Active silicon acid salt stabilized micro-nano ferrous sulfide slurry, and preparation method and application thereof

Abstract

The application discloses a kind of active controllable silicate stabilized micro-nano ferrous sulfide slurry and its preparation method and application, including silicate stabilized ferrous sulfide composite material, it has core-shell structure;Nanometer ferrous sulfide is core, shell is silicate interface layer;Silicate interface layer is combined with nanometer ferrous sulfide core by Fe-O-Si chemical bond.It is prepared as follows: soluble silicate is dissolved in deoxygenated water to form silicate solution, soluble ferrous salt solution and sulfur source solution are sequentially added, co-precipitation reaction is carried out, and the slurry is obtained.The material has excellent dispersibility and antioxidant stability during storage;When used for treating wastewater containing heavy metals and halogenated pollutants, the interaction of silicate and heavy metals can trigger the "interface activity switch" mechanism of the material, and long-term stable synergistic removal performance can be maintained in various actual water bodies.

Description

Technical Field

[0001] This invention relates to a slurry for water treatment, its preparation method and application, and more particularly to an active controllable silicate stabilized micro-nano ferrous sulfide slurry, its preparation method and application. Background Technology

[0002] Iron-sulfur based materials, especially nano-ferrous sulfide (n-FeS), have attracted widespread attention in the water treatment field due to their simultaneous presence of both Fe(II) and S(-II) reducing active centers, demonstrating excellent reduction and fixation capabilities for heavy metal ions and good dehalogenation potential for halogenated organic compounds. For example, n-FeS can effectively remove heavy metals such as chromium (Cr(VI)) and cadmium (Cd(II)) from water through adsorption, co-precipitation, and reduction, and promote the degradation of halogenated organic compounds such as tetrabromobisphenol A (TBBPA) through electron transfer.

[0003] However, n-FeS faces two key bottlenecks in practical applications: First, its inherent stability is poor. The high surface energy of nanoparticles makes them prone to aggregation and rapid oxidation and deactivation in air or oxygenated water, severely impairing their reactivity and long-term effectiveness. Second, there is an inherent contradiction between "stability" and "reactivity." To improve stability, stabilizers (such as organic polymers like carboxymethyl cellulose and humic acid, or inorganic substances like silicates) are often introduced to coat or disperse n-FeS. While these measures can improve the storage stability and dispersibility of the material, they often form physical or chemical barriers on the material surface, inhibiting the contact between active sites (Fe(II), S(-II)) and contaminants, leading to a significant decrease in the material's reactivity, i.e., a "passivation" effect. For example, while simple carboxymethyl cellulose and humic acid can improve the antioxidant properties of n-FeS, they may also significantly weaken its ability to reduce organic pollutants. Existing modification technologies (such as loading onto biochar, mineral supports, or using organic stabilizers) primarily focus on improving the physical stability of n-FeS or providing dispersion support, but they fail to fundamentally resolve the dynamic contradiction of "the material needs high stability during storage and transportation, while rapidly releasing high activity during application." Furthermore, many modification methods suffer from problems such as low content of effective active components, potential secondary pollution from introduced organic stabilizers, weak resistance to interference in complex water bodies after modification, and the risk of re-release of pollutants due to insecure fixation after long-term use.

[0004] Especially considering the coexistence of heavy metals and halogenated organic compounds in water bodies polluted by electronic waste, existing technologies often struggle to achieve efficient simultaneous removal of both. Traditional adsorption or precipitation methods have limited effectiveness in removing halogenated organic compounds, while conventional reducing agents are difficult to stabilize in complex water conditions and synergistically act on two types of pollutants with vastly different properties.

[0005] Therefore, developing a novel modified n-FeS material that achieves both stable storage and efficient reaction has become a pressing technical challenge in this field. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to provide an active and controllable silicate-stabilized micro-nano ferrous sulfide slurry that can maintain excellent stability during storage and be "intelligently" activated upon contact with target pollutants, instantly switching to a highly active state, thereby achieving a balance between stable storage and efficient reaction, and possessing the ability to synergistically remove complex pollutants.

[0007] The second objective of this invention is to provide a method for preparing the above-mentioned active controllable silicate stabilized micro / nano ferrous sulfide slurry; the third objective is to provide an application of the above-mentioned active controllable silicate stabilized micro / nano ferrous sulfide slurry.

[0008] Technical solution: The active and controllable silicate-stabilized micro / nano ferrous sulfide slurry of the present invention includes a silicate-stabilized ferrous sulfide composite material, the composite material having a core-shell structure; wherein, the core is nano-ferrous sulfide, and the shell is a silicate interface layer; the silicate interface layer is bonded to the nano-ferrous sulfide core through Fe-O-Si chemical bonds.

[0009] The silicate is at least one of sodium silicate, potassium silicate, sodium disilicate, sodium methylsilicate, or potassium methylsilicate.

[0010] The silicon content in the composite material is from 1.0 wt% to 10.0 wt%.

[0011] The average particle size of the composite material is between 80 nm and 240 nm.

[0012] The preparation method of the above-mentioned active controllable silicate stabilized micro / nano ferrous sulfide slurry includes the following steps:

[0013] (1) Dissolve soluble silicates in deoxygenated water under an oxygen-free atmosphere to form a silicate solution;

[0014] (2) Add soluble ferrous salt solution and sulfur source solution sequentially to silicate solution to carry out co-precipitation reaction. After the reaction is completed, active controllable silicate stabilized micro-nano ferrous sulfide slurry is obtained.

[0015] In step (2), the molar concentration ratio of the soluble silicate, ferrous ions and sulfide ions is (0.001-0.01):0.043:0.085.

[0016] The reaction time in step (2) is 40-90 min, and the reaction is carried out in an inert atmosphere.

[0017] In step (2), after the reaction is completed, the product is filtered and washed, and the solid product is dispersed in a solvent to obtain active controllable silicate stabilized micro-nano ferrous sulfide slurry.

[0018] The above-mentioned active controllable silicate stabilized micro-nano ferrous sulfide slurry is used in the simultaneous removal of heavy metals and halogenated organic pollutants.

[0019] Specifically, an effective amount of the above-mentioned active controllable silicate stabilized micro-nano ferrous sulfide slurry is added to the water body to be treated containing heavy metals and halogenated organic pollutants; the interaction between heavy metals and silicates triggers the activation of the composite material interface, thereby achieving the immobilization of heavy metals and the adsorption and reduction degradation of halogenated organic pollutants.

