Preparation method and application of lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel bead

Abstract

The invention discloses a preparation method and application of lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads, coal gangue and alginate are compounded by adopting a strategy of multi-component blending and treatment of waste with waste, and are cross-linked in lanthanum chloride and calcium chloride solutions to synthesize the composite hydrogel beads, so that the lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads are prepared. The hydrogel bead has excellent adsorption performance and structural stability, fluoride in water can be efficiently removed, the obtained composite hydrogel can effectively remove fluoride in surface water or underground water, and the treatment effect meets the requirement for the concentration of fluorine in drinking water.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel bead, belonging to the technical field of water treatment. Background Art

[0002] Fluoride widely exists in nature and industrial applications. An appropriate amount of fluoride is beneficial to human health, conducive to bone development and prevention of dental caries. However, excessive fluoride accumulation can cause toxic effects, mainly manifested as damage to bones and teeth, such as dental fluorosis, skeletal fluorosis, arthritis, osteomalacia, etc. Fluoride exposure may also affect thyroid immune function, damage organ function, lead to metabolic disorders, and even affect the nervous system.

[0003] For fluoride pollution, there are currently various technologies being studied and applied, including chemical precipitation method, adsorption method, ion exchange method, membrane separation technology, and biological treatment method, etc. Each method has its unique advantages and applicable scenarios. The adsorption method is one of the most widely applicable water treatment technologies at present. In terms of deep fluoride removal, by exchanging other ions or groups on the adsorbent with groundwater or surface water, fluoride is left on the adsorbent, thereby achieving the removal of fluoride. It has certain advantages in terms of cost, adsorption performance, selectivity, etc., and has good treatment effects and strong operability.

[0004] Coal gangue is a solid waste generated during the extraction and washing of raw coal. It is composed of various minerals, water, and a small amount of organic matter, rich in various clay minerals and beneficial metal oxides, and itself has a certain pore structure and surface activity.

[0005] In view of the limitations of existing adsorption technical means in treating water bodies with excessive fluoride, there is an urgent need to prepare a material to effectively treat fluoride in water bodies and improve its treatment efficiency and safety. Summary of the Invention

[0006] The present invention provides a preparation method and application of a lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel bead. The obtained composite hydrogel can effectively remove fluoride from water bodies, including surface water or groundwater, and the treatment effect meets the requirements of the fluoride concentration in the effluent of drinking water (≤1.5 mg / L).

[0007] The technical solution of the present invention is as follows: A preparation method of a lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel bead, comprising the following steps: First step: Add sodium alginate and coal gangue powder into deionized water. After ultrasonic treatment, stir evenly to obtain a mixed solution; Second step: Add lanthanum chloride heptahydrate and anhydrous calcium chloride into deionized water, and stir evenly to obtain a metal solution; Step 3: Slowly drop the mixed solution obtained in Step 1 into the metal solution through a syringe. Under the cross-linking action of lanthanum ions and calcium ions, composite hydrogel beads are formed. Step 4: Let the formed composite hydrogel beads stand for storage to ensure a complete cross-linking reaction. Step 5: Wash the prepared hydrogel several times with deionized water until it is neutral to remove excess metal ions. Freeze-dry the gel beads to obtain the final composite hydrogel beads.

[0008] Preferably, in Step 1, the concentration of sodium alginate in the mixed solution is 10 - 30 g / L, and the concentration of coal gangue is 10 - 80 g / L.

[0009] Preferably, in Step 1, the ultrasonic treatment time is 10 - 30 min.

[0010] Preferably, in Step 2, the molar ratio of lanthanum chloride heptahydrate and calcium chloride added is (1 - 3):(1 - 3), and the total metal concentration in the metal solution is 1 - 3 mol / L.

[0011] Preferably, in Step 3, the volume ratio of the mixed solution to the metal solution is 10:3 - 4.

[0012] Preferably, in Step 4, the standing time is 24 - 48 h.

[0013] Preferably, in Step 5, the freeze-drying time is 24 - 48 h, and the temperature is -40 °C.

[0014] The present invention also provides a lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel bead prepared by the above-mentioned preparation method for removing fluoride in fluoride-containing water. The composite hydrogel bead prepared by the present invention has excellent adsorption performance and structural stability, can efficiently remove fluoride in water, and the treatment effect meets the fluoride concentration requirement in drinking water (≤1.5 mg / L).

