Double-shell calcium carbonate / calcium sulfide supported biochar adsorbent and its preparation and application

Abstract

The invention discloses a double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent and its preparation and application, belonging to the technical field of adsorbents. The double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent uses kelp biochar as the core, calcium sulfide as the inner shell layer, and calcium carbonate as the outer shell layer. The preparation method is as follows: pretreat kelp powder with calcium sulfite to obtain pretreated kelp particles; carbonize the pretreated kelp particles to obtain calcium oxide / calcium sulfide loaded biochar; the calcium oxide / calcium sulfide loaded biochar is subjected to two aging treatments to obtain the double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent. The double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent of the invention has the characteristics of easily available raw materials, green, environmental-friendly and convenient preparation method, rich adsorption sites, etc., has a high adsorption capacity for Cd(II), and can be used for the repair of Cd(II)-polluted water bodies.

Description

Technical Field

[0001] The present invention relates to the technical field of adsorbents, in particular to a double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent and its preparation and application. Background Art

[0002] At present, there are many methods for treating Cd(II)-containing wastewater, such as ion exchange method, chemical precipitation method and adsorption method, etc. Among them, the adsorption technology has become the first choice because of its renewable, environmentally friendly, low cost and outstanding effect. Biochar has good application potential in the removal of heavy metals due to its rich porous structure and various functional groups. However, the adsorption effect of general raw biochar is limited and it is impossible to achieve efficient removal of heavy metal cadmium (Cd). Therefore, it is necessary to explore reasonable biochar modification strategies to adapt to the complex wastewater environment and reduce the pollution degree of heavy metal Cd(II) to the environment. Summary of the Invention

[0003] The purpose of the present invention is to provide a double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent and its preparation and application to solve the problems existing in the above-mentioned prior art.

[0004] To achieve the above purpose, the present invention provides the following solutions:

[0005] One of the technical solutions of the present invention: A double-shell calcium carbonate / calcium sulfide (CaCO3 / CaS) loaded biochar adsorbent, wherein the double-shell calcium carbonate / calcium sulfide (CaCO3 / CaS) loaded biochar adsorbent has kelp biochar as the core, calcium sulfide (CaS) as the inner shell layer, and calcium carbonate (CaCO3) as the outer shell layer.

[0006] That is, the double-shell CaCO3 / CaS loaded biochar adsorbent takes kelp biochar as the matrix, and a double-shell structure with CaS as the inner shell layer (or called the inner layer) and CaCO3 as the outer shell layer (or called the surface layer) is loaded on the surface of the kelp biochar.

[0007] The surface of the double-shell CaCO3 / CaS loaded biochar adsorbent of the present invention has a double-layer structure of CaCO3 / CaS. Through the stabilizing effect of the outer shell layer of CaCO3 on the inner shell layer of CaS (due to the slightly soluble nature of CaS, it has higher reactivity, and it can only stably play an adsorption role in the inner layer under the protection of the outer shell layer of CaCO3. Otherwise, CaS will dissolve in water and form intractable flocculent precipitates with Cd(II)), the inner and outer shell layers interact with cadmium ions synchronously during the adsorption process (during the diffusion of Cd(II) into the biochar, part of it is adsorbed by the surface layer of CaCO3 first, and the unadsorbed part of Cd(II) that enters the inner layer of CaS will be continuously adsorbed). Based on the synergistic adsorption effect of CaCO3 / CaS, the double-shell CaCO3 / CaS loaded biochar adsorbent of the present invention has a large Cd(II) adsorption capacity.

[0008] The second technical solution of the present invention: The preparation method of the above-mentioned double-shell calcium carbonate / calcium sulfide (CaCO3 / CaS) loaded biochar adsorbent includes the following steps:

[0009] Pretreat kelp powder with calcium sulfite (CaSO3) to obtain pretreated kelp particles; carbonize the pretreated kelp particles to obtain calcium oxide / calcium sulfide (CaO / CaS) loaded biochar; perform a first aging treatment on the calcium oxide / calcium sulfide (CaO / CaS) loaded biochar to obtain calcium hydroxide / calcium sulfide (Ca(OH)2 / CaS) loaded biochar; perform a second aging treatment on the calcium hydroxide / calcium sulfide (Ca(OH)2 / CaS) loaded biochar to obtain the double-shell calcium carbonate / calcium sulfide (CaCO3 / CaS) loaded biochar adsorbent.

[0010] First, through the action of sodium alginate (SA) rich in kelp, insoluble CaSO3 is captured and stably dispersed on kelp powder to obtain pretreated kelp particles. Next, during the carbonization of the pretreated kelp particles, the kelp powder is converted into reducing biochar. Under high-temperature conditions, the action between CaSO3 on the surface of the kelp powder and the reducing biochar has a distance limitation, such that part of the CaSO3 in contact with the reducing biochar in the inner layer is reduced to CaS, while part of the CaSO3 in the outer layer is transformed into CaO at high temperature, obtaining CaO / CaS-loaded biochar with a double-layer loading of CaO and CaS (the CaO layer is the surface layer and the CaS layer is the inner layer). Next, during the first aging treatment (artificial aging treatment), in a high-humidity environment (relative humidity of 80 - 90%) at 105 °C, the CaO layer on the surface of the CaO / CaS-loaded biochar can be fully transformed into Ca(OH)2, obtaining Ca(OH)2 / CaS-loaded biochar. During the further second aging treatment (natural aging treatment), the Ca(OH)2 on the surface of the Ca(OH)2 / CaS-loaded biochar is further transformed into CaCO3, finally obtaining a double-shell CaCO3 / CaS-loaded biochar adsorbent with a double-layer loading of CaCO3 and CaS (the CaCO3 layer is the surface layer and the CaS layer is the inner layer) (the two-step aging process only causes the transformation of CaO on the surface layer into CaCO3).

