Silicon-aluminium-iron composite material, process for producing it and use thereof

Abstract

A silicon-aluminum-iron composite material comprising an inner core and an outer shell enclosing the inner core, wherein the inner core is a hollow sphere based on silicon-aluminum; the outer shell consists of an iron element; the holes are distributed between the inner core and the outer shell, the particle size of the silicon-aluminum-iron composite material is 0.2 µm to 0.3 µm, and wherein the silicon-aluminum-iron composite material is used as an adsorbent.

Description

TECHNICAL FIELD The present invention relates to the technical field of wastewater treatment, in particular to a silicon-aluminum-iron composite material as well as a manufacturing process and its use. BACKGROUND With the increase in production capacity in sectors such as mining and metallurgy, approximately 30 to 40 billion tons of wastewater, sludge, solvents, and other pollutants contaminated with heavy metals from industrial activities are discharged into water bodies annually. Heavy metal ions pose a threat to humans and to flora and fauna that come into contact with water bodies. Manganese is one of the heavy metals that contribute to poor intellectual and cognitive development in humans. Excessive accumulation of manganese in certain brain regions can lead to neurotoxicity and degenerative brain diseases. When the concentration of manganese ions in water exceeds 240 µg / L, it can cause impairments in speed, short-term memory, and visual perception in children. The main source of manganese pollution is industrial wastewater from sewage treatment plants, mines, and quarries, among others.Therefore, wastewater contaminated with heavy metals must be treated, otherwise it will cause serious environmental problems. The main technologies for treating manganese-containing wastewater include chemical precipitation and ion exchange. Although these water treatment processes can remove manganese to a certain extent, current methods have shortcomings in terms of processing capacity, facility space requirements, process complexity, application scope, maintenance and operating costs, etc. Adsorption is an efficient and economical water treatment process used to remove various heavy metals due to its high efficiency, simplicity, and environmental friendliness. However, existing adsorbents are inadequate for treating manganese-containing wastewater. Therefore, there is an urgent need to develop an adsorbent that can efficiently remove manganese.US 2015 / 0306573 A1 relates to novel core-shell particles consisting of an aluminum oxide core and a cobalt oxide shell. The particles are spherical with a number-average diameter, measured by TEM, between 10 and 30 nm. This invention also relates to the process for producing these core-shell particles and to their use in the production of a catalyst. WO 2017 / 200169 A1 discloses hollow aluminosilicate particles and a method for their production. The method comprises reacting a matrix core containing an organic polymer in micellar or reverse micellar form with a silane compound and an aluminum precursor to synthesize core-shell particles having an aluminosilicate shell. These particles are then reacted with a basic or acidic aqueous solution, simultaneously forming fine pores in the shell and removing the core, thereby forming hollow aluminosilicate particles. A hydrothermal reaction is then performed to increase the density of the hollow aluminosilicate particles.This process allows the formation of a uniform shell even without additional surface treatment of the core by producing a complex oxide through the reaction of an aluminum precursor and a silicon dioxide precursor during shell formation, creating negative charges, resulting in hollow particles in which the shell does not break during the high-density reaction but is uniform. SUMMARY The following provides an overview of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims. The present invention aims to solve at least one of the above-mentioned technical problems of the prior art. To this end, the present invention provides a silicon-aluminum-iron composite material with a hollow core-shell structure that increases the specific surface area of the silicon-aluminum-iron composite material. When used for the adsorption of heavy metal ions, the adsorption sites are correspondingly enlarged, which improves the adsorption capacity for heavy metal ions. The present invention also provides a process for producing the above-mentioned silicon-aluminum-iron composite material. The present invention also provides a use of an adsorbent comprising the above-mentioned silicon-aluminum-iron composite