CN116969439A - Method for constructing lanthanum carbonate hydroxide on surface of biochar and application of method - Google Patents

Abstract

The invention belongs to the technical field of biomass charcoal, and particularly relates to a method for constructing lanthanum carbonate hydroxide on the surface of biomass charcoal and application thereof, wherein the method comprises the following steps: firstly, biomass and LaCl are mixed ₃ Mixing the solution and alkaline solution, and treating with hydrothermal method, or mixing biochar with LaCl ₃ Mixing the solution and the alkaline solution uniformly, and then carrying out chemical precipitation; further treating in air at 240-400deg.C for 20-240 min. The La load of the biochar-lanthanum carbonate hydroxide composite material prepared by the invention is about 40%, and the influence of pH and coexisting ions is smaller in the phosphorus adsorption process. When the method is used for recovering the phosphorus in the wastewater, the removal rate reaches 99.87 percent, and the residual concentration of the phosphorus is only 012mg/L, has excellent removal effect, and the leaching amount of La is only 0.002mg/L, thus having higher safety and sustainability. Lanthanum has targeted adsorption effect on phosphorus in wastewater, and basic lanthanum carbonate has fluorescence property, so that the method can be used for quantitatively detecting the concentration of phosphorus in wastewater.

Description

A method of constructing basic lanthanum carbonate on the surface of biochar and its application

Technical field

The invention belongs to the technical field of biomass carbon, and specifically relates to a new method of constructing basic lanthanum carbonate on the surface of biochar and its application.

Background technique

Lanthanum (La) is a versatile element that has been extensively studied over the past few decades, for example, as a La-containing adsorbent in the environment and as a micronutrient in agriculture. The widespread application of La is attributed to its multiple advantages, such as multifunctionality, high abundance in the earth's crust (close to nickel and copper), high biocompatibility, and low toxicity. In particular, its high affinity for oxygen-containing anions or Lewis hard bases has attracted widespread attention in environmental applications. However, as a rare earth element, La is more expensive to use directly in the environment. Therefore, in current research, La composite materials are often prepared to improve the use efficiency of La. The application of biochar as a functional material in the environmental field has attracted widespread attention. The current preparation methods of biochar mainly include hydrothermal, pyrolysis and gasification. However, raw biochar is always inefficient during application and even has adverse effects in some cases. To improve the performance of biochar in specific applications, further modifications are required. Generally speaking, these modification methods can be divided into: surface modification with organic functional groups (such as oxidation, amination), pore structure development (such as physical and chemical activation), and interaction with external phases (such as minerals, nanomaterials) complex. Among these modification strategies, biochar is combined with lanthanum (La) to improve the adsorption performance of phosphate, and at the same time develop multifunctional uses of the material based on the characteristics of the exogenous phase, which has attracted more and more attention in recent years. focus on.

The main pollutants in urban and agricultural wastewater include nitrogen, phosphorus and other nutrients, heavy metals, organic matter, antibiotics and pathogenic microorganisms. Direct discharge of wastewater without treatment will lead to excessive phosphorus content in natural water bodies, leading to eutrophication of water bodies. At present, many scholars are committed to research on phosphorus removal from wastewater, but there are still technical barriers. At present, in wastewater phosphorus treatment technology, economy and safety are the key and difficult issues in research. Biological treatment is currently the most common phosphorus treatment method for farm wastewater. Some typical microbial phosphorus removal processes, such as anaerobic/aerobic (A/O) processes, etc., have the main disadvantages of long treatment time and influencing factors. More, it may take up to a month, and large equipment and enough space need to be provided to maintain the long process, seriously increasing production costs and making it difficult to completely remove. For the detection of phosphorus in wastewater, ammonium molybdate spectrophotometry (GB/T 11893-1989) is currently commonly used. This method is complicated to operate, and the molybdate and concentrated sulfuric acid solutions used increase the detection cost and Risks of secondary pollution to the environment, therefore, an economical and sustainable method for phosphorus removal and detection remains to be developed.

