Application method of hydrothermal carbon loaded oxalyte in heavy metal adsorption

Abstract

The invention discloses an application method of hydrothermal carbon loaded oxalyte in heavy metal adsorption. According to the application method, the effect of the hydrothermal carbon-loaded oxalatite on the adsorption of the arsenic element and the cadmium element is found for the first time, the effect of the hydrothermal carbon-loaded oxalatite on the combined and synergistic adsorption of the arsenic element and the cadmium element is particularly found, and particularly, the existence of the arsenic element can promote the adsorption of the cadmium element. According to the method, competitive adsorption between cadmium and arsenic can be avoided, the method has high adsorption capacity on both cadmium and arsenic, and a new way is provided for rapidly, efficiently and synchronously treating arsenic and cadmium in water.

Description

Technical Field

[0001] The present invention relates to heavy metal adsorbents, and particularly to the application of hydrothermal carbon supported iron oxalate in heavy metal adsorption. Background Art

[0002] Cadmium and arsenic are two of the most typical heavy metals in wastewater pollution, with high biological toxicity, poor degradability, and biological enrichment effects. They can exist in the environment for a long time, posing a serious threat to the ecosystem and human health. Currently, the main methods for removing cadmium and arsenic heavy metal ions in the water environment include chemical precipitation, ion exchange, electrochemistry, membrane separation, and adsorption. Among them, the adsorption method has the advantages of simple operation, low cost, and good removal effect on low-concentration metal ions, so it has become the most widely used treatment technology in production activities.

[0003] Traditional adsorbents often cannot synchronously adsorb cadmium and arsenic in wastewater because positively charged cadmium and negatively charged arsenic in wastewater tend to adsorb on surfaces with different electricities due to electrostatic action, and they will also compete for adsorption sites through surface complexation.

[0004] In recent years, studies have found that iron-carbon composites have a porous structure, a high specific surface area, and negatively charged surface oxygen-containing functional groups, which can achieve the synchronous removal of cadmium and arsenic to a certain extent. However, current iron-carbon composites still inevitably have competitive adsorption between the two when adsorbing cadmium and arsenic complex pollution, and the maximum adsorption capacities for cadmium and arsenic are not ideal. In view of the above problems, there is an urgent need to develop a new material that can avoid competitive adsorption between cadmium and arsenic and has a high adsorption capacity for both cadmium and arsenic.

[0005] Hydrothermal carbon supported iron oxalate synthesized by a one-step method (disclosed in the invention patent CN202110958312.3) is a new type of iron-carbon composite. Among them, Fe(III) is in-situ reduced to Fe(II), and iron oxalate is distributed on the surface of hydrothermal carbon in a relatively dispersed form, which is beneficial to the synergistic effect of the two in the heterogeneous (pseudo) Fenton catalytic process. It can be used as a photocatalyst in the heterogeneous (pseudo) Fenton catalytic reaction for organic matter degradation. However, whether it can be applied to the treatment of inorganic substances or heavy metal adsorption has not been fully studied. Summary of the Invention

[0006] Aiming at the defects of the prior art, the purpose of the present invention is to propose an application method of hydrothermal carbon supported iron oxalate in heavy metal adsorption. This application method first discovers that hydrothermal carbon supported iron oxalate synthesized by a one-step method can simultaneously adsorb cadmium and arsenic, and the presence of arsenic can enhance the adsorption of cadmium by the material.

[0007] The technical solution of the present invention is as follows:

[0008] A method for the application of iron oxalate loaded on hydrothermal carbon in heavy metal adsorption, which is to adsorb arsenic elements in water by the iron oxalate loaded on hydrothermal carbon.

[0009] The inventors unexpectedly found that the prepared iron oxalate loaded on hydrothermal carbon has a particularly significant adsorption effect on arsenic elements in addition to its original organic matter catalytic degradation effect, with a removal rate exceeding 90%, and is not affected by the presence of other heavy metal elements, especially cadmium elements, in the water body.