material. According to one aspect of the present invention, there is provided a silicon-aluminum-iron composite material comprising an inner core and an outer shell enclosing the inner core; the inner core is a silicon-aluminum-based hollow sphere; the outer shell is made of an iron element; holes are distributed between the inner core and the outer shell; the particle size of the silicon-aluminum-iron composite material is 0.2 µm to 3 µm; and the silicon-aluminum-iron composite material is used as an adsorbent. According to a preferred embodiment, the present invention has at least the following advantageous effects: To a certain extent, the specific surface area of an adsorbent is positively correlated with the adsorption capacity of the adsorbent. The silicon-aluminum-iron composite material provided by the present invention has both a hollow structure and a pore structure, so it has a high specific surface area and exhibits a high adsorption capacity when used as an adsorbent. In some embodiments of the present invention, the pore volume of the silicon-aluminum-iron composite material is 0.55 cm3 / g to 0.7 cm3 / g. In some embodiments of the present invention, the specific surface area of the silicon-aluminum-iron composite material is 40 m2 / g to 42.5 m2 / g. In some embodiments of the present invention, the removal efficiency of the silicon-aluminum-iron composite material for manganese in wastewater is ≥99.72%. In some embodiments of the present invention, the adsorption capacity of the silicon-aluminum-iron composite material for manganese is ≥107.2 mg / g. In some embodiments of the present invention, the main materials of the silicon-aluminum-based hollow sphere include silica and aluminum hydroxide. In some embodiments of the present invention, the main material of the outer shell is one or more selected from the group consisting of elemental iron, iron hydroxide, and iron hydroxide. According to another aspect of the present invention, there is provided a method for producing the silicon-aluminum-iron composite material, comprising the following steps: S1. Mixing a silicon-aluminum oxide powder and an alkaline solution for reaction to obtain a mixture solution; wherein the alkaline solution is a mixed solution of NaOH and Na2CO3; and the silicon-aluminum oxide powder is a mixture of alumina and silicon oxide. S2. Adding an iron salt to the mixture solution obtained in step S1 and reacting a resulting mixture under ultraviolet irradiation to obtain a silicon-aluminum-iron composite material. In step S1, the silicon-alumina powder is dissolved to produce sodium silicate and sodium metaaluminate, whereby, among other things, the following specific reactions occur: SiO2+2NaOH=Na2SiO3+H2O; Al2O3+2NaOH=2NaAlO2+H2O; In step S2, the hydrolysis of iron salt can increase the acidity in the system and promote the precipitation of sodium silicate and sodium metaaluminate to produce silicic acid and colloidally precipitated aluminum hydroxide, which means a process of promoting the remodeling of the solid substance; silicic acid will form amorphous silicon dioxide (silica gel) in a supersaturated solution; and the newly formed solid substance has higher porosity and specific surface area, thereby improving the adsorption performance. Since the acid provided by the iron salt is relatively mild, the process of transforming the solid substance in step S2 is slower than the process of dissolving the silicon alumina powder by the alkaline solution, so that microspheres with a hollow structure can be produced; that is, the iron salt has a conductive effect to a hollow structure. In step S2, ultraviolet irradiation can electrolyze water to generate hydroxyl and hydrogen radicals. Hydroxyl, as a strong oxidizing substance, can accelerate the rupture of Si-O-Si or Al-O bonds, thus promoting the dissolution of the silicon-alumina powder. Furthermore, the micro- and nanoparticles such as silica gel produced in step S2 have a photocatalytic effect. After irradiation with ultraviolet rays, they generate photogenerated charge carriers (electron-hole pairs), which can reduce the iron ions in the iron salt to elemental iron. This results in the combination of unreduced iron ions with hydroxide in the system to produce iron hydroxide.The generated elemental iron and iron hydroxide accumulate on the surface of the silicon-aluminum-iron composite material to form a core-shell structure; in addition, the generated elemental iron can be combined with silica gel to further enhance the photocatalytic effect and increase the generation ratio of elemental iron. According to a preferred embodiment of the present invention, the method has at least the following advantageous effects:The