Silicate-chlorapatite composite material and preparation method and application thereof

Abstract

The present application relates to the technical field of adsorption material preparation and heavy metal treatment, and particularly relates to a silicate-chloroapatite composite material, a preparation method and application thereof. The present application proposes a mechanism of "mineral phase reconstruction and functional component synergistic construction of high-density and high-energy adsorption sites", utilizes the characteristic of coexistence of multiple mineral components, and through synergistic induction of calcium source and phosphorus source, promotes the original mineral phase to be reconstructed into an amorphous porous silicate matrix with higher activity (adsorption site energy is higher), and in-situ generates chloroapatite with strong immobilization capacity for heavy metals. This not only realizes mineral structure activation and porous structure construction, but also forms a synergistic effect of silicate and chloroapatite in the adsorption process: chloroapatite and heavy metals such as lead form stable phosphorus-chlorine-lead ore solidification products, and the reconstructed silicate and calcium ions provide efficient ion exchange sites, improve the site energy of the adsorption sites, and thus improve the removal efficiency of heavy metals in a wide concentration range.

Description

Technical Field

[0001] This invention relates to the field of adsorption material preparation and heavy metal treatment technology, and in particular to a silicate-chlorapatite composite material, its preparation method and application. Background Technology

[0002] Heavy metal ions (such as lead, cadmium, and chromium) are chemically stable and difficult to biodegrade, allowing them to accumulate in organisms through drinking water and the food chain. Treatment of heavy metal pollution, especially heavy metal wastewater, faces two main technological challenges: First, traditional chemical precipitation methods cannot achieve deep purification of trace heavy metals (e.g., concentrations below 1 ppm) in complex industrial wastewater, failing to meet increasingly stringent emission standards. Second, traditional chemical precipitation methods require the addition of large amounts of reagents, easily generating large quantities of heavy metal-containing sludge, posing a risk of secondary pollution and increasing subsequent treatment costs.

[0003] Adsorption is considered one of the most promising technologies due to its ease of operation, wide applicable concentration range, and ability to achieve deep purification. Adsorption can efficiently capture heavy metal ions through various mechanisms such as electrostatic adsorption, ion exchange, and surface complexation, and is theoretically applicable to various pollution scenarios ranging from high concentrations (>200 ppm) to ultra-low concentrations (<10 ppm). However, existing commercial adsorbents generally suffer from limited adsorption capacity or poor performance when treating heavy metals over a wide concentration range, hindering their large-scale application.

[0004] In summary, developing an "all-around" adsorption material that combines high adsorption capacity, wide concentration range, excellent deep purification capability, low cost, and environmental friendliness has become an urgent problem to be solved in this field. Summary of the Invention

[0005] In view of this, the present invention provides a silicate-chloriapatite composite material, its preparation method and application. The active silicate-chloriapatite composite material provided by the present invention has high adsorption capacity, wide concentration range and excellent deep purification ability, and is low in cost and environmentally friendly.

[0006] The present invention provides a silicate-chloriapatite composite material, comprising a silicate phase and a chloriapatite phase compounded with the silicate phase; the surface of the silicate-chloriapatite composite material contains active silanol groups (Si-O-) and phosphorooxy groups (PO-) active sites; the interior of the silicate-chloriapatite composite material contains channels.

[0007] Preferably, the silicate in the silicate phase is an amorphous porous silicate, and the silicate in the silicate phase transformed from the reconstruction of the natural mixed clay structure includes aluminum silicate, magnesium silicate and iron silicate.

[0008] Preferably, the chlorapatite phase comprises chlorapatite.

[0009] Preferably, the specific surface area of ​​the silicate-chlorapatite composite material is 80~110 m². 2 / g, pore volume is 0.1~0.2 cm³ 3 / g; the average diameter of the pores in the silicate-chlorapatite composite material is 6~8 nm.

[0010] The present invention also provides a method for preparing the silicate-chlorapatite composite material described above, comprising the following steps: The silicate-chlorapatite composite material is obtained by mixing natural mixed clay, calcium source, phosphorus source, reaction aid and solvent to carry out mineral reconstruction-chlorapatite formation synergistic reaction.

[0011] Preferably, the chemical composition of the natural mixed clay includes silicon, oxygen, magnesium, aluminum and iron; the natural mixed clay includes two or more of the following: attapulgite clay, illite, chlorite, montmorillonite, illite-montmorillonite clay, kaolinite, talc, quartz, calcite, amorphous hematite, dolomite and mica.

[0012] Preferably, the mass ratio of the calcium source to the natural mixed clay is 20~200:100; the mass ratio of the phosphorus source to the natural mixed clay is 20~200:100.

[0013] Preferably, the reaction aid comprises at least one selected from ammonia, methylamine, acetic acid, tetramethylammonium hydroxide, glycine, ethylenediamine, and choline chloride, and hydrochloric acid; wherein at least one selected from ammonia, methylamine, acetic acid, tetramethylammonium hydroxide, glycine, ethylenediamine, and choline chloride accounts for 10-99.1% of the reaction aid by mass; the mass ratio of the reaction aid to natural mixed clay is 1-100:100; and the mass proportion of hydrochloric acid in the reaction aid is 0.9-90%.

[0014] Preferably, the synergistic reaction of mineral reconstruction-chlorapatite formation is carried out in an oxygen-containing atmosphere; the temperature of the synergistic reaction of mineral reconstruction-chlorapatite formation is 500~800 degrees Celsius, and the holding time is 0.5~6 hours.