The adsorption method is widely used in water treatment due to its advantages such as simple operation, high cost-effectiveness, easy operation, wide source of raw materials, and mild treatment conditions. Lanthanum has a strong affinity for phosphorus and is often used in the development of phosphorus adsorption materials. The most common form of lanthanum currently is lanthanum hydroxide, but lanthanum hydroxide has a higher risk of leaching in solution. For example, the La loss rate of La(OH) ₃ -doped porous biochar reached 44.31% at pH=2 and dropped sharply to 0.82% at pH=3, while the La(OH) _3- doped magnetic biochar adsorbed The La concentration after phosphate is 26.48 mg/L at pH=2. In addition, studies have shown that La(OH) ₃ has strong stress on microorganisms in the environment. The basic carbonate of lanthanum can also achieve efficient phosphorus adsorption, with lower solubility and higher stability. It is often used in oral drugs for human hyperphosphatemia, and the basic carbonate structure of lanthanum has Lanthanum has fluorescence properties that other compound states do not have, so it can be used to detect phosphorus concentration in wastewater. In recent years, more and more studies have reported materials based on basic lanthanum carbonate. At present, basic carbonates of lanthanum are still prepared through chemical deposition in solution. A variety of organic and inorganic reagents (such as urea and sodium carbonate) are commonly used, and wastewater is produced, making it difficult to prepare on a large scale. There is still a lack of greener, more efficient Simple preparation method. Based on these research status, the present invention proposes a new preparation method, that is, first loading lanthanum hydroxide on the surface of biochar, and then using thermochemical methods to construct basic lanthanum carbonate on the surface of biochar. The main reaction paths include:

C+O ₂ →CO ₂ (1)La(OH) ₃ +CO ₂ →LaOHCO ₃ +H ₂ O(2)

In addition, research results show that the biochar loaded with basic lanthanum carbonate obtained in the present invention has significantly better phosphorus adsorption performance than the biochar composite loaded with lanthanum hydroxide. In particular, the biochar loaded with basic lanthanum carbonate of the present invention has efficient phosphorus adsorption capacity in real wastewater (anaerobic effluent from pig farms), and the unit adsorption capacity is even better than that of this material in the simulated solution configured in the experiment. Phosphorus adsorption capacity, and the fluorescence intensity in different concentrations of phosphorus-containing wastewater shows a good linear relationship, and can be used for simultaneous detection of phosphorus removal in wastewater. Therefore, the material preparation method and its application proposed by the present invention are significantly innovative and progressive, and have good practical application prospects. Ultimately, the present invention not only provides a new method for high-value utilization of waste biomass, but also provides new materials and methods for the adsorption, recovery and detection of wastewater phosphorus.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for constructing basic lanthanum carbonate on the surface of biochar and its application.

The object of the present invention is achieved through the following technical solution: a method for constructing basic lanthanum carbonate on the surface of biochar, including the following steps:

S1. Mix the biomass and LaCl ₃ solution evenly, add alkaline solution, and undergo hydrothermal treatment to obtain biochar loaded with lanthanum hydroxide; or directly use biochar as raw material, mix the biochar and LaCl ₃ solution, Then add an alkaline solution and obtain biochar loaded with lanthanum hydroxide after chemical precipitation;

S2. Treat the lanthanum hydroxide-loaded hydrothermal carbon obtained in step S1 in an air atmosphere of 240-400°C for 20-240 minutes. According to the thermogravimetric experiment results, the surface lanthanum hydroxide is converted into basic lanthanum carbonate at 240-400°C. , converted into lanthanum oxycarbonate at higher temperatures to obtain basic lanthanum carbonate-loaded biochar.

Further, in step S1, the biomass includes agricultural biomass and forestry biomass.

Agricultural biomass is waste in the agricultural production process, such as crop straw (corn straw, sorghum straw, wheat straw, rice straw, soybean straw, cotton straw, etc.) remaining in the farmland during crop harvest; waste from the agricultural processing industry, such as Rice husks left over from the agricultural production process, etc.

Forestry biomass is the biomass provided for forest growth and forestry production processes, such as firewood forest, scattered wood in forest tending and thinning operations, residual branches, leaves and sawdust, etc.; branches and sawdust in the process of wood mining and processing , sawdust, tips, bark and truncation, etc.; forestry by-product waste, such as fruit shells and cores.

Further, in step S1, the mass ratio range of the biomass and LaCl ₃ is 1%-20%.

Further, in step S1, the alkali in the alkaline solution is one of urea, potassium hydroxide or sodium hydroxide; the pH after addition of the alkaline solution is = 8-12.

Further, in step S1, the conditions of the hydrothermal method are reaction at 150-250°C for 1-12 hours.

Further, in step S1, the obtained hydrothermal carbon loaded with lanthanum hydroxide needs to be washed multiple times. It is preferred to wash with ultrapure water three times and then dry in an oven at 65°C. This step can remove some soluble impurities and improve the adsorption effect on phosphorus.

