A composite modified attapulgite clay adsorbent, its preparation method and application

Abstract

The present application belongs to the field of mineral composite adsorption materials, and provides a composite modified attapulgite clay adsorbent as well as a preparation method and application thereof. In the present application, the in-situ hydrolysis deposition is induced by the water phase pH of ferric chloride hexahydrate, so that the hydrated iron oxide (calculated as Fe(OH)3) is anchored on the surface of attapulgite clay, the intercrystalline pore channels of attapulgite clay, and the inner connected pore walls of particles. Then, the wet material kneading, granulation, drying, screening, and optional heat treatment are performed to form a granular composite modified body, so that the stable dispersion of active iron phase, low iron leaching, particle crushing strength, and wear resistance in water are considered, the operability of adsorption treatment of phosphorus-containing wastewater is improved, the problem of incoordination between particle integrity and adsorption performance, and between iron phase dispersion and low leaching is solved, and the present application is suitable for fixed bed, filter bag, and stirring adsorption reactor.

Description

Technical Field

[0001] This invention relates to the field of mineral composite adsorbent materials, specifically to a composite modified attapulgite clay adsorbent, its preparation method, and its application. Background Technology

[0002] With increasing demands for advanced industrial wastewater treatment and resource utilization, granular adsorption materials suitable for phosphorus-, arsenic-, and fluoride-containing wastewater have received continuous attention. Compared to powdered adsorbents, granular materials are more suitable for engineering applications such as fixed beds, filter bags, and stirred adsorption reactors, requiring properties such as easy packing, easy separation, resistance to water erosion, low secondary release, and recyclability. Attapulgite clay, with its rod-like structure, porous characteristics, and mineral framework stability, is suitable as a matrix for composite adsorption materials; hydrated iron oxide has an affinity for oxygen-containing anionic pollutants, making it suitable as an active adsorption phase. However, practical industrial wastewater treatment not only requires full exposure of the active phase but also demands that the particles maintain their intact morphology during soaking, shaking, and regeneration. Therefore, the development focus of this type of material lies in establishing a coordinated relationship between the mineral framework, active phase distribution, and particle forming process, enabling the material to provide effective adsorption sites while meeting the engineering requirements of continuous operation, regeneration, and batch production.

[0003] Existing mineral-supported iron-based adsorbents typically introduce the active iron phase into the mineral carrier through impregnation, deposition, or mixed granulation. However, powder-supported methods present challenges in engineering applications, including difficulties in recovery and the risk of secondary release. Direct granulation may reduce pore accessibility and active site utilization due to framework densification. Publicly available technologies propose loading hydrated iron oxide onto attapulgite for phosphorus removal. For example, Chinese patent CN107265548B discloses a method for deep adsorption and phosphorus removal using attapulgite loaded with hydrated iron oxide. This method involves steps such as attapulgite purification, loading with hydrated iron oxide, granulation, and regeneration after adsorption saturation. However, this approach still requires further addressing the coupling issues between active iron phase dispersion, maintenance of interconnected pores within the particles, low iron leaching, and particle mechanical stability. Another CN101249417A discloses an attapulgite clay-aluminum hydroxide / iron nanocomposite adsorbent that can be used for water treatment, showing that attapulgite combined with iron or aluminum-iron components has an application basis, but there is still room for improvement in the fixation state of the active phase in granular form, batch stability and engineering addition adaptation. Summary of the Invention

[0004] The purpose of this invention is to provide a composite modified attapulgite clay adsorbent, its preparation method, and its application, which solves the problems of difficulty in balancing the integrity of particle structure and adsorption performance of current granular adsorbent materials, as well as the difficulty in coordinating the dispersion stability of hydrated iron oxide with low iron leaching.

[0005] This invention uses pH-induced in-situ hydrolysis deposition in an aqueous phase to distribute and anchor hydrated iron oxide (calculated as Fe(OH)3) on the surface of attapulgite clay, in the channels between rod-crystal bundles, and in the walls of interconnected pores within the particles. Combined with granulation molding and heat treatment control, the mutual constraint between the exposure and fixation of the active phase and the strength of the particle skeleton is synergistically balanced.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A composite modified attapulgite clay adsorbent, the adsorbent comprising a granulated hydrated iron oxide in-situ anchored attapulgite clay composite modifier.

[0008] With a dry basis total mass of 100 wt%, the adsorbent comprises, in its final form:

[0009] Attapulgite clay, 75-94 wt%;

[0010] Hydrated iron oxide, calculated as Fe(OH)3, 6-22 wt%;

[0011] The auxiliary molding solid components, excluding the attapulgite clay and the hydrated iron oxide, are 0-3 wt%;

[0012] The sum of the mass percentages of the attapulgite clay, the hydrated iron oxide, and the auxiliary molding solid components is 100 wt%.

[0013] The hydrated iron oxide is formed by in-situ hydrolysis and deposition of ferric chloride hexahydrate induced by pH in an aqueous phase, and the adsorbent is granular.

[0014] In this invention, the content of hydrated iron oxide is calculated by converting the total iron content of the sample after acid digestion into Fe(OH)3. Unless otherwise stated, the content of hydrated iron oxide in the specification and claims adopts this conversion method.

[0015] Furthermore, the hydrated iron oxide is formed on the surface of the attapulgite clay and in the channels between the bar crystal bundles, and the average iron leaching concentration of the adsorbent after 24 hours in deionized water with a pH of 6.0-8.0 is ≤1.00 mg / L, as determined by HJ700-2014 or its current effective version.

[0016] Furthermore, the hydrated iron oxide in-situ anchored attapulgite clay intermediate in the granulated hydrated iron oxide in-situ anchored attapulgite clay composite modifier is prepared through the following steps:

[0017] A1. Disperse attapulgite clay in deionized water to obtain attapulgite clay dispersion slurry;

[0018] A2. Dissolve ferric chloride hexahydrate in deionized water to obtain an aqueous solution of ferric chloride hexahydrate;

[0019] A3. Add the aqueous solution of ferric chloride hexahydrate to the attapulgite clay dispersion slurry and mix;

[0020] A4. Add an aqueous solution of sodium hydroxide or anhydrous sodium carbonate to the system from step A3, control the pH of the system to 6.8-8.2, and then age the system.

[0021] A5. The solid obtained in step A4 is subjected to solid-liquid separation, washing and drying to obtain the hydrated iron oxide in-situ anchored attapulgite clay intermediate;

[0022] In the hydrated iron oxide in-situ anchored attapulgite clay intermediate, the content of hydrated iron oxide, calculated as Fe(OH)3 on a dry basis, is 6-22 wt%, and the average proportion of free hydrated iron oxide to the total mass of hydrated iron oxide is ≤15 wt%.

[0023] Furthermore, the preparation of the hydrated iron oxide in-situ anchored attapulgite clay intermediate satisfies the following conditions:

[0024] In step A1, the solid content of the attapulgite clay dispersion slurry is 10-25 wt%.

[0025] In step A3, the aqueous solution of ferric chloride hexahydrate is added at 35-70°C;

[0026] In step A4, the aging temperature is 45-70℃ and the aging time is 1-4 hours;

[0027] In step A5, the filtrate is washed until the pH value is 6.0-8.0, and the drying temperature is 80-120℃.

[0028] Furthermore, the attapulgite clay used in step A1 is pretreated attapulgite clay, which is prepared through the following steps:

[0029] B1. Mix attapulgite clay with deionized water or a 0.05-0.50 mol / L hydrochloric acid aqueous solution;

[0030] B2. Stir at 25-60℃;

[0031] B3. After solid-liquid separation, wash with deionized water until the pH of the washing solution is 6.0-8.0;

[0032] B4. The pretreated attapulgite clay is obtained by drying at 80-110℃ and sieving.

[0033] The pH value of the pretreated attapulgite clay dispersion slurry in water is 6.0-8.5.

[0034] Furthermore, the granulated hydrated iron oxide in-situ anchored attapulgite clay composite modifier is prepared through the following steps:

[0035] C1. Mix the hydrated iron oxide in-situ anchored attapulgite clay intermediate obtained in step A5 with deionized water to obtain a wet material;

[0036] C2. Knead the wet material;

[0037] C3. Extruding, rounding, or pressing the wet material into granules to obtain wet granules;

[0038] C4. The wet particles are dried and sieved to obtain the granulated hydrated iron oxide in-situ anchored attapulgite clay composite modifier.

[0039] In steps C1-C4, in addition to the hydrated iron oxide in-situ anchoring attapulgite clay intermediate and the deionized water, the amount of auxiliary molding solid components added is 0-3 wt%, based on the total dry mass of the final adsorbent.

[0040] Furthermore, after step C4, a heat treatment at 120-220℃ for 0.5-3.0h is included to obtain adsorbent particles with an average crushing strength of 3-35N / particle and an average wear rate ≤8.00wt% after oscillation in water for 24h.

[0041] Furthermore, the hydrated iron oxide is distributed on the surface of the rod crystals, the channels between the rod crystal bundles, and the walls of the interconnected pores within the particles of the attapulgite clay, and the average proportion of free hydrated iron oxide to the total mass of hydrated iron oxide in the adsorbent is ≤12wt%; the coefficient of variation between batches of hydrated iron oxide content (calculated as Fe(OH)3) in the adsorbents prepared in three consecutive batches is ≤15%.

[0042] As a concept of this invention, the design of a granulated hydrated iron oxide in-situ anchored attapulgite clay composite modifier is mainly used to achieve a synergistic balance between particle structure integrity and adsorption performance. Conventional granulation densification and heat treatment are beneficial for enhancing the particle skeleton but may reduce pore accessibility and active site exposure, thus affecting adsorption utilization. Conventionally increasing the hydrated iron oxide loading and exposure may weaken particle stability and increase the risk of iron phase migration. This invention uses pH-induced in-situ hydrolysis deposition of ferric chloride hexahydrate in the aqueous phase to distribute hydrated iron oxide (calculated as Fe(OH)3) on the surface of attapulgite clay, in the channels between rod-crystal bundles, and in the interconnected pore walls within the particles. By controlling the content ratio, granulation, and heat treatment, the active phase is fixed, the particle skeleton is maintained, and the pollutant contact path is coordinated, thereby forming a stable balance between low iron leaching, particle wear resistance, and adsorption accessibility.

