Iron-silicon composite adsorbent, preparation method and method for removing hexavalent chromium in water body

Abstract

The invention provides an iron-silicon composite adsorbent, a preparation method and a method for removing hexavalent chromium in a water body, and belongs to the technical field of adsorbents. Tetraethyl orthosilicate is used as a silicon source, ferric salt is doped in the process of preparing silicon dioxide wet gel by adopting a sol-gel method, and then the obtained wet gel is aged, dried, ground and sieved to obtain the iron-silicon composite adsorbent. Wherein the molar ratio of the Si element in the tetraethoxysilane to the iron element in the ferric salt is (0.01-0.4): (0.01-0.5). The ferric salt is doped in the preparation process of the silicon dioxide aerogel, the problems that ferric salt particles are prone to agglomeration and loss are solved, meanwhile, the advantages that the silicon dioxide aerogel is high in porosity, high in specific surface area, low in price and easy to obtain and the like are combined, iron-based salt particles are efficiently utilized, and the obtained adsorbent is high in adsorption speed and high in removal rate for hexavalent chromium in a water body.

Description

Technical Field

[0001] This invention relates to the field of adsorbent technology, and in particular to an iron-silicon composite adsorbent, its preparation method, and a method for removing hexavalent chromium from water. Background Technology

[0002] In recent years, industries using chromium compounds, such as electroplating, chemicals, printing and dyeing, and leather, have seen significant economic benefits, greatly promoting the large-scale production of chromium salt plants. However, the resulting environmental problems have become increasingly prominent. The chromium-containing waste residue and high concentrations of hexavalent chromium ions (Cr) in the wastewater generated during chromium salt production are significant issues. 6+ High concentrations of hexavalent chromium (HC) severely pollute groundwater after being washed away by rainwater or discharged into the environment. It is toxic to humans, crops, and livestock, inducing various diseases, and is a common carcinogen. Therefore, further research and development of new methods for the treatment of high-concentration HC are urgently needed.

[0003] Extensive research has been conducted on hexavalent chromium removal technologies, with current remediation methods including adsorption, ion exchange, phytoremediation, chemical precipitation, coagulation, and membrane separation. Adsorption is widely adopted due to its simplicity, high efficiency, low cost, and adaptability to varying water volumes. The preparation of adsorbents with excellent adsorption properties is crucial for reducing hexavalent chromium in water. Commonly used adsorbents include inorganic, organic, and composite adsorbents. However, some inorganic adsorbents have low adsorption efficiency, organic adsorbents may cause secondary pollution, and the preparation process of composite adsorbents is complex. Among the many developed adsorbents, iron and its oxides have a stronger affinity for chromium ions, and their preparation methods are simple with widely available raw materials, leading to their large-scale application in treating high-chromium water. However, in practical applications, iron salt particles inevitably experience aggregation, leaching, and separation difficulties. Therefore, it is necessary to find porous carriers to support Fe to effectively address these problems.

[0004] SiO2 aerogels have been extensively studied in the field of environmental adsorption. Existing technologies include loading Fe onto SiO2 aerogels for arsenic removal; however, the Fe only adheres to the surface of the SiO2 aerogel, resulting in poor adsorption of arsenic in water. Furthermore, there are no reports on its effectiveness in removing hexavalent chromium from water. Therefore, exploring SiO2 aerogels as an adsorbent carrier material for the removal of hexavalent chromium has significant practical implications. Summary of the Invention

[0005] Therefore, the present invention aims to provide an iron-silicon composite adsorbent, a preparation method, and a method for removing hexavalent chromium from water. The adsorbent provided by the present invention enables efficient utilization of iron-based salt particles and can efficiently and rapidly remove hexavalent chromium from water.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing an iron-silicon composite adsorbent, wherein tetraethyl orthosilicate is used as the silicon source, iron salt is added during the preparation of silica wet gel by sol-gel method, and the obtained wet gel is aged, dried, ground, and sieved to obtain the iron-silicon composite adsorbent.

[0007] The molar ratio of Si in the tetraethyl orthosilicate to iron in the iron salt is (0.01-0.4):(0.01-0.5).