method provided by the present disclosure has a simple process and low cost, which are favorable for large-scale production. In some embodiments of the present invention, in step S1, the mesh number of the silicon-alumina powder is 100 to 200 mesh. In some embodiments of the present invention, in step S1, the mass ratio of silicon oxide to aluminum oxide in the silicon oxide-alumina powder is 1:1-2. In some embodiments of the present invention, the concentration of the alkaline solution in step S1 is 0.5 mol / L to 2 mol / L. In some embodiments of the present invention, the concentration of the alkaline solution in step S1 is about 1 mol / L. In some embodiments of the present invention, in step S1, the molar ratio of NaOH to Na2CO3 in the alkaline solution is 2-3:1. When NaOH and Na2CO3 are mixed in a molar ratio of 2-3:1, a mixed solution with a eutectic point can be obtained, which promotes the diffusion of NaOH and Na2CO3 into the silicon alumina powder, thereby promoting the dissolution of the silicon alumina powder. In some embodiments of the present invention, in step S1, the mass-to-volume ratio of the silicon-alumina powder to the alkaline solution is 1 g: 20-30 ml. In some embodiments of the present invention, the reaction in step S1 lasts 1 h to 2 h. In some embodiments of the present invention, the reaction in step S1 is carried out with stirring, and the stirring speed is 100 rpm to 200 rpm. In some embodiments of the present invention, the molar ratio between the silicon oxide powder and the iron salt is 15-30:1. In some embodiments of the present invention, the iron salt in step S2 is one or more selected from the group consisting of a trivalent iron salt and a divalent iron salt. In some embodiments of the present invention, the trivalent iron salt is one or more selected from the group consisting of ferric nitrate (Fe(NO3)3), ferric chloride (FeCl3), and ferric sulfate (Fe2(SO4)3). In some embodiments of the present invention, the divalent iron salt is one or more selected from the group consisting of ferric chloride (FeCl2) and ferrous sulfate (FeSO4). In some embodiments of the present invention, in step S2, the ultraviolet irradiation occurs at a wavelength of <400 nm. In some embodiments of the present invention, in step S2, a source for the ultraviolet irradiation is one or more selected from the group consisting of a mercury lamp, a xenon lamp, and a xenon-mercury lamp. In some embodiments of the present invention, the power of the ultraviolet radiation source is 300 W to 1200 W. In some embodiments of the present invention, in step S2 the reaction is carried out at a temperature of 60°C to 90°C. In some embodiments of the present invention, the reaction in step S2 lasts 6 to 12 hours. In some embodiments of the present invention, step S2 further comprises washing the resulting solid with water until it is nearly neutral, followed by drying after the reaction. In some embodiments of the present invention, “nearly neutral” refers to a pH between 6.5 and 7.5. In some embodiments of the present invention, drying is carried out at a temperature of 60°C to 90°C. In some embodiments of the present invention, drying takes 12 to 24 hours. According to a further aspect of the present invention, there is provided an adsorbent made with a material comprising the silicon-aluminum-iron composite material or a silicon-aluminum-iron composite material produced by the method. A preferred adsorbent according to the present invention has at least the following advantageous effects. Under the conditions of room temperature and atmospheric pressure, the maximum adsorption capacity of the adsorbent for manganese reaches 115.4 mg / g, which is better than the common manganese removal adsorbents on the market. In some embodiments of the present invention, the adsorbent may be the silicon-aluminum-iron composite material or a combination thereof with an auxiliary material. In some embodiments of the present invention, the auxiliary material is one or more selected from the group consisting of a conductive agent and a binder. According to another aspect of the present invention, an adsorbent is used for the treatment of heavy metal wastewater. In some embodiments of the present invention, the use comprises adsorption treatment of the heavy metal wastewater with the adsorbent. In some embodiments of the present invention, the heavy metal wastewater contains 50 mg / l to 100 mg / l manganese ions. In some embodiments of the present invention, the adsorption treatment is carried out at a temperature of 20°C to 30°C. In some embodiments of the present invention, the adsorption treatment is carried out at a pH of 3 to 9. In some embodiments of the present