[0043] This invention also discloses a method for preparing a composite modified attapulgite clay adsorbent, comprising the following steps:

[0044] S1. Preparation of an intermediate for in-situ anchoring attapulgite clay with hydrated iron oxide, comprising: dispersing attapulgite clay in deionized water to obtain an attapulgite clay dispersion slurry; dissolving ferric chloride hexahydrate in deionized water to obtain an aqueous solution of ferric chloride hexahydrate; adding the aqueous solution of ferric chloride hexahydrate to the attapulgite clay dispersion slurry and mixing; adding an aqueous solution of sodium hydroxide or anhydrous sodium carbonate to the obtained system, controlling the pH value of the system to 6.8-8.2, and aging; performing solid-liquid separation, washing, and drying on the aged solid to obtain the intermediate for in-situ anchoring attapulgite clay with hydrated iron oxide;

[0045] S2. Mix the hydrated iron oxide in-situ anchored attapulgite clay intermediate with deionized water to obtain a wet material;

[0046] S3. The wet material is kneaded and then granulated to obtain wet granules;

[0047] S4. The wet particles are dried and sieved to obtain a composite modified attapulgite clay adsorbent;

[0048] In steps S2-S4, in addition to the hydrated iron oxide in-situ anchoring attapulgite clay intermediate and the deionized water, the amount of auxiliary molding solid components added is 0-3 wt%, based on the total dry mass of the final adsorbent.

[0049] Further, in step S1, the preparation process of the hydrated iron oxide in-situ anchored attapulgite clay intermediate uses deionized water as the liquid medium, and the pH value of the system is controlled to 6.8-8.2 using sodium hydroxide aqueous solution or anhydrous sodium carbonate aqueous solution; in step S2, the mass ratio of the hydrated iron oxide in-situ anchored attapulgite clay intermediate to deionized water is 100:25-80; in step S3, the kneading temperature is 20-60℃; in step S4, the drying temperature is 80-120℃, and particles of 0.50-1.80mm are obtained by sieving after drying.

[0050] Furthermore, after step S4, a heat treatment at 120-220℃ for 0.5-3.0h is included, so that the average wear rate of the composite modified attapulgite clay adsorbent after oscillating in water for 24h is ≤8.00wt.

[0051] This invention also discloses the application of a composite modified attapulgite clay adsorbent in the adsorption treatment of industrial wastewater, wherein the industrial wastewater is phosphorus-containing wastewater.

[0052] The composite modified attapulgite clay adsorbent is used in a fixed bed, filter bag, or stirred adsorption reactor. When used in a fixed bed, the influent pH is 5.0-9.0 and the hydraulic retention time is 5-60 min. After adsorption treatment, it is regenerated with a 0.05-1.00 mol / L sodium hydroxide aqueous solution.

[0053] Furthermore, the composite modified attapulgite clay adsorbent is dried and then sieved to obtain adsorbent particles with a sieve particle size of 0.50-1.80 mm. The obtained adsorbent particles are used for fixed bed filling, filter bag filling, or addition to stirred adsorption reactors.

[0054] Furthermore, in the preparation of the hydrated iron oxide in-situ anchored attapulgite clay intermediate, 100 parts by mass of attapulgite clay are dispersed in 300-900 parts by mass of deionized water to form an attapulgite clay dispersion slurry with a solid content of 10-25 wt%. The resulting attapulgite clay dispersion slurry then enters the iron salt contact and in-situ deposition steps.

[0055] Furthermore, in preparing the intermediate for in-situ anchoring of attapulgite clay with hydrated iron oxide, 15-75 parts by mass of ferric chloride hexahydrate are dissolved in 100-500 parts by mass of deionized water to obtain an aqueous solution of ferric chloride hexahydrate. The obtained aqueous solution of ferric chloride hexahydrate is then added to the attapulgite clay dispersion slurry for mixing.

[0056] Further, an aqueous solution of ferric chloride hexahydrate is added to the attapulgite clay dispersion slurry at 35-70°C, and mixing is continued for 0.5-2.0 h after addition to obtain a mixed system containing iron ions and attapulgite clay. The mixed system then enters the pH-induced hydrolysis deposition step.

[0057] Furthermore, the mixture of iron ions and attapulgite clay was adjusted with a 0.5-3.0 mol / L sodium hydroxide aqueous solution or a 0.5-2.0 mol / L anhydrous sodium carbonate aqueous solution. The pH value of the system was controlled to 6.8-8.2 within 0.5-4.0 h, and then aged at 45-70℃ for 1-4 h to obtain a solid-liquid mixture of in-situ hydrated iron oxide deposits.

[0058] Furthermore, the solid-liquid mixture of the in-situ sediment containing hydrated iron oxide was subjected to solid-liquid separation, and the filtrate was washed with deionized water until the pH value of the filtrate was 6.0-8.0. Then, it was dried at 80-120℃ for 2-8 hours to obtain the intermediate of hydrated iron oxide in-situ anchored attapulgite clay.

[0059] Furthermore, the pretreated attapulgite clay is obtained through water washing or acid washing. During water washing, 100 parts by weight of attapulgite clay are mixed with 300-1000 parts by weight of deionized water and stirred at 25-60℃ for 0.5-2.0 h. During acid washing, 100 parts by weight of attapulgite clay are mixed with 200-600 parts by weight of a 0.05-0.50 mol / L hydrochloric acid aqueous solution and stirred at 25-60℃ for 0.5-2.0 h. After solid-liquid separation, the clay is washed with deionized water until the pH of the washing solution is 6.0-8.0, and then dried at 80-110℃ for 2-8 h before sieving to a particle size of 0.048-0.125 mm to obtain the pretreated attapulgite clay.

[0060] Furthermore, in preparing the granulated hydrated iron oxide in-situ anchored attapulgite clay composite modifier, 100 parts by mass of the hydrated iron oxide in-situ anchored attapulgite clay intermediate are mixed with 25-80 parts by mass of deionized water to obtain a wet material; in addition to the hydrated iron oxide in-situ anchored attapulgite clay intermediate and the deionized water, the added auxiliary molding solid components are 0-3 wt% based on the total dry mass of the final adsorbent.

[0061] Furthermore, the auxiliary molding solid component is a silicon-aluminum inorganic binder powder.

[0062] Furthermore, the wet material is kneaded at 20-60℃ for 0.2-1.5 hours. The kneaded wet material is then granulated by extrusion, rounding, or pressing to form wet particles. The resulting wet particles then proceed to the drying and sieving steps. During the kneading and granulation process, hydrated iron oxide anchors the attapulgite clay intermediate and the separable iron components in situ, which then enter the particle skeleton. After drying and heat treatment, the particle skeleton is fixed, ensuring that the proportion of separable iron components in the final adsorbent particles is lower than or equal to the proportion of separable iron components in the intermediate.

[0063] Further, the wet granules are dried at 80-120℃ for 2-8 hours, and then sieved to obtain granules with a sieved particle size of 0.50-1.80 mm. The sieved granules are then heat-treated at 120-220℃ for 0.5-3.0 hours to obtain composite modified attapulgite clay adsorbent granules.

[0064] Furthermore, the iron leaching concentration of the adsorbent particles was determined by water sample testing. Adsorbent particles with a sieve diameter of 0.50-1.80 mm were placed in deionized water with a pH of 6.0-8.0 and contacted at a fixed solid-liquid ratio for 24 hours. After solid-liquid separation, water samples were obtained, and the iron concentration in the water samples was determined according to HJ700-2014 or its current effective version. The obtained iron concentration was taken as the iron leaching concentration of the adsorbent particles. The fixed solid-liquid ratio was calculated as the mass of dried adsorbent particles divided by the volume of deionized water and remained consistent in the same group of iron leaching comparison tests.

[0065] Furthermore, the proportion of free hydrated iron oxide to the total mass of hydrated iron oxide was determined by converting the separable iron component and the total iron component of the same sample. The dry basis sample was shaken in deionized water without the addition of acid, alkali and complexing agent for 24 hours. After solid-liquid separation, the iron-containing solid separated from the attapulgite clay matrix was collected. The iron content in the iron-containing solid was determined and converted into the mass of free hydrated iron oxide. At the same time, the total iron content of the same sample was determined and converted into the total mass of hydrated iron oxide according to Fe(OH)3. The proportion of free hydrated iron oxide was calculated as free hydrated iron oxide mass / total hydrated iron oxide mass × 100%. The obtained proportion was used to characterize the fixed state of hydrated iron oxide in intermediates or adsorbent particles. The proportion of free hydrated iron oxide was not calculated for samples without hydrated iron oxide.

[0066] Furthermore, the crushing strength of the particles was determined by a single-particle compression test. Dry adsorbent particles with a sieve size of 0.50-1.80 mm were taken as test samples. Compressive loads were applied to each particle of the test sample until the particles broke. The maximum load when a single particle broke was recorded and expressed in N / particle as the crushing strength.

[0067] Furthermore, the wear rate after 24 hours of oscillation in water was calculated by the change in dry basis mass. Adsorbent particles with a sieve particle size of 0.50-1.80 mm and a dry basis mass of m0 (g) were placed in water and oscillated for 24 hours. After solid-liquid separation, the retained particle components were collected and dried to a mass of m1 (g). The wear rate after 24 hours of oscillation in water was calculated as (m0−m1) / m0×100%.

[0068] Furthermore, the 24-hour static phosphorus adsorption capacity was calculated by the change in phosphorus concentration in the water sample before and after treatment. Adsorbent particles with a dry basis mass of m (g) were contacted with phosphorus-containing water samples with a volume of V (L) and a pH value of 5.0-9.0 for 24 hours. The phosphorus concentration C0 (mg / L) before contact and the phosphorus concentration Ct (mg / L) after contact were measured. The 24-hour static phosphorus adsorption capacity was calculated by (C0−Ct)×V / m, and the obtained value was expressed as mgP / g.

[0069] Furthermore, the stability of consecutive batches was calculated by measuring the content of hydrated iron oxide in the adsorbent particles prepared in three consecutive batches. The content of hydrated iron oxide (calculated as Fe(OH)3) in the adsorbent particles of the first, second, and third batches was measured respectively, and the average value and standard deviation of the hydrated iron oxide content of the three batches were calculated. The inter-batch coefficient of variation was calculated by multiplying the standard deviation by the average value by 100%. When the average value of the hydrated iron oxide content of the three batches was 0, the inter-batch coefficient of variation was not calculated.

[0070] Furthermore, the adsorbent particles after adsorption treatment are subjected to solid-liquid separation and then enter the regeneration step; the adsorbent particles after adsorption treatment are contacted with a 0.05-1.00 mol / L sodium hydroxide aqueous solution for 0.5-8.0 h, and after solid-liquid separation, regenerated adsorbent particles are obtained, which are then used for subsequent adsorption treatment.

[0071] As another aspect of this invention, the present invention employs in-situ anchoring of hydrated iron oxide in the preparation of wet attapulgite clay intermediates through kneading, granulation, drying, sieving, and optional heat treatment. This is primarily used to achieve, fix, or amplify the aforementioned synergistic effects. This method does not simply involve mixing iron-phase powder with mineral powder and then molding. Instead, it first establishes a bond between hydrated iron oxide and the surface and intercellular channels of attapulgite clay through pH-induced in-situ hydrolysis deposition. Then, by synergistically controlling the moisture content of the wet material, kneading temperature, granulation method, drying, and heat treatment, the strength of the interconnected pore walls and framework within the particles is controlled, ensuring a stable distribution of the active phase during preparation and use. The application of this invention's composite modified attapulgite clay adsorbent in industrial wastewater adsorption treatment is mainly used to maintain the aforementioned synergistic effects in fixed-bed, bag filter, or stirred adsorption reactors, allowing the material to meet the requirements of loading operation, adsorption contact, and regeneration under different influent pH and residence time conditions.