The present invention also provides a lanthanum carbonate-loaded biochar obtained by the above method.

The present invention also provides an application of the above-mentioned basic lanthanum carbonate-loaded biochar in the adsorption, recovery and fixation of phosphorus.

The present invention also provides an application of the above-mentioned lanthanum carbonate-loaded biochar for detecting phosphorus concentration in soil/wastewater.

The beneficial effects of the present invention are:

The present invention prepares a new biochar-basic lanthanum carbonate composite material (LHCB) through a new method of hydrothermal doping coupled with hot air oxidation modification. The La loading capacity is about 40%. During the phosphorus adsorption process, it is affected by pH and coexisting ions. The impact is smaller. When used to recover phosphorus in wastewater, the removal rate reaches 99.87%, the remaining concentration of phosphorus is only 0.12mg/L, which has excellent removal effect, and the leaching amount of La is only 0.002mg/L, which has better High safety and sustainability. Lanthanum has a targeted adsorption effect on phosphorus in wastewater, and basic lanthanum carbonate has fluorescence properties and can be used to quantitatively detect the concentration of phosphorus in wastewater.

Description of the drawings

Figure 1 shows the results of thermogravimetric experiments;

Figure 2 is a flow chart of the method of the present invention;

Figure 3 shows the X-ray diffraction spectrum images of LHB and LHCB;

Figure 4 shows the SEM images of LHB and LHCB;

Figure 5 shows the element distribution diagram of LHB and LHCB;

Figure 6 shows the high-resolution XPS spectra of LHB and LHCB;

Figure 7 shows the comparison of phosphorus adsorption capacity of LHCB prepared from different raw materials;

Figure 8 shows the effect of different pH on the adsorption performance of LHCB;

Figure 9 shows the effect of different pH on LHB adsorption performance;

Figure 10 shows the effect of different interfering ions on the adsorption properties of LHB and LHCB;

Figure 11 shows the phosphorus adsorption performance of LHCB and LHB in aquaculture wastewater;

Figure 12 (a) Cycling performance of LHCB and LHB (b) Comparison of La leakage amount in LHCB and LHB solutions;

Figure 13 shows the changes in fluorescence intensity of LHCB in different concentrations of phosphorus-containing wastewater;

Figure 14 shows the correlation analysis of LHCB fluorescence intensity.

Detailed ways

The technical solution of the present invention will be described in further detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following description.

Example 1 Preparation of biochar supported by basic lanthanum carbonate

It was found through thermogravimetric analysis (Figure 1) that lanthanum hydroxide loses water and is converted into LaOOH at 240°C. In the presence of carbon dioxide, basic lanthanum carbonate (LaCO ₃ OH) is generated at 290°C. Under these conditions, further heating will It will cause the basic lanthanum carbonate to lose water and form La ₂ O ₂ CO _3. Therefore, the temperature of 300°C is preferred for material preparation in the present invention.

Preparation of the material of the present invention: Take 30g of crushed corn straw and place it in 500mL of polytetrafluoroethylene, add 270ml of 0.1M LaCl ₃ solution, stir continuously for 30 minutes with a glass rod to mix the straw powder and LaCl ₃ solution evenly, and then add 30 ml of 3M KOH solution was stirred continuously for 30 min again, then reacted at 200°C for 10 h, naturally cooled to room temperature, and washed three times with deionized water to obtain a hydrothermal carbon loaded with lanthanum hydroxide labeled LHB. Weigh 5g of LHB into a 100ml quartz crucible. Under hot air conditions in a muffle furnace, react at 300°C for 30 minutes at a temperature rise rate of 10°C/min to obtain basic lanthanum carbonate-loaded biochar labeled LHCB. The experimental flow chart is as shown in the figure. 2 shown.