[0010] Among them, the preparation method of the iron oxalate loaded on hydrothermal carbon is as follows:

[0011] Perform hydrothermal reaction on the reaction solution of the aqueous solution containing ferric salt and the precursor of iron oxalate loaded on hydrothermal carbon; freeze-dry the reaction product obtained after the hydrothermal reaction; wherein, the precursor of iron oxalate loaded on hydrothermal carbon is selected from at least one of glucose, fructose, sucrose, maltose, starch, cellulose and lignin; the ferric salt is selected from at least one of ferric nitrate and ferric chloride; the temperature of the freeze-drying is -30°C to -50°C, and the time is 10 - 14h; the mass ratio of the ferric salt to the precursor of iron oxalate loaded on hydrothermal carbon, that is, the iron-carbon ratio, is (0.1 - 5):1; the reaction temperature of the hydrothermal reaction is 170 - 350°C, and the reaction time is 2 - 8h.

[0012] According to some preferred embodiments of the present invention, the iron-carbon ratio in the iron oxalate loaded on hydrothermal carbon is 1:1 or 2:1.

[0013] The inventors unexpectedly found that under this preferred embodiment, the iron oxalate loaded on hydrothermal carbon has the best arsenic element adsorption effect.

[0014] The present invention also provides another application method of the iron oxalate loaded on hydrothermal carbon in heavy metal adsorption, which is to adsorb cadmium elements in water by the iron oxalate loaded on hydrothermal carbon.

[0015] The inventors unexpectedly found that the iron oxalate loaded on hydrothermal carbon can also achieve the adsorption and fixation of cadmium elements.

[0016] The present invention also provides another application method of the iron oxalate loaded on hydrothermal carbon in heavy metal adsorption, which is to jointly and synergistically adsorb arsenic elements and cadmium elements in water by the iron oxalate loaded on hydrothermal carbon. The joint and synergistic adsorption includes: simultaneously adsorbing arsenic elements and cadmium elements, first adsorbing arsenic elements and then cadmium elements, and first adsorbing cadmium elements and then arsenic elements, and enhancing the adsorption of cadmium elements by the iron oxalate loaded on hydrothermal carbon through the adsorption of arsenic elements during the adsorption process.

[0017] Preferably, the combined adsorption is for adsorbing arsenic and cadmium elements, or first adsorbing arsenic elements and then adsorbing cadmium elements.

[0018] The inventors unexpectedly found that the hydrothermal carbon-supported iron oxalate can simultaneously adsorb arsenic and cadmium elements with adsorption competition. In particular, the presence of arsenic can promote the adsorption of cadmium by the hydrothermal carbon-supported iron oxalate.

[0019] For example, in the absence of arsenic, the adsorption capacity of the hydrothermal carbon-supported iron oxalate for cadmium can reach 21.9 mg / g, while in the presence of 50 mg / L of arsenic in the water body, the adsorption capacity of the hydrothermal carbon-supported iron oxalate for cadmium can increase to 28.5 mg / g.

[0020] According to some preferred embodiments of the present invention, the adsorption is carried out at room temperature.

[0021] According to some preferred embodiments of the present invention, the adsorption time is 12 - 24 h.

[0022] According to some preferred embodiments of the present invention, the pH of the water body is adjusted to 5 - 6.

[0023] According to some preferred embodiments of the present invention, the addition amount of the hydrothermal carbon-supported iron oxalate in the water body is 0.9 - 1.1 g / L.

[0024] According to some preferred embodiments of the present invention, the combined synergistic adsorption has an adsorption capacity for arsenic elements reaching 165 - 170 mg / g and an adsorption capacity for cadmium elements reaching 28 - 30 mg / g.

[0025] According to some preferred embodiments of the present invention, the adsorption concentration of the combined synergistic adsorption for arsenic elements in the water body reaches 82.5 - 85 mg / L, and the adsorption concentration for cadmium elements reaches 28 - 30 mg / L.

[0026] According to some preferred embodiments of the present invention, the iron-carbon ratio in the hydrothermal carbon-supported iron oxalate is 1:5 or 5:1.

[0027] The inventors unexpectedly found that at this iron-carbon ratio, the hydrothermal carbon-supported iron oxalate has similar adsorption and removal capabilities for arsenic and cadmium elements.

