Synthesis method and application of sludge biochar Schwertmannite composite material capable of synchronously mineralizing cadmium and arsenic

Abstract

The invention belongs to the technical field of heavy metal treatment, and particularly relates to a synthesis method and application of a sludge biochar Schwertmannite composite material capable of synchronously mineralizing cadmium and arsenic. Municipal or industrial sludge is used as a raw material, sludge biochar rich in Ca, Fe and alkaline functional groups is prepared through pyrolysis, then the sludge biochar is deeply compounded with Schwertmannite through a high-energy ball milling technology, a core-shell-like nested structure is formed through induction, and a large number of reaction sites are exposed. Under the condition that As / Cd coexists, the surface of the composite material can be induced to generate stable minerals, a synchronous precipitation mechanism is formed, and As and Cd have an adsorption synergistic enhancement effect. The process is wide in raw material source, clean and efficient in preparation process and free of high-temperature hydrothermal or organic reagents, has cation exchangeability, alkali energy storage and carbon immobilization value, provides a new theory and material support for long-term environment immobilization of multi-metal pollutants, and has large-scale application potential.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heavy metal treatment, and particularly relates to a synthesis method and application of sludge biochar-schwertmannite composite material for synchronous mineralization of cadmium and arsenic. BACKGROUND

[0002] With the accelerated industrialization and agricultural activities, anionic and cationic heavy metal pollutants have been widely distributed in global water and soil environments, becoming a major threat to ecological safety and public health. Among them, arsenic (As) is a typical anionic heavy metal, mainly derived from mining, metallurgy, groundwater exploitation, and application of arsenic-containing pesticides, often existing in the form of pentavalent arsenate (H2AsO 4- , HAsO 2- ) and other forms. Cadmium (Cd) is a common cationic heavy metal pollutant, widely derived from electroplating, battery manufacturing, plastic additives, and industrial wastewater discharge, usually existing in the form of Cd 2+ .

[0003] It is worth noting that As and Cd often coexist in contaminated environments. Studies have shown that such anionic and cationic heavy metal coexistence pollution system is not only more complex, but also may have synergistic or mutual promotion effects in terms of migration and transformation, biological accumulation, and toxicity expression, exacerbating the enrichment risk in aquatic ecosystems and food chains. For example, Cd can affect the desorption behavior of As through competitive adsorption, while As can also affect the morphological transformation and migration pathway of Cd. This combined pollution pattern significantly increases the difficulty of treatment, especially traditional treatment materials mostly only show selective adsorption of one type of ion (anion or cation), making it difficult to achieve simultaneous and efficient fixation and long-term stable control of As and Cd.

[0004] Currently, common heavy metal removal methods mainly include chemical precipitation, ion exchange, membrane separation, electrochemical method, and adsorption method. Among them, the adsorption method has attracted widespread attention in the field of pollution control due to its advantages such as simple operation, low cost, and environmental friendliness. Sludge-derived biochar is a carbon-based material rich in alkaline functional groups such as carboxyl, hydroxyl, and carbonate, as well as exchangeable metal ions, and has good cation exchange capacity, suitable for removing Cd and other cationic heavy metals. Schwertmannite is a kind of hydrated iron oxide mineral rich in Fe-OH functional groups and having a high specific surface area, which can efficiently and selectively adsorb anionic heavy metals such as As through internal sphere complexation mechanism. Therefore, both of them show good adsorption performance in dealing with their respective target pollutants, but it is still difficult to achieve synergistic and efficient synchronous removal and mineralization fixation in As-Cd coexistence system.

[0005] In summary, there are still the following deficiencies in heavy metal removal at present: (1) strong single pollutant removal ability, but unable to remove anionic and cationic heavy metals at the same time: traditional adsorption materials are usually only suitable for a certain type of ion (such as cationic Cd or anionic As), and when As and Cd coexist, only selective adsorption can be achieved, and synchronous removal cannot be achieved. (2) Limited assembly method of composite materials, low utilization rate of material activity: at present, the commonly used composite strategies (such as simple physical mixing, impregnation, static coprecipitation and the like) still have problems such as insufficient interface contact, uneven distribution of active sites, poor synergistic effect and the like. (3) Lack of stable fixation mechanism for multi-metal coexisting pollution system: there are few adsorption materials that can realize synchronous mineralization or coprecipitation of As and Cd, and the fixation method is mainly weak adsorption, which has the risk of secondary release and poor long-term stability. (4) High cost of raw materials or limited source: most of the existing adsorption materials are derived from special carbon sources and functional nanomaterials, which are high in cost and are not conducive to large-scale popularization and application. Therefore, it is necessary to develop a new type of composite material with synchronous adsorption and mineralization capacity to realize efficient and stable fixation of coexisting anionic and cationic cadmium heavy metals in water and soil. SUMMARY

[0006] In order to overcome the deficiencies of the prior art, the present application focuses on the core goal of "waste resourceization driven anionic and cationic heavy metal (As / Cd) synergistic mineralization remediation", and develops a composite adsorption material taking sludge-derived biochar as the functional main material and Schieffelin mineral as the regulation and enhancement component, which realizes efficient and stable fixation of coexisting anionic arsenic (As) and cationic cadmium (Cd) in water and soil.

