CN111346591B

CN111346591B - Iron-based-bentonite/carbon composite porous material, and preparation method and application thereof

Info

Publication number: CN111346591B
Application number: CN202010200894.4A
Authority: CN
Inventors: 屈敏; 陈辉霞; 王兴润; 黄涛; 李书鹏; 徐红彬
Original assignee: Institute of Process Engineering of CAS
Current assignee: Institute of Process Engineering of CAS
Priority date: 2020-03-20
Filing date: 2020-03-20
Publication date: 2021-07-09
Anticipated expiration: 2040-03-20
Also published as: CN111346591A

Abstract

The invention relates to an iron-based-bentonite/carbon composite porous material, a preparation method and application thereof. The composite porous material comprises a bentonite porous framework, and iron powder and carbon which are distributed on the outer surface and the inner surface of the pores of the bentonite porous framework. The composite porous material has controllable structure, high compressive strength and good stability, can effectively remove hexavalent chromium, has a removal rate of over 85 percent, and has good application prospects in the aspects of chromium-containing wastewater treatment, chromium-containing groundwater permeable reactive barrier repair and the like. The preparation method has simple process, can realize the regulation and control of the structure of the composite porous material by matching of all the raw materials and the process, and has the characteristics of low production cost and easy large-scale production.

Description

Iron-based-bentonite/carbon composite porous material, and preparation method and application thereof

Technical Field

The invention relates to the technical field of environmental remediation, in particular to an iron-based-bentonite/carbon composite porous material, and a preparation method and application thereof.

Background

Environmental pollution becomes a focus of attention of people, wherein underground water pollution is the most serious, and iron powder is used as a commonly used reducing agent, so that the iron powder has a removing effect on various pollutants (such as chromium, arsenic, cadmium, copper and chlorine-containing organic matters), is environment-friendly, cheap and easy to obtain. In recent 20 years, iron powder has been widely used for groundwater and sewage treatment. However, the iron powder corrosion and the ferric hydroxide deposition lead to the volume expansion of the iron powder, the long-acting activity of the reaction medium is reduced, and the permeability of the reaction wall is reduced. Therefore, the iron powder needs to be fixed and dispersed to prepare the iron-based composite filler, so that a loose and porous framework with good stability is provided for the iron powder.

Currently, the fixed dispersion for iron powder is mainly divided into two types: gel curing dispersion and inorganic porous skeleton dispersion. Gel-fixing dispersion is an organic composite filler formed by dispersing iron powder in a sodium alginate solution and then calcifying the iron powder/gel dispersion system, but the main problem of the filler is that the strength is too low. The inorganic porous framework dispersion is formed by simply mechanically mixing iron powder, a pore-forming agent and a framework material, adding water for forming or pressing for forming to obtain a pyrolysis precursor, and roasting and pyrolyzing to obtain the loose and porous inorganic roasted composite filler.

The inorganic porous skeleton dispersion is an inorganic filler which is cheap and easy to obtain and has large specific surface area, and is a skeleton material with excellent performance due to good water resistance. Some studies on inorganic composite fillers have been conducted.

CN106006854A discloses a bentonite-based iron-carbon ceramsite filler and a preparation method thereof, wherein the bentonite-based iron-carbon ceramsite filler is composed of scrap iron, activated carbon powder, bentonite and poplar wood powder, and the preparation method comprises the following steps: uniformly mixing the sieved scrap iron, activated carbon powder, bentonite and poplar wood powder, adding water to adjust the dryness of the mixture to 80%, pressing the mixture into a mud cake, and then granulating and firing the mud cake to obtain the bentonite-based iron-carbon ceramsite filler.

CN105967284A discloses a preparation method of a diatomite-based iron-carbon ceramsite filler, which comprises the following steps: (1) sieving scrap iron, activated carbon powder and diatomite and preparing a starch solution, (2) mixing the scrap iron, the activated carbon powder, the diatomite, ammonium sulfate and the starch solution in proportion and pressing into a mud cake, (3) feeding the mud cake into a granulator to prepare spherical filler with the diameter of 10-15 mm, and then firing to obtain the spherical diatomite-based iron-carbon ceramsite filler.

CN109911990A discloses a preparation method of a high-activity iron-carbon micro-electrolysis filler, which mainly comprises the following steps: (1) mixing an iron-based material and a carbon-based material precursor in proportion, and performing ultrasonic strengthening, (2) carbonizing the mixture in the step (1) to obtain an iron-based material carbide, (3) mechanically forming the iron-based material carbide and a binder to obtain an iron-carbon material precursor, and (4) sintering the iron-carbon material precursor at a high temperature to obtain the high-activity iron-carbon micro-electrolysis filler.

However, these prior studies have been directed to simply mechanically mixing iron powder with a pyrolytic precursor followed by mechanical granulation or press forming. The problems with these methods are: the density difference between the iron powder and other powder is large, and the dispersion is not uniform; the water adding amount needs to be accurately controlled in the water adding forming process, and the iron powder is easily coated in the framework in the pressing forming process.

Therefore, the development of a composite material with controllable structure, high compressive strength and macroporous structure enables iron powder to be uniformly distributed on the surface of the framework and to be firmly combined with the framework, and becomes the key point of current research.

Disclosure of Invention

In view of the problems in the prior art, the invention provides an iron-based-bentonite/carbon composite porous material, and a preparation method and application thereof. The composite porous material has high compressive strength and controllable structure, and the iron powder in the composite porous material is uniformly distributed on the outer surface and the inner surface of the hole of the bentonite framework, so that the iron powder is ensured to be fully contacted with reactants, and the composite porous material has good application prospects in the aspects of chromium-containing wastewater treatment, chromium-containing underground water permeable reactive wall repair and the like when being used as a filler. The preparation method has the advantages of simple process, low production cost and easy large-scale production.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides an iron-based-bentonite/carbon composite porous material, which comprises a bentonite porous framework, and iron powder and carbon distributed on the outer surface and the inner surface of pores of the bentonite porous framework.