[0015] The introduction of coal gangue in the present invention can improve the mechanical strength of the sodium alginate hydrogel, endow it with a larger adsorption capacity, thereby overcoming the defect of the short cracking period of the traditional hydrogel and effectively removing fluoride. Modifying with metal elements lanthanum and calcium can not only improve the adsorption capacity of the hydrogel, but also enhance the selectivity of the hydrogel for fluoride adsorption, effectively remove fluoride, and overcome the defect of the short cracking period of the traditional hydrogel.

[0016] In the present invention, sodium alginate (SA), as one of the most common natural polysaccharides, has abundant hydroxyl and carboxyl groups in its structure, shows strong affinity for positively charged multivalent metal ions (such as Ca, Al, La, etc.), and can develop stable metal-biopolymer composites through cross-linking. Coal gangue has a porous structure and a high specific surface area, and has good adsorption performance. The lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel beads prepared in the present invention combine the advantages of sodium alginate hydrogel and coal gangue, use coal gangue to improve the mechanical strength of sodium alginate hydrogel, and effectively remove fluoride in water through the synergistic action of multiple mechanisms such as the formation of insoluble precipitates, in-sphere complexation, and adsorption fixation.

[0017] In the present invention, the metal elements lanthanum and calcium are used for modification, which can not only improve the adsorption capacity of the hydrogel but also enhance the selectivity of the hydrogel for fluoride adsorption.

[0018] In the lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel beads prepared in the present invention, a strategy of multi-component blending and treating waste with waste is adopted. Coal gangue is combined with sodium alginate and cross-linked in lanthanum chloride and calcium chloride solutions to synthesize composite hydrogel beads. Description of the Drawings

[0019] Figure 1 Removal rate of different dosages of coal gangue in lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel beads; Figure 2 Removal rate of different lanthanum-calcium ratios in lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel beads; Figure 3 Removal rate of the dosage of adsorbent in lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel beads; Figure 4 Removal rate of lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel beads in different initial fluoride concentrations; Figure 5 Removal rate of lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel beads in fluoride solutions with different pH values; Figure 6 Removal rate of lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel beads after being reused 5 times. Detailed Description of the Invention

[0020] The present invention will be further described in detail below in conjunction with embodiments, but the present invention is not limited to the given embodiments.

[0021] Example 1

[0022] Add 2 g of sodium alginate to 100 mL of deionized water, and perform ultrasonic stirring for 10 min to obtain a mixed solution; Add 11.14 g of lanthanum chloride heptahydrate and 3.33 g of anhydrous calcium chloride to 30 mL of deionized water, and stir evenly to obtain a metal solution; Slowly drop the mixed solution into the metal solution with a syringe to form hydrogel balls, let it stand and crosslink for 24 h, wash the prepared hydrogel several times with deionized water until neutral to remove excess metal ions, and obtain lanthanum-calcium bimetal modified alginate composite hydrogel beads. After draining the obtained hydrogel, freeze-dry it at -40 °C for 48 h for storage.

[0023] Example 2

[0024] Add 2 g of sodium alginate and 1 g of coal gangue to 100 mL of deionized water, and perform ultrasonic stirring for 20 min to obtain a mixed solution; Add 11.14 g of lanthanum chloride heptahydrate and 3.33 g of anhydrous calcium chloride to 30 mL of deionized water, and stir evenly to obtain a metal solution; Slowly drop the mixed solution into the metal solution with a syringe. Under the crosslinking action of lanthanum ions and calcium ions, form composite hydrogel beads, let it stand and crosslink for 24 h, wash the prepared hydrogel several times with deionized water until neutral to remove excess metal ions, and obtain lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads. After draining the obtained hydrogel, freeze-dry it at -40 °C for 48 h for storage.

[0025] Example 3

[0026] Add 2 g of sodium alginate and 2 g of coal gangue to 100 mL of deionized water, and perform ultrasonic stirring for 20 min to obtain a mixed solution; Add 11.14 g of lanthanum chloride heptahydrate and 3.33 g of anhydrous calcium chloride to 30 mL of deionized water, and stir evenly to obtain a metal solution; Slowly drop the mixed solution into the metal solution with a syringe. Under the crosslinking action of lanthanum ions and calcium ions, form composite hydrogel beads, let it stand and crosslink for 36 h, wash the prepared hydrogel several times with deionized water until neutral to remove excess metal ions, and obtain lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads. After draining the obtained hydrogel, freeze-dry it at -40 °C for 36 h for storage.

