mixture, and dry it overnight in an oven;

[0087] S6: Pyrolyze the dried solid in a tube furnace (OTF-1200X, Kejing, China) at a gas flow rate of 60 mL / min in a nitrogen atmosphere, heat it to 700 °C at a rate of 10 °C / min, and pyrolyze and carbonize it at 700 °C for 2 h;

[0088] S7: After carbonization, cool it to room temperature, wash it with deionized water until neutral, filter it and dry it to a constant weight at 85 °C, grind the dried product, and pass it through a 100-mesh sieve to obtain composite modified pig manure sludge biochar (SMgBM-BC).

[0089] Example 6:

[0090] S1: Rinse the collected pig manure and sludge twice with distilled water to remove the dust particles adhering to the surface, then place them in an oven at 85 °C until a constant weight is obtained, and then crush them through a 20-mesh sieve to obtain pig manure and sludge powder.

[0091] S2: Take the mixed powder of pig manure and sludge with 50% pig manure by mass, and add 2 ml (60% wt) of sulfuric acid (H2SO4) to every 1 g of the mixed powder of pig manure and sludge and stir for 12 h;

[0092] S3: After stirring, wash the carbonized material with distilled water to remove the excess sulfuric acid until the pH value of the washing liquid reaches neutrality to obtain a precipitate;

[0093] S4: Put the precipitate into a drying oven and dry for 12 h, pour the dried precipitate into an agate pot, and ball-mill at a ball-mill rotation speed of 200 rmp for 7 h to obtain biochar;

[0094] S5: Immerse 2 g of biochar in 25 mL of 1 mol / L magnesium chloride solution and stir for 24 hours, separate the solid from the mixture, and dry it overnight in an oven;

[0095] S6: Pyrolyze the dried solid in a tube furnace (OTF-1200X, Kejing, China) at a gas flow rate of 60 mL / min in a nitrogen atmosphere, heat it to 700 °C at a rate of 10 °C / min, and pyrolyze and carbonize it at 700 °C for 2 h;

[0096] S7: After carbonization, cool to room temperature, wash with deionized water until neutral, filter and dry at 85 °C to constant weight, grind the dried product to pass through a 100-mesh sieve to obtain composite modified pig manure sludge biochar (SMgBM-BC).

[0097] Example 7:

[0098] S1: Rinse the collected pig manure and sludge twice with distilled water to remove the dust particles adhering to the surface, then place them in an oven at 85 °C until a constant weight is obtained, and then crush them through a 20-mesh sieve to obtain pig manure and sludge powder.

[0099] S2: Take the mixed powder of pig manure and sludge with 50% pig manure by mass, and add 2 ml (60% wt) of sulfuric acid (H2SO4) to every 1 g of the mixed powder of pig manure and sludge and stir for 12 h;

[0100] S3: After stirring, wash the carbonized material with distilled water to remove the excess sulfuric acid until the pH value of the washing liquid reaches neutrality to obtain a precipitate;

[0101] S4: Place the precipitate in a drying oven and dry it for 12 h. Pour the dried precipitate into an agate pot and ball mill it at a ball milling speed of 600 rmp for 7 h to obtain biochar.

[0102] S5: Immerse 2 g of biochar in 25 mL of 1 mol / L magnesium chloride solution and stir for 24 h. Separate the solid from the mixture and dry it overnight in an oven.

[0103] S6: Pyrolyze the dried solid in a tube furnace (OTF-1200X, Kejing, China) at a gas flow rate of 60 mL / min in a nitrogen atmosphere. Heat it to 700 °C at a rate of 10 °C / min and pyrolyze and carbonize it at 700 °C for 2 h.

[0104] S7: After carbonization, cool it to room temperature, wash it with deionized water until neutral, filter it and dry it to a constant weight at 85 °C. Grind the dried product to pass through a 100-mesh sieve to obtain composite modified pig manure sludge biochar (SMgBM-BC).

