NL2033737B1

NL2033737B1 - Modified ball-milled biochar as well as preparation method and use thereof

Info

Publication number: NL2033737B1
Application number: NL2033737A
Authority: NL
Inventors: Wang Junxia; Ma Zhiqiang; Wang Yuting; Gan Ping; Yan Beibei; Li Xiangming; Cui Xiaoqiang; Meng Nan; Chen Guanyi; Yang Hefeng; Yang Lihong
Original assignee: China Energy Conservation Dadi Env Remediation Co Ltd; Univ Tianjin
Priority date: 2022-12-16
Filing date: 2022-12-16
Publication date: 2024-02-02

Abstract

The disclosure discloses a preparation method of a modiﬁed ball-milled biochar. The method comprises: washing wheat straws with deionized water and then air drying the washed wheat straws, and drying and smashing; modifying the smashed wheat straws with an alkaline solution, heating the wheat straws to 300°C-5000C at 10 OC/min after modification for oxygen-insulating carbonization reaction, and then cooling to room temperature after heat preservation for 1.5-2.5 h, so as to obtain a modiﬁed biochar after carbonization, and rinsing the modiﬁed biochar until pH is constant, and then performing ball milling to obtain the modiﬁed ball-milled biochar. In the disclosure, the modiﬁed ball-milled biochar obtained by a preparation process of “alkaline modification + oxygen-insulating carbonization + ball milling” based on wheat straws as raw materials has rich surface functional groups and can efﬁciently adsorb ammonia nitrogen in water, meanwhile the ammonia nitrogen adsorption ability of biochar is improved.

Description

MODIFIED BALL-MILLED BIOCHAR AS WELL AS PREPARATION

METHOD AND USE THEREOF

TECHNICAL FIELD

[0001] The disclosure relates to the technical field of agriculture resource utilization, particularly to a modified ball-milled biochar as well as a preparation method and use thereof.

BACKGROUD OF THE PRESENT INVENTION

[0002] Crop straws contain huge biomass energy, so it is crucial for how to efficiently utilize the crop straws. In the past, straws were mainly disposed by burning and returning it to the field. With the attention paid to the atmospheric environment quality and the recognition that the biomass energy contained in the straws can be reused, this method has been prohibited. How to more effectively develop and utilize waste straw biomass to improve environmental and economic benefits while conducting harmless treatment is an important research subject at present.

[0003] In the currently known disposal methods, pyrolysis is a promising technology. Under anoxic conditions, biomass raw materials are placed in a sealed heating furnace or a pyrolysis furnace with a corresponding temperature (300-700°C) to form biochar with stable property and structure as volatile organic carbon and oxygen-containing functional groups linked thereto are decomposed during the pyrolysis.

[0004] The biochar is a novel carbon material rich in carbon elements, which comprises organic components and inorganic components. Where, the organic components support a skeleton structure of biochar, and their constituent elements mainly comprise C, H, O and N. The functional groups on the biochar contain

C=C as well as carboxyl, hydroxyl and the like, temperatures and used biomass are main factors determining the types of functional groups and presence existence morphology of carbon. The product biochar obtained by using a pyrolysis technology often has good combustion performance, nutrient characteristics and the like, and has wide application prospect as fuel, a soil conditioner and the like. In addition, an abundant pore structure allows the biochar to have strong adsorption ability. Therefore, the biochar is an ideal contaminated water treatment material, and can be used as an adsorbent for multiple pollutants such as nitrogen, phosphorus, organic matters and heavy metals. Ammonia nitrogen, as a water pollutant, is mainly present in a form of NHs", and excessive ammonia nitrogen causes the reduction in concentration of dissolved oxygen in water, leads to blank and smelly water and reduced water quality, and affects survival of aquatic animals and plants. Therefore, it is important for treatment of ammonia nitrogen in wastewater.

[0005] In general, application of biochar is limited due to its poor ammonia nitrogen adsorptivity, so it is often needed to modify ammonia nitrogen in order to make biochar have better adsorptivity. Modification of biochar with acid or alkaline can increase the quantity and components of oxygen-containing functional groups and components on the surface of the biochar, changes the specific surface area and surface structure features of the biochar, and improves the ammonia nitrogen adsorbing ability of biochar. In addition, ball milling modification, as a new-developing modification method, has the advantages of green, low cost, simple operation and large-scale production, and the biochar subjected to ball milling modification has more excellent physical and chemical properties than original unmodified biochar. Ball milling can reduce the particle size of biochar and increase the types and quantity of functional groups on the surface of the biochar, enlarge the specific surface area, and then improve the pollutant adsorbing ability of biochar. However, there few reports on improvement of a ammonia nitrogen removing ability of biochar in water by utilizing coupling of chemical modification and ball milling modification.

