Lanthanum-titanium modified autoclaved aerated concrete as well as preparation method and application thereof

Abstract

The invention relates to the field of environmental water treatment, and discloses lanthanum-titanium modified autoclaved aerated concrete as well as a preparation method and application thereof. The preparation method comprises the following steps: adding autoclaved aerated concrete (CAAC) into a mixed solution of tetrabutyl titanate and ethanol; adding a mixed solution of glacial acetic acid, hydrochloric acid, water and ethanol, and stirring until gel is formed; drying and grinding the gel; adding into lanthanum nitrate, adjusting the pH value of the solution, stirring and standing; and washing the precipitate, drying, and calcining again to obtain the lanthanum-titanium modified autoclaved aerated concrete (La-Ti-CAAC). The specific surface area is 50.94 m < 2 > / g, and the aperture is 8.02 nm. The adsorption capacities of the La-Ti-CAAC on the fluoride and the phosphate respectively reach 20.99 mg / g and 24.26 mg / g. The adsorption effect is good under the condition that the pH value is 3-10, the selectivity is good, and the good adsorption capacity is still achieved after four times of circulation.

Description

Technical Field

[0001] This invention relates to the field of environmental water treatment, and more specifically, to a lanthanum-titanium modified autoclaved aerated concrete, its preparation method, and its application. Background Technology

[0002] With the acceleration of industrialization, fluorides and phosphates are prevalent in wastewater from industries such as semiconductor manufacturing, lithium battery recycling, and fertilizer production. Excessive accumulation in water bodies not only affects drinking water safety but also causes environmental problems such as eutrophication. Especially in actual wastewater, fluorides and phosphates often coexist, exhibiting competitive adsorption effects, rendering traditional single-method removal ineffective.

[0003] Among numerous water treatment methods, adsorption is considered an effective approach due to its low cost, lack of secondary pollution, and recyclability. Natural minerals (such as zeolite, kaolin, and bauxite) and industrial solid wastes (such as fly ash, straw, and CAAC) have been used as adsorption substrates, but their adsorption capacity is limited and easily affected by environmental conditions such as pH. For example, while alkali- or aluminum-modified autoclaved aerated concrete materials significantly improve phosphorus removal performance, their adsorption capacity for fluorides is insufficient, and they struggle to simultaneously and efficiently remove both fluorides and phosphates.

[0004] In recent years, rare earth metals have attracted attention due to their strong coordination ability with fluoride and phosphorus. Single La or Ti modified materials have shown good fluoride or phosphorus removal effects in experiments. Existing research (Hydrothermally Shape-Controlled Synthesis of TiO2 / Graphene for Fluoride Adsorption Studies) uses titanium dioxide supported on graphene to prepare a recyclable adsorbent for removing fluoride from water, achieving an adsorption capacity of 342 mg / g at pH 6.0. However, in actual wastewater treatment, the complex composition of water bodies can lead to a significant decrease in the adsorption capacity of single metal oxides. Furthermore, in complex wastewater systems, the adsorption performance of single metal oxides tends to decline drastically. Patent CN117299081A proposes a chitosan-biochar-zeolite-based composite adsorbent, loaded with titanium dioxide and lanthanum hydroxide, for treating high-concentration wastewater containing heavy metals and organic pollutants. However, this technology mainly targets heavy metal ions and organic matter, and its efficient synergistic removal of fluoride and phosphate has not been studied in depth. Meanwhile, its adsorption is concentrated on the specific surface area of ​​biochar and the complexation effect on the surface of metal oxides, and it cannot achieve the removal of anions in the competing adsorption system.

[0005] Therefore, there is an urgent need to develop a novel composite modified adsorbent material based on autoclaved aerated concrete that can balance high adsorption capacity and environmental adaptability, thereby achieving efficient and synergistic removal of fluoride- and phosphorus-containing wastewater. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, such as limited adsorption capacity and inability to simultaneously adsorb fluorides and phosphates in a competing adsorption system, this invention provides a lanthanum-titanium modified autoclaved aerated concrete.