In the invention, the distribution is preferably uniform, that is, the iron powder and the carbon are uniformly distributed on the outer surface and the inner surface of the pores of the porous bentonite framework.

According to the iron-based-bentonite/carbon composite porous material provided by the invention, iron powder is uniformly distributed on the outer surface and the inner surface of the pores of the bentonite porous framework, and the unique structure enables the iron powder to be firmly contacted with the framework and uniformly dispersed, so that the contact area between the iron powder and a reactant is increased; on the other hand, the specific surface area of the material is increased by the pore structure in the porous framework, so that the diffusion of pollutants in a water phase is facilitated and the reaction rate is increased when the material is used for water treatment. The composite porous material has controllable structure, high compressive strength, good stability and water resistance, and can remove hexavalent chromium in chromium-containing wastewater through adsorption, reduction and coprecipitation, wherein iron powder plays a main role in removing hexavalent chromium.

Compared with the prior art, the iron-based-bentonite/carbon composite porous material provided by the invention has the advantages that iron powder is uniformly distributed on the outer surface and the inner surface of the pores of the bentonite framework, the problem that part of iron powder is wrapped in the bentonite in the prior art and cannot fully play a role is solved, the problem that the iron powder is hardened and blocked in the water treatment process is also solved, and the iron-based-bentonite/carbon composite porous material has good application prospects in the aspects of chromium-containing wastewater treatment, chromium-containing groundwater permeable reactive wall repair and the like.

Preferably, the iron powder comprises any one of reduced iron powder, cast iron powder or recycled iron powder or a combination of at least two thereof, among which typical but non-limiting combinations are: reduced iron powder and cast iron powder, reduced iron powder and regenerated iron powder, cast iron powder and regenerated iron powder, preferably reduced iron powder.

Preferably, the particle size of the iron powder is in the range of 100 to 600 mesh, and may be, for example, 100 mesh, 105 mesh, 110 mesh, 120 mesh, 150 mesh, 200 mesh, 250 mesh, 300 mesh, 350 mesh, 400 mesh, 450 mesh, 500 mesh, 550 mesh, 600 mesh, or the like, but is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned value range are also applicable, and 300 to 400 mesh is preferable. The particle size of the iron powder affects the uniformity and activity of its distribution.

Preferably, the carbon comprises porous carbon which enhances the adsorption capacity of the composite porous material.

Preferably, the composite porous material contains macropores having a pore size in the range of 5 to 50 μm, for example, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm, but not limited to the above-mentioned values, and other values not mentioned in the above-mentioned value range are also applicable, and preferably 5 to 20 μm. If the pore diameter is less than 5 mu m, the pore channels are fewer, which is not beneficial to the diffusion of pollutants in the water phase; the aperture is larger than 20 mu m, and the iron powder is wrapped by amorphous carbon due to excessive pore-forming agent addition, so that the contact area of pollutants and the iron powder is reduced.

Preferably, the shape of the composite porous material comprises a sphere and/or a column.

Preferably, the particle size of the composite porous material is in mm, the particle size is preferably 3 to 10mm, and may be, for example, 3mm, 5mm, 8mm, 10mm, etc., but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

In the invention, the "particle size is in millimeter level" means that the diameter of the spherical composite porous material is in millimeter level, and the diameter and the length of the columnar composite porous material are in millimeter level.

In a second aspect, the present invention provides a method for preparing an iron-based-bentonite/carbon composite porous material as described in the first aspect, the method comprising the steps of:

(1) mixing a sodium alginate solution with iron powder for the first time, and then mixing the sodium alginate solution with bentonite and a pore-forming agent for the second time to obtain a mixture;

(2) adding the mixture obtained in the step (1) into a solution containing calcium ions for solidification to form a pyrolysis precursor;

(3) and (3) roasting the pyrolysis precursor obtained in the step (2) in an inert atmosphere for two sections to obtain the iron-based-bentonite/carbon composite porous material.

According to the preparation method provided by the invention, sodium alginate is an organic compound capable of being dispersed in water, is a good dispersing agent, and can play a role in dispersing iron powder, so that the iron powder is prevented from being agglomerated, and the iron powder is uniformly distributed in a sodium alginate solution; sodium alginate is also used as a forming agent of a pyrolysis precursor, and can generate a crosslinking reaction with calcium ions to form a crosslinking network, so that a sodium alginate solution and calcium ion crosslinking method is a good material forming method; in addition, the sodium alginate and the pore-forming agent are roasted to obtain the amorphous carbon.

According to the preparation method provided by the invention, iron powder plays a main role in removing hexavalent chromium, so that the composite porous material can remove hexavalent chromium in chromium-containing wastewater through adsorption, reduction and coprecipitation. The bentonite is an inorganic compound with a layered structure, has a stable structure after losing bound water at high temperature, and can improve the compressive strength of the composite porous material.

According to the preparation method provided by the invention, the iron powder is uniformly dispersed in the sodium alginate solution through the dispersion effect of the sodium alginate, and then is mixed with the pore-forming agent and the bentonite, so that the iron powder and the carbon are uniformly distributed on the outer surface and the inner surface of the pore of the bentonite through the combination of the cross-linking and curing of calcium ions and the sodium alginate, the regulation and control of the pore-forming agent and the roasting process. The method has simple process, can realize the regulation and control of the structure of the composite porous material by matching various raw materials and processes, has the characteristics of low production cost and easy large-scale production, and has higher application value.

Preferably, the concentration of the sodium alginate solution in step (1) is 1-4 wt%, such as 1 wt%, 1.5 wt%, 2 wt%, 2.5wt%, 3 wt%, 3.5 wt%, or 4wt%, but not limited to the recited values, and other values within the range are also applicable, preferably 1.5-2.5 wt%. If the concentration is lower than 1 wt%, the viscosity is not enough, and the iron powder is easy to aggregate and precipitate and is not beneficial to uniform dispersion of the iron powder; the concentration is higher than 4wt%, the viscosity is too high, the difficulty of uniform dispersion is increased, and simultaneously, the waste of resources is also caused.

