A trivalent chromium ion adsorbent and its preparation method and application

Abstract

The present invention belongs to the field of functional material preparation and primarily relates to a trivalent chromium ion adsorbent, its preparation method, and application. The method utilizes sodium alginate loaded with nano-hydroxyapatite and chitosan. The mixed solution is then uniformly dripped into a calcium chloride solution at a predetermined speed using a rubber-tipped dropper. After cross-linking, spherical particles are formed to obtain a high-performance trivalent chromium adsorbent. The adsorbent utilizes numerous groups, such as hydroxyl, amino, and carboxyl groups, attached to the spherical surface to chelate trivalent chromium, allowing the trivalent chromium to adhere to the particle surface, achieving the effect of efficiently removing trivalent chromium from aqueous solutions. The method is simple to operate, flexible, and highly practical, with broad application value.

Description

Technical Field

[0001] The invention belongs to the field of functional materials and mainly relates to a trivalent chromium ion adsorbent and a preparation method and application thereof. Background Art

[0002] Chromium is one of the main toxic metals that pollute the environment. 3+ Chromium compounds are essential to the human body, but excessive intake can be harmful and carcinogenic. Currently, chromium compounds are widely used in industrial technologies such as leather tanning, electroplating, and IT. The wastewater generated during their production and processing contains large amounts of trivalent chromium ions (Cr(III)). This heavy metal wastewater is difficult to degrade by microorganisms. Furthermore, because trivalent chromium ions are easily converted to the more toxic hexavalent chromium ions (Cr(VI)) under natural conditions, they cause water pollution, endangering human health and polluting the environment. Currently, the main methods for treating chromium-containing wastewater include physical adsorption and chemical precipitation, such as electrocoagulation, electrochemistry, ion exchange, and membrane separation. In recent years, there has been much research on the treatment of hexavalent chromium, while less research has been conducted on the removal of trivalent chromium. Although trivalent chromium is less toxic than hexavalent chromium, it can be converted to hexavalent chromium in nature. Furthermore, colloids in the environment strongly adsorb trivalent chromium, allowing chromium to enter the soil from water. Preventing further soil contamination from chromium in wastewater, and given the ease with which hexavalent chromium is reduced to trivalent chromium, research on the removal of trivalent chromium is of great significance.

[0003] Currently, many researchers have conducted research on the removal of trivalent chromium from wastewater or soil. For example, CN109046293B discloses a method for preparing a trivalent chromium ion adsorbent. The method uses a silane coupling agent to functionalize a mesoporous material with amino groups. Then, 2-acetylthiophene is grafted onto the mesoporous material via a Schiff base reaction between the amino groups on the surface of the mesoporous material and 2-acetylthiophene, resulting in a high-performance trivalent chromium ion adsorbent. This adsorbent, through the ingenious combination of mesoporous materials and organic molecules, not only significantly improves the adsorption capacity of the mesoporous material for trivalent chromium ions but also addresses the shortcomings of organic molecules in practical applications, such as poor biocompatibility, strong toxic side effects, and difficulty in recycling. The adsorbent has an adsorption rate of over 95% for Cr(III) at an initial concentration of 40 mg / L. While the adsorbent exhibits good adsorption performance for low-concentration Cr(III), no further research has been conducted on the treatment of medium- and high-concentration Cr(III). For the treatment of medium and high concentrations of Cr(III), CN112604674B discloses "a fiber-based adsorption material, its preparation method, and the removal of trivalent chromium in water." The fiber-based adsorption material is based on polypropylene. Amino groups are first introduced by radiation grafting and then prepared by chemical grafting. It has a good adsorption effect on medium and high concentrations of Cr(III), and its maximum dynamic adsorption capacity can reach 218 mg / g. However, the preparation method of the fiber-based adsorption material is too complicated, and its pretreatment is time-consuming, which makes the entire adsorbent preparation process too long. Summary of the Invention

[0004] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art and to provide a high-efficiency trivalent chromium ion adsorbent and a preparation method and application thereof.

[0005] The technical solutions of the present invention are as follows:

[0006] A method for preparing a trivalent chromium ion adsorbent comprises the following steps: firstly mixing nano-hydroxyapatite, sodium alginate, chitosan and ammonium sulfate, and then cross-linking them in a calcium chloride solution to obtain spherical particles for adsorbing trivalent chromium ions.

[0007] Furthermore, the molar ratio of the nano-hydroxyapatite, sodium alginate, chitosan and ammonium sulfate is 4:4:1:2.

[0008] Further, the following steps are included:

[0009] Step 1: Dissolve sodium alginate powder in ultrapure water and stir at 40-60°C for 0.5-1h to obtain a sodium alginate solution;

[0010] Step 2: dissolving the nanohydroxyapatite in ultrapure water, stirring at 40-60° C. for 0.25-0.5 h to obtain a nanohydroxyapatite solution;

[0011] Step 3: After mixing the sodium alginate solution and the nano-hydroxyapatite solution, add chitosan and ammonium sulfate, and stir evenly at 40-80°C at a stirring speed of 800-1000 rpm min -1 , obtaining a mixed solution;

[0012] Step 4: dripping the mixed solution into a calcium chloride solution containing acetic acid at a rate of 6-10 mL / min to form spherical particles; and then drying to obtain a trivalent chromium ion adsorbent.