[0072] Attapulgite clay primarily serves as the support for the particle skeleton and pores, contributing to improved structural integrity. However, when used alone, it lacks sufficient active adsorption sites, limiting its ability to treat phosphorus-containing water. Hydrated iron oxide mainly provides phosphate binding sites, enhancing adsorption performance. However, if present in a free or highly exposed state, it is prone to aggregation, migration, and iron leaching, weakening particle stability. This invention utilizes pH-induced in-situ hydrolysis and deposition of ferric chloride hexahydrate in the aqueous phase to distribute hydrated iron oxide on the surface of attapulgite clay, in the pores between rod-shaped crystal bundles, and within the interconnected pore walls of the particles. By matching the attapulgite clay content, hydrated iron oxide content, auxiliary molding solid component content, and granulation heat treatment conditions, the mineral skeleton spatially confines the active iron phase, while the active iron phase maintains accessible sites. Ultimately, this achieves a balance between particle structural integrity and adsorption performance, as well as iron phase dispersion stability and low iron leaching.

[0073] Beneficial technical effects

[0074] 1. In-situ hydrolysis and deposition of ferric chloride hexahydrate in aqueous phase induced by pH allows hydrated iron oxide to form on the surface of attapulgite clay, in the channels between rod-shaped crystal bundles and in the interconnected pores within the particles. This reduces the proportion of free iron phase caused by simple mixed loading, which is beneficial for balancing adsorption site dispersion and iron leaching control.

[0075] 2. By matching the mass percentages of attapulgite clay, hydrated iron oxide, and auxiliary molding solid components, a mutually restrictive relationship is formed between the mineral framework, active iron phase, and auxiliary molding components within the particles. This can improve the accessibility of active sites in phosphorus-containing wastewater treatment while maintaining the granular engineering morphology.

[0076] 3. By kneading, extruding, rounding or pressing into granules, drying and sieving, and optional heat treatment of wet materials, the crushing strength of the particles and the wear rate after oscillation in water can be controlled. Compared with powder adsorbent materials, it is easier to fill fixed beds, filter bags and add to stirred adsorption reactors, reducing the difficulty of operation and separation.

[0077] 4. By pretreating attapulgite clay, contacting with iron salts, pH-induced deposition, washing and drying, and batch stability control, the content of hydrated iron oxide, the proportion of free hydrated iron oxide, and the particle size can be repeatedly adjusted during the preparation process, which is beneficial to improving the compositional stability of the adsorbent prepared in continuous batches.

[0078] 5. By limiting the influent pH, hydraulic retention time, and sodium hydroxide aqueous solution regeneration conditions in the application, the adsorbent can be adapted to various treatment methods for phosphorus-containing wastewater and enter the regeneration step after adsorption treatment, thereby improving the cost of existing disposable adsorbent materials and reducing post-treatment pressure. Attached Figure Description

[0079] Figure 1 The figure shows the effect of hydrated iron oxide content on the static phosphorus adsorption amount and particle crushing strength in this scheme over 24 hours.

[0080] Figure 2 The figure shows the effect of pH value on the static phosphorus adsorption amount and particle crushing strength of the pH-induced hydrolysis deposition scheme in this scheme over 24 hours.

[0081] Figure 3 The figure shows the effect of heat treatment temperature on the static phosphorus adsorption amount and particle crushing strength after 24 hours.

[0082] Figure 4 The graph shows the effect of the sieved particle size on the static phosphorus adsorption amount and particle crushing strength in this scheme over 24 hours.

[0083] Figure 5 The diagram shows the determination of iron phase separation by oscillation in water in Examples 1, 10, and 11.

[0084] Figure 6 This is a comparison chart of iron leaching concentrations in Example 1, Comparative Example 10, and Comparative Example 11.

[0085] Figure 7 The SEM-EDS field-view statistical Fe element area fraction plots for Example 1, Comparative Example 9, and Comparative Example 10 are shown.

[0086] Figure 8 The SEM-EDS field-view statistical Fe distribution variation coefficient plots are for Example 1, Comparative Example 10, and Comparative Example 11.

[0087] Figure 9 The graph shows a comparison of particle crushing strength and water abrasion rate for Examples 1, 6, and 7.

[0088] Figure 10 The diagram shows the particle cross-sectional pore area fraction of Example 1, Comparative Example 7, and Comparative Example 8.

[0089] Figure 11 The graph shows the particle cross-sectional pore wall continuity rating for Example 1, Comparative Example 7, and Comparative Example 8.

[0090] Figure 12 The graph shows the stability of hydrated iron oxide content in three consecutive batches of Examples 1, 4, and 5.

[0091] Figure 13 This is a comparison chart of the static phosphorus adsorption capacity of Example 1, Comparative Example 9, Comparative Example 10 and Comparative Example 11 over 24 hours.

[0092] Figure 14 The images show a comparison of the SEM morphology of the final product of Example 1 and the final product of Comparative Example 10; where a is a low-magnification SEM image of the final product of Example 1; b is a low-magnification SEM image of the final product of Comparative Example 10; c is a medium-magnification SEM image of the final product of Example 1; d is a medium-magnification SEM image of the final product of Comparative Example 10; e is a high-magnification SEM image of the final product of Example 1; and f is a high-magnification SEM image of the final product of Comparative Example 10.

[0093] Figure 15 The images show a comparison of the TEM structures of the final product of Example 1 and the final product of Comparative Example 10; where a is a bright-field TEM image of the final product of Example 1; b is a bright-field TEM image of the final product of Comparative Example 10; c is an HRTEM image of the final product of Example 1; d is an HRTEM image of the final product of Comparative Example 10; e is a SAED and elemental distribution map of the final product of Example 1; and f is a SAED and elemental distribution map of the final product of Comparative Example 10.

[0094] Figure 16 The image shows the evolution of macroscopic optical photographs from S1 to the final product in Example 1; where a is a macroscopic optical photograph of commercially available attapulgite clay raw material in S1; b is a macroscopic optical photograph of pretreated attapulgite clay in S2; c is a macroscopic optical photograph of the sampled product of the mixed system containing iron ions and attapulgite in S3; and d is a macroscopic optical photograph of the intermediate attapulgite clay with in-situ anchored hydrated iron oxide in S4. Detailed Implementation

[0095] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0096] Example 1

[0097] S1: With the goal of preparing 1000g of composite modified attapulgite clay adsorbent particles on a dry basis, the final dry basis composition of this embodiment is set as follows: 940g of attapulgite clay, 60g of hydrated iron oxide (calculated as Fe(OH)3), and 0g of auxiliary molding solid components. The attapulgite clay is a commercially available mineral powder with a dry basis content ≥95wt%, and pre-sieve agglomerates are crushed before use; ferric chloride hexahydrate is an analytical grade reagent; sodium hydroxide is prepared into an aqueous solution using an analytical grade reagent; and the conductivity of deionized water is ≤5μS / cm.

[0098] S2: Preparation of pretreated attapulgite clay. 100 parts by weight of attapulgite clay were mixed with 1000 parts by weight of deionized water and mechanically stirred for 0.5 hours at 25°C, normal pressure, and air atmosphere at a stirring speed of 300 rpm. After solid-liquid separation, the mixture was washed with deionized water until the pH of the washing solution reached 6.0. It was then dried at 80°C for 2 hours and sieved to a particle size of 0.048 mm to obtain the pretreated attapulgite clay. In this embodiment, the pH of the pretreated attapulgite clay dispersion slurry in water was 6.0.

[0099] S3: Preparation of an intermediate for in-situ anchoring attapulgite clay with hydrated iron oxide. 100 parts by mass of pretreated attapulgite clay were added to 900 parts by mass of deionized water and mechanically stirred at 25°C for 30 min to obtain an attapulgite clay dispersion slurry with a solid content of 10 wt%. Separately, 15 parts by mass of ferric chloride hexahydrate were dissolved in 500 parts by mass of deionized water to obtain an aqueous solution of ferric chloride hexahydrate. The attapulgite clay dispersion slurry was heated to 35°C, and the aqueous solution of ferric chloride hexahydrate was added to the dispersion slurry at a mechanical stirring speed of 400 rpm for 20 min. After addition, mixing continued for 0.5 h to obtain a mixed system containing iron ions and attapulgite clay.

[0100] S4: pH-induced hydrolysis deposition was performed on a mixed system containing iron ions and attapulgite clay. The pH of the system was adjusted using a 0.5 mol / L sodium hydroxide aqueous solution, and the pH was controlled to 6.8 within 0.5 h. During the adjustment process, the temperature was maintained at 45 °C and the stirring speed at 400 rpm. After the pH reached 6.8, the system was aged at 45 °C for 1 h. After aging, solid-liquid separation was performed, and the filtrate was washed with deionized water until the pH of the filtrate was 6.0. Then, it was dried at 80 °C for 2 h to obtain an intermediate of hydrated iron oxide anchored in attapulgite clay. In this embodiment, the intermediate contained 6 wt% hydrated iron oxide (Fe(OH)3) on a dry basis, and the proportion of free hydrated iron oxide to the total mass of hydrated iron oxide was 15 wt%.

[0101] S5: 100 parts by mass of hydrated iron oxide in-situ anchored attapulgite clay intermediate were mixed with 25 parts by mass of deionized water to obtain a wet material; no auxiliary molding solid components were added in this embodiment. The wet material was kneaded at 20°C for 0.2 hours at a kneading speed of 40 rpm. At the end of kneading, the wet material was in the form of a uniform plastic agglomerate with no obvious dry powder. The kneaded wet material was extruded and granulated to form wet granules. The wet granules were dried at 80°C for 2 hours and then sieved to obtain granules with a sieve particle size of 0.50 mm. The sieved granules were heat-treated at 120°C for 0.5 hours and then naturally cooled to room temperature (25°C) to obtain composite modified attapulgite clay adsorbent granules.

[0102] S6: Quality Testing Methods and Results. The hydrated iron oxide content was calculated using the total iron content as Fe(OH)3, and the test was repeated three times, yielding a result of 6.0 ± 0.2 wt%. Adsorbent particles with a sieve diameter of 0.50 mm were placed in deionized water at pH 6.0 at a fixed solid-liquid ratio for 24 hours. After solid-liquid separation, a water sample was obtained, and the iron concentration in the water sample was determined according to HJ700-2014 or its current effective version. The iron leaching concentration was 1.00 ± 0.02 mg / L. A dry basis sample was shaken in deionized water without the addition of acid, alkali, or complexing agents for 24 hours. Separable iron-containing solids were collected and converted; the proportion of free hydrated iron oxide to the total mass of hydrated iron oxide in the adsorbent particles was 12.0 ± 0.5 wt%. The single-particle compression test yielded a particle crushing strength of 3.0 ± 0.2 N / particle. Particles with a dry basis mass of m0 (g) were placed in water and shaken for 24 h, then recovered and dried to m1 (g). Based on the mass change, the attenuation rate after shaking in water for 24 h was 8.00 ± 0.10 wt%. Adsorbent particles with a dry basis mass of m (g) were contacted with a phosphorus-containing water sample of volume V (L) and pH 5.0 for 24 h. Based on the change in phosphorus concentration before and after treatment, the static phosphorus adsorption capacity after 24 h was 5.0 ± 0.3 mg P / g. The inter-batch coefficient of variation for the hydrated iron oxide content (calculated as Fe(OH)3) of the adsorbent particles prepared in three consecutive batches was 15.0%.

[0103] S7: Features and application scenarios of this embodiment. This embodiment adopts a relatively conservative low-ratio scheme, with low hydrated iron oxide content, low moisture content in the wet material, mild preparation conditions, and small particle size, making it suitable for fixed-bed rapid contact applications with an influent pH of 5.0 and a hydraulic retention time of 5 min. The adsorption-treated particles are contacted with a 0.05 mol / L sodium hydroxide aqueous solution for 0.5 h followed by solid-liquid separation, and can then be used for subsequent adsorption treatment.

[0104] Example 2

[0105] Raw materials and proportions: Composite modified attapulgite clay adsorbent particles were prepared at a dry basis of 1000g. The final dry basis composition of this embodiment includes 750g of attapulgite clay, 220g of hydrated iron oxide (calculated as Fe(OH)3), and 30g of auxiliary molding solid component. The auxiliary molding solid component is a commercially available silica-alumina inorganic binder powder with a total silica and alumina content ≥90wt% and an average particle size ≤45μm. The attapulgite clay is a commercially available mineral powder with a dry basis content ≥95wt%; ferric chloride hexahydrate, sodium hydroxide, and hydrochloric acid are all analytical grade reagents; the conductivity of deionized water is ≤5μS / cm.

[0106] Pretreatment process: 100 parts by weight of attapulgite clay were mixed with 600 parts by weight of 0.50 mol / L hydrochloric acid aqueous solution, and stirred for 2.0 h at 60℃, normal pressure, and air atmosphere, with a stirring speed of 500 rpm. After solid-liquid separation, the mixture was washed with deionized water until the pH of the washing solution was 8.0, dried at 110℃ for 8 h, and then sieved to a particle size of 0.125 mm to obtain pretreated attapulgite clay. In this embodiment, the pH of the pretreated attapulgite clay dispersion slurry in water was 8.5.

[0107] Intermediate preparation process: 100 parts by mass of pretreated attapulgite clay were dispersed in 300 parts by mass of deionized water and stirred at 35°C for 40 min to obtain an attapulgite clay dispersion slurry with a solid content of 25 wt%. 75 parts by mass of ferric chloride hexahydrate were dissolved in 100 parts by mass of deionized water to obtain an aqueous solution of ferric chloride hexahydrate. The attapulgite clay dispersion slurry was heated to 70°C, and the aqueous solution of ferric chloride hexahydrate was added at a stirring speed of 500 rpm over 30 min. After addition, mixing continued for 2.0 h. Subsequently, the pH of the system was adjusted to 8.2 using a 3.0 mol / L sodium hydroxide aqueous solution over 4.0 h, and aged at 70°C for 4 h. The aged solid-liquid mixture was subjected to solid-liquid separation, washed with deionized water until the pH of the filtrate was 8.0, and then dried at 120°C for 8 h to obtain an intermediate of hydrated iron oxide-anchored attapulgite clay. In this embodiment, the intermediate, calculated on a dry basis, contains 22 wt% hydrated iron oxide (Fe(OH)3), and the proportion of free hydrated iron oxide to the total mass of hydrated iron oxide is 8.0 wt%.

[0108] Granulation and Post-processing: 100 parts by weight of hydrated iron oxide-anchored attapulgite clay intermediate were mixed with 80 parts by weight of deionized water, and 3 wt% of commercially available silica-alumina inorganic binder powder (based on the total dry weight of the final adsorbent) was added to obtain a wet material. The wet material was kneaded at 60℃ for 1.5 h at a kneading speed of 60 rpm. At the end of kneading, the surface of the wet material was uniform, could be formed into continuous strips, and had no obvious free water. The kneaded wet material was then granulated by rounding to form wet granules. The wet granules were dried at 120℃ for 8 h, and then sieved to obtain granules with a sieve diameter of 1.80 mm. The sieved granules were heat-treated at 220℃ for 3.0 h, and then naturally cooled to room temperature (25℃) to obtain composite modified attapulgite clay adsorbent granules.

[0109] Quality testing methods and results: The content of hydrated iron oxide was calculated by converting the total iron content to Fe(OH)3. The test was repeated three times, and the result was 22.0±0.4wt%. Adsorbent particles with a sieve diameter of 1.80 mm were placed in deionized water with a pH of 8.0 at a fixed solid-liquid ratio for 24 hours. After solid-liquid separation, water samples were obtained, and the iron concentration in the water samples was determined according to HJ700-2014 or its current effective version. The iron leaching concentration was 0.15±0.01 mg / L. Based on the conversion between separable iron components and total iron components, the proportion of free hydrated iron oxide in the adsorbent particles to the total mass of hydrated iron oxide was 6.0±0.4wt%. The single-particle compression test yielded a particle crushing strength of 35.0±1.5 N / particle. Calculated based on dry basis mass change, the abrasion rate after 24 hours of shaking in water was 2.00±0.15wt%. Adsorbent particles with a dry basis mass of m (g) were contacted with a phosphorus-containing water sample with a volume of V (L) and a pH of 9.0 for 24 h. Based on the change in phosphorus concentration before and after treatment, the static phosphorus adsorption capacity after 24 h was calculated to be 45.0 ± 1.8 mg P / g. The inter-batch coefficient of variation of the hydrated iron oxide content (calculated as Fe(OH)3) of the adsorbent particles prepared in three consecutive batches was 5.0%.

[0110] The features of this embodiment are as follows: This embodiment adopts an optimized scheme with a relatively high loading, a high content of hydrated iron oxide, and a high moisture content in the wet material. It also utilizes a silica-alumina inorganic binder powder to assist in molding, making it suitable for fixed-bed deep contact applications with an influent pH of 9.0 and a hydraulic retention time of 60 min. The adsorption-treated particles are contacted with a 1.00 mol / L sodium hydroxide aqueous solution for 8.0 h followed by solid-liquid separation, and can then be used for subsequent adsorption treatment.

[0111] Example 3

[0112] In this embodiment, 1000g of composite modified attapulgite clay adsorbent particles (dry basis) were used as the preparation material. The final dry basis composition was set as follows: 860g of attapulgite clay, 140g of hydrated iron oxide (calculated as Fe(OH)3), and 0g of auxiliary molding solid components. The attapulgite clay was commercially available mineral powder with a dry basis content ≥95wt%; ferric chloride hexahydrate was prepared using analytical grade reagent; anhydrous sodium carbonate was prepared into an aqueous solution using analytical grade reagent; and the conductivity of deionized water was ≤5μS / cm.

[0113] Key parameters and sample conditions are as follows: Pretreatment adopted a water washing route; the solid content of the attapulgite clay dispersion slurry was 18 wt%; the amount of ferric chloride hexahydrate was 45 parts by mass; the amount of deionized water used to prepare the ferric chloride hexahydrate aqueous solution was 300 parts by mass; the iron salt contact temperature was 52℃; mixing continued for 1.2 h after addition; pH-induced hydrolysis deposition was carried out using a 2.0 mol / L anhydrous sodium carbonate aqueous solution; the system pH value was controlled at 7.5; the pH adjustment time was 2.0 h; the aging temperature was 58℃; the aging time was 2.5 h; the mass ratio of hydrated iron oxide in situ anchoring of attapulgite clay intermediate to deionized water in the granulated wet material was 100:50; the kneading temperature was 40℃; the kneading time was 0.8 h; the sieve particle size was 1.10 mm.

[0114] In the preparation process, 100 parts by weight of attapulgite clay were first mixed with 300 parts by weight of deionized water and stirred for 2.0 h at 60°C, normal pressure, and air atmosphere, with a stirring speed of 450 rpm. After solid-liquid separation, the mixture was washed with deionized water until the pH of the washing solution was 7.0, dried at 95°C for 5 h, and then sieved to a particle size of 0.080 mm to obtain pretreated attapulgite clay. In this embodiment, the pH of the pretreated attapulgite clay dispersion slurry in water was 7.2.

[0115] Subsequently, 100 parts by mass of pretreated attapulgite clay were dispersed in approximately 456 parts by mass of deionized water to prepare an attapulgite clay dispersion slurry with a solid content of 18 wt%. 45 parts by mass of ferric chloride hexahydrate were dissolved in 300 parts by mass of deionized water to obtain an aqueous solution of ferric chloride hexahydrate. The aqueous solution of ferric chloride hexahydrate was added to the attapulgite clay dispersion slurry at 52 °C, and mixing continued for 1.2 h at a stirring speed of 450 rpm. The pH of the system was controlled to 7.5 within 2.0 h using a 2.0 mol / L anhydrous sodium carbonate aqueous solution, and then aged at 58 °C for 2.5 h. After aging, solid-liquid separation was performed, and the filtrate was washed with deionized water until the pH of the filtrate was 7.0. The filtrate was then dried at 100 °C for 5 h to obtain an intermediate of hydrated iron oxide-anchored attapulgite clay. In this embodiment, the intermediate, calculated on a dry basis, contains 14 wt% hydrated iron oxide (Fe(OH)3), and the proportion of free hydrated iron oxide to the total mass of hydrated iron oxide is 10.0 wt%.

[0116] During molding, 100 parts by weight of hydrated iron oxide in-situ anchored attapulgite clay intermediate were mixed with 50 parts by weight of deionized water to obtain a wet material. The wet material was kneaded at 40℃ for 0.8 hours at a kneading speed of 50 rpm. At the end of kneading, the wet material exhibited uniform plasticity and did not crack at the edges after pressing. The kneaded wet material was then granulated by pressing to form wet granules. The wet granules were dried at 100℃ for 5 hours and then sieved to obtain granules with a sieve particle size of 1.10 mm. The sieved granules were then heat-treated at 160℃ for 1.5 hours and cooled to room temperature (25℃) to obtain composite modified attapulgite clay adsorbent granules.