Preferably, the iron powder in step (1) comprises any one of or a combination of at least two of cast iron powder, reduced iron powder or recycled iron powder, wherein the typical but non-limiting combination is: the iron powder is preferably reduced iron powder which has less impurities and higher activity.

Preferably, the particle size of the iron powder in step (1) is in the range of 100 to 600 mesh, and may be 100 mesh, 200 mesh, 300 mesh, 400 mesh, 500 mesh, 600 mesh, etc., but is not limited to the recited values, and other values in the range of the recited values are also applicable, and preferably 300 to 400 mesh; if the size is larger than 300 meshes, the distribution effect of the iron powder is influenced, and porous framework pore channels are blocked; if the particle size of the iron powder is smaller than 400 meshes, the cost is greatly increased.

In the step (1), the mass ratio of the iron powder to the sodium alginate solution is preferably (2-10): 100, and may be, for example, 2:100, 3:100, 5:100, 8:100, or 10:100, but the ratio is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned range are also applicable, and preferably (3-5): 100. If the mass ratio is less than 2:100, the iron content in the material is low, so that the chromium removal efficiency of the material is reduced; if the mass ratio is more than 10:100, the dispersion of the iron powder is not uniform, resulting in waste of the iron powder.

The mass ratio of bentonite to sodium alginate solution in step (1) is preferably (6-30): 100, and may be, for example, 6:100, 8:100, 10:100, 15:100, 20:100, 25:100, or 30:100, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable, and preferably (8-20): 100. If the mass ratio is less than 6:100, the strength of the finally obtained material is reduced; if the mass ratio is greater than 30:100, the strength of the finally obtained material is higher, and the porosity of the material is reduced.

Preferably, the pore-forming agent in step (1) comprises any one or a combination of at least two of starch, glucose or sucrose, preferably starch, which has good solubility and generates more pores when being roasted.

In the step (1), the mass ratio of the pore-forming agent to the sodium alginate solution is preferably (0 to 15):100, and may be, for example, 0:100, 0.5:100, 1:100, 3:100, 5:100, 8:100, 10:100, 12:100, or 15:100, but is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned range are also applicable, and preferably (0.5 to 4): 100. If the mass ratio is more than 15:100, the number of the material pore channels is increased, but too much pore-forming agent can lead the iron powder to be wrapped by carbon, the chromium removal effect is seriously reduced, and too much pore-forming agent can lead the compressive strength to be reduced.

Preferably, the primary mixing and the secondary mixing in step (1) independently include any one or a combination of at least two of mechanical stirring, ultrasonic dispersion or oscillatory dispersion, and the term "independently" means that the primary mixing and the secondary mixing are not mutually affected, and if the primary mixing is mechanical stirring, the secondary mixing may be mechanical stirring, ultrasonic dispersion or oscillatory dispersion.

Preferably, the time for the first mixing and the second mixing in step (1) is independently 30 to 180min, such as 30min, 60min, 120min, 150min or 180min, but not limited to the recited values, and other non-recited values within the range are also applicable, preferably 30 to 60 min. The term "independently" means that the time of the first mixing and the time of the second mixing are not affected, and if the time of the first mixing is 30min, the time of the second mixing may be 30min or 40 min.

Preferably, the calcium ion-containing solution in step (2) includes any one of or a combination of at least two of a calcium chloride solution, a calcium sulfate solution, a calcium nitrate solution, or a calcium hydroxide solution, wherein typical but non-limiting combinations are a calcium chloride solution and a calcium sulfate solution, a calcium sulfate solution and a calcium nitrate solution, a calcium chloride solution, a calcium sulfate solution and a calcium nitrate solution, and the like.

Preferably, the calcium ion concentration in the calcium ion-containing solution in step (2) is 0.1 to 1mol/L, for example, 0.1mol/L, 0.2mol/L, 0.3mol/L, 0.4mol/L, 0.5mol/L, 0.6mol/L, 0.7mol/L, 0.8mol/L, 0.9mol/L, or 1mol/L, but not limited to the values listed, and other values not listed in the range of the values are also applicable, preferably 0.3 to 0.5 mol/L. If the concentration is lower than 0.1mol/L, the crosslinking reaction in the step (2) is not firm, and a pyrolysis precursor with a fixed morphology cannot be obtained; the concentration is higher than 1mol/L, the performance of the product cannot be improved, and the raw materials are wasted to increase the cost.

Preferably, the molar ratio of calcium ions to sodium alginate in the calcium ion-containing solution in step (2) is (0.2-3): 1, and may be, for example, 0.2:1, 0.5:1, 0.6:1, 0.9:1, 1.2:1, 1.5:1, 2:1, 2.5:1 or 3:1, but is not limited to the values listed, and other values not listed within this range are also applicable, and are preferably (0.5-1.5): 1. If the mass ratio is less than 0.5:1, the crosslinking effect of the sodium alginate is poor, so that the molding of the material is not facilitated; the mass ratio is more than 3:1, which has no better benefit on the forming effect and can cause the waste of resources.

Preferably, the manner of addition in step (2) comprises dropwise addition.

In the present invention, the method of dropwise addition is not particularly limited, and any method commonly used by those skilled in the art can be applied to the present invention.

Preferably, the method of dropwise addition comprises injection extrusion and/or mechanical delivery.

Preferably, the curing time in step (2) is 1 to 10 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours, but not limited to the recited values, and other values not recited in the range of the values are also applicable, preferably 3 to 6 hours. If the curing time is less than 1h, incomplete crosslinking reaction of the sodium alginate can be caused, and the appearance of the pyrolysis precursor is unstable; the curing time is more than 10h, so that the performance of the product cannot be improved, and the production period is increased.