[0028] The present invention has the following beneficial effects:

[0029] The present invention first discovers the application of one-step synthesized hydrothermal carbon-supported iron oxalate in the adsorption of heavy metals cadmium and arsenic, and unexpectedly discovers that it has a synchronous fixation effect on these two elements that originally had a competitive adsorption effect, providing an application method for a new material that can avoid competitive adsorption between cadmium and arsenic and has a high adsorption capacity for both cadmium and arsenic;

[0030] The present invention unexpectedly discovers that in the Cd-As composite adsorption, the presence of cadmium does not affect the adsorption and fixation efficiency of arsenate (As(V)) by iron oxalate loaded on hydrothermal carbon, while the presence of As(V) promotes the adsorption capacity of iron oxalate loaded on hydrothermal carbon for cadmium;

[0031] The present invention unexpectedly discovers that in iron oxalate loaded on hydrothermal carbon, the main adsorption sites occupied by Cd and As(V) are different. Cd can be fixed on the surface through electrostatic interaction and functional group complexation and coordination, while As is fixed on the surface by forming iron arsenate through ligand exchange in an inner-sphere coordination manner. In addition, after adsorbing a large amount of As(V), it can also enhance the electrostatic interaction by reducing the surface charge and promote the fixation of Cd by forming an Fe-As-Cd ternary complex with anionic As(V) as the bridge, realizing the synchronous and enhanced removal of Cd-As. Description of the Drawings

[0032] Figure 1 Statistical chart of the co-adsorption performance of iron oxalate loaded on hydrothermal carbon with different iron-carbon ratios obtained in Example 3 for Cd-As;

[0033] Figure 2 Adsorption kinetic curves obtained in Example 4, where (a) is the kinetic curve of arsenate adsorption by iron oxalate loaded on hydrothermal carbon at different cadmium concentrations; (b) is the kinetic curve of cadmium adsorption by iron oxalate loaded on hydrothermal carbon at different arsenate concentrations;

[0034] Figure 3 Isothermal adsorption curves obtained in Example 4, where (a) is the isothermal adsorption curve of the adsorption capacity of arsenate by iron oxalate loaded on hydrothermal carbon at different cadmium concentrations, and (b) is the isothermal adsorption curve of the adsorption capacity of cadmium by iron oxalate loaded on hydrothermal carbon at different arsenate concentrations;

[0035] Figure 4 Curves showing the influence of different addition sequences of Cd and As on the adsorption capacity of iron oxalate loaded on hydrothermal carbon obtained in Example 5, where (a) is the influence on the adsorption capacity of As by iron oxalate loaded on hydrothermal carbon, and (b) is the influence on the adsorption capacity of Cd by iron oxalate loaded on hydrothermal carbon;

[0036] Figure 5 XPS full spectra of iron oxalate loaded on hydrothermal carbon before adsorption (a), after separately adsorbing Cd (b), after separately adsorbing As (c), and after co-adsorbing As-Cd (d) obtained in Example 6;

[0037] Figure 6 XPS O 1s full spectra of iron oxalate loaded on hydrothermal carbon before adsorption (a), after separately adsorbing Cd (b), after separately adsorbing As (c), and after co-adsorbing As-Cd (d) obtained in Example 6;

[0038] Figure 7 TEM image (a) of the hydrothermal carbon-supported iron oxalate raw material obtained in Example 6 and the EDS surface scan images (b) of Fe, O, and C elements therein;

[0039] Figure 8 TEM image (a) of the hydrothermal carbon-supported iron oxalate after adsorbing cadmium and arsenic obtained in Example 6 and the EDS surface scan images (b) of Fe, O, and C elements therein. Detailed implementation manners

[0040] The technical solutions in the present invention will be further described below in conjunction with the embodiments of the present invention. The following described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0041] Example 1

[0042] The hydrothermal carbon-supported iron oxalate was obtained through the following process:

[0043] (1) 10 g of anhydrous glucose reagent and 70 mL of ultrapure water were respectively placed in 5 200-mL beakers, and ultrasonicated and stirred to make them fully mixed;