[0007] In order to achieve the above purpose, the technical scheme adopted by the present application is:

[0008] The first aspect of the present application provides a preparation method of sludge biochar Schieffelin mineral composite material, which comprises the following steps:

[0009] S1, after drying the municipal or industrial dewatered sludge, the sludge biochar (BC) rich in Ca, Fe and alkaline functional groups is prepared by limited oxygen pyrolysis;

[0010] S2, Schieffelin mineral (Sch) is prepared by solution chemistry method: iron salt is dissolved in water, the pH is adjusted to 2.5-3.0, and Fe 2+ is oxidized to Fe 3+ under the conditions of aeration and stirring to form an orange yellow precipitate, and after continuing the reaction, the precipitate is placed, centrifuged, washed to remove sulfate and residual ions, and then dried to obtain a powder product;

[0011] S3, the sludge biochar and the schreyerite are mixed and added into a ball mill, and the sludge biochar and the schreyerite are subjected to high-energy impact by ball milling to form a new structure with interface fusion, particle size reduction, specific surface area increase and lattice defect enhancement, and finally the sludge biochar schreyerite composite material is obtained.

[0012] Preferably, the mass ratio of the sludge biochar and the schreyerite in S3 is 1:3.

[0013] The traditional single adsorbent has advantages in dealing with As or Cd pollution, and the sludge biochar is suitable for cation removal, and the schreyerite has specific affinity for anion. However, the two lack effective synergistic effect, and it is difficult to meet the needs of composite pollution repair. As a mechanical composite method driven by mechanical energy, the ball milling technology can realize high uniform mixing of different material particles, surface structure reconstruction, interface defect induction and active site exposure under high energy effect, so as to form a synergistic effect. Therefore, the schreyerite (Sch) and the sludge-derived biochar (BC) are mechanically compounded by ball milling to prepare a composite material BM-Sch / BC with multiple mechanisms and multiple functions. 3:1 , and then the synchronous mineralization and stabilization treatment of anion and cation heavy metals are realized.

[0014] Preferably, in S3, the ball-to-material ratio is 9-11:1, the ball milling speed is 1000-1300 rpm, and the time is 2-4 h.

[0015] Preferably, the temperature of the limited oxygen pyrolysis in S1 is 700-900 DEG C, and the time is 150-250 min.

[0016] Preferably, in S2, the iron salt includes ferric sulfate, ferric chloride and ferric nitrate.

[0017] Preferably, the concentration of the iron salt in S2 is 0.07-0.3 mol / L.

[0018] Preferably, the stirring speed of the aeration stirring in S2 is 300-500 rpm, the dissolved oxygen is greater than 5 mg / L, and the time is 40-50 hours.

[0019] Preferably, the particle size of the sludge biochar and the schreyerite is controlled within 100 meshes.

[0020] The second aspect of the present application provides a sludge biochar schreyerite composite material prepared by the preparation method of the first aspect.

[0021] The third aspect of the present application provides an application of the sludge biochar schreyerite composite material in the synergistic mineralization repair of anion and cation heavy metal ions of arsenic-cadmium.

[0022] The research shows that the maximum adsorption capacity is: Cd>90mg / g, As>70mg / g; under the condition of synergistic adsorption, the adsorption efficiency is improved by more than 50%, and the release rate of metal ions after adsorption is less than 5%.

[0023] Preferably, the arsenic-cadmium anion-cation heavy metal ions include coexisting anionic arsenic (As) and cationic cadmium (Cd) in water bodies and soil.

[0024] Preferably, the dosage of the sludge biochar Schottky mineral composite material is 0.1-10g / L.

[0025] Preferably, the composite material is suitable for a pollution system with pH 3.0-9.0, has high adsorption efficiency and good material stability. Further, the pH condition for synergistic mineralization repair of arsenic-cadmium anion-cation heavy metal ions is 5-7.