[0020] The dosage of the slurry is from 50 mg / L to 200 mg / L.

[0021] The slurry of the present invention can maintain excellent physicochemical stability during storage and transportation thanks to the silicate interface layer. When it is introduced into polluted water containing specific heavy metals (such as Cd(II)), it can be rapidly "activated" by heavy metal ions, releasing high reactivity, thereby resolving the contradiction between stability and reactivity.

[0022] The core mechanism of this invention's slurry application lies in the "interfacial activity switch" mechanism triggered by contaminants:

[0023] 1. Stable state (storage / transport): The strong Fe-O-Si interfacial bonding and the steric hindrance effect of the silicate layer keep the material dispersed and stable and inhibit the pre-oxidation of the n-FeS core.

[0024] 2. Activation and Reaction State (Use): When the material is added to water containing Cd(II) as described above, Cd(II) preferentially binds to Si-O sites in the silicate interface layer (forming species such as CdSiO3), disrupting the original Fe-O-Si bond structure. This neutralizes the negative charge on the material surface, inducing controlled aggregation and interface layer dissociation; on the other hand, it promotes the controlled decomposition of the "unlocked" n-FeS cores, accelerating the release of highly reducing Fe(II). The released active Fe(II) and exposed active sites undergo a reduction reaction with TBBPA, achieving its debromination and degradation; simultaneously, Cd(II) itself is rapidly fixed through the formation of CdS precipitates and surface complexes.

[0025] 3. Synergistic Removal: Through the above steps, in the single addition and reaction process, the synergistic removal of Cd(II) with high capacity fixation (adsorption capacity up to 1292 mg / g) and TBBPA from weak adsorption to deep reduction conversion (debromination rate up to 38%) is achieved simultaneously.

[0026] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0027] (1) It resolves the contradiction between stability and activity: By constructing an Fe-O-Si interface structure, the material is endowed with the intelligent switching characteristic of "stable during storage and activated when encountering target pollutants", achieving a balance between long-term stability and instantaneous high activity. (2) It achieves synergistic and efficient removal of composite pollutants: Through a simple material addition step, it can simultaneously and efficiently remove Cd(II) (adsorption capacity up to 1292 mg / g) and TBBPA (from weak adsorption to complete removal and debromination), which is especially suitable for typical composite pollution scenarios such as electronic waste pollution. (3) It has good environmental adaptability and safety: The material itself uses environmentally friendly silicate as a stabilizer, and there is no risk of secondary organic pollution. When applied in actual water bodies (electroplating wastewater, groundwater, lake water, tap water, etc.), it shows strong anti-interference ability and long-lasting treatment effect (complete removal of Cd(II) within 14 days, TBBPA removal rate >73%), and the ecotoxicity of the treated effluent is significantly reduced. (4) The application method is simple and efficient and easy to implement: The application method provided is simple to operate, without the need for complex equipment or harsh conditions. After the material is added, the reaction is triggered by the pollutants themselves, which has low energy consumption and is easy to promote in actual water treatment projects. (5) The preparation process is simple and easy to promote: The raw materials used are cheap and readily available. The in-situ co-precipitation method is simple and mild, which is convenient for large-scale preparation and storage and has good prospects for industrial application. Attached Figure Description

[0028] Figure 1 Images of sodium silicate-stabilized ferrous sulfide slurries with different silicon contents;

[0029] Figure 2 SEM image of pure ferrous sulfide slurry (a), SEM image of FeS-MS in Example 1 (b), Zeta potential (c) and Fourier transform infrared image (d);

[0030] Figure 3 The graph shows the removal performance of TBBPA by FeS-MS in ordinary FeS and FeS in Example 1.

[0031] Figure 4 Experimental evidence (b) for Cd(II)-triggered changes in FeS-MS surface properties (a) and stability.

[0032] Figure 5 Performance diagram of TBBPA removal for sodium silicate-stabilized ferrous sulfide slurry with different silicon contents. Detailed Implementation

[0033] The present invention will now be described in further detail.

[0034] Example 1

[0035] In this embodiment, silicate-stabilized micro / nano ferrous sulfide slurry is prepared using an in-situ co-precipitation method.

[0036] Step 1: Solution Preparation. Under a nitrogen atmosphere, high-purity nitrogen gas was bubbled through a reaction flask containing 250 mL of deoxygenated ultrapure water with a resistivity of 18.2 MΩ·cm for 30 minutes to fully remove dissolved oxygen. Then, 2.6 g of Na₂SiO₃·9H₂O, containing 5.0 wt% silicon, was added and magnetically stirred until completely dissolved to obtain a sodium silicate solution.

[0037] Step 2: Coprecipitation reaction. While maintaining a continuous nitrogen purging, slowly add the following solutions sequentially to the solution from Step 1: 20 mL of 0.43 M FeSO4·7H2O solution and 40 mL of 0.85 M Na2S·9H2O solution. Control the dropping rate to ensure slow mixing. After the addition is complete, continue stirring at 200 rpm for 60 minutes at room temperature (25°C) to obtain a black slurry containing a silicate-stabilized ferrous sulfide composite material.

[0038] Finally, a black FeS-MS slurry with a silicon content of 5.0 wt% was collected for subsequent processing. A photograph of the slurry is shown below. Figure 1 The slurry bottle is indicated by the number 3 in the middle.

[0039] Characterization: The FeS-MS slurry was freeze-dried to obtain a silicate-stabilized ferrous sulfide composite material, which was then characterized. Figure 2 As shown in (b), the SEM results indicate that FeS-MS particles are more dispersed, and the average particle size of the composite material is approximately 150 nm; Figure 2 As shown in (c), the surface Zeta potential is -41.6 mV; Figure 2 As shown in (d), the infrared spectrum at 530 cm⁻¹ -1 The presence of characteristic Fe-O-Si absorption peaks nearby indicates that silicate is successfully stabilized on the FeS surface through Fe-O-Si bonds in this composite material.

[0040] Example 2

[0041] In this embodiment, silicate-stabilized micro / nano ferrous sulfide slurry is prepared using an in-situ co-precipitation method.

[0042] Step 1: Solution Preparation. Under a nitrogen atmosphere, high-purity nitrogen gas was passed through a reaction flask containing 250 mL of deoxygenated ultrapure water with a resistivity of 18.2 MΩ·cm for 30 minutes to fully remove dissolved oxygen. Then, 1.3 g of Na₂SiO₃·9H₂O, containing 2.5 wt% silicon, was added and magnetically stirred until completely dissolved to obtain a sodium silicate solution.

[0043] Step 2: Coprecipitation reaction. While maintaining a continuous nitrogen purging, slowly add the following solutions sequentially to the solution from Step 1: 20 mL of 0.43 M FeSO4·7H2O solution and 40 mL of 0.85 M Na2S·9H2O solution. Control the dropping rate to ensure slow mixing. After the addition is complete, continue stirring at 200 rpm for 60 minutes at room temperature (25°C). Finally, collect the FeS-MS black slurry for subsequent processing.

[0044] Characterization: The FeS-MS slurry was freeze-dried to obtain a silicate-stabilized ferrous sulfide composite material. The composite material was characterized. SEM results showed that the FeS-MS was more dispersed, with a surface zeta potential of -25.6 mV, an average particle size of approximately 350 nm, and an infrared spectrum at 530 cm⁻¹. -1 The presence of characteristic Fe-O-Si absorption peaks nearby confirms that silicate has been successfully stabilized on the FeS surface via Fe-O-Si bonds, but the stabilization effect is not as good as that of 5 wt% sodium silicate in Example 1. 2.5 wt% sodium silicate cannot completely coat the n-FeS surface, as... Figure 1 As shown in the slurry bottles marked with numbers 1 and 2, the FeS-MS slurry containing 2.5 wt% sodium silicate is superior to FeS without sodium silicate, but it still settles and turns yellow after being left for a period of time.

[0045] Example 3

[0046] In this embodiment, silicate-stabilized micro / nano ferrous sulfide slurry is prepared using an in-situ co-precipitation method.

[0047] Step 1: Solution Preparation. Under a nitrogen atmosphere, high-purity nitrogen gas was bubbled into a reaction flask containing 250 mL of deoxygenated ultrapure water with a resistivity of 18.2 MΩ·cm for 30 minutes to fully remove dissolved oxygen. Then, 1.4 g of K₂SiO₃, with a silicon content of 5.0 wt%, was added and magnetically stirred until completely dissolved to obtain a sodium silicate solution.

[0048] Step 2: Coprecipitation reaction. While maintaining a continuous nitrogen purging, slowly add the following solutions sequentially to the solution from Step 1: 20 mL of 0.43 M FeSO4·7H2O solution and 40 mL of 0.85 M Na2S·9H2O solution. Control the dropping rate to ensure slow mixing. After the addition is complete, continue stirring at 200 rpm for 60 minutes at room temperature (25°C). Finally, collect the FeS-MS(K) black slurry for subsequent processing.

[0049] Characterization: The FeS-MS(K) slurry was characterized. SEM results showed that the FeS-MS(K) was more dispersed, with a surface Zeta potential of -35.6 mV, an average particle size of approximately 250 nm, and an infrared spectrum at 530 cm⁻¹. -1 The presence of characteristic Fe-O-Si absorption peaks nearby confirms that silicate is successfully stabilized on the FeS surface via Fe-O-Si bonds. However, the stabilization effect is not as good as that of sodium silicate in Example 1. This is because Na... + With a smaller radius and stronger hydration, its ion association with silicate is generally weaker than that of K. + Therefore, in solution, sodium silicate is more likely to maintain good dispersibility and reactivity, allowing silica species to contact the n-FeS surface more uniformly, which is more conducive to the formation of a stable surface silicate coating layer or Fe-O-Si interface structure.

[0050] Example 4

[0051] Based on Example 1, the difference is that the silicon content is 10 wt%. Figure 1 As can be seen from the slurry bottles marked with numbers 3 and 4, the FeS-MS slurry exhibits good stability and antioxidant properties with increasing silicon content. However, high stability does not necessarily translate to high pollutant removal efficiency. Figure 5 It can be seen that when the silicon content is 10 wt%, the TBBPA removal rate of the slurry is not as high as that with a silicon content of 5 wt%. Therefore, considering stability, antioxidant properties, pollutant removal capacity, and economic benefits, a silicon content of 5% offers better cost-effectiveness.

[0052] Example 5

[0053] This embodiment verifies the synergistic removal performance of the prepared FeS-MS for heavy metal-organic composite pollutants.

[0054] Step 1: Preparation of pollutant solutions. Prepare stock solutions of Cd(II) at different concentrations of 80 mg / L and stock solutions of TBBPA at a concentration of 500 μM.

[0055] Step 2: Reaction Process. A series of 250 mL blue-capped glass bottles were used as reactors. 50 mL of the Cd(II) solution from Step 1 and 4 mL of TBBPA solution were added to each bottle, and the volume was adjusted to 100 mL with ultrapure water. At this point, the solution contained both Cd(II) and TBBPA. 10 mg of the FeS-MS dry powder prepared in Example 1 was added to each reaction bottle, bringing the material concentration to 100 mg / L. The reaction bottles were placed in a constant-temperature shaker and reacted in the dark at 25°C and 180 rpm.

[0056] Results: After the material was added to water containing Cd(II) using the above method, Cd(II) preferentially combined with Si-O sites in the silicate interface layer (forming species such as CdSiO3), disrupting the original Fe-O-Si bond structure. This neutralizes the negative charge on the material surface, inducing controllable aggregation and interface layer dissociation. Figure 4 On the other hand, it promotes the controlled decomposition of the "unlocked" n-FeS core, accelerating the release of Fe(II) with high reducing activity. Figure 4 The released active Fe(II) and exposed active sites undergo a reduction reaction with TBBPA, achieving its debromination and degradation. Simultaneously, Cd(II) itself is rapidly immobilized through the formation of CdS precipitate and surface complexes. Within 10 minutes of the reaction initiation, the removal rate of Cd(II) reaches 100%. As the reaction proceeds, the removal rate of TBBPA gradually increases, reaching complete removal at 240 minutes. Analysis of the post-reaction liquid revealed the release of bromide ions, and the calculated debromination rate of TBBPA was 38%. These results indicate that FeS-MS is effectively activated in the presence of Cd(II), achieving ultra-rapid immobilization of Cd(II) and simultaneous reduction and degradation of TBBPA.

[0057] Example 6

[0058] This embodiment verifies the removal efficiency and environmental adaptability of FeS-MS for complex pollutants in actual water bodies from different sources.

[0059] Four types of actual water samples were collected: electroplating wastewater, groundwater, lake water, and tap water. After pretreatment, simulated polluted water samples containing 50 mg / L Cd(II) and 15 μM TBBPA were prepared. FeS-MS powder from Example 1 was added to each water sample to a concentration of 100 mg / L. The system was placed at 25°C and stirred at low speed to simulate a 14-day continuous treatment process. Samples were taken on days 1, 3, 7, and 14 to analyze the residual concentrations of Cd(II) and TBBPA, total dissolved iron concentration, and total organic carbon (TOC) concentration.

[0060] Pollutant Removal: During the 14-day experimental period, FeS-MS maintained a near 100% Cd(II) removal rate in all four water bodies. For TBBPA, the removal rates on day 14 were: electroplating wastewater >73%, groundwater ~100%, lake water >51%, and tap water >67%. These results demonstrate the effective removal capabilities of FeS-MS in real-world water bodies with complex ionic compositions and varying organic matter content.

[0061] Secondary pollution control: The total dissolved iron concentration in all effluent samples was below 0.8 mg / L, far below the national wastewater discharge standard (1 mg / L), indicating that very little iron was dissolved from the material. The TOC concentration was higher than that in the influent, confirming that TBBPA was degraded into small molecule organic products, rather than a simple phase transfer.

[0062] Conclusion: FeS-MS demonstrates efficient, durable, and safe treatment capabilities for complex pollutants in real water bodies, and shows promising prospects for engineering applications.

[0063] Example 7

[0064] This embodiment demonstrates how coexisting ions affect the interface state of FeS-MS, thereby regulating its reactivity and confirming its "interface switch" characteristics.

[0065] Two reaction groups were set up: the control group consisted of a system containing 40 mg / L Cr(VI) and 50 mg / L FeS-MS suspension; the experimental group consisted of the control group plus calcium chloride, so that Ca... 2+ The final concentration was 100 mM. Both groups reacted under identical conditions, and the Cr(VI) removal kinetics were monitored. Simultaneously, a potentiometric particle size analyzer was used to monitor changes in particle zeta potential and hydrodynamic diameter in real time during the initial reaction phase (within 10 minutes).

[0066] Remove performance changes: Adding Ca 2+ Subsequently, the removal rate of Cr(VI) by FeS-MS increased by approximately 8% compared to the control group. During the reaction, a white flocculent precipitate appeared in the experimental group.

[0067] Interface status change: Monitoring shows that Ca 2+ After addition, the negative charge on the FeS-MS surface was quickly neutralized, the absolute value of the Zeta potential decreased significantly, the particles underwent controlled agglomeration, and the particle size increased.

[0068] Mechanism analysis: Analysis of the white precipitate revealed the presence of calcium silicate. (Ca) 2+The reaction with silicate ions in the FeS-MS interface layer produces calcium silicate precipitate, disrupting the original Fe-O-Si stabilized structure and partially exposing the encapsulated FeS active sites. This restores some of the reducing activity and promotes the removal of Cr(VI). This process confirms that pollutants or coexisting ions can trigger dynamic changes in the material interface structure, achieving activity regulation.

[0069] Conclusion: This embodiment demonstrates that the activity of FeS-MS can be mediated by coexisting ions in the environment (such as Ca). 2+ It can be regulated by the environment, and the switching between its "steady state" and "active state" is environmentally responsive.

[0070] Comparative Example 1

[0071] Performance comparison of unstabilized nano-ferrous sulfide (n-FeS) slurry:

[0072] This comparative example is intended to be compared with Examples 1, 2, and 3 to illustrate the defects of the original n-FeS slurry that has not undergone silicate stabilization treatment.

[0073] Based on steps 1, 2, and 3 of Example 1, the difference from Example 1 is that, without adding any silicates (i.e., with a silicon element content of 0 wt%), only FeSO4 solution and Na2S solution were mixed and reacted in oxygen-free water to prepare the original n-FeS slurry. A photograph of this slurry is shown below. Figure 1 As shown in 'a'.

[0074] The same characterization was performed as in Example 1: Figure 2 The scanning electron microscope (SEM) image (a) shows severe aggregation of n-FeS particles, forming irregular large aggregates with sizes reaching several micrometers, making it difficult to distinguish the initial nanomorphology. This indicates strong van der Waals forces and extremely poor dispersibility. Figure 2 As shown in (c), the zeta potential in water, measured using a nanoparticle size analyzer and zeta potential meter, is approximately -15 mV. This low absolute value indicates weak electrostatic repulsion between particles, making it ineffective in resisting aggregation. Figure 2 As shown in (d), the infrared spectrum at 530 cm⁻¹ -1 No Fe-O-Si characteristic absorption peaks were observed nearby.

[0075] The original n-FeS slurry prepared in this comparative example exhibits a strong tendency to agglomerate and extremely poor oxidative stability. Its low surface potential prevents it from maintaining its nano-dispersion state and ferrous reduction activity in aqueous or air conditions. These inherent defects make it difficult to store and transport, and its limited number of active sites and rapid decay of reaction efficiency during application render it impractical for real-world applications.

[0076] Comparative Example 2

[0077] Preparation and characterization of sodium carboxymethyl cellulose (CMC) stabilized FeS slurry:

[0078] Based on the steps of Example 1, but differing from Example 1, 0.8 g of sodium carboxymethyl cellulose (CMC, viscosity ~1500 mPa·s) was added to water under continuous nitrogen purging and stirring, and stirred until completely dissolved to form a homogeneous viscous solution. Maintaining an anaerobic environment, 20 mL of a 0.43 mol / L FeSO4 solution and 40 mL of a 0.85 mol / L Na2S solution were slowly added dropwise. The reaction was carried out at 25°C and 200 rpm for 60 minutes. Subsequent centrifugation, washing (with deoxygenated water and ethanol), and drying (60°C, N2) steps were the same as in Example 1, yielding a brownish-black powder product, designated as FeS-CMC slurry.