[0011] The uniform and stable dispersion of CaSO3 on kelp powder caused by sodium alginate rich in kelp enables both the subsequently prepared CaO / CaS-loaded biochar and the CaCO3 / CaS-loaded biochar adsorbent to exhibit the characteristic of uniform dispersion of the surface loading, which can provide more adsorption sites on the surface of the adsorbent.

[0012] Further, the pretreatment of kelp powder with CaSO3 to obtain pretreated kelp particles includes: adding kelp powder into a CaSO3 suspension, mixing for 30 - 90 min under ultrasonic and stirring to obtain a mixed solution, and then drying the mixed solution to obtain the pretreated kelp particles.

[0013] Further, the CaSO3 suspension is prepared from CaSO3 and water with a dosage ratio of 1 - 2 g:100 - 200 mL.

[0014] Further, the mass ratio of the kelp powder to CaSO3 in the CaSO3 suspension is 10 g:1 - 2 g.

[0015] Further preferably, the CaSO3 suspension is prepared from CaSO3 and water with a dosage ratio of 2 g:125 mL; the mass ratio of the kelp powder to CaSO3 in the CaSO3 suspension is 10:2; the mixing time under ultrasonic and stirring is 30 min.

[0016] Further, the drying temperature of the mixed solution is 50 - 80 °C.

[0017] Further preferably, the drying temperature of the mixed solution is 65 °C and the time is 10 h.

[0018] Further, the carbonization conditions include: the heat preservation temperature is 600 - 800 °C and the heat preservation time is 30 - 90 min.

[0019] Further, the carbonization conditions also include: the heating rate is 5 - 10 °C / min.

[0020] Further, the carbonization is carried out in an inert gas atmosphere; the inert gas is preferably nitrogen.

[0021] Further preferably, the carbonization conditions include: the heating rate is 5 °C / min, the heat preservation temperature is 700 °C, and the heat preservation time is 60 min.

[0022] During the high-temperature carbonization process, CaSO3 on the surface of the kelp biochar carrier reacts with the reduced carbon on the carrier at high temperature to form CaS, and the unreduced CaSO3 on the surface layer forms CaO under high-temperature conditions. Therefore, the control of the carbonization temperature is particularly important. The reactions occurring in the inner and outer layers during the carbonization process are as follows:

[0023] Inner layer: 2CaSO3 + 3C → 2CaS + 3CO2↑;

[0024] Outer layer: CaSO3 → CaO + SO2↑.

[0025] Further, the steps of the first aging treatment include: placing the CaO / CaS-loaded biochar in a water vapor environment at 105 °C for 8 - 16 h.

[0026] Further preferably, the CaO / CaS-loaded biochar is placed in a water vapor environment at 105 °C for 12 - 16 h.

[0027] Further, the 105 °C water vapor environment is a high-humidity environment with a relative humidity of 80 - 90%.

[0028] Further, the steps of the second aging treatment include: placing the Ca(OH)2 / CaS-loaded biochar at 20 - 30 °C for 7 days.

[0029] Further, there are no special requirements for the environmental humidity during the second aging process. The Ca(OH)2 / CaS-loaded organism can be placed in a natural indoor environment at 20-30 °C for 7 days.

[0030] Further, the preparation steps of the kelp powder include: cleaning the kelp with water to remove impurities, soaking it in water for 24 h, then drying and pulverizing it to obtain the kelp powder.

[0031] Further, the drying temperature is 50-80 °C and the time is 8-48 h.

[0032] More preferably, the drying temperature is 65 °C and the time is 24 h.

[0033] The third technical solution of the present invention: Application of the above-mentioned double-shell CaCO3 / CaS-loaded biochar adsorbent in adsorbing Cd(II) in wastewater.

[0034] The present invention discloses the following technical effects:

[0035] (1) The surface of the double-shell CaCO3 / CaS-loaded biochar adsorbent of the present invention has a double-layer structure of CaCO3 / CaS. Based on the synergistic adsorption effect of CaCO3 / CaS, the double-shell CaCO3 / CaS-loaded biochar adsorbent has a large Cd(II) adsorption capacity.

[0036] (2) The surface layer of the double-shell CaCO3 / CaS-loaded biochar adsorbent of the present invention is a CaCO3 shell layer, which can effectively prevent the dissolution of internal alkaline substances such as CaS, making the adsorption process stable and not forming difficult-to-treat flocculent precipitates during the adsorption process.

