CN110449114B - Preparation method and application of aluminum-doped xonotlite material - Google Patents
Preparation method and application of aluminum-doped xonotlite material Download PDFInfo
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Abstract
The invention discloses a preparation method and application of an aluminum-doped xonotlite material, which is prepared by mixing Ca (OH)2Adding the powder into deionized water, and uniformly mixing to obtain a high-dispersion suspension A; then SiO2Adding the powder into KOH, then adding deionized water, and uniformly mixing to obtain a high-dispersion suspension B; slowly dripping the high-dispersion suspension B into the high-dispersion suspension A under the continuous action of ultrasonic waves, and slowly adding NaAlO2Adding a foaming agent into the solution, carrying out ultrasonic reaction, then aging, washing, drying, grinding and sieving the obtained product to obtain the aluminum-doped xonotlite powder. The invention adopts an ultrasonic chemical method, and AlO is doped for the first time in the process of preparing xonotlite2 ‑Substitute for SiO in xonotlite3 2‑The aluminum-doped xonotlite is prepared, and the material can efficiently adsorb heavy metal lead in wastewater.
Description
Technical Field
The invention relates to the technical field of material synthesis, in particular to a preparation method and application of an aluminum-doped xonotlite material.
Background
With the high-speed development of economy and the promotion of industrialization process, the demand on nonferrous metals is increased year by year, the ecological environment polluted by the nonferrous metals becomes the current important environmental problem, the quality of human health and life is harmed to a great extent, and high attention of all countries is attracted. Lead can be accumulated in the liver and the kidney, so that anemia occurs in the synthesis disorder of hemoglobin, the biochemical and physiological activities of organisms are interfered, and the healthy life of local human beings is seriously endangered in partial areas of Hunan China due to the fact that industrial lead-containing wastewater is discharged into natural water bodies unqualified to cause a plurality of blood lead incidents. The prior method for treating the lead-containing wastewater mainly comprises a chemical precipitation method, an ion exchange method, a membrane separation method, a biological method, an electrocoagulation method, an adsorption method and the like. The chemical precipitation method has low cost and is easy to cause secondary pollution to the environment; the ion exchange method has multiple selectivity but high operation cost; although the membrane separation technology, the biological method and the electrocoagulation method have high efficiency, the operation is complex, the cost is high and the like. The adsorption method is concerned by the fact that materials are easy to obtain, low in price, good in removal effect and strong in reproducibility, and embodies a green concept in the field of wastewater treatment.
Xonotlite [ Ca ]6Si6O17(OH)2]The porous structure has larger specific surface area, is a good thermal insulation material, and is widely applied to industries such as mining industry, electric power industry, building industry and the like. Some domestic scholars of xonotlite prepare xonotlite by hydrothermal method, try to treat some heavy metal-containing waste water with obvious effect and higher removal rate, and inhibit the xonotlite from being popularized and applied in environmental management due to harsh preparation material conditions, low yield, poor dispersibility, low heavy metal ion adsorption capacity and other factors.
Therefore, it is an urgent technical problem for those skilled in the art to improve the dispersibility and internal pore structure of xonotlite to effectively increase the removal rate and adsorption amount of heavy metals.
Disclosure of Invention
In view of the above, the invention provides a method for preparing an aluminum-doped xonotlite material, which comprises the steps of doping AlO for the first time in the process of preparing xonotlite by adopting an ultrasonic chemical method2 -Substitute for SiO in xonotlite3 2-The aluminum-doped xonotlite (Al-CSH for short) is prepared, and the material can efficiently adsorb heavy metal lead in wastewater.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for preparing an aluminum-doped xonotlite material comprises the following steps:
1) preparation of highly dispersed suspension a: reacting Ca (OH)2Adding the powder into deionized water, and uniformly mixing to obtain a high-dispersion suspension A;
2) preparation of highly dispersed suspension B: mixing SiO2Adding the powder into KOH, then adding deionized water, and uniformly mixing to obtain a high-dispersion suspension B;
3) preparing an aluminum-doped xonotlite material: slowly dripping the high-dispersion suspension B into the high-dispersion suspension A under the continuous action of ultrasonic waves, and then slowly adding NaAlO2Adding a foaming agent into the solution, carrying out ultrasonic reaction for 30-35min, then aging for 24-26h, washing, drying, grinding and sieving the obtained product to obtain the aluminum-doped xonotlite powder.
Preferably, in the preparation method, Ca (OH) is added according to the stoichiometric ratio of n (Ca)/n (Si + Al) ═ 1.0-2.0, and n (Al)/n (Si + Al) ═ 5%2、SiO2、NaAlO2。
Preferably, the highly dispersed suspension B is slowly dripped into the highly dispersed suspension A under the continuous action of ultrasonic waves at 50-60 ℃ in the step 3).
Preferably, the blowing agent is NH4HCO3Or urea.
Preferably, the washing in the step 3) is sequentially performed by using dilute hydrochloric acid, deionized water and absolute ethyl alcohol.
The invention also aims to apply the prepared aluminum-doped xonotlite material to wastewater treatment, remove lead, cadmium, copper, zinc and chromium in wastewater and keep the pH value at 4.5-5.5.