SUMMARY OF PRESENT INVENTION

The objective of the disclosure is to provide a modified ball-milled biochar prepared by using wheat straws as well as a preparation method and use thereof.

The preparation method is simple, and the obtained modified biochar has high yield and strong adsorbing ability of ammonia nitrogen in water.

[0006] Specific technical solution is as follows:

[0007] The disclosure provides a preparation method of a modified ball-milled biochar, comprising:

[0008] (1) washing wheat straws with deionized water and then air drying the washed wheat straws, and drying and smashing;

[0009] (2) modifying the smashed wheat straws with an alkaline solution, heating the wheat straws to 300°C-500°C at 10 °C/min after modification for oxygen-insulating carbonization reaction, and then cooling to room temperature after heat preservation for 1.5-2.5 h, so as to obtain a modified biochar after carbonization; and

[0010] (3) rinsing the modified biochar until pH is constant, and then performing ball milling to obtain the modified ball-milled biochar.

[0011] The oxygen-insulating carbonization reaction described above refers to a fact that under the atmosphere of nitrogen/carbon dioxide, raw materials are put into a crucible to be placed in a box furnace, and a sufficient amount of nitrogen/carbon dioxide is introduced into the box furnace so as to ensure the reaction environment is in an anaerobic condition.

[0012] The carbonization process of biochar is a decomposition reaction of organic matters in biomass, that is, generally, high-temperature heating is performed under the condition of oxygen deficiency, no oxygen or continuous supply of an inert gas, volatile organic carbon and oxygen-containing functional groups linked thereto are decomposed as the temperature is continuously increased, and the biochar with a certain fixed carbonite and a basic fine porous structure is finally produced. The biochar can be prepared by carbonization of the wheat straws with cellulose as a main component. However, the yield and pollutant adsorbing ability of biochar require extremely strict carbonization conditions, the maximum yield and optimal ammonia nitrogen adsorbing ability of biochar can be achieved only under the special carbonization conditions.

[0013] Preferably, in step (1), the wheat straws are cut into 8-10 sections and then washed with deionized water; the air drying time is 2-6 days.

[0014] In the process of drying the wheat straws, the proper drying temperature and time are important factors determining the smashing particle size and carbonization effect of the wheat straws; further, in step (1), the drying temperature 1s 90-105°C, and the drying time is 1.5-2 h.

[0015] The wheat straws need to be ground before pyrolysis, its particle size is an important factor determining the carbonization effect of the wheat straws and the particle size and specific surface area of the obtained biochar, preferably, the ground wheat straw has a particle size of between 0.7 mm and 0.9 mm.

[0016] The alkaline solution is used to modify the dried wheat straws, the types and concentrations of the alkaline solutions are important factors determining the modification effect, preferably, in step (2), the alkaline solution is sodium hydroxide or potassium hydroxide, the concentration of the alkaline solution is 0.8-1.2 mol/L, and the soaking time is 10-14 h.

[0017] Preferably, in step (2), the wheat straws are heated to 300°C-500°C at 10 °C/min after modification for oxygen-insulating carbonization reaction, and then cooled to room temperature after heat preservation for 2 h.

[0018] Preferably, in step (3), a method for ball milling is as follows: agate ball-milling beads are mixed with the modified biochar rinsed in step (3) in a mass ratio of 1:60-1:20, and then the obtained mixture is placed in a ball milling tank, and then ball milling tank operates for 1-2 h at the rotation speed of 500-600 r/min.

[0019] Preferably, the diameter of the agate ball-milling bead is 5-7 mm, and the agate ball-milling bead overturns every 8-10 min of operation.

[0020] The disclosure also provides a modified ball-milled biochar prepared by utilizing the preparation method.

[0021] The disclosure also provides use of the modified ball-milled biochar as an ammonia nitrogen adsorbent in treatment of contaminated water.

[0022] Compared with the prior art, the disclosure has the beneficial effects:

[0023] 1n the disclosure, the modified ball-milled biochar is obtained by a preparation process of “alkaline modification + oxygen-insulating carbonization + ball milling” based on wheat straws as raw materials, and the modified ball-milled biochar contains abundant surface functional groups and can efficiently adsorb ammonia nitrogen in water, meanwhile the ammonia nitrogen adsorption ability of biochar is improved by optimizing the reaction conditions of the modification and carbonization process of wheat straws.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0024] The disclosure will be further described in combination with specific 5 embodiments, the following listed examples are only specific embodiments of the disclosure, but the protective scope of the disclosure is not limited thereto.