[0044] (2) 1 g, 2 g, 10 g, 20 g, and 50 g of Fe(NO3)3·9H2O were added to these 5 beakers, and ultrasonicated and stirred continuously until they were completely dissolved to obtain a mixed reaction solution;

[0045] (3) The 5 kinds of mixed reaction solutions were respectively transferred into 5 100-mL autoclaves, hydrothermally reacted at 180 °C for 8 h, and filtered by a mixed cellulose microporous membrane with a pore size of 0.22 μm to obtain the reacted hydrothermal products;

[0046] (4) The obtained hydrothermal products were placed in a freeze dryer at -40 °C for 12 h to obtain hydrothermal carbon-supported iron oxalates with iron-carbon ratios (i.e., the mass ratio of Fe(NO3)3·9H2O to glucose) of 1:10, 1:5, 1:1, 2:1, and 5:1, respectively.

[0047] Example 2

[0048] Adsorption solutions with different concentrations of Cd and As were prepared through the following process:

[0049] (1) Weigh cadmium chloride and / or sodium arsenate quantitatively according to the concentration requirements, put them into a container, and make up to 1L with ultrapure water to prepare the adsorption solution; the concentrations of As element in the adsorption solution are 0, 10, 20, 30, 50mg / L respectively, and the concentrations of Cd element are 0, 10, 20, 30, 50mg / L respectively. There are 25 mixing methods in total to obtain 25 adsorption solutions;

[0050] (2) Use NaOH and / or HCl to adjust the pH of the adsorption solution to 5.

[0051] Example 3

[0052] The test on the influence of raw material ratio on the adsorption capacity is carried out through the following process:

[0053] (1) Add 20mg of hydrothermal carbon loaded with iron oxalate ore with different iron-carbon ratios obtained in Example 1 and 20mL of the adsorption solution containing 50mg / L of Cd and 50mg / L of As obtained in Example 2 into a 50mL centrifuge tube;

[0054] (2) Use a mixer to continuously stir the centrifuge tube at a speed of 80rpm at room temperature for 24h to achieve adsorption equilibrium;

[0055] (3) Pipette 1mL of the suspension obtained after adsorption equilibrium, filter it through a 0.22μm filter membrane, and collect the filtrate;

[0056] (4) Determine the As content in the filtrate by an atomic fluorescence spectrometer equipped with a liquid chromatography unit, and determine the Cd content in the filtrate by an inductively coupled plasma mass spectrometer.

[0057] The test results are as shown in the appendix Figure 1 It can be seen that the hydrothermal carbon loaded with iron oxalate ore of the present invention has good removal effects on both As and Cd. When the iron-carbon ratio is 2:1, the adsorption effects on As and Cd reach the best at the same time. And at specific iron-carbon ratios (1:1 or 2:1), the removal effect on As is particularly significant. At some other specific iron-carbon ratios (1:5 or 5:1), the removal rates of As and Cd are similar.

[0058] Example 4

[0059] The As-Cd co-adsorption test is carried out through the following process:

[0060] (1) Add 20mg of hydrothermal carbon loaded with iron oxalate ore with an iron-carbon ratio of 2:1 obtained in Example 1 and 20mL of the adsorption solution with an As concentration of 30mg / L and Cd concentrations of 0, 10, 20, 30mg / L obtained in Example 2 into a 50mL centrifuge tube to test the adsorption kinetics of As by hydrothermal carbon loaded with iron oxalate ore at different Cd concentrations;

[0061] (2) Add 20 mg of the iron oxalate mineral loaded on hydrothermal carbon with an iron-to-carbon ratio of 2:1 obtained in Example 1 and 20 mL of the adsorption solution obtained in Example 2 with a Cd concentration of 30 mg / L and As concentrations of 0, 10, 20, and 30 mg / L into a 50 mL centrifuge tube to test the adsorption kinetics of the iron oxalate mineral loaded on hydrothermal carbon for Cd at different As concentrations;