invention, a pH adjusting agent selected from the group consisting of an aqueous NaOH solution and an aqueous HCl solution is used in the adsorption treatment, and the concentration of the pH adjusting agent is 0.5 mol / L. In some embodiments of the present invention, the adsorption treatment lasts 4 to 6 hours. In some embodiments of the present invention, the mass-volume ratio of the adsorbent to the heavy metal wastewater in the adsorption treatment is 1 g: 20-40 ml. In some embodiments of the present invention, the use further comprises performing solid-liquid separation after adsorption to obtain purified water and used adsorbent. In some embodiments of the present invention, the adsorbent used can be regenerated. In some embodiments of the present invention, regeneration consists in regenerating the used adsorbent in a regenerating agent. In some embodiments of the present invention, the regenerating agent is one or more selected from the group consisting of an aqueous NaCl solution, an aqueous NaOH solution, and an aqueous sodium acetate solution. In some embodiments of the present invention, regeneration takes 4 to 6 hours. In some embodiments of the present invention, the ratio between the adsorbent used and the regenerating agent is 1 g: 5-10 mL. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described in more detail with reference to the accompanying drawings and examples, in which: Fig. 1 is a transmission electron microscope image of the silicon-aluminum-iron composite material obtained in Example 1 of the present invention. DETAILED DESCRIPTION The concept of the present invention and the resulting technical effects are described clearly and fully below in conjunction with the examples in order to fully understand the purpose, features and effects of the present invention. Example 1 In this example, a silicon-aluminum-iron composite was prepared, and the specific procedure included: S1. 1 g of silicon-alumina powder was added to an alkaline solution and reacted at a rotation speed of 100 rpm for 1 h to obtain a mixture; the silicon-alumina powder was a mixture with a mass ratio of 1:1.2 of silicon dioxide to alumina; the alkaline solution was a mixture of 15 mL of NaOH with a concentration of 1 mol / L and 5 mL of Na2CO3 with a concentration of 1 mol / L; S2.1 g of Fe(NO3)3 was added to 100 ml of the mixture obtained in step S1, placed in a water bath and heated to 60°C, and then irradiated with ultraviolet rays for 6 h; after solid-liquid separation, the obtained solid was washed to a pH of 7 and dried at 60°C for 12 h to obtain the silicon-aluminum-iron composite material; the wavelength of the ultraviolet rays was <400 nm and the ultraviolet rays source was a mercury lamp with a power of 1200 W. The morphology of the silicon-aluminum-iron composite obtained in this example is shown in Fig. 1. Example 2 In this example, a silicon-aluminum-iron composite was prepared, and the specific procedure included: S1. 1 g of silicon-alumina powder (as in Example 1) was added to an alkaline solution and reacted at a rotation speed of 120 rpm for 1.5 h to obtain a mixture; the alkaline solution was a mixture of 15 mL of NaOH with a concentration of 1 mol / L and 7 mL of Na2CO3 with a concentration of 1 mol / L; S2.1 g of Fe(NO3)3 was added to 100 mL of the mixture obtained in step S1, placed in a water bath and heated to 70°C, and then irradiated with ultraviolet rays for 7 h. After solid-liquid separation, the obtained solid was washed to a neutral pH and dried at 70°C for 15 h to obtain the silicon-aluminum-iron composite material. The wavelength of the ultraviolet rays was <400 nm, and the ultraviolet rays source was a mercury lamp with a power of 800 W. Example 3 In this example, a silicon-aluminum-iron composite was prepared, and the specific procedure included: S1. 1 g of silicon-alumina powder (as in Example 1) was added to an alkaline solution and reacted at a rotation speed of 160 rpm for 1.5 h to obtain a mixture; the alkaline solution was a mixture of 18 mL of NaOH with a concentration of 1 mol / L and 8 mL of Na2CO3 with a concentration of 1 mol / L; S2.1 g of Fe(NO3)3 was added to 100 mL of the mixture obtained in step S1, placed in a water bath and heated to 60°C, and then irradiated with ultraviolet rays for 10 h. After solid-liquid separation, the obtained solid was washed to a neutral pH and dried at 60°C for 18 h to obtain the silicon-aluminum-iron composite material. The wavelength of the ultraviolet rays was <400 nm, and the ultraviolet rays source was a mercury lamp with a power of 600 W. Example 4 In this example, a silicon-aluminum-iron composite was prepared, and the specific procedure included: S1. 