[0025] Measurement methods involved by the following examples are as follows:

[0026] (1) measurement method of yield: the weight of a crucible is recorded as ml, 15-25 g of biomass is weighed into the crucible, a total weight is recorded as m2, the crucible is placed into a box furnace for temperature programming, cooled to room temperature after the program is ended, a total weight at this moment is recorded as m3, and the yield is calculated as follows: yield (%)=(m3-m1)/(m2-m1l); examples 2, 4, 6 and 7 and comparative example 3 correspond to the same pyrolysis products, the subsequent ball milling modification has no influence on the yield, and comparative examples 3 and 5 are the same above.

[0027] (2) Measurement method of ash content: the weight of a crucible is recorded as ml, 0.3 g of sample is taken and put into the crucible, and a total weight at this moment is recorded as m2; the crucibles are arranged in a certain sequence, then a furnace door of a muffle furnace is closed, and then this situation stays for 5 h at 750°C; after firing is ended, the temperature in the muftle furnace 1s reduced to 200°C, then the furnace door is opened, the crucible in the drier is taken out and dried and cooled, the temperature is decreased to room temperature after cooling, and a total weight is weighed and recorded as m3; the ash content is calculated as follows: ash content (%)=(m3-m1)/(m2-m1). Examples 2, 4, 6 and 7 and comparative example 3 correspond to the same pyrolysis product, the subsequent ball milling modification has no influence on the yield, and comparative examples 3 and 5 are the same above.

[0028] (3) Measurement method of pH: the biochar is mixed with deionized water in a mass ratio of 1:100 to be put in a glass bottle, and then the glass bottle is continuously oscillated for 6 h at the rotation speed of 120 r/min followed by measurement.

[0029] Example 1

[0030] 200 g of wheat straws were taken, the impurities of the wheat straws were removed, and then the wheat straws without impurities were subjected to natural air drying in a ventilated environment; the wheat straws were dried in an oven for 2 h under the temperature condition of 105°C and smashed, the smashed wheat straws were evenly mixed with a 1 mol/L NaOH solution in a mass ratio of 1:5 and stood for 12 h, and then the obtained mixture was dried in the oven at 80°C until the weight was constant. Then, the modified wheat straws were put into a box furnace into which a sufficient amount of carbon dioxide was introduced, after air was evacuated, the furnace was sealed for high-temperature oxygen-insulating carbonization, the box furnace was heated to 450°C at the temperature raising rate of 10°C/min, heat preservation was performed on the box furnace for 2 h, the carbonized wheat straws were cooled to room temperature, and the obtained biochar was washed with deionized water until pH was constant and then dried. The dried biochar was mixed with agate ball milling beads with a diameter of 6 mm in a mass ratio of 1:6 and then subjected to ball milling treatment at the rotation speed of 500 r/min, the agate ball milling beads overturned every 10 min, and the modified biochar was obtained after 1 h.

[0031] The modified biochar produced in this example is as shown in Table 1, the yield is 50.5%, pH is 10.79, and the ash content is 56.20%.

[0032] Three 0.1 g dried modified biochar samples in example 1 were weighed and placed in 30 mL glass bottles respectively, 30 mL of ammonia nitrogen-containing 60 mg/L water samples were added into the glass bottles, then the glass bottles were sealed and vibrated for 24 h on a thermostatic shaker at 25°C at 120 r/min, and finally, supernatant was removed by filtration, and then ammonia nitrogen in the supernatant was analyzed and calculated using Nessler’s reagent spectrophotometry.

[0033] By detection, the NH: adsorbing ability of the modified biochar in example 1 is 4351 mg/kg.

[0034] Example 2

[0035] 200 g of wheat straws were taken, the impurities of the wheat straws were removed, and then the wheat straws without impurities were subjected to natural air drying in a ventilated environment; the wheat straws were dried in an oven for 2 h under the temperature condition of 105°C and smashed, the smashed wheat straws were evenly mixed with a 1 mol/L NaOH solution in a mass ratio of 1:5 and stood for 12 h, and then the obtained mixture was dried in the oven at 80°C until the weight was constant. Then, the modified wheat straws were put into a box furnace into which a sufficient amount of nitrogen was introduced, after air was evacuated, the furnace was sealed for high-temperature oxygen-insulating carbonization, the box furnace was heated to 500°C at the temperature raising rate of 10°C/min, heat preservation was performed on the box furnace for 2 h, the carbonized wheat straws were cooled to room temperature, and the obtained biochar was washed with deionized water until pH was constant and then dried.

The dried biochar was mixed with agate ball milling beads with a diameter of 6 mm in a mass ratio of 1:6 and then subjected to ball milling treatment at the rotation speed of 500 r/min, the agate ball milling beads overturned every 10 min, and the modified biochar was obtained after 1 h.

