CN110586038B - Biochar loaded nano zero-valent iron material and application thereof - Google Patents
Biochar loaded nano zero-valent iron material and application thereof Download PDFInfo
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Abstract
The invention discloses a biochar loaded nano zero-valent iron material and application thereof, wherein the preparation method of the zero-valent iron material comprises the following steps: 1. crushing biomass and carrying out primary chemical modification to obtain modified biomass; 2. in the nitrogen atmosphere, firstly heating the pyrolysis furnace to 450-550 ℃, then placing the modified biomass in the pyrolysis furnace for pyrolysis, and then heating to 650-750 ℃ at the average speed of 2-3 ℃/min to obtain biochar; 3. carrying out deep chemical modification on the biochar to obtain modified biochar; 4. uniformly mixing absolute ethyl alcohol, ferrous salt, ultrapure water and modified biochar to obtain a suspension; 5. and (3) dropwise adding a reducing agent into the suspension to reduce ferrous ions in the nitrogen atmosphere, and after dropwise adding is completed, performing aging reaction for 0.5-1h to obtain the biomass loaded nano zero-valent iron material. The zero-valent iron material is prepared by adopting a modification and temperature-changing calcination mode, so that the performance of the zero-valent iron material is greatly improved, the zero-valent iron material can be used for removing selenium in desulfurization wastewater, and the removal effect of selenite is mainly better.
Description
Technical Field
The invention belongs to the technical field of material preparation and water treatment, and particularly relates to a biochar loaded nano zero-valent iron material and application thereof.
Background
Selenium is a trace element required by organisms and is one of the important components for maintaining normal life activities of the organisms. However, once an organism ingests an excessive amount of selenium, the health of the organism may be compromised, causing some diseases and even death.
Relevant research and research in the last ten years shows that in the desulfurization wastewater of coal-fired power generation and partial industrial and agricultural wastewater, the content of selenium element is far beyond the average level in the nature, and finally the selenium element is enriched in a human body under the action of biological enrichment, so that the health and the life quality of the human body are influenced. Even if the selenium content in the water body exceeds the standard, the selenium content is relatively low, and the selenium form in the water is complex, mainly compounds of tetravalent (Se (IV) selenium and hexavalent (Se (VI)) selenium.
The nano zero-valent iron has a strong reaction desorption effect on pollutants in a plurality of water bodies due to the large specific surface area and surface energy, and is widely applied to the remediation of the polluted water bodies as a high-efficiency reductive remediation material. However, the preparation process of the nano zero-valent iron is complex, the preparation cost is high, various forms of inactivation such as oxidation, agglomeration and the like are easy to occur during use, and the nano zero-valent iron is easy to enter a human body to cause biological toxicity after being used, so that the application of the nano zero-valent iron in actual life is limited to a certain extent.
Biochar is a novel means for resource utilization of agricultural wastes, and is widely researched by a plurality of experts and scholars in recent years. Because the raw material of the biochar is easy to obtain and has the characteristics of high surface porosity, high adsorption functional groups and the like, researchers carry out extensive and intensive research on the application of the biochar in the aspects of soil remediation, pollutant adsorption and the like. Most of pure biomass cokes have unsatisfactory adsorption effects on a plurality of pollutants, and the activated carbon with good adsorption effect has complex process period and high cost, thereby causing obstruction to the popularization and application of the biochar.
The biochar is modified in a biomass raw material stage or a biochar stage, or other exogenous substances are loaded to form a composite material with a hybrid system, so that the method is an effective method for improving the using effect of the biochar. By researching the biomass raw material modification or biochar stage modification methods or the types and loading modes of the loaded substances in different application channels, the adsorption and removal effects of biochar on specific substances in a specific environment can be effectively improved, the application channels and the fields of biochar are expanded, and a new thought and a new method are provided for solving the problems in the corresponding fields. The novel material prepared based on the mode of dispersing the nano zero-valent iron by the biochar provides a new method for removing a plurality of pollutants in the water body, and overcomes the defects that the nano zero-valent iron is easy to agglomerate and is difficult to separate when the nano zero-valent iron is simply used in the prior art.