[0027] Example 4

[0028] Add 2 g of sodium alginate and 4 g of coal gangue to 100 mL of deionized water, and perform ultrasonic stirring for 20 min to obtain a mixed solution; Add 11.14 g of lanthanum chloride heptahydrate and 3.33 g of anhydrous calcium chloride to 30 mL of deionized water, and stir evenly to obtain a metal solution; Slowly drip the mixed solution into the metal solution with a syringe. Under the cross-linking action of lanthanum ions and calcium ions, composite hydrogel beads are formed. Let it stand for cross-linking for 24 h, wash the prepared hydrogel several times with deionized water until it is neutral to remove excess metal ions, and obtain lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads. After draining the obtained hydrogel, freeze-dry it at -40 °C for 48 h and store it.

[0029] Example 5

[0030] Add 2 g of sodium alginate and 6 g of coal gangue to 100 mL of deionized water, and perform ultrasonic stirring for 20 min to obtain a mixed solution; Add 11.14 g of lanthanum chloride heptahydrate and 3.33 g of anhydrous calcium chloride to 30 mL of deionized water, and stir evenly to obtain a metal solution; Slowly drip the mixed solution into the metal solution with a syringe. Under the cross-linking action of lanthanum ions and calcium ions, composite hydrogel beads are formed. Let it stand for cross-linking for 24 h, wash the prepared hydrogel several times with deionized water until it is neutral to remove excess metal ions, and obtain lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads. After draining the obtained hydrogel, freeze-dry it at -40 °C for 48 h and store it.

[0031] Example 6

[0032] Add 2 g of sodium alginate and 8 g of coal gangue to 100 mL of deionized water, and perform ultrasonic stirring for 20 min to obtain a mixed solution; Add 11.14 g of lanthanum chloride heptahydrate and 3.33 g of anhydrous calcium chloride to 30 mL of deionized water, and stir evenly to obtain a metal solution; Slowly drip the mixed solution into the metal solution with a syringe. Under the cross-linking action of lanthanum ions and calcium ions, composite hydrogel beads are formed. Let it stand for cross-linking for 24 h, wash the prepared hydrogel several times with deionized water until it is neutral to remove excess metal ions, and obtain lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads. After draining the obtained hydrogel, freeze-dry it at -40 °C for 48 h and store it.

[0033] Example 7

[0034] Add 1 g of sodium alginate and 6 g of coal gangue to 100 mL of deionized water, and perform ultrasonic stirring for 10 min to obtain a mixed solution; Add 11.14 g of lanthanum chloride heptahydrate and 3.33 g of anhydrous calcium chloride to 35 mL of deionized water, and stir evenly to obtain a metal solution; Slowly drip the mixed solution into the metal solution with a syringe. Under the cross-linking action of lanthanum ions and calcium ions, composite hydrogel beads are formed. Let it stand for cross-linking for 36 h, wash the prepared hydrogel several times with deionized water until it is neutral to remove excess metal ions, and obtain lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads. After draining the obtained hydrogel, freeze-dry it at -40 °C for 24 h for storage.

[0035] Example 8

[0036] Add 3 g of sodium alginate and 8 g of coal gangue to 100 mL of deionized water, and perform ultrasonic stirring for 30 min to obtain a mixed solution; Add 11.14 g of lanthanum chloride heptahydrate and 3.33 g of anhydrous calcium chloride to 40 mL of deionized water, and stir evenly to obtain a metal solution; Slowly drip the mixed solution into the metal solution with a syringe. Under the cross-linking action of lanthanum ions and calcium ions, composite hydrogel beads are formed. Let it stand for cross-linking for 48 h, wash the prepared hydrogel several times with deionized water until it is neutral to remove excess metal ions, and obtain lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads. After draining the obtained hydrogel, freeze-dry it at -40 °C for 36 h for storage.