[0036] The modified biochar produced in this example is as shown in Table 1, the yield is 53.7%, pH is 10.82, and the ash content is 52.82%.

[0037] Three 0.1 g dried modified biochar samples in example 2 were weighed and placed in 50 mL glass bottles respectively, 30 mL of ammonia nitrogen-containing 60 mg/L water samples were added into the glass bottles, then the glass bottles were sealed and vibrated for 24 h on a thermostatic shaker at 25°C at 120 r/min, and finally, supernatant was removed by filtration, and then ammonia nitrogen in the supernatant was analyzed and calculated using Nessler’s reagent spectrophotometry.

[0038] By detection, the NH4* adsorbing ability of the modified biochar in example 2 1s 4784 mg/kg.

[0039] Example 3

[0040] 200 g of wheat straws were taken, the impurities of the wheat straws were removed, and then the wheat straws without impurities were subjected to natural air drying in a ventilated environment; the wheat straws were dried in an oven for 2 h under the temperature condition of 105°C and smashed, the smashed wheat straws were evenly mixed with a 1 mol/L NaOH solution in a mass ratio of 1:5 and stood for 12 h, and then the obtained mixture was dried in the oven at 80°C until the weight was constant. Then, the modified wheat straws were put into a box furnace into which a sufficient amount of carbon dioxide was introduced, after air was evacuated, the furnace was sealed for high-temperature oxygen-insulating carbonization, the box furnace was heated to 500°C at the temperature raising rate of 10°C/min, heat preservation was performed on the box furnace for 2 h, the carbonized wheat straws were cooled to room temperature, and the obtained biochar was washed with deionized water until pH was constant and then dried. The dried biochar was mixed with agate ball milling beads with a diameter of 6 mm in a mass ratio of 1:6 and then subjected to ball milling treatment at the rotation speed of 500 r/min, the agate ball milling beads overturned every 10 min, and the modified biochar was obtained after 1 h.

[0041] The modified biochar produced in this example is as shown in Table 1, the yield is 52.8%, pH is 10.61, and the ash content is 54.26%

[0042] Three 0.1 g dried modified biochar samples in example 3 were weighed and placed in 50 mL glass bottles respectively, 30 mL of ammonia nitrogen-containing 60 mg/L water samples were added into the glass bottles, then the glass bottles were sealed and vibrated for 24 h on a thermostatic shaker at 25°C at 120 r/min, and finally, supernatant was removed by filtration, and then ammonia nitrogen in the supernatant was analyzed and calculated using Nessler’s reagent spectrophotometry.

[0043] By detection, the NH," adsorbing ability of the modified biochar in example 3 is 4811 mg/kg.

[0044] Example 4

[0045] 200 g of wheat straws were taken, the impurities of the wheat straws were removed, and then the wheat straws without impurities were subjected to natural air drying in a ventilated environment; the wheat straws were dried in an oven for 2 h under the temperature condition of 105°C and smashed, the smashed wheat straws were evenly mixed with a 1 mol/L NaOH solution in a mass ratio of 1:5 and stood for 12 h, and then the obtained mixture was dried in the oven at 80°C until the weight was constant. Then, the modified wheat straws were put into a box furnace into which a sufficient amount of nitrogen was introduced, after air was evacuated, the furnace was sealed for high-temperature oxygen-insulating carbonization, the box furnace was heated to S00°C at the temperature raising rate of 10°C/min, heat preservation was performed on the box furnace for 2 h, the carbonized wheat straws were cooled to room temperature, and the obtained biochar was washed with deionized water until pH was constant and then dried.

The dried biochar was mixed with agate ball milling beads with a diameter of 6 mm in a mass ratio of 1:20 and then subjected to ball milling treatment at the rotation speed of 500 r/min, the agate ball milling beads overturned every 10 min, and the modified biochar was obtained after 4 h.

[0046] The modified biochar produced in this example is as shown in Table 1, the yield 1s 53.7%, pH is 10.70, and the ash content is 52.82%.

[0047] Three 0.1 g dried modified biochar samples in example 4 were weighed and placed in 50 mL glass bottles respectively, 30 mL of ammonia nitrogen-containing 60 mg/L water samples were added into the glass bottles, then the glass bottles were sealed and vibrated for 24 h on a thermostatic shaker at 25°C at 120 r/min, and finally, supernatant was removed by filtration, and then ammonia nitrogen in the supernatant was analyzed and calculated using Nessler’s reagent spectrophotometry.

[0048] By detection, the NH4" adsorbing ability of the modified biochar in example 4 1s 5351 mg/kg.

[0049] Example 5

[0050] 200 g of wheat straws were taken, the impurities of the wheat straws were removed, and then the wheat straws without impurities were subjected to natural air drying in a ventilated environment; the wheat straws were dried in an oven for 2 h under the temperature condition of 105°C and smashed, the smashed wheat straws were evenly mixed with a 1 mol/L NaOH solution in a mass ratio of

1:5 and stood for 12 h, and then the obtained mixture was dried in the oven at 80°C until the weight was constant. Then, the modified wheat straws were put into a box furnace into which a sufficient amount of nitrogen was introduced, after air was evacuated, the furnace was sealed for high-temperature oxygen-insulating carbonization, the box furnace was heated to 500°C at the temperature raising rate of 10°C/min, heat preservation was performed on the box furnace for 2 h, the carbonized wheat straws were cooled to room temperature, and the obtained biochar was washed with deionized water until pH was constant and then dried.

The dried biochar was mixed with agate ball milling beads with a diameter of 6

IO mm in a mass ratio of 1:6 and then subjected to ball milling treatment at the rotation speed of 500 r/min, the agate ball milling beads overturned every 10 min, and the modified biochar was obtained after 1 h.

[0051] The modified biochar produced in this example is as shown in Table 1, the yield is 55.3%, pH is 10.04, and the ash content is 52.37%.

[0052] Three 0.1 g dried modified biochar samples in example 5 were weighed and placed in 50 mL glass bottles respectively, 30 mL of ammonia nitrogen-containing 60 mg/L water samples were added into the glass bottles, then the glass bottles were sealed and vibrated for 24 h on a thermostatic shaker at 25°C at 120 r/min, and finally, supernatant was removed by filtration, and then ammonia nitrogen in the supernatant was analyzed and calculated using Nessler’s reagent spectrophotometry.

[0053] By detection, the NH4" adsorbing ability of the modified biochar in example 5 is 3838 mg/kg.

[0054] Example 6

[0055] 200 g of wheat straws were taken, the impurities of the wheat straws were removed, and then the wheat straws without impurities were subjected to natural air drying in a ventilated environment; the wheat straws were dried in an oven for 2 h under the temperature condition of 105°C and smashed, the smashed wheat straws were evenly mixed with a | mol/L NaOH solution in a mass ratio of 1:5 and stood for 12 h, and then the obtained mixture was dried in the oven at 80°C until the weight was constant. Then, the modified wheat straws were put into a box furnace into which a sufficient amount of nitrogen was introduced, after air was evacuated, the furnace was sealed for high-temperature oxygen-insulating carbonization, the box furnace was heated to S00°C at the temperature raising rate of 10°C/min, heat preservation was performed on the box furnace for 2 h, the carbonized wheat straws were cooled to room temperature, and the obtained biochar was washed with deionized water until pH was constant and then dried.

The dried biochar was mixed with agate ball milling beads with a diameter of 6 mm in a mass ratio of 1:20 and then subjected to ball milling treatment at the rotation speed of 500 r/min, the agate ball milling beads overturned every 10 min, and the modified biochar was obtained after 8 h.

[0056] The modified biochar produced in this example is as shown in Table I, the yield is 53.7%, pH is 10.58, and the ash content is 52.82%.

[0057] Three 0.1 g dried modified biochar samples in example 6 were weighed and placed in 50 mL glass bottles respectively, 30 mL of ammonia nitrogen-containing 60 mg/L water samples were added into the glass bottles, then the glass bottles were sealed and vibrated for 24 h on a thermostatic shaker at 25°C at 120 r/min, and finally, supernatant was removed by filtration, and then ammonia nitrogen in the supernatant was analyzed and calculated using Nessler’s reagent spectrophotometry.

[0058] By detection, the NH4" adsorbing ability of the modified biochar in example 6 is 5351 mg/kg.

[0059] Example 7

[0060] 200 g of wheat straws were taken, the impurities of the wheat straws were removed, and then the wheat straws without impurities were subjected to natural air drying in a ventilated environment; the wheat straws were dried in an oven for 2 h under the temperature condition of 105°C and smashed, the smashed wheat straws were evenly mixed with a 1 mol/L NaOH solution in a mass ratio of 1:5 and stood for 12 h, and then the obtained mixture was dried in the oven at 80°C until the weight was constant. Then, the modified wheat straws were put into a box furnace into which a sufficient amount of nitrogen was introduced, after air was evacuated, the furnace was sealed for high-temperature oxygen-insulating carbonization, the box furnace was heated to 500°C at the temperature raising rate of 10°C/min, heat preservation was performed on the box furnace for 2 h, the carbonized wheat straws were cooled to room temperature, and the obtained biochar was washed with deionized water until pH was constant and then dried.