[0105] Comparative Example 1: Preparation of pig manure sludge biochar (BC)

[0106] S1: Rinse the collected pig manure and sludge twice with distilled water to remove the dust particles adhering to the surface, then place them in an 85 °C oven until a constant weight is obtained, and then crush them through a 20-mesh sieve to obtain pig manure and sludge powder.

[0107] S2: Put the mixed powder of pig manure and sludge with a pig manure mass ratio of 50% into a tube furnace (OTF-1200X, Kejing, China) and pyrolyze it in a nitrogen atmosphere at a gas flow rate of 60 mL / min. Heat it to 700 °C at a rate of 10 °C / min and pyrolyze and carbonize it at 700 °C for 2 h.

[0108] S3: After carbonization, cool it to room temperature, wash it with deionized water until neutral, filter it and dry it to a constant weight at 85 °C. Grind the dried product to pass through a 100-mesh sieve to obtain pig manure sludge biochar (BC).

[0109] Comparative Example 2: Preparation of biomass

[0110] Rinse the collected pig manure and sludge twice with distilled water to remove the dust particles adhering to the surface, then place them in an 85 °C oven until a constant weight is obtained, and then crush them through a 20-mesh sieve to obtain pig manure and sludge powder. The mixed powder of pig manure and sludge with a pig manure mass ratio of 50% is the biomass.

[0111] Experimental Example 1:

[0112] Investigate the adsorption amounts of cadmium in Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Comparative Example 1, and Comparative Example 2.

[0113] Take 50 mg (0.2 g / L) of the composite modified swine manure sludge biochar prepared in Examples 1 - 7, the swine manure sludge biochar prepared in Comparative Example 1, and the biomass prepared in Comparative Example 2, and add them to 50 mL centrifuge tubes containing 25 mL of Cd 2+ solution (100 mg / L, pH = 5). After constant temperature oscillation for 24 h, the suspension is centrifuged at 10000 rpm for 10 min. The supernatant is collected and filtered through a 0.45 μm filter membrane. The supernatant is collected and filtered through a 0.45 μm filter membrane, and the Cd 2+ concentration in the filtrate is determined by AAS (AA - 300, PerkinElmer Ltd, USA).

[0114]

[0115] Where: Qe is the adsorption amount (mg·g -1 ); C0 is the initial concentration (mg / L); C1 is the solution concentration at adsorption equilibrium (mg / L); V is the volume of the solution (L); M is the sample mass (g).

[0116] Table 1: Adsorption amounts of cadmium by biomass, swine manure sludge biochar (BC), and composite modified swine manure sludge biochar (SMgBM - BC)

[0117]

[0118]

[0119] As can be seen from Table 1, the composite modified swine manure sludge biochar (SMgBM - BC) prepared in Example 4 with a ball - milling speed of 400 rmp for 13 h and a swine manure proportion of 50% has the highest cadmium adsorption amount of 20.0696 mg·g -1 , which is 10.9571 mg·g -1 higher than that of the biomass without carbonization ball - milling and magnesium modification treatment, and 8.5354 mg·g -1 higher than that of the swine manure sludge biochar (BC) without magnesium modification.

[0120] The experimental data are optimized by the response surface method to obtain the optimized conditions for the adsorption reaction of the composite modified swine manure sludge biochar (SMgBM - BC).

[0121] Substitute the experimental data in Table 1 into the multiple quadratic regression equation to fit the functional relationship between the factors and the response value, then use graphical techniques to plot the response surface, and further find the optimal condition combination or the best region for preparing the composite modified pig manure sludge biochar (SMgBM-BC).

[0122] The second-order response surface model is as follows:

[0123]

[0124] In the formula: α0, α i , α ii and α ij are all undetermined coefficients of the polynomial terms; n is the number of parameters; x i and x j are the respective formulation parameters; ε is the fitting error; f(x) is the corresponding target value.