[0037] Example 9

[0038] Add 2 g of sodium alginate and 6 g of coal gangue to 100 mL of deionized water, and perform ultrasonic stirring for 20 min to obtain a mixed solution; Add 16.71 g of lanthanum chloride heptahydrate and 1.66 g of anhydrous calcium chloride to 30 mL of deionized water, and stir evenly to obtain a metal solution; Slowly drip the mixed solution into the metal solution with a syringe. Under the cross-linking action of lanthanum ions and calcium ions, composite hydrogel beads are formed. Let it stand for cross-linking for 24 h, wash the prepared hydrogel several times with deionized water until it is neutral to remove excess metal ions, and obtain lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads. After draining the obtained hydrogel, freeze-dry it at -40 °C for 48 h for storage.

[0039] Example 10

[0040] Add 2 g of sodium alginate and 6 g of coal gangue to 100 mL of deionized water, and perform ultrasonic stirring for 20 min to obtain a mixed solution; Add 14.85 g of lanthanum chloride heptahydrate and 2.22 g of anhydrous calcium chloride to 30 mL of deionized water, and stir evenly to obtain a metal solution; Slowly drip the mixed solution into the metal solution with a syringe. Under the cross-linking action of lanthanum ions and calcium ions, composite hydrogel beads are formed. Let it stand for cross-linking for 24 h, and wash the prepared hydrogel several times with deionized water until it is neutral to remove excess metal ions, obtaining lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads. After draining the obtained hydrogel, freeze-dry it at -40 °C for 48 h for storage.

[0041] Example 11

[0042] Add 2 g of sodium alginate and 6 g of coal gangue to 100 mL of deionized water, and perform ultrasonic stirring for 20 min to obtain a mixed solution; Add 7.43 g of lanthanum chloride heptahydrate and 4.44 g of anhydrous calcium chloride to 30 mL of deionized water, and stir evenly to obtain a metal solution; Slowly drip the mixed solution into the metal solution with a syringe. Under the cross-linking action of lanthanum ions and calcium ions, composite hydrogel beads are formed. Let it stand for cross-linking for 24 h, and wash the prepared hydrogel several times with deionized water until it is neutral to remove excess metal ions, obtaining lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads. After draining the obtained hydrogel, freeze-dry it at -40 °C for 48 h for storage.

[0043] Example 12

[0044] Add 2 g of sodium alginate and 6 g of coal gangue to 100 mL of deionized water, and perform ultrasonic stirring for 20 min to obtain a mixed solution; Add 5.57 g of lanthanum chloride heptahydrate and 5.09 g of anhydrous calcium chloride to 30 mL of deionized water, and stir evenly to obtain a metal solution; Slowly drip the mixed solution into the metal solution with a syringe. Under the cross-linking action of lanthanum ions and calcium ions, composite hydrogel beads are formed. Let it stand for cross-linking for 24 h, and wash the prepared hydrogel several times with deionized water until it is neutral to remove excess metal ions, obtaining lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads. After draining the obtained hydrogel, freeze-dry it at -40 °C for 48 h for storage.

[0045] Example 13

[0046] The removal effect of lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads on fluoride in water is as follows: The composite hydrogels prepared in Examples 1 to 12 were respectively added into the fluoride-containing solution. The initial dosage was 0.5 g / L, the initial fluoride concentration in the reaction flask was 5.0 mg / L, the initial pH value of the fluoride-containing solution was 7.0, the adsorption temperature was 25 °C, and they were oscillated and adsorbed in a constant-temperature air bath oscillator for 0 to 10 hours at a rotation speed of 180 r / min. 1 mL of the solution was taken out at 0, 0.5, 1, 2, 3, 5, 7, and 10 hours respectively, and the fluoride concentration after adsorption was measured with a fluoride ion selective electrode.

[0047] After the adsorption was completed, the lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads had a complete structure and did not rupture. Figure 1 The removal rates of coal gangue by the hydrogel beads with different dosages of coal gangue in Examples 1-6 were shown. It can be seen that the hydrogel beads had the best effect when the dosage of coal gangue was 6% (Example 5). Figure 2 The removal rates of coal gangue by the hydrogel beads with different lanthanum-calcium ratios added in Examples 5, 9, 10, 11, and 12 were shown. It can be seen that when the dosage of coal gangue was 6% and the lanthanum-calcium ratio was changed, the adsorption effect was the best when the lanthanum-calcium ratio was 1:2 (Example 11), and the fluoride removal rate could reach 87.49%, indicating that the hydrogel had good fluoride adsorption performance.