[0013] Furthermore, in step 1, the concentration of the sodium alginate solution is 10-20 g / L.

[0014] Furthermore, in step 2, the concentration of the nano-hydroxyapatite solution is 10-30 g / L.

[0015] Furthermore, in step 4, the mass volume ratio of calcium chloride to the solution is 1-4% (g / ml).

[0016] Furthermore, the amount of acetic acid added is 1-2% of the volume of the calcium chloride solution.

[0017] The present invention also discloses a trivalent chromium ion adsorbent, which is prepared by any of the above preparation methods.

[0018] The present invention also discloses an application of the above-mentioned high-efficiency trivalent chromium ion adsorbent in adsorbing heavy metal Cr(III). Preferably, the concentration of the heavy metal Cr(III) is 20-100 mg / L.

[0019] The present invention has the following beneficial effects: a trivalent chromium adsorbent material is provided, using sodium alginate as a carrier, introducing hydroxyl, amino, and carboxyl groups by adding nanohydroxyapatite and chitosan, and then adding ammonium sulfate as a surfactant during the crosslinking process with a calcium chloride solution. This helps stabilize the crosslinking system and effectively improves the efficiency of sodium alginate loading with nanohydroxyapatite and chitosan, facilitating the loading process. The addition of acetic acid promotes the crosslinking reaction between the material and the calcium chloride solution, accelerating the crosslinking reaction rate and adjusting the crosslinking density to achieve a more uniform crosslinking network. This method is simple to operate, flexible, and highly practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 1 is a schematic flow chart of the preparation method of the trivalent chromium ion adsorbent in Example 4;

[0021] Figure 2 is the adsorption performance of different trivalent chromium ion adsorbents in Examples 1-4;

[0022] Figure 3This is a graph showing the changes before and after the trivalent chromium ion adsorbent (nHAP+CS)@SA adsorbs trivalent chromium in Example 4;

[0023] Figure 4 This is a graph showing the change in adsorption performance of the trivalent chromium ion adsorbent (nHAP+CS)@SA in Example 5 for trivalent chromium in wastewater at different cycle times. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described below with reference to specific embodiments and accompanying drawings.

[0025] The nano-hydroxyapatite, sodium alginate and chitosan in the following examples were purchased from Sinopharm Chemical Pharmaceutical Co., Ltd., and the preparation process was referenced to Figure 1 .

[0026] Example 1

[0027] 1.0 g of sodium alginate powder was dissolved in ultrapure water and the volume was adjusted to 50 ml. The solution was stirred at 60° C. for 1 h. Then, when the solution was cooled to room temperature, it was dripped into a calcium chloride solution containing acetic acid at a uniform speed (6-10 mL / min) using a rubber-tipped dropper for crosslinking for 4 h. The mass volume ratio of the calcium chloride solution was 2% (g / ml) and the liquid volume ratio of acetic acid was 1%. After crosslinking, the solution was rinsed twice with ultrapure water and placed at room temperature for 2 h. The surface moisture was then drained to obtain a trivalent chromium adsorbent SA. 1.0 g was weighed and placed in a 100 mg / L Cr(III) solution for adsorption for 12 h and 24 h. The residual Cr(III) in the solution was measured and the adsorption rate was calculated.

[0028] Example 2

[0029] 1.0 g of sodium alginate powder and 0.25 g of chitosan were dissolved in ultrapure water respectively, stirred at 60 ° C for 1 hour, and then the two were mixed evenly. When the mixed liquid was cooled to room temperature, it was dripped into a calcium chloride solution containing acetic acid at a uniform speed (6-10 mL / min) with a rubber-tipped dropper for crosslinking for 4 hours. The mass volume ratio of the calcium chloride solution was 2% (g / ml) and the liquid volume ratio of acetic acid was 1%. After crosslinking, it was rinsed twice with ultrapure water and placed at room temperature for 2 hours. After draining its surface moisture, the trivalent chromium adsorbent CS@SA was obtained. 1.0 g was weighed and placed in a Cr(III) solution with a concentration of 100 mg / L. After adsorption for 12 hours and 24 hours, the residual Cr(III) in the solution was measured and the adsorption rate was calculated.