Disclosure of Invention
Based on the prior art, the invention provides a biochar loaded nano zero-valent iron material and application thereof, the zero-valent iron material is prepared by adopting a modification and variable-temperature calcination mode, the performance of the zero-valent iron material is greatly improved, and the zero-valent iron material can be used for removing selenium element in desulfurization wastewater and selenite (SeO)3 2-) The removal effect of (2) has obvious advantages.
The technical scheme adopted for realizing the above purpose of the invention is as follows:
a biochar loaded nano zero-valent iron material is prepared by the following method:
1. crushing biomass to obtain biomass powder, crushing the biomass to perform primary chemical modification, washing and drying to obtain modified biomass;
2. in the nitrogen atmosphere, firstly heating the pyrolysis furnace to 550 ℃ plus 450 ℃, then putting the modified biomass into the pyrolysis furnace for pyrolysis, then heating to 750 ℃ plus 650 ℃ at the average speed of 2-3 ℃/min, and then cooling to room temperature to obtain biochar;
3. carrying out deep chemical modification on the biochar to obtain modified biochar;
4. uniformly mixing absolute ethyl alcohol, ferrous salt, ultrapure water and modified biochar to obtain a suspension;
5. and (3) dropwise adding a reducing agent into the suspension to reduce ferrous ions in the nitrogen atmosphere, aging and reacting for 0.5-1h after dropwise adding is finished, filtering after the reaction is finished, washing and drying a filter cake, and crushing to obtain the biomass loaded nano zero-valent iron material.
Further, the biomass is one of coconut shells, walnut shells, rice straws and bamboo powder, or any combination of several of the above.
Further, the biomass or the biochar is soaked in 0.3-0.7mol/L hydrochloric acid, 0.3-0.7mol/L sodium hydroxide solution or 12-18wt% hydrogen peroxide solution for 6-10h, and then washed and dried.
Further, the biomass or the biochar is soaked in 0.8-1.2mol/L hydrochloric acid, 0.8-1.2mol/L sodium hydroxide solution or 25-35wt% hydrogen peroxide solution for 20-28h, and then washed and dried.
Further, the mass ratio of the modified biochar to the iron element is 1-3: 1.
Further, the reducing agent is sodium borohydride, and the ferrous salt is ferrous sulfate heptahydrate.
Further, the molar ratio of the sodium borohydride to the ferrous sulfate heptahydrate is 1: 1.1-1.3.
An application of a biochar loaded nano zero-valent iron material in removing selenium element in a water body.
Further, when the concentration of the selenium element in the water body is 10mg/L, the dosage of the biochar loaded nano zero-valent iron material is 0.7-1.3g/L of the water body, and when the concentration of the selenium element in the water body is increased by 10mg/L, the dosage of the biochar loaded nano zero-valent iron material is increased by 0.7-1.3g/L of the water body.
Compared with the prior art, the invention has the beneficial effects and advantages that:
1. the biochar loaded nano zero-valent iron material disclosed by the invention has the advantages that the biochar is used for loading and dispersing zero-valent iron, so that the material is in an active state for a long time, and the selenium (especially sodium selenite) removal efficiency is improved.
2. The biochar loaded nano zero-valent iron material is easy to separate from water, and has no biotoxicity of the traditional nano zero-valent iron.
3. The method adopts two special means of modification and temperature-changing calcination to prepare the biochar loaded nano zero-valent iron material, and the two ways greatly improve the biochar loaded nano zero-valent iron material, thereby greatly improving the selenium adsorption efficiency.
Drawings
Fig. 1 is an infrared spectrum of the biochar-supported nano zero-valent iron materials prepared in example 1, example 2, example 3 and comparative example 2.
Fig. 2 is a graph showing the adsorption removal effect of the biochar-supported nano zero-valent iron materials prepared in example 1, comparative example 2 and comparative example 3 on sodium selenite.
Fig. 3 is a graph showing the adsorption removal effect of the biochar-supported nano zero-valent iron material prepared in example 1, example 2, example 3 and comparative example 2 on sodium selenite.
Fig. 4 is a graph showing the adsorption removal effect of the biochar-supported nano zero-valent iron material prepared in example 1, example 7 and example 8 on sodium selenite.
Fig. 5 is a graph showing the adsorption removal effect of the biochar-supported nano zero-valent iron material prepared in example 3, example 4, example 5 and example 6 on sodium selenite.