[0037] (3) The raw materials of the double-shell CaCO3 / CaS-loaded biochar adsorbent of the present invention are easily available, the preparation process is simple, no toxic and harmful reagents are used during the preparation process, and a green preparation method is adopted, which is beneficial to the production of the adsorbent. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0039] Figure 1 It is a schematic diagram of the preparation principle and process of the double-shell CaCO3 / CaS-loaded biochar adsorbent in the present invention;

[0040] Figure 2 Schematic diagram of the self-made device used in step (2) of Examples 1-3;

[0041] Figure 3 SEM images of CaO / CaS loaded biochar (product of step (3)) and double-shell CaCO3 / CaS loaded biochar adsorbent (product of step (5)) in Example 1, and calcium-loaded rice straw biochar CAC@Ca in Comparative Example 1;

[0042] Figure 4 Energy spectrum diagrams corresponding to the S element and Ca element distributions of the SEM images of CaO / CaS loaded biochar (product of step (3)) in Example 1 and calcium-loaded rice straw biochar CAC@Ca in Comparative Example 1;

[0043] Figure 5 XRD patterns of CaO / CaS loaded biochar (KAC@CaS-CaO), Ca(OH)2 / CaS loaded biochar (KAC 12 @CaS-Ca(OH)2), and double-shell CaCO3 / CaS loaded biochar adsorbent (KAC 12 @CaS-CaCO3) in Example 1;

[0044] Figure 6 FTIR spectra of CaO / CaS loaded biochar (KAC@CaS-CaO), Ca(OH)2 / CaS loaded biochar (KAC 12 @CaS-Ca(OH)2), and double-shell CaCO3 / CaS loaded biochar adsorbent (KAC 12 @CaS-CaCO3) in Example 1;

[0045] Figure 7 S 2p spectra of sulfur element in X-ray photoelectron spectroscopy of CaO / CaS loaded biochar (KAC@CaS-CaO), Ca(OH)2 / CaS loaded biochar (KAC 12 @CaS-Ca(OH)2), and double-shell CaCO3 / CaS loaded biochar adsorbent (KAC 12 @CaS-CaCO3) in Example 1;

[0046] Figure 8 Double-shell CaCO3 / CaS loaded biochar adsorbents (KAC8@CaS-CaCO3, KAC 12 @CaS-CaCO3, KAC 16 @CaS-CaCO3) obtained in Examples 1-3 and unloaded aged kelp biochar KC obtained in Comparative Example 212 The curve of the adsorption capacity varying with time;

[0047] Figure 9 For the double-shell CaCO3 / CaS-loaded biochar adsorbents (KAC8@CaS-CaCO3, KAC 12 @CaS-CaCO3, KAC 16 @CaS-CaCO3) obtained in Examples 1-3 and the CaO / CaS-loaded biochar (KAC@CaS-CaO) at the adsorption end point in Cd(II) waste liquid. Detailed implementation manners

[0048] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0049] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0050] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0051] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the present invention specification, which are obvious to those skilled in the art. Other implementation manners obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and examples are only exemplary.

[0052] Regarding "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0053] It should be noted that those aspects not described in detail in the present invention are all conventional operation means in the art and are not the focus of the present invention.

[0054] As a first aspect of the present invention, the present invention provides a double-shell CaCO3 / CaS loaded biochar adsorbent, wherein the double-shell CaCO3 / CaS loaded biochar adsorbent uses kelp biochar as the core, CaS as the inner shell layer, and CaCO3 as the outer shell layer.

[0055] As a second aspect of the present invention, the present invention provides a preparation method of the above double-shell CaCO3 / CaS loaded biochar adsorbent (the preparation principle and process schematic diagram are as Figure 1 shown), including the following steps:

[0056] Pretreat kelp powder with CaSO3 to obtain pretreated kelp particles (i.e., kelp particles loaded with CaSO3); carbonize the pretreated kelp particles to obtain CaO / CaS loaded biochar; perform a first aging treatment on the CaO / CaS loaded biochar to obtain Ca(OH)2 / CaS loaded biochar; perform a second aging treatment on the Ca(OH)2 / CaS loaded biochar to obtain the double-shell CaCO3 / CaS loaded biochar adsorbent.

[0057] As an embodiment of the present invention, the step of pretreating kelp powder with CaSO3 to obtain pretreated kelp particles includes: adding kelp powder to a CaSO3 suspension, mixing under ultrasonic and stirring for 30 - 90 min to obtain a mixed solution, and then drying the mixed solution to obtain the pretreated kelp particles.

[0058] As an embodiment of the present invention, the CaSO3 suspension is prepared from CaSO3 and water with a dosage ratio of 1 - 2 g:100 - 200 mL.

[0059] As an embodiment of the present invention, the mass ratio of the kelp powder to CaSO3 in the CaSO3 suspension is 10 g:1 - 2 g.

[0060] As a preferred embodiment of the present invention, the CaSO3 suspension is prepared from CaSO3 and water with a dosage ratio of 2 g:125 mL; the mass ratio of the kelp powder to CaSO3 in the CaSO3 suspension is 10:2; the mixing time under ultrasonic and stirring is 30 min.

[0061] As an embodiment of the present invention, the drying temperature of the mixed solution is 50 - 80 °C, preferably 65 °C, and the time is 10 h.

[0062] As an embodiment of the present invention, the carbonization conditions include: a heating rate of 5 - 10 °C / min, a holding temperature of 600 - 800 °C, and a holding time of 30 - 90 min.