[0026] Preferably, the contact time of the sludge biochar Schottky mineral composite material with arsenic-cadmium anion-cation heavy metal ions is 12-48h.

[0027] Compared with the prior art, the beneficial effects of the present application are:

[0028] Compared with the existing adsorption material or combined process, the Schottky mineral-sludge biochar composite material Sch / BC constructed by the ball milling technology of the present application has the following remarkable advantages and innovative effects:

[0029] (1) Achieve simultaneous and efficient removal of anion-cation heavy metals: existing adsorption materials are mostly selective adsorption, only having affinity for cationic or anionic pollutants, and being difficult to cope with coexisting arsenic and cadmium systems. The composite material constructed by the ball milling of the present application has both Fe-OH / SO4 2- sites (adsorbing As) and carboxyl / Ca 2+ sites (adsorbing Cd) in terms of structure and functional groups, which can simultaneously and efficiently adsorb two types of ionic pollutants, break through the selectivity limitation of the material, and achieve synergistic management.

[0030] (2) Construct a multi-mechanism synergistic mineralization and fixation platform to enhance the treatment stability: through ball milling to induce interface activity and microstructure regulation, the composite material constructed can further induce As and Cd to co-mineralize on the surface to form a stable precipitate phase after adsorption, thereby realizing simultaneous fixation and greatly improving the long-term environmental stability and avoiding secondary release, which is significantly superior to traditional weak adsorption materials.

[0031] (3) Innovatively adopt ball milling composite technology to realize deep coupling and performance enhancement of the material: unlike traditional impregnation, mixing or precipitation methods, the present application adopts high-speed ball milling to induce particle fragmentation, increase specific surface area and activate defects, thereby improving the number of active sites, reactivity and structural stability of the composite material, and enhancing its adsorption capacity and mineralization efficiency for heavy metals.

[0032] (4) Material green, low cost, wide source, with engineering promotion: The present application uses dewatered sludge as carbon source raw material, combined with common iron salt to synthesize schmidekite, the raw material is cheap, renewable and easy to obtain, significantly reduces the production cost, has good environmental adaptability and practical engineering application potential, meets the sustainable development requirements under the background of "solid waste resource" and "double carbon".

[0033] (5) Applied to water and soil, strong adaptability, good practicability: The composite material constructed by the present application is suitable for the simultaneous removal of As and Cd in water phase and soil phase, and still shows excellent adsorption performance under low pollution concentration at pH 5-7, has good environmental adaptability and engineering applicability, and provides a new material selection for actual heavy metal pollution remediation. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 For BM-Sch / BC 3:1 XRD pattern after adsorbing As and Cd.

[0035] Figure 2 For the relationship between mineralization rate and BM-Sch / BC 3:1 dosage. DETAILED DESCRIPTION

[0036] The specific embodiments of the present application will be further described below. It should be noted that the description of these embodiments is used to help understand the present application, but does not constitute a limitation on the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0037] The experimental methods in the following examples are all conventional methods unless otherwise specified, and the test materials used in the following examples are all commercially available unless otherwise specified.

[0038] To verify the synergistic adsorption and mineralization fixation ability of the ball-milled composite schmidekite-sludge biochar composite material (BM-Sch / BC) proposed by the present application to arsenic (As) and cadmium (Cd), the following specific examples and experiments were carried out with BM-Sch / BC 3:1 For example.

[0039] Example 1: Preparation of ball-milled composite schmidekite-sludge biochar composite material (BM-Sch / BC 3:1 )

[0040] (1) Preparation of sludge biochar (BC)

[0041] Municipal sludge (dewatered and dried sludge after being pressed into a cake with iron and calcium salts as conditioners) was dried at 60°C for 24 hours, and then pyrolyzed at 800°C for 200 minutes under limited oxygen conditions (nitrogen atmosphere) to produce biochar rich in Ca and Fe. The resulting sample was ground to ≤100 mesh after cooling and stored.

[0042] (2) Synthesis of Sch

[0043] A 0.1 mol / L FeSO4·7H2O solution was adjusted to a pH of 2.7, and Fe 2+ was oxidized to Fe 3+ by stirring and aeration (dissolved oxygen > 5 mg / L) at 400 rpm to form an orange-yellow precipitate. After 48 hours of continuous reaction, the sample was allowed to stand, centrifuged, washed with water, and dried at low temperature (50°C) to obtain Sch powder with a particle size controlled within 100 μm.