[0015] The present invention also provides the application of the silicate-chlorapatite composite material described in the above-described scheme or the silicate-chlorapatite composite material prepared by the above-described scheme in the field of heavy metal adsorption.

[0016] This invention provides a silicate-chloriapatite composite material. The silicate-chloriapatite composite material provided by this invention has high adsorption capacity, a wide applicable concentration range, and excellent deep purification capabilities. It is also low in cost, environmentally friendly, and does not introduce secondary pollution.

[0017] Natural clay minerals, such as attapulgite clay or bentonite, are abundant, inexpensive, and possess good ion exchange capacity and adsorption potential. However, natural clay minerals are often mixed systems of multiple minerals (such as quartz, illite, and chlorite), with complex mineral compositions, making direct purification difficult and costly. More importantly, their naturally occurring adsorption active sites are limited, and their specific surface area is not fully utilized. This results in generally low adsorption capacity for heavy metals and low removal rates for low concentrations of heavy metals. There is an inherent trade-off between adsorption capacity and removal efficiency, which cannot meet the requirements for highly efficient adsorption. To overcome the aforementioned bottlenecks, this invention proposes a mechanism of "mineral phase reconstruction and synergistic construction of high-density, high-energy adsorption sites through functional components." This avoids the complex physical purification of natural mixed clays, instead utilizing their multi-mineral coexistence characteristic. By introducing calcium and phosphorus sources for synergistic induction, the original mineral phases (e.g., illite and chlorite) are reconstructed into an amorphous porous silicate matrix with higher adsorption site density and site energy during a thermochemical process. Simultaneously, chlorapatite, which has a strong immobilization ability for heavy metals, is generated in situ. This process not only activates the mineral structure and constructs a porous structure but also forms high-density, highly active adsorption sites synergistically generated by silicates and chlorapatite. During adsorption, a synergistic effect occurs: chlorapatite can form stable phosphochlorite-based solidified products with heavy metals such as lead, while the reconstructed silicates and calcium ions provide efficient ion exchange sites, increasing the site energy of the adsorption sites. This enhances the adsorption and removal efficiency of heavy metals over a wide concentration range, achieving efficient removal of metal ions across high and low concentrations. The silicate-chloriapatite composite material provided by this invention fully retains the cost and environmentally friendly advantages of natural mixed clay, while achieving a qualitative leap in adsorption performance. It exhibits excellent removal capabilities and extremely high saturation adsorption capacity for both high concentrations and trace amounts of heavy metals. To date, there are no precedents, domestically or internationally, for directly reconstructing porous silicate-chloriapatite composite materials from complex natural mixed clay through synergistic modification with calcium phosphate compounds. This invention provides a new approach for mineral deep processing and environmental pollution remediation. Specifically: (1) The silicate-chlorapatite composite material provided by the present invention is effective against lead (Pb) 2+ Heavy metals such as Pb exhibit extremely high saturation adsorption capacity and ultimate purification ability. 2+Its saturated adsorption capacity is 9.37 times that of natural mixed clay and 22.97 times that of commercially available activated carbon. It can purify lead-containing wastewater with an initial concentration of 1000 μg / L to 0.02 μg / L, which is close to complete removal.

[0018] (2) This invention forms a composite structure of amorphous porous silicate and chlorapatite through the "mineral phase reconstruction-in-situ composite" mechanism. The above structure not only provides abundant pores, but also the active silanol (Si-O-) and phosphorooxyl (PO-) active sites on its surface have a synergistic effect with the solid-phase precipitation of chlorapatite and the ion exchange of calcium ions, which together achieve efficient chemical complexation and stable solidification of heavy metal ions.

[0019] (3) The silicate-chlorapatite composite material provided by this invention has significant effects on the purification of heavy metals in water and the passivation of heavy metals in soil. The results of the examples show that, in Pb... 2+ Adding the silicate-chloriapatite composite material of this invention to contaminated soil can significantly reduce the Pb content (dry weight) in plant roots from 21.68 mg / kg to 0.52 mg / kg, with a passivation effect far superior to that of an equal amount of natural mixed clay (which only reduces the Pb content to 15.44 mg / kg). In Cd-contaminated soil, adding the silicate-chloriapatite composite material of this invention can significantly reduce the Cd content (dry weight) in plant roots from 33.54 mg / kg to 0.63 mg / kg, which is significantly lower than that of adding an equal amount of natural mixed clay (25.36 mg / kg), demonstrating extremely strong environmental application value.

[0020] This invention also provides a method for preparing the silicate-chloriapatite composite material described above. This invention utilizes the reconstructing of various mineral components in natural mixed clay into amorphous silicates during the reaction process, which are then combined with the generated chloriapatite to form a composite material with a porous structure. The silicate-chloriapatite composite material provided by this invention exhibits excellent removal capabilities for both high concentrations (not less than 1000 ppm) and low concentrations (not more than 1 ppm) of heavy metals through the stabilizing combination of chloriapatite and heavy metals, as well as calcium ion exchange. Its saturated adsorption capacity is significantly higher than that of similar products. The preparation method provided by this invention uses widely available raw materials, is low in cost, has simple steps, and is easy to scale up for production.