1 g of silicon-alumina powder (as in Example 1) was added to an alkaline solution and reacted at a rotation speed of 200 rpm for 2 h to obtain a mixture; the alkaline solution was a mixture of 22 mL of NaOH with a concentration of 1 mol / L and 8 mL of Na2CO3 with a concentration of 1 mol / L; S2.1 g of Fe(NO3)3 was added to 100 mL of the mixture obtained in step S1, placed in a water bath and heated to 90°C, and then irradiated with ultraviolet rays for 12 h. After solid-liquid separation, the obtained solid was washed to a neutral pH and dried at 90°C for 24 h to obtain the silicon-aluminum-iron composite material. The wavelength of the ultraviolet rays was <400 nm, and the ultraviolet rays source was a mercury lamp with a power of 300 W. Example 5 In this example, the silicon-aluminum-iron composite obtained in Example 1 was used as an adsorbent to treat manganese-containing heavy metal wastewater. The specific steps were: 2.5 g of the silicon-aluminum-iron composite obtained in Example 1 was added to 100 mL of wastewater with a manganese ion concentration of 50 mg / L. Adsorption was carried out under conditions of room temperature and atmospheric pressure (25°C, 1 atmosphere), pH 3, and a rotation speed of 120 rpm with stirring for 4 hours. After filtration, a purified aqueous solution and a used adsorbent were obtained. Example 6 In this example, the silicon-aluminum-iron composite obtained in Example 2 was used as an adsorbent for the treatment of manganese-containing heavy metal wastewater. The specific steps were: 100 mL of wastewater with a manganese ion concentration of 60 mg / L was added with 3 g of the silicon-aluminum-iron composite obtained in Example 2. Adsorption was carried out under conditions of room temperature and atmospheric pressure (25°C, 1 atmosphere), pH 5, and a rotation speed of 140 rpm with stirring for 4.5 h. After filtration, a purified aqueous solution and a used adsorbent were obtained. Example 7 In this example, the silicon-aluminum-iron composite obtained in Example 3 was used as an adsorbent for the treatment of manganese-containing heavy metal wastewater. The specific steps were as follows: 100 mL of wastewater with a manganese ion concentration of 80 mg / L was added with 3.5 g of the silicon-aluminum-iron composite obtained in Example 3. Adsorption was carried out under conditions of room temperature and atmospheric pressure (25°C, 1 atmosphere), pH 6, and a rotation speed of 160 rpm with stirring for 5 hours. After filtration, a purified aqueous solution and a used adsorbent were obtained. Example 8 In this example, the silicon-aluminum-iron composite obtained in Example 4 was used as an adsorbent for the treatment of manganese-containing heavy metal wastewater. The specific steps were: 100 mL of wastewater with a manganese ion concentration of 100 mg / L was added with 4.0 g of the silicon-aluminum-iron composite obtained in Example 4. Adsorption was carried out under conditions of room temperature and atmospheric pressure (25°C, 1 atmosphere), pH 6, and a rotation speed of 180 rpm with stirring for 6 h. After filtration, a purified aqueous solution and a used adsorbent were obtained. Example 9 In this example, the adsorbent obtained in Example 5 was used to treat manganese-containing heavy metal wastewater. The following steps were performed: 100 mL of wastewater with a manganese ion concentration of 100 mg / L was added with 4.5 g of the adsorbent obtained in Example 5. Adsorption was carried out under conditions of room temperature and atmospheric pressure (25°C, 1 atmosphere), pH 5, and a rotation speed of 140 rpm with stirring for 4.5 h. After filtration, a purified aqueous solution and a used adsorbent were obtained. Comparative Example 1 In this comparative example, an adsorbent was prepared, and the difference between Comparative Example 1 and Example 4 was: In step S2, ultraviolet irradiation was carried out directly without adding Fe(NO3)3. Comparative Example 2 In this Comparative Example, the adsorbent obtained in Comparative Example 1 was used to treat manganese-containing heavy metal wastewater, and the specific difference between Comparative Example 2 and Example 8 was:Instead of the silicon-aluminum-iron composite material obtained in Example 4, the material obtained in Comparative Example 1 was used. Example of a test In this test example, the silicon-aluminum-iron composites obtained in Examples 1 to 4 and the adsorbent prepared in Comparative Example 1 were tested for their physical and chemical properties. The specific surface area and pore volume were determined using BET. The particle size was measured using a Malvern particle size analyzer. The adsorption capacity was tested and calculated by (c0-ce)v / m; where c0 represented the initial mass concentration of heavy metals in the heavy metal wastewater; ce represented the concentration of heavy metals in the heavy metal wastewater after adsorption equilibrium; v represented the volume (L) of the heavy metal wastewater; and m represented the mass (g) of the adsorbent; and c0 and ce were measured by ICP-OES. The test results are shown in Table 1. Table 1 Physical and chemical properties of the materials obtained in Examples 1 to 4 and Comparative Example 1 Table 1 Physical and chemical properties of the materials obtained in Examples 1 to 4 and Comparative Example 1 Example 140.30.240.67107.2 Example 241.70.290.62112.3 Example 342.10.260.58115.4 Example 441.20.270.63110.6 Comparative example 135.10.430.4282.5 Table 1 showed that the silicon-aluminum-iron composite material provided by the present invention had a smaller particle size, a larger pore volume, and a larger specific surface area, and thus had a higher adsorption capacity than the adsorbent obtained in Comparative Example 1. This indicates that the addition of iron salt can indeed lead to the formation of a silicon-aluminum-iron composite material with a hollow core-shell structure, and this structure could indeed improve the adsorption capacity for manganese. In this test example, the adsorption performance of each adsorbent in Examples 5 to 9 and Comparative Example 2 was also tested. The manganese removal efficiency was calculated as (manganese concentration in the initial heavy metal wastewater - manganese concentration in the purified aqueous solution) / manganese concentration in the initial heavy metal wastewater; and the manganese concentration was measured by ICP-OES. The test results showed that the manganese removal efficiency in Examples 5 to 8 and Comparative Example 2 was 99.72%, 99.91%, 99.99%, 99.95%, and 87.5%, respectively. These results demonstrated that the manganese adsorption performance of the silicon-aluminum-iron composite materials obtained in Examples 1 to 4 of the present invention was significantly better than that of the iron-free adsorbent obtained in Comparative Example 1.In Example 9, the adsorbent used was used to remove manganese and achieved a manganese removal efficiency of 95% and an adsorption capacity of 95 mg / g, which indicates that the adsorbent used still has a good ability to remove manganese.

Claims

[1] A silicon-aluminium-iron composite material comprising an inner core and an outer shell enclosing the inner core, wherein, the inner core is a hollow sphere based on silicon and aluminum; the outer shell consists of an iron element; the holes are distributed between the inner core and the outer shell, the particle size of the silicon-aluminum-iron composite material is 0.2 µm to 0.3 µm, and the silicon-aluminum-iron composite material is used as an adsorbent. [2] The silicon-aluminium-iron composite material according to claim 1, wherein the pore volume of the silicon-aluminium-iron composite material is 0.55 cm 3 / g up to 0.7 cm 3 / g. [3] The silicon-aluminium-iron composite material according to claim 1, wherein the specific surface area of the silicon-aluminium-iron composite material is 40 m 2 / g up to 42.5 m 2 / g. [4] A method for providing the silicon-aluminium-iron composite material according to any one of claims 1 to 3, comprising the following steps: S1. Mixing a silicon-alumina powder and an alkaline solution for reaction to obtain a mixed solution; wherein the alkaline solution is a mixed solution of NaOH and Na2CO3; and the silicon-alumina powder is a mixture of silicon oxide and aluminum oxide, and S2. Adding an iron salt to the mixed solution obtained in step S1 and reacting the resulting mixture under ultraviolet irradiation to obtain a silicon-aluminum-iron composite material. [5] The method according to claim 4, wherein in step S1 the concentration of the alkaline solution is 0.5 mol / L to 2 mol / L. [6] The method according to claim 4, wherein in step S1 the molar ratio of NaOH to Na2CO3 in the alkaline solution is 2-3:

1. [7] The method according to claim 4, wherein in step S1 the mass-volume ratio of the silicon-alumina powder to the alkaline solution is 1 g: 20-30 mL. [8] The process according to claim 4, wherein the molar ratio of the silicon-alumina powder to the iron salt is 15-30:

1. [9] An adsorbent produced with a material comprising the silicon-aluminium-iron composite material according to any one of claims 1 to 3 or produced with a material comprising the silicon-aluminium-iron composite material produced by the process according to any one of claims 4 to 8. [10] Use of the adsorbent according to claim 9 in the treatment of heavy metal waste water.

Images