[0117] Quality testing methods and results: The content of hydrated iron oxide was calculated by converting the total iron content to Fe(OH)3. The test was repeated three times, and the result was 14.0±0.3wt%. Adsorbent particles with a sieve diameter of 1.10 mm were placed in deionized water with a pH of 7.0 at a fixed solid-liquid ratio for 24 hours. After solid-liquid separation, water samples were obtained, and the iron concentration in the water samples was determined according to HJ700-2014 or its current effective version. The iron leaching concentration was 0.45±0.03 mg / L. Based on the conversion between separable iron components and total iron components, the proportion of free hydrated iron oxide in the adsorbent particles to the total mass of hydrated iron oxide was 9.0±0.5wt%. The single-particle compression test yielded a particle crushing strength of 18.0±0.8 N / particle. Calculated based on dry basis mass change, the abrasion rate after 24 hours of shaking in water was 4.00±0.20wt%. Adsorbent particles with a dry basis mass of m (g) were contacted with a phosphorus-containing water sample with a volume of V (L) and a pH of 7.0 for 24 h. Based on the change in phosphorus concentration before and after treatment, the static phosphorus adsorption capacity after 24 h was calculated to be 28.0 ± 1.0 mg P / g. The inter-batch coefficient of variation of the hydrated iron oxide content (calculated as Fe(OH)3) of the adsorbent particles prepared in three consecutive batches was 8.0%.

[0118] The applicable scenario for this embodiment: This embodiment uses anhydrous sodium carbonate aqueous solution to adjust the pH value of the system. The ratio and process parameters are in the middle range, taking into account both granulation processability and the dispersion state of the active phase. It is suitable for medium-intensity operation in fixed bed, filter bag, or stirred adsorption reactors. The adsorption-treated particles are contacted with 0.50 mol / L sodium hydroxide aqueous solution for 4.0 h for solid-liquid separation and can be used for subsequent adsorption treatment.

[0119] Example 4

[0120] I. Preparation Object and Raw Material State: Composite modified attapulgite clay adsorbent particles were prepared at a dry basis of 1000g. The final dry basis composition of this embodiment includes 820g of attapulgite clay, 160g of hydrated iron oxide (calculated as Fe(OH)3), and 20g of auxiliary molding solid component. The auxiliary molding solid component is a commercially available silica-alumina inorganic binder powder with a total silica and alumina content ≥90wt% and an average particle size ≤45μm. The attapulgite clay is a commercially available mineral powder with a dry basis content ≥95wt%; ferric chloride hexahydrate, anhydrous sodium carbonate, and hydrochloric acid are analytical grade reagents; the conductivity of deionized water is ≤5μS / cm.

[0121] II. Preparation of Pretreated Attapulgite Clay: 100 parts by weight of attapulgite clay were mixed with 200 parts by weight of 0.05 mol / L hydrochloric acid aqueous solution. The mixture was stirred for 0.5 h at 25°C, normal pressure, and air atmosphere, with a stirring speed of 350 rpm. After solid-liquid separation, the mixture was washed with deionized water until the pH of the washing solution was 6.0, and then dried at 80°C for 2 h. The resulting solution was then sieved to a particle size of 0.048 mm to obtain pretreated attapulgite clay. In this embodiment, the pH of the pretreated attapulgite clay dispersion slurry in water was 6.5.

[0122] III. In-situ Deposition of Hydrated Iron Oxide: 100 parts by mass of pretreated attapulgite clay were dispersed in 650 parts by mass of deionized water to form an attapulgite clay dispersion slurry with a solid content of approximately 13.3 wt%. 50 parts by mass of ferric chloride hexahydrate were dissolved in 200 parts by mass of deionized water to obtain an aqueous solution of ferric chloride hexahydrate. The aqueous solution of ferric chloride hexahydrate was added to the attapulgite clay dispersion slurry at 60°C, and mixing continued for 1.5 h at a stirring speed of 450 rpm. The pH of the system was controlled to 8.2 within 0.5 h using a 0.5 mol / L anhydrous sodium carbonate aqueous solution, and then aged at 70°C for 1 h to obtain a solid-liquid mixture containing hydrated iron oxide in-situ deposits.

[0123] IV. Washing and Drying of Intermediate: The solid-liquid mixture containing hydrated iron oxide in situ sediment was subjected to solid-liquid separation, and washed with deionized water until the pH of the filtrate was 8.0. The filtrate was then dried at 120°C for 2 hours to obtain an intermediate containing hydrated iron oxide in situ anchored attapulgite clay. In this embodiment, the intermediate contained 16 wt% hydrated iron oxide (Fe(OH)3) on a dry basis, and the proportion of free hydrated iron oxide to the total mass of hydrated iron oxide was 11.0 wt%.

[0124] V. Granulation Process: 100 parts by weight of hydrated iron oxide-anchored attapulgite clay intermediate were mixed with 35 parts by weight of deionized water, and 2 wt% of commercially available silica-alumina inorganic binder powder (based on the total dry weight of the final adsorbent) was added to obtain a wet material. The wet material was kneaded at 25°C for 1.5 hours at a kneading speed of 45 rpm. At the end of kneading, the wet material had a uniform color, no obvious dry powder agglomeration, and could be continuously pressed into shape. The kneaded wet material was granulated by pressing to form wet granules. The wet granules were dried at 120°C for 8 hours, and then sieved to obtain granules with a sieve particle size of 1.50 mm. The sieved granules were heat-treated at 200°C for 0.5 hours and cooled to room temperature (25°C) to obtain composite modified attapulgite clay adsorbent granules.

[0125] VI. Quality Testing Methods and Results: The content of hydrated iron oxide was calculated by converting the total iron content to Fe(OH)3. The test was repeated three times, and the result was 16.0±0.3wt%. Adsorbent particles with a sieve diameter of 1.50 mm were placed in deionized water with a pH of 8.0 at a fixed solid-liquid ratio for 24 hours. After solid-liquid separation, water samples were obtained, and the iron concentration in the water samples was determined according to HJ700-2014 or its current effective version. The iron leaching concentration was 0.30±0.02 mg / L. Based on the conversion between separable iron components and total iron components, the proportion of free hydrated iron oxide in the adsorbent particles to the total mass of hydrated iron oxide was 10.0±0.4wt%. The single-particle compression test yielded a particle crushing strength of 26.0±1.0 N / particle. Calculated based on dry basis mass change, the abrasion rate after 24 hours of shaking in water was 3.20±0.20wt%. When the same batch of granules was used on phosphorus-containing water samples, the static phosphorus adsorption capacity after 24 hours was 32.0 ± 1.2 mg P / g. The coefficient of variation between batches of hydrated iron oxide content (calculated as Fe(OH)3) in the adsorbent granules prepared in three consecutive batches was 10.0%.

[0126] VII. Process Features and Application Directions of this Embodiment: This embodiment employs a low-concentration hydrochloric acid aqueous solution for pretreatment and anhydrous sodium carbonate aqueous solution for rapid pH adjustment of the system. It also utilizes silica-alumina inorganic binder powder to assist in particle forming, making it suitable for filter bag filling or addition to stirred adsorption reactors. The adsorption-treated particles are contacted with a 1.00 mol / L sodium hydroxide aqueous solution for 0.5 hours for solid-liquid separation, and can then be used for subsequent adsorption treatment.

[0127] Comparative Example 1: It is basically the same as Example 1, except that in step S2, no water washing pretreatment is performed. The crushed commercially available attapulgite clay is directly screened to a particle size of 0.048 mm and then proceeds to step S3. Other conditions remain unchanged.

[0128] Comparative Example 2: It is basically the same as Example 1, except that the amount of ferric chloride hexahydrate in step S3 is adjusted from 15 parts by mass to 10 parts by mass. The ferric chloride hexahydrate is still dissolved in 500 parts by mass of deionized water, and other conditions remain unchanged.

[0129] Comparative Example 3: It is basically the same as Example 1, except that the temperature when adding the ferric chloride hexahydrate aqueous solution to the attapulgite clay dispersion slurry in step S3 is adjusted from 35°C to 25°C, while other conditions remain unchanged.

[0130] Comparative Example 4: Basically the same as Example 1, except that in step S4, a 0.5 mol / L sodium hydroxide aqueous solution was used to control the pH of the system to 6.2 within 0.5 h, while other conditions remained unchanged.

[0131] Comparative Example 5: It is basically the same as Example 1, except that in step S4, after the pH value reaches 6.8, it is aged at 45°C for 0.3 hours, while other conditions remain unchanged.

[0132] Comparative Example 6: It is basically the same as Example 1, except that in step S5, 100 parts by mass of the hydrated iron oxide in-situ anchored attapulgite clay intermediate is mixed with 15 parts by mass of deionized water to obtain a wet material, and other conditions remain unchanged.

[0133] Comparative Example 7: It is basically the same as Example 1, except that the sieved particles in step S5 are not subjected to heat treatment at 120°C for 0.5 hours, and are naturally cooled to room temperature of 25°C after sieving, while other conditions remain unchanged.

[0134] Comparative Example 8: It is basically the same as Example 1, except that in step S5, after drying, the particles were sieved to obtain particles with a sieve size of 2.20 mm. Other conditions remain unchanged.

[0135] Comparative Example 9: Essentially the same as Example 1, except that ferric chloride hexahydrate aqueous solution was not added in step S3, and pH-induced hydrolysis deposition was not performed in step S4. The pretreated attapulgite clay obtained in step S2 was directly subjected to solid-liquid separation, washed until the pH of the filtrate was 6.0, and dried at 80°C for 2 hours. Then, it was mixed with 25 parts by mass of deionized water according to step S5, kneaded, extruded and granulated, dried, sieved, and heat-treated, with other conditions remaining unchanged. This comparative example was used to verify the synergistic effect of attapulgite clay and hydrated iron oxide.

[0136] Comparative Example 10: This example is essentially the same as Example 1, except that instead of using the in-situ anchoring method of hydrated iron oxide on attapulgite clay, hydrated iron oxide solid was prepared in an aqueous phase without the addition of attapulgite clay, following the iron salt dosage, pH value, temperature, stirring, and aging conditions of steps S3 and S4 in Example 1. The solid was washed until the pH of the filtrate reached 6.0, dried at 80°C for 2 hours, and then ground through a 0.048 mm sieve. Pretreated attapulgite clay and the hydrated iron oxide dry powder were then mechanically mixed at a dry weight ratio of 94:6 for 30 minutes. Subsequently, wet material preparation, kneading, extrusion granulation, drying, sieving, and heat treatment were performed according to step S5, with other conditions remaining unchanged. This comparative example was used to verify the synergistic effect between the in-situ anchoring interface of hydrated iron oxide and the attapulgite clay carrier.