[0044] (3) BM-Sch / BC 3:1 Preparation of composite material

[0045] BC and Sch were mixed at a mass ratio of 3:1, and stainless steel balls were added (ball-to-material ratio of 10:1) for ball milling at 1200 rpm for 3 hours, followed by intermittent cooling (ball milling for 15 minutes, intermittent cooling for 15 minutes, and this process was repeated for 3 hours). Finally, BM-Sch / BC 3:1 composite powder was obtained.

[0046] Example 2: BM-Sch / BC 3:1 Verification of adsorption performance on As and Cd

[0047] 1.1, BM-Sch / BC 3:1 Adsorption effect on As and Cd

[0048] (1) Adsorption experiment conditions

[0049] A mixed solution containing 100 mg / L Cd 2+ and 100 mg / L As 5+ was prepared, and the pH was adjusted to 4.0-5.0. Then, 0.5 g / L of BM-Sch / BC 3:1 material was added, and the sample was oscillated at 25°C for 24 hours. After filtration, the residual concentration of metal ions was determined by ICP-OES.

[0050] (2) Adsorption experiment setup

[0051] To highlight the adsorption performance of BM-Sch / BC 3:1 material, different comparisons were set up, and the specific adsorption experiment groups are shown in Table 1.

[0052] Table 1 Adsorption experiment grouping

[0053]

[0054] (3) Adsorption performance results:

[0055] The experimental results in Table 2 show that BM-Sch / BC 3:1 It exhibits a significant synergistic enhancement effect under conditions of coexistence of anions and cations, and its total adsorption capacity is significantly better than that of traditional materials or physical mixtures.

[0056] Table 2 Adsorption performance results of different experimental groups

[0057]

[0058] 1.2, BM-Sch / BC 3:1 Adsorption mechanism verification

[0059] After the adsorption experiment, samples were taken for XRD (X-ray diffraction).

[0060] Figure 1 XRD analysis revealed characteristic peaks of the mineral phase in the synergistic adsorption group, confirming the occurrence of the mineralization reaction. This demonstrates the effectiveness of the composite material BM-Sch / BC constructed in this invention. 3:1 Make Cd 2+ And As 5+ The two cation and cation metals combine to form minerals and are fixed as Fe3(AsO4)2·8H2O and Cd2(As2O7), possessing long-term stability and deep fixation capabilities.

[0061] 1.3 Stability Evaluation

[0062] BM-Sch / BC 3:1 The materials and soil are thoroughly mixed in different proportions (BM-Sch / BC) 3:1 The concentrations of the ions were 10, 20, 30, 40, 50, 60, and 80 g / kg, respectively. The available forms of As and Cd were then extracted from the soil, and the residual metal ion concentrations were determined using ICP-OES. The method for extracting the available forms of As and Cd from the soil was as follows: Soil was mixed with 0.1 mol / L calcium chloride solution at a material-to-liquid ratio of 1:10 (g:mL) and shaken at 180 rpm for 24 hours to obtain extractable Cd. Simultaneously, soil was treated with 0.5 mol / L sodium bicarbonate at a material-to-liquid ratio of 1:30 (g:mL) under the same shaking conditions to obtain extractable As.

[0063] The results show ( Figure 2At all the above concentrations, the available forms of As and Cd in the soil can be stably and significantly reduced without significant fluctuations or failure due to changes in the material addition ratio. This fully demonstrates that the material has excellent environmental stability in improving the available forms of heavy metals in soil.

[0064] 1.4 Water Adaptability Experiment and Results

[0065] To verify the composite material BM-Sch / BC constructed in this invention 3:1 The application effects in different types of aquatic environments were investigated. Tap water, Pearl River water, and aquaculture wastewater (from a shrimp farming base) were selected, and an equal concentration (100 mg / L) of As was added. 5+ and Cd 2+ Mixed contaminants, while adding 100 mg / L of As to pure water. 5+ and Cd 2+ A simulated wastewater composition of mixed pollutants was then added to the above-mentioned water. 3:1 The material was examined to assess its removal performance in different media.

[0066] The experimental results in Table 3 show that even in complex environments containing competing ions, natural organic matter, or high salt concentrations, the composite material constructed in this invention still exhibits good synergistic removal capabilities for heavy metals, and possesses broad environmental adaptability and engineering application potential.

[0067] Table 3 Adsorption effects in different water environments

[0068]

[0069] As can be seen from Example 2, BM-Sch / BC 3:1 The material combines anion and cation adsorption with synergistic mineralization, enabling efficient and simultaneous treatment of As and Cd, and possesses good practicality and prospects for widespread application.