The dried biochar was mixed with agate ball milling beads with a diameter of 6 mm in a mass ratio of 1:20 and then subjected to ball milling treatment at the rotation speed of 500 r/min, the agate ball milling beads overturned every 10 min, and the modified biochar was obtained after 12 h.

[0061] The modified biochar produced in this example is as shown in Table 1, the yield is 53.7%, pH is 10.55, and the ash content is 52.82%.

[0062] Three 0.1 g dried modified biochar samples in example 7 were weighed and placed in 50 mL glass bottles respectively, 30 mL of ammonia nitrogen-containing 60 mg/L water samples were added into the glass bottles, then the glass bottles were sealed and vibrated for 24 h on a thermostatic shaker at 25°C at 120 r/min, and finally, supernatant was removed by filtration, and then ammonia nitrogen in the supernatant was analyzed and calculated using Nessler’s reagent spectrophotometry.

[0063] By detection, the NH4" adsorbing ability of the modified biochar in example 7 is 5027 mg/kg.

[0064] Comparative example 1

[0065] 200 g of wheat straws were taken, the impurities of the wheat straws were removed, and then the wheat straws without impurities were subjected to natural air drying in a ventilated environment; the wheat straws were dried in an oven for 2 h under the temperature condition of 105°C and smashed; then the smashed wheat straws were put into a box furnace and a sufficient amount of nitrogen was introduced, after air was evacuated, the furnace was sealed for high-temperature oxygen-insulating carbonization, the box furnace was heated to 300°C at the temperature raising rate of 10°C/min, heat preservation was performed on the box furnace for 2 h, the carbonized wheat straws were cooled to room temperature, so as to finally obtain the biochar.

[0066] The modified biochar produced in this comparative example is as shown in Table 1, the yield 1s 40.9%, pH is 8.24, and the ash content is 30.38%.

[0067] Three 0.1 g dried modified biochar samples in comparative example 1 were weighed and placed in 50 mL glass bottles respectively, 30 mL of ammonia nitrogen-containing 60 mg/L water samples were added into the glass bottles, then the glass bottles were sealed and vibrated for 24 h on a thermostatic shaker at 25°C at 120 r/min, and finally, supernatant was removed by filtration, and then ammonia nitrogen in the supernatant was analyzed and calculated using Nessler’s reagent spectrophotometry.

[0068] By detection, the NH4" adsorbing ability of the modified biochar in comparative example 1 is 1811 mg/kg.

[0069] Comparative example 2

[0070] 200 g of wheat straws were taken, the impurities of the wheat straws were removed, and then the wheat straws without impurities were subjected to natural air drying in a ventilated environment; the wheat straws were dried in an oven for 2 h under the temperature condition of 105°C and smashed; then the smashed wheat straws were put into a box furnace and a sufficient amount of nitrogen was introduced, after air was evacuated, the furnace was sealed for high-temperature oxygen-insulating carbonization, the box furnace was heated to 450°C at the temperature raising rate of 10°C/min, heat preservation was performed on the box furnace for 2 h, the carbonized wheat straws were cooled to room temperature, so as to finally obtain the biochar.

[0071] The modified biochar produced in this comparative example is as shown in Table 1, the yield is 41.3%, pH is 10.26, and the ash content is 43.96%.

[0072] Three 0.1 g dried modified biochar samples in comparative example 2 were weighed and placed in 30 mL glass bottles respectively, 30 mL of ammonia nitrogen-containing 60 mg/L water samples were added into the glass bottles, then the glass bottles were sealed and vibrated for 24 h on a thermostatic shaker at 25°C at 120 r/min, and finally, supernatant was removed by filtration, and then ammonia nitrogen in the supernatant was analyzed and calculated using Nessler’s reagent spectrophotometry.

[0073] By detection, the NH4" adsorbing ability of the modified biochar in comparative example 2 is 2108 mg/kg.

[0074] Comparative example 3

[0075] 200 g of wheat straws were taken, the impurities of the wheat straws were removed, and then the wheat straws without impurities were subjected to natural air drying in a ventilated environment; the wheat straws were dried in an oven for 2 h under the temperature condition of 105°C and smashed; then the smashed wheat straws were put into a box furnace and a sufficient amount of nitrogen was introduced, after air was evacuated, the furnace was sealed for high-temperature oxygen-insulating carbonization, the box furnace was heated to 500°C at the temperature raising rate of 10°C/min, heat preservation was performed on the box furnace for 2 h, the carbonized wheat straws were cooled to room temperature, so as to finally obtain the biochar.

[0076] The modified biochar produced in this comparative example is as shown in Table 1, the yield is 41.6%, pH is 10.39, and the ash content is 45.32%.