Experimental Example 1 Structural characterization of biochar supported by basic lanthanum carbonate

The XRD pattern reflects the crystallinity changes on the material surface. By comparing the peaks with the standard sample PDF card, the surface crystal type can be explored. The X-ray diffraction spectrum images of the above-mentioned LHB and LHCB are shown in Figure _3. The diffraction peaks of LHB at 27.2°, 27.9°, 41.5°, 49.9°, 58.6°, 65.8°, and 74.8° respectively correspond to the ( 110), (101), (210), (102), (310), (400), (103) crystal planes, indicating the formation of La(OH) ₃ crystals on the surface of LHB; while LHCB is at 15.9°, 20.5° , 20.8°, 23.8°, 26.2°, 30.1°, and 38.4° diffraction peaks respectively correspond to (011), (110), (020), (111), (012), (121), (131) of LaCO ₃ OH ) crystal plane, indicating that the LHB surface crystals are oxidized by hot air to form LaCO ₃ OH crystals. The broad diffraction peak of LHB at 24° corresponds to the (002) crystal plane of graphitic carbon, indicating that under hydrothermal conditions, the degree of carbonization of LHB is low and the carbon crystal structure is disordered. The broad peak of the graphitic carbon (002) crystal plane of LHCB prepared by further hot air oxidation appears at 29°, and a new broad peak appears at 44° corresponding to the graphitic carbon (100) crystal plane. The oxidation treatment greatly improves the mineral composition in The content of the biochar surface, the relative content of the reduced carbon matrix, the shift of the peak position to a higher position and the emergence of new characteristic peaks indicate the increase in the degree of carbonization, and the structure changes from disordered carbon to ordered composite carbon, in hot air During the oxidation process, the participation of La reduces the apparent activation energy of pyrolysis and promotes pyrolysis.

The surface morphology and element distribution of LHB and LHCB are shown in Figures 4 and 5. It can be seen from the figure that a large number of rough particles gather and stack on the surface of LHB, causing the pores to be blocked, while the pores on the surface of LHCB are more obvious. There are a large number of La and O elements in LHCB. After oxidation by hot air, a layer of surface particles is formed. The structure, the surface is rough and there are more pores, which can provide more loading sites for La. Figure 4 shows the content and proportion of each element. Compared with LHB, the lanthanum element in LHCB increased from 10.41% to 42.17%. This may be due to the decrease in C content after hot air oxidation and the increase in specific surface area and functional groups. Increase the load rate of La. After hot air oxidation, the proportion of C element content in LHCB decreases, which is related to the increase in La and O in biochar, which also allows the biochar pores to develop, providing more loading sites for La. The C content of biochar after hot air oxidation decreases, while the O content increases, which may be due to the full carbonization of biomass during the activation process and the increase in oxygen-containing functional groups during the oxidation process. By comparing Figure 4(c)(f), LHC has a more uniform distribution of La than LHB, while La on the surface of LHB has obvious agglomeration. The agglomeration reduces the reaction contact with the adsorbate, thus leading to adsorption. amount decreases.

Figure 6 shows the XPS spectra of LHCB and LHB. As shown in the figure, the main binding energy of C 1s is around 280eV, and the main binding energy of O 1s is around 530eV. After hot air oxidation, there is an obvious valence state distribution of the La element at around 830eV, 200eV and 150eV. , and compared with LHB, LHCB has a higher proportion of La, which is consistent with the previous conclusion from EDS-mapping and FTIR that the lanthanum loading increases. The increase in the C/O ratio in LHCB indicates that during the hot air oxidation process, The abundance of oxygen-containing functional groups on its surface.

Example 2 Preparation of biochar loaded with different basic lanthanum carbonates

Cotton straw, rice straw, sawdust, walnut shells, and coffee grounds were respectively used to replace the corn straw in Example 1 to prepare LHCB. Other experimental conditions were the same.

Experimental Example 2 Comparison of biochar performance with different loadings of basic lanthanum carbonate

1. Compare the phosphorus adsorption capacity of different LHCBs obtained in Examples 1 and 2 in the solution. The experimental results are shown in Figure 7. Different LHCBs all reach more than 100 mg/g, which shows that this method is generally applicable to biomass materials. sex.

2. Select LHCB and LHB prepared from corn straw, and measure the adsorption performance under different pH (the addition amount of LHCB and LHB in all experiments of the present invention is 1g/L, and the initial phosphorus concentration is 200mg/L). The experimental results are respectively As shown in Figures 8 and 9, it can be seen that not only the adsorption capacity of LHCB is much higher than that of LHB, but also LHCB is less affected by pH.

3. Select LHCB and LHB prepared from corn straw, and measure the effect of different interfering ions on the adsorption performance of LHB and LHCB (the interfering ion concentration is 0.01 or 0.1mol/L). The experimental results are shown in Figure 10. You can also see The adsorption capacity of LHCB is much higher than that of LHB, and LHCB is less affected by interfering ions.