[0125] As Figure 1-3 shown, based on the RSM response surface analysis, the reaction conditions are further optimized to seek the best reaction conditions to maximize the response value, as shown in Table 2.

[0126] Table 2: Optimization conditions for the activated carbon adsorption reaction

[0127]

[0128]

[0129] As shown in Table 2, the reaction conditions for the highest adsorption amount after optimization are: the proportion of pig manure in the pig manure sludge mixed powder is 62.2%, the ball milling speed is 543.887 rpm, and the ball milling time is 13 h. Under these conditions, the adsorption amount is 23.376 mg·g -1 .

[0130] Experimental Example 2:

[0131] This example examines the thermal stability of the biomass prepared in Comparative Example 2, the pig manure sludge biochar (BC) prepared in Comparative Example 1, and the composite modified pig manure sludge biochar (SMgBM-BC) prepared in Experimental Example 4.

[0132] Use a Labsys Evo type thermogravimetric analyzer to perform thermogravimetric analysis to study the thermal decomposition of the biomass, pig manure sludge biochar (BC), and composite modified pig manure sludge biochar (SMgBM-BC).

[0133] Use tweezers to place the crucibles of biomass, pig manure sludge biochar (BC), and composite modified pig manure sludge biochar (SMgBM-BC) on the balance, tare and zero it. Use a micro spatula to evenly spread the sample on the bottom of the crucible, avoiding accumulation. Record the sample mass. Place the crucible with the sample on the TGA sample holder, ensuring it is centered.

[0134] Select the preset temperature program of 25°C → 8900°C, 10°C / min in the software interface. Set the gas flow rate to 50 mL / min and ventilate for 5 minutes to remove the residual gas in the system. After confirming that the parameters are correct, start the test. The instrument automatically records the mass change (TG curve) and the differential thermogravimetric curve (DTG). Each sample is tested 2 - 3 times to ensure data reproducibility.

[0135] As Figure 4 shown, the TGA curve of biomass is in an inverted S shape, and the total weight loss rate is 68.73%. The decomposition process of biomass is divided into three stages.

[0136] The first stage of decomposition occurs in the range of 30 - 180°C. This is due to the combustion of highly volatile substances and dehydrated compounds, external moisture and internally encapsulated water. The mass loss in the first stage is approximately 9.98%.

[0137] The second stage is in the range of 180 - 330°C, mainly due to the presence of cellulose and hemicellulose in the sample. The mass loss in the second stage is approximately 31.84%.

[0138] The third stage is mainly related to the destruction of lignin content, proteins, ethers, and the decomposition of total fatty acids. The mass loss in the third stage is approximately 33.18%.

[0139] As Figure 5 shown, the thermal stability of the composite modified pig manure sludge biochar (SMgBM-BC) is lower than that of BC, which is due to the decrease in the thermal stability of SMgBM-BC caused by the impregnation of H2SO4 and MgCl2.

[0140] Pig manure sludge biochar (BC) has a peak at approximately 821.5°C, which is related to the decomposition of CaCO3.

[0141] The peak at 234.6 °C of the composite modified pig manure sludge biochar (SMgBM-BC) is attributed to the introduction of sulfonic acid groups (-SO3H) promoted by sulfuric acid, which has low thermal stability. The peak at 417.2 °C of the composite modified pig manure sludge biochar (SMgBM-BC) is mainly due to the decomposition of cellulose, hemicellulose and dietary fiber, which are mainly converted into light molecular compounds and released in the form of pyrolysis vapor. Cellulose, hemicellulose and dietary fiber start to decompose at around 320.4 °C. The peak at 626.1 °C of the biomass may be related to the decomposition of lignin. This is due to the breakage of various types of lignin unit bonds, especially C=C and C=O.

[0142] Therefore, the composite modified pig manure sludge biochar (SMgBM-BC) has better thermal stability than biomass, but its thermal stability is lower than that of pig manure sludge biochar (BC).