[0021] This invention also provides the application of the silicate-chloriapatite composite material described in the above-described scheme or the silicate-chloriapatite composite material prepared by the above-described scheme in the field of heavy metal adsorption. The silicate-chloriapatite composite material provided by this invention has high adsorption capacity, a wide applicable concentration range, excellent deep purification ability, and high adsorption efficiency. It can be used for heavy metal pollution control and can be widely applied in heavy metal wastewater treatment, contaminated soil remediation, radioactive element prevention and control, and rare and precious metal enrichment. It is suitable for various water bodies such as freshwater and seawater, realizing the high-value utilization of non-metallic mineral resources, especially multi-component symbiotic natural mixed clay, and providing a new technological approach to broaden its application fields. 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 The images show a comparison of scanning electron microscope (SEM) images of the natural mixed clay of Example 1 and the silicate-chloriapatite composite materials prepared in Examples 1-3 of this invention; where a is the natural mixed clay, b is the silicate-chloriapatite composite material prepared in Example 1, c is the silicate-chloriapatite composite material prepared in Example 2, and d is the silicate-chloriapatite composite material prepared in Example 3. Figure 2 The X-ray diffraction (XRD) comparison spectra of the natural mixed clay of Example 1 and the silicate-chlorapatite composite materials prepared in Examples 1-3 of this invention are shown. Figure 3 The pore size distribution curves are for the natural mixed clay of Example 1 and the silicate-chlorapatite composite material prepared in Example 1 of this invention. Figure 4 The site energy distribution curves are for natural mixed clay, commercially available activated carbon, and silicate-chlorapatite composite material (CPC1) prepared in Example 1 of this invention. Detailed Implementation

[0024] The present invention provides a silicate-chlorapatite composite material, comprising a silicate phase and a chlorapatite phase compounded with the silicate phase; the surface of the silicate-chlorapatite composite material contains active silanol groups and phosphorooxyl active sites; the interior of the silicate-chlorapatite composite material contains channels.

[0025] In this invention, the silicate in the silicate phase is preferably an amorphous porous silicate, specifically preferably including aluminum silicate, magnesium silicate and iron silicate.

[0026] In this invention, the composition of the chlorapatite phase preferably includes chlorapatite.

[0027] In this invention, the mass ratio of the silicate phase to the chlorapatite phase is preferably 1:0.5 to 1:2, more preferably 1:0.8 to 1:1.5.

[0028] In this invention, the specific surface area of ​​the silicate-chloriapatite composite material is preferably 80~110 m². 2 / g, more preferably 90~100m 2 / g, with a pore volume preferably of 0.1~0.2cm³. 3 / g, more preferably 0.13~0.18cm 3 / g; the average diameter of the pores in the silicate-chlorapatite composite material is preferably 6~8nm, more preferably 7nm.

[0029] The present invention also provides a method for preparing the silicate-chlorapatite composite material described above, comprising the following steps: Natural mixed clay, calcium source, phosphorus source, reaction aid and solvent are mixed (denoted as the first mixture) and subjected to a synergistic reaction of mineral reconstruction-chlorapatite formation to obtain the silicate-chlorapatite composite material.

[0030] In this invention, the chemical composition of the natural mixed clay preferably includes silicon, oxygen, magnesium, aluminum and iron; the natural mixed clay preferably includes two or more of attapulgite clay, illite, chlorite, montmorillonite, illite-montmorillonite clay, kaolinite, talc, quartz, calcite, amorphous hematite, dolomite and mica.

[0031] In this invention, the natural mixed clay is preferably crushed and pulverized sequentially before use; the target particle size of the pulverized material is preferably less than 80 mesh, more preferably 80~200 mesh.

[0032] In this invention, the calcium source preferably includes at least one of calcium hydroxide, calcium oxide, calcium chloride, calcium hypochlorite, calcium perchlorate, calcium silicate, calcium carbonate, calcium acetate, calcium citrate, calcium phytate, and dolomite; the mass ratio of the calcium source to natural mixed clay is preferably 20~200:100, more preferably 50~150:100, and even more preferably 100:100.

[0033] In this invention, the phosphorus source preferably includes at least one of ammonium hypophosphite, ammonium polyphosphate, choline phosphate, phosphorus oxychloride, trimethyl phosphate, triethyl phosphate, tributyl phosphate, ethyl dichlorophosphate, tri(1-chloro-2-propyl) phosphate, sodium phosphate, potassium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, and potassium dihydrogen phosphate; the mass ratio of the phosphorus source to natural mixed clay is preferably 20~200:100, more preferably 50~150:100, and even more preferably 100:100.

[0034] In this invention, the reaction aid preferably includes at least one of ammonia, methylamine, acetic acid, tetramethylammonium hydroxide, glycine, ethylenediamine, and choline chloride, along with hydrochloric acid. The mass ratio of at least one of ammonia, methylamine, acetic acid, tetramethylammonium hydroxide, glycine, ethylenediamine, and choline chloride to the reaction aid is preferably 10-99.1%, more preferably 30-70%, and even more preferably 50%. The mass ratio of the reaction aid to the natural mixed clay is preferably 1-100:100, more preferably 10-70:100, and even more preferably 40:100.

[0035] In this invention, the solvent is preferably an alcohol; the alcohol is preferably a C2-C6 alcohol; the C2-C6 alcohol is preferably ethanol; the solvent preferably also includes water; the water is preferably deionized water.

[0036] In this invention, the mass ratio of the natural mixed clay to the solvent is preferably 1:0.5~5, more preferably 1:1~3.