Experimental Example 3 The effect of practical application of LHCB in aquaculture wastewater

The present invention explores the phosphorus adsorption performance of corn straw LHCB and LHB in aquaculture wastewater. As shown in Figure 11, the maximum adsorption capacity of phosphorus in aquaculture wastewater by LHB is Qe = 62.98 mg/g, and the remaining concentration of phosphorus in the adsorbed aquaculture wastewater is 30.72 mg/L, making it difficult to achieve the goal of phosphorus removal from aquaculture wastewater. The phosphorus adsorption capacity of LHCB in aquaculture wastewater reaches Qe=91.88mg/g. After adsorption, the phosphorus concentration in the wastewater is reduced to 0.12mg/L, and the removal rate reaches 99.87%. Therefore, LHCB may be a potential candidate for treating actual wastewater. The ideal phosphorus remover.

Experimental Example 4 Reusability of LHCB

The reusability of adsorbents is of great significance for the development of cost-effective wastewater treatment processes. In the present invention, NaOH was used as the resolving agent, and five adsorption-desorption cycles were performed on LHCB and LHB in sequence, and the results are shown in Figure 12. The purpose of the regeneration test is to verify the phosphorus adsorption effect of LHCB and LHB after desorption. It can be seen that after 5 cycles of regeneration, both LHCB and LHB showed good cycle performance for phosphate, and LHCB was slightly better than LHB. This may be related to the leakage amount of La in the solution, and the leakage amount of LHB It is 0.02mg/L, while LHCB is only 0.002mg/L compared to LHB, and the dissolution amount of La is reduced by 10 times. Therefore, LHCB has better cycle performance and more reliable safety.

Experimental Example 5 Application of LHCB for detecting phosphorus content in wastewater

LHCB and LHB were placed in phosphorus-containing wastewater of different concentrations. Through the detection of fluorescence intensity, it was found that LHB did not have luminescent properties, while the fluorescence intensity of LHCB increased as the concentration of phosphorus in the solution increased, as shown in Figure 13.

Through correlation analysis of the fluorescence intensity of LHCB in 0-75 mg/L phosphorus-containing wastewater (as shown in Figure 14), R ² =0.9974 has a good correlation. Therefore, this method can be used for phosphorus-containing wastewater. Concentration testing of wastewater.

The above are only preferred embodiments of the present invention. It should be understood that the present invention is not limited to the form disclosed herein and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and Modifications can be made within the scope of the ideas described herein through the above teachings or technology or knowledge in related fields. Any modifications and changes made by those skilled in the art that do not depart from the spirit and scope of the present invention shall be within the protection scope of the appended claims of the present invention.

Claims (8)

1. A method for constructing lanthanum basic carbonate on the surface of biochar, which is characterized by comprising the following steps: S1. Mix the biomass and LaCl ₃ solution evenly, add alkaline solution, and undergo hydrothermal treatment to obtain biochar loaded with lanthanum hydroxide; or directly use biochar as raw material, mix the biochar and LaCl ₃ solution, Then add an alkaline solution and obtain biochar loaded with lanthanum hydroxide after chemical precipitation; S2. Treat the lanthanum hydroxide-loaded biochar obtained in step S1 in an air atmosphere of 240-400°C for 20-240 minutes to obtain basic lanthanum carbonate-loaded biochar. 2. A method of constructing basic lanthanum carbonate on the surface of biochar according to claim 1, characterized in that in step S1, the biomass includes agricultural biomass and forestry biomass. 3. A method for constructing basic lanthanum carbonate on the surface of biochar according to claim 1, characterized in that in step S1, the mass ratio of the biomass or biochar to _LaCl is 1%-20%. . 4. A method for constructing basic lanthanum carbonate on the surface of biochar according to claim 1, characterized in that, in step S1, the alkali in the alkaline solution is urea, sodium hydroxide or potassium hydroxide. One; the pH after adding the alkaline solution=8-12. 5. A method for constructing basic lanthanum carbonate on the surface of biochar according to claim 1, characterized in that in step S1, the conditions of the hydrothermal method are reaction at 150-250°C for 1-12 hours. 6. Biochar loaded with lanthanum basic carbonate obtained by the method of constructing lanthanum basic carbonate on the surface of biochar according to any one of claims 1 to 5. 7. Application of the basic lanthanum carbonate-loaded biochar in the adsorption, recovery and immobilization of phosphorus according to claim 6. 8. Application of the lanthanum basic carbonate-loaded biochar according to claim 6 for detecting phosphorus concentration in soil/wastewater.