[0079] The same characterization was performed as in Example 1: SEM showed that the aggregation phenomenon was improved compared to the original n-FeS, and the particle size was reduced, but many aggregates were still visible in the dry state. Short-term (within several hours) dispersibility in water was acceptable. The measured Zeta potential was approximately -35 mV, a significant increase compared to the original n-FeS (-15 mV), mainly due to the negative charge generated by the ionization of carboxylate groups on the CMC long chain. Characteristic absorption peaks of CMC (such as COC stretching vibration, -COO) were simultaneously observed in the FTIR spectrum. - The characteristic peaks of FeS (antisymmetric stretching vibration) and FeS were detected, but novel inorganic interface bonding features such as Fe-O-Si, which are clearly identified in the FeS-MS of this invention, were not detected.

[0080] CMC, as an organic stabilizer, mainly coats the FeS surface through physical adsorption and steric hindrance, improving its dispersibility and stability in the short term. However, this stabilizing effect depends on the integrity of the organic polymer chains, posing a risk of long-term degradation, and it fails to form a strong and durable chemical bond interface with the FeS core. The introduction of a large amount of organic matter also brings potential secondary organic pollution problems, and the material properties are dominated by the properties of the organic layer, lacking the intelligent response characteristics of the inorganic interface like the FeS-MS of this invention.

[0081] Comparative Example 3

[0082] Removal performance of ordinary nano-ferrous sulfide (n-FeS) slurry for Cd(II) and tetrabromobisphenol A (TBBPA):

[0083] This experiment completely replicated the conditions of Example 2: 10.0 mg of ordinary n-FeS powder (concentration 100 mg / L) was added to 100 mL of a mixed water sample containing 80 mg / L Cd(II) and 20 μM TBBPA, and the reaction was carried out in the dark at 25°C and 180 rpm. Samples were taken at the same time points to analyze the concentrations of Cd(II), TBBPA, and bromide ions (Br). - )release.

[0084] Under the same experimental conditions, ordinary n-FeS exhibited significantly different properties from the FeS-MS material of this invention. Ordinary n-FeS showed an adsorption capacity of approximately 800 mg / g for Cd(II), but exhibited slight desorption during the 4-hour reaction period. In contrast, the FeS-MS of this invention demonstrated an adsorption capacity as high as 1292 mg / g for Cd(II), achieving complete and stable immobilization within 10 minutes. Figure 3 As shown, for the removal of TBBPA, ordinary n-FeS only achieved a removal rate of about 52% after 4 hours, and no significant Br was detected in the reaction solution. - The release indicates that its removal mechanism is mainly physical adsorption, with virtually no reductive debromination capability. In stark contrast, the FeS-MS slurry of this invention, in the presence of Cd(II), can completely remove TBBPA and achieve a debromination rate of 38%, proving that it triggers a highly efficient adsorption-reduction synergistic degradation pathway.

[0085] The most crucial difference lies in the synergistic effect. In the ordinary n-FeS system, the presence of Cd(II) does not significantly promote the removal of TBBPA, and the removal processes of the two pollutants are relatively independent. However, in the FeS-MS system of this invention, Cd(II) plays a key role as an "activation switch," and its presence is a necessary condition for triggering the reductive degradation of TBBPA, achieving intelligent linkage and strong synergy in the removal of the two pollutants.

[0086] This comparative example directly demonstrates that, under the same experimental conditions as in Example 2 of this invention, ordinary unstabilized n-FeS exhibits inherent defects when treating Cd(II) and TBBPA complex pollution: limited and unstable Cd(II) fixation capacity, only adsorption of TBBPA without degradation, rapid self-oxidation and deactivation, and a lack of synergistic effects between pollutants. In contrast, the FeS-MS material of this invention, with its unique silicate-stable interface and "pollutant-triggered switch" mechanism, achieves ultra-high capacity stable fixation of Cd(II), deep reduction and degradation of TBBPA, long-term material stability, and intelligent synergistic removal of pollutants, demonstrating significantly superior comprehensive performance and engineering application potential.

[0087] Comparative Example 4

[0088] Comparison of removal efficiency and stability of ordinary nano-ferrous sulfide (n-FeS) slurry for complex pollutants in actual water bodies:

[0089] This comparative example aims to evaluate the effectiveness, stability, and environmental adaptability of unstabilized ordinary nano-ferrous sulfide (n-FeS) slurry in treating complex pollutants in real water bodies through experiments conducted in strict parallel with Example 6 (performance of FeS-MS slurry in actual water bodies), thereby further highlighting the engineering application advantages of the material (FeS-MS slurry) of this invention in complex environmental contexts.

[0090] Following the conditions of Example 6, four actual water samples—electroplating wastewater, groundwater, lake water, and tap water—were collected. After pretreatment, simulated polluted water samples containing 50 mg / L Cd(II) and 15 μM TBBPA were prepared. FeS- powder from Comparative Example 1 was added to each water sample to a concentration of 100 mg / L. The system was placed at 25°C and stirred at low speed to simulate a continuous treatment process for 14 days. Samples were taken on days 1, 3, 7, and 14 to analyze the residual concentrations of Cd(II) and TBBPA, the total dissolved iron concentration, and the total organic carbon (TOC) concentration.

[0091] Pollutant removal: such as Figure 3 As shown, on day 1 of the reaction, the removal rate of Cd(II) by ordinary n-FeS reached 70%-90% in different water bodies, demonstrating a certain initial capacity. However, its removal efficiency decreased sharply with reaction time. By day 14, the Cd(II) removal rate had dropped below 30% in electroplating wastewater and lake water, and only maintained at 40%-60% in groundwater and tap water. This was far from achieving the nearly 100% removal rate maintained by FeS-MS in Example 6. A rebound in Cd(II) concentration in the filtrate was detected in some water samples (especially electroplating wastewater) in the later stages, indicating weak fixation and a risk of re-release. The removal rate of TBBPA by ordinary n-FeS remained very low (<20% in all water bodies on day 14), and no bromide ion release was detected throughout the entire experimental period. This indicates that it can only produce extremely limited physical adsorption of TBBPA and has no ability to reduce and degrade it, which is in stark contrast to the deep removal (>51%-100%) and significant debromination achieved by FeS-MS in Example 6.