[0037] In this invention, the first mixing preferably includes the following steps: premixing natural mixed clay and calcium source to obtain a premix; mixing the premix with a portion of solvent (denoted as Mix A) to obtain a calcium-containing material; heating and mixing the calcium-containing material with a phosphorus source and the remaining solvent (denoted as Mix B) to obtain a phosphorus-containing material; and adding a reaction aid dropwise to the phosphorus-containing material while stirring and then heating and mixing (denoted as Mix C).

[0038] In this invention, the premixing is preferably mechanical grinding; the premixing time is preferably 10-60 minutes, more preferably 30-40 minutes. This invention, through mechanical grinding, ensures thorough mixing and activation of the materials, resulting in ground materials with good uniformity and reactivity.

[0039] In this invention, the partial solvent accounts for 30% to 100% of the total solvent by mass; when the phosphorus source is a liquid compound, the partial solvent accounts for 100% of the total solvent by mass.

[0040] In this invention, the mixing A preferably includes sequential mechanical stirring, ultrasonic treatment, and heating stirring; the mechanical stirring time is preferably 10-60 minutes, more preferably 30 minutes; the ultrasonic treatment power is preferably 100-500W, more preferably 300W, and the time is preferably 10-30 minutes, more preferably 20 minutes; the heating stirring temperature is preferably 40-80 degrees Celsius, more preferably 55-65 degrees Celsius, and the holding time is preferably 0.5-2 hours, more preferably 1-1.5 hours. This invention, through mixing A, dissolves soluble substances and uniformly disperses insoluble substances.

[0041] In this invention, the mixture B is preferably stirred and mixed; the temperature of the mixture B is preferably 40-80 degrees Celsius, more preferably 55-65 degrees Celsius, and the heat preservation time is preferably 0.5-2 hours, more preferably 1-1.5 hours.

[0042] In this invention, the dropping rate during stirring is preferably 1~10 mL / min; when the reaction aid is a solid, an aqueous solution or an organic solution of the reaction aid is preferably used.

[0043] In this invention, the mixing C is preferably stirred; the temperature of the mixing C is preferably 40-80 degrees Celsius, more preferably 55-65 degrees Celsius, and the holding time is preferably 5-20 hours, more preferably 10-15 hours. This invention, through mixing C, allows most of the solvent to evaporate, forming a paste-like precursor material.

[0044] In this invention, the synergistic reaction of mineral reconstruction-chlorapatite formation preferably includes heating; the heating rate is preferably 5 to 20 degrees Celsius per minute, more preferably 10 to 15 degrees Celsius per minute.

[0045] In this invention, the synergistic reaction of mineral reconstruction-chlorapatite formation is preferably carried out in a crucible; the synergistic reaction of mineral reconstruction-chlorapatite formation is preferably carried out in an oxygen-containing atmosphere; the oxygen-containing atmosphere is preferably air or oxygen; the temperature of the synergistic reaction of mineral reconstruction-chlorapatite formation is preferably 500~800 degrees Celsius, more preferably 600~700 degrees Celsius, and the holding time is preferably 0.5~6 hours, more preferably 2~4 hours.

[0046] In this invention, the synergistic reaction of mineral reconstruction-chlorapatite formation preferably further includes sequentially cooling, crushing, washing and drying the resulting product.

[0047] In this invention, the cooling is preferably natural cooling; the target particle size for crushing is preferably 100-300 mesh; the washing reagent is preferably deionized water or ethanol; the drying temperature is preferably 80-120 degrees Celsius, and the heat preservation time is preferably 6-24 hours.

[0048] In this invention, the drying process preferably further includes sieving or molding the resulting dried product. By sieving, this invention obtains a silicate-chlorapatite composite material in powder form; by molding, it obtains a silicate-chlorapatite composite material in spherical, strip, or honeycomb form, with different states selectable depending on the application.

[0049] The present invention also provides the application of the silicate-chlorapatite composite material described in the above-described scheme or the silicate-chlorapatite composite material prepared by the above-described scheme in the field of heavy metal adsorption.

[0050] The silicate-chlorapatite composite material provided by this invention has high adsorption capacity, wide applicable concentration range, excellent deep purification ability, and high adsorption efficiency. It can be used for heavy metal pollution control and can be widely used in heavy metal wastewater treatment, contaminated soil remediation, radioactive element prevention and control, and rare and precious metal enrichment. It is suitable for various water bodies such as freshwater and seawater, and realizes the high-value utilization of non-metallic mineral resources, especially multi-component symbiotic natural mixed clay, providing a new technological approach to broaden its application fields.

[0051] 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.

[0052] Example 1: Take 10 kg of natural mixed clay ore (containing 30% attapulgite clay, 31% illite, 15% quartz, 14% calcite, 6% iron oxide, and 4% water by mass ratio), crush it using a jaw crusher, grind it into powder using a Raymond mill, and then pass it through an 80-mesh sieve to obtain mineral powder. Mix the obtained mineral powder with 5 kg of calcium hydroxide and mechanically grind it for 10 minutes. Transfer the uniformly mixed material to a reaction vessel, add 10 kg of ethanol, mechanically stir for 30 minutes, and then ultrasonically treat it at 300W for 20 minutes to ensure thorough dispersion. Subsequently, keep it at 40 degrees Celsius and continue stirring for 1.5 hours to obtain a slurry. Dissolve 5 kg of phosphorus oxychloride in 10 kg of ethanol and slowly add it to the above slurry, maintaining the temperature and stirring for 1 hour. Subsequently, a reaction aid consisting of 1.8 g concentrated hydrochloric acid (36.5% by mass) and 198.2 g ammonia (25% by mass) (total 200 g, of which hydrochloric acid accounts for 0.9%) was added dropwise at a rate of 5 mL / min, and the mixture was stirred at this temperature for 5 hours to form a paste-like precursor. The resulting paste-like precursor was transferred to a crucible and placed in a high-temperature resistance furnace under an air atmosphere. The temperature was increased to 500 degrees Celsius at a rate of 20 °C / min, held at this temperature for 6 hours, and then allowed to cool naturally. The cooled product was crushed to 100-300 mesh, washed with deionized water, dried at 100 degrees Celsius for 12 hours, and sieved to obtain a silicate-chlorapatite composite material, denoted as CPC1.