[0077] Three 0.1 g dried modified biochar samples in comparative example 3 were weighed and placed in 50 mL glass bottles respectively, 30 mL of ammonia nitrogen-containing 60 mg/L water samples were added into the glass bottles, then the glass bottles were sealed and vibrated for 24 h on a thermostatic shaker at 25°C at 120 r/min, and finally, supernatant was removed by filtration, and then ammonia nitrogen in the supernatant was analyzed and calculated using Nessler’s reagent spectrophotometry.

[0078] By detection, the NH4" adsorbing ability of the modified biochar in comparative example 3 is 2000 mg/kg.

[0079] Comparative example 4

[0080] 200 g of wheat straws were taken, the impurities of the wheat straws were removed, and then the wheat straws without impurities were subjected to natural air drying in a ventilated environment; the wheat straws were dried in an oven for 2 h under the temperature condition of 105°C and smashed, the smashed wheat straws were evenly mixed with a 1 mol/L NaOH solution in a mass ratio of 1:5 and stood for 12 h, and then the obtained mixture was dried in the oven at 80°C until the weight was constant. Then, the modified wheat straws were put into a box furnace into which a sufficient amount of nitrogen was introduced, after air was evacuated, the furnace was sealed for high-temperature oxygen-insulating carbonization, the box furnace was heated to S00°C at the temperature raising rate of 10°C/min, heat preservation was performed on the box furnace for 2 h, the carbonized wheat straws were cooled to room temperature, and the obtained biochar was washed with deionized water until pH was constant and then dried.

[0081] The modified biochar produced in this comparative example is as shown in Table 1, the yield is 53.7%, pH is 10.41, and the ash content is 52.82%.

[0082] Three 0.1 g dried modified biochar samples in comparative example 4 were weighed and placed in 50 mL glass bottles respectively, 30 mL of ammonia nitrogen-containing 60 mg/L water samples were added into the glass bottles, then the glass bottles were sealed and vibrated for 24 h on a thermostatic shaker at 25°C at 120 r/min, and finally, supernatant was removed by filtration, and then ammonia nitrogen in the supernatant was analyzed and calculated using Nessler’s reagent spectrophotometry.

[0083] By detection, the NH4" adsorbing ability of the modified biochar in comparative example 4 is 2595 mg/kg.

[0084] Comparative example 5

[0085] 200 g of wheat straws were taken, the impurities of the wheat straws were removed, and then the wheat straws without impurities were subjected to natural air drying in a ventilated environment; the wheat straws were dried in an oven for 2 h under the temperature condition of 105°C and smashed; then the smashed wheat straws were put into a box furnace into which a sufficient amount of nitrogen was introduced, after air was evacuated, the furnace was sealed for high-temperature oxygen-insulating carbonization, the box furnace was heated to 500°C at the temperature raising rate of 10°C/min, heat preservation was performed on the box furnace for 2 h, the carbonized wheat straws were cooled to room temperature. The obtained biochar was mixed with agate ball milling beads with a diameter of 6 mm in a mass ratio of 1:6 and then subjected to ball milling treatment at the rotation speed of 500 r/min, the agate ball milling beads overturned every 10 min, and the modified biochar was obtained after 1 h.

[0086] The modified biochar produced in this comparative example is as shown in Table 1, the yield is 41.6%, pH is 10.36, and the ash content is 45.32%.

[0087] Three 0.1 g dried modified biochar samples in comparative example 5 were weighed and placed in 50 mL glass bottles respectively, 30 mL of ammonia nitrogen-containing 60 mg/L water samples were added into the glass bottles, then the glass bottles were sealed and vibrated for 24 h on a thermostatic shaker at 25°C at 120 r/min, and finally, supernatant was removed by filtration, and then ammonia nitrogen in the supernatant was analyzed and calculated using Nessler’s reagent spectrophotometry.

[0088] By detection, the NH4" adsorbing ability of the modified biochar in comparative example 5 is 1892 mg/kg.

[0089]

[0090] Table 1: Physical and chemical properties and apparent structure comparison of modified biochar prepared under different carbonization conditions . Adsorption

Yields Ash content

Samples pH amount of NH:* (%) (%) (mg/kg)