Preferably, the pyrolysis precursor in step (2) has a shape including a sphere and/or a column, preferably a sphere.

Preferably, the gas of the inert atmosphere in step (3) comprises any one of nitrogen, argon or helium or a combination of at least two thereof, a typical but non-limiting combination being a combination of nitrogen and argon.

Preferably, the gas flow rate of the inert atmosphere in step (3) is 5 to 400mL/min, for example, 5mL/min, 10mL/min, 30mL/min, 50mL/min, 100mL/min, 150mL/min, 200mL/min, 250mL/min, 300mL/min, 350mL/min, or 400mL/min, but not limited to the values listed, and other values not listed in the range of the values are also applicable, preferably 30 to 200 mL/min.

As a preferred technical scheme of the invention, the two-stage roasting in the step (3) comprises primary roasting and secondary roasting which are sequentially carried out. The primary roasting evaporates the water in the material, improves the carbon yield in the secondary roasting, and avoids the problem that the iron powder cannot be firmly embedded into the framework due to overlarge pore channels; the secondary roasting is carried out to increase the roasting temperature, the organic matters (sodium alginate and pore-forming agent) are pyrolyzed to obtain amorphous carbon, and meanwhile, the structure is changed to form porous carbon; the bentonite loses interlayer bound water to form a high-strength framework structure.

Preferably, the temperature of the primary baking is 80 to 150 ℃, for example, 80 ℃, 90 ℃, 100 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃ or 150 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable, preferably 100 to 120 ℃. The setting of the primary roasting temperature ensures the evaporation of water in the material, if the primary roasting is omitted, the temperature is directly raised to a higher temperature (for example, more than 500 ℃), the excessive loss of inorganic carbon obtained by the pyrolysis of organic matters can be caused, the unstable skeleton can be caused by the excessive decomposition of carbon, the iron powder is not firmly fixed, and finally the quality of the iron-based-bentonite/carbon composite porous material is seriously degraded.

Preferably, the temperature increase rate of the primary baking is 1 to 10 ℃/min, and for example, 1 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min, 5 ℃/min, 6 ℃/min, 7 ℃/min, 8 ℃/min, or 10 ℃/min, etc., but not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable, and preferably 4 to 8 ℃/min.

Preferably, the time for the first baking is 0.1 to 6 hours, for example, 0.1 hour, 0.5 hour, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable, preferably 0.5 to 2 hours.

Preferably, the temperature of the secondary baking is 100 to 1000 ℃, for example, 400 ℃, 500 ℃, 600 ℃, 700 ℃, or 800 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable, preferably 400 to 800 ℃. The second-stage temperature is set by selecting proper temperature according to different pore-forming agents so as to ensure that all organic components in the pore-forming agents are converted into inorganic carbon, and simultaneously, bentonite loses interlayer bound water in secondary roasting, so that the prepared iron-based-bentonite/carbon composite porous material is loose and porous and has a stable structure.

Preferably, the temperature increase rate of the secondary baking is 1 to 10 ℃/min, and for example, 1 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min, 5 ℃/min, 6 ℃/min, 7 ℃/min, 8 ℃/min, or 10 ℃/min, etc., but not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable, and preferably 4 to 8 ℃/min.

Preferably, the time for the secondary baking is 1 to 10 hours, for example, 1 hour, 1.5 hours, 2 hours, 4 hours, 5 hours, 7 hours, 9 hours, 10 hours, etc., but is not limited to the recited values, and other values within the range are also applicable, preferably 2 to 4 hours.

As a further preferred embodiment of the present invention, the method comprises the steps of:

(1) preparing 1.5-2.5 wt% of sodium alginate solution;

(2) mixing iron powder and a sodium alginate solution, controlling the mass ratio of the iron powder to the sodium alginate solution to be (3-5): 100, then mixing the mixture with bentonite and starch, controlling the mass ratio of the bentonite to the sodium alginate solution to be (8-20): 100, controlling the mass ratio of the starch to the sodium alginate solution to be (0.5-4): 100, and mechanically stirring the mixture for 30-60 min to obtain a mixture;

(3) adding the mixture obtained in the step (2) into a calcium ion solution with the calcium ion concentration of 0.3-0.5 mol/L in an injector extrusion manner, and curing for 3-6 h to form a columnar or spherical pyrolysis precursor, wherein the pyrolysis precursor is collected by using filter cloth;

(4) placing the pyrolysis precursor obtained in the step (3) in an atmosphere furnace, and roasting in an inert atmosphere for two sections, wherein the primary roasting temperature is 100-120 ℃, the heating rate is 4-8 ℃/min, and the roasting time is 0.5-2 h; and (3) roasting for 2-4 hours at the secondary roasting temperature of 400-800 ℃ and the heating rate of 4-8 ℃/min to obtain the iron-based-bentonite/carbon composite porous material.

In a third aspect, the invention provides a use of the iron-based-bentonite/carbon composite porous material as described in the first aspect, and the composite porous material is used as a filler in the fields of chromium-containing wastewater treatment and chromium-polluted groundwater infiltration reactive barrier repair.