According to the technical scheme, compared with the prior art, the invention has the following beneficial effects:
the invention is based on an ultrasonic chemical method, and AlO is doped for the first time in the process of preparing xonotlite2-Substitute for SiO in xonotlite3 2-The preparation method has the advantages that the preparation material is simple in process and high in yield (the yield is 88% -95%), the internal porous structure is changed, the specific surface area is increased, the dispersibility of particles is improved, the crystallinity of the particles is reduced, the contact surface and adsorption sites of the xonotlite on the wastewater containing heavy metals are effectively increased, and the removal rate and adsorption capacity of the xonotlite on the heavy metal ions in the wastewater are effectively improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a graph showing the results of IR spectroscopy on xonotlite (CSH) and doped aluminum xonotlite (Al-CSH);
FIG. 2 is a scanning electron micrograph of Al-CSH;
FIG. 3 is a graph showing the energy spectrum of Al-CSH;
FIG. 4 is an X-ray diffraction pattern of an Al-CSH sample;
FIG. 5 is a diagram showing the existence of Pb ions;
FIG. 6 is a graph showing the effect of pH on Al-CSH adsorption of Pb;
FIG. 7 is a graph showing the effect of the amount of Al-CSH used on the adsorption of Pb (II);
FIG. 8 is a graph showing the effect of initial Pb concentration on adsorption at different temperatures;
FIG. 9 is a graph showing the effect of action time on Al-CSH adsorption of Pb (II);
FIG. 10 is a Langmuir isothermal adsorption fit model;
FIG. 11 is a Freundlich isothermal adsorption fit model;
FIG. 12 is a D-R isothermal adsorption fitting model;
FIG. 13 is a graph of a pseudo-first order kinetic model;
FIG. 14 is a graph of a pseudo-secondary kinetic model;
FIG. 15 is a schematic representation of the weber-Mrris kinetic model;
FIG. 16 is a 16 Elovich kinetic model;
FIG. 17 shows lnK0And T-1Fitting a linear graph;
FIG. 18 is a graph showing the reproducibility of Al-CSH after adsorbing Pb (II).
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example (taking adsorption of lead in wastewater as an example)
Firstly, preparing the aluminum-doped xonotlite material
Under the continuous action of ultrasonic waves at 50-60 ℃ according to the stoichiometric ratio of n (Ca)/n (Si + Al) to 1.0 and n (Al)/n (Si + Al) to 5 percent, the high-dispersion suspension B (0.095 mol of SiO is weighed out)2The powder, 1.0g of KOH and 100ml of deionized water are added slowly dropwise to the highly disperse suspension A (0.1 mol of Ca (OH) are weighed out)2Powder, 100ml deionized water) and 50ml 0.1mol/L NaAlO2And (3) solution. 8.0g NH was added4HCO3As a foaming agent, carrying out ultrasonic reaction for 30min, and then aging for 24 h. Washing the obtained product with dilute hydrochloric acid, deionized water and absolute ethyl alcohol in sequence, drying, grinding and sieving to obtain Al-CSH powder (aluminum-doped xonotlite powder).
And secondly, testing the prepared new material by adopting various characterization means, optimizing factors influencing adsorption, and further explaining the adsorption performance and adsorption mechanism of the aluminum-doped xonotlite on Pb (II).
1. Reagent and apparatus
The reagents used in the experiment are analytically pure, and the 1g/LPb (II) stock solution is prepared from analytically pure Pb (NO)3)2Adding deionized water to prepare the lead-free Pb (II) solution, and diluting the lead-free Pb (II) solution by using stock solution to obtain the lead-free Pb (II) solution.
The main experimental apparatus: autosorb iQ model specific surface area and pore structure tester (Congta instruments, USA), EVO10 scanning electron microscope band energy spectrum (Zeiss, Germany), Rigaku MiniFlex 600 model X diffractometer (Rigaku, Japan), PH330i type precision acidimeter (WTW, Germany), TAS-990AFG atomic absorption spectrophotometer (Beijing general analytical instruments, Inc.), AD-6 automatic electronic balance (PE, USA).
2. Characterization of the aluminum-doped xonotlite samples
BET specific surface area and pore size distribution of the sample on an adsorption apparatus by N2Adsorption determination, specific surface area from N using BET equation2And (4) obtaining an adsorption isotherm. The phase analysis of the samples was determined on an X-ray diffractometer under the following conditions: the Cu target excites Ka radiation to be a radiation source, the scanning range is 10-80 degrees (2 theta), and the scanning speed is 4 degrees/min. And observing the surface morphology of the sample by using a scanning electron microscope.
3. Experimental methods
Transferring 100mL of 200mg/L Pb (II) simulated wastewater into a 250mL conical flask, adjusting the pH value with HCl and NaOH, adding 0.06g of Al-CSH, placing on an oscillator for oscillation, keeping the temperature at 313K, keeping the oscillation speed at 150r/min, reacting for 60min, performing centrifugal separation, and taking supernatant to determine the content of residual Pb (II). The removal rate ρ (%) and the adsorption capacity Q were calculated respectively as followse(mg/g)：
ρ＝(C0-Ce)/C0×100％ (1)
Qe＝(C0-Ce)V/m (2)
In the formula, C0Is the initial concentration (mg/L) of Pb (II), CeThe equilibrium concentration (mg/L) of Pb (II) after adsorption is shown, V is the volume (L) of the solution, and m is the amount (g) of Al-CSH.
Third, result and discussion
1. Material characterization
The specific surface area and porosity of pure xonotlite (CSH) and aluminum-doped xonotlite (Al-CSH) were characterized and are reported in table 1. Referring to the classification of porous material, the pore diameter of 2-20 nm is mesoporous (i.e. mesopore), which indicates that xonotlite is a mesoporous material, which has large specific surface area, pore diameter and pore volume and is a good adsorption functional material. Table 1 shows that the specific surface area, pore volume and pore diameter of the modified Al-CSH are slightly larger than those of the unmodified CSH, which indicates that the xonotlite can create a better adsorption environment through modification and is more advantageