A method for adsorbing heavy metal cadmium ions

Abstract

This scheme discloses a method for adsorbing cadmium ions in the field of heavy metal adsorption technology, specifically: using acylhydrazone-sodium alginate-Ca 2+ Composite adsorbent for heavy metal Cd 2+ Adsorption occurs, wherein the acylhydrazone-sodium alginate-Ca 2+ The composite adsorbent is prepared by reacting salicylhydrazine with sodium hydroxide after alkalization and oxidation with sodium periodate to form a salicylhydrazone compound, which is then cross-linked with sodium alginate. The method described in this application can simultaneously reduce the amount of distiller's grains and the heavy metal Cd. 2+ Pollution.

Description

Technical Field

[0001] This invention belongs to the field of heavy metal adsorption technology, and specifically relates to a method for adsorbing heavy metal cadmium ions. Background Technology

[0002] Distillery lees are a major waste product in the production of baijiu (Chinese liquor). They are characterized by high moisture content and acidity, and are difficult to manage and store. Large quantities of lees, if not properly managed, are highly susceptible to mold growth and environmental pollution, leading to ecological damage, economic losses, and resource waste. Therefore, the resource utilization of lees is crucial. In contrast, heavy metals are ubiquitous in the natural environment. Currently, the five most harmful heavy metals to human health are identified as Hg, Cd, As, Cr, and Pb. The most common sources of heavy metals in daily life are industrial and domestic wastewater. If this wastewater is not treated properly or is discharged directly into rivers, it will cause devastating environmental damage, making it impossible for the natural environment to recover for decades.

[0003] Therefore, designing a heavy metal adsorbent based on distiller's grains and then using it for heavy metal adsorption is of great significance for reducing pollution from distiller's grains and heavy metals. Summary of the Invention

[0004] The present invention aims to provide a method for adsorbing heavy metal cadmium ions, so as to simultaneously reduce the amount of cadmium ions from distiller's grains. 2+ Pollution.

[0005] One method for adsorbing heavy metal cadmium ions in this scheme is as follows: using acylhydrazone-sodium alginate-Ca 2+ Composite adsorbent for heavy metal Cd 2+ Adsorption occurs, wherein the acylhydrazone-sodium alginate-Ca 2+ The composite adsorbent is prepared by reacting salicylhydrazine with sodium hydroxide after alkalization and oxidation with sodium periodate to form a salicylhydrazone compound, and then cross-linking it with sodium alginate.

[0006] Furthermore, the alkalization of the lees includes the following steps: adding a 0.08-0.12 mol / L NaOH solution to the lees and stirring magnetically for 5-8 hours, then adding hydrochloric acid dropwise until neutral, centrifuging, removing the precipitate, drying, and grinding to obtain alkalized lees powder; the ratio of lees to NaOH solution is 90-110 g: 1 L.

[0007] Furthermore, the oxidation process of the distiller's grains includes the following steps: Anhydrous ethanol is added to the alkalized distiller's grains powder at a ratio of 4.5–5.5 mL: 1 g and magnetically stirred. Then, the mixture is heated in a water bath for 8–12 minutes at a temperature of 40–50 °C. Next, sodium periodate solution is added and stirred for 12–18 minutes. Then, hydrochloric acid is added dropwise until the pH reaches 4 and the mixture is stirred for 22–26 hours for oxidation. After oxidation, ethylene glycol is added and stirred for 1.5–2.5 hours. Then, anhydrous ethanol and deionized water are mixed and poured into the distiller's grains solution, filtered, dried, and then anhydrous ethanol is added again and filtered. Finally, the solid is removed, air-dried, and ground to obtain the oxidized distiller's grains. The sodium periodate solution consists of sodium periodate and deionized water at a ratio of 5 g: 40 mL, and the weight ratio of sodium periodate to the alkalized distiller's grains powder is 1:2.

[0008] Furthermore, the salicylhydrazine reaction process includes the following steps: oxidized lees and anhydrous ethanol are mixed and stirred for 1.8 to 2.5 hours at a ratio of 1 g to 25 to 35 mL. After stirring, salicylhydrazine and glacial acetic acid are added, and the mixture is heated in a water bath at 40 to 50°C and stirred for 22 to 25 hours. The mixture is then filtered, and the solid and liquid are separated. Finally, the solid is air-dried and ground to obtain the salicylhydrazone compound.

[0009] Furthermore, during the salicylhydrazine reaction, after solid-liquid separation, the solid is rinsed with anhydrous ethanol and then air-dried. Rinsing with anhydrous ethanol helps to remove residual chemical reagents and excess moisture from the surface of the solid (salicylic acid hydrazone compound), accelerating the drying process.