[0007] Another objective of this invention is to provide a method for preparing lanthanum-titanium modified autoclaved aerated concrete;

[0008] Another object of the present invention is to provide an application of lanthanum-titanium modified autoclaved aerated concrete.

[0009] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0010] A method for preparing lanthanum-titanium modified autoclaved aerated concrete includes the following steps:

[0011] S1. Add autoclaved aerated concrete (CAAC) to a mixture of tetrabutyl titanate and ethanol;

[0012] S2. Add the mixture of glacial acetic acid, hydrochloric acid, water and ethanol, and stir until a gel forms.

[0013] S3. After drying and grinding the gel, calcination is performed to obtain Ti-CAAC;

[0014] S4. Add Ti-CAAC to lanthanum nitrate, adjust the pH of the solution, stir, and let stand.

[0015] S5. After washing, settling, drying, and calcining again, the lanthanum-titanium modified autoclaved aerated concrete is obtained.

[0016] Preferably, the CAAC composition includes SiO2, Al2O3 and CaO.

[0017] Preferably, the lanthanum nitrate is La(NO3)3·6H2O.

[0018] Preferably, the CAAC that has passed through a 100-mesh sieve is first soaked in ultrapure water for 12 hours, and then dried at 80°C for 24 hours for later use.

[0019] Furthermore, in S1, the mass ratio of autoclaved aerated concrete to tetrabutyl titanate is 1:1.5 to 3.5.

[0020] Preferably, in S1, the mass ratio of autoclaved aerated concrete to tetrabutyl titanate is 13:30.

[0021] Furthermore, in S1, the volume ratio of tetrabutyl titanate to ethanol is 3:8 to 12.

[0022] Preferably, in S2, the volume ratio of glacial acetic acid: concentrated hydrochloric acid: ethanol is 3-5:0.5-0.7:15-25.

[0023] Preferably, in step S3, the material is ground through an 80-120 mesh sieve.

[0024] Preferably, in S3, calcination is carried out at 400-450°C for 2-2.5 hours.

[0025] Preferably, in S3, drying is carried out at 70°C for 8 hours; in S5, drying is carried out at 105°C for 8 hours.

[0026] Furthermore, in S4, lanthanum nitrate is added at a molar ratio of La to Ti of 1:1 to 6.

[0027] Preferably, in S4, lanthanum nitrate is added at a molar ratio of La to Ti of 1:1 to 5.

[0028] Preferably, in S4, lanthanum nitrate is added at a molar ratio of La to Ti of 1:5.

[0029] Furthermore, in S4, the pH of the solution is adjusted to 9–11.

[0030] Preferably, in step S4, the pH of the solution is adjusted to 9.

[0031] Preferably, in step S4, the mixture is continuously stirred at 200 rpm and 25°C for 4 hours, and then allowed to stand for 24 hours.

[0032] Furthermore, in S5, the temperature for recalcination is 100–600°C.

[0033] Preferably, in S5, the temperature for the second calcination is 300–450°C.

[0034] Preferably, in step S5, the temperature is increased to the calcination temperature at a rate of 5°C / min, and calcined for 3 hours.

[0035] A lanthanum-titanium modified autoclaved aerated concrete is prepared by the aforementioned preparation method.

[0036] An application of lanthanum-titanium modified autoclaved aerated concrete for the preparation of adsorbents.

[0037] Furthermore, it can simultaneously adsorb fluorides and phosphates.

[0038] Preferably, the treatment involves removing fluorides and phosphates from the wastewater.

[0039] Preferably, the wastewater also includes Cl. - NO3 - SO4 2- .

[0040] Furthermore, adsorption was carried out at a pH of 3–10.

[0041] Preferably, the ratio of fluoride to phosphate is 0-10:0-10.

[0042] The removal mechanisms of fluoride and phosphate by La-Ti-CAAC mainly include electrostatic attraction and ion exchange, supplemented by precipitation reactions, complexation reactions, and physical adsorption. Due to the synergistic effect of the material's elemental composition and modified components, the competitive adsorption problem between fluoride and phosphate is effectively alleviated, thereby improving the simultaneous removal efficiency. The unique porous structure of CAAC, combined with the loading of La and Ti, endows the material with multiple adsorption mechanisms, making it excellent in the treatment of complex pollution. This invention follows the concept of a circular economy, transforming construction waste concrete fragments into a multifunctional adsorbent, providing a sustainable solution for the efficient removal of fluoride and phosphate from wastewater.