Detailed Description
The present invention will be described in detail with reference to specific examples.
Example 1
1. Crushing the cleaned and dried rice straw, and sieving the crushed rice straw with a 100-mesh sieve to obtain rice straw powder;
2. soaking the rice straw powder in 0.5mol/L hydrochloric acid, stirring at a constant speed for 8h with a solid-liquid ratio of 1:50, washing with ultrapure water until the filtrate is neutral, and drying in a drying box at 105 ℃ for 12h to obtain modified rice straw powder;
3. heating a pyrolysis furnace to 500 ℃, introducing nitrogen into the pyrolysis furnace to enable the pyrolysis furnace to be in a nitrogen atmosphere, weighing 5g of modified rice straw powder, placing the modified rice straw powder into the pyrolysis furnace, heating to 700 ℃ at a speed of 2 ℃/min, and cooling to room temperature to obtain biochar;
4. soaking biochar in 1mol/L hydrochloric acid, stirring at a constant speed for 24h, washing with ultrapure water until the filtrate is neutral, and drying in a drying oven at 105 ℃ for 12h to obtain modified biochar, wherein the solid-to-liquid ratio is 1: 50;
5. into the Erlenmeyer flask were added 75ml of ultrapure water and 2.482g of ferrous sulfate heptahydrate (FeSO)4·7H2O), stirring to completely dissolve ferrous sulfate heptahydrate, adding 1g of modified biochar (carbon-iron ratio C: Fe is 2:1) into a conical flask, adding 75ml of absolute ethyl alcohol into the conical flask to disperse the biochar, and magnetically stirring the conical flask to uniformly disperse the biochar;
6. continuously introducing nitrogen into the conical flask, slowly dripping 50mL of 20g/L sodium borohydride solution into the conical flask after oxygen is removed completely, aging and reacting for 1h, filtering the obtained mixed solution after the reaction is finished, alternately cleaning a filter cake for three times by using absolute ethyl alcohol and ultrapure water, putting the obtained solid into a vacuum drying oven at 45 ℃ for drying for 24h, and finally crushing by using an agate mortar to obtain the biochar loaded nano zero-valent iron material which is recorded as BC-HCL-nZVI.
Example 2
1. Crushing the cleaned and dried rice straw, and sieving the crushed rice straw with a 100-mesh sieve to obtain rice straw powder;
2. soaking the rice straw powder in 15 wt% hydrogen peroxide and hydrochloric acid, stirring at a constant speed for 8h with a solid-to-liquid ratio of 1:50, washing with ultrapure water until the filtrate is neutral, and drying in a drying box at 105 ℃ for 12h to obtain modified rice straw powder;
3. heating a pyrolysis furnace to 500 ℃, introducing nitrogen into the pyrolysis furnace to enable the pyrolysis furnace to be in a nitrogen atmosphere, weighing 5g of modified rice straw powder, placing the modified rice straw powder into the pyrolysis furnace, heating to 700 ℃ at a speed of 2 ℃/min, and cooling to room temperature to obtain biochar;
4. soaking the biochar in 30 wt% hydrogen peroxide and stirring at a constant speed for 24 hours, wherein the solid-liquid ratio is 1:50, washing with ultrapure water until filtrate is neutral, then placing the filtrate into a drying box, and drying at 105 ℃ for 12 hours to obtain modified biochar;
5. into the Erlenmeyer flask were added 75ml of ultrapure water and 2.482g of ferrous sulfate heptahydrate (FeSO)4·7H2O), stirring to completely dissolve ferrous sulfate heptahydrate, adding 1g of modified biochar (carbon-iron ratio C: Fe is 2:1) into a conical flask, adding 75ml of absolute ethyl alcohol into the conical flask to disperse the biochar, and magnetically stirring the conical flask to uniformly disperse the biochar;
6. continuously introducing nitrogen into the conical flask, slowly dripping 50mL of 20g/L sodium borohydride solution into the conical flask after oxygen is removed completely, aging and reacting for 1h, filtering the obtained mixed solution after the reaction is finished, alternately cleaning a filter cake for three times by using absolute ethyl alcohol and ultrapure water, putting the obtained solid into a vacuum drying oven at 45 ℃ for drying for 24h, and finally crushing by using an agate mortar to obtain the biochar loaded nano zero-valent iron material which is recorded as BC-HCL-nZVI.