[0137] Comparative Example 11: This example is essentially the same as Example 1, except that the order of in-situ deposition and granulation of hydrated iron oxide is changed. First, the pretreated attapulgite clay obtained in step S2 is mixed with 25 parts by mass of deionized water, kneaded, extruded and granulated, dried at 80°C for 2 hours, and sieved to 0.50 mm particles. Then, the particles are placed in an aqueous solution of ferric chloride hexahydrate, and the pH of the system is controlled to 6.8 using a 0.5 mol / L sodium hydroxide aqueous solution at 45°C and 400 rpm, and aged for 1 hour to achieve a final dry basis hydrated iron oxide content of 6 wt% (based on Fe(OH)3). The filtrate is then washed until the pH is 6.0, dried at 80°C for 2 hours, and heat-treated at 120°C for 0.5 hours, with other conditions remaining unchanged. This comparative example is used to verify the synergistic effect of in-situ anchoring of hydrated iron oxide and the control of the granulation sequence.

[0138] Characterization and performance testing:

[0139] Unless otherwise stated, the iron leaching concentration, free hydrated iron oxide ratio, 24-hour static phosphorus adsorption, particle crushing strength, and abrasion rate after 24 hours of shaking in water are all judged using the arithmetic mean of no less than three parallel samples as the corresponding parameter caliber. The values ​​after “±” in Table 1 represent the standard deviation of parallel tests, and the inter-batch coefficient of variation is calculated as the standard deviation / average of the hydrated iron oxide content of three consecutive batches × 100%, which is a separately calculated value.

[0140] The hydrated iron oxide content and batch-to-batch stability experiment was used to evaluate the active iron phase loading level and consistency of continuous preparation in the adsorbent. Dry granules were ground uniformly, digested with acid, and the total iron content was determined by ICP-OES or ICP-MS. The hydrated iron oxide content was then converted to Fe(OH)3 based on the mass of iron. Three batches of samples were prepared consecutively, with each batch tested in triplicate. The mean, standard deviation, and batch-to-batch coefficient of variation were calculated. The corresponding data recording fields for this experiment are the mean hydrated iron oxide content, the standard deviation of hydrated iron oxide content, and the batch-to-batch coefficient of variation, in units of wt%, wt%, and %, respectively. The hydrated iron oxide content was evaluated within a set range; a lower batch-to-batch coefficient of variation indicates better stability. When the mean hydrated iron oxide content is 0, the batch-to-batch coefficient of variation is not applicable.

[0141] Iron leaching experiments are used to evaluate the immobilization state of hydrated iron oxide in particles and its safety in the aquatic environment. Dry adsorbent particles with a sieve diameter of 0.50-1.80 mm are placed in deionized water with a pH of 6.0-8.0 at a fixed solid-liquid ratio for 24 hours. After solid-liquid separation, a supernatant sample is taken, and the iron concentration is determined according to HJ700-2014 or its current valid version, with at least three parallel samples. The corresponding data recording fields for this experiment are the average iron leaching concentration and the standard deviation of the iron leaching concentration, in mg / L. Lower values ​​indicate a better iron phase immobilization state. The fixed solid-liquid ratio is calculated as the mass of dry adsorbent particles divided by the volume of deionized water and is kept consistent throughout the same group of iron leaching comparison tests.

[0142] The free hydrated iron oxide ratio experiment is used to evaluate the degree of anchoring between hydrated iron oxide and attapulgite clay. Dry granular samples are placed in deionized water without added acid, alkali, or complexing agents and shaken for 24 hours. After solid-liquid separation, the iron-containing solid separated from the attapulgite clay matrix is ​​collected. The iron content in this solid is determined and converted to the mass of free hydrated iron oxide. Simultaneously, the total iron content of the same sample is determined and converted to the total mass of hydrated iron oxide as Fe(OH)3. The corresponding data recording fields for this experiment are the average and standard deviation of the free hydrated iron oxide ratio, in wt%. Lower values ​​indicate a more stable anchoring state. The free hydrated iron oxide ratio is not applicable to samples without hydrated iron oxide and with a total hydrated iron oxide mass of 0.

[0143] The 24-hour static phosphorus adsorption experiment was used to evaluate the removal capacity of the adsorbent for phosphate in phosphorus-containing wastewater. Adsorbent particles with a dry basis mass of m (g) were contacted with a phosphorus-containing water sample of volume V (L) for 24 hours. The pH value of the water sample was set and recorded according to the sample application conditions. The phosphorus concentrations C0 (mg / L) and Ct (mg / L) were measured before and after contact. The 24-hour static phosphorus adsorption capacity was calculated as (C0−Ct)×V / m. At least three parallel samples were used, and obvious operational anomalies were discarded. The corresponding data recording fields for this experiment are the average and standard deviation of the 24-hour static phosphorus adsorption capacity, in mgP / g. Higher values ​​indicate better adsorption performance.

[0144] The particle crushing strength test is used to evaluate the structural integrity of granular adsorbents in fixed-bed, filter-bag, and stirred-adsorption scenarios. Dry adsorbent particles with a sieve diameter of 0.50-1.80 mm are taken and subjected to individual particle compression tests on a single-particle compression testing device until the particles break. The maximum load at the moment of breakage is recorded. At least 30 particles are tested for each sample. After removing obviously non-spherical or broken particles, the mean and standard deviation are calculated. The corresponding data recording fields for this experiment are the mean and standard deviation of particle crushing strength, in N / particle. Higher values ​​indicate better particle compressive integrity.

[0145] The abrasion rate experiment after 24 hours of oscillation in water was used to evaluate the abrasion resistance of particles under hydraulic disturbance. Sieve particles with a dry basis mass of m0 (g) were placed in deionized water and oscillated for 24 hours. After oscillation, solid-liquid separation was performed, and the retained particles were collected and dried to a constant weight of m1 (g). The abrasion rate was calculated as (m0−m1) / m0 × 100%. At least three parallel samples were set up for each sample, and the oscillation frequency, solid-liquid ratio, and drying conditions were recorded. The corresponding data recording fields for this experiment are the average and standard deviation of the abrasion rate after 24 hours of oscillation in water, in wt%. The lower the value, the better the particle's resistance to water disturbance.

[0146] SEM-EDS field-of-view statistics were used to evaluate the loading level and dispersion of the iron phase in the micro-regions of particles. Dry particle samples were subjected to SEM-EDS surface scanning. The same sample preparation method, observation magnification, field-of-view selection rules, and energy dispersive spectroscopy (EDS) acquisition parameters were used for the same set of comparative samples. The Fe elemental area fraction was statistically analyzed as the proportion of the Fe signal region within the total field of view according to the same threshold rule. The Fe distribution coefficient of variation was calculated as the standard deviation / average of the Fe elemental area fraction across multiple fields of view × 100%. The corresponding data recording fields for this experiment are the Fe elemental area fraction and the Fe distribution coefficient of variation, which are used to characterize the iron phase loading level and the uniformity of iron phase distribution, respectively.

[0147] Figures 1 to 4This method is used to illustrate the synergistic effect of key process parameters on the adsorption performance and particle mechanical stability of the composite modified attapulgite clay adsorbent. Addressing the common contradiction in existing iron-containing adsorbents—limited adsorption capacity when iron phase loading is insufficient, and decreased particle strength or easy detachment of the iron phase when iron phase loading is too high—this method first uses the preparation conditions of Example 1 as a basis, only changing the hydrated iron oxide content, and investigates its effect on the 24-hour static phosphorus adsorption capacity and particle crushing strength. Figure 1 As shown, when the hydrated iron oxide content varies within the range of 4–26 wt%, with the increase of hydrated iron oxide content, the effective iron phase points available for phosphate binding in the material increase, and the static phosphorus adsorption capacity at 24 h is significantly improved. Simultaneously, an appropriate amount of iron phase can fill and strengthen the attapulgite particle skeleton, thus improving the particle crushing strength. However, when the hydrated iron oxide content is further too high, the iron phase is prone to local enrichment or agglomeration, weakening the continuity of the attapulgite skeleton and leading to a decrease in particle crushing strength. Therefore, a higher hydrated iron oxide content is not necessarily more beneficial; rather, a content around 16 wt% can better balance phosphorus adsorption performance and particle structure stability. This indicates that the proposed method can effectively balance adsorption capacity and engineering performance by controlling the iron phase loading. The above patterns are the results of a single-variable investigation under the preparation conditions of Example 1. Examples 2-4, by simultaneously adjusting the moisture content of the wet material, the amount of auxiliary molding solid components, and the heat treatment temperature, achieved higher particle crushing strength at higher hydrated iron oxide contents. Figure 1 The univariate trends shown have different applicable conditions.

[0148] Based on the established significant impact of iron phase content on overall performance, the influence of pH-induced hydrolysis deposition conditions on the in-situ formation and fixation of hydrated iron oxide was further investigated. Figure 2 As shown, based on the preparation conditions of Example 1, when only the deposition pH value is adjusted within the range of 6.4–8.6, too low a pH leads to insufficient hydrolysis of iron ions, resulting in low deposition and effective loading of hydrated iron oxide, thus limiting phosphorus adsorption and particle reinforcement. Conversely, too high a pH causes excessively rapid iron phase hydrolysis and deposition, easily leading to non-uniform deposition or local agglomeration, reducing particle structure uniformity and adversely affecting crushing strength. When the deposition pH is controlled at approximately 7.5, the 24-hour static phosphorus adsorption and particle crushing strength of the sample are at optimal levels, indicating that moderate pH conditions are beneficial for the gradual hydrolysis and deposition of iron ions on the surface and in the pore structure of attapulgite, forming a stable, effective, and dispersed hydrated iron oxide loading structure.

[0149] Figure 3The effect of heat treatment temperature on the stabilization process of composite particles is further explained. Based on Example 1, by simply changing the heat treatment temperature and controlling it within the range of 100–240℃, as the heat treatment temperature increases, the internal moisture of the particles is gradually removed, the bond between the attapulgite framework and the iron phase becomes more stable, and the crushing strength of the particles increases accordingly. However, when the temperature is too high, hydrated iron oxide may undergo excessive dehydration or structural densification, resulting in a reduction in the hydroxyl sites and effective contact area that can participate in phosphate adsorption, thereby weakening the static phosphorus adsorption capacity. The results show that a heat treatment temperature of around 180℃ can improve the mechanical stability of the particles while maintaining the adsorption activity of the iron phase, indicating that the appropriate heat treatment in this scheme can avoid both the problems of "insufficient strength at low temperatures" and "reduced adsorption activity at high temperatures".

[0150] Figure 4 The effectiveness of this scheme in balancing mass transfer performance and usage intensity was further verified from a particle size perspective. Based on the preparation conditions of Example 1, only the particle size was varied, ranging from 0.30 to 2.20 mm. The results showed that when the particle size was too small, the particle skeleton had insufficient load-bearing capacity and was easily broken under water disturbance or external force, resulting in low crushing strength. When the particle size was too large, although the stability of the single particle structure was improved, the internal diffusion path was prolonged, and the migration of phosphate to the active sites inside the particle was restricted, leading to a decrease in the static phosphorus adsorption capacity over 24 hours. When the particle size was controlled within the range of 0.90–1.10 mm, the sample was able to maintain good adsorption capacity and crushing strength simultaneously, indicating that reasonable particle size control is beneficial to shortening the mass transfer path and maintaining particle integrity, thereby meeting the dual requirements of adsorption efficiency and mechanical stability under fixed bed, oscillating contact, or continuous water treatment conditions.