Compared with the prior art, the invention has the beneficial effects that:

(1) according to the iron-based-bentonite/carbon composite porous material provided by the invention, the iron powder is uniformly distributed on the outer surface and the inner surface of the pores of the bentonite framework, the unique structure enables the iron powder to be firmly and uniformly contacted with the framework and to be uniformly dispersed, the contact area of the iron powder and a reactant is increased, and meanwhile, the specific surface area of the material is increased due to the pore structure in the porous framework, so that when the iron-based-bentonite/carbon composite porous material is used for water treatment, the diffusion of pollutants in a water phase is facilitated, and the; the composite porous material has controllable structure, high compressive strength, good stability and water resistance; furthermore, the particle size of the composite porous material is 3-10 mm, the composite porous material contains uniformly distributed macropores, and the specific surface area is high;

(2) according to the preparation method provided by the invention, the sodium alginate solution is used as a dispersing agent of the iron powder, so that the iron powder is uniformly distributed in the sodium alginate solution and is crosslinked with calcium ions to form a crosslinked network, and then the bentonite, the pore-forming agent and a specific process are combined, so that the iron powder and carbon in the composite porous material are uniformly distributed on the outer surface and the inner surface of the pore of the bentonite framework;

(3) the iron-based-bentonite/carbon composite porous material provided by the invention can be used as a filler, has an adsorption effect and a reduction effect in the application of chromium-containing wastewater treatment and chromium-containing underground water permeable reactive wall restoration, can prevent iron powder from being hardened and blocked in the water treatment process, improves the contact area of the iron powder and a water phase, and has a hexavalent chromium removal rate of more than 85% under the condition of no external electrolyte.

Drawings

Fig. 1 is an SEM image of the iron-based-bentonite/carbon composite porous material prepared in example 1.

Fig. 2(a) to 2(d) are SEM images of the iron-based bentonite/carbon composite porous material prepared in example 2, respectively.

Fig. 3(a) to 3(d) are SEM images of the iron-based bentonite/carbon composite porous material prepared in example 3, respectively.

Fig. 4 is a graph comparing the effect of chromium removal of the composite materials prepared in example 3, comparative example 2, and comparative example 5 with that of iron powder in comparative example 6.

Fig. 5(a) to 5(d) are SEM images of the iron-based bentonite/carbon composite porous material prepared in comparative example 4, respectively.

Detailed Description

The technical solution of the present invention will be further described with reference to the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

Example 1

The embodiment provides a preparation method of an iron-based-bentonite/carbon composite porous material, which comprises the following specific steps:

(1) preparing 2 wt% sodium alginate solution as dispersant for iron powder and forming agent for precursor;

(2) mechanically mixing 1g of reduced iron powder with the size of 400 meshes, 3g of bentonite and 20mL of the solution obtained in the step (1) for 35min to obtain a pasty mixture;

(3) adding the pasty mixture obtained in the step (2) into a 0.5mol/L calcium ion solution in a dropping manner by using an injector, and curing for 4 hours to obtain a spherical pyrolysis precursor;

(4) and (3) placing the pyrolysis precursor obtained in the step (3) into an atmosphere furnace, and roasting in a nitrogen atmosphere, wherein the temperature of primary roasting is 100 ℃, the heating rate is 5 ℃/min, the roasting time is 0.5h, the temperature of secondary roasting is 600 ℃, the heating rate is 5 ℃/min, and the roasting time is 2h, so that the iron-based-bentonite/carbon composite porous material is obtained.

The iron-based-bentonite/carbon composite porous material prepared in this example is spherical, has a particle size of 8mm, and has a pore size of 5 μm, and an SEM image of the porous material is shown in fig. 1, which shows that the surface of the iron-based-bentonite/carbon composite porous material has a pore structure and is uniformly distributed.

The iron-based-bentonite/carbon composite porous material prepared in the embodiment is subjected to chromium removal performance test, and the test method comprises the following steps: 3g of the obtained iron-based-bentonite/carbon composite porous material is placed in a plastic bottle filled with 250mL of Cr (VI) solution with the concentration of 20mg/L, the temperature of a water bath shaker is 25 ℃, the rotating speed is 100rpm, and the removal rate of hexavalent chromium after 24 hours of reaction is 94%.

Example 2

(2) mechanically mixing 1g of reduced iron powder with the size of 400 meshes, 0.1g of starch, 3g of bentonite and 20mL of the solution in the step (1) for 35min to obtain a pasty mixture;

The fe-based bentonite/carbon composite porous material prepared in this example is spherical, has a particle size of 8mm, and has a pore size of 8 μm, and SEM images thereof are shown in fig. 2(a) to 2(d), which show that the fe-based bentonite/carbon composite porous material has a pore structure on the surface and is uniformly distributed.

The iron-based-bentonite/carbon composite porous material prepared in the embodiment is subjected to chromium removal performance test, the test method is the same as that of the embodiment 1, and the removal rate of hexavalent chromium after 24 hours of reaction is 97%.

Example 3

(2) mechanically mixing 1g of reduced iron powder with the size of 400 meshes, 0.3g of starch, 3g of bentonite and 20mL of the solution in the step (1) for 35min to obtain a pasty mixture;

The fe-based bentonite/carbon composite porous material prepared in this example is spherical, has a particle size of 8mm, and has a pore size of 14 μm, and SEM images thereof are shown in fig. 3(a) to 3(d), which show that the fe-based bentonite/carbon composite porous material has a pore structure on the surface and is uniformly distributed.

The iron-based-bentonite/carbon composite porous material prepared in the embodiment is subjected to chromium removal performance test, the test method is the same as that of the embodiment 1, and the removal rate of hexavalent chromium after 24 hours of reaction is 99%.

Example 4

(2) mechanically mixing 1g of reduced iron powder with the size of 400 meshes, 0.5g of starch, 3g of bentonite and 20mL of the solution in the step (1) for 35min to obtain a pasty mixture;

The iron-based bentonite/carbon composite porous material prepared in the example is spherical, the particle size is 8mm, and the pore diameter of a macropore is 18 μm.

The iron-based-bentonite/carbon composite porous material prepared in the embodiment is subjected to chromium removal performance test, the test method is the same as that of the embodiment 1, and the removal rate of hexavalent chromium after 24 hours of reaction is 96%.

Example 5

(2) mechanically mixing 1g of reduced iron powder with the size of 400 meshes, 0.7g of starch, 3g of bentonite and 20mL of the solution in the step (1) for 35min to obtain a pasty mixture;

The iron-based-bentonite/carbon composite porous material prepared in the embodiment is subjected to chromium removal performance test, the test method is the same as that of the embodiment 1, and the removal rate of hexavalent chromium after 24 hours of reaction is 88%.