Example 3
1. Crushing the cleaned and dried rice straw, and sieving the crushed rice straw with a 100-mesh sieve to obtain rice straw powder;
2. soaking the rice straw powder in 0.5mol/L sodium hydroxide, stirring at a constant speed for 8h with a solid-liquid ratio of 1:50, washing with ultrapure water until the filtrate is neutral, then placing into a drying oven, and drying at 105 ℃ for 12h to obtain modified rice straw powder;
3. heating a pyrolysis furnace to 500 ℃, introducing nitrogen into the pyrolysis furnace to enable the pyrolysis furnace to be in a nitrogen atmosphere, weighing 5g of modified rice straw powder, placing the modified rice straw powder into the pyrolysis furnace, heating to 700 ℃ at a speed of 2 ℃/min, and cooling to room temperature to obtain biochar;
4. soaking the biochar in 1mol/L sodium hydroxide, stirring at a constant speed for 24 hours, washing with ultrapure water until the filtrate is neutral, then placing the filtrate into a drying box, and drying at 105 ℃ for 12 hours to obtain modified biochar, wherein the solid-to-liquid ratio is 1: 50;
5. into the Erlenmeyer flask were added 75ml of ultrapure water and 2.482g of ferrous sulfate heptahydrate (FeSO)4·7H2O), stirring to completely dissolve ferrous sulfate heptahydrate, adding 1g of modified biochar (carbon-iron ratio C: Fe is 2:1) into a conical flask, adding 75ml of absolute ethyl alcohol into the conical flask to disperse the biochar, and magnetically stirring the conical flask to uniformly disperse the biochar;
6. continuously introducing nitrogen into the conical flask, slowly dripping 50mL of 20g/L sodium borohydride solution into the conical flask after oxygen is completely removed, aging and reacting for 1h after the dripping is completed, filtering the obtained mixed solution after the reaction is completed, alternately cleaning a filter cake for three times by using absolute ethyl alcohol and ultrapure water, putting the obtained solid into a vacuum drying oven at 45 ℃ for drying for 24h, and finally crushing by using an agate mortar to obtain the biochar loaded nano zero-valent iron material which is recorded as BC-NaOH-nZVI.
Example 4
The same procedure and procedure as in example 3 were followed, with the only difference that 2g of modified biochar was added to the erlenmeyer flask (carbon to iron ratio C: Fe ═ 4: 1).
Example 5
The same procedure and procedure as in example 3 were followed, except that 3g of modified biochar was added to the erlenmeyer flask (carbon to iron ratio C: Fe ═ 6: 1).
Example 6
The same procedure and procedure as in example 3 were followed, except that 0.5g of modified biochar was added to the erlenmeyer flask (carbon to iron ratio C: Fe ═ 1: 1).
Example 7
The procedure and procedure were the same as in example 1, except that the rice straw was replaced with wood chips.
Example 8
The operation method and the steps are the same as those of the example 1, and the only difference is that the rice straws are changed into the bamboo powder.
Comparative example 1
1. Crushing the cleaned and dried rice straw, and sieving the crushed rice straw with a 100-mesh sieve to obtain rice straw powder;
2. soaking the rice straw powder in 0.5mol/L hydrochloric acid, stirring at a constant speed for 8h with a solid-liquid ratio of 1:50, washing with ultrapure water until the filtrate is neutral, and drying in a drying box at 105 ℃ for 12h to obtain modified rice straw powder;
3. heating a pyrolysis furnace to 700 ℃, simultaneously introducing nitrogen into the pyrolysis furnace to enable the pyrolysis furnace to be in a nitrogen atmosphere, weighing 5g of modified rice straw powder, placing the modified rice straw powder into the pyrolysis furnace, pyrolyzing the modified rice straw powder for 100min at 700 ℃, and cooling the modified rice straw powder to room temperature to obtain biochar;
4. soaking biochar in 1mol/L hydrochloric acid, stirring at a constant speed for 24h, washing with ultrapure water until the filtrate is neutral, and drying in a drying oven at 105 ℃ for 12h to obtain modified biochar, wherein the solid-to-liquid ratio is 1: 50;
5. into the Erlenmeyer flask were added 75ml of ultrapure water and 2.482g of ferrous sulfate heptahydrate (FeSO)4·7H2O), stirring to completely dissolve ferrous sulfate heptahydrate, adding 1g of modified biochar (carbon-iron ratio C: Fe is 2:1) into a conical flask, adding 75ml of absolute ethyl alcohol into the conical flask to disperse the biochar, and magnetically stirring the conical flask to uniformly disperse the biochar;
6. continuously introducing nitrogen into the conical flask, slowly dripping 50mL of 20g/L sodium borohydride solution into the conical flask after oxygen is completely removed, aging and reacting for 1h after the dripping is completed, filtering the obtained mixed solution after the reaction is completed, alternately cleaning a filter cake for three times by using absolute ethyl alcohol and ultrapure water, drying the obtained solid in a vacuum drying oven at 45 ℃ for 24h, and finally crushing by using an agate mortar to obtain the biochar loaded nano zero-valent iron material.