[0151] Figures 5 to 8 This method is used to further characterize the effectiveness of in-situ anchoring of hydrated iron oxide in terms of the iron phase fixation state, iron leaching behavior, and uniformity of elemental distribution in the micro-area. Figure 5 The proportion of free hydrated iron oxide in Example 1, Comparative Example 10, and Comparative Example 11 was compared by measuring the iron phase separation through oscillation in water. The results showed that the proportion of free iron phase in Example 1 was significantly lower than that in Comparative Examples 10 and 11. This indicates that in this scheme, the hydrated iron oxide does not adhere to the particle surface through simple physical mixing or weak bonding, but rather forms a more stable bonded structure with the attapulgite particle matrix through a pH-induced hydrolysis deposition process. Therefore, under hydraulic disturbance conditions, the iron phase in Example 1 is less prone to peeling or migration, reducing the risk of iron phase loss and secondary pollution during adsorbent use from the source.

[0152] and Figure 5 The results of the free iron phase determination shown correspond to the results of the free iron phase determination shown. Figure 6The iron phase immobilization strength was further evaluated by the iron leaching concentration in the aqueous phase. The iron leaching concentration in Example 1 was significantly lower than that in Comparative Examples 10 and 11, while Comparative Examples 10 and 11 exhibited higher iron leaching levels due to weaker iron binding or insufficient structural stability. This result indicates that the proposed solution, through in-situ anchoring and subsequent structural stabilization treatment, can reduce the risk of leaching and detachment of hydrated iron oxide during water treatment, improve the long-term stability of the adsorbent in actual aquatic environments, and directly address the technical problems of "easy loss of iron-containing active components and insufficient material stability" that this solution aims to solve.

[0153] Figure 7 and Figure 8 Further, from a micro-statistical perspective, it can be explained that the iron phase can not only be effectively loaded, but also achieve a relatively uniform distribution. Figure 7 SEM-EDS field-view statistical Fe element area fraction maps of Examples 1, 9, and 10 were used to evaluate the iron phase loading level by measuring the Fe element area fraction under multiple fields of view. The results show that Example 1 has a relatively stable Fe element distribution, indicating that hydrated iron oxide can be sufficiently loaded into the attapulgite particles; Comparative Example 9, due to the lack of effective iron phase loading, has a significantly weaker Fe signal, resulting in limited subsequent adsorption performance; Although a higher Fe signal can be detected in Comparative Example 10, the fluctuations between different fields of view are large, indicating that mechanical mixing easily creates localized iron-rich and iron-poor regions. Furthermore, Figure 8 The dispersion of Fe element was evaluated by statistically analyzing the coefficient of variation of Fe distribution in the SEM-EDS fields of Example 1, Comparative Example 10, and Comparative Example 11. The results show that the coefficient of variation in Example 1 is significantly lower, indicating a more uniform iron phase distribution and reducing local agglomeration and heterogeneous deposition. These results collectively demonstrate that this method achieves sufficient and uniform loading of hydrated iron oxide in attapulgite particles through in-situ deposition, which is more conducive to maximizing the utilization of the active iron phase compared to simple mechanical mixing or unstable deposition methods.

[0154] Figures 9 to 11 This is to illustrate that the particle structure formed by this scheme can simultaneously meet the requirements of mechanical integrity and internal mass transfer. Figure 9The particle crushing strength and water abrasion rate of Example 1, Comparative Example 6, and Comparative Example 7 were compared. The results showed that Example 1 exhibited both high crushing strength and low water abrasion rate, indicating that its particle skeleton maintained good integrity under pressure and hydraulic disturbance conditions. Comparative Examples 6 and 7, however, showed problems such as reduced crushing strength or increased abrasion rate, indicating that if the molding, stabilization, or structural control conditions are inappropriate, the particles are prone to pulverization, breakage, or surface erosion during water treatment operation. This demonstrates that the particles obtained in this scheme are more suitable for long-term oscillation, flow contact, or engineering filling conditions, and can alleviate the problems of difficult recovery, easy loss, and easy effluent turbidity caused by powdered iron-containing adsorbent materials.

[0155] While ensuring mechanical stability, this scheme also ensures the diffusion efficiency of phosphate to active sites by regulating the internal pore structure of the particles. Figure 10 The diagram shows the pore area fraction of the particle cross-sections for Examples 1, 7, and 8. The results show that Example 1 has a higher and more stable pore area fraction, indicating that sufficient mass transfer channels are formed inside the particle, which is beneficial for the diffusion of phosphate from the water into the particle and its contact with the active sites of hydrated iron oxide. Comparative Examples 7 and 8, however, suffer from insufficient pore structure or large fluctuations in different regions, which can easily lead to limited mass transfer or insufficient utilization of adsorption sites. Further combined with… Figure 11 The particle cross-section pore wall continuity score shows that Example 1 has a higher pore wall continuity score, indicating that its pore structure is not simply formed by disordered fragmentation or structural defects, but rather forms a porous network capable of mass transfer while maintaining a continuous framework. Therefore, this solution can improve the pore mass transfer capacity while maintaining the integrity of the particle framework, effectively resolving the technical contradiction between porosity and strength maintenance.

[0156] Figure 12 This method is used to illustrate the batch stability and repeatability of the preparation process. By comparing the hydrated iron oxide content (calculated as Fe(OH)3) of three consecutive batches of samples from Example 1, Comparative Example 4, and Comparative Example 5, it can be seen that the batch-to-batch variation of hydrated iron oxide content in Example 1 is relatively stable, indicating that under the defined conditions of water washing pretreatment, iron source introduction, pH-induced hydrolysis deposition, heat treatment, and sieving, the iron phase loading can be stably controlled. In contrast, Comparative Examples 4 and 5 show varying degrees of lower content or batch-to-batch fluctuations, indicating that deviations from the key process conditions of this method can easily affect the iron phase formation and fixation process. These results demonstrate that this method not only achieves superior performance in single batches but also has a good foundation for process scale-up and reliable reproducible preparation, which is beneficial for the stable acquisition of the target adsorbent in actual production.

[0157] Figure 13The phosphate removal capabilities of Example 1, Comparative Examples 9, 10, and 11 were comprehensively evaluated from the perspective of core application performance. The results showed that Example 1 maintained a high static phosphate adsorption capacity over 24 hours, indicating that the hydrated iron oxide loading structure formed by this method can provide sufficient and effective phosphate binding sites. Comparative Example 9 had a significantly lower adsorption capacity due to the lack of an effective iron phase loading. While Comparative Examples 10 and 11 exhibited some adsorption capacity, their binding capacity was limited. Figure 5 and Figure 6 It is evident that the iron phase fixation stability is insufficient, posing a risk of iron phase detachment or leaching. Therefore, this approach does not simply pursue high iron content or high initial adsorption capacity, but rather achieves a more reasonable comprehensive balance among iron phase loading, distribution uniformity, particle strength, pore structure mass transfer, and stability in water. This more effectively addresses the problem of existing adsorbents struggling to balance adsorption performance and material stability.

[0158] Figure 14 The image shows a comparison of the SEM morphology of the final product of Example 1 and the final product of Comparative Example 10, which is used to further characterize the effect of the in-situ anchoring process on the dispersion state and interfacial bonding state of hydrated iron oxide from the microscopic morphology. Figure 14 a shows the overall particle morphology of the final product of Example 1 under low-magnification SEM. The sieved particle size is 0.50 mm, the particle structure is relatively intact, and the surface distribution is relatively uniform, indicating that the composite modified attapulgite clay adsorbent obtained in this scheme can form stable shaped particles. In comparison, Figure 14 b shows the overall morphology of Comparative Example 10 at the same 0.50 mm particle size, which can be used to illustrate that mechanically mixed samples are more prone to localized iron-rich agglomeration or surface inhomogeneity. Further magnification reveals... Figure 14 c shows the local surface of the particles in Example 1, the micron-sized pores, and the accumulation state of the attapulgite framework, indicating that the particle surface structure is continuous after in-situ deposition, and there is good synergy between the pores and the framework; while Figure 14 Figure d shows the local surface morphology under mechanical mixing conditions in Comparative Example 10, indicating that pre-hydrated iron oxide is more likely to form localized enrichment areas. Further observation under high-magnification SEM... Figure 14 e shows that in Example 1, hydrated iron oxide is dispersed and loaded on the surface of attapulgite rod crystal bundles, indicating that there is sufficient contact between the iron phase and the support; Figure 14 f shows the contact state between the hydrated iron oxide aggregates and the attapulgite framework in Comparative Example 10, further indicating that mechanical mixing is insufficient to achieve a uniform and robust interface structure. The above SEM results are consistent with... Figures 5 to 8 The statistical results of iron phase fixation and element distribution corroborate each other, indicating that the in-situ anchoring route of this scheme exhibits better iron phase distribution and fixation than the simple post-mixing route under the test conditions.

[0159] Figure 15The image shows a TEM structure comparison of the final product of Example 1 and the final product of Comparative Example 10, used to further characterize at the nanoscale the formation of a tighter local composite interface between hydrated iron oxide and the attapulgite carrier. Figure 15 Image a is a bright-field TEM image of the final product of Example 1. The object of observation is the attapulgite-hydrated iron oxide composite fragment obtained after the composite particles are dispersed. The image shows the bonding state of hydrated iron oxide on the surface of attapulgite rod crystals or rod crystal bundles. This observation result is consistent with the judgment that in-situ anchoring forms nanoscale contact. Figure 15 b is a bright-field TEM image of the final product of Comparative Example 10, used to show the distribution of pre-hydrated iron oxide and attapulgite fragments in the mechanically mixed sample, indicating that this method is more likely to result in phase separation or aggregation. Figure 15 c is an HRTEM image of the final product of Example 1, which shows the locally ordered structure of hydrated iron oxide, the low crystallinity region and its contact state with the attapulgite interface. This result is consistent with the judgment that a composite interface is formed by in-situ deposition. Figure 15 d is an HRTEM image of the final product of Comparative Example 10, which can show the agglomeration region of the iron phase or the discontinuous region of the interface in the mechanically mixed sample, further illustrating that its interface bonding is not as sufficient as that of Example 1. Figure 15 e is the SAED and elemental distribution diagram of the final product of Example 1, showing the spatial distribution or low crystallinity diffraction characteristics of elements such as Fe, O, Si, Mg, and Al in the local composite region, indicating that the iron phase and the attapulgite support have good spatial coupling. Figure 15 f shows the SAED and elemental distribution diagram of the final product of Comparative Example 10, used to illustrate the local enrichment or uneven distribution of iron in the mechanically mixed sample. This indicates that the hydrated iron oxide formed by in-situ hydrolysis deposition in this scheme is not simply attached to the outer surface of the carrier, but rather forms a more continuous and compact composite interface with attapulgite at the nanoscale, thus providing a structural basis for adsorption performance, anti-detachment performance, and particle stability.