[0063] As an embodiment of the present invention, the carbonization is carried out in an inert gas atmosphere; the inert gas is preferably nitrogen.

[0064] As a preferred embodiment of the present invention, the conditions for the carbonization include: a heating rate of 5 °C / min, a holding temperature of 700 °C, and a holding time of 60 min.

[0065] As an embodiment of the present invention, the steps of the first aging treatment include: placing the CaO / CaS-loaded biochar in a water vapor environment at 105 °C for 8 - 16 h, preferably 12 - 16 h.

[0066] As an embodiment of the present invention, the 105 °C water vapor environment is a high-humidity environment with a relative humidity of 80 - 90%.

[0067] As a preferred embodiment of the present invention, the first aging treatment is carried out in a device capable of generating a high-humidity environment, and Figure 2 the self-made device shown can be selected as the device for generating a high-humidity environment. Figure 2 The device shown can keep the sample in a high-humidity environment, and the environmental temperature of 105 °C can be achieved by placing the device in an oven. Figure 2 The principle of the device shown is as follows: at an environmental temperature of 105 °C, while the CaO / CaS-loaded biochar is heated, the water in the container beaker will also be heated and evaporated, and the generated water vapor will age the CaO / CaS-loaded biochar placed in the inner liner across the water (i.e., promote the transformation of surface CaO to Ca(OH)2), thereby realizing the aging of the biochar by creating a high-humidity heating environment; in addition, to prevent excessive humidity, the top cover of the container is provided with through holes to discharge part of the water vapor, so that the relative humidity in the inner liner always remains at 80 - 90%. The device used for the first aging treatment is not a limitation to the present invention, and any other device capable of generating a high-humidity environment can be selected as long as it ensures that the sample is aged in a high-humidity environment (relative humidity of 80 - 90%) at 105 °C. The high-humidity environment can enable the CaO layer on the surface of the CaO / CaS-loaded biochar to be fully transformed into Ca(OH)2, which is beneficial to the formation of the CaCO3 layer during the second aging treatment (natural aging treatment).

[0068] As an embodiment of the present invention, the steps of the second aging treatment include: placing the Ca(OH)2 / CaS-loaded biochar at 20 - 30 °C for 7 days.

[0069] As an embodiment of the present invention, there are no special requirements for the environmental humidity during the second aging process. The Ca(OH)2 / CaS-supported organism can be placed in a natural indoor environment at 20~30 °C for 7 days.

[0070] As an embodiment of the present invention, the preparation steps of the kelp powder include: cleaning the kelp with water to remove impurities, soaking it in water for 24 h, and then drying and pulverizing it to obtain the kelp powder.

[0071] As an embodiment of the present invention, the drying temperature is 50~80 °C and the time is 8~48 h.

[0072] As a preferred embodiment of the present invention, the drying temperature is 65 °C and the time is 24 h.

[0073] As the third aspect of the present invention, the present invention provides the application of the above-mentioned double-shell CaCO3 / CaS-supported biochar adsorbent in adsorbing Cd(II) in wastewater.

[0074] The technical solutions of the present invention will be further described below with reference to specific examples.

[0075] The room temperature involved in the specific embodiment of the present invention specifically refers to 20~30 °C;

[0076] All raw materials used in the specific embodiment of the present invention are obtained through commercial channels.

[0077] Example 1

[0078] A double-shell CaCO3 / CaS-supported biochar adsorbent is prepared according to the following steps:

[0079] (1) Clean the kelp with water to remove impurities, soak it in water for 24 h, take it out, dry it at 65 °C for 24 h, pulverize it, and pass it through an 80-mesh sieve to obtain kelp powder.

[0080] (2) Take 10 g of the kelp powder obtained in step (1) and add it to the ultrasonically dispersed CaSO3 suspension. The addition ratio of CaSO3 to deionized water in the CaSO3 suspension is 2 g:125 mL. Mix it under ultrasonic and mechanical stirring (ultrasonic power is 100 W, rotation speed is 800 rpm) for 30 min to obtain a mixed solution, and then dry it at 65 °C for 10 h and grind it to obtain pretreated kelp particles.

[0081] (3) The pretreated kelp particles obtained in step (2) are carbonized at a high temperature of 700 °C under a nitrogen protection atmosphere. The heating rate of the tubular furnace used is 5 °C / min, the heat preservation time is 60 min, and after the reaction is completed, it is naturally cooled to room temperature to obtain biochar loaded with CaO / CaS, which is named KAC@CaS-CaO.

[0082] (4) Place the biochar loaded with CaO / CaS obtained in step (3) in a self-made device (the schematic diagram of the self-made device is as Figure 2 shown), and place the device in an oven at 105 °C and react for 12 h in an environment with a high humidity (relative humidity of 80 - 90%) at 105 °C to obtain biochar loaded with Ca(OH)2 / CaS, which is named KAC 12 @CaS-Ca(OH)2.

[0083] (5) Place the biochar loaded with Ca(OH)2 / CaS obtained in step (4) in a natural indoor environment at 20 - 30 °C for 7 days to obtain a double-shell CaCO3 / CaS loaded biochar adsorbent, which is named KAC 12 @CaS-CaCO3.