Comparative example 2
1. Crushing the cleaned and dried rice straw, and sieving the crushed rice straw with a 100-mesh sieve to obtain rice straw powder;
2. heating a pyrolysis furnace to 500 ℃, simultaneously introducing nitrogen into the pyrolysis furnace to enable the pyrolysis furnace to be in a nitrogen atmosphere, weighing 5g of rice straw powder, placing the rice straw powder into the pyrolysis furnace, heating to 700 ℃ at the speed of 2 ℃/min, and cooling to room temperature to obtain biochar;
3. into the Erlenmeyer flask were added 75ml of ultrapure water and 2.482g of ferrous sulfate heptahydrate (FeSO)4·7H2O), stirring to completely dissolve ferrous sulfate heptahydrate, adding 1g of biochar (carbon-iron ratio C: Fe is 2:1) into the conical flask, adding 75ml of absolute ethyl alcohol into the conical flask to disperse the biochar, and magnetically stirring the conical flask to uniformly disperse the biochar;
4. continuously introducing nitrogen into the conical flask, slowly dripping 50mL of 20g/L sodium borohydride solution into the conical flask after oxygen is completely removed, aging and reacting for 1h after the dripping is completed, filtering the obtained mixed solution after the reaction is completed, alternately cleaning a filter cake for three times by using absolute ethyl alcohol and ultrapure water, putting the obtained solid into a vacuum drying oven at 45 ℃ for drying for 24h, and finally crushing by using an agate mortar to obtain the biochar loaded nano zero-valent iron material which is recorded as BC-nZVI.
Comparative example 3
1. Crushing the cleaned and dried rice straw, and sieving the crushed rice straw with a 100-mesh sieve to obtain rice straw powder;
2. heating a pyrolysis furnace to 700 ℃, simultaneously introducing nitrogen into the pyrolysis furnace to enable the pyrolysis furnace to be in a nitrogen atmosphere, weighing 5g of rice straw powder, placing the rice straw powder into the pyrolysis furnace, pyrolyzing the rice straw powder for 100min at 700 ℃, and cooling the rice straw powder to room temperature to obtain biochar;
3. into the Erlenmeyer flask were added 75ml of ultrapure water and 2.482g of ferrous sulfate heptahydrate (FeSO)4·7H2O), stirring to completely dissolve ferrous sulfate heptahydrate, adding 1g of biochar (carbon-iron ratio C: Fe is 2:1) into the conical flask, adding 75ml of absolute ethyl alcohol into the conical flask to disperse the biochar, and magnetically stirring the conical flask to uniformly disperse the biochar;
4. continuously introducing nitrogen into the conical flask, slowly dripping 50mL of 20g/L sodium borohydride solution into the conical flask after oxygen is completely removed, aging and reacting for 1h after the dripping is completed, filtering the obtained mixed solution after the reaction is completed, alternately cleaning a filter cake for three times by using absolute ethyl alcohol and ultrapure water, drying the obtained solid in a vacuum drying oven at 45 ℃ for 24h, and finally crushing by using an agate mortar to obtain the biochar loaded nano zero-valent iron material.
