CN112980446B

CN112980446B - Preparation process and application of iron modified eggshell biochar capable of synchronously immobilizing cadmium and arsenic

Info

Publication number: CN112980446B
Application number: CN202110158329.0A
Authority: CN
Inventors: 默罕默德·沙菲克·伊斯兰姆; 陈雅丽; 李永涛; 马杰; 翁莉萍
Original assignee: Agro Environmental Protection Institute Ministry of Agriculture
Current assignee: Agro Environmental Protection Institute Ministry of Agriculture
Priority date: 2021-02-05
Filing date: 2021-02-05
Publication date: 2021-11-02
Anticipated expiration: 2041-02-05
Also published as: CN112980446A

Abstract

The invention relates to a preparation process of iron modified eggshell biochar for synchronously immobilizing cadmium and arsenic, which comprises the following steps: 1) drying and grinding eggshells; 2) mixing egg shell powder with 0.4-1.2mol/L FeSO₄Mixing and modifying the solution; 3) pyrolyzing and cooling to room temperature; 4) drying at 70-90 deg.C for 48h to obtain the final product. The method is applied to the treatment of the rice soil pollution, calcium carbonate is not additionally added to the iron modified eggshell biochar to keep the adsorption and immobilization capacity of the biochar on cadmium, the magnetic property is achieved, the adsorbed pollutants can be effectively separated and removed through magnetic force, the adsorption capacity of the iron modified eggshell biochar on cadmium and arsenic in an alkaline environment can reach over 50mg/g, the adsorption material which can simultaneously have the capacity of adsorbing Cd and As and can effectively remove the Cd and As from the polluted soil/water body is provided, and the important research and development and application significance are realized.

Description

Preparation process and application of iron modified eggshell biochar capable of synchronously immobilizing cadmium and arsenic

Technical Field

The invention belongs to the field of environmental protection, relates to a soil pollution treatment technology, and particularly relates to a preparation process and application of iron modified eggshell biochar capable of synchronously immobilizing cadmium and arsenic.

Background

According to literature records, the exceeding rate of the point location of the cultivated land soil in China reaches 19.4%, wherein the exceeding rate of the point location of cadmium pollution is the highest among 8 inorganic pollutants, arsenic pollution is ranked the third, and the exceeding rates of the point location of the cadmium pollution and the arsenic pollution reach 7.0% and 2.7% respectively. Cadmium and arsenic are both extremely toxic to organisms. Research shows that heavy metals in soil enter the soil through atmospheric sedimentation, livestock and poultry manure, chemical fertilizers and the like, so that the heavy metals in the soil are accumulated and exceed the standard; on the other hand, a considerable amount of cadmium and arsenic also enter underground water through various ways (such as discharge or leakage of polluted waste water in mine mining tailings reservoirs and chemical industry, tanning, paper making and other industries related to heavy metal cadmium and arsenic) so as to aggravate the cadmium and arsenic pollution of the underground water.

The biochar is a porous carbonaceous solid material which is rich in carbon and highly aromatic and is generated by low-temperature thermal cracking of biomass under the anaerobic or oxygen-limited condition. Because the biochar has a porous structure, a high specific surface area and rich functional groups, a plurality of pollutants in the soil can be immobilized, so that the biological effectiveness of the pollutants in the soil is effectively reduced, and the biochar becomes a research hotspot in the field of soil pollution remediation. The eggshell has high calcium carbonate content (about 95-98%), can be used as a substitute of other lime materials, is used for fixing heavy metals in wastewater and soil, and can reduce the pollution of the eggshell to the environment by recycling or reusing the eggshell.

The chemical behaviors of cadmium and arsenic are opposite, the method and the material for treating the cadmium-polluted soil are usually not suitable for treating the arsenic pollution, the biological carbon can effectively fix the cadmium and can increase the mobility and the effectiveness of the arsenic by reducing the arsenic, and meanwhile, the current soil pollution remediation material mainly passivates heavy metals and cannot remove the heavy metals from the soil aiming at the heavy metal pollution of the soil. Therefore, the development of the adsorption material which has the capacity of adsorbing cadmium and arsenic at the same time and can be effectively removed from the polluted soil/water body based on the eggshells is of great significance.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a preparation process and application of iron modified eggshell biochar for synchronously immobilizing cadmium and arsenic.