[0084] Example 2

[0085] A double-shell CaCO3 / CaS loaded biochar adsorbent is prepared as follows:

[0086] (1) After cleaning and removing impurities from kelp with water, soak it in water for 24 h, take it out and dry it at 65 °C for 24 h, then crush it and pass it through an 80-mesh sieve to obtain kelp powder.

[0087] (2) Take 10 g of the kelp powder obtained in step (1) and add it to a CaSO3 suspension with ultrasonic dispersion. The ratio of the addition amount of CaSO3 to deionized water in the CaSO3 suspension is 2 g:125 mL. Mix them under ultrasonic and mechanical stirring (ultrasonic power is 100 W, rotation speed is 800 rpm) for 30 min to obtain a mixed solution, and then dry it at 65 °C for 10 h and grind it to obtain pretreated kelp particles.

[0088] (3) The pretreated kelp particles obtained in step (2) are carbonized at a high temperature of 700 °C under a nitrogen protection atmosphere. The heating rate of the tubular furnace used is 5 °C / min, the heat preservation time is 60 min, and after the reaction is completed, it is naturally cooled to room temperature to obtain biochar loaded with CaO / CaS, which is named KAC@CaS-CaO.

[0089] (4) Place the biochar loaded with CaO / CaS obtained in step (3) in a self-made device (the schematic diagram of the self-made device is as Figure 2As shown), and the device was placed in an oven at 105 °C and reacted for 8 h in an environment of 105 °C and high humidity (relative humidity of 80 - 90%) to obtain Ca(OH)₂ / CaS-loaded biochar, which was named KAC8@CaS-Ca(OH)₂.

[0090] (5) The Ca(OH)₂ / CaS-loaded biochar obtained in step (4) was placed in a natural indoor environment at 20 - 30 °C for 7 days to obtain a double-shell CaCO₃ / CaS-loaded biochar adsorbent, which was named KAC8@CaS-CaCO₃.

[0091] Example 3

[0092] A double-shell CaCO₃ / CaS-loaded biochar adsorbent was prepared as follows:

[0093] (1) After cleaning and removing impurities from kelp with water, it was soaked in water for 24 h, taken out, dried at 65 °C for 24 h, crushed, and sieved through an 80-mesh sieve to obtain kelp powder.

[0094] (2) 10 g of the kelp powder obtained in step (1) was added to an ultrasonically dispersed CaSO₃ suspension. The ratio of the addition amount of CaSO₃ to deionized water in the CaSO₃ suspension was 2 g:125 mL. It was mixed for 30 min under ultrasonic and mechanical stirring (ultrasonic power of 100 W and rotation speed of 800 rpm) to obtain a mixed solution, and then dried at 65 °C for 10 h and ground to obtain pretreated kelp particles.

[0095] (3) The pretreated kelp particles obtained in step (2) were carbonized at 700 °C under a nitrogen protection atmosphere. The heating rate of the used tubular furnace was 5 °C / min, and the holding time was 60 min. After the reaction ended, it was naturally cooled to room temperature to obtain CaO / CaS-loaded biochar, which was named KAC@CaS-CaO.

[0096] (4) The CaO / CaS-loaded biochar obtained in step (3) was placed in a self-made device (the schematic diagram of the self-made device is as Figure 2 shown), and the device was placed in an oven at 105 °C and reacted for 16 h in an environment of 105 °C and high humidity (relative humidity of 80 - 90%) to obtain Ca(OH)₂ / CaS-loaded biochar, which was named KAC 16 @CaS-Ca(OH)₂.

[0097] (5) The Ca(OH)₂ / CaS-loaded biochar obtained in step (4) was placed in a natural indoor environment at 20 - 30 °C for 7 days to obtain a double-shell CaCO₃ / CaS-loaded biochar adsorbent, which was named KAC 16@CaS-CaCO3。

[0098] Comparative Example 1

[0099] A calcium-loaded rice straw biochar was prepared as follows:

[0100] (1) After washing and removing impurities from rice straw with water, it was soaked in water for 24 h, taken out and dried at 65 °C for 24 h, then pulverized and sieved through a 80-mesh sieve to obtain rice straw powder.

[0101] (2) 10 g of the rice straw powder obtained in step (1) was added to a CaSO3 suspension dispersed by ultrasound. The addition ratio of CaSO3 to deionized water in the CaSO3 suspension was 2 g:125 mL. It was mixed for 30 min under ultrasound and mechanical stirring (ultrasound power was 100 W, rotation speed was 800 rpm) to obtain a mixed solution, and then dried at 65 °C for 10 h and ground to obtain pretreated rice straw particles.

[0102] (3) The pretreated rice straw particles obtained in step (2) were carbonized at 700 °C under a nitrogen protection atmosphere. The heating rate of the used tubular furnace was 5 °C / min, and the holding time was 60 min. After the reaction ended, it was naturally cooled to room temperature to obtain calcium-loaded rice straw biochar, which was named CAC@Ca.

[0103] Comparative Example 2

[0104] Unloaded aged kelp biochar was prepared as follows:

[0105] (1) After washing and removing impurities from kelp with water, it was soaked in water for 24 h, taken out and dried at 65 °C for 24 h, then pulverized and sieved through a 80-mesh sieve to obtain kelp powder.