[0010] Furthermore, the crosslinking process between distiller's grains and sodium alginate includes the following steps: Deionized water is added to sodium alginate at a ratio of 160–240 mL: 1 g and stirred until the sodium alginate is completely dissolved. Then, a salicylic acid hydrazone compound with twice its weight of sodium alginate is added and dissolved. Next, 1,4-butanediol diglycidyl ether crosslinking agent is added and stirred for 10–14 h to obtain the acylhydrazone-sodium alginate compound. Finally, a 5% calcium chloride solution is added to the acylhydrazone-sodium alginate compound and stirred for 20–30 h to obtain the acylhydrazone-sodium alginate-Ca... 2+ Composite adsorbent.

[0011] Furthermore, during the crosslinking process of distiller's grains and sodium alginate, after the 1,4-butanediol diglycidyl ether crosslinking agent is added and stirred, the acylhydrazone-sodium alginate compound is frozen for 5-7 hours to form a block; then it is vacuum dried in a freeze dryer for 45-50 hours.

[0012] Furthermore, during the crosslinking process of distiller's grains and sodium alginate, after adding and stirring a calcium chloride solution, the acylhydrazone-sodium alginate-Ca... 2+ The composite adsorbent is frozen for 5-7 hours until it becomes a block; then it is vacuum dried in a freeze dryer for 45-50 hours.

[0013] Acylhydrazone-sodium alginate-Ca 2+ Composite adsorbent adsorption of Cd 2+ At that time, acylhydrazone-sodium alginate-Ca 2+ Composite adsorbent with Cd 2+ Simply mix the solutions and shake or stir.

[0014] This application utilizes distiller's grains to prepare a product with Cd adsorption capacity. 2+ Functional acylhydrazone-sodium alginate-Ca 2+ Composite adsorbents are effective in reducing the levels of distillers' grains and Cd. 2+ It has positive practical significance. Attached Figure Description

[0015] Figure 1 For SDG, ODG, SDG-A@Ca 2+ Infrared spectra of the adsorbent after desorption;

[0016] Figure 2 For SDG(a), ODG(b), SDG-A@Ca 2+ (c) Desorption of SDG-A@Cd 2+ (d) EDS elemental analysis plot;

[0017] Figure 3 For SDG(a), ODG(b), SDG-A@Ca 2+ (c) Desorption of SDG-A@Cd 2+ (d) SEM image;

[0018] Figure 4 Thermogravimetric (TG) analysis charts of distiller's grains before and after modification;

[0019] Figure 5 For SDG-A@Ca 2+ Zero potential point diagram;

[0020] Figure 6 pH for SDG-A@Ca 2+ Schematic diagram illustrating the influence of adsorbent adsorption performance;

[0021] Figure 7 For the initial concentration of SDG-A@Ca 2+ Schematic diagram showing the effect of adsorption capacity of adsorbent;

[0022] Figure 8 For SDG-A@Ca 2+ For Cd 2+ Adsorption isotherms of heavy metal ions; Langmuir and Freundlich adsorption isotherm model diagrams.

[0023] Figure 9For different adsorption times, SDG-A@Ca 2+ A schematic diagram of the adsorption capacity curve of the adsorbent for heavy metal ions;

[0024] Figure 10 SDG-A@Ca is a modified adsorbent 2+ Adsorption of Cd 2+ Fitting curves of quasi-first-order and quasi-second-order dynamic models;

[0025] Figure 11 For SDG-A@Ca 2+ A schematic diagram of the equilibrium adsorption capacity of the adsorbent at 25℃, 35℃, and 45℃;

[0026] Figure 12 For SDG-A@Ca 2+ Thermodynamic curves of adsorption of heavy metal ions by the adsorbent;

[0027] Figure 13 For SDG-A@Ca 2+ Repeated experiments were conducted to assess the adsorption rate of heavy metal ions. Detailed Implementation

[0028] The following detailed description illustrates the specific implementation method:

[0029] Acylhydrazone-sodium alginate-Ca 2+ The preparation method of the composite adsorbent includes the following steps:

[0030] Alkalization of distiller's grains: Take 200g of distiller's grains in a beaker, add 2L of 0.1mol / L NaOH, stir at 45℃ with a magnetic stirrer for 6h, add hydrochloric acid (HCl) dropwise until neutral, centrifuge, pour the precipitate and an appropriate amount of distilled water into a beaker and wash until neutral (add NaOH or HCl), then centrifuge, take out the precipitate, dry it, grind it into powder, and obtain alkalized distiller's grains powder (ADG) for later use.