The technical problem to be solved by the invention is realized by adopting the following technical scheme:

a preparation process of iron modified eggshell biochar for synchronously immobilizing cadmium and arsenic comprises the following specific process steps:

1) cleaning eggshell with deionized water, drying at 50-90 deg.C for 24 hr, grinding, and sieving with 50-100 mesh sieve;

2) mixing the eggshell powder ground in the step 1) with 0.4-1.2mol/L FeSO₄Mixing the solutions at a solid-to-liquid ratio of 0.05-2:2-8, stirring thoroughly with a magnetic stirrer for 12h, and baking at 70 deg.C for 48 h;

3) putting the iron-containing eggshell sample into a muffle furnace for carbonization, heating to 450-650 ℃ at the speed of 10 ℃/min, pyrolyzing for 1-2 hours, and taking out after cooling to room temperature;

4) taking out the sample, sieving with 50-100 mesh sieve, washing until pH has no obvious change, and oven drying at 70-90 deg.C for 48h to obtain the final product.

And, FeSO in step 2)₄The concentration of the solution was 0.8 mol/L.

Furthermore, the egg shell powder and FeSO in the step 2)₄The solid-liquid ratio of the solution mixture is 1: 5.

Furthermore, the pyrolysis and cooling to room temperature in step 3) are carried out in an anaerobic or oxygen-limited environment.

Furthermore, under anaerobic conditions, the mixture was introduced into a muffle furnace at a distance of 300cm³Nitrogen was introduced at a rate of/min.

And the initial pH value of the finished product of the iron modified eggshell charcoal is 7-8, and the solid-to-liquid ratio is 1: 20.

An iron modified eggshell charcoal capable of synchronously immobilizing cadmium and arsenic is applied to the treatment of rice soil pollution.

Moreover, the rice variety is hybrid rice of 1377 Jingliangyou.

Furthermore, the treatment method comprises mixing the prepared iron-modified eggshell charcoal completely into 4.0kg of rice soil at a mass ratio of 1.0% to 2.0%, and then filling into a plastic bucket to add CO (NH) before potting₂)₂(0.1g N/kg soil)、P₂O₅(0.25g P/kg soil) and K₂O (0.15g K/kg soil) is used as a base fertilizer, all plastic buckets are flooded with tap water before the rice is transplanted, the water level is 3cm, 10 days, two rice seedlings growing for 19 days are transplanted in each pot, the soil is kept flooded for 3cm from the 1 st day to the 27 th day of the transplantation, the soil is kept flooded for 6cm from the 28 th day to the 10 th day before the harvest, and the total planting period of the rice is 117 days.

The invention has the advantages and positive effects that:

1. the biochar disclosed by the invention is rich in source, the waste eggshells are effectively utilized, the eggshells are collected and comprehensively utilized, the economic benefit is increased, and the pollution to the environment ecology is avoided.

2. The preparation process of the iron modified eggshell biochar is simple, and the introduced FeSO₄The calcium sulfate reacts with Ca element in the eggshell to form gypsum calcium sulfate, and the gypsum can be used as a fertilizer to promote crop production and can also be used as an alkaline soil conditioner.

3. The method is applied to the treatment of the rice soil pollution, the iron modified eggshell biochar has magnetism, can effectively separate and remove adsorbed pollutants through magnetic force, has the adsorption capacity of more than 50mg/g for cadmium and arsenic in an alkaline environment, provides an adsorption material which can simultaneously have the capacity of adsorbing cadmium and arsenic and realize the effective removal of the cadmium and arsenic from the polluted soil/water body, and has important research and development and application significance.

Drawings

FIG. 1 is a diagram of the energy spectrum analysis of the iron-modified eggshell biochar of the present invention;

FIG. 2 is an XRD analysis chart of the iron modified eggshell biochar of the present invention;

FIG. 3 is a scanning electron microscope analysis of the original eggshell biochar (a) and the iron-modified eggshell biochar (b) of the present invention;

FIG. 4 is a thermogravimetric analysis of the iron-modified eggshell biochar of the present invention;

FIG. 5 is a magnetization curve of the iron-modified eggshell biochar of the present invention;

FIG. 6 is a graph showing the adsorption kinetics of cadmium and arsenic by using the iron-modified eggshell biochar of the present invention;