[0048] Example 14

[0049] Verify the influence of the dosage of lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads on the removal effect of fluoride in water.

[0050] The composite hydrogel prepared in Example 11 was added into the fluoride-containing solution. The dosage each time was 0.1, 0.3, 0.5, 0.7, 1.0 g / L. The initial fluoride concentration in the reaction flask was 5.0 mg / L, the initial pH value of the fluoride-containing solution was 7.0, the adsorption temperature was 25 °C, and they were oscillated and adsorbed in a constant-temperature air bath oscillator for 0 to 10 hours at a rotation speed of 180 r / min. 1 mL of the solution was taken out at 0, 0.5, 1, 2, 3, 5, 7, and 10 hours respectively, and the fluoride concentration after adsorption was measured with a fluoride ion selective electrode.

[0051] The influence results of the dosage of lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads on the fluoride removal effect in water are as Figure 3As shown in the figure, from the experimental result data: with the increase of adsorption time, the removal effect of adsorbents with different dosages on fluoride in water has been improved. When the adsorption time is 10 hours, the adsorbents with different dosages can all control the fluoride concentration in the effluent below 1.5 mg / L. When the dosage of lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel beads is 0.3 g / L, the highest removal rate of fluoride in water is 87.44%. It can be seen that when the dosage of lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel beads is 0.3 g / L, its adsorption effect is the best.

[0052] Example 15

[0053] Verify the removal effect of lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel beads on different fluoride concentrations in water.

[0054] The composite hydrogels prepared in Example 11 were respectively added into fluoride solutions with a dosage of 0.3 g / L. The initial fluoride concentration gradients in the reaction flasks were: 3.0, 5.0, 7.0, 10.0, 15.0 mg / L. The initial pH value of the fluoride solution was 7.0, the adsorption temperature was 25 °C, and the adsorption was carried out by shaking in a constant-temperature air bath oscillator for 0 - 10 hours at a rotation speed of 180 r / min. 1 mL of the solution was taken out at 0, 0.5, 1, 2, 3, 5, 7, and 10 hours respectively, and the fluoride concentration after adsorption was measured with a fluoride ion selective electrode.

[0055] The influence results of different initial fluoride concentrations on the fluoride removal effect in water are as Figure 4 shown. From the experimental result data: when the initial fluoride concentration is 3 mg / L, the removal rate of fluoride in water by the composite hydrogel is 80.45%; when the initial fluoride concentration is 10 mg / L, the removal rate of fluoride in water increases to 86.63%, and the adsorption capacity of the adsorbent tends to be stable; when the initial fluoride concentration is 15 mg / L, the removal rate of fluoride in water is 82.34%.

[0056] It can be seen that when the fluoride concentration in water is low, the adsorption capacity of the lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel bead adsorbent is not fully exerted; when the fluoride concentration in water gradually increases, the adsorption capacity of the lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel bead adsorbent will increase, but there is a certain limit.

[0057] Example 16

[0058] Verify the effect of pH value on the removal of fluoride by lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel beads in water.

[0059] The composite hydrogel prepared in Example 11 was added to the fluoride-containing solution at an addition amount of 0.3 g / L. The initial fluoride concentration in the reaction flask was 10.0 mg / L, the initial pH value of the fluoride solution was 5.5, 6.0, 7.0, 8.0, 9.0, the adsorption temperature was 25 °C, and it was oscillated and adsorbed in a constant-temperature air bath oscillator for 0 - 10 hours at a rotation speed of 180 r / min. 1 mL of the solution was taken out at 0, 0.5, 1, 2, 3, 5, 7, and 10 hours respectively, and the fluoride concentration after adsorption was measured using a fluoride ion selective electrode.

[0060] The influence results of different initial pH values on the fluoride removal effect in water are as Figure 5 shown. From the experimental result data: when the initial pH = 5.5 - 8.0, the fluoride concentration in the effluent was less than 1.5 mg / L, and the removal rate of fluoride in water by the adsorbent was higher than 72%; among them, when the initial pH = 6.0, the concentration of fluoride in water was the lowest and was 0.65 mg / L, and the removal rate of fluoride in water by the adsorbent was the highest and was 87.83%. When the initial pH = 9.0, the fluoride concentration was the highest and was 1.70 mg / L, and the removal rate of fluoride in water was the lowest and was 67.74%.