[0053] Example 2: Take 10 kg of natural mixed clay ore (containing 30% attapulgite clay, 31% illite, 15% quartz, 14% calcite, 6% iron oxide, and 4% water by mass ratio), crush it using a jaw crusher, grind it into powder using a Raymond mill, and then pass it through an 80-mesh sieve to obtain mineral powder. Mix the obtained mineral powder with 10 kg of calcium chloride and mechanically grind it for 30 minutes. Transfer the uniformly mixed material to a reaction vessel, add 15 kg of ethanol, and mechanically stir for 30 minutes, followed by ultrasonic treatment at 300 W for 20 minutes to ensure thorough dispersion. Then, keep it at 60 degrees Celsius and continue stirring for 1 hour to obtain a slurry. Mix 10 kg of triethyl phosphate with 5 kg of ethanol and slowly add it to the above slurry, maintaining the temperature and stirring for 2 hours. Subsequently, a reaction auxiliary consisting of 5 g concentrated hydrochloric acid (36.5% by mass) and 45 g methylamine (total 50 g, of which hydrochloric acid accounts for 10%) was added dropwise at a rate of 5 mL / min, and the mixture was kept at this temperature and stirred for 10 h to form a paste-like precursor. The resulting paste-like precursor was heated to 650 °C at 10 °C / min in air, held at this temperature for 4 hours, and then naturally cooled. The cooled product was crushed to 100-300 mesh, washed with deionized water, dried at 100 °C for 16 h, and sieved to obtain a silicate-chlorapatite composite material, denoted as CPC2.

[0054] Example 3: Following the preparation method of Example 1, 10 kg of natural mixed clay powder passing through an 80-mesh sieve was prepared. The obtained powder was mixed with 20 kg of calcium carbonate and mechanically ground for 60 minutes. The material was transferred to a reaction vessel, 30 kg of ethanol was added, and the mixture was mechanically stirred for 30 minutes and ultrasonically dispersed at 300 W for 20 minutes. The mixture was then kept at 80°C and stirred for 1.5 hours to obtain a slurry. 20 kg of ammonium polyphosphate was dissolved in 30 kg of deionized water (the mass ratio of ammonium polyphosphate to deionized water was 1:1.5) and slowly added to the slurry, maintaining the temperature and stirring for 1 hour. Subsequently, a reaction aid consisting of 30 g of concentrated hydrochloric acid (mass fraction 36.5%) and 70 g of tetramethylammonium hydroxide (total 100 g, of which hydrochloric acid accounts for 30%) was added dropwise at a rate of 5 mL / min, and the mixture was kept at the temperature and stirred for another 20 hours to obtain a paste-like precursor. The obtained paste-like precursor was heated to 800°C at 5°C / min in air, kept at that temperature for 2 hours, and then naturally cooled. The cooled product was crushed to 100-300 mesh, washed with deionized water, dried at 100 degrees Celsius for 20 hours, and sieved to obtain a silicate-chlorapatite composite material, denoted as CPC3.

[0055] Example 4: Following the preparation method of Example 1, 10 kg of natural mixed clay powder passing through an 80-mesh sieve was prepared. The obtained powder was mixed with 8 kg of calcium oxide and mechanically ground for 20 minutes. The material was transferred to a reaction vessel, 12 kg of ethanol was added, and the mixture was mechanically stirred for 30 minutes and ultrasonically dispersed at 300 W for 20 minutes. The mixture was then kept at 50°C and stirred for 1 hour to obtain a slurry. 15 kg of phosphorus oxychloride (liquid phosphorus source, for direct use) was slowly added, and the temperature and stirring were maintained for 1.5 hours. Subsequently, a reaction aid consisting of 540 g of concentrated hydrochloric acid (36.5% by mass) and 60 g of glycine (total 600 g, of which hydrochloric acid accounts for 90%) was added dropwise at a rate of 5 mL / min, and the mixture was kept at the temperature and stirred for another 15 hours to obtain a paste-like precursor. The obtained paste-like precursor was heated to 600°C at 15°C / min in air, kept at that temperature for 3 hours, and then naturally cooled. The cooled product was crushed to 100-300 mesh, washed with ethanol, dried at 100 degrees Celsius for 24 hours, and sieved to obtain a silicate-chlorapatite composite material, denoted as CPC4.

[0056] Example 5: Following the preparation method of Example 1, 10 kg of natural mixed clay powder passing through an 80-mesh sieve was prepared. The obtained powder was mixed with 15 kg of calcium acetate and mechanically ground for 45 minutes. The material was transferred to a reaction vessel, 25 kg of ethanol was added, and the mixture was mechanically stirred for 30 minutes and ultrasonically dispersed at 300 W for 20 minutes. The mixture was then kept at 70°C and stirred for 1 hour to obtain a slurry. A mixed phosphorus source of 12 kg of triethyl phosphate and 8 kg of ammonium polyphosphate aqueous solution was added to the slurry, and the temperature was maintained and stirred for 2 hours. Subsequently, a reaction aid consisting of 10 g of concentrated hydrochloric acid (36.5% by mass) and 20 g of choline chloride (total 30 g, of which hydrochloric acid accounts for 33.3%) was added dropwise at a rate of 5 mL / min, and the mixture was kept at the temperature and stirred for 8 hours to obtain a paste-like precursor. The obtained paste-like precursor was heated to 750°C at 8°C / min in air, kept at that temperature for 1 hour, and then naturally cooled. The cooled product was crushed to 100-300 mesh, washed with ethanol, dried at 100 degrees Celsius for 10 hours, and sieved to obtain a silicate-chlorapatite composite material, denoted as CPC5.

[0057] Comparative Example 1 (Physically Mixed Materials): Take 10 kg of the same natural mixed clay mineral powder as in Example 1, and mechanically mix it with 10 kg of calcium chloride and 5 kg of commercial chlorapatite (Ca2PO4Cl) until uniform. Without high-temperature reconstruction, use it directly as a comparative material, denoted as D1.

[0058] Comparative Example 2 (calcium source added only, phosphorus source not added): Take 10 kg of the same natural mixed clay mineral powder as in Example 1, mix it with 10 kg of calcium chloride, and mechanically grind it for 30 minutes. Transfer it to a reaction vessel, add 15 kg of ethanol, mechanically stir for 30 minutes, and then ultrasonically disperse it at 300 W for 20 minutes. Keep it at 60 degrees Celsius and stir for 10 hours to form a paste precursor. Heat the paste precursor to 650 degrees Celsius in air at 10°C / min, keep it at that temperature for 4 hours, and then let it cool naturally. Crush it to 100-300 mesh, wash it with deionized water, dry it at 100 degrees Celsius for 12 hours, and sieve it to obtain the comparative material, denoted as D2.

[0059] Comparative Example 3 (phosphorus source only, no calcium source): Take 10 kg of the same natural mixed clay mineral powder as in Example 1, mix it with 10 kg of triethyl phosphate, and mechanically grind it for 30 minutes. Transfer it to a reaction vessel, add 15 kg of ethanol, mechanically stir for 30 minutes, and then ultrasonically disperse it at 300 W for 20 minutes. Keep it at 60 degrees Celsius and stir for 10 hours to form a paste precursor. Heat the paste precursor to 650 degrees Celsius in air at 10°C / min, keep it at that temperature for 4 hours, and then let it cool naturally. Crush it to 100-300 mesh, wash it with deionized water, dry it at 100 degrees Celsius for 12 hours, and sieve it to obtain the comparative material, denoted as D3.

[0060] Comparative Example 4 (Low-ratio Sample): Take 10 kg of the same natural mixed clay mineral powder as in Example 1, mix it with 1.9 kg of calcium chloride (mass ratio 19:100, lower than the lower limit of 20:100 of this invention), and mechanically grind for 30 minutes. Transfer to a reaction vessel, add 15 kg of ethanol, mechanically stir for 30 minutes, and ultrasonically disperse at 300 W for 20 minutes. Then, keep it at 60 degrees Celsius and stir for 1.5 hours to obtain a slurry. Mix 1.9 kg of triethyl phosphate (mass ratio 19:100, lower than the lower limit of 20:100 of this invention) with 5 kg of ethanol and slowly add it to the slurry, maintaining the temperature and stirring for 1 hour. Then, add a reaction aid consisting of 5 g of concentrated hydrochloric acid (36.5%) and 45 g of methylamine dropwise at a rate of 5 mL / min, and continue to keep it at the temperature and stir for 10 hours to form a paste-like precursor. The obtained paste-like precursor was heated to 650 degrees Celsius at 10°C / min in air atmosphere, kept at that temperature for 4 hours, and then naturally cooled. It was crushed to 100-300 mesh, washed with deionized water, dried at 100 degrees Celsius for 12 hours, and then sieved to obtain the control material, denoted as D4.

[0061] Test Example 1: The structures of the silicate-phosphate composites of Examples 1-3 and the natural mixed clay of Example 1 were characterized using scanning electron microscopy (SEM), and the results are as follows: Figure 1 As shown. According to Figure 1 It can be seen that the natural mixed clay exhibits a morphology of various minerals coexisting, including rod-shaped, flaky, and blocky forms. The microstructure of the silicate-phosphate composite material shows significant changes: CPC1 still contains a small amount of large blocks, CPC2 exhibits uniformly dispersed small particles, and CPC3 shows obvious small particle aggregates. These significant morphological changes indicate that the original minerals in the natural mixed clay have undergone effective transformation and reconstruction.

[0062] Test Example 2: X-ray diffraction (XRD) was used to analyze the silicate-phosphate composites of Examples 1-3 and the natural mixed clay of Example 1. The results are as follows: Figure 2 As shown. According to Figure 2 The XRD patterns show that the natural mixed clay mainly contains quartz (JCPDS No. 46-1045) and calcite (JCPDS No. 47-1743) crystalline phases. The diffraction peaks of the silicate-chloriapatite composite material provided by this invention are highly consistent with the standard card of chloriapatite (Ca2PO4Cl, JCPDS No. 19-0247), confirming that its main crystalline phase is chloriapatite. Specifically, the calcite phase in CPC1 has essentially disappeared; the diffraction patterns of CPC2 and CPC3 are more closely related to the pure chloriapatite phase, with the original quartz and calcite diffraction peaks completely disappearing, transforming into amorphous silicates. This result corroborates the morphology reconstruction observed by SEM, jointly confirming the successful transformation of the mineral phase.