[0070] In summary, this invention uses sludge-derived biochar as the main functional material and Schiele mineral as the regulating and enhancing component to achieve synergistic mineralization and remediation of anionic and cationic heavy metals (As / Cd). It has the following advantages: (1) It realizes the high-value utilization of sludge-based functional materials: This invention uses municipal or industrial sludge as raw material and prepares sludge biochar rich in Ca, Fe and alkaline functional groups through pyrolysis. As the main structural framework of the composite material, it has the combined functions of cation exchange, alkaline energy storage and carbon fixation, realizing the high-value-added resource utilization of solid waste. (2) Ball milling induces multi-mechanism interface construction: The high-energy ball milling technology is used to deeply composite Schiele mineral with sludge biochar, inducing the formation of a core-shell nested structure, exposing a large number of Fe-OH, carboxyl, Ca and other reaction sites, and improving the As 5+ and Cd2+ (3) The mechanism of synergistic mineralization was established: under the coexistence of As / Cd, stable minerals can be induced on the surface of the composite, forming a synchronous precipitation mechanism, which provides new theoretical and material support for the long-term environmental fixation of multi-metal pollutants.(4) Synergistic enhancement effect under the coexistence of pollution: the experimental system verifies the synergistic mechanism that As can promote Cd adsorption and Cd can enhance the stability of As, which is a rare double-metal coexistence induced deposition behavior in current literature, and has obvious unpredictability.(5) Green and simple process with potential for large-scale application: the raw materials are widely available (dewatered sludge + iron salt), the preparation process is clean, efficient and does not require high-temperature hydrothermal or organic reagents, which is convenient for popularization to contaminated farmland, mining area and water treatment engineering, and conforms to the "double carbon" strategy and solid waste reduction policy orientation.

[0071] The embodiments of the present application are described in detail above, but the present application is not limited to the described embodiments. For those skilled in the art, various changes, modifications, replacements and variations of the embodiments can be made without departing from the principles and spirits of the present application, and still fall within the protection scope of the present application.

Claims

1. A method for preparing a sludge biochar Scheringer mineral composite material, characterized in that, Includes the following steps: S1. After drying municipal or industrial dewatered sludge, it is pyrolyzed with limited oxygen to produce sludge biochar rich in Ca, Fe and alkaline functional groups. S2. Preparation of Schiele minerals using solution chemistry: Iron salts are dissolved in water, the pH is adjusted to 2.5-3.0, and Fe is stirred under aeration to allow Fe to react. 2+ Oxidized to Fe 3+ An orange-yellow precipitate is formed. After the reaction continues, the product is allowed to stand, centrifuged, washed to remove sulfate and residual ions, and then dried to obtain the powder product. S3. Add the sludge biochar and Schiele mineral to a ball mill. Through ball milling, the sludge biochar and Schiele mineral form a new structure with interface fusion, reduced particle size, increased specific surface area and enhanced lattice defects under high-energy impact, and finally obtain the sludge biochar Schiele mineral composite material.

2. The method for preparing a sludge biochar-Schwarz mineral composite material according to claim 1, characterized in that, The mass ratio of sludge biochar and Schiele minerals in S3 is 1:

3.

3. The method for preparing a sludge biochar Scherstein mineral composite material according to claim 1, characterized in that, In S3, the ball-to-material ratio is 9-11:1, the ball milling speed is 1000-1300 rpm, and the time is 2-4 hours.

4. The method for preparing a sludge biochar Scherstein mineral composite material according to claim 1, characterized in that, The oxygen-limited pyrolysis described in S1 is performed at a temperature of 700-900℃ for a time of 150-250 min.

5. The method for preparing a sludge biochar Scherstein mineral composite material according to claim 1, characterized in that, In S2, the iron salt includes ferric sulfate, ferric chloride, and ferric nitrate.

6. The method for preparing a sludge biochar Scherstein mineral composite material according to claim 1, characterized in that, The concentration of the iron salt in S2 is 0.07-0.3 mol / L.

7. The method for preparing a sludge biochar Scherstein mineral composite material according to claim 1, characterized in that, The stirring speed for the aeration and stirring described in S2 is 300-500 rpm, dissolved oxygen > 5 mg / L, and the time is 40-50 hours.

8. The method for preparing a sludge biochar-Schwarz mineral composite material according to claim 1, characterized in that, The particle size of both sludge biochar and Schiele minerals is controlled to be within 100 mesh.

9. The sludge biochar Scherstein mineral composite material prepared by the preparation method according to any one of claims 1-8.

10. The application of the sludge biochar Scheres mineral composite material according to claim 9 in the synergistic mineralization remediation of arsenic-cadmium anion and cation heavy metal ions.

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