Example 1 50.5 56.20 10.79 4351

Example 2 53.7 52.82 10.82 4784

Example 3 52.8 54.26 10.61 4811

Example 4 53.7 52.82 10.70 5351

Example 5 553 52.37 10.04 3838

Example 6 53.7 52.82 10.58 5351

Example 7 53.7 52.82 10.55 5027

Comparative 40.9 30.38 8.24 1811 example 1

Comparative 413 43.96 10.26 2108 example 2

Comparative 41.6 45.32 10.39 2000 example 3

Comparative 53.7 52.82 10.41 2595 example 4

Comparative 41.6 45.32 10.36 1892 example 5

PREFERRED EMBODIMENTS

1. A preparation method of a modified ball-milled biochar, comprising: (1) washing wheat straws with deionized water and then air drying the washed wheat straws, and drying and smashing; (2) modifying the smashed wheat straws with an alkaline solution, heating the wheat straws to 300°C-500°C at 10 °C/min after modification for oxygen-insulating carbonization reaction, and then cooling to room temperature after heat preservation for 1.5-2.5 h, so as to obtain a modified biochar after carbonization; and

(3) rinsing the modified biochar until pH is constant, and then performing ball milling to obtain the modified ball-milled biochar.

2. The preparation method of the modified ball-milled biochar according to claim 1, wherein in step (1), the wheat straws are cut into 8-10 sections and then washed with deionized water; the air drying time is 2-6 days.

3. The preparation method of the modified ball-milled biochar according to claim 1, wherein in step (1), the drying temperature is 90-105°C, and the drying time is 1.5-2 h.

4. The preparation method of the modified ball-milled biochar according to claim 1, wherein in step (2), the alkaline solution is sodium hydroxide or potassium hydroxide, the concentration of the alkaline solution is 0.8-1.2 mol/L, and the soaking time is 10-14 h.

5. The preparation method of the modified ball-milled biochar according to claim 1, wherein in step (2), the wheat straws are heated to 300°C-500°C at 10 °C/min after modification for oxygen-insulating carbonization reaction, and then cooled to room temperature after heat preservation for 2 h.

6. The preparation method of the modified ball-milled biochar according to claim 1, wherein in step (3), a method for ball milling is as follows: agate ball-milling beads are mixed with the modified biochar rinsed in step (3) in a mass ratio of 1:6-1:20, and then the obtained mixture is placed in a ball milling tank, and then ball milling tank operates for 1-2 h at the rotation speed of 500-600 r/min.

7. The preparation method of the modified ball-milled biochar according to claim 6, wherein the diameter of the agate ball-milling bead is 5-7 mm; the agate ball-milling bead overturns every 8-10 min of operation.

8. A modified ball-milled biochar prepared by utilizing the preparation method according to any one of claims 1-7. 9. Use of the modified ball-milled biochar according to claim 8 as an ammonia nitrogen adsorbent in treatment of contaminated water.

Claims

CONCLUSIONS

1. A method of preparing a modified ball-milled biochar consists of: (1) washing wheat straws with deionized water and then air-drying the washed wheat straws, and drying and crushing; (2) modifying the crushed wheat straws with an alkaline solution, heating the wheat straws to 300°C-500°C at 10°C/min after modifying for an anoxic carbonization reaction, and then cooling to room temperature after heat preservation for 1.5-2.5 hours, so that a modified biochar is obtained after carbonization; (3) rinsing the modified biochar until the pH is constant, and then performing ball-milling to obtain the modified ball-milled biochar.

2. The preparation method of the modified ball-milled biochar according to claim 1, wherein in step (1) the wheat straws are cut into 8-10 cm sections and then washed with deionized water; the air drying time is 2-6 days.

3. The preparation method of the modified ball-milled biochar according to claim 1, wherein in step (1) the drying temperature is 90-105°C, and the drying time is 1.5-2 hours.

4. The preparation method of the modified ball-milled biochar according to claim 1, where in step (2) the alkaline solution is sodium hydroxide or potassium hydroxide, the concentration of the alkaline solution is 0.8-1.2 mol/L, and the soaking time 10-14 hours.

5. The preparation method of the modified ball-milled biochar according to claim 1, wherein in step (2), the wheat straws after modification are heated to 300°C-500°C at 10°C/min for an anoxic carbonization reaction, and then cooled to room temperature after heat retention for 2 hours.

6. The preparation method of the modified ball-milled biochar according to claim 1, wherein in step (3) a ball-milling method is as follows: agate ball mill granules are mixed with the modified biochar rinsed in step (3) in a mass ratio of 1 :6-1:20, and then the obtained mixture is placed in a ball-milling tank, and then the ball-milling tank works for 1-12 hours at a rotation speed of 500-600 r/min.

7. The preparation method of the modified ball-milled biochar according to claim 6, wherein the diameter of the agate ball-milled grain is 5-7 mm; the agate ball mill grain rotates every 8-10 min when working.

8. A modified ball-milled biochar prepared using the preparation method according to any of claims 1-7.

9. Use of the modified ball-milled biochar according to claim 8 as ammonia nitrogen adsorbent in the treatment of contaminated water.