FIG. 7 is a drawing showing a binary system and a ternary system of cadmium and arsenic in the iron-modified eggshell biochar of the present invention;

FIG. 8 is a graph showing the effect of iron-modified eggshell biochar on the cadmium arsenic binding morphology of soil;

FIG. 9 is a graph showing the effect of iron-modified eggshell biochar on rice growth;

FIG. 10 is a graph showing the effect of the iron-modified eggshell biochar of the present invention on the accumulation of cadmium and arsenic in different organs of rice;

FIG. 11 is a graph showing the effect of the iron-modified eggshell biochar of the present invention on the iron film on the rice root surface and the accumulation of cadmium and arsenic therein.

Detailed Description

The present invention is further illustrated by the following specific examples, which are intended to be illustrative, not limiting and are not intended to limit the scope of the invention.

China is the first egg laying big country in the world, more than 400 million tons of eggshells are produced every year, and sufficient sources are provided for the preparation of the iron modified eggshell biochar; the method of the invention collects the eggshells for comprehensive utilization, which not only increases economic benefits, but also avoids pollution to environment ecology.

The process method provided by the invention is very simple and easy to operate, and calcium carbonate is not required to be additionally added to maintain the adsorption and immobilization capacity of the biochar on cadmium; FeSO₄The calcium sulfate reacts with Ca element in the eggshell to form gypsum calcium sulfate, and the gypsum can be used as a fertilizer to promote crop production and can also be used as an alkaline soil conditioner, especially sulfur-deficient soil; the iron modified eggshell charcoal cadmium and arsenic has good synchronous immobilization effect, and the adsorption capacity of cadmium and arsenic can reach more than 50mg/g in an alkaline environment; has magnetism, and can effectively separate and remove the adsorbed pollutants through magnetic force.

2) mixing the eggshell powder ground in the step 1) with 0.4-1.2mol/L FeSO₄Mixing the solutions (with optimal concentration of 0.8mol/L) (solid-to-liquid ratio of 0.05-2:2-8, and optimal concentration of 1:5), stirring with magnetic stirrer for 12 hr, and oven drying at 70 deg.C for 48 hr;

3) and (3) putting the iron-containing eggshell sample into a muffle furnace for carbonization, heating to 450-650 ℃ at the speed of 10 ℃/min, pyrolyzing for 1-2 hours, and taking out after cooling to room temperature. The pyrolysis and cooling to room temperature may be in an anaerobic or limited oxygen environment. If under anaerobic conditions, the anaerobic sludge can be fed into a muffle furnace for 300cm³Nitrogen was introduced at a rate of/min.

4) Taking out the sample, sieving with 50-100 mesh sieve, washing until pH has no obvious change, oven drying at 70-90 deg.C for 48 hr until the initial pH (solid-to-liquid ratio of 1:20) of the iron modified eggshell charcoal is 7-8.

The iron modified eggshell biochar provided by the invention can be used for treating cadmium and arsenic compound polluted water and soil. 2g of the iron modified eggshell charcoal is put into 1L of water body with cadmium and arsenic combined pollution (40mg/L arsenic +80mg/L cadmium, pH is 7), the adsorption capacity of the iron modified eggshell charcoal to cadmium and arsenic in the water body reaches more than 27mg/g and 16mg/g, the removal rate is about 80 percent and 70 percent respectively, the adsorption capacity and the removal rate of the charcoal are increased along with the increase of pH, and pollutants can be removed from the water body through magnetic force after the adsorption is finished; the iron modified biochar and the cadmium-arsenic composite polluted soil are mixed according to the mass ratio of 1-2:100, so that the bioavailable cadmium and arsenic in the soil can be respectively reduced by 23.6-27.8% and 8.1-12.8%, the cadmium and arsenic content in rice grains can be further reduced (respectively reduced by 38-67% and 71-83%), and the rice yield can be increased by about 11% under the mixing ratio of 1: 100.

Example 1

2) mixing the eggshell powder ground in the step 1) with 0.4mol/L FeSO₄Mixing the solutions (solid-to-liquid ratio of 0.05:2), stirring thoroughly with magnetic stirrer for 12 hr, and baking at 70 deg.C for 48 hrUsing;

4) Taking out the sample, sieving with a 50-100 mesh sieve, washing until pH is not changed obviously, drying at 70-90 deg.C for 48h to obtain iron modified eggshell biochar with initial pH (solid-to-liquid ratio of 1:20) of about 7.60.