[0160] Figure 16 This is a macroscopic optical photographic evolution diagram from S1 to the final product in Example 1, used to demonstrate from the perspective of the preparation process that the composite modified attapulgite clay adsorbent particles can be stably formed according to the steps of this scheme. Figure 16 a shows the initial powder appearance of commercially available S1 attapulgite clay raw material after crushing, used to characterize the state of the carrier raw material; Figure 16 b shows the appearance of S2 pretreated attapulgite clay. The sample was washed with water to pH 6.0, dried at 80℃ for 2 hours and sieved to 0.048 mm, indicating that the pretreatment process can obtain attapulgite carriers with well-defined particle sizes that are suitable for subsequent iron phase introduction. Figure 16c shows the sample product of the mixed system of S3 containing iron ions and attapulgite. The appearance of the sample changed after the iron source was introduced, indicating that the iron ions have entered the attapulgite dispersion system. Figure 16 Figure d shows the in-situ anchoring of S4 hydrated iron oxide into attapulgite clay intermediates. The hydrated iron oxide content (calculated as Fe(OH)3) is 6 wt%, and the proportion of free hydrated iron oxide to the total mass of hydrated iron oxide is 15 wt%, indicating that an iron-containing composite intermediate has been formed after pH-induced hydrolysis and deposition. The evolution results of this process demonstrate that this method can progressively construct shaped composite adsorbent particles containing hydrated iron oxide from raw mineral powder, and exhibits observable and controllable process continuity in the processes of iron phase introduction, in-situ anchoring, particle formation, and structural stabilization.

[0161] In conclusion, Figures 1 to 16 The effectiveness of this scheme was characterized by optimizing key parameters, ensuring the stability of the iron phase fixation, achieving uniformity of elemental distribution, improving particle mechanics and pore structure, batch repeatability, enhancing phosphorus adsorption performance, and analyzing the microscopic interface construction and macroscopic preparation process evolution. Results showed that by controlling the content of hydrated iron oxide (calculated as Fe(OH)3), pH-induced hydrolysis deposition conditions, heat treatment temperature, and particle size, this scheme enabled the hydrated iron oxide to achieve sufficient, uniform, and stable in-situ anchorage within attapulgite particles. Simultaneously, the resulting particles exhibited high phosphorus adsorption capacity, low risk of iron phase detachment and leaching, high crushing strength, low abrasion rate in water, and a favorable internal mass transfer pore structure. Therefore, this scheme effectively overcomes the challenge of simultaneously satisfying the requirements of adsorption capacity, iron phase fixation stability, particle mechanical strength, and engineering application adaptability in existing iron-phosphorus adsorbent materials, demonstrating promising prospects for water treatment applications.

[0162] Table 1 Performance of Examples and Comparative Examples

[0163]

[0164] As can be seen from the performance of the examples and comparative examples in Table 1, Examples 1-4 established a relatively complete correspondence between hydrated iron oxide content, iron leaching concentration, free hydrated iron oxide ratio, 24-hour static phosphorus adsorption, particle crushing strength, abrasion rate after 24-hour shaking in water, and batch-to-batch stability. Examples 2-4 improved phosphorus adsorption and particle strength simultaneously while maintaining low iron leaching and abrasion rates by increasing the hydrated iron oxide loading, optimizing pH-induced deposition, adjusting the granulation moisture content, and heat treatment conditions. Comparative Examples 1-8 showed that deviations in a single raw material, process, or structural parameter would decrease at least one of the following: loading stability, adsorption activity, or particle integrity. Comparative Examples 9-11 further showed that phosphorus adsorption was lower when hydrated iron oxide was missing, and the free iron phase and iron leaching-related indicators deviated significantly when physical mixing was used or the deposition and granulation sequence was changed, indicating that in-situ anchoring interface and sequence control are crucial for overall performance.

[0165] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A composite modified attapulgite clay adsorbent, characterized in that, The adsorbent comprises a granulated hydrated iron oxide in-situ anchored attapulgite clay composite modifier. With a dry basis total mass of 100 wt%, the adsorbent comprises, in its final form: Attapulgite clay, 75-94 wt%; Hydrated iron oxide, calculated as Fe(OH)3, 6-22 wt%; The auxiliary molding solid components, excluding the attapulgite clay and the hydrated iron oxide, are 0-3 wt%; The sum of the mass percentages of the attapulgite clay, the hydrated iron oxide, and the auxiliary molding solid components is 100 wt%. The hydrated iron oxide is formed by in-situ hydrolysis and deposition of ferric chloride hexahydrate induced by pH in an aqueous phase, and the adsorbent is granular.

2. The composite modified attapulgite clay adsorbent according to claim 1, characterized in that, The hydrated iron oxide is formed on the surface of the attapulgite clay and in the channels between the bar crystal bundles, and the average iron leaching concentration of the adsorbent after 24 hours in deionized water with a pH of 6.0-8.0 is ≤1.00 mg / L, as determined by HJ700-2014 or its current effective version.

3. The composite modified attapulgite clay adsorbent according to claim 1, characterized in that, The hydrated iron oxide in-situ anchored attapulgite clay intermediate in the granulated hydrated iron oxide in-situ anchored attapulgite clay composite modifier is prepared through the following steps: A1. Disperse attapulgite clay in deionized water to obtain attapulgite clay dispersion slurry; A2. Dissolve ferric chloride hexahydrate in deionized water to obtain an aqueous solution of ferric chloride hexahydrate; A3. Add the aqueous solution of ferric chloride hexahydrate to the attapulgite clay dispersion slurry and mix; A4. Add an aqueous solution of sodium hydroxide or anhydrous sodium carbonate to the system from step A3, control the pH of the system to 6.8-8.2, and then age the system. A5. The solid obtained in step A4 is subjected to solid-liquid separation, washing and drying to obtain the hydrated iron oxide in-situ anchored attapulgite clay intermediate; In the hydrated iron oxide in-situ anchored attapulgite clay intermediate, the content of hydrated iron oxide, calculated as Fe(OH)3 on a dry basis, is 6-22 wt%, and the average proportion of free hydrated iron oxide to the total mass of hydrated iron oxide is ≤15 wt%.

4. The composite modified attapulgite clay adsorbent according to claim 3, characterized in that, The preparation of the hydrated iron oxide in-situ anchored attapulgite clay intermediate satisfies the following conditions: In step A1, the solid content of the attapulgite clay dispersion slurry is 10-25 wt%. In step A3, the aqueous solution of ferric chloride hexahydrate is added at 35-70°C; In step A4, the aging temperature is 45-70℃ and the aging time is 1-4 hours; In step A5, the filtrate is washed until the pH value is 6.0-8.0, and the drying temperature is 80-120℃.

5. The composite modified attapulgite clay adsorbent according to claim 3, characterized in that, The attapulgite clay used in step A1 is pretreated attapulgite clay, which is prepared through the following steps: B1. Mix attapulgite clay with deionized water or a 0.05-0.50 mol / L hydrochloric acid aqueous solution; B2. Stir at 25-60℃; B3. After solid-liquid separation, wash with deionized water until the pH of the washing solution is 6.0-8.0; B4. The pretreated attapulgite clay is obtained by drying at 80-110℃ and sieving. The pH value of the pretreated attapulgite clay dispersion slurry in water is 6.0-8.

5.

6. The composite modified attapulgite clay adsorbent according to claim 3, characterized in that, The granulated hydrated iron oxide in-situ anchored attapulgite clay composite modifier is prepared through the following steps: C1. Mix the hydrated iron oxide in-situ anchored attapulgite clay intermediate obtained in step A5 with deionized water to obtain a wet material; C2. Knead the wet material; C3. Extruding, rounding, or pressing the wet material into granules to obtain wet granules; C4. The wet particles are dried and sieved to obtain the granulated hydrated iron oxide in-situ anchored attapulgite clay composite modifier. In steps C1-C4, in addition to the hydrated iron oxide in-situ anchoring attapulgite clay intermediate and the deionized water, the amount of auxiliary molding solid components added is 0-3 wt%, based on the total dry mass of the final adsorbent.

7. The composite modified attapulgite clay adsorbent according to claim 6, characterized in that, Step C4 is followed by a heat treatment at 120-220℃ for 0.5-3.0h to obtain adsorbent particles with an average crushing strength of 3-35N / particle and an average wear rate of ≤8.00wt% after 24h of shaking in water.

8. The composite modified attapulgite clay adsorbent according to claim 1, characterized in that, The hydrated iron oxide is distributed on the surface of the rod crystals, the channels between the rod crystal bundles, and the walls of the interconnected pores within the particles of the attapulgite clay, and the average proportion of free hydrated iron oxide to the total mass of hydrated iron oxide in the adsorbent is ≤12wt%; the coefficient of variation of the hydrated iron oxide content (calculated as Fe(OH)3) in the adsorbent prepared in three consecutive batches is ≤15%.

9. A method for preparing a composite modified attapulgite clay adsorbent as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Preparation of an intermediate for in-situ anchoring attapulgite clay with hydrated iron oxide, comprising: dispersing attapulgite clay in deionized water to obtain an attapulgite clay dispersion slurry; dissolving ferric chloride hexahydrate in deionized water to obtain an aqueous solution of ferric chloride hexahydrate; adding the aqueous solution of ferric chloride hexahydrate to the attapulgite clay dispersion slurry and mixing; adding an aqueous solution of sodium hydroxide or anhydrous sodium carbonate to the obtained system, controlling the pH value of the system to 6.8-8.2, and aging; performing solid-liquid separation, washing, and drying on the aged solid to obtain the intermediate for in-situ anchoring attapulgite clay with hydrated iron oxide; S2. Mix the hydrated iron oxide in-situ anchored attapulgite clay intermediate with deionized water to obtain a wet material; S3. The wet material is kneaded and then granulated to obtain wet granules; S4. The wet particles are dried and sieved to obtain a composite modified attapulgite clay adsorbent; In steps S2-S4, in addition to the hydrated iron oxide in-situ anchoring attapulgite clay intermediate and the deionized water, the amount of auxiliary molding solid components added is 0-3 wt%, based on the total dry mass of the final adsorbent.

10. The application of the composite modified attapulgite clay adsorbent according to claim 1 in the adsorption treatment of industrial wastewater, characterized in that, The industrial wastewater is phosphorus-containing wastewater; The composite modified attapulgite clay adsorbent is used in a fixed bed, filter bag, or stirred adsorption reactor. When used in a fixed bed, the influent pH is 5.0-9.0 and the hydraulic retention time is 5-60 min. After adsorption treatment, it is regenerated with a 0.05-1.00 mol / L sodium hydroxide aqueous solution.

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