[0031] Sodium periodate oxidation: Weigh 10g of ADG powder into a brown bottle, add 50mL of anhydrous ethanol, stir with a magnetic stirrer, and heat in a 45℃ water bath for 10min. Then, add NaIO4 solution dropwise to the brown bottle and stir for 15min. The NaIO4 solution is obtained by mixing 5g of sodium periodate (NaIO4,s) and 40mL of deionized water. Add HCl dropwise until the pH reaches 4, and stir for 24h, maintaining the pH at 4 during stirring. After oxidation, add 5mL of ethylene glycol and stir for 2h. Mix 50mL of anhydrous ethanol with 40mL of deionized water and pour into the distiller's grains solution, then filter using a Buchner funnel. After drying, add another 50mL of anhydrous ethanol and filter again. Remove the solid and air dry it in a fume hood for 4-6h. Grind it into powder to obtain oxidized distiller's grains (ODG), and store it in a desiccator for later use.

[0032] Salicylic acid hydrazide modification: 1 g of ODG powder and 30 mL of anhydrous ethanol were placed in a round-bottom flask and stirred at room temperature for 2 hours. After stirring, 3 g of salicylic acid hydrazide and 2 mL of glacial acetic acid were added successively. The mixture was heated in a water bath at 45 °C with a serpentine condenser and stirred for 24 hours (if the liquid level was too low, 10 mL of anhydrous ethanol was added; the standard for judging that the liquid level was too low was that the system color deepened and the viscosity increased). The Schiff base reaction was carried out to obtain a salicylic acid hydrazone-modified distillers' grains compound. The mixture was filtered, and after solid-liquid separation, 10 mL of anhydrous ethanol was added to rinse away residual chemical reagents and remove excess water. The mixture was then quickly air-dried. The solid was then placed in a fume hood and air-dried naturally for 6 hours. The solid was then ground into powder to obtain the salicylic acid hydrazone compound (SDG) for later use.

[0033] Pour 100 mL of deionized water and 0.5 g of sodium alginate (SA) into a beaker and stir with a magnetic stirrer at room temperature until SA is completely dissolved. Then slowly add 1 g of SDG to ensure complete dissolution. Add 1 mL of 1,4-butanediol diglycidyl ether (BDE) crosslinking agent and stir at room temperature for 12 h. After stirring, pour the mixture into a petri dish and freeze it in an ultra-low temperature freezer at -55℃ for 6 h. After vacuum drying in a freeze dryer, a foamy acylhydrazone-sodium alginate compound (SDG-A) is obtained.

[0034] 1 g of acylhydrazone-sodium alginate compound (SDG-A) was soaked in 100 mL of 5% calcium chloride solution for 24 h to induce a calcium ion exchange reaction, enhancing the hydrophobicity and heavy metal ion adsorption performance of the adsorbent. Simultaneously, it dissolved water-soluble impurities, improving the purity of the adsorbent. After vacuum filtration, it was frozen at -55℃ for 6 h, and then vacuum dried using a freeze dryer to obtain foamy acylhydrazone-sodium alginate-Ca 2+ Composite adsorbent (SDG-A@Ca) 2+ ).

[0035] Acylhydrazone-sodium alginate-Ca 2+ Composite adsorbent for Cd 2+ Adsorption experiment verification

[0036] 1.Cd 2+ Adsorption experiment

[0037] Weigh 2755 mg of cadmium nitrate and place it in a 100 mL volumetric flask to prepare a 1000 mg / L solution for later use. Take 10 mL of cadmium nitrate solution and 10 mg of SDG-A@Ca 2+ After adsorption equilibrium was reached by placing the sample in a constant temperature shaking incubator for 6 hours, the concentration was measured using an atomic absorption spectrophotometer. Finally, the concentration difference before and after the adsorption was calculated to obtain the Cd concentration. 2+ Adsorption capacity.

[0038] 2. Calculation Method

[0039] Modified adsorbent for Cd2+ Adsorption capacity q e Formulas 2-1 and 2-2 are used to calculate (mg / g) and removal rate R (%):

[0040]

[0041]

[0042] Where: C0 is the initial concentration of heavy metal ions; C e V is the concentration at equilibrium; V is the total volume of the sample solution; and m is the mass of the adsorbent.

[0043] 3. Measurement of equipotential points

[0044] Prepare 100 mL of 0.1 mol / L KCl solution, take 10 mL into 7 glass bottles, adjust the pH to 1, 2, 3, 4, 5, 6 and 7 respectively, and label them. Then add 10 mg of adsorbent, place the 7 groups of glass bottles in a constant temperature shaking incubator at 25℃ and 180 r / min for 6 h, and measure their pH value with a pH meter after shaking.

[0045] 4. Adsorption experiments under different pH conditions

[0046] Prepare 100 mL, 100 mg / L Cd 2+ 10 mL of the solution was taken into 7 groups of glass bottles, and HCl or NaOH was added to adjust the pH to 1, 2, 3, 4, 5, 6 and 7 respectively. The bottles were then numbered. 10 mg of adsorbent was added, and the 7 groups of glass bottles were placed in a constant temperature shaking incubator at 25℃ and shaken at 180 r / min for 6 h. After shaking, the bottles were taken out and the adsorption amount was measured by AAS.

[0047] 5.Cd 2+ Experiment on the effect of initial concentration on adsorption performance of adsorbent

[0048] Cd concentrations of 25 mg / L, 50 mg / L, 100 mg / L, 200 mg / L, 400 mg / L, 600 mg / L, 800 mg / L, and 1000 mg / L were respectively used. 2+ 10 mL of the solution was taken into each of the eight groups of glass bottles. 10 mg of adsorbent was weighed into each of the eight groups of glass bottles and placed in a constant temperature shaking incubator at 25 °C and 180 r / min for 6 h of shaking adsorption. After shaking, the adsorption rate was measured using AAS.

[0049] 6. Adsorption kinetics experiment

[0050] Prepare 150 mL of 1000 mg / L Cd solution 2+The solution was prepared by adding 150 mg of adsorbent and placing it in a constant temperature shaking incubator at 25°C and 180 r / min. 10 mL samples were taken at time points of 5, 10, 15, 20, 30, 60, 90, 120, 150, 180, 210, 240, 300, 330, and 360 min, and the adsorption capacity was measured in an AAS.

[0051] 7. Adsorption thermodynamics experiment

[0052] Three groups of Cd were prepared at concentrations of 25, 50, 100, 200, 400, 600, 800, and 1000 mg / L respectively. 2+ For each solution, take 10 mL of sample solution and weigh 10 mg of adsorbent. Incubate the solution at 25℃, 35℃, 45℃ and 180 r / min for 6 h. After incubation, measure the adsorption amount using AAS.

[0053] 8. Adsorption-desorption reuse experiment

[0054] Weigh 200 mg of adsorbent and prepare 200 mL of 100 mg / L Cd. 2+ The solution was placed in an Erlenmeyer flask and shaken at 25°C and 180 rpm for 6 hours. After shaking, 10 mL was transferred to a centrifuge tube and labeled. Separately, the adsorbent solid-liquid mixture was filtered using a Buchner funnel. The filtered adsorbent and 50 mL of 0.1 mol / L HCl solution were placed in a beaker and stirred for 3 hours to facilitate desorption. After stirring, the adsorbent was filtered again, and an appropriate amount of deionized water was added. The pH was adjusted to 7 with NaOH, filtered again, placed in a petri dish, and dried in an oven. This process was repeated.

[0055] Results and Analysis

[0056] 9.SDG-A@Ca 2+ FT-IR and EDS-mapping scans and analysis

[0057] Figure 1 It’s SDG, ODG, SDG-A@Ca 2+ The Fourier Transform Infrared (FT-IR) spectra of the adsorbent after desorption and resorption can be used to determine the shifts in characteristic absorption peaks of functional groups in the distiller's grains before and after modification, and whether new characteristic peaks are generated, thereby determining the SDG-A@Ca... 2+ Was the preparation successful? The absorption peak was at 3323 cm⁻¹. -1 This may be caused by stretching vibrations of functional groups such as -OH and -COOH; 2851 cm -1 This is caused by the stretching and contraction vibration of the CH structure. 1628cm in ODG -1 The peak value is caused by C=O stretching, compared to SDG-A@Ca. 2 +The absence of this peak in ADG indicates that the -OH functional group has been oxidized to an aldehyde group; the 1603 cm⁻¹ peak appears due to the substitution of C=O by the C=N structure. -1 Significant peak and C-N stretching vibration peak value 1095 cm⁻¹ -1 The peak is present in the ODG sample, but not in the Schiff base reaction, indicating that an acylhydrazone structure was formed.