[0008] Preferably, the molar ratio of Si in the tetraethyl orthosilicate to iron in the iron salt is 0.05:(0.01-0.3).

[0009] Preferably, the iron salt is ferric chloride hexahydrate.

[0010] Preferably, the step of incorporating iron salt in the process of preparing silica wet gel by sol-gel method is as follows: mix tetraethyl orthosilicate, anhydrous ethanol and iron salt and stir in a water bath, then adjust the pH while stirring until gel is formed.

[0011] More preferably, the water bath stirring temperature is 30-50℃, the time is 1 hour, and the stirring speed is 200-600 r / min; the pH value is 5-8.5.

[0012] Preferably, the aging method is to immerse the wet gel in anhydrous ethanol for aging; the aging temperature is 40-60℃ and the time is 10-15h.

[0013] Preferably, the drying temperature is 85-100℃.

[0014] The present invention also provides an iron-silicon composite adsorbent prepared by the preparation method described above, wherein the iron-silicon composite adsorbent is composed of a silica aerogel made of ferric chloride hexahydrate and tetraethyl orthosilicate; wherein the molar ratio of Si element in tetraethyl orthosilicate and iron element in ferric chloride hexahydrate is (0.01-0.4):(0.01-0.5).

[0015] The present invention also provides a method for removing hexavalent chromium from water, wherein the pH of the chromium-containing wastewater is adjusted to 2-7, and the iron-silicon composite adsorbent is added to the chromium-containing wastewater at room temperature and stirred to remove chromium; the dosage of the iron-silicon composite adsorbent is 0.2-1.4 g / L.

[0016] Beneficial technical effects:

[0017] 1. In the preparation process of silica aerogel, iron salt is doped, which solves the problem of easy agglomeration and loss of iron salt particles. At the same time, combined with the advantages of silica aerogel such as high porosity, high specific surface area, low cost and easy availability, the iron-based salt particles are efficiently utilized.

[0018] 2. The hexavalent chromium adsorbent prepared by this invention uses tetraethyl orthosilicate, anhydrous ethanol, and ferric chloride hexahydrate as raw materials. It has low preparation cost, wide availability, simple preparation process, and good product stability.

[0019] 3. The adsorbent provided by this invention has a high removal rate of hexavalent chromium in water, a fast adsorption speed, and an adsorption efficiency of up to 99% for chromium in water.

[0020] 4. This invention is the first to incorporate iron salts into the preparation process of silica aerogel to form a novel composite adsorbent for chromium removal, providing a new approach for removing hexavalent chromium from water. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 Microscopic morphology of the adsorbent prepared in Example 1;

[0023] Figure 2 The graph shows the effect of different dosages of the adsorbent obtained in Example 1 on the adsorption capacity of hexavalent chromium.

[0024] Figure 3 The graph shows the effect of the adsorbent obtained in Example 1 on the adsorption capacity of hexavalent chromium at different initial pH values.

[0025] Figure 4 The graph shows the effect of the adsorbent obtained in Example 1 on the adsorption capacity of hexavalent chromium at different adsorption times. Detailed Implementation

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0028] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0029] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0030] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0031] This invention provides a method for preparing an iron-silicon composite adsorbent, using tetraethyl orthosilicate as the silicon source, incorporating iron salts during the preparation of silica wet gel using the sol-gel method, and then aging, drying, grinding, and sieving the resulting wet gel to obtain the iron-silicon composite adsorbent.

[0032] The molar ratio of Si in the tetraethyl orthosilicate to iron in the iron salt is preferably (0.01-0.4):(0.01-0.5), more preferably (0.01-0.2):(0.01-0.3), and most preferably 0.05:(0.01-0.3).