[0030] Example 3

[0031] 1.0 g of sodium alginate powder and 1.0 g of nanohydroxyapatite were dissolved in ultrapure water respectively. The sodium alginate was stirred at 60°C for 1 h, and the nanohydroxyapatite was stirred at 60°C for 0.5 h. The two were then mixed evenly. When the mixture cooled to room temperature, it was dripped into a calcium chloride solution containing acetic acid at a uniform speed (6-10 mL / min) using a rubber-tipped dropper for crosslinking for 4 h. The mass volume ratio of the calcium chloride solution was 2% (g / ml) and the liquid volume ratio of the acetic acid was 1%. After crosslinking, it was rinsed twice with ultrapure water and placed at room temperature for 2 h. The surface moisture was then drained to obtain the trivalent chromium adsorbent nHAP@SA. 1.0 g was weighed and placed in a 100 mg / L Cr(III) solution for adsorption for 12 h and 24 h. The residual Cr(III) in the solution was measured and the adsorption rate was calculated.

[0032] Example 4

[0033] 1.0 g of sodium alginate powder, 1.0 g of nanohydroxyapatite, and 0.25 g of chitosan were dissolved in ultrapure water respectively. Sodium alginate was stirred at 60°C for 1 h, and nanohydroxyapatite and chitosan were stirred at 60°C for 0.5 h. Then the three were mixed evenly. When the mixture was cooled to room temperature, it was dripped into a calcium chloride solution containing acetic acid at a uniform speed (6-10 mL / min) using a rubber-tipped dropper for crosslinking for 4 h. The mass volume ratio of the calcium chloride solution was 2% (g / ml) and the liquid volume ratio of acetic acid was 1%. After crosslinking, it was rinsed twice with ultrapure water and placed at room temperature for 2 h. The surface moisture was drained to obtain a trivalent chromium adsorbent (nHAP+CS)@SA. 1.0 g was weighed and placed in a 100 mg / L Cr(III) solution for adsorption for 12 h and 24 h. The residual Cr(III) in the solution was measured and the adsorption rate was calculated.

[0034] Example 5

[0035] Weigh 0.5g of the high-efficiency trivalent chromium ion adsorbent (nHAP+CS)@SA prepared according to Example 4 and 3+ The aqueous solution was subjected to cyclic adsorption treatment, that is, after one adsorption, the surface of the adsorption material was rinsed 2-3 times with ultrapure water, and then placed in a Cr(III) solution with an initial concentration of 100 mg / L for adsorption, and this cycle was repeated 5 times.

[0036] The adsorption performance of Examples 1-4 is shown in Figure 2 ,It can be seen from the figure that the best adsorption ,performance is obtained from Example 4, i.e. the (nHAP+CS)@SA adsorption ,material.

[0037] At the same time, the changes before and after the adsorption of trivalent chromium by the efficient trivalent chromium ion adsorbent (nHAP+CS)@SA in Example 4 are shown in FIG. Figure 3 ;from Figure 3It can be seen that the color of the material surface changes significantly before and after adsorption, indicating that Cr(III) is adsorbed onto the material.

[0038] The adsorption performance of the efficient trivalent chromium ion adsorbent (nHAP+CS)@SA for trivalent chromium in wastewater at different cycle times in Example 5 is shown in FIG. Figure 4 As can be seen from the figure, after 5 cycles, the adsorption rate of Cr(III) with a concentration of 100 mg / L is still 86.05%, reflecting the excellent adsorption performance of the material for Cr(III).

[0039] Under the premise that no conflict occurs, those skilled in the art may freely combine and superimpose the above-mentioned additional technical features.

[0040] The above description is only a preferred embodiment of the present invention. Any technical solution that achieves the purpose of the present invention by substantially the same means shall fall within the scope of protection of the present invention.

Claims

1. Application of a trivalent chromium ion adsorbent in adsorbing heavy metal Cr(III), characterized in that: The heavy metal Cr(III) concentration is 100 mg / L; Preparation method of the trivalent chromium ion adsorbent: Nano-hydroxyapatite, sodium alginate, chitosan and ammonium sulfate are mixed in a mass ratio of 4:4:1:2, and then cross-linked in a calcium chloride solution to prepare spherical particles adsorbing trivalent chromium ions; the method comprises the following steps: Step 1: Dissolve sodium alginate powder in ultrapure water and stir at 40-60°C for 0.5-1h to obtain a sodium alginate solution; Step 2: dissolving the nanohydroxyapatite in ultrapure water, stirring at 40-60° C. for 0.25-0.5 h to obtain a nanohydroxyapatite solution; Step 3: After mixing the sodium alginate solution and the nano-hydroxyapatite solution, chitosan and ammonium sulfate are added, and the mixture is stirred at 40-80° C. at a stirring speed of 800-1000 rpm to obtain a mixed solution; Step 4: dripping the mixed solution into a calcium chloride solution containing acetic acid at a rate of 6-10 mL / min to form spherical particles; and then drying to obtain a trivalent chromium ion adsorbent.

2. The use according to claim 1, characterized in that In the step 1, the concentration of the sodium alginate solution is 10-20 g / L.

3. The use according to claim 1, characterized in that In the step 2, the concentration of the nano-hydroxyapatite solution is 10-30 g / L.

4. The use according to claim 1, characterized in that The amount of acetic acid added is 1-2% of the volume of the calcium chloride solution.

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