Example 2

2) mixing the eggshell powder ground in the step 1) with 0.8mol/L FeSO₄Mixing the solutions (solid-to-liquid ratio is 1:5), stirring thoroughly with a magnetic stirrer for 12h, and finally baking at 70 deg.C for 48 h;

Example 3

2) mixing the eggshell powder ground in the step 1) with 1.2mol/L FeSO₄Mixing the solutions (solid-to-liquid ratio is 2:8), stirring thoroughly with a magnetic stirrer for 12h, and finally baking at 70 deg.C for 48 h;

The verification experiment was as follows:

1) characterization of iron-modified Eggshell biochar

The physicochemical properties of the iron-modified eggshell biochar are shown in table 1.

TABLE 1 analysis result of iron-modified eggshell biochar element content

As shown in FIG. 1, the results of scanning electron microscopy energy spectrum analysis show that the iron-modified eggshell biochar mainly contains C, O, Ca, Fe, S and other elements. An obvious Fe peak is generated on the iron modified eggshell biochar, which indicates that the biochar surface is successfully loaded with Fe. As shown in fig. 2 and 3, the X-ray diffraction (XRD) results further confirmed that Fe may exist mainly in the form of goethite, and at the same time, the iron-modified eggshell biochar exists mainly in the form of calcium carbonate with calcium sulfate being generated. As shown in fig. 4, the thermogravimetric analysis result shows that the iron-modified eggshell biochar has a weight loss temperature of 654 ℃, and has higher thermal stability, as shown in fig. 5, the hysteresis loop of the iron-modified eggshell biochar is in an S shape, and the saturation magnetization is about 5emu/g, which is enough to separate the iron-modified eggshell biochar from the aqueous solution by a permanent magnet. In fig. 5, the left side is a process for demonstrating natural precipitation and separation of iron modified eggshell biochar, and the right side is a process for demonstrating separation of the iron modified eggshell biochar from an aqueous solution by a permanent magnet.

2) Kinetics experiment of adsorption of iron modified eggshell biochar on cadmium and arsenic

The iron-modified eggshell biochar prepared in example 1 was used. Weighing 0.02g of biochar into a 20ml centrifuge tube, adding 10ml of 40mg/LAs (V) and/or 80mg/L Cd (II) solution into the centrifuge tube, adjusting the pH of the solution to 7, oscillating at 25 ℃ and 180rpm, sampling at 15min, 30min, 1h, 2h, 4h, 6h, 8h, 12h and 24h respectively, and determining the content of arsenic or cadmium in the solution. The background ionic strength is 0.01mol of NaNO₃. Each process set 3 replicates.

As shown in fig. 6, regardless of the binary system (cadmium/arsenic + biochar) or the ternary system (cadmium + arsenic + biochar), the adsorption of cadmium and arsenic by the iron-modified eggshell biochar reaches equilibrium within 24 hours, and the time for the ternary system to reach adsorption equilibrium is relatively shorter. The fitting results of the quasi-first-stage and quasi-second-stage kinetic models show that the adsorption of the biochar on cadmium and arsenic is more in line with the quasi-second-stage kinetic models, and the correlation coefficient R²Above 0.98. Compared with a binary system, the adsorption and immobilization effect of cadmium and arsenic in the ternary system is better, the removal rate of cadmium and arsenic in the solution is improved, and the iron modified eggshell charcoal has a good synchronous adsorption effect on cadmium and arsenic and is stable in adsorption.

3) Isothermal experiment for adsorption of cadmium and arsenic by iron modified eggshell biochar

The iron-modified eggshell biochar prepared in example 1 was used. 0.02g of biochar is weighed into a 20ml centrifuge tube, and 10ml of 5-40mg/LAs (V) and/or 10-80mg of L-1Cd (II) solution is added. For the cadmium and arsenic mixed solution, the adding proportion is Cd: as 2:1, e.g., 10mg Cd (II) and 5mg As (v). The background ionic strength of the mixture is 0.01mol of NaNO₃With 0.5mol/L HNO₃And 0.1mol/L NaOH was added to adjust the pH of the solution to 3-9, and the solution was shaken at 180rpm and 25 ℃ for 24 hours. And finally, measuring the content of arsenic or cadmium in the solution. Each process set 3 replicates.

As shown in fig. 7, the adsorption capacity of the iron-modified eggshell biochar for cadmium and arsenic increases with the increase of the pH of the solution. With the increase of the initial concentration of cadmium and arsenic in the solution, the adsorption capacity of the iron modified eggshell biochar to cadmium and arsenic is also obviously increased, and then the adsorption balance is gradually reached; meanwhile, the cadmium and arsenic adsorption capacity of the iron modified eggshell biochar in the ternary system is obviously larger than that of the binary system. For the binary system, the data were fitted using Langmuir and Frundlich models, respectively, and the results showed that the adsorption of cadmium and arsenic by the iron-modified eggshell biochar both conformed to the Langmuir model, indicating that the adsorption of cadmium and arsenic by this biochar is a single layer adsorption and reaches maximum adsorption capacities at pH 9 of 38.63mg/g and 8.76mg/g, respectively (table 2). For the ternary system, the adsorption process is not balanced, so model fitting is not performed, and as can be seen from fig. 7, the adsorption capacity of the iron-modified biochar in the ternary system is significantly improved and is highest under alkaline conditions.

Table 2 iron modified eggshell biochar adsorption kinetics fitting parameters for cadmium and arsenic

TABLE 3 adsorption isothermality fitting parameters of iron-modified eggshell biochar to cadmium and arsenic in binary system

4) Remediation experiment for arsenic and cadmium composite polluted paddy field soil

The paddy soil is collected from arsenic and cadmium combined polluted surface soil (0-20cm) in a certain county of Hunan province. And (5) naturally drying the soil, and screening the soil by using a 2mm sieve for later use. The basic physicochemical properties of the soil are shown in table 4. The rice variety is the hybrid rice 1377 with Jingliangyou. The iron-modified eggshell biochar prepared in example 2 was thoroughly mixed into 4.0kg of rice soil in a mass ratio of 1.0% to 2.0% and then charged into a plastic bucket (diameter 20cm, height 25 cm). Adding CO (NH) before potting₂)₂(0.1gN/kg soil), P₂O₅(0.25g P/kg soil) and K₂O (0.15g K/kg soil) is used as a base fertilizer. Before transplanting rice, all plastic barrels are flooded with tap water (water surface height 3cm) for 10 days to balance the distribution of water in the soil. Two rice seedlings growing for 19 days are transplanted in each pot. From transplanting No. 1The soil is kept submerged for 3cm from day to day 27; from 28 days to 10 days before harvest, the water is kept 6 cm. The total planting period of rice was 117 days.

TABLE 4 basic physicochemical Properties of the soil for testing potted plants

As shown in FIG. 8, five binding forms of arsenic (F1: non-obligate adsorption state; F2: obligate adsorption state; F3: amorphous iron manganese oxide binding state; F4: crystalline iron manganese oxide binding state; F5: residue state) and four binding forms of cadmium (F1: water soluble state, exchangeable state and carbonate binding state; F2: reducible state; F3: oxidizable state; F4: residue state) were obtained by a continuous extraction method. After the iron modified eggshell biochar is added, compared with a control group, the contents of bioavailable cadmium (F1) and arsenic (F1+ F2) are obviously reduced by 23.6-27.8% and 8.1-12.8%, respectively.

As shown in FIG. 9, the arsenic and cadmium contents in the rice roots, stems and seeds are all significantly reduced, and the degree of reduction is increased with the addition amount. When the addition amount of the biochar is 1%, the arsenic content and the cadmium content in the brown rice are both 0.3mg/kg and are respectively reduced by 38% and 71% relative to a control. When the addition amount of the biochar is increased to 2 percent, the arsenic and cadmium content in the brown rice reaches the safety quality standard (less than or equal to 0.2mg/kg) of agricultural products, and the reduction degrees are 67 percent and 83 percent respectively. Therefore, the biochar prepared by the method can synchronously and efficiently passivate heavy metals arsenic and cadmium in soil, so that the absorption and accumulation of the rice on the arsenic and the cadmium are reduced.