The biochar loaded nano zero-valent iron materials prepared in example 1, example 2, example 3 and comparative example 2 are subjected to infrared spectrum analysis, the obtained Fourier infrared spectrum (FTIR) spectrum is shown in figure 1, and 3500-4000cm-1The absorption peak at (B) represents an-OH group, 2800-3000cm-1The absorption peak at (A) represents the fatty C-H bond, 1650-1770cm-1The absorption peak at (A) represents a carbonyl group C ═ O bond, 1450--1The absorption peak at (B) represents aromatic C ═ C bond, 1000--1The absorption peak at (A) represents an ether bond C-O bond, 650-910cm-1The absorption peak represents a benzene ring substitution area, and the modified biochar has more abundant functional groups beneficial to adsorption.
First, the test for removing selenium in water by using the biochar loaded nano zero-valent iron material
The test method comprises the following steps:
respectively putting 50mL of 10mg/L sodium selenite solution into 450 mL centrifuge tubes, respectively adding 50mg of the biochar-loaded nano zero-valent iron material prepared in example 1 and comparative examples 1, 2 and 3 into the centrifuge tubes, uniformly mixing, putting the centrifuge tubes into a constant-temperature water bath shaking table, performing shaking adsorption for 2 hours at 25 ℃ and 300r/min, taking out the centrifuge tubes, putting the centrifuge tubes into a centrifuge, centrifuging for 10 minutes at the rotating speed of 4000r/min, taking 10mL of supernate after centrifugation, measuring the final concentration of sodium selenite in the supernate by using an atomic absorption spectrophotometer, and calculating the removal rate of the sodium selenite according to the initial concentration and the final concentration of the sodium selenite.
And (3) test results:
the removal rate of sodium selenite from the biochar-supported nano zero-valent iron material prepared in example 1 is 82.1%, the removal rate of sodium selenite from the biochar-supported nano zero-valent iron material prepared in comparative example 1 is 64.7%, the removal rate of sodium selenite from the biochar-supported nano zero-valent iron material prepared in comparative example 2 is 71.8%, and the removal rate of sodium selenite from the biochar-supported nano zero-valent iron material prepared in comparative example 3 is 45.5%, and the specific result is shown in fig. 2, and the adsorption effect of the biochar-supported nano zero-valent iron material on selenium in a water body can be improved by using a modification and temperature-changing pyrolysis mode.
Second test, test for removing selenium in water body by using biochar loaded nano zero-valent iron material obtained by different modification methods
The test method comprises the following steps:
respectively putting 50mL of 10mg/L sodium selenite solution into four 50mL centrifuge tubes, respectively adding 50mg of the biochar-loaded nano zero-valent iron material prepared in the example 1, the example 2, the example 3 and the comparative example 2 into the four centrifuge tubes, uniformly mixing, putting the centrifuge tubes into a constant-temperature water bath shaking table, performing oscillation adsorption for 2 hours at 25 ℃ and 300r/min, taking out the centrifuge tubes, putting the centrifuge tubes into a centrifuge, centrifuging for 10 minutes at the rotating speed of 4000r/min, taking 10mL of supernate after centrifugation, measuring the final concentration of sodium selenite in the supernate by using an atomic absorption spectrophotometer, and calculating the removal rate of the sodium selenite according to the initial concentration and the final concentration of the sodium selenite.
And (3) test results:
as shown in fig. 3, it can be seen from fig. 3 that the effect of removing selenium of the biochar-supported nano zero-valent iron material obtained after the modification treatment with the sodium hydroxide solution and the hydrochloric acid is better than that of the biochar-supported nano zero-valent iron material obtained without the modification treatment, and the effect of removing the biochar-supported nano zero-valent iron material obtained after the modification treatment with the sodium hydroxide solution is the best and is as high as 90% in the modification treatment with the hydrochloric acid and the sodium hydroxide solution.
Third, the test of removing selenium in water body by the biochar loaded nano zero-valent iron material obtained from different biomass raw materials
The test method comprises the following steps:
respectively putting 50mL of 10mg/L sodium selenite solution into three 50mL centrifuge tubes, respectively adding 50mg of the biochar-loaded nano zero-valent iron material prepared in example 1, example 7 and example 8 into the two centrifuge tubes, uniformly mixing, putting the centrifuge tubes into a constant-temperature water bath shaker, performing shaking adsorption for 2 hours at 25 ℃ and 300r/min, taking out the centrifuge tubes, putting the centrifuge tubes into a centrifuge, centrifuging for 10 minutes at the rotating speed of 4000r/min, taking 10mL of supernate after centrifugation, measuring the final concentration of sodium selenite in the supernate by using an atomic absorption spectrophotometer, and calculating the removal rate of the sodium selenite according to the initial concentration and the final concentration of the sodium selenite.