[0063] Test Example 3: The pore structure of the natural mixed clay of Example 1, the silicate-chloriapatite composite materials prepared in Examples 1-5, and the D1-D4 prepared in Comparative Examples 1-4 were tested. The particle size of the tested samples was no greater than 100 micrometers. The results are as follows: Figure 3 As shown in Table 1.

[0064] Table 1. Pore structure of natural mixed clay and silicate-phosphate composite materials:

[0065] according to Figure 3 As shown in Table 1, although both natural mixed clay and CPC1 are mesoporous materials, their pore size distributions differ significantly. The average pore size of CPC1 is approximately 7.2 nm, indicating that the natural mixed clay has been transformed into a porous material with uniform channels during the reaction process. Combined with the data in Table 1, it can be seen that the pore volume of CPC1 is increased compared to that of the natural mixed clay. This uniform and well-developed pore structure is beneficial for the mass transfer of heavy metal ions within the silicate-chloriapatite composite material, thereby greatly improving the utilization rate of active adsorption sites.

[0066] Test Example 4: The adsorption sites of natural mixed clays mainly originate from broken bonds on the mineral surface and exchangeable cations between layers, which has three limitations: First, the density of active silanol sites is low, and most silicon-oxygen bonds are bound inside the crystal lattice; second, the mixing of multiple minerals leads to a wide distribution of site energy, with low-energy sites dominating; and third, the pore structure is underdeveloped (specific surface area is only 56 m²). 2 / g, pore volume 0.06cm³ 3 / g), many sites are inaccessible.

[0067] The limitations mentioned above are fundamentally overcome in this invention's silicate-chloriapatite composite material after mineral phase reconstruction. First, highly crystalline minerals such as illite and chlorite are transformed into amorphous porous silicates, exposing the silicon-oxygen bonds within the crystal lattice to the surface and significantly increasing the density of silanol sites. Simultaneously, the in-situ generated chloriapatite provides phosphorooxyl active sites, forming a bifunctional site system. After reconstruction, the specific surface area and pore volume of the silicate-chloriapatite composite material are significantly increased compared to natural clay.

[0068] More importantly, the site energy has undergone a qualitative change. Low-energy sites in natural mixed clays affect Pb... 2+ The binding energy is mainly based on physical adsorption and weak ion exchange, which cannot effectively capture trace amounts of Pb. 2+ The introduction of the chlorapatite phase in this invention leads to a chemical precipitation mechanism: chlorapatite reacts with Pb... 2+ The reaction produces lead phosphate ore (Pb5(PO4)3Cl, Ksp≈10). -85 The reaction free energy is much higher than that of ordinary ion exchange. Calcium ions in reconstructed silicates are in a metastable state due to lattice distortion, and their reaction with Pb... 2+ The exchange potential energy is also significantly increased.

[0069] Adsorption data directly reflect the difference in site energy: In lead-containing wastewater with an initial concentration of 1 mg / L, the residual Pb concentration after treatment with natural mixed clay was 59.14 μg / L, while the silicate-chloriapatite composite material CPC1 prepared in Example 1 of this invention could reduce the residual Pb concentration to 0.02 μg / L, a difference of approximately 3000 times. This difference is essentially due to the order-of-magnitude increase in adsorption site energy. Using adsorption isotherm data at different initial concentrations, the site energy distribution curves were obtained by fitting the Langmuir-Freundlich model, and 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 15.84 to 37.09 kJ / mol (peak value 27.31 kJ / mol), the site energy distribution of commercially available activated carbon ranges from 20.89 to 35.12 kJ / mol (peak value 26.46 kJ / mol), while the site energy distribution of CPC1 ranges from 17.4 to 55.12 kJ / mol (peak value 40.02 kJ / mol). This demonstrates that CPC1 has a higher site density and energy per unit site, as well as a wider energy distribution of adsorption sites, which gives it a strong adsorption capacity for both high and low concentrations of heavy metal ions.

[0070] Furthermore, the mineral phase reconstruction eliminates inert components such as quartz and calcite in natural clay, resulting in a highly homogenized site type (mainly Si-O-), and the site energy distribution changes from "wide and low" to "narrow and high." This explains why the silicate-chlorapatite composite material of this invention maintains high adsorption efficiency across a wide concentration range: in the high concentration range (>200 ppm), it relies on high-density sites to achieve large capacity, while in the low concentration range (<10 ppm), it relies on high-energy sites to overcome mass transfer limitations and achieve deep purification.

[0071] Test Example 5: High-concentration Pb was applied to the natural mixed clay of Example 1, the silicate-chloriapatite composite materials prepared in Examples 1-3, and commercially available activated carbon of the present invention. 2+ Saturated adsorption test, the sample particle size is no greater than 100 micrometers, Pb 2+ The initial concentration was not less than 1 g / L, and the results are shown in Table 2.

[0072] Table 2 High concentrations of Pb 2+ and Cd 2+ Saturated adsorption capacity:

[0073] As shown in Table 2, the silicate-chloriapatite composite material CPC1 prepared in this invention has a high Pb content. 2+ The saturated adsorption capacity reached 1139 mg / g, which is 9.37 times that of natural mixed clay and 22.97 times that of commercially available activated carbon. Regarding Cd... 2+ The saturated adsorption capacity reached as high as 312 mg / g, which is 5.57 times that of natural mixed clay and 8.21 times that of commercially available activated carbon. The adsorption performance test results fully demonstrate the high saturated adsorption capacity advantage of the silicate-chloriapatite composite material of this invention.