[0143] Experimental Example 3:

[0144] The composite modified pig manure sludge biochar (SMgBM-BC) prepared by the method of the present invention can be used to remove heavy metal ions Cd in water 2+ .

[0145] This example examines the adsorption efficiency and adsorption capacity (adsorption amount) of cadmium treatment by the pig manure sludge biochar (BC) prepared in Comparative Example 1 and the composite modified pig manure sludge biochar (SMgBM-BC) in Experimental Example 4.

[0146] 25 mg (1 g / L), 50 mg (2 g / L), 125 mg (5 g / L), 25 mg (10 g / L), 500 mg (20 g / L) of the composite modified pig manure sludge biochar (SMgBM-BC) were separately sampled and added to a 50 mL centrifuge tube containing 25 mL of Cd 2+ solution (100 mg / L, pH = 5). After constant temperature oscillation (25 °C ± 0.5 °C, 180 rpm) for 24 h, the suspension was centrifuged at 10000 rpm for 10 min. The supernatant was collected, filtered through a 0.45 μm filter membrane, and the Cd in the filtrate was measured by AAS (AA-300, PerkinElmer Ltd, USA) 2+ concentration.

[0147]

[0148] Where: Q e为 adsorption amount (mg·g -1 ); E% is the removal rate; C0 is the initial concentration (mg / L); C1 is the solution concentration at adsorption equilibrium (mg / L); V is the volume of the solution (L); M is the sample mass (g).

[0149] AsFigure 6 As shown, it is preferred to add 2 g / L of composite modified pig manure sludge biochar (SMgBM-BC) for adsorption treatment. The composite modified pig manure sludge biochar (SMgBM-BC) shows a significant enhancement in the adsorption capacity per unit mass compared to pig manure sludge biochar (BC) for Cd 2+ .

[0150] As the adsorbent dosage of composite modified pig manure sludge biochar (SMgBM-BC) increased from 1 to 20 g / L, the adsorption capacity per unit mass of Cd 2+ decreased significantly. At low adsorbent dosages, the adsorption sites are utilized to the maximum extent, resulting in a higher unit adsorption capacity. However, the limited adsorption sites mean that Cd 2+ in the solution cannot be completely adsorbed. With the increase in adsorbent dosage, the significant reduction in the unit adsorption capacity is due to the limited concentration of Cd 2+ in the solution and the aggregation of the adsorbent, which hinders the full utilization of the adsorption sites. With the increase in adsorbent dosage, the adsorption efficiency of Cd 2+ increased rapidly initially and tended to stabilize after the adsorbent dosage exceeded 2 g / L. This stability indicates that the equilibrium of the adsorption sites was reached at this specific dosage.

[0151] Experimental Example 4:

[0152] In this example, in order to investigate the recycling efficiency of composite modified pig manure sludge biochar (SMgBM-BC), the change in the adsorption efficiency after desorption and re-adsorption saturation was studied.

[0153] Take 0.05 g of composite modified pig manure sludge biochar (SMgBM-BC) and adsorb it until saturation at a concentration of 100 mg / L of Cd 2+ to obtain the initial adsorption capacity (Q0).

[0154] Mix 0.05 g of the biochar adsorbed until saturation at a concentration of 100 mg / L of Cd 2+ with 25 mL of 0.1 mol / L HNO3 for desorption, and shake it at a constant temperature for 24 h (25 ± 0.5 °C, 180 rpm). After desorption, centrifuge it at 5000 rpm to separate the biochar from the aqueous phase, and wash it again with distilled water. Add the desorbed biochar back into the 100 mg / L Cd 2+ solution and shake it at a constant temperature for 24 h (25 ± 0.5 °C, 180 rpm) again to obtain the adsorption capacity (Q1) of the first cycle of adsorption. This process was repeated 5 times, and the adsorption capacities (Q n ) of the 1st - 5th cycles of adsorption.