[0062] (3) Add 20 mg of the iron oxalate mineral loaded on hydrothermal carbon with an iron-to-carbon ratio of 2:1 obtained in Example 1 and 20 mL of the adsorption solution with different As concentrations and different Cd concentrations obtained in Example 2 into a 50 mL centrifuge tube to obtain the influence of different Cd concentrations on the As adsorption capacity of the iron oxalate mineral loaded on hydrothermal carbon and the influence of different As concentrations on the Cd adsorption capacity of the iron oxalate mineral loaded on hydrothermal carbon;

[0063] (4) Use a mixer to continuously stir the centrifuge tube at a speed of 80 rpm at room temperature to achieve adsorption equilibrium;

[0064] (5) Take samples from the centrifuge tubes in steps (1) and (2) at 0, 0.3, 0.5, 1, 2, 3, 6, 12, and 24 h during the stirring in step (4), and take samples from the centrifuge tubes in step (3) after stirring for 24 h in step (4);

[0065] (6) When sampling, pipette 1 mL of the suspension obtained after adsorption equilibrium, filter it through a 0.22 μm filter membrane, and collect the filtrate;

[0066] (7) Determine the As content in the filtrate by an atomic fluorescence spectrometer equipped with a liquid chromatography unit, and determine the Cd content in the filtrate by an inductively coupled plasma mass spectrometer.

[0067] According to the measurement results, perform data analysis through SPSS to obtain the kinetic curve as shown in the appendix Figure 2 and the isothermal adsorption curve as shown in the appendix Figure 3 .

[0068] From appendix Figure 2 (a) and appendix Figure 3 (a), it can be seen that the iron oxalate mineral loaded on hydrothermal carbon after adsorption in the adsorption solution with different Cd concentrations can achieve complete removal of As in about 10 h, and the increase in the Cd concentration in the adsorption solution does not affect the As adsorption capacity of the iron oxalate mineral loaded on hydrothermal carbon, indicating that the presence of Cd does not inhibit the adsorption and fixation of As by the iron oxalate mineral loaded on hydrothermal carbon.

[0069] From appendix Figure 2 (b) and appendix Figure 3(b) It can be seen that as the original concentration of As in the adsorption solution increases, the adsorption capacity of hydrothermal carbon-supported iron oxalate for Cd also increases correspondingly, enhancing the adsorption ability of hydrothermal carbon-supported iron oxalate for Cd, indicating that the presence of As will promote the fixation of Cd by hydrothermal carbon-supported iron oxalate.

[0070] Example 5

[0071] The tests of Cd adsorption first and then As adsorption and As adsorption first and then Cd adsorption were carried out through the following process:

[0072] (1) Add 20 mg of hydrothermal carbon-supported iron oxalate with an iron-carbon ratio of 2:1 obtained in Example 1 and 20 mL of the adsorption solution containing 50 mg / L Cd obtained in Example 2 into a 50 mL centrifuge tube;

[0073] (2) Use a mixer to continuously stir the centrifuge tube at a speed of 80 rpm at room temperature for 24 h;

[0074] (3) Add As to the centrifuge tube after the Cd adsorption reaches equilibrium so that the concentration of As in the solution is 50 mg / L;

[0075] (4) Continuously stir the centrifuge tube at a speed of 80 rpm at room temperature for 24 h;

[0076] (5) Add 20 mg of hydrothermal carbon-supported iron oxalate with an iron-carbon ratio of 2:1 obtained in Example 1 and 20 mL of the adsorption solution containing 50 mg / L As obtained in Example 2 into a 50 mL centrifuge tube;

[0077] (6) Use a mixer to continuously stir the centrifuge tube at a speed of 80 rpm at room temperature for 24 h;

[0078] (7) Add Cd to the centrifuge tube after the As adsorption reaches equilibrium so that the concentration of Cd in the solution is 50 mg / L;

[0079] (8) Continuously stir the centrifuge tube at a speed of 80 rpm at room temperature for another 24 h;

[0080] (9) During the 24 h adsorption process in steps (2) and (6), samples are taken at 0, 0.5, 1, 2, 6, 12, and 24 h respectively. During the 24 h adsorption process in steps (4) and (8), samples are taken at 0, 0.5, 1, 2, 6, 12, and 24 h respectively, filtered through a 0.22 μm filter membrane, and the filtrate is collected;

[0081] (10) Determine the As content in the filtrate by an atomic fluorescence spectrometer equipped with a liquid chromatography unit, and determine the Cd content in the filtrate by an inductively coupled plasma mass spectrometer.

