An amorphous iron-magnesium-aluminum silicate, a method for preparing the same and use thereof

Abstract

This invention relates to the fields of adsorbent preparation and heavy metal remediation technology, and particularly to an amorphous iron-magnesium-aluminum silicate, its preparation method, and its applications. This invention utilizes molten salt-mediated ion exchange and lattice recombination under high-temperature conditions to completely and uniformly transform various silicate minerals from complex and inconsistent natural clay minerals into a non-naturally formed, structurally homogeneous, and stable amorphous iron-magnesium-aluminum silicate. This overcomes the limitation of traditional adsorbents having a narrow applicable concentration range, exhibiting extremely strong removal capabilities for heavy metal ions from high to low concentrations, achieving deep purification. Based on the theory of "increasing configurational entropy," this invention proposes the design of a silicate network framework with dense, highly active sites and multiple metals, breaking through the traditional approach of "simple modification" of natural clay minerals. It fundamentally reconstructs their material composition, providing a material that combines low cost with revolutionary adsorption performance.

Description

Technical Field

[0001] This invention relates to the field of adsorption material preparation and heavy metal treatment technology, and in particular to an amorphous iron-magnesium-aluminum silicate, its preparation method and application. Background Technology

[0002] The deep purification of heavy metal wastewater, especially low-concentration heavy metal wastewater, is one of the main challenges in heavy metal treatment. Adsorption is considered one of the most promising deep treatment methods due to its ability to selectively transfer and immobilize heavy metal ions. However, adsorption has long been limited by the performance bottleneck of adsorbents: existing mainstream adsorbents, such as activated carbon and zeolite, generally suffer from the problem of not being able to simultaneously achieve adsorption capacity and deep purification efficiency. They may have a certain adsorption capacity at high concentrations, but cannot reduce the residual concentration to extremely low levels (e.g., below 1 ppm); or although they are effective for low-concentration heavy metals, their adsorption capacity is limited and easily saturated, the adsorption rate is slow, the selectivity is poor, and they are easily interfered with by high-concentration interfering substances. These performance limitations severely restrict the large-scale application of adsorption in complex practical scenarios.

[0003] Using abundant and inexpensive natural clay minerals as alternative adsorbents is considered a promising direction. However, natural clay minerals are essentially mixtures of various minerals, containing a large amount of "inert" components such as quartz and feldspar, which have no adsorption activity for heavy metals, resulting in an inherently limited adsorption capacity. Traditional acid, alkali, or organic modification methods can only optimize the surface properties of natural clay minerals in a simple way, which is a quantitative improvement and cannot convert ineffective "inert" components into effective components, thus limiting the performance improvement.

[0004] Furthermore, while existing methods for the artificial synthesis of polymetallic silicates (such as sol-gel, hydrothermal, or coprecipitation methods) can produce materials with controllable composition, they are often cumbersome, time-consuming, and costly. They also struggle to achieve atomic-level uniform dispersion of multiple metal elements such as magnesium, aluminum, and iron within the silicate framework, resulting in low utilization of active sites. More importantly, the materials prepared by these methods are typically thermodynamically stable crystalline structures. Their ordered lattice frameworks exhibit high selectivity barriers for isomorphic substitution of heavy metal ions, hindering broad-spectrum adsorption of multiple heavy metals. Simultaneously, existing crystalline silicate adsorbents generally suffer from a narrow applicable concentration range. They easily become saturated at high concentrations and lack sufficient mass transfer driving force at low concentrations, making it difficult to simultaneously achieve high capacity retention of high-concentration heavy metals and maximal depth removal of low-concentration heavy metals. This severely restricts the large-scale application of adsorption methods in complex real-world scenarios.

[0005] Therefore, there is an urgent need for a preparation method that can efficiently convert all components of natural clay minerals and construct a high-entropy disordered structure to overcome the lattice selectivity barrier, thereby providing a material that combines low cost and disruptive adsorption performance, and can simultaneously meet the requirements for deep purification of heavy metals across the entire concentration range. Summary of the Invention

[0006] In view of this, the present invention provides an amorphous iron-magnesium-aluminum silicate, its preparation method and application. The amorphous iron-magnesium-aluminum silicate provided by the present invention can transform and reconstruct the entire composition of natural clay minerals, and can simultaneously meet the requirements of high capacity retention of high concentration heavy metals and extreme depth removal of low concentration heavy metals, thus achieving efficient purification across the entire concentration range.

[0007] This invention provides an amorphous iron-magnesium-aluminum silicate, the structure of which is interconnected by Si-O-Si bonds and Si-OM bonds to form a silicate network framework, wherein M represents a metal, and the metal includes alkali metals, iron, magnesium and aluminum; the alkali metal includes one or two of sodium and potassium; the alkali metal, iron, magnesium and aluminum are randomly bonded to Si-O groups to form Si-O-Na or Si-OK structural units, Si-O-Fe structural units, Si-O-Mg structural units and Si-O-Al structural units, forming an amorphous network.

[0008] Preferably, in the amorphous iron-magnesium-aluminum silicate, the molar ratio of metal to silicon is 0.5~2.5:1; the molar ratio of alkali metal to silicon is 0.1~0.9:1; the molar ratio of iron to silicon is 0.1~1.0:1; the molar ratio of magnesium to silicon is 0.1~1.2:1; and the molar ratio of aluminum to silicon is 0.15~0.35:1.

[0009] Preferably, the specific surface area of ​​the amorphous iron-magnesium-aluminum silicate is 155~366 m². 2 / g, pore volume is 0.105~0.242 cm³ 3 / g, with an average pore size of 2.44~2.70 nm.

[0010] This invention also provides a method for preparing the amorphous iron-magnesium-aluminum silicate described above, comprising the following steps: Natural clay minerals, magnesium source, iron source and additives are first mixed and subjected to a solid-phase reaction to obtain the amorphous iron-magnesium-aluminum silicate.

[0011] Preferably, the natural clay minerals include one or more of attapulgite, illite, chlorite, montmorillonite, illite-montmorillonite clay, kaolinite, talc, quartz, calcite, dolomite, amorphous hematite, feldspar, and mica; the additives include one or more of sodium hydroxide, potassium hydroxide, sodium oxide, sodium peroxide, potassium carbonate, sodium carbonate, sodium chloride, potassium chloride, sodium tetraborate, lithium tetraborate, and lithium metaborate.

[0012] Preferably, the mass ratio of the magnesium source to the natural clay mineral is 50~200:100; the mass ratio of the iron source to the natural clay mineral is 50~500:100; and the mass ratio of the additive to the natural clay mineral is 20~200:100.

[0013] Preferably, the magnesium source includes one or more of magnesium nitrate, magnesium sulfate, magnesium chloride, magnesium oxide, magnesium carbonate, and magnesium acetate; the iron source includes one or more of ferric nitrate, ferric sulfate, ferric chloride, ferric acetylacetone, and ferric acetate.

[0014] Preferably, the first mixing is a grinding mixing; the grinding mixing speed is not less than 300 rpm; and the first mixing time is 10 to 60 minutes.

[0015] Preferably, the solid-phase reaction includes a heating reaction stage and an isothermal reaction stage in sequence; the heating rate of the heating reaction stage is 5~20 ℃ / min; the temperature of the isothermal reaction stage is 600~1000 degrees Celsius, and the holding time is 0.5~4 hours.

[0016] The present invention also provides the application of the amorphous iron-magnesium-aluminum silicate described in the above-described scheme or the amorphous iron-magnesium-aluminum silicate obtained by the preparation method described in the above-described scheme in the field of heavy metal adsorption.

[0017] This invention provides an amorphous iron-magnesium-aluminum silicate. Based on theoretical research on the adsorption process, this invention recognizes that balancing the "adsorption driving force" at high concentrations with the "mass transfer efficiency" at low concentrations is key to achieving deep purification across the entire concentration range. This invention constructs a multi-metal silicate network framework with densely packed, highly active sites based on the theory of "increasing configurational entropy." This silicate network framework exhibits a long-range disordered framework structure with high configurational entropy and charge density, thus facilitating the adsorption of heavy metal ions. On the one hand, high configurational entropy lowers the Gibbs free energy of the multi-metal silicate system, making the silicate network framework thermodynamically more inclined to maintain a metastable amorphous structure, suppressing the deactivation of active sites caused by crystalline phase precipitation during long-term use; on the other hand, high configurational entropy enhances the lattice's tolerance to isomorphic substitution of heavy metal ions, making Pb... 2+ Cd 2+ Heavy metal ions can more easily replace Mg in the silicate network framework. 2+ Fe 3+ The isotope structure enables efficient chemical fixation. This entropy-based material construction concept is the essence that distinguishes this invention from the traditional "simple modification" approach.

[0018] This invention breaks through the traditional approach of "simple modification" of natural clay minerals, fundamentally reconstructing their material composition. It provides a material that combines low cost with revolutionary adsorption performance, simultaneously achieving high-capacity retention of high-concentration heavy metals and extreme depth removal of low-concentration heavy metals. This results in highly efficient purification across the entire concentration range and is suitable for broad-spectrum, highly efficient deep removal of heavy metals across the entire concentration range. Specifically: This invention utilizes molten salt-mediated ion exchange and lattice recombination under high-temperature conditions to completely and uniformly transform various silicate minerals from complex and inconsistent natural clay minerals into a non-naturally formed, structurally homogeneous, and stable amorphous iron-magnesium-aluminum silicate. This overcomes the limitation of traditional adsorbents' narrow applicable concentration range, exhibiting extremely strong removal capabilities for heavy metal ions from high to low concentrations, achieving deep purification: it deeply purifies high-concentration heavy metal wastewater (up to 1000 ppm) (reducing it to below 1 ppm), while maintaining excellent performance (reducing it to below 0.1 ppm) for low-concentration wastewater (below 1 ppm). The amorphous iron-magnesium-aluminum silicate provided by this invention has good environmental compatibility, is inherently green and non-toxic, and has good environmental compatibility. It can be used not only for the purification of heavy metals in various water bodies such as industrial wastewater and polluted surface water, but also for the passivation and fixation of heavy metals in soil and the prevention of heavy metal leakage from solid waste, with a wide range of applications.

[0019] This invention also provides a method for preparing the amorphous iron-magnesium-aluminum silicate described in the above-mentioned scheme. The preparation method provided by this invention disrupts the original structure of natural clay minerals and forms a new amorphous iron-magnesium-aluminum silicate crystal phase structure rich in active sites. This significantly increases the specific surface area and makes the surface charge more negative, exhibiting extremely strong chemical complexation, electrostatic adsorption, and ion exchange capabilities for heavy metal ions. Therefore, it demonstrates excellent adsorption and fixation capabilities for heavy metal ions from high to low concentrations. The preparation method provided by this invention uses inexpensive and readily available raw materials, involves simple steps, and is environmentally friendly, showing higher cost-effectiveness potential. It is easy to scale up and control, requiring no complex equipment or harsh conditions, making it very suitable for large-scale industrial production and with broad market application prospects. On the one hand, this invention provides an efficient and low-cost solution for heavy metal remediation, achieving broad-spectrum, efficient, and stable fixation of various heavy metals such as lead, cadmium, and copper, with performance far exceeding conventional adsorption materials. On the other hand, it opens up new avenues for the high-value utilization of natural clay minerals, representing a breakthrough in material preparation concepts.

[0020] Furthermore, the present invention regulates the proportion of the above-mentioned structural units by controlling the ratio of metals (magnesium, aluminum, iron, alkali metals) to silicates.

[0021] This invention also provides the application of the amorphous iron-magnesium-aluminum silicate described in the above-described scheme or the amorphous iron-magnesium-aluminum silicate prepared by the above-described scheme in the field of heavy metal adsorption. The amorphous iron-magnesium-aluminum silicate of this invention, as an adsorbent, can balance high adsorption capacity and extreme depth purification capability. Example results show that it is effective against Pb. 2+ Cd 2+ Cu 2+ and Zn 2+ The adsorption capacities of these materials reached 4.37 times, 11.12 times, 8.64 times, and 7.40 times that of natural clay minerals, respectively, and were 10.72 times, 27.84 times, 11.49 times, and 10.48 times that of commercially available activated carbon. Particularly noteworthy is its extremely strong deep purification capability, capable of removing Pb from an initial concentration of 1 mg / L. 2+ Cd 2+ The concentrations of metal ions in the solution were reduced to 0.06 µg / L and 0.01 µg / L, respectively, which are far below the stringent drinking water standards. This achieves truly efficient removal across the entire concentration range and has broad application prospects in environmental protection, chemical industry, heavy metal wastewater treatment, and heavy metal soil remediation. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 Scanning electron microscope (SEM) images of natural clay minerals and amorphous iron-magnesium-aluminum silicates prepared in Examples 1-3; wherein, a is natural clay minerals, b is amorphous iron-magnesium-aluminum silicates prepared in Example 1, c is amorphous iron-magnesium-aluminum silicates prepared in Example 2, and d is amorphous iron-magnesium-aluminum silicates prepared in Example 3. Figure 2 X-ray diffraction (XRD) patterns of natural clay minerals and amorphous iron-magnesium-aluminum silicates prepared in Examples 1-3; Figure 3 Nitrogen adsorption-desorption curves and pore size distribution curves of natural clay minerals and amorphous iron-magnesium-aluminum silicate (MgAlFeSi-1) prepared in Example 1; where a is the nitrogen adsorption-desorption curve and b is the pore size distribution curve. Figure 4 The site energy distribution curves are for natural clay minerals, commercially available activated carbon, and amorphous iron-magnesium-aluminum silicate (MgAlFeSi-1) prepared in Example 1. Detailed Implementation

[0024] This invention provides an amorphous iron-magnesium-aluminum silicate, the structure of which is interconnected by Si-O-Si bonds and Si-OM bonds to form a silicate network framework, wherein M represents a metal, and the metal includes alkali metals, iron, magnesium and aluminum; the alkali metal includes one or two of sodium and potassium; the alkali metal, iron, magnesium and aluminum are randomly bonded to Si-O groups to form Si-O-Na or Si-OK structural units, Si-O-Fe structural units, Si-O-Mg structural units and Si-O-Al structural units, forming an amorphous network.

[0025] In this invention, the molar ratio of metal to silicon in the amorphous iron-magnesium-aluminum silicate is preferably 0.5-2.5:1, more preferably 0.7-2:1, and even more preferably 1-1.5:1; the molar ratio of alkali metal to silicon is preferably 0.1-0.9:1, more preferably 0.3-0.7:1, and even more preferably 0.5:1; the molar ratio of iron to silicon is preferably 0.1-1.0:1, more preferably 0.3-0.7:1, and even more preferably 0.5:1; the molar ratio of magnesium to silicon is preferably 0.1-1.2:1, more preferably 0.5-1:1, and even more preferably 0.8:1; and the molar ratio of aluminum to silicon is preferably 0.15-0.35:1, more preferably 0.2-0.3:1, and even more preferably 0.25:1.

[0026] In this invention, the specific surface area of ​​the amorphous iron-magnesium-aluminum silicate is 155~366 m². 2 / g, pore volume is 0.105~0.242 cm³ 3 / g, with an average pore size of 2.44~2.70 nm.

[0027] This invention also provides a method for preparing the amorphous iron-magnesium-aluminum silicate described above, comprising the following steps: Natural clay minerals, magnesium source, iron source and additives are mixed (denoted as the first mixture) and subjected to a solid-phase reaction to obtain the amorphous iron-magnesium-aluminum silicate.

[0028] In this invention, the natural clay mineral is preferably crushed and then pulverized before use; the target particle size of the pulverized material is preferably less than 380 micrometers, more preferably 180~350 micrometers.

[0029] In this invention, the natural clay minerals preferably include one or more of the following: attapulgite, illite, chlorite, montmorillonite, illite-montmorillonite clay, kaolinite, talc, quartz, calcite, dolomite, amorphous hematite, feldspar, and mica.

[0030] In this invention, the magnesium source is preferably a magnesium-containing compound; the magnesium-containing compound preferably includes one or more of magnesium nitrate, magnesium sulfate, magnesium chloride, magnesium oxide, magnesium carbonate, and magnesium acetate; the mass ratio of the magnesium source to the natural clay mineral is preferably 50~200:100, more preferably 100~150:100.

[0031] In this invention, the iron source is preferably an iron-containing compound; the iron-containing compound preferably includes one or more of ferric nitrate, ferric sulfate, ferric chloride, ferric acetylacetone, and ferric acetate; the ferric nitrate is preferably ferric nitrate nonahydrate; the mass ratio of the iron source to the natural clay mineral is preferably 50~500:100, more preferably 150~300:100.

[0032] In this invention, the additive preferably includes one or more of sodium hydroxide, potassium hydroxide, sodium oxide, sodium peroxide, potassium carbonate, sodium carbonate, sodium chloride, potassium chloride, sodium tetraborate, lithium tetraborate, and lithium metaborate; the mass ratio of the additive to the natural clay mineral is preferably 20~200:100, more preferably 60~150:100.

[0033] In this invention, the first mixing is preferably grinding; the grinding is preferably mechanical grinding; the grinding speed is preferably not less than 300 rpm; the first mixing time is preferably 10-60 minutes, more preferably 30-40 minutes. This invention, through mechanical grinding, enables the raw materials to be mixed uniformly and induces a mechanochemical reaction, thereby enhancing the reactivity.

[0034] In this invention, the solid-state reaction is preferably carried out in a crucible; the equipment for the solid-state reaction is preferably a high-temperature furnace; the solid-state reaction preferably includes a heating reaction stage and a isothermal reaction stage in sequence; the heating rate of the heating reaction stage is preferably 5~20 ℃ / min, more preferably 10~15 ℃ / min; the temperature of the isothermal reaction stage is preferably 600~1000 degrees Celsius, more preferably 700~800 degrees Celsius, and the holding time is preferably 0.5~4 hours, more preferably 1~3 hours.

[0035] In this invention, the solid-phase reaction preferably includes cooling the resulting product system; the cooling is preferably carried out in the furnace to below 200 degrees Celsius, and then the product is taken out and naturally cooled to room temperature.

[0036] In this invention, the cooling process preferably includes pulverizing the resulting product and then granulating it; the target particle size of the pulverization is preferably 80-500 mesh; the granulation is preferably disc granulation or extrusion granulation; and the target particle size of the granulation is preferably 0.1-1 mm.

[0037] The present invention also provides the application of the amorphous iron-magnesium-aluminum silicate described in the above-described scheme or the amorphous iron-magnesium-aluminum silicate obtained by the preparation method described in the above-described scheme in the field of heavy metal adsorption.

[0038] The amorphous iron-magnesium-aluminum silicate provided by this invention can be used as an adsorbent for the removal of heavy metal pollutants in water, the passivation of heavy metals in soil, or the prevention and control of heavy metal leakage from solid waste.

[0039] To further illustrate the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1: Weigh 10.0 kg of crushed, pulverized, and sieved natural clay mineral powder (passed through an 80-mesh sieve) and mix it with 10.0 kg of magnesium nitrate hexahydrate (magnesium source, 100% of the natural clay mineral weight), 20.0 kg of ferric chloride hexahydrate (iron source, 200% of the natural clay mineral weight), 5.0 kg of sodium chloride (auxiliary agent, 50% of the natural clay mineral weight), and 5.0 kg of potassium carbonate (auxiliary agent, 50% of the natural clay mineral weight). Grind the mixture using a pot mill at 300 rpm for 30 minutes. Transfer the mixture to a crucible and place it in a high-temperature resistance furnace. Heat the furnace to 800°C at a rate of 10°C / min and hold at that temperature for 3 hours. After the reaction is complete, cool the furnace to below 200°C and remove the mixture, allowing it to cool naturally to room temperature. Crush and grind the resulting sintered mass to obtain amorphous iron-magnesium-aluminum silicate, denoted as MgAlFeSi-1.

[0041] Example 2: Weigh 10.0 kg of crushed, pulverized, and sieved through an 80-mesh sieve (approximately 180 micrometers) of natural clay mineral powder, and mix it with 5.0 kg of magnesium sulfate (magnesium source, accounting for 50% of the natural clay mineral weight), 5.0 kg of ferric nitrate nonahydrate (iron source, accounting for 50% of the natural clay mineral weight), and 5.0 kg of sodium hydroxide (auxiliary agent, accounting for 50% of the natural clay mineral weight). Grind the mixture using a pot mill at 300 rpm for 10 minutes. Transfer the homogeneous mixture to a crucible and place it in a high-temperature resistance furnace. Heat the furnace to 900°C at a rate of 20°C / min and hold at that temperature for 1 hour. After the reaction is complete, stop heating and allow the mixture to cool to below 200°C in the furnace before removing it and allowing it to cool naturally to room temperature. Crush and grind the resulting sintered mass to obtain amorphous iron-magnesium-aluminum silicate, denoted as MgAlFeSi-2.

[0042] Example 3: Weigh 10.0 kg of crushed, pulverized, and sieved natural clay mineral powder, and mix it with 20.0 kg of magnesium chloride hexahydrate (magnesium source, 200% of the natural clay mineral mass), 50.0 kg of ferric chloride hexahydrate (iron source, 500% of the natural clay mineral mass), 10.0 kg of sodium chloride (auxiliary agent, 100% of the natural clay mineral mass), and 10.0 kg of sodium hydroxide (auxiliary agent, 100% of the natural clay mineral mass). Grind the mixture using a pot mill at 300 rpm for 60 minutes. Transfer the mixture to a crucible and place it in a high-temperature resistance furnace. Heat the furnace to 700°C at a rate of 5°C / min and hold at that temperature for 4 hours. After the reaction is complete, cool the furnace to below 200°C and remove the mixture, allowing it to cool naturally to room temperature. Crush and grind the resulting sintered mass to obtain amorphous iron-magnesium-aluminum silicate, denoted as MgAlFeSi-3.

[0043] Example 4: Weigh 10.0 kg of crushed, pulverized, and sieved natural clay mineral powder (approximately 380 micrometers) and mix it with 5.0 kg of magnesium oxide (magnesium source, accounting for 50% of the natural clay mineral mass), 30.0 kg of ferric sulfate (iron source, accounting for 300% of the natural clay mineral mass), and 2.0 kg of sodium oxide (auxiliary agent, accounting for 20% of the natural clay mineral mass). Grind the mixture using a ball mill at 300 rpm for 45 minutes. Transfer the mixture to a crucible and place it in a high-temperature furnace, raising the temperature to 600°C at a rate of 15°C / min and holding it at that temperature for 2 hours. After the reaction is complete, cool the furnace to room temperature. Crush and grind the resulting product directly to obtain amorphous magnesium-iron aluminum silicate, denoted as MgAlFeSi-4.

[0044] Example 5: Weigh 10.0 kg of crushed, pulverized, and sieved natural clay mineral powder, and mix it with 15.0 kg of magnesium carbonate (magnesium source, accounting for 150% of the natural clay mineral mass), 15.0 kg of ferric nitrate nonahydrate (iron source, accounting for 150% of the natural clay mineral mass), and 20.0 kg of sodium tetraborate (auxiliary agent, accounting for 200% of the natural clay mineral mass). Grind the mixture using a pot mill at 300 rpm for 15 minutes. Transfer the mixture to a crucible and place it in a high-temperature resistance furnace. Heat the furnace to 1000°C at a rate of 20°C / min and hold for 0.5 hours. After the reaction is complete, cool the furnace to below 200°C and remove the mixture. Crush and grind the resulting sintered mass, then granulate it using a disc granulator to obtain 0.1–1 mm granular amorphous iron-magnesium-aluminum silicate, denoted as MgAlFeSi-5.

[0045] Comparative Example 1: Weigh 10.0 kg of crushed, pulverized, and sieved natural clay mineral powder (passed through an 80-mesh sieve) and mix it with 5.0 kg of sodium hydroxide (an additive, accounting for 50% of the natural clay mineral weight), without adding any magnesium or iron source. Grind the mixture using a pot mill at 300 rpm for 30 minutes. Transfer the mixture to a crucible and place it in a high-temperature resistance furnace. Heat the furnace to 800°C at a rate of 10°C / min and hold at that temperature for 3 hours. After the reaction is complete, cool the furnace to below 200°C and remove the mixture, allowing it to cool naturally to room temperature. Crush and grind the resulting sintered block, and designate it as CS-1.

[0046] Comparative Example 2: Weigh 10.0 kg of crushed, pulverized, and sieved natural clay mineral powder (passed through an 80-mesh sieve) and mix it with 20.0 kg of magnesium nitrate hexahydrate (magnesium source, accounting for 200% of the natural clay mineral content), without adding iron sources or additives. The grinding, mixing, heating, holding, and cooling procedures were the same as in Example 1. The resulting product is designated CS-2.

[0047] Comparative Example 3: Weigh 10.0 kg of crushed, pulverized, and sieved natural clay mineral powder (passed through an 80-mesh sieve) and mix it with 20.0 kg of ferric chloride hexahydrate (iron source, accounting for 200% of the natural clay mineral content), without adding magnesium source or additives. The grinding, mixing, heating, holding, and cooling procedures were the same as in Example 1. The resulting product is designated CS-3.

[0048] Comparative Example 4: Weigh 10.0 kg of crushed, pulverized, and sieved natural clay mineral powder, and mix it with 10.0 kg of magnesium nitrate hexahydrate (magnesium source, accounting for 100% of the natural clay mineral weight) and 20.0 kg of ferric chloride hexahydrate (iron source, accounting for 200% of the natural clay mineral weight), without adding sodium chloride and potassium carbonate additives. The grinding, mixing, heating, holding, and cooling procedures are the same as in Example 1. The resulting product is designated CS-4.

[0049] Test Example 1: The amorphous iron-magnesium-aluminum silicates prepared in Examples 1-3 were characterized for physical properties and their adsorption efficiency was tested.

[0050] 1) The microstructures of the amorphous iron-magnesium-aluminum silicates prepared in Examples 1-3 and the natural clay minerals in Example 1 were observed using scanning electron microscopy (SEM). The results are as follows: Figure 1 As shown. According to Figure 1It can be seen that natural clay minerals are composed of a mixture of various minerals, including rod-shaped, flaky, and massive forms, with uneven morphology; the morphology of amorphous iron-magnesium-aluminum silicates undergoes significant changes: MgAlFeSi-1 is massively stacked; MgAlFeSi-2 exhibits a clustered structure with surface wrinkles and porous structures; MgAlFeSi-3 shows a trend towards sintering and densification; the above evolution process indicates that natural clay minerals have undergone structural reorganization and formed new phases.

[0051] 2) The phase composition of the amorphous iron-magnesium-aluminum silicates prepared in Examples 1-3 and the natural clay mineral in Example 1 was analyzed by X-ray powder diffraction (XRD). The results are as follows: Figure 2 As shown. According to Figure 2 As can be seen, the XRD pattern further reveals the phase transformation. The diffraction peaks of the original crystal phases such as quartz, attapulgite and calcite in the natural clay minerals completely disappeared after the reaction. The new crystal phase NaAlSiO4 appeared in MgAlFeSi-1, while MgAlFeSi-2 and MgAlFeSi-3 were both amorphous. This proves that the present invention has achieved the transformation of all components and the homogenization of the structure of natural clay minerals.

[0052] 3) The physical properties of the amorphous iron-magnesium-aluminum silicates prepared in Examples 1-5 and Comparative Examples 1-4, and the natural clay mineral of Example 1 were characterized, including specific surface area and pore structure. The sample particle size was no greater than 100 micrometers. The specific surface area and pore size distribution were determined by nitrogen adsorption-desorption method. The results are as follows: Figure 3 As shown in Table 1.

[0053] Table 1. Physical properties of natural clay minerals and amorphous iron-magnesium-aluminum silicates:

[0054] according to Figure 3 It can be seen that both the natural clay minerals and MgAlFeSi-1 have type IV mesoporous structures; MgAlFeSi-1 exhibits H2 type hysteresis rings, indicating that its pores are regular and its structure is complex; the natural clay minerals are H3 type, with a wide and uneven pore size distribution. Table 1 shows the specific surface areas of MgAlFeSi-1 to MgAlFeSi-5 (155~366 m²). 2 / g) was significantly higher than that of natural clay minerals (43 m) 2 The average pore size is concentrated in the range of 2.44~2.70 nm, with a narrower distribution and mainly mesoporous structure, which further confirms the uniformity and optimization of the material structure of amorphous iron-magnesium-aluminum silicate.