[0092] Secondary pollution control: On the first day of the reaction, the total dissolved iron concentration in each water body reached as high as 5-15 mg / L, far exceeding the national discharge standard (1 mg / L), and remained at a high level throughout the experimental period. This indicates that ordinary n-FeS underwent severe non-selective oxidative dissolution, not only wasting iron resources but also causing serious secondary pollution and sludge disposal problems. Unlike Example 6, where TOC increased appropriately due to degradation products, the TOC concentration in the ordinary n-FeS system did not change significantly, further confirming that its removal of TBBPA was mainly through adsorption and fixation rather than degradation and transformation, and the pollutant was not completely eliminated.

[0093] This comparative example, through a 14-day parallel experiment in the same real-world water environment as Example 6, fully demonstrates that unstabilized ordinary n-FeS, due to its rapid oxidation, susceptibility to disturbance and instability, and lack of intelligent response mechanism, exhibits low, unstable, and unsustainable removal efficiency for Cd(II) and TBBPA combined pollution in practical applications, and introduces serious secondary iron ion pollution problems. In contrast, the results of Example 6 show that the FeS-MS material of this invention, with its superior antioxidant and anti-interference capabilities and unique "interfacial active switch" characteristics endowed by the silicate interface, can synergistically remove heavy metals and organic pollutants in complex real-world water environments in a long-term, efficient, stable, and safe manner, truly possessing engineering application value to address real-world environmental remediation challenges. This comparison strongly highlights the significant progress of this invention in solving the bottlenecks in the practical application of iron-based materials.

[0094] Comparative Example 5

[0095] The effect of high-concentration sodium silicate stabilized ferrous sulfide slurry (FeS-MS-20%) on the removal performance of Cd(II) and TBBPA:

[0096] This comparative example aims to investigate the regulatory effect of sodium silicate addition on material properties. A stabilized slurry with a significantly increased sodium silicate content (denoted as FeS-MS-20%) was prepared and its performance was compared with that of Example 2 of this invention (FeS-MS slurry).

[0097] Following the process flow of Example 1, only the dosage of sodium silicate was changed: sodium silicate nonahydrate, several times the amount used in Example 1, was added to 250 mL of deoxygenated water to achieve a concentration of 20% wt in the total system. Subsequent addition of ferrous salt and sulfur source, and reaction steps, remained consistent with Example 1, yielding FeS-MS-20% slurry. Under identical conditions (80 mg / L Cd(II), 20 μM TBBPA, material dosage 100 mg / L, reaction time 4 h), the removal performance of the FeS-MS-20% slurry was tested and compared with the results of Example 2.

[0098] Cd(II) removal: The FeS-MS-20% slurry still achieved complete Cd(II) removal within 10 minutes, with an adsorption capacity comparable to FeS-MS, maintaining a high level of approximately 1290 mg / g. This indicates that even with increased silicate layer thickness, the interface still allows Cd(II) to rapidly enter and be effectively immobilized via precipitation / complexation, a process with relatively low requirements for interfacial permeability.

[0099] Removal of TBBPA: its performance changes significantly.

[0100] Figure 5 The TBBPA removal rate test results for the slurries of Comparative Example 1, Examples 1, 4, and Comparative Example 5 are as follows: It can be seen that for slurries with different Si content, their TBBPA removal rate is higher than that of ordinary n-FeS. However, when the added Si content reaches 10%, the TBBPA removal rate decreases. In particular, the 4-hour TBBPA removal rate of the FeS-MS-20% slurry drops to approximately 30%, and the debromination rate is extremely low (<5%), far lower than the 100% TBBPA removal rate of the FeS-MS slurry in Example 1 of this invention, which has a debromination rate as high as 38%. This reveals a key phenomenon: excessive silicate leads to excessive "passivation".

[0101] Characterization analysis confirmed that excess sodium silicate formed a denser and thicker interfacial layer. While this thick layer enhanced physical stability, it also severely hindered interfacial electron transfer and the release of active Fe(II) species. For TBBPA, which requires Cd(II) to trigger interfacial dissociation and relies on the subsequent release of active Fe(II) for reductive degradation, this excessive shielding effect is fatal. However, for Cd(II) primarily fixed through surface reactions and precipitation, its removal process is less affected. This comparative example demonstrates that simply increasing the amount of stabilizer can enhance stability, but excessive passivation severely sacrifices the material's reductive activity against organic pollutants. This, conversely, confirms the scientific validity and necessity of the optimized sodium silicate addition ratio in Examples 1 and 2 of this invention: this ratio perfectly balances "storage stability" and "activatable activity during use," achieving optimal synergistic removal of two types of pollutants with vastly different properties, which is one of the key aspects of this invention.

[0102] Comparative Example 6

[0103] Preparation and evaluation of the anti-ionic interference performance of sodium methylsilicate stabilized ferrous sulfide (FeS-PMS) slurry:

[0104] This comparative example aims to investigate the effect of another silicate—sodium methylsilicate (PMS)—as a stabilizer, with a focus on its performance with common coexisting ions (in the form of Ca). 2+The stability and activity response of the sodium silicate (MS) system selected in this invention are compared to highlight its universality and reliability in complex aquatic environments.

[0105] Based on the steps of Example 1, but differing from Example 1, sodium methylsilicate was used as a stabilizer. An equivalent molar amount of sodium methylsilicate as in Example 1 was dissolved under continuous nitrogen purging and stirring. Maintaining an anaerobic environment, 20 mL of a 0.43 mol / L FeSO4 solution and 40 mL of a 0.85 mol / L Na2S solution were slowly added dropwise. The reaction was carried out at 25°C and 200 rpm for 60 minutes. A black slurry was obtained, denoted as FeS-PMS.

[0106] Two reaction groups were set up according to the conditions in Example 5: the control group was a system containing 40 mg / L Cr(VI) and 50 mg / L FeS-PMS suspension; the experimental group was based on the control group with the addition of calcium chloride, so that Ca... 2+ The final concentration was 100 mM. Both groups reacted under identical conditions, and the Cr(VI) removal kinetics were monitored. Simultaneously, a potentiometric particle size analyzer was used to monitor changes in particle zeta potential and hydrodynamic diameter in real time during the initial reaction phase (within 10 minutes).