[0043] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0044] The specific surface area of ​​La-Ti-CAAC prepared from CAAC increased from the original 6.74 m². 2 / g increased to 50.94m 2 / g, pore volume increased from the original 0.021m 3 / g increased to 0.95cm 3 The pore size has also increased from 6.88 nm to 8.02 nm. Experiments show that La-Ti-CAAC can effectively capture fluoride and phosphate, with maximum adsorption capacities reaching 20.99 mg / g and 24.26 mg / g, respectively. The adsorption process is affected by pH, with good adsorption performance under pH conditions of 4–7. Furthermore, it exhibits good selectivity for target phosphorus and fluoride in the presence of other anions. Regenerated La-Ti-CAAC still retains good adsorption capacity after four cycles. This invention not only proposes a new and promising candidate material for remediating water bodies with dual fluoride and phosphate pollution, but also provides a new possibility for the utilization of waste concrete. Attached Figure Description

[0045] Figure 1 Flowchart of La-Ti-CAAC preparation and adsorption; Figure 2 XRD patterns of CAAC and La-Ti-CAAC composites; Figure 3 The microstructure images of the La-Ti-CAAC composite material are shown in SEM (a~c), and the elemental distribution diagrams of La (d) and Ti (e) are also shown. Figure 4 This refers to the adsorption in solutions where fluorides and phosphates coexist. Figure 5 The effect of pH on the adsorption efficiency of La-Ti-CAAC for fluoride and phosphate ions; Figure 6 For Cl - NO3 - SO4 2- CO3 2- HCO3 - The competitive adsorption of fluoride ions (a) and phosphate ions (b) by humic acid; Figure 7 The reusability of La-Ti-CAAC after four adsorption-desorption cycles; Detailed Implementation

[0052] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0053] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0054] CAAC (Autoclaved Aerated Concrete) mainly originates from the scrap material generated during the production process of an autoclaved aerated concrete (AAC) manufacturing plant in Guangzhou. Before use, it is ground to below 100 mesh. Its main components include SiO2, Al2O3, and CaO, with the following chemical composition: SiO2 48.11%, CaO 28.59%, Al2O3 8.25%, Fe2O3 5.39%, MgO 0.74%, K2O 0.72%, Na2O 0.19%, and SO3 0.67%. Sodium fluoride and anhydrous ethanol were purchased from Tianjin Damao Chemical Reagent Factory. Lanthanum nitrate, tetrabutyl titanate, and potassium dihydrogen phosphate were purchased from Shanghai Maclean Biochemical Co., Ltd. Sodium hydroxide, potassium persulfate, and ammonium molybdate were purchased from Tianjin Kemei Chemical Reagent Co., Ltd. Ascorbic acid and potassium antimony tartrate were purchased from Guangzhou Chemical Reagent Factory. Sodium chloride, glacial acetic acid, and concentrated hydrochloric acid were purchased from Tianjin Zhiyuan Chemical Reagent Factory. Phosphate and fluoride stock solutions were prepared by dissolving KH₂PO₄ and NaF in deionized water, respectively. All chemical reagents used in this invention are analytical grade.