Example 6

(1) preparing 1 wt% sodium alginate solution as dispersant of iron powder and forming agent of pyrolytic precursor;

(2) ultrasonically dispersing 1g of regenerated iron powder with the size of 400 meshes, 0.1g of glucose, 3g of bentonite and 20mL of the solution obtained in the step (1) for 35min to obtain a pasty mixture;

(3) adding the pasty mixture in the step (2) into 0.1mol/L calcium ion solution in a mechanical conveying mode, and curing for 1h to form a columnar pyrolysis precursor;

(4) and (4) placing the pyrolysis precursor obtained in the step (3) into an atmosphere furnace, roasting in a helium atmosphere, wherein the temperature of primary roasting is 80 ℃, the heating rate is 1 ℃/min, the roasting time is 0.1h, the temperature of secondary roasting is 100 ℃, the heating rate is 10 ℃/min, and the roasting time is 1h, so that the iron-based-bentonite/carbon composite porous material is obtained.

The iron-based bentonite/carbon composite porous material prepared in the example is columnar, the particle size is 8mm, and the pore diameter of macropores is 3 μm.

Example 7

(1) preparing 4wt% sodium alginate solution as dispersant for iron powder and forming agent for precursor;

(2) 1g of 400-mesh cast iron powder, 0.7g of cane sugar, 3g of bentonite and 20mL of the solution obtained in the step (1) are vibrated and dispersed for 60min to obtain a pasty mixture;

(3) adding the pasty mixture in the step (2) into 1mol/L calcium ion solution by adopting a mechanical conveying mode, and curing for 10h to obtain a spherical pyrolysis precursor;

(4) and (3) placing the pyrolysis precursor obtained in the step (3) into an atmosphere furnace, and roasting in a helium atmosphere, wherein the temperature of primary roasting is 100 ℃, the heating rate is 10 ℃/min, the roasting time is 6h, the temperature of secondary roasting is 800 ℃, the heating rate is 10 ℃/min, and the roasting time is 1h, so that the iron-based-bentonite/carbon composite porous material is obtained.

The iron-based bentonite/carbon composite porous material prepared in the example is spherical, the particle size is 8mm, and the pore diameter of a macropore is 8 μm.

Example 8

The only difference compared to example 2 is that 3g of bentonite in step (2) was replaced by 1.2g of bentonite.

The iron-based bentonite/carbon composite porous material prepared in the example is spherical, the particle size is 8mm, and the pore diameter of a large pore is 10 μm.

Example 9

The only difference compared to example 2 is that 3g of bentonite in step (2) was replaced by 12g of bentonite.

The iron-based bentonite/carbon composite porous material prepared in the example is spherical, the particle size is 8mm, and the pore diameter of a macropore is 1 μm.

Example 10

The only difference compared with example 2 is that 1g of iron powder in step (2) was replaced with 0.8g of iron powder.

Example 11

The only difference compared with example 2 is that 1g of iron powder in step (2) was replaced with 4g of iron powder.

Example 12

The only difference compared to example 2 is that the curing time in step (3) was replaced by 1 h.

The iron-based bentonite/carbon composite porous material prepared in the example is spherical, the particle size is 8mm, and the pore diameter of a macropore is 6 μm.

Example 13

The only difference compared to example 2 is that the curing time in step (3) was replaced by 10 h.

The iron-based bentonite/carbon composite porous material prepared in the example is spherical, the particle size is 8mm, and the pore diameter of a macropore is 4 μm.

Example 14

The only difference compared with example 2 is that the primary firing temperature in step (4) was replaced with 150 ℃.

Example 15

The only difference compared to example 2 is that the secondary firing temperature in step (4) was replaced with 300 ℃.

Example 16

The only difference compared to example 2 is that the secondary firing temperature in step (4) was replaced with 700 ℃.

Example 17

The only difference compared to example 2 is that the secondary firing temperature in step (4) was replaced with 800 ℃.

Comparative example 1

The specific procedure of this comparative example is as in example 1, except that no bentonite is added in step (2).

As a result, the porous material finally produced is loose and brittle, and is not easy to handle practically.

Comparative example 2

The specific process of this comparative example is as in example 3 except that no iron powder is added in step (1).

As a result, the composite porous material finally obtained has no effect of iron powder, and the hexavalent chromium is removed only by 20% within 24 hours.

Comparative example 3

The specific process of this comparative example is referred to example 1 except that the second firing is raised to 1000 ℃ in step (5). The result is that although the final product can obtain the iron-based-bentonite/carbon composite porous material, the bentonite is seriously sintered, so that the specific surface area of the porous material is obviously reduced, the pore channel is blocked, and the removal rate of hexavalent chromium is seriously reduced.

Comparative example 4

The specific process of this comparative example is referred to example 1, except that the calcification molding stage in step (3) is omitted.

As a result, the iron-based bentonite/carbon composite porous material can be obtained as the final product, but the structure is loose (see fig. 5(a) to 5(d)), and it is difficult to maintain a good structure in water, resulting in a serious loss of iron powder, and the removal rate of hexavalent chromium is only 60% under the same conditions.

Comparative example 5

The specific process of this comparative example is referred to example 1 with the difference that the starch content in step (2) is added at 1 g.

As a result, although the iron-based bentonite/carbon composite porous material can be obtained from the finally obtained product, the iron powder is wrapped by the starch due to the excessive content of the starch, and the chromium removal efficiency is only 58% under the same conditions.

Comparative example 6

The same chromium removal experiment was performed without any treatment using 3g of reduced iron powder having a size of 400 mesh in this comparative example.

As a result, under the same operating conditions, the removal rate of hexavalent chromium by pure iron powder is only 1.5%.