As shown in fig. 10, the rice growth was significantly promoted at a low addition amount (1%) after the addition of the iron-modified eggshell biochar, which is shown in that the tiller number (+ 19%), the root dry weight (+ 16%), the stem dry weight (+ 22%), and the brown rice dry weight (+ 11%) were increased to different degrees relative to the control; the addition amount (2%) was increased, and the tillering number (-12%), the dry weight of the root (-25%), the dry weight of the stem (-16%), and the dry weight of brown rice (-18%) were decreased to different degrees with respect to the control, because of CaCO₃Too high a content is not beneficial to the growth of crops. Therefore, the biochar prepared by the invention not onlyThe cadmium and arsenic in the soil can be passivated efficiently and synchronously, the absorption of the rice to the cadmium and the arsenic is reduced, and meanwhile, the growth of the rice can be promoted and the yield of the rice can be increased remarkably under a low application amount.

Fig. 11 shows that the iron-modified eggshell charcoal significantly promotes the formation of iron film on the rice root surface, and the increase degree increases with the addition amount; meanwhile, the content of the fixed arsenic and cadmium in the iron film on the surface of the root is increased, which shows that the biological carbon remarkably improves the fixation and control capacity of the root system to the cadmium and the arsenic by promoting the formation of the iron film on the surface of the rice root, and effectively inhibits the accumulation of the cadmium and the arsenic in the rice.

Although the embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that: various substitutions, changes and modifications are possible without departing from the spirit and scope of the invention and the appended claims, and therefore the scope of the invention is not limited to the embodiments disclosed.

Claims

1. A preparation process of iron modified eggshell biochar capable of synchronously immobilizing cadmium and arsenic is characterized by comprising the following steps of: the specific process steps are as follows:

2. The preparation process of the iron modified eggshell biochar for synchronously immobilizing cadmium and arsenic according to claim 1, which is characterized by comprising the following steps of: FeSO in step 2)₄The concentration of the solution was 0.8mol/L。

3. The preparation process of the iron modified eggshell biochar for synchronously immobilizing cadmium and arsenic according to claim 1, which is characterized by comprising the following steps of: the eggshell powder and FeSO in the step 2)₄The solid-liquid ratio of the solution mixture is 1: 5.

4. The preparation process of the iron modified eggshell biochar for synchronously immobilizing cadmium and arsenic according to claim 1, which is characterized by comprising the following steps of: the pyrolysis and cooling to room temperature in step 3) are carried out in an anaerobic or oxygen-limited environment.

5. The preparation process of the iron modified eggshell biochar for synchronously immobilizing cadmium and arsenic according to claim 4, which is characterized in that: under anaerobic condition, the mixture is put into a muffle furnace for 300cm³Nitrogen was introduced at a rate of/min.

6. An iron modified eggshell charcoal with cadmium and arsenic synchronously immobilized according to claim 1 applied to the treatment of rice soil pollution.

7. The application of the iron modified eggshell biochar synchronously immobilizing cadmium and arsenic in the rice soil pollution treatment according to claim 6 is characterized in that: the rice variety is the hybrid rice of 1377 Jinliangyou.

8. The application of the iron modified eggshell biochar synchronously immobilizing cadmium and arsenic in the rice soil pollution treatment according to claim 6 is characterized in that: the treatment method comprises mixing iron modified eggshell charcoal prepared by 1.0% and 2.0% by mass into 4.0kg of paddy soil, loading into plastic bucket, adding CO (NH) before potting with no charcoal as control₂)₂、P₂O₅And K₂Using O as base fertilizer, before transplanting rice, all plastic barrels are flooded with tap water, the water surface is 3cm high, the water surface is kept for 10 days, two rice seedlings growing for 19 days are transplanted in each pot, from 1 day to 27 days of transplantation, the soil is kept flooded for 3cm, from 28 days to harvestThe water is kept 6cm for 10 days before the rice is harvested, and the total planting period of the rice is 117 days.

9. The application of the iron modified eggshell biochar synchronously immobilizing cadmium and arsenic according to claim 8 to the treatment of rice soil pollution is characterized in that: addition of CO (NH)₂)₂、P₂O₅、K₂O is used as a base fertilizer, so that the N, P, K content in the soil is respectively 0.1g N/kg of soil, 0.25g P/kg of soil and 0.15g K/kg of soil.