[0106] (2) The kelp powder obtained in step (1) was carbonized at 700 °C under a nitrogen protection atmosphere. The heating rate of the used tubular furnace was 5 °C / min, and the holding time was 60 min. After the reaction ended, it was naturally cooled to room temperature to obtain kelp biochar, which was named KC.

[0107] (3) The kelp biochar obtained in step (2) was placed in a self-made device (the schematic diagram of the self-made device is as Figure 2 shown), and the device was placed in an oven at 105 °C and reacted for 12 h in an environment of 105 °C and high humidity (relative humidity was 80 - 90%).

[0108] (4) The product after the reaction in step (3) was placed in a natural indoor environment at 20 - 30 °C for 7 days to obtain unloaded aged kelp biochar, which was named KC 12 。

[0109] Test Example 1

[0110] Morphology and composition characterization

[0111] 1. SEM analysis

[0112] The CaO / CaS-loaded biochar KAC@CaS-CaO (the product of step (3) in Example 1) and the double-shell CaCO3 / CaS-loaded biochar adsorbent KAC 12 @CaS-CaCO3 (the product of step (5)) in Example 1 and the calcium-loaded rice straw biochar CAC@Ca sample in Comparative Example 1 were respectively blown onto the conductive adhesive with an ear bulb, stuck on the SEM specimen stage, and then the specimen was sputter-coated with gold to prevent the surface charge accumulation from affecting the imaging quality. After transferring to the sample chamber and evacuating, ion sputtering was carried out for 30 seconds. The specimens were photographed using JSM-7800FPrime SEM, and the magnification range was 25 - 1000000 times. The results are as Figure 3 shown.

[0113] As Figure 3 can be seen, there are uniformly distributed fine particles on the surfaces of the two loaded biochars (KAC@CaS-CaO and KAC 12 @CaS-CaCO3) in Example 1, which indicates that the uniformly loaded CaO / CaS biochar can be effectively prepared by the method of Example 1, and during the first aging treatment (artificial aging treatment) and the second aging treatment (natural aging treatment), the distribution of the loaded substances remains almost unchanged. The uniformly dispersed fine CaCO3 / CaS particles can provide abundant adsorption sites for the CaCO3 / CaS-loaded biochar adsorbent to improve its adsorption capacity for Cd(II). While the surface of the calcium-loaded rice straw biochar CAC@Ca in Comparative Example 1 is aggregated and large spherical particles, which indicates that kelp as a raw material has an obvious effect on the uniform distribution of the loaded substances during the loading process, while using rice straw as a raw material does not have this effect.

[0114] 2. SEM-EDS analysis

[0115] For the samples CaO / CaS-loaded biochar KAC@CaS-CaO (the product of step (3) in Example 1) and calcium-loaded rice straw biochar CAC@Ca (Comparative Example 1) in the SEM observation state as Figure 3 shown, the distribution of S and Ca elements was analyzed using a scanning electron microscope / energy dispersive spectrometer (IE250X-Max50, Germany). The results are as Figure 4 shown.

[0116] As Figure 4It can be seen that the S and Ca elements in the CaO / CaS-loaded biochar KAC@CaS-CaO in Example 1 are relatively evenly distributed, that is, the surface-loaded CaO / CaS is evenly distributed. This is mainly due to the role of sodium alginate in kelp. As a stabilizer for nanoparticles, sodium alginate can effectively capture and stabilize the ultrasonically dispersed CaSO3 particles during the pretreatment process in step (2) of Example 1, which makes the CaO / CaS on the surface of the carbonized product KAC@CaS-CaO have good dispersibility. In addition, compared with the uniform distribution of S elements on the surface of KAC@CaS-CaO, the distribution of Ca elements shows the characteristics of strong signal distribution in granular form. These stronger Ca element signals are due to the CaO generated by the pyrolysis of CaSO3 that does not contact the reduced carbon on the surface. Therefore, it is preliminarily confirmed that the surface of KAC@CaS-CaO is composed of a double shell layer of CaO and CaS. In Comparative Example 1, the S and Ca elements in the calcium-loaded rice straw biochar CAC@Ca are unevenly distributed, and it matches the distribution of spherical particles on the surface in the corresponding SEM image, further indicating that using rice straw as a raw material does not have the effect of evenly distributing the loaded substances.

[0117] 3. XRD Analysis

[0118] The crystal structures of the CaO / CaS-loaded biochar KAC@CaS-CaO (the product of step (3)) in Example 1, the Ca(OH)2 / CaS-loaded biochar KAC 12 @CaS-Ca(OH)2 (the product of step (4)), and the double-shell CaCO3 / CaS-loaded biochar adsorbent KAC 12 @CaS-CaCO3 (the product of step (5)) were respectively characterized by an X-ray diffractometer (XRD, Smartlab SE, Rigaku, Japan), and the results are as Figure 5 shown.

[0119] It can be seen from Figure 5 that significant characteristic diffraction peaks of CaS can be observed in the XRD patterns of KAC@CaS-CaO, KAC 12 @CaS-Ca(OH)2, and KAC 12 @CaS-CaCO3. During the aging treatment process from step (4) to step (5) of Example 1 for the CaO on the surface of KAC@CaS-CaO, it changes from CaO to Ca(OH)2 and then to CaCO3, and the rapid aging treatment process has little effect on the inner CaS.