And (3) test results:
as shown in fig. 4, it can be seen from fig. 4 that the biochar-supported nano zero-valent iron material prepared by using bamboo powder as the biomass raw material has the best effect of removing selenium by adsorption, and the adsorption rate is as high as 90% or more.
Fourth, the invention uses the biological charcoal obtained by different carbon-iron ratios to load the nano zero-valent iron material to remove the selenium in the water body
The test method comprises the following steps:
respectively putting 50mL of 10mg/L sodium selenite solution into three 50mL centrifuge tubes, respectively adding 50mg of the biochar-loaded nano zero-valent iron material prepared in the examples 3, 4, 5 and 6 into the two centrifuge tubes, uniformly mixing, putting the centrifuge tubes into a constant-temperature water bath shaker, oscillating and adsorbing for 2 hours at 25 ℃ and 300r/min, taking out the centrifuge tubes, putting the centrifuge tubes into a centrifuge, centrifuging for 10min at the rotating speed of 4000r/min, taking 10mL of supernate after centrifugation, measuring the final concentration of sodium selenite in the supernate by using an atomic absorption spectrophotometer, and calculating the removal rate of the sodium selenite according to the initial concentration and the final concentration of the sodium selenite.
And (3) test results:
as shown in fig. 5, it can be seen from fig. 5 that the biochar loaded nano zero-valent iron material prepared at a carbon-iron ratio of 2:1 has the best effect of removing selenium by adsorption, and the adsorption rate is as high as 90% or more.
Claims (3)
1. A biochar loaded nano zero-valent iron material is characterized by being prepared by the following method:
1.1, crushing biomass to obtain biomass powder, crushing the biomass to perform primary chemical modification, washing and drying to obtain modified biomass;
1.2, under the nitrogen atmosphere, firstly heating the pyrolysis furnace to 550 ℃ below zero at 450-;
1.3, carrying out deep chemical modification on the biochar to obtain modified biochar;
1.4, uniformly mixing absolute ethyl alcohol, ferrous salt, ultrapure water and modified biochar to obtain a suspension;
1.5, dropwise adding a reducing agent into the suspension to reduce ferrous ions in the nitrogen atmosphere, after the dropwise adding is completed, carrying out aging reaction for 0.5-1h, after the reaction is completed, filtering, washing and drying a filter cake, and crushing to obtain the biochar loaded nano zero-valent iron material;
the biomass is one or any combination of sawdust, coconut shells, walnut shells, rice straws and bamboo powder;
the primary chemical modification method comprises the following steps: soaking biomass in 0.3-0.7mol/L hydrochloric acid, 0.3-0.7mol/L sodium hydroxide solution or 12-18wt% hydrogen peroxide solution for 6-10 hr, washing and drying;
the deep chemical modification method comprises the following steps: firstly, soaking the biochar for 20-28h by using 0.8-1.2mol/L hydrochloric acid, 0.8-1.2mol/L sodium hydroxide solution or 25-35wt% hydrogen peroxide solution, and then washing and drying;
the same modifier is used in the primary chemical modification and the deep chemical modification;
the mass ratio of the modified biochar to the iron element is 1-6: 1;
the reducing agent is sodium borohydride, and the ferrous salt is ferrous sulfate heptahydrate;
the molar ratio of the sodium borohydride to the ferrous sulfate heptahydrate is 1: 1.1-1.3.
2. The application of the biochar-loaded nano zero-valent iron material of claim 1 in removing selenium in water.
3. The application of the biochar-loaded nano zero-valent iron material according to claim 2, wherein the biochar-loaded nano zero-valent iron material comprises the following components in percentage by weight: when the concentration of the selenium element in the water body is 10mg/L, the dosage of the biochar loaded nano zero-valent iron material is 0.7-1.3g/L of the water body, and when the concentration of the selenium element in the water body is increased by 10mg/L, the dosage of the biochar loaded nano zero-valent iron material is increased by 0.7-1.3g/L of the water body.
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