[0074] Test Example 6: Low-concentration Pb was applied to the natural mixed clay of Example 1, the silicate-chloriapatite composite materials prepared in Examples 1-3, and commercially available activated carbon of the present invention. 2+ and Cd 2+ Deep purification test, the test sample particle size is no larger than 100 micrometers, Pb 2+ and Cd 2+ The initial concentrations were all 1 mg / L, and the results are shown in Table 3.

[0075] Table 3 Low concentrations of Pb 2+ and Cd 2+ Deep purification effect:

[0076] As shown in Table 3, CPC1 is effective against low concentrations of Pb. 2+(Initial concentration 1 mg / L) exhibited extremely strong removal capabilities, reducing the residual metal concentration to 0.02 µg / L. Its purification effect was far superior to that of natural mixed clay (residual metal concentration 59.14 µg / L) and commercially available activated carbon (residual metal concentration 44.28 µg / L). CPC1 also showed excellent removal efficiency for low concentrations of Cd. 2+ (Initial concentration 1 mg / L) It exhibits extremely strong removal ability, reducing the residual metal concentration to 0.08 µg / L. Its purification effect is far superior to that of natural mixed clay (residual metal concentration of 89.68 µg / L) and commercially available activated carbon (residual metal concentration of 56.31 µg / L).

[0077] Test Example 7: The passivation effect of the silicate-chlorapatite composite materials prepared in Examples 1-3 and the natural mixed clay in Example 1 was tested. The particle size of the test samples was no more than 100 micrometers. The evaluation index of the passivation effect was the Pb or Cd content in the plant roots (based on dry weight). A blank control group (no substance was added to the soil) was set up. The results are shown in Table 4.

[0078] Table 4. Data on the passivation effect of Pb or Cd in soil:

[0079] As shown in Table 4, adding 1% CPC1 to Pb-contaminated soil reduced the Pb content (dry weight) in plant roots to 0.52 mg / kg, significantly lower than that after adding an equal amount of natural mixed clay (15.44 mg / kg) and the blank control group (21.68 mg / kg). Similarly, adding 1% CPC1 to Cd-contaminated soil reduced the Cd content (dry weight) in plant roots to 0.63 mg / kg, significantly lower than that after adding an equal amount of natural mixed clay (25.36 mg / kg) and the blank control group (33.54 mg / kg). These results demonstrate that the silicate-chlorapatite composite material provided by this invention can effectively reduce the plant bioavailability of Pb or Cd in soil and possesses excellent passivation properties.

[0080] 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. A silicate-chlorapatite composite material, characterized in that, It includes a silicate phase and a chlorapatite phase composited with the silicate phase; the silicates in the silicate phase include aluminum silicate, magnesium silicate, and iron silicate; the surface of the silicate-chlorapatite composite material contains active silanol groups and phosphorooxyl active sites; the interior of the silicate-chlorapatite composite material contains channels.

2. The silicate-chlorapatite composite material according to claim 1, characterized in that, The silicate in the silicate phase is an amorphous porous silicate.

3. The silicate-chlorapatite composite material according to claim 1 or 2, characterized in that, The chlorapatite phase comprises chlorapatite.

4. The silicate-chlorapatite composite material according to claim 1, characterized in that, The specific surface area of ​​the silicate-chlorapatite composite material is 80~110 m². 2 / g, pore volume is 0.1~0.2 cm³ 3 / g; the average diameter of the pores in the silicate-chlorapatite composite material is 6~8 nm.

5. The method for preparing the silicate-chlorapatite composite material according to any one of claims 1 to 4, characterized in that, Includes the following steps: Natural mixed clay, calcium source, phosphorus source, reaction aid and solvent are mixed and subjected to a synergistic reaction of mineral reconstruction-chlorapatite formation to obtain the silicate-chlorapatite composite material; The chemical composition of the natural mixed clay includes silicon, oxygen, magnesium, aluminum and iron; the natural mixed clay includes two or more of the following: attapulgite clay, illite, chlorite, montmorillonite, illite-montmorillonite clay, kaolinite, talc, quartz, calcite, amorphous hematite, dolomite and mica. The mass ratio of the calcium source to the natural mixed clay is 20~200:100; the mass ratio of the phosphorus source to the natural mixed clay is 20~200:

100. The reaction aid comprises at least one selected from ammonia, methylamine, acetic acid, tetramethylammonium hydroxide, glycine, ethylenediamine, and choline chloride, and hydrochloric acid. The mass percentage of at least one of the ammonia, methylamine, acetic acid, tetramethylammonium hydroxide, glycine, ethylenediamine, and choline chloride in the reaction aid is 10-99.1%. The mass ratio of the reaction aid to natural mixed clay is 1-100:

100. The mass percentage of hydrochloric acid in the reaction aid is 0.9-90%. The synergistic reaction of mineral reconstruction and chlorapatite formation is carried out in an oxygen-containing atmosphere; the temperature of the synergistic reaction of mineral reconstruction and chlorapatite formation is 500~800 degrees Celsius, and the holding time is 0.5~6 hours.

6. The application of the silicate-chlorapatite composite material according to any one of claims 1 to 4 or the silicate-chlorapatite composite material obtained by the preparation method according to any one of claims 5 in the field of heavy metal adsorption.

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