[0033] This invention is the first to incorporate iron salts during the preparation of silica wet gel to form a novel composite adsorbent for chromium removal. Iron and hexavalent chromium have a special affinity, therefore, the introduction of iron salts is often considered when preparing adsorbents for hexavalent chromium removal. When the iron content is low, the adsorbent has a small adsorption capacity for hexavalent chromium; when the iron content is too high, the pore structure on the surface of the composite adsorbent is reduced, resulting in a blocky structure, which inevitably reduces the material's adsorption performance. The adsorbent prepared by this invention exhibits excellent adsorption performance for hexavalent chromium. The main adsorption mechanism is as follows: hexavalent chromium in solution diffuses to the surface of the composite material through a liquid film; the porous structure of the composite material promotes its diffusion into the interior; chemisorption of hexavalent chromium with O-containing functional groups occurs, forming a stable complex with hexavalent chromium.

[0034] In some embodiments, the iron salt is ferric chloride hexahydrate. Ferric chloride hexahydrate selected in this invention exhibits better adsorption performance for hexavalent chromium compared to ferrous salts.

[0035] In some embodiments, the step of incorporating iron salts during the preparation of silica wet gel using the sol-gel method is as follows: tetraethyl orthosilicate, anhydrous ethanol, and iron salts are mixed and stirred in a water bath, and then the pH is adjusted while stirring until a gel is formed.

[0036] In a preferred embodiment, the water bath stirring temperature is 30-50℃, the time is 1 hour, and the stirring speed is 200-600 r / min; the pH value is 5-8.5. Preferably, during the water bath stirring process, NaOH or HCl solution is slowly added dropwise to adjust the pH. Excessively high stirring temperature will accelerate the evaporation rate of anhydrous ethanol, while excessively low temperature will lead to incomplete mixing of various reactants, affecting the synthesis of the adsorbent. Therefore, the above parameter ranges are preferred in this invention.

[0037] In a preferred embodiment, the aging method involves immersing the wet gel in anhydrous ethanol for aging; the aging temperature is 40-60°C, and the time is 10-15 hours. The gel aging process aims to enhance the network structure of the silica aerogel. Too short an aging time will result in incomplete formation of the silica aerogel structure, while too long an aging time increases time costs. Too high an aging temperature will cause the sol-gel aerogel to melt, while too low an aging temperature will slow down the rate of network structure enhancement. Therefore, the above parameter ranges are preferred in this invention.

[0038] In some embodiments, the drying temperature is 85-100°C. The present invention does not impose any particular limitation on the drying method; any method well-known to those skilled in the art can be used.

[0039] In some embodiments, the preparation method of the iron-silicon composite adsorbent specifically includes the following steps:

[0040] (1) Mix tetraethyl orthosilicate, anhydrous ethanol and ferric chloride hexahydrate in a molar ratio of (0.01-0.4):(1-7):(0.01-0.5), stir in a water bath, and then slowly add NaOH solution or HCl solution dropwise while stirring to adjust the pH until a wet gel is formed.

[0041] (2) The formed wet gel was aged by immersing it in anhydrous ethanol;

[0042] (3) After the aged wet gel is dried at normal pressure, it is ground and sieved to obtain iron-silicon composite adsorbent.

[0043] The present invention also provides an iron-silicon composite adsorbent prepared by the preparation method described above, wherein the iron-silicon composite adsorbent is composed of a silica aerogel made of ferric chloride hexahydrate and tetraethyl orthosilicate; wherein the molar ratio of Si element in tetraethyl orthosilicate and iron element in ferric chloride hexahydrate is (0.01-0.4):(0.01-0.5).

[0044] The present invention also provides a method for removing hexavalent chromium from water, wherein the pH of the chromium-containing wastewater is adjusted to 2-7, and the iron-silicon composite adsorbent is added to the chromium-containing wastewater at room temperature and stirred to remove chromium; the dosage of the iron-silicon composite adsorbent is 0.2-1.4 g / L.

[0045] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0046] Unless otherwise specified, all instruments and reagents used in the examples are available through commercial channels.

[0047] Example 1

[0048] (1) Mix 22.3 ml tetraethyl orthosilicate, 58 ml anhydrous ethanol and 13.5 g ferric chloride hexahydrate in proportion, stir in a water bath at 50°C for 1 h at a stirring rate of 300 r / min, and then slowly add 0.1 M NaOH solution and 0.1 M HCl solution dropwise while stirring to adjust the pH to 7 until gel is formed;

[0049] (2) The formed wet gel was soaked in anhydrous ethanol at 40°C for 10 hours to age;

[0050] (3) After drying the aged wet gel at 95°C and normal pressure for 12 hours, it was ground and sieved to obtain the iron-silicon composite adsorbent.