[0120] 4. FTIR Analysis

[0121] For the CaO / CaS-loaded biochar KAC@CaS-CaO, Ca(OH)2 / CaS-loaded biochar KAC 12 @CaS-Ca(OH)2, and the double-shell CaCO3 / CaS-loaded biochar adsorbent KAC 12 @CaS-CaCO3 in Example 1, Fourier transform infrared spectroscopy (FTIR, VERTEX 70, Bruker) was used for the analysis of the substance composition, and the results are as Figure 6 shown.

[0122] From Figure 6 it can be clearly observed that after the first aging treatment (artificial aging treatment) of the sample CaO / CaS-loaded biochar (KAC@CaS-CaO), a distinct characteristic peak of Ca(OH)2 appears at the peak position of 3638 cm 12 in the FTIR of Ca(OH)2 / CaS-loaded biochar (KAC -1 @CaS-Ca(OH)2), and this characteristic peak is not found in the sample CaCO3 / CaS-loaded biochar adsorbent (KAC 12 @CaS-CaCO3) after natural aging. This further illustrates the process of CaO being converted to Ca(OH)2 and then to CaCO3.

[0123] 5. Elemental analysis

[0124] For the CaO / CaS-loaded biochar KAC@CaS-CaO, Ca(OH)2 / CaS-loaded biochar KAC 12 @CaS-Ca(OH)2, and the double-shell CaCO3 / CaS-loaded biochar adsorbent KAC 12 @CaS-CaCO3 samples in Example 1, elemental analysis was carried out, and the results are shown in Table 1.

[0125] Table 1 Changes in elemental content of samples before and after aging

[0126]

[0127] As can be seen from Table 1, the content of S element has a small change during the aging process. Combining with the introduction of C and O elements during the aging process, the total mass of the sample increases, and it can be considered that the change of S element is not significant.

[0128] 6. Analysis of the sulfur element S 2p spectrum in XPS

[0129] For the CaO / CaS-loaded biochar KAC@CaS-CaO, Ca(OH)2 / CaS-loaded biochar KAC 12 @CaS-Ca(OH)2, and the double-shell CaCO3 / CaS-loaded biochar adsorbent KAC12 The S 2p spectra of @CaS-CaCO3 were analyzed using X-ray photoelectron spectroscopy (XPS, Thermo ESCALAB 250XI), and the results are as Figure 7 shown.

[0130] Since the effective test depth of XPS is approximately 2 nm, this analysis mainly characterizes the surface S element composition. Comparing the S 2p spectra of KAC@CaS-CaO, KAC 12 @CaS-Ca(OH)2 and KAC 12 @CaS-CaCO3, it can be found that the aging process has a greater impact on the surface sulfur-containing compounds. There is basically no CaS in KAC 12 @CaS-Ca(OH)2 and KAC 12 @CaS-CaCO3. Combining the results of XRD and elemental analysis, it shows that after the aging treatment process, a small amount of CaS exposed on the surface disappears, while the overall CaS loss is small, mainly concentrated in the inner layer of the double shell.

[0131] Therefore, it can be confirmed that the CaCO3 / CaS-loaded biochar adsorbent obtained in step (5) of Example 1 has a loaded structure of CaCO3 / CaS double layers, that is, a double-shell structure. This enables the CaCO3 / CaS loaded on the surface to play a synergistic adsorption role during the Cd(II) adsorption process, thereby effectively improving the adsorption capacity of the CaCO3 / CaS-loaded biochar adsorbent.

[0132] Test Example 2

[0133] Adsorption performance test

[0134] 1. Adsorption capacities of the double-shell CaCO3 / CaS-loaded biochar adsorbents with different aging times and the unloaded aged kelp biochar

[0135] Cadmium nitrate was dissolved in deionized water with a pH of 5 to obtain an aqueous solution with a cadmium element concentration of 200 mg / L; 20 mg of the double-shell CaCO3 / CaS-loaded biochar adsorbent was weighed into a 125 mL conical flask, and 50 mL of the aqueous solution with a cadmium element concentration of 200 mg / L was added. It was placed in a water bath constant temperature oscillator and shaken thoroughly. The temperature was 25 °C, and the oscillator rotation speed was 150 rpm. Samples were taken at 0 min, 10 min, 30 min, 60 min, 90 min, 120 min, 360 min, 600 min, 1200 min, 1800 min, and 3000 min respectively, and the Cd(II) concentration in the adsorbed solution was measured using an atomic flame absorption spectrometer to calculate the adsorption capacity of the adsorbent.

[0136] Figure 8 For the double-shell CaCO3 / CaS-loaded biochar adsorbents KAC8@CaS-CaCO3, KAC 12 @CaS-CaCO3, KAC 16 @CaS-CaCO3 prepared in Examples 1-3, and the unloaded aged kelp biochar KC prepared in Comparative Example 2 12 The curve graph showing the change of adsorption capacity with time. The results show that the maximum adsorption capacities of KAC8@CaS-CaCO3, KAC 12 @CaS-CaCO3, KAC 16 @CaS-CaCO3 and KC 12 are 435.2 mg / g, 386.4 mg / g, 297.2 mg / g and 16.0 mg / g respectively.