[0058] To further understand SDG-A@Ca 2+ Structure and adsorption properties of SDG(a), ODG(b), and SDG-A@Ca 2+ (c) and adsorbed Cd 2+ The adsorbent SDG-A@Cd 2+ (d) Elemental analysis using EDS-mapping scanning: through Figure 2 ODG(a) and SDG-A@Ca 2+ (c) As shown in Table 1, Na atoms almost disappeared, with their content decreasing from 0.69% to 0; N and Ca atoms appeared, with their contents increasing from 0 to 9.99% and 5.9%, respectively; indicating that the oxidation and grafting modification were relatively successful. In Table 1, SDG-A@Ca... 2+ (c) and SDG-A@Cd 2+ (d) The Ca content increased from 5.59% to 0.04%, and the Cd content increased from 0% to 67.29%, demonstrating that during adsorption, it was not only the acylhydrazone groups that affected Cd. 2+ It has a very strong complexing ability, undergoes coordination reactions, and at the same time, Ca... 2+ and Cd 2+ Ion exchange occurs between them; from the FT-IR and EDS analysis, the formation of new and old functional groups and the changes in elemental content indicate that the acylhydrazone-modified distillers' grains adsorbent was successfully synthesized.

[0059] Table 1 Elemental Content Table

[0060]

[0061] 10. SEM

[0062] ADG(a), ODG(b), and SDG-A@Ca can be observed using SEM. 2+ (c) and SDG-A@Cd 2+ The structure following (d) is analyzed. Figure 3 In the ADG electron microscopy image, small particles with few pores, varying sizes, and smooth surfaces are observed, which, with oxidation, modification, and Ca... 2+ The exchange process results in a large specific surface area, a porous and non-uniform surface, and enhanced structural stability. After adsorbing cadmium ions, the surface roughness increases, the wrinkles become dense, the internal pore structure expands, and the pore rigidity increases.

[0063] 11. Thermogravimetric analysis

[0064] To determine the role of modified distiller's grains in Cd adsorption 2+ The thermal stability during the process was analyzed by heating the modified distiller's grains (a and b) in high-purity nitrogen using a thermogravimetric analyzer to assess their weight loss (e.g., Figure 4 The weight loss process of the distillers' grains before and after modification was found to be divided into three stages: In the first stage, when the temperature rose to 160K, the weight loss increased from 4.788% to 8.361%, which was likely due to the volatilization of free and bound water; in the second stage, when the temperature was between 160K and 230K, the weight loss decreased from 38.251% to 26.662%, which was likely due to the breakage of hydroxyl and hydrazone structures; in the third stage, when the temperature rose to 230K-420K, the weight loss was 49.248%, which was likely due to the excessively high temperature causing the modified distillers' grains to carbonize into ash, resulting in a sharp decrease in weight. By comparing the data of the distillers' grains before and after modification, the results show that the modified adsorbent has better thermal stability.

[0065] 12. Analysis of the effect of isoelectric point and different pH values ​​on the adsorption performance of the adsorbent

[0066] Depend on Figure 5 It can be seen that SDG-A@Ca 2+ The isoelectric point is 2.66, SDG-A@Ca 2+ When pH < 2.66, it carries a positive charge; when pH > 2.66, it carries a negative charge.

[0067] The pH of the solution is one of the factors affecting the efficiency of the adsorbent. Considering Cd... 2+ It forms a precipitate under alkaline conditions, but can form ions under acidic conditions; therefore, the experimental pH range is 1-7. Figure 6 It can be seen that as pH increases, Cd 2+ The removal rate increased, reaching a maximum adsorption rate of 81.6% at pH=6. Figure 5 Isotope plot analysis shows that the adsorbent is positively charged before pH = 2.6, and reacts with Cd. 2+ Like charges repel each other, and given the abundance of protons in this environment, they will react with Cd in the solution. 2+ Competition for a large amount of active potential leads to a low adsorption rate; as pH increases, the relative number of protons decreases, and SDG-A@Ca 2+ After 2.6, it carries a negative charge, in Cd 2+ Through chemical bonds and physical forces, it interacts with Cd 2+ Opposites attract; when pH > 6, the OH groups in the system... - Gradually increase, with Cd 2+ The formation of Cd(OH)2 hydroxide precipitate directly leads to the adsorbent's absorption of Cd. 2+The actual adsorption rate decreases. Therefore, SDG-A@Ca 2+ Adsorption of heavy metal ions Cd 2+ The optimal pH is 6.

[0068] 13. Adsorption isotherm analysis

[0069] At 25℃, different initial concentrations of Cd were compared. 2+ Adsorption experiments were conducted on SDG-A@Ca. 2+ Adsorption isotherms, such as Figure 7 As shown. From Figure 7 It can be seen that when Cd 2+ As the initial concentration of the solution increases, the adsorption capacity also increases; when the initial concentration of heavy metal is 400 mg / L, adsorption tends to reach equilibrium. This can be understood as the adsorbent having a sufficient number of active functional groups at its active sites, resulting in a higher adsorption capacity at lower Cd concentrations. 2+ At concentrations, Cd 2+ It cannot bind to all active sites; however, as the concentration gradually increases, all active sites bind to heavy metals, SDG-A@Ca 2+ The hole was Cd 2+ With coverage, the adsorption capacity tends to stabilize. Under these conditions, the saturated adsorption capacity is 92.9 mg / g.