[0051] Observe the microstructure of the iron-silicon composite adsorbent obtained in Example 1. Figure 1 It can be seen that the composite adsorbent exhibits an uneven porous structure on its surface, and has a rough surface and a large specific surface area, thus possessing a good adsorption structure.

[0052] Example 2

[0053] (1) Mix 22.3 ml of tetraethyl orthosilicate, 58 ml of anhydrous ethanol and 27 g of ferric chloride hexahydrate in proportion, stir in a water bath at 50°C for 1 h at a stirring rate of 300 r / min, and then slowly add 0.1 M NaOH solution and 0.1 M HCl solution dropwise while stirring to adjust the pH to 7 until gel is formed;

[0054] (2) The formed wet gel was soaked in anhydrous ethanol at 50°C for 15 hours to age;

[0055] (3) After drying the aged wet gel at 85°C and normal pressure for 12 hours, it was ground and sieved to obtain the iron-silicon composite adsorbent.

[0056] Example 3

[0057] (1) Mix 11.2 ml tetraethyl orthosilicate, 58 ml anhydrous ethanol and 27 g ferric chloride hexahydrate in proportion, stir in a water bath at 50°C for 1 h at a stirring rate of 300 r / min, and then slowly add 0.1 M NaOH solution and 0.1 M HCl solution dropwise while stirring to adjust the pH to 7 until gel is formed;

[0058] (2) The formed wet gel was soaked in anhydrous ethanol at 40°C for 12 hours to age;

[0059] (3) After drying the aged wet gel at 85°C and normal pressure for 12 hours, it was ground and sieved to obtain the iron-silicon composite adsorbent.

[0060] Effect verification example

[0061] 1. The adsorbent used was the iron-silicon composite adsorbent prepared in Example 1, and the treatment target was laboratory-simulated hexavalent chromium-contaminated water. The initial concentration of Cr(VI) was 100 mg / L. Seven 100 mL portions of laboratory-simulated hexavalent chromium-contaminated wastewater were poured into 100 mL capped glass bottles, and 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, and 0.14 g of the composite adsorbent from Example 1 were added, corresponding to dosages of 0.2, 0.4, 0.6, 0.8, 1, 1.2, and 1.4 g / L, respectively. The bottles were placed in a constant temperature water bath shaking chamber, and the relevant parameters were set. The rotation speed was 350 r / min, and the reaction temperature was 25 °C. After the reaction, the bottles were removed and filtered, and the remaining chromium content in the chromium-contaminated water was detected by ICP. The adsorption capacity Qe (mg·g) was calculated. -1 The adsorption capacity of chromium varies with the adsorbent dosage as follows: (The text abruptly ends here, so the translation stops as well.) Figure 2 .Depend on Figure 2 It can be seen that the adsorption of chromium increases with the increase of dosage, and the optimal dosage is 0.5 g / L.

[0062] 2. The adsorbent used was the iron-silicon composite adsorbent prepared in Example 1, and the target material was laboratory-simulated hexavalent chromium-contaminated water. The initial concentration of Cr(VI) was 100 mg / L. Nine 100 mL portions of laboratory-simulated chromium-contaminated wastewater were poured into 100 mL capped glass bottles. The pH values ​​of the nine chromium wastewater portions were adjusted sequentially to 2, 3, 4, 5, 6, 7, 8, 9, and 10 using 0.1 M NaOH and 0.1 M HCl, respectively. 0.06 g of the composite adsorbent from Example 1 was added to each glass bottle. The bottles were placed in a constant temperature water bath shaking chamber, and the relevant parameters were set. The rotation speed was 350 r / min, and the reaction temperature was 25 °C. After the reaction, the bottles were removed and filtered, and the remaining chromium content in the chromium-contaminated water was detected by ICP. The adsorption capacity Qe (mg·g) was calculated. -1 The adsorption capacity of chromium varies with pH as shown in the figure. Figure 3 .Depend on Figure 3 It can be seen that the adsorption capacity of chromium gradually decreases with the increase of pH. In order to ensure the adsorption capacity of chromium, the optimal adsorption pH of chromium wastewater is determined to be 2.