[0055] 4) High-concentration ion saturation adsorption tests were conducted on the amorphous iron-magnesium-aluminum silicates prepared in Examples 1-5 and Comparative Examples 1-4, the natural clay minerals of Example 1, and commercially available activated carbon. The initial concentration of each ion was 500 mg / L. The results are shown in Table 2.

[0056] Table 2. High concentrations of Pb 2+ Cd 2+ Cu 2+ and Zn 2+ Saturated adsorption capacity of ions:

[0057] As shown in Table 2, the amorphous iron-magnesium-aluminum silicate provided by this invention supports Pb 2+ Cd 2+ Cu 2+ and Zn 2+ The saturated adsorption capacities of these materials are 4.37 to 12.05 times that of natural clay minerals and 10.72 to 30.18 times that of commercially available activated carbon. This demonstrates that the amorphous iron-magnesium-aluminum silicate provided by this invention exhibits a very high saturated adsorption capacity for high concentrations of heavy metal ions.

[0058] 5) The amorphous iron-magnesium-aluminum silicates prepared in Examples 1-5 and Comparative Examples 1-4, the natural clay minerals of Example 1, and the commercially available activated carbon were subjected to extreme purification tests for low-concentration ions. The initial concentration of each ion was 1 mg / L. The results of the residual concentration after deep purification are shown in Table 3.

[0059] Table 3. For low concentrations of Pb 2+ Cd 2+ Cu 2+ and Zn 2+ Residual amount after ion treatment:

[0060] As shown in Table 3, the amorphous iron-magnesium-aluminum silicate of this invention can reduce the residual concentration of heavy metal solutions with an initial concentration of 1 mg / L to 0.01–1.67 µg / L, meeting WHO drinking water standards. In contrast, commercially available activated carbon can only reduce the heavy metal concentration to 20.48–144.39 µg / L; natural clay minerals can only reduce the heavy metal ion concentration to 42.65–522.72 µg / L, and their removal efficiency for heavy metal ions is significantly lower than that of the amorphous iron-magnesium-aluminum silicate of this invention. In summary, the amorphous iron-magnesium-aluminum silicate provided by this invention exhibits excellent deep purification capabilities across the entire concentration range.

[0061] Test Example 2: The adsorption sites of natural clay minerals mainly originate from the broken bond structure on the mineral surface and the exchangeable cations between layers. However, their adsorption capacity is limited by three structural defects: (1) The density of active silanol (Si-OH) sites is low, and most of the silicon-oxygen bonds are bound inside the crystal lattice, making it difficult to participate in the adsorption reaction; (2) The mixture of multiple minerals results in a wide range of site energy distribution, with low-energy sites dominating and weak binding force to heavy metal ions; (3) The pore structure is underdeveloped, and a large number of potential sites are inaccessible and cannot effectively contribute to the adsorption process.

[0062] This invention fundamentally solves the aforementioned problems through mineral phase reconstruction. After mineral phase reconstruction, the originally highly crystalline minerals in natural clay minerals are transformed into an amorphous porous silicate framework. The silicon-oxygen bonds, originally confined within the crystal lattice, are fully exposed on the surface, significantly increasing the density of silanol sites. Simultaneously, the magnesium-iron silicate network generated in situ during mineral phase reconstruction provides active sites and also significantly increases the specific surface area, improving site accessibility. Furthermore, the energy state distribution of adsorption sites undergoes a fundamental change before and after mineral phase reconstruction. Low-energy sites in natural clay minerals are more effective at adsorbing Pb. 2+ The binding of Pb mainly occurs through physical adsorption and weak ion exchange, which is effective for trace amounts of Pb. 2+ The capture capacity of the original is obviously insufficient; however, the amorphous iron-magnesium-aluminum silicate reconstructed by the present invention constructs a network structure rich in high-energy active groups (such as Si-O-), and the mass transfer efficiency and exchange potential energy are significantly improved.

[0063] To quantitatively characterize the aforementioned energy state evolution, this test case uses the Langmuir-Freundlich model to fit the adsorption isotherm data at different initial concentrations, obtaining the site energy distribution curves. The results are as follows: Figure 4 As shown. According to Figure 4 It can be seen that the site energy distribution of natural clay minerals ranges from 16.49 to 36.89 kJ / mol, with a peak value of 27.37 kJ / mol; the site energy distribution of commercially available activated carbon ranges from 20.81 to 34.00 kJ / mol, with a peak value of 25.73 kJ / mol; while the site energy distribution range of MgAlFeSi-1 provided by this invention is broadened to 19.51 to 55.64 kJ / mol, with the peak value increased to 39.11 kJ / mol. This demonstrates that after the natural clay minerals are reconstructed into amorphous iron-magnesium-aluminum silicates by this invention, the site energy distribution transforms from "wide and low" to "narrow and high"—possessing higher site density, higher unit point energy, and a wider high-energy site distribution range. This energy state characteristic endows the material with dual adsorption advantages: in the high concentration region (>200 ppm), the high density of sites ensures large capacity retention; in the low concentration region (<10 ppm), the high energy sites overcome mass transfer limitations, achieving deep removal of trace heavy metals.