[0137] 2. Adsorption end state of CaO / CaS-loaded biochar and double-shell CaCO3 / CaS-loaded biochar adsorbents

[0138] The double-shell CaCO3 / CaS-loaded biochar adsorbents KAC8@CaS-CaCO3, KAC 12 @CaS-CaCO3, KAC 16 @CaS-CaCO3 prepared in Examples 1-3 and the CaO / CaS-loaded biochar KAC@CaS-CaO in Example 1 were taken out and placed in an ampoule to take digital photos after adsorbing for 3000 min in the aqueous solution with a cadmium element concentration of 200 mg / L (other adsorption conditions were the same as those in the above adsorption capacity test process) to study their states at the adsorption end point. The results are as Figure 9 shown.

[0139] It can be seen from Figure 9 that due to the easy solubility and strong alkalinity of the CaO loaded on the CaO / CaS-loaded biochar KAC@CaS-CaO, a large amount of difficult-to-treat flocculent precipitates were formed after adsorption, and the precipitate was yellow, which originated from CdS formed by the reaction of dissolved CaS with Cd(II); while for the double-shell CaCO3 / CaS-loaded biochar adsorbent, because the surface layer is insoluble CaCO3, it has a good protective effect on the inner layer CaS. The adsorption conditions of the double-shell CaCO3 / CaS-loaded biochar adsorbents with different aging times are significantly better than those of the CaO / CaS-loaded biochar. Specifically, a small amount of flocculent precipitate was generated after the adsorption of KAC8@CaS-CaCO3, and the adsorbent was difficult to settle and disperse in the solution, while KAC 12 @CaS-CaCO3 and KAC 16@CaS-CaCO3 hardly forms intractable flocculent precipitates and can be separated from the solution by filtration. From the above conclusions, it can be seen that by controlling the aging treatment time in steps (4) of Examples 1-3, the adsorption behavior during the adsorption process can be effectively improved, intractable flocculent precipitates can be effectively avoided, and the separation of the adsorbent from the solution is facilitated, which is beneficial for the actual Cd(Ⅱ) treatment process. It further illustrates that the prepared double-shell CaCO3 / CaS-loaded biochar adsorbent is a promising adsorbent.

[0140] The above-described embodiments are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent, characterized in that: The double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent has kelp biochar as a core, calcium sulfide as an inner shell, and calcium carbonate as an outer shell; The preparation steps of the double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent include: Calcium sulfite is used to pretreat kelp powder to obtain pretreated kelp particles; the pretreated kelp particles are carbonized to obtain calcium oxide / calcium sulfide loaded biochar; the calcium oxide / calcium sulfide loaded biochar is subjected to a first aging treatment to obtain calcium hydroxide / calcium sulfide loaded biochar; the calcium hydroxide / calcium sulfide loaded biochar is subjected to a second aging treatment to obtain the double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent; The first aging treatment step comprises: placing the calcium oxide / calcium sulfide loaded biochar in a 105° C. water vapor environment for 8 to 16 hours; The second aging treatment step includes placing the calcium hydroxide / calcium sulfide loaded biochar at 20-30° C. for 7 days.

2. The method for preparing a double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent according to claim 1, characterized in that: The following steps are involved: Calcium sulfite is used to pretreat kelp powder to obtain pretreated kelp particles; the pretreated kelp particles are carbonized to obtain calcium oxide / calcium sulfide loaded biochar; the calcium oxide / calcium sulfide loaded biochar is subjected to a first aging treatment to obtain calcium hydroxide / calcium sulfide loaded biochar; the calcium hydroxide / calcium sulfide loaded biochar is subjected to a second aging treatment to obtain the double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent; The first aging treatment step comprises: placing the calcium oxide / calcium sulfide loaded biochar in a 105° C. water vapor environment for 8 to 16 hours; The second aging treatment step includes placing the calcium hydroxide / calcium sulfide loaded biochar at 20-30° C. for 7 days.

3. The method for preparing a double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent according to claim 2, characterized in that: The method of pretreating kelp powder with calcium sulfite to obtain pretreated kelp particles comprises: adding kelp powder to calcium sulfite suspension, mixing for 30 to 90 minutes under ultrasound and stirring to obtain a mixed solution, and then drying the mixed solution to obtain the pretreated kelp particles.

4. The method for preparing a double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent according to claim 3, characterized in that: The calcium sulfite suspension is prepared by mixing calcium sulfite and water in a dosage ratio of 1-2 g:100-200 mL.

5. The method for preparing a double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent according to claim 3, characterized in that: The mass ratio of the kelp powder to the calcium sulfite in the calcium sulfite suspension is 10:1-2.

6. The method for preparing a double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent according to claim 2, characterized in that: The carbonization conditions include: a holding temperature of 600-800° C. and a holding time of 30-90 min.

7. The method for preparing a double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent according to claim 2, characterized in that: The preparation steps of the kelp powder include: washing the kelp with water to remove impurities, soaking the kelp in water for 24 hours, and then drying and crushing to obtain the kelp powder.

8. Use of the double-shell calcium carbonate / calcium sulfide loaded biochar adsorbent as claimed in claim 1 in adsorbing Cd(II) in wastewater.

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