[0055] Example 1

[0056] La-Ti-CAAC was synthesized using an impregnation-calcination method. First, CAAC that had passed through a 100-mesh sieve was soaked in ultrapure water for 12 hours, then dried at 80℃ for 24 hours. 5.2 g of CAAC was added to a mixture of 12 mL tetrabutyl titanate and 40 mL ethanol. Then, at 30℃, a mixture of 4 mL glacial acetic acid, 0.6 mL concentrated hydrochloric acid, 9 mL ultrapure water, and 20 mL ethanol was added, and the mixture was stirred until a gel formed. The gel was placed in a 70℃ oven for 8 hours, ground, and then passed through a 100-mesh sieve. Finally, it was calcined in a muffle furnace at 450℃ for 2 hours to obtain Ti-CAAC. La(NO3)3·6H2O was dissolved in 100 mL ultrapure water at a La / Ti molar ratio of 1:5. Ti-CAAC was added, and then 2 mol / L NaOH was added dropwise until the pH of the solution reached 9. The solution was stirred continuously at 200 rpm and 25℃ in a water bath for 4 hours, and then allowed to stand for 24 hours. The precipitate was repeatedly washed with ultrapure water to remove impurity ions, and then dried in a drying oven at 105°C for 8 hours. The resulting precipitate was then calcined at 300°C with a heating rate of 5°C / min for 3 hours to obtain the target adsorbent material La-Ti-CAAC. The preparation and adsorption process is as follows: Figure 1 As shown.

[0057] Example 2

[0058] The technical solutions of Examples 2 to 13 are similar to those of Example 1, except that the molar ratio of La / Ti, the pH of the solution after adding Ti-CAAC, and the temperature of the second calcination are different, as shown in Table 1.

[0059] Table 1

[0060] Example La / Ti pH T(℃) 2 1:1 9 100 3 1:5 9 100 4 1:10 9 100 5 1:20 9 100 6 1:5 3 100 7 1:5 5 100 8 1:5 7 100 9 1:5 9 100 10 1:5 11 100 11 1:5 9 100 12 1:5 9 300 13 1:5 9 600

[0061] Detection methods

[0062] 1. Batch adsorption and desorption experiments

[0063] The simultaneous adsorption performance of phosphates and fluorides was tested. In the mixed solution, the fluoride-to-phosphorus concentration ratios were set to 5:0, 10:0, 5:5, 5:10, 10:5, 10:10, 0:10, and 0:5 (mg / L). Other experimental procedures were the same as described above. The effect of pH on adsorption performance was evaluated by adjusting the initial pH value within the range of 3.0–12.0. The adsorption performance was assessed for coexisting anions Cl... - NO3 - SO4 2- HCO3 - PO4 3- Three intensity gradients (100, 300, 500 mg / L) of humic acid (HA) were set to detect the competitive adsorption of phosphate and fluoride.

[0064] The adsorbed La-Ti-CAAC samples were regenerated, and four consecutive adsorption-desorption cycles were performed to evaluate their reusability. Each adsorption test was conducted in 30 mL of solution containing 1 g / L adsorbent. The saturated adsorbent was then collected and eluted with 0.5 mol / L sodium hydroxide solution before the next adsorption-desorption test. The reusability of the La-Ti-CAAC adsorbent was estimated based on the removal efficiency of the target anion after each adsorption-desorption cycle.

[0065] 2. Characterization and Analysis Methods

[0066] Surface elemental analysis and surface morphology analysis of the material were performed using field emission scanning electron microscopy (FE-SEM, Helios G4CX, Germany) and energy dispersive X-ray spectroscopy (EDS, Oxford X-Max 50, Germany). The crystal structure of the prepared adsorbent was determined by X-ray diffraction (XRD, Ultima IV, Japan).

[0067] Analysis and Explanation

[0068] 1. Adsorption capacity for fluoride ions and phosphate ions

[0069] As shown in Table 2, the adsorption performance of La-Ti-CAAC for fluoride ions varies with synthesis conditions. The best performance is observed when the La / Ti ratio is 1:5; the adsorption capacity decreases slightly when the ratio is further increased to 1:10 or 1:20. pH significantly affects performance; the adsorption capacity is lower under acidic conditions, while it exceeds 9 mg / g in the pH range of 9–11 when the La / Ti ratio is not less than 1:5. High performance is maintained at calcination temperatures ranging from 100 to 600℃, with the highest adsorption capacity (12.12 mg / g) observed at 450℃.

[0070] Table 2 Adsorption performance of La-Ti-CAAC for phosphate ions

[0071] Example <![CDATA[q e (mg / g)]]> Example <![CDATA[q e (mg / g)]]> 1 12.12 8 8.47 2 9.21 9 10.84 3 10.84 10 10.26 4 8.11 11 10.84 5 7.09 12 11.94 6 5.14 13 10.34 7 6.87

[0072] As shown in Table 3, the adsorption performance of La-Ti-CAAC for phosphate ions varies with synthesis conditions. The best performance is observed when the La / Ti ratio is 1:5; the adsorption capacity decreases slightly when the ratio is further increased to 1:10 or 1:20. pH significantly affects performance; the adsorption capacity is lower under acidic conditions, while it exceeds 14 mg / g in the pH range of 9–11 when the La / Ti ratio is not less than 1:5. High performance is maintained at calcination temperatures ranging from 100 to 600℃, with the highest adsorption capacity (22.34 mg / g) observed at 300℃.

[0073] Table 3. Adsorption performance of La-Ti-CAAC for phosphates

[0074] Example <![CDATA[q e (mg / g)]]> Example <![CDATA[q e (mg / g)]]> 1 15.64 8 17.21 2 17.21 9 14.21 3 6.11 10 17.21 4 4.08 11 22.34 5 8.21 12 20.78 6 10.74 13 20.11 7 11.23

[0075] 2. Characterization of the synthesized adsorbent like Figure 2 As shown, the XRD analysis angle (2θ) ranges from 5° to 90°. The peaks corresponding to the crystallization of the raw material CAAC mainly represent silica, hydrated calcium silicate, calcium carbonate, and calcium sulfate. Figure 2 The diffraction peaks at 2θ = 20°–35° indicate that CAAC contains amorphous silicates, which may contain calcium, iron, aluminum, and other metals. (Comparison...) Figure 2 It can be seen that, in addition to the original characteristic peaks of CAAC, characteristic peaks of TiO2 also appeared at corresponding angles of 27.61° (110), 31.54° (101), 45.36° (111), 47.86° (210), 54.44° (211), 61.32° (220), 66.08° (002), and 75.26° (301). Furthermore, characteristic peaks of La(OH)3 appeared at corresponding angles of 15.65° (100), 27.97° (110), 39.49° (201), and 47.06° (300). This indicates that both TiO2 and La were successfully loaded onto CAAC.

[0077] pass Figure 3 It can be seen that the surface of La-Ti-CAAC is relatively rough. Figure 3 a~c), uniformly covered with oxides of lanthanum and titanium ( Figure 3 (d~e). The smaller particle size on the surface facilitates the adsorption of fluorides and phosphates. Simultaneously, La-Ti-CAAC possesses a large number of porous structures, which promotes solution diffusion and thus enhances adsorption efficiency. EDS elemental mapping of La-Ti-CAAC shows that La and Ti are indeed loaded onto the CAAC, with Ti having a relatively higher content. This invention first loads Ti to increase the framework of the CAAC, facilitating better loading of lanthanides onto the material and increasing the contact area with pollutants, thereby improving removal efficiency.

[0078] 3. Co-adsorption experiment of fluoride ions and phosphate ions

[0079] like Figure 4As shown, the adsorption capacity of La-Ti-CAAC for phosphate ions was higher than that for fluoride ions, indicating that anions with higher charges are more attractive to La-Ti-CAAC materials. When the initial fluoride ion concentration in the solution was 5 mg / L, the adsorption capacity increased by 35% after adding 5 mg / L of phosphate ions. With continuous increase in phosphate ion concentration, the adsorption capacity of fluoride ions continued to increase. When the fluoride ion concentration reached 10 mg / L, the presence of phosphate ions also had a similar positive effect on fluoride ion adsorption, indicating that the presence of phosphate ions in the binary solution promotes the adsorption of fluoride ions by La-Ti-CAAC. Although the presence of fluoride ions slightly decreased the phosphate ion removal rate, the effect was minimal. Unlike other reports on La-based adsorbents, this invention shows that the presence of phosphate ions promotes the adsorption of fluoride ions at a certain content ratio.