[0082] According to the measurement results, after data processing by SPSS, the curve as shown in the appendix Figure 4 is obtained. The appendix Figure 4 a shows the influence of different addition sequences of Cd and As on the adsorption amount of As by hydrothermal carbon-supported iron oxalate. It can be seen that the three adsorption scenarios have no obvious influence on the kinetic process of As adsorption by hydrothermal carbon-supported iron oxalate, and the complete removal of As is achieved at 24 h, indicating that the presence of Cd does not affect the adsorption of As by hydrothermal carbon-supported iron oxalate.

[0083] The appendix Figure 4 b shows the influence of different addition sequences of Cd and As on the adsorption amount of Cd by hydrothermal carbon-supported iron oxalate. It can be seen that in the experimental groups with coexistence of Cd and As and addition of As first followed by Cd, the adsorption amount of Cd increases from 22.1 mg / g to 28.1 mg / g. While in the experimental group with addition of Cd first followed by As, the adsorption amount of Cd first reaches 22.1 mg / g after 24 h, and then rapidly rises to 28.1 mg / g after addition of As. It shows that the presence of As significantly promotes the adsorption and removal of Cd.

[0084] Example 6

[0085] Furthermore, XPS characterization is carried out on the adsorbates (denoted as Hum / HTC-Cd, Hum / HTC-As and Hum / HTC-Cd / As respectively) of hydrothermal carbon-supported iron oxalate with an iron-carbon ratio of 2:1 in Example 1 (hereinafter denoted as Hum / HTC) after single Cd adsorption, single As adsorption and Cd-As composite adsorption at the same concentration (concentration is 50 mg / L). The results are as shown in the appendix Figure 5 and the fine spectrum of O1s in the XPS full spectrum is analyzed. The results are as shown in the appendix Figure 6 as follows.

[0086] Furthermore, the adsorbates are analyzed by transmission electron microscopy combined with energy spectrum analysis technology (TEM mapping) to obtain the transmission electron microscopy and elemental surface scan map of the original hydrothermal carbon-supported iron oxalate as shown in the appendix Figure 7 and the transmission electron microscopy and elemental surface scan map of hydrothermal carbon-supported iron oxalate after Cd-As composite adsorption as shown in the appendix Figure 8 as follows.

[0087] From the appendix Figure 5It can be seen that the original Hum / HTC has characteristic peaks of Fe 2p, O 1s, and C 1s, indicating that the main elements in this material are C, Fe, and O. After single Cd adsorption treatment, a signal peak of Cd 3d appears in the full spectrum, confirming that iron oxalate loaded on hydrothermal carbon can effectively adsorb and fix Cd. After single As adsorption treatment, a signal peak of As 3d appears in the full spectrum, also confirming that iron oxalate loaded on hydrothermal carbon can effectively adsorb and fix As. After simultaneous Cd-As adsorption treatment, signal peaks of both Cd 3d and As 3d appear in the full spectrum, and the signal peak intensity of Cd 3d is stronger than that of single Cd adsorption treatment. This indicates that the iron oxalate loaded on hydrothermal carbon can achieve synchronous fixation of Cd-As, and the presence of As will promote the adsorption and fixation of Cd.

[0088] For the Figure 6 analysis of the fine spectrum of O 1s in the XPS full spectrum, the O 1s spectrum is mainly composed of four main peaks, corresponding to metal oxides (M-O), hydroxyl groups bonded to metals (M-OH), hydroxyl groups on the HTC surface (C-OH), and adsorbed water molecules (H2O) in the material. From the Figure 6It can be seen that after the adsorption of Cd or As by Hum / HTC, a decrease in the relative area of C-OH and an increase in the relative areas of M-OH and M-O were observed. This indicates that -OH on the surface of hydrothermal carbon may act as adsorption sites to promote the adsorption and fixation of Cd and As. Among them, the decrease in C-OH in the Cd treatment was greater than that in the As treatment, meaning that Cd has a stronger ability to occupy the hydroxyl sites on the surface of hydrothermal carbon than As. Consequently, most of the Cd may be fixed on the surface of hydrothermal carbon. After the co-treatment of Cd-As, the content of C-OH further decreased, indicating that more surface hydroxyl sites were occupied. This may be because after a large amount of As was adsorbed by the goethite-loaded hydrothermal carbon, the surface electronegativity increased, enhancing the electrostatic interaction between the goethite-loaded hydrothermal carbon and Cd, resulting in more hydroxyl sites being occupied by Cd. The increase in the intensity of Fe-OH may be due to the occurrence of inner-sphere coordination complexation reactions on the surface of Hum / HTC (e.g., (FeOH)2CdOH and Fe2O2AsOH). This reaction may lead to a significant enhancement in the adsorption capacity of the material for As(V). At the same time, the peak percentage (56.2%) in the Hum / HTC-Cd / As sample was significantly higher than that in Hum / HTC-Cd (49.0%) and Hum / HTC-As (54.3%). This shows that the presence of As greatly promotes the adsorption of Cd, indicating that the presence of As greatly promotes the adsorption of Cd. The adsorption capacity of Hum / HTC for As is much greater than that for Cd, meaning that in the As-Cd co-adsorption system, it is easier to form a Fe-As-Cd ternary complex in the form of anionic As bridging to promote the fixation of Cd. In summary, Cd may be mostly fixed by occupying the hydroxyl sites on the surface of hydrothermal carbon, while As(V) is more easily adsorbed and fixed on the surface of goethite. And after a large amount of As(V) is adsorbed by the goethite-loaded hydrothermal carbon, it will promote the fixation of Cd(II) by reducing the surface charge, enhancing the electrostatic interaction, and forming a Fe-As-Cd ternary complex with anionic As(V) as the bridge.

[0089] From the attachment Figure 7 It can be more clearly observed that the goethite nanoparticles are uniformly loaded on the surface of the hydrothermal carbon spheres. The surface scan results show that the main element distributions in this area are C, O, and Fe. From the attachment Figure 8 It can be more clearly observed that there are obvious differences in the distribution of Cd and As. Among them, the Cd element is mainly uniformly distributed on the surface of the hydrothermal carbon spheres, showing a good correlation with the distribution of the carbon element. As has a stronger signal in the area where goethite is distributed, showing a good correlation with the distribution of the iron element. This indicates that the adsorption sites occupied by Cd and As may be different. Cd is mainly fixed on the surface of hydrothermal carbon, while As is fixed on the surface of goethite. Therefore, Hum / HTC mainly fixes Cd on the surface of hydrothermal carbon through electrostatic interaction and functional group complexation coordination, while the fixation of As is mainly through ligand exchange to form iron arsenate and is fixed on the surface of goethite.

[0090] It should be noted that the above are only the preferred embodiments of the present invention, and they should not limit the protection scope of the technical solutions of the present invention. Any modifications made by those of ordinary skill in the art to the technical solutions described in the foregoing embodiments, and any equivalent replacements of technical features, should all be included within the protection scope of the present invention.

Claims

1. A method for the application of iron oxalate mineral loaded on hydrothermal carbon in heavy metal adsorption, characterized in that, Adsorb arsenic elements in water by using the iron oxalate loaded on hydrothermal carbon. Among them, the preparation method of the iron oxalate loaded on hydrothermal carbon includes: performing hydrothermal reaction on a reaction solution of an aqueous solution containing ferric salt and a precursor of iron oxalate loaded on hydrothermal carbon; freeze-drying the reaction product obtained after the hydrothermal reaction. Among them, the precursor of the iron oxalate loaded on hydrothermal carbon is selected from one or more of glucose, fructose, sucrose, maltose, starch, cellulose and lignin; the ferric salt is selected from ferric nitrate and / or ferric chloride; the temperature of the freeze-drying is -30°C to -50°C, and the time is 10-14h; the mass ratio of the ferric salt to the precursor of the iron oxalate loaded on hydrothermal carbon, that is, the iron-carbon ratio, is (0.1-5):1; the reaction temperature of the hydrothermal reaction is 170-350°C, and the reaction time is 2-8h.