[0070] 14. Effect of initial concentration on adsorption capacity

[0071] The adsorption isotherms were fitted using the Langmuir and Freundlich models to determine the experimental parameters. The formulas are as follows:

[0072] Langmuir adsorption isotherm equation:

[0073]

[0074] Freundlich adsorption isotherm equation:

[0075]

[0076] In the formula: C e The concentration of the heavy metal solution at equilibrium is expressed in mg / L; q e The adsorption amount at equilibrium is expressed in mg / g; q m Saturated adsorption capacity, mg / g; K L K is the Langmuir constant; F Here, is the Freundlich constant; n is a constant.

[0077] Table 2 Fitting parameters for Langmuir and Freundlich isotherm models of adsorbed heavy metal ions.

[0078]

[0079] 15. Adsorption kinetics experimental analysis

[0080] Research on the effect of modified distiller's grains on Cd 2+ The change in the adsorption rate of the solution over time is shown in the following results. Figure 9 As shown: the adsorption rate significantly increased after 20 minutes, then the increase gradually slowed down, finally reaching equilibrium at 210 minutes with an adsorption rate of 80%. e The concentration was 80 mg / g. Analysis revealed that initially, the functional groups on the adsorbent surface provided numerous adsorption sites, and calcium ions exchanged with cadmium ions in the solution, thereby promoting the absorption of Cd ions in the solution. 2+ The removal efficiency slows down with prolonged contact time, possibly due to the reduction of active sites and the decrease in heavy metal ion concentration. Figure 10 The SDG-A@Ca dynamic model was analyzed using pseudo-first-order and pseudo-second-order dynamic models. 2+ Adsorption of Cd in solution 2+ The adsorption process was fitted, and the data obtained are shown in Table 3.

[0081] Subsequently, a quasi-first-order dynamical model (PFO) and a quasi-second-order dynamical model (PSO) were used to fit the equations, as follows:

[0082] PFO:

[0083] ln(q e -q t )=lnq e -k1t (3-3)

[0084] PSO:

[0085]

[0086] In the formula: q t Let q be the adsorption amount at time t (mg / g). e k is the adsorption amount at equilibrium (mg / g); k1 is the pseudo-first-order adsorption rate constant (min). -1 k2 is the pseudo-second-order adsorption rate constant (mg / g(min)). 1 / 2 ).

[0087] Table 3 Adsorption kinetic parameters of heavy metal ions

[0088]

[0089] As can be seen from the above, the adsorption of Cd in the PSO model 2+ coefficient R 2 The correlation coefficient was 0.99859, which is much higher than the correlation coefficient R of the PFO model.2 The value of 0.90156 indicates that the adsorbent's adsorption of heavy metals is a mixed adsorption process, mainly based on chemical adsorption.

[0090] 16. Adsorption Thermodynamic Experimental Analysis

[0091] To further understand the adsorption performance of the adsorbent, thermodynamic experiments can be designed to determine the internal energy transformation of the entire adsorption system. Using van der Hoff's equations (e.g., 3-5, 3-6, 3-7) and relevant experimental data, Gibbs free energy (ΔG) can be calculated. θ (kJ / mol), entropy change (ΔS) θ J / (mol·K) and enthalpy change (ΔH) θ By knowing the system's endothermic and exothermic conditions (kJ / mol) and isothermal parameters, we can control factors to improve adsorption efficiency. The formula is as follows:

[0092]

[0093]

[0094] ΔG θ =ΔH θ -TΔS θ (3-7)

[0095] Where: R is the molar gas constant, 8.314 J / (mol·K); T is the absolute temperature, K; K a It is the dimensionless standard equilibrium constant.