[0080] 6. Effect of pH on adsorption efficiency

[0081] like Figure 5 As shown, La-Ti-CAAC is more favorable for adsorbing fluoride ions under acidic conditions and more favorable for adsorbing phosphate ions under alkaline conditions. La-Ti-CAAC exhibits the highest adsorption efficiency for fluoride ions at pH 3–8, with a removal rate reaching 90% at pH 3. The removal rate of fluoride ions gradually decreases as the initial pH of the solution increases. The removal rate of phosphate ions by La-Ti-CAAC increases with increasing pH, reaching 96% at pH 9. However, the removal rate decreases at strongly alkaline pH. At pH 8–10, phosphate groups are adsorbed as H₂PO₄. - and HPO2 - It exists and combines with the released cations to form insoluble crystalline precipitates. Simultaneously, the La-Ti-CAAC surface is positively charged, and due to electrostatic interactions, the removal rate reaches its maximum.

[0082] 7. The Influence of Environmental Factors on Adsorption

[0083] In natural water bodies, fluoride and phosphate ions often coexist with other ions and organic matter. These ions and organic matter compete with fluoride and phosphate ions for active adsorption sites on the adsorbent, leading to a decrease in adsorption efficiency. For example... Figure 6 As shown, the adsorption of fluoride ions and phosphate ions by La-Ti-CAAC is basically unaffected by Cl. - NO3 - SO4 2-The influence of these factors indicates that La-Ti-CAAC exhibits strong selectivity for fluoride and phosphate ions. Humic substances tend to interact with La to form La-HA complexes, and appropriate amounts of humic acid promote the removal of fluoride ions.

[0084] 8. Adsorbent regeneration

[0085] like Figure 7 As shown, in the initial adsorption experiments, the removal efficiencies of fluoride ions and phosphate ions were 85.5% and 92.8%, respectively. With increasing regeneration cycles, the removal efficiencies of fluoride ions and phosphate ions gradually decreased. After four desorption-adsorption cycles, the removal rates of fluoride ions and phosphate ions remained at 65.1% and 75.3%, respectively. This indicates that the obtained La-Ti-CAAC is a sustainable, easily regenerated, and highly efficient adsorbent.

[0086] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for producing a lanthanum titanium modified autoclaved aerated concrete, characterized by, The method comprises the following steps: S1, adding autoclaved aerated concrete into a mixture of tetrabutyl titanate and ethanol; S2, adding a mixture of glacial acetic acid, hydrochloric acid, water and ethanol, and stirring until gel formation; S3, drying and grinding the gel, and calcining to obtain Ti-CAAC; S4, adding Ti-CAAC into lanthanum nitrate, adjusting the pH of the solution, stirring and standing; S5, washing and drying the precipitate, and calcining again to obtain the lanthanum-titanium modified autoclaved aerated concrete.

2. The method for preparing lanthanum-titanium modified autoclaved aerated concrete according to claim 1, characterized in that, In S4, lanthanum nitrate is added in a molar ratio of La to Ti of 1:1-6.

3. The method for preparing lanthanum-titanium modified autoclaved aerated concrete according to claim 1, characterized in that, In S4, the pH of the solution is adjusted to 9-11.

4. The method for preparing lanthanum-titanium modified autoclaved aerated concrete according to claim 1, characterized in that, In S5, the temperature for calcining again is 100-600℃.

5. The method for preparing lanthanum-titanium modified autoclaved aerated concrete according to claim 1, characterized in that, In S1, the mass ratio of tetrabutyl titanate to autoclaved aerated concrete is 1.5-3.5:

1.

6. The method for preparing lanthanum-titanium modified autoclaved aerated concrete according to claim 1, characterized in that, In S1, the volume ratio of tetrabutyl titanate to ethanol is 3:8-12, and the volume ratio of glacial acetic acid: concentrated hydrochloric acid: ethanol is 3-5: 0.5-0.7: 15-25.

7. A lanthanum-titanium-modified autoclaved aerated concrete, characterized by Prepared by the method of any one of claims 1-6.

8. Use of lanthanum titanium modified autoclaved aerated concrete, characterized in that For preparing an adsorbent.

9. Use of the lanthanum titanium modified autoclaved aerated concrete according to claim 8, characterized in that Can simultaneously adsorb fluoride and phosphate.

10. Use of the lanthanum titanium modified autoclaved aerated concrete according to claim 8, characterized in that Adsorption is carried out at a pH of 3-10.

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