[0155]

[0156] In the formula: is the adsorption efficiency; Q0 is the initial adsorption capacity (mg / g); Q n is the adsorption capacity (mg / L) at the nth cycle of cyclic adsorption;

[0157] Table 3: Table of the change of adsorption efficiency with the number of cycles

[0158]

[0159] As Figure 7 shown, after five adsorption-desorption cycles, due to the partial saturation of the surface active sites of the composite modified pig manure sludge biochar (SMgBM-BC) and the depletion of its surface functional groups, the adsorption efficiency decreased, and the adsorption capacity of the composite modified pig manure sludge biochar (SMgBM-BC) decreased somewhat. However, the adsorption capacity of the composite modified pig manure sludge biochar (SMgBM-BC) still remained above 80%, and the adsorption efficiency had a good retention effect.

Claims

1. A composite modified pig manure sludge biochar, characterized by: The composite modified pig manure sludge biochar is mainly prepared by pyrolysis of a mixture of pig manure and sludge, and the pig manure sludge biochar is prepared by modification with sulfuric acid and magnesium chloride solution. The pig manure mass accounts for 10% to 90% of the pig manure and sludge powder of the composite modified pig manure sludge biochar.

2. The composite modified pig manure sludge biochar according to claim 1, characterized in that: The adsorption capacity of the composite modified pig manure sludge biochar is 13.5339-20.0696 mg·g -1 .

3. A method for preparing composite modified pig manure sludge biochar, comprising the following steps: S1: The collected pig manure and sludge are rinsed with distilled water to remove dust particles adhering to the surface, and then placed in an oven for drying until a constant weight is obtained, and then crushed and sieved to obtain pig manure and sludge powder. S2: Mix the pig manure and sludge powder with sulfuric acid (H2SO4) and stir; S3: After the stirring is completed, the carbonized material is washed with distilled water to remove excess sulfuric acid until the pH value of the washing liquid reaches neutral to obtain a precipitate; S4: putting the precipitate into a drying box for drying, pouring the dried precipitate into an agate tank, and ball milling to obtain pig manure sludge biochar; S5: soaking the biochar in a magnesium chloride solution and stirring, separating the solid from the mixture and drying it in an oven overnight; S6: pyrolyzing the dried solid in a tube furnace under a nitrogen atmosphere; S7: After carbonization, cool to room temperature, wash with deionized water until neutral, filter and dry to constant weight, grind the dried product, and sieve to obtain composite modified pig manure sludge biochar.

4. The method for preparing composite modified pig manure sludge biochar according to claim 1, characterized in that: In step S2, the weight of pig manure in the mixed powder of pig manure and sludge accounts for 10% to 90%.

5. The method for preparing composite modified pig manure sludge biochar according to claim 1, characterized in that: In step S4, the ball milling speed is 200 rpm to 600 rpm, and the ball milling time is 1 h to 13 h.

6. The method for preparing composite modified pig manure sludge biochar according to claim 1, characterized in that: In step S4, the agate tank is filled with agate balls, the mass ratio of agate balls to pig manure sludge mixed powder is 50:1, the diameters of the agate balls are 5, 8 and 15 mm, and the mass ratio of 5 mm agate balls: 8 mm agate balls: 15 mm agate balls is 3:5:

2.

7. The method for preparing composite modified pig manure sludge biochar according to claim 1, characterized in that: In step S5, 2 g of biochar was soaked in 25 mL of 1 mol / L magnesium chloride solution.

8. The method for preparing composite modified pig manure sludge biochar according to claim 3, characterized in that: The prepared composite modified pig manure sludge biochar was used for adsorption test. The experimental data were optimized by response surface methodology to obtain the optimal conditions for the adsorption reaction of composite modified pig manure sludge biochar. The pig manure accounted for 62.2%, the ball milling speed was 543.887 rpm, and the ball milling time was 13 h. Under these conditions, the adsorption capacity of composite modified pig manure sludge biochar was 23.376 mg g -1 .

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