[0061] It can be seen from this that the lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel bead adsorbent has poor alkali resistance, and the optimal adsorption pH value range of the lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel bead adsorbent is 5.5 - 8.0.

[0062] Example 17

[0063] Verify the desorption and regeneration ability of the lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel bead adsorbent: The composite hydrogel prepared in Example 11 was added to the fluoride-containing solution at an addition amount of 0.3 g / L. The initial fluoride concentration in the reaction flask was 5 mg / L, the initial pH value of the fluoride solution was 7.0, the adsorption temperature was 25 °C, and it was oscillated and adsorbed in a constant-temperature air bath oscillator at a rotation speed of 180 r / min. After the adsorption process was completed, the hydrogel beads were regenerated using a dilute alkali solution (dilute NaOH solution) to remove the adsorbed fluoride, washed with deionized water until neutral, and then the hydrogel beads were placed in a new fluoride-containing solution again for an adsorption experiment to test whether their adsorption performance was restored. The adsorption and regeneration steps were repeated 5 times to evaluate the adsorption stability and regeneration ability of the hydrogel beads, and the removal rate of fluoride after each cycle was recorded to determine the adsorption stability.

[0064] The defluorination effect of the lanthanum-calcium bimetal modified coal gangue / alginate composite hydrogel beads after 5 regenerations is as Figure 6As shown, from the experimental result data, after 5 cycles, the concentration of fluoride in the water body is 0.96 mg / L, and the removal rate of fluoride in the water by the adsorbent is 81.49%. The adsorption efficiency of the lanthanum-calcium bimetal modified coal gangue / sodium alginate composite hydrogel bead adsorbent remains, indicating its good reusability.

[0065] 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 them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing lanthanum-calcium bimetallic modified coal gangue / alginate composite hydrogel beads, characterized in that: The following steps are involved: The first step is to add sodium alginate and coal gangue powder into deionized water, and after ultrasonic treatment, stir evenly to obtain a mixed solution; Step 2: Add lanthanum chloride heptahydrate and anhydrous calcium chloride into deionized water and stir evenly to obtain a metal solution; Step 3: slowly drop the mixed solution into the metal solution to form composite hydrogel beads under the cross-linking action of lanthanum ions and calcium ions; Step 4: leaving the formed composite hydrogel beads to stand; Step 5: Wash the hydrogel with deionized water until it is neutral and then freeze-dry it to obtain composite hydrogel beads.

2. The method for preparing the lanthanum-calcium bimetallic modified coal gangue / alginate composite hydrogel beads according to claim 1, characterized in that: In the first step, the concentration of sodium alginate in the mixed solution is 10-30 g / L, and the concentration of coal gangue is 10-80 g / L.

3. The method for preparing the lanthanum-calcium bimetallic modified gangue / alginate composite hydrogel beads according to claim 1, characterized in that: In the first step, the ultrasonic treatment time is 10 to 30 minutes.

4. The method for preparing the lanthanum-calcium bimetallic modified coal gangue / alginate composite hydrogel beads according to claim 1, characterized in that: In the second step, the molar ratio of lanthanum chloride heptahydrate to anhydrous calcium chloride is (1~3):(1~3), and the metal concentration in the metal solution is 1~3 mol / L.

5. The method for preparing the lanthanum-calcium bimetallic modified coal gangue / alginate composite hydrogel beads according to claim 1, characterized in that: In the third step, the volume ratio of the mixed solution to the metal solution is 10:(3~4).

6. The method for preparing the lanthanum-calcium bimetallic modified gangue / alginate composite hydrogel beads according to claim 1, characterized in that: In the fourth step, the standing time is 24 to 48 hours.

7. The method for preparing the lanthanum-calcium bimetallic modified gangue / alginate composite hydrogel beads according to claim 1, characterized in that: In the fifth step, the freeze-drying time is 24 to 48 hours at a temperature of -40°C.

8. The lanthanum-calcium bimetallic modified gangue / alginate composite hydrogel beads prepared by the preparation method of the lanthanum-calcium bimetallic modified gangue / alginate composite hydrogel beads according to claim 1 are used to remove fluoride from fluoride-containing water.

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