[0096] Table 4. Thermodynamic Experimental Parameters

[0097]

[0098] As shown in Table 4 above, ΔG θ A value <0 indicates that the adsorption process of heavy metal ions occurs spontaneously by the adsorbent, and temperature affects the adsorption process; within a certain range, increasing the temperature is beneficial for adsorption. ΔH θ The value >0 indicates that the adsorption process of heavy metal ions is endothermic. As the temperature increases, the diffusion rate of the adsorbate into the internal microchannels accelerates, enhancing the capture ability of the functional groups on the adsorbate, which becomes highly favorable for the adsorption of metal ions; ΔS θThe entropy change is greater than zero because during the adsorption process, the adsorbent adsorbs the adsorbate from the aqueous solution, while simultaneously desorbing the solvent from the adsorbent surface. The former decreases entropy, while the latter increases it. The desorption of water molecules from the solvent increases entropy, raising the system's degrees of freedom and leading to increased disorder at the solid-liquid interface. Heavy metal ions in the aqueous phase are always hydrated metal ions, and the adsorption process between the adsorbent and metal ions is always accompanied by the desorption of bound water from the metal ions. When ions undergo coordination adsorption with the adsorbent, the metal ions adhere to the adsorbent surface and enter the solid phase from the liquid phase, resulting in a decrease in the degrees of freedom of this process, manifested as an entropy decrease. Conversely, the bound water from the hydrated metal ions enters the solvent system, increasing the degrees of freedom of this process, manifested as an entropy increase. Therefore, the entropy increase caused by water molecule desorption is far greater than the entropy decrease caused by metal ion adsorption, resulting in an increase in the overall system's degrees of freedom and thus an entropy change greater than zero during the adsorption process. Throughout the adsorption process, the system becomes increasingly disordered, exhibiting spontaneous and endothermic behavior. As the temperature rises, the system reaches its required temperature, the equilibrium shifts to the right, and the adsorption rate increases. In summary, the adsorption process of heavy metal ions by adsorbents is a spontaneous process of entropy increase and endothermic reaction.

[0099] 17. Adsorption-desorption reuse experiment analysis

[0100] Reuse efficiency is also one of the important factors in evaluating adsorbents. From Figure 13 It can be seen that after performing the operation 5 times, SDG-A@Ca 2+ The reuse rate gradually decreased, from 78.4% to 37%. The reason for this decrease in reuse rate is: SDG-A@Ca 2+ with cd 2+ They are mainly bonded by chemical bonds, and during desorption, SDG-A@Ca 2+ A large amount of Cd 2+ Coverage, H + Unable to make internal Cd 2+ The principle of displacement and sustainable use: According to the hard-soft acid-base theory, central atoms with high charge, small size, and low polarizability are called hard acids and hard bases; conversely, they are called soft acids and soft bases. In this system, soft acid-soft base pairings and hard acid-hard base pairings easily form stable systems. HCl is a hard acid, SDG-A@Ca 2+ -Cd 2+ It is a hard acid-soft base system, therefore H + It can reduce SDG-A@Ca 2+ -Cd 2 + Its coordination ability allows it to be used continuously.

[0101] 18. Modified distiller's grains on Cd 2+ Adsorption mechanism analysis

[0102] Combined with SDG-A@Ca 2+ Based on the characterization methods and experimental studies of its performance, our research team believes that SDG-A@Ca 2+ The adsorption mechanism is multifaceted and multi-layered. The analysis is as follows:

[0103] Firstly: SDG-A@Ca 2+ Surface and Cd 2+ Electrostatic adsorption exists, and the peak length is 3323 cm⁻¹. -1 The presence of functional groups such as hydroxyl groups in the SDG provides numerous adsorption sites, playing a crucial role in ion exchange and complexation coordination during adsorption; subsequently, the salicylhydrazone structure in SDG interacts with Ca... 2+ Coordination occurs to form a complex (SDG-A@Ca) 2+ ), SDG-A@Ca 2+ Adsorption of Cd 2+ Ion exchange occurs (from), and then precipitates into the pores. It further adsorbs and attracts complexes, causing heavy metal precipitation and aggregation, which reduces the pore size. The surface is gradually covered by heavy metal, reducing the specific surface area.

[0104] Secondly, combining the isoelectric point diagram and the optimal pH diagram, the adsorbent carries a negative charge at pH > 2.6. At this point, the number of protons in the solution system is relatively small, while the Cd in the solution is relatively large. 2+ It is positively charged and attracts negatively charged adsorbents, so the adsorption efficiency is significantly improved after the pH of the system is 2.6.

[0105] Based on the above data analysis, the following conclusions can be drawn:

[0106] (1) Under the structural characterization by FT-IR, SEM and EDS, the structure before and after modification has changed significantly, with the surface pore size increasing, the number of pores increasing, and the specific surface area increasing.