The removal rate of hexavalent chromium by the materials of the present comparative example, example 3, comparative example 2, and comparative example 5 is shown in fig. 4. The composite porous material of example 3 has a high removal rate of hexavalent chromium because the iron powder of the composite porous material is uniformly distributed on the outer surface and the inner surface of the pores of the bentonite framework, the contact area with hexavalent chromium is large, the porous structure is favorable for the diffusion of hexavalent chromium, the reaction rate is increased, and more hexavalent chromium can be removed under the same conditions.

Comparative example 7

This comparative example provides a method for preparing an iron-based-bentonite/carbon composite, using the method in CN 106006854A.

Evaluation of chromium removal performance of the material:

the materials prepared in the above examples and comparative examples were tested for chromium removal performance in the same manner as in example 1, and the removal rate of hexavalent chromium after 24 hours of reaction is shown in table 1.

TABLE 1

The following points can be seen from table 1:

(1) it can be seen from the comprehensive examples 1-5 that the removal rate of the example 5 is low, because the starch added in the example 5 is more, and the iron powder is wrapped by carbon after roasting, so that the chromium removal effect is seriously reduced;

(2) it can be seen from the combination of example 2 and examples 8 and 9 that the removal rate of examples 8 and 9 is relatively low, because too much bentonite can make the pore channel too small, which affects the diffusion of the contaminant in the water phase, and too small bentonite can cause the material structure to be unstable, and the material is easy to loosen;

(3) it can be seen from the combination of example 2, example 10 and example 11 that the removal rate of example 10 is low, and the removal rate of example 11 is the same as that of example 2, because too little iron powder reduces the amount of reducing agent of the material, thereby causing the chromium removal performance to be reduced, but too much iron powder causes the remaining iron powder to be coated in the framework and cannot play a role in reduction;

(4) it can be seen from the combination of example 2, example 12 and example 13 that the removal rate of example 12 and example 13 is low, because too short curing time causes the internal crosslinking reaction of the material to be not fully reacted, the pore channel collapse is easily caused during the roasting process, and too long curing time causes the reaction aging of the iron powder and water, thereby reducing the activity;

(5) combining example 2 with example 14, it can be seen that the chromium removal performance of the material is reduced when the first stage firing temperature of example 14 is too high, because the water is evaporated too fast, resulting in the collapse of the internal channel structure;

(6) combining example 2 with example 17, it can be seen that the excessive temperature of the second stage of example 17 can result in the decrease of the chromium removing performance of the material, because the excessive temperature causes the bentonite to lose water and sinter, and the internal microporous structure collapses;

(7) by combining the example 1 with the comparative example 1, the removal rate of the comparative example 1 is low, because bentonite is not added, the obtained material has a loose and fragile structure and is not beneficial to chromium removal; in addition, the bentonite plays a key role in the forming effect of the material, and the bentonite is a supporting material with higher strength after being dehydrated;

(8) combining example 3 with comparative example 2, it can be seen that the removal rate of example 3 is higher and that the iron powder plays a key role in the hexavalent chromium removal capability of the material because the iron powder has reducing properties;

(9) it can be seen from the combination of example 1 and comparative example 3 that the secondary calcination temperature of comparative example 3 is too high, which causes the chromium removal efficiency to be reduced, because the temperature is too high, which causes the bentonite to be sintered, and the microporous structure per se disappears;

(10) it can be seen from the combination of example 1 and comparative example 4 that the removal rate of comparative example 4 is low, because comparative example 4 is not calcified, the structure of the baked porous material is unstable, and further, calcification is a key molding step;

(11) it can be seen from the combination of example 1 and comparative example 5 that the starch added in comparative example 5 is more, and the iron powder is wrapped by carbon after roasting, thus the chromium removal effect is seriously reduced;

(12) it can be seen from the combination of example 1 and comparative example 6 that the chromium removal efficiency of the iron powder which is not loaded in comparative example 6 is seriously reduced under the same conditions, because the iron powder is hardened and agglomerated in water, which leads to the serious reduction of the contact area with the pollutants in the solution;

(13) it can be seen from the combination of example 1 and comparative example 7 that the chromium removal efficiency of the press-formed material in comparative example 7 is low because the iron powder of the press-formed material is mostly coated in the skeleton and thus has low activity.

In conclusion, the preparation method of the iron-based-bentonite/carbon composite porous material provided by the invention obtains the composite porous material with the iron powder and the carbon uniformly distributed on the outer surface and the inner surface of the hole of the bentonite framework through raw material matching, uniform mixing of the raw materials and two-stage roasting.

The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims

1. An iron-based-bentonite/carbon composite porous material is characterized in that the composite porous material comprises a bentonite porous framework, and iron powder and carbon which are distributed on the outer surface and the inner surface of pores of the bentonite porous framework;

the composite porous material is prepared by the following preparation method, and the preparation method comprises the following steps:

(1) mixing a sodium alginate solution with iron powder for the first time, and then mixing the sodium alginate solution with bentonite and a pore-forming agent for the second time to obtain a mixture; wherein, the pore-forming agent comprises any one or the combination of at least two of starch, glucose or sucrose;

(3) roasting the pyrolysis precursor obtained in the step (2) in an inert atmosphere for two sections to obtain the iron-based-bentonite/carbon composite porous material; the two-stage roasting comprises primary roasting and secondary roasting which are sequentially carried out, wherein the temperature of the primary roasting is 80-150 ℃, and the temperature of the secondary roasting is 400-800 ℃;

wherein, the amorphous carbon is obtained by roasting the sodium alginate and the pore-forming agent.

2. The composite porous material of claim 1, wherein the iron powder comprises any one of reduced iron powder, cast iron powder, or recycled iron powder, or a combination of at least two thereof.

3. The composite porous material of claim 2, wherein the iron powder is a reduced iron powder.

4. The composite porous material of claim 1, wherein the iron powder has a particle size ranging from 100 to 600 mesh.

5. The composite porous material of claim 4, wherein the iron powder has a particle size in the range of 300 to 400 mesh.