2. The application method according to claim 1, characterized in that, The iron-carbon ratio in the iron oxalate loaded on hydrothermal carbon is 1:1 or 2:

1.

3. A method for the application of iron oxalate loaded on hydrothermal carbon in heavy metal adsorption, characterized in that, Adsorb cadmium elements in water by using the iron oxalate loaded on hydrothermal carbon. Among them, the preparation method of the iron oxalate loaded on hydrothermal carbon includes: performing hydrothermal reaction on a reaction solution of an aqueous solution containing ferric salt and a precursor of iron oxalate loaded on hydrothermal carbon; freeze-drying the reaction product obtained after the hydrothermal reaction. Among them, the precursor of the iron oxalate loaded on hydrothermal carbon is selected from one or more of glucose, fructose, sucrose, maltose, starch, cellulose and lignin; the ferric salt is selected from ferric nitrate and / or ferric chloride; the temperature of the freeze-drying is -30°C to -50°C, and the time is 10-14h; the mass ratio of the ferric salt to the precursor of the iron oxalate loaded on hydrothermal carbon, that is, the iron-carbon ratio, is (0.1-5):1; the reaction temperature of the hydrothermal reaction is 170-350°C, and the reaction time is 2-8h.

4. A method for the application of iron oxalate mineral loaded on hydrothermal carbon in heavy metal adsorption, characterized in that, Perform combined and synergistic adsorption of arsenic elements and cadmium elements in water by using the iron oxalate loaded on hydrothermal carbon. The combined and synergistic adsorption includes: simultaneously adsorbing arsenic elements and cadmium elements, first adsorbing arsenic elements and then cadmium elements, and first adsorbing cadmium elements and then arsenic elements, and enhancing the adsorption of cadmium elements by the iron oxalate loaded on hydrothermal carbon through the adsorption of arsenic elements during the adsorption process. Among them, the preparation method of the iron oxalate loaded on hydrothermal carbon includes: performing hydrothermal reaction on a reaction solution of an aqueous solution containing ferric salt and a precursor of iron oxalate loaded on hydrothermal carbon; freeze-drying the reaction product obtained after the hydrothermal reaction. Among them, the precursor of the iron oxalate loaded on hydrothermal carbon is selected from one or more of glucose, fructose, sucrose, maltose, starch, cellulose and lignin; the ferric salt is selected from ferric nitrate and / or ferric chloride; the temperature of the freeze-drying is -30°C to -50°C, and the time is 10-14h; the mass ratio of the ferric salt to the precursor of the iron oxalate loaded on hydrothermal carbon, that is, the iron-carbon ratio, is (0.1-5):1; the reaction temperature of the hydrothermal reaction is 170-350°C, and the reaction time is 2-8h.

5. The application method according to claim 4, characterized in that The adsorption is carried out at room temperature.

6. The application method according to claim 4, characterized in that, The adsorption time is 12-24h.

7. The application method according to claim 4, characterized in that The pH of the water body is adjusted to 5 - 6.

8. The application method according to claim 4, wherein The addition amount of the hydrothermal carbon-supported iron oxalate in the water body is 0.9 - 1.1 g / L.

9. The application method according to claim 4, wherein The adsorption amount of arsenic element by the combined synergistic adsorption reaches 165 - 170 mg / g, and the adsorption amount of cadmium element reaches 28 - 30 mg / g; and / or, the adsorption concentration of arsenic element in the water body by the combined synergistic adsorption reaches 82.5 - 85 mg / L, and the adsorption concentration of cadmium element reaches 28 - 30 mg / L.

10. The application method according to claim 4, characterized in that The iron-carbon ratio in the hydrothermal carbon-supported iron oxalate is 1:5 or 5:1.

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