[0063] 3. The adsorbent used was the iron-silicon composite adsorbent prepared in Example 1, and the treatment target was laboratory-simulated hexavalent chromium-contaminated water. The initial concentration of Cr(VI) was 100 mg / L. 100 mL of the laboratory-simulated chromium-contaminated wastewater was poured into a 100 mL capped glass bottle, and the pH of the chromium-containing wastewater was adjusted to 2 using 0.1 M NaOH and 0.1 M HCl. 0.06 g of the composite adsorbent from Example 1 was added. The bottle was placed in a constant temperature water bath shaking chamber, and the relevant parameters were set. The rotation speed was 350 r / min, and the reaction temperature was 25℃. Samples were taken and filtered sequentially at 5 min, 15 min, 30 min, 1 h, 2 h, 4 h, 6 h, 8 h, 12 h, 24 h, 48 h, 72 h, and 96 h. The remaining chromium content in the chromium-contaminated water was detected by ICP, and the adsorption capacity Qe (mg·g) was calculated. -1 ).Depend on Figure 4 It can be seen that adsorption equilibrium is reached at an adsorption time of 12 hours.

[0064] The iron-silicon composite adsorbents prepared in Examples 2 and 3 were subjected to the same effect verification. The verification results were similar to those of the iron-silicon composite adsorbent in Example 1. When the pH of the chromium-containing wastewater was 2-7, the dosage of the iron-silicon composite adsorbent was 0.2-1.4 g / L, with the optimal dosage being 0.4-0.6 g / L. Adsorption equilibrium was reached after 12 hours of adsorption.

[0065] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an iron-silicon composite adsorbent, characterized in that, Using tetraethyl orthosilicate as the silicon source, iron salts are incorporated into the preparation of silica wet gel by the sol-gel method. The resulting wet gel is then aged, dried, ground, and sieved to obtain the iron-silicon composite adsorbent. The molar ratio of Si in the tetraethyl orthosilicate to iron in the iron salt is (0.01-0.4):(0.01-0.5).

2. The preparation method according to claim 1, characterized in that, The molar ratio of Si in the tetraethyl orthosilicate to iron in the iron salt is 0.05:(0.01-0.3).

3. The preparation method according to claim 1 or 2, characterized in that, The iron salt is ferric chloride hexahydrate.

4. The preparation method according to claim 1, characterized in that, The step of incorporating iron salts in the preparation of silica wet gel using the sol-gel method is as follows: Tetraethyl orthosilicate, anhydrous ethanol, and iron salts are mixed and stirred in a water bath, and then the pH is adjusted while stirring until gel is formed.

5. The preparation method according to claim 4, characterized in that, The water bath stirring temperature is 30-50℃, the time is 1 hour, and the stirring speed is 200-600 r / min; the pH value is 5-8.

5.

6. The preparation method according to claim 1, characterized in that, The aging method involves immersing the wet gel in anhydrous ethanol for aging; the aging temperature is 40-60℃ and the time is 10-15h.

7. The preparation method according to claim 1, characterized in that, The drying temperature is 85-100℃.

8. The iron-silicon composite adsorbent prepared by the preparation method according to any one of claims 1-7, characterized in that, The iron-silicon composite adsorbent is composed of silica aerogel made of ferric chloride hexahydrate and tetraethyl orthosilicate; the molar ratio of Si in tetraethyl orthosilicate to iron in ferric chloride hexahydrate is (0.01-0.4):(0.01-0.5).

9. A method for removing hexavalent chromium from water, characterized in that, Adjust the pH of the hexavalent chromium-containing wastewater to 2-7, add the iron-silicon composite adsorbent to the wastewater at room temperature, and stir to remove hexavalent chromium; the dosage of the iron-silicon composite adsorbent is 0.2-1.4 g / L.

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