6. The composite porous material of claim 1, wherein the carbon comprises porous carbon.

7. The composite porous material according to claim 1, wherein the composite porous material contains macropores, and the pore diameter of the macropores is in a range of 5-50 μm.

8. The composite porous material according to claim 7, wherein the pore size of the macropores is in the range of 5 to 20 μm.

9. The composite porous material of claim 1, wherein the shape of the composite porous material comprises spheres and/or columns.

10. The composite porous material according to claim 1, characterized in that the particle size of the composite porous material is in the millimeter scale.

11. The composite porous material according to claim 10, wherein the particle size is 3 to 10 mm.

12. The composite porous material as claimed in claim 1, wherein the concentration of the sodium alginate solution in the step (1) in the preparation method is 1-4 wt%.

13. The composite porous material as claimed in claim 12, wherein the concentration of the sodium alginate solution is 1.5-2.5 wt%.

14. The composite porous material of claim 1, wherein the mass ratio of the iron powder to the sodium alginate solution in the step (1) in the preparation method is (2-10): 100.

15. The composite porous material as claimed in claim 14, wherein the mass ratio of the iron powder to the sodium alginate solution is (3-5): 100.

16. The composite porous material as claimed in claim 1, wherein the mass ratio of the bentonite in the step (1) to the sodium alginate solution in the preparation method is (6-30): 100.

17. The composite porous material as claimed in claim 16, wherein the mass ratio of the bentonite to the sodium alginate solution is (8-20): 100.

18. The composite porous material according to claim 1, wherein the pore former of step (1) in the preparation method is starch.

19. The composite porous material as claimed in claim 1, wherein the mass ratio of the pore-forming agent in the step (1) to the sodium alginate solution is (0-15): 100.

20. The composite porous material as claimed in claim 19, wherein the mass ratio of the pore-forming agent to the sodium alginate solution is (0.5-4): 100.

21. The composite porous material according to claim 1, wherein the primary mixing and the secondary mixing in step (1) in the preparation method independently comprise any one of mechanical stirring, ultrasonic dispersion or oscillatory dispersion or a combination of at least two thereof.

22. The composite porous material according to claim 1, wherein the time for the primary mixing and the secondary mixing in step (1) in the preparation method is independently 30 to 180 min.

23. The composite porous material according to claim 22, wherein the time for the primary mixing and the secondary mixing is independently 30 to 60 min.

24. The composite porous material according to claim 1, wherein the calcium ion-containing solution in step (2) of the preparation method comprises any one of a calcium chloride solution, a calcium sulfate solution, a calcium nitrate solution, or a calcium hydroxide solution, or a combination of at least two thereof.

25. The composite porous material according to claim 1, wherein in the preparation method, in the calcium ion-containing solution in the step (2), the concentration of calcium ions is 0.1-1 mol/L.

26. The composite porous material according to claim 25, wherein the calcium ion concentration is 0.3 to 0.5 mol/L.

27. The composite porous material of claim 1, wherein the molar ratio of calcium ions to sodium alginate in the calcium ion-containing solution in step (2) in the preparation method is (0.2-3): 1.

28. The composite porous material of claim 27, wherein the molar ratio of calcium ions to sodium alginate in the solution containing calcium ions is (0.5-1.5): 1.

29. The composite porous material according to claim 1, wherein the manner of addition in step (2) in the preparation method comprises dropwise addition.

30. The composite porous material according to claim 29, characterized in that the method of drop-wise addition comprises injection extrusion and/or mechanical transport.

31. The composite porous material according to claim 1, wherein the curing time in the step (2) in the preparation method is 1-10 h.

32. The composite porous material according to claim 31, wherein the curing time is 3 to 6 hours.

33. The composite porous material according to claim 1, wherein the shape of the pyrolysis precursor in step (2) in the preparation method comprises a spherical shape and/or a columnar shape.

34. The composite porous material of claim 33, wherein the pyrolytic precursor is spherical in shape.

35. The composite porous material according to claim 1, wherein the gas of the inert atmosphere in step (3) in the preparation method comprises any one of nitrogen, argon or helium or a combination of at least two of nitrogen, argon or helium.

36. The composite porous material according to claim 1, wherein the inert atmosphere in the step (3) in the preparation method has a gas flow rate of 5-400 mL/min.

37. The composite porous material according to claim 36, wherein the inert atmosphere has a gas flow rate of 30 to 200 mL/min.

38. The composite porous material according to claim 1, wherein the temperature of the primary roasting in the preparation method is 100-120 ℃.

39. The composite porous material according to claim 1, wherein the temperature rise rate of the primary roasting in the preparation method is 1-10 ℃/min.

40. The composite porous material of claim 39, wherein the temperature rise rate of the primary roasting in the preparation method is 4-8 ℃/min.

41. The composite porous material of claim 1, wherein the time for the primary roasting in the preparation method is 0.1-6 h.

42. The composite porous material as claimed in claim 41, wherein the time for the primary roasting in the preparation method is 0.5-2 h.

43. The composite porous material according to claim 1, wherein the temperature rise rate of the secondary roasting in the preparation method is 1-10 ℃/min.

44. The composite porous material of claim 43, wherein the temperature rise rate of the secondary roasting in the preparation method is 4-8 ℃/min.

45. The composite porous material of claim 1, wherein the secondary roasting time in the preparation method is 1-10 h.

46. The composite porous material as claimed in claim 45, wherein the secondary roasting time in the preparation method is 2-4 h.

47. The composite porous material according to claim 1, characterized in that the preparation method comprises the following steps:

(1) preparing 1.5-2.5 wt% of sodium alginate solution;

48. Use of the iron-based-bentonite/carbon composite porous material according to any one of claims 1 to 47, as a filler in the field of chromium-containing wastewater treatment and chromium-contaminated groundwater infiltration reactive wall remediation.