[0107] Remove performance changes: Adding Ca 2+ Subsequently, the removal rate of Cr(VI) by FeS-PMS dropped sharply to approximately 22%, with a performance degradation of over 66%. Crucially, the removal rate did not improve as in FeS-MS of Example 6, but rather decreased significantly.

[0108] Interface status change: Monitoring shows that Ca 2+ The addition did not neutralize the negative charge on the FeS-PMS surface, and the absolute value of the Zeta potential did not decrease significantly.

[0109] Mechanism analysis: The stabilizing layer formed by sodium methylsilicate on the FeS surface is mainly stabilized by hydrophobic interactions (-CH3) and steric hindrance. The addition of Ca... 2+ Subsequently, no interfacial chemical reconstruction (such as the specific destruction of Fe-O-Si bonds) was triggered to activate the FeS core. This comparative example demonstrates through rigorous parallel experiments that the ferrous sulfide material stabilized with sodium methylsilicate (PMS) (FeS-PMS) does not possess the "ion-triggered intelligent active switch" characteristics of the preferred sodium silicate (MS) system of this invention. It is less effective in the face of common coexisting ions such as Ca2+. 2+ At that time, there was no active switching characteristic. This strongly confirms, from the opposite perspective, the uniqueness and superiority of the Fe-O-Si interface structure constructed by this invention (FeS-MS): it not only provides stability, but also can block interference factors in the environment (such as Ca).2+ This transforms into a "key" to activating the reactivity of materials, achieving a higher level of unity between stability and activity. This characteristic is difficult to achieve with other types of silicate stabilizers (such as PMS), and constitutes one of the core innovations of this invention.

[0110] Comparative Example 7

[0111] Preparation and performance comparison of post-loaded silicate-modified ferrous sulfide materials:

[0112] This comparative example aims to illustrate that silicates must participate in co-precipitation in situ during the FeS formation process in order to construct a stable and triggerable Fe-O-Si interface structure; if a later surface coating or post-loading method is used, it is difficult to achieve the same stabilization effect and "interface activity switch" function as the present invention.

[0113] Following the process conditions of Example 1, a conventional n-FeS slurry was first prepared under anaerobic conditions using the method described in Comparative Example 1. Subsequently, under nitrogen protection, an equal volume of sodium silicate solution (as in Example 1) was added to the obtained n-FeS slurry, and the mixture was stirred at room temperature for 60 minutes to allow silicates to adhere to the FeS surface via a "post-adsorption" process. After the reaction was complete, solid-liquid separation and washing were performed to obtain a post-silicate-loaded ferrous sulfide slurry, denoted as FeS / MS-post.

[0114] The FeS / MS-post was analyzed according to the characterization method described in Example 1. SEM results showed that the agglomeration of this material was somewhat alleviated compared to the original n-FeS, but large agglomerates were still present, and the particle uniformity was worse than that of the FeS-MS obtained in Example 1. The zeta potential was measured to be approximately -24 mV to -30 mV, which, although lower than that of the original n-FeS, was still significantly higher than the absolute value of the negative potential of FeS-MS in Example 1. FTIR analysis did not observe the characteristic Fe-O-Si absorption peaks of the same intensity and clarity as those observed in the FeS-MS of this invention, indicating that under the post-loading method, silicates were mainly attached in a physical adsorption form, failing to effectively construct a strong chemically bonded interface.

[0115] The removal performance of FeS / MS-post for the combined pollutants Cd(II) and TBBPA was further investigated under the conditions of Example 5. The results showed that FeS / MS-post still had a certain ability to immobilize Cd(II), but its adsorption capacity and immobilization stability were lower than those of FeS-MS in Example 1; the removal of TBBPA was mainly by adsorption, with a low debromination rate, and the promoting effect of Cd(II) coexistence on the removal of TBBPA was not obvious.

[0116] This comparative example demonstrates that simply adsorbing silicate onto the FeS surface in the later stages cannot form the Fe-O-Si interface structure required by this invention, nor can it achieve the intelligent switching between the "stable state" and the "activated state". Only by constructing the silicate interface layer through in-situ co-precipitation can both storage stability and high activity triggered by contaminants be achieved.

[0117] Comparative Example 8

[0118] Comparison of silicate-ferrous sulfide materials prepared by changing the feeding order:

[0119] This comparative example aims to illustrate that the order in which silicates, Fe(II), and S(-II) are added plays a crucial role in the construction of the interfacial structure in this invention. Changing the order of addition weakens the formation of the Fe-O-Si interface, leading to a decrease in material stability and responsiveness.

[0120] Referring to the formulation of Example 1, under anaerobic conditions, FeSO4·7H2O solution and Na2S·9H2O solution were first mixed to form a black n-FeS precipitate. Then, sodium silicate solution was added to the system, and stirring was continued for 60 min. The remaining washing and separation steps were the same as in Example 1, and the resulting material was denoted as FeS-MS-rev.

[0121] The FeS-MS-rev was characterized. SEM results showed that the material had uneven particle distribution and many agglomerates; the average particle size was larger than that of the FeS-MS obtained in Example 1. The zeta potential was approximately -20 mV to -28 mV, indicating that its surface electrostatic stability was limited. The FTIR results showed weak Fe-O-Si related characteristic peaks, indicating that the addition of silicate after the formation of FeS cores could only achieve limited surface adsorption or local coating, making it difficult to form a uniform and continuous interface stable layer.

[0122] Its removal performance was tested in the same composite pollution system as in Example 5. The results showed that the material had a certain removal effect on Cd(II), but the removal rate and long-term fixation ability were weaker than those in Example 1; the removal rate of TBBPA decreased significantly, and Br... - The low release amount indicates that its reductive debromination ability was not effectively established. In particular, no significant "trigger enhancement effect" as observed in the presence of Cd(II) was observed in the FeS-MS of this invention.

[0123] This comparative example illustrates that generating FeS first and then introducing silicate cannot achieve the in-situ interface reconstruction effect required by this invention. In the embodiments of this invention, the process route of pre-existing silicate followed by the sequential addition of Fe(II) and S(-II) is beneficial for simultaneously constructing a stable Fe-O-Si interface during the nucleation and growth stages, which is a key step in achieving high material stability and activatability.

[0124] Comparative Example 9

[0125] Comparison of FeS-MS removal performance for halogenated organic pollutants under heavy metal-free triggering conditions:

[0126] This comparative example aims to further demonstrate that the efficient removal and dehalogenation of halogenated organic pollutants by the material of the present invention is not due to the intrinsic continuous high activity of the material, but rather depends on the "interfacial active switch" mechanism triggered by heavy metal ions.

[0127] Following the experimental conditions of Example 5, only Cd(II) was removed from the reaction system to prepare a simulated polluted water sample containing only TBBPA. 10 mg of the FeS-MS material prepared in Example 1 was added to 100 mL of water containing 20 μM TBBPA, making the concentration 100 mg / L. The reaction was carried out at 25°C, 180 rpm, and in the dark for 4 h, while simultaneously monitoring the TBBPA concentration and Br⁻ concentration. - Release status.

[0128] The results showed that FeS-MS still had a certain removal effect on TBBPA in the absence of Cd(II), but its removal rate was significantly lower than that of the Cd(II)-TBBPA composite system in Example 5, and the Br content in the reaction solution was also lower. - The release is extremely low or difficult to detect, indicating that the removal of TBBPA at this time mainly relies on physical adsorption or weak surface interaction, and no significant reductive dehalogenation reaction has occurred.

[0129] Further analysis of surface property changes reveals that, in the absence of Cd(II), the Fe-O-Si interface structure on the material surface remains relatively intact, the silicate interface layer is not effectively destroyed, and the highly active Fe(II) in the FeS core is not fully released. Therefore, the material maintains a "stable state" rather than an "activated state".

[0130] This comparative example directly demonstrates that the material of this invention does not simply rely on high adsorption capacity to remove TBBPA, but rather depends on the competitive coordination disruption of the Fe-O-Si interface by heavy metal ions, triggering the release of FeS activity and establishing an adsorption-reduction synergistic removal pathway. Heavy metals such as Cd(II) are not only the targets for removal in this invention, but also key factors in activating the material's performance.

[0131] Comparative Example 10

[0132] Comparison of material properties after air exposure and aging:

[0133] This comparative example aims to illustrate that the silicate interface layer constructed in this invention can significantly improve the oxidation stability of FeS materials under storage and exposure conditions, thereby ensuring their continued reactivity in subsequent applications.

[0134] FeS-MS slurry prepared in Example 1 and ordinary n-FeS slurry prepared in Comparative Example 1 were respectively placed in air for 7 days under the same conditions. No additional protection was provided during storage; they were simply kept sealed at room temperature. After storage, equal amounts of each material were taken and used to treat a complex contamination system containing 80 mg / L Cd(II) and 20 μM TBBPA under the same conditions as in Example 5, and their pollutant removal performance was determined.

[0135] The results showed that after 7 days of air exposure, the color of ordinary n-FeS slurry changed significantly from black to grayish-brown, indicating significant oxidation. After redispersement, severe particle agglomeration occurred, reactivity decreased significantly, the removal rate of Cd(II) slowed considerably, the removal rate of TBBPA further decreased, and Br2 removal was virtually nonexistent. - Release. In contrast, FeS-MS slurry retains a good black appearance and dispersion state after storage, has good redispersion performance, still has the ability to quickly remove Cd(II), and retains high TBBPA removal efficiency and a certain debromination ability.

[0136] Mechanism analysis shows that ordinary n-FeS is easily oxidized in air, resulting in the formation of an iron oxide / hydroxide layer on the surface and a large loss of active Fe(II). However, the FeS-MS of this invention has a silicate interface layer and Fe-O-Si bonding structure on its surface, which can effectively inhibit the erosion of the daughter core FeS by oxygen and moisture, so that the material can maintain a high level of activity reserves during storage.

[0137] This comparative example further demonstrates that the material of the present invention has significantly better oxidation resistance and structural stability than ordinary n-FeS during the storage stage. This characteristic of "stable storage first, and activation triggered by pollutants later" is an important advantage that distinguishes it from existing FeS materials.

Claims

1. An active silicon pyrosalt stabilized micro-nano ferrous sulfide slurry, characterized in that, The invention includes a silicate-stabilized ferrous sulfide composite material having a core-shell structure; wherein the core is nano-ferrous sulfide and the shell is a silicate interface layer; the silicate interface layer is bonded to the nano-ferrous sulfide core through Fe-O-Si chemical bonds.

2. The active controllable silicate-stabilized micro- and nano-ferrous sulfide slurry according to claim 1, characterized in that, The silicate is at least one of sodium silicate, potassium silicate, sodium disilicate, sodium methylsilicate, or potassium methylsilicate.

3. The active controllable silicon pyrosalt stabilized micro-nano ferrous sulfide slurry according to claim 1, wherein, The silicon content in the composite material is from 1.0 wt% to 10.0 wt%.

4. The active controllable silicon pyrosalt-stabilized micro- and nano-ferrous sulfide slurry according to claim 1, characterized in that, The average particle size of the composite material is between 80 nm and 240 nm.

5. A method for preparing the active controllable silicate-stabilized micro / nano ferrous sulfide slurry according to claim 1, characterized in that, Includes the following steps: (1) Dissolve soluble silicates in deoxygenated water under an oxygen-free atmosphere to form a silicate solution; (2) Add soluble ferrous salt solution and sulfur source solution sequentially to silicate solution to carry out co-precipitation reaction. After the reaction is completed, active controllable silicate stabilized micro-nano ferrous sulfide slurry is obtained.

6. The preparation method according to claim 5, characterized in that, In step (2), the molar concentration ratio of soluble silicate, ferrous ions and sulfide ions is (0.001-0.01):0.043:0.

085.

7. The preparation method according to claim 5, characterized in that, The reaction time for step (2) is 40-90 min; the reaction is carried out in an inert atmosphere.

8. The application of the silicate-stabilized micro / nano ferrous sulfide slurry of claim 1 in the simultaneous removal of heavy metals and halogenated organic pollutants.

9. The application according to claim 8, characterized in that, An effective amount of the silicate-stabilized micro / nano ferrous sulfide slurry as described in claim 1 is added to the water body to be treated containing heavy metals and halogenated organic pollutants; the interaction between heavy metals and silicates triggers the activation of the composite material interface, thereby achieving the immobilization of heavy metals and the adsorption and reduction degradation of halogenated organic pollutants.

10. The application according to claim 9, characterized in that, The dosage of the slurry is from 50 mg / L to 200 mg / L.

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