[0107] (2) In the adsorption isotherm experiment, SDG-A@Ca 2+ The adsorption process of Cd is more consistent with the Freundlich model than the Langmuir model, indicating that the adsorption process involves multilayer adsorption. Compared to PFO, Cd 2+ The adsorption process of SDG-A@Ca is more consistent with PSO, and kinetic experiments show that... 2+ The adsorption process is dominated by chemisorption, with physical adsorption forces playing a secondary role. The entire energy system of the isothermal experiment is a spontaneous and endothermic process. Desorption-adsorption experiments have demonstrated its good reusability.

[0108] The results of the influence of various factors on the adsorption performance showed that at 45℃, pH=6, CO=25 and 50 mg / L, SDG-A@Ca 2 + For Cd2+ The adsorption rates were 91.09% and 82.7%.

[0109] The above descriptions are merely embodiments of the present invention, and well-known characteristics and other common knowledge in the solutions are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for adsorbing heavy metal cadmium ions, characterized in that: Using acylhydrazone-sodium alginate-Ca 2+ Composite adsorbent for heavy metal Cd 2+ Adsorption occurs, wherein the acylhydrazone-sodium alginate-Ca 2+ The composite adsorbent is prepared by reacting salicylhydrazine with sodium hydroxide after alkalization and oxidation with sodium periodate to generate salicylhydrazone compound, and then crosslinking it with sodium alginate. The alkalization process includes the following steps: adding a 0.08–0.12 mol / L NaOH solution to the distiller's grains and stirring magnetically for 5–8 hours; then adding hydrochloric acid dropwise until neutral; centrifuging; removing the precipitate; drying; and grinding to obtain alkalized distiller's grains powder; the ratio of distiller's grains to NaOH solution is 90–110 g: 1 L. The oxidation process includes the following steps: adding anhydrous ethanol to the alkalized distiller's grains powder at a ratio of 4.5–5.5 mL: 1 g and stirring magnetically; then heating in a water bath for 8–12 hours. The process involves adding sodium periodate solution and stirring for 12-18 minutes, then adding hydrochloric acid dropwise until the pH reaches 4 and stirring for 22-26 hours for oxidation. After oxidation, ethylene glycol is added and stirred for 1.5-2.5 hours. Anhydrous ethanol and deionized water are then mixed and poured into the lees solution, filtered, dried, and then anhydrous ethanol is added again and filtered. Finally, the solid is removed, air-dried, and ground to obtain the oxidized lees. The sodium periodate solution consists of sodium periodate and deionized water in a ratio of 5g:40mL, with a weight ratio of sodium periodate to alkalized lees powder of 1:

2. The salicylhydrazine reaction process includes the following steps: mixing the oxidized lees and anhydrous ethanol in a ratio of 1g:25-35mL and stirring for 1.8-2.5 hours, then adding salicylhydrazine and glacial acetic acid, and heating in a water bath at 40-50°C with stirring for 22-25 hours. h, filtration, solid-liquid separation, and finally air-drying and grinding of the solid to obtain salicylhydrazone compound; the crosslinking process of distiller's grains and sodium alginate includes the following steps: adding deionized water to sodium alginate at a ratio of 160-240 mL: 1 g and stirring until sodium alginate is completely dissolved, then adding twice the weight of salicylhydrazone compound to dissolve, then adding 1,4-butanediol diglycidyl ether crosslinking agent, stirring for 10-14 h to obtain acylhydrazone-sodium alginate compound; adding 5% calcium chloride solution to acylhydrazone-sodium alginate compound and stirring for 20-30 h to obtain acylhydrazone-sodium alginate-Ca 2+ Composite adsorbent.

2. The method for adsorbing heavy metal cadmium ions according to claim 1, characterized in that: In the reaction of salicylhydrazide, after solid-liquid separation, the solid is washed with anhydrous ethanol and then air-dried.

3. The method for adsorbing heavy metal cadmium ions according to claim 2, characterized in that: During the crosslinking process of distiller's grains and sodium alginate, after the 1,4-butanediol diglycidyl ether crosslinking agent is added and stirred, the acylhydrazone-sodium alginate compound is frozen for 5-7 hours to form a block; then it is vacuum dried in a freeze dryer for 45-50 hours.

4. The method for adsorbing heavy metal cadmium ions according to claim 3, characterized in that: During the crosslinking process of distiller's grains and sodium alginate, after adding and stirring the calcium chloride solution, the acylhydrazone-sodium alginate-Ca... 2+ The composite adsorbent is frozen for 5-7 hours until it becomes a block; then it is vacuum dried in a freeze dryer for 45-50 hours.

5. A method for adsorbing heavy metal cadmium ions according to any one of claims 1 to 4, characterized in that: Acylhydrazone-sodium alginate-Ca 2+ Composite adsorbent with Cd 2+ Simply mix the solutions and shake or stir.

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