[0064] Furthermore, the mineral phase reconstruction completely eliminated inert components such as quartz and calcite in natural clay minerals, resulting in a highly homogenized type of active sites (primarily Si-O). - (Primarily based on the principle of adsorption), avoiding site competition and energy dispersion caused by multi-component mixing, further ensuring the high efficiency and stability of the material's adsorption behavior across the entire concentration range.

[0065] The embodiments of the present invention have been described above; however, these embodiments are merely illustrative and not intended to limit the scope of the invention. Although various embodiments have been described above, this does not mean that the measures in the embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the invention, and all such substitutions and modifications should fall within the scope of the invention.

Claims

1. An amorphous iron-magnesium-aluminum silicate, characterized in that, Its structure is interconnected by Si-O-Si bonds and Si-OM bonds, forming a silicate network framework, where M represents a metal, including alkali metals, iron, magnesium, and aluminum; the alkali metals include one or two of sodium and potassium; the alkali metals, iron, magnesium, and aluminum are randomly bonded to Si-O groups to form Si-O-Na or Si-OK structural units, Si-O-Fe structural units, Si-O-Mg structural units, and Si-O-Al structural units, forming an amorphous network.

2. The amorphous iron-magnesium-aluminum silicate according to claim 1, characterized in that, In the amorphous iron-magnesium-aluminum silicate, the molar ratio of metal to silicon is 0.5~2.5:1; the molar ratio of alkali metal to silicon is 0.1~0.9:1; the molar ratio of iron to silicon is 0.1~1.0:1; the molar ratio of magnesium to silicon is 0.1~1.2:1; and the molar ratio of aluminum to silicon is 0.15~0.35:

1.

3. The amorphous iron-magnesium-aluminum silicate according to claim 1 or 2, characterized in that, The specific surface area of ​​the amorphous iron-magnesium-aluminum silicate is 155~366 m². 2 / g, pore volume is 0.105~0.242 cm³ 3 / g, with an average pore size of 2.44~2.70 nm.

4. A method for preparing amorphous iron-magnesium-aluminum silicate, characterized in that, The amorphous iron-magnesium-aluminum silicate is the amorphous iron-magnesium-aluminum silicate according to any one of claims 1 to 3, comprising the following steps: Natural clay minerals, magnesium source, iron source and additives are first mixed and subjected to a solid-phase reaction to obtain the amorphous iron-magnesium-aluminum silicate.

5. The preparation method according to claim 4, characterized in that, The natural clay minerals include one or more of attapulgite, illite, chlorite, montmorillonite, illite-montmorillonite clay, kaolinite, talc, quartz, calcite, dolomite, amorphous hematite, feldspar, and mica; the additives include one or more of sodium hydroxide, potassium hydroxide, sodium oxide, sodium peroxide, potassium carbonate, sodium carbonate, sodium chloride, potassium chloride, sodium tetraborate, lithium tetraborate, and lithium metaborate.

6. The preparation method according to claim 4, characterized in that, The mass ratio of the magnesium source to the natural clay mineral is 50~200:100; the mass ratio of the iron source to the natural clay mineral is 50~500:100; and the mass ratio of the additive to the natural clay mineral is 20~200:

100.

7. The preparation method according to claim 4, characterized in that, The magnesium source includes one or more of magnesium nitrate, magnesium sulfate, magnesium chloride, magnesium oxide, magnesium carbonate, and magnesium acetate; the iron source includes one or more of ferric nitrate, ferric sulfate, ferric chloride, ferric acetylacetone, and ferric acetate.

8. The preparation method according to claim 4, characterized in that, The first mixing is a grinding mixing, and the grinding mixing speed is not less than 300 rpm; the first mixing time is 10~60 minutes.

9. The preparation method according to claim 4, characterized in that, The solid-phase reaction includes a heating reaction stage and an isothermal reaction stage; the heating rate of the heating reaction stage is 5~20 ℃ / min; the temperature of the isothermal reaction stage is 600~1000 degrees Celsius, and the holding time is 0.5~4 hours.

10. An application of an amorphous iron-magnesium-aluminum silicate in the field of heavy metal adsorption, characterized in that, The amorphous iron-magnesium-aluminum silicate is the amorphous iron-magnesium-aluminum silicate according to any one of claims 1 to 3 or the amorphous iron-magnesium-aluminum silicate obtained by the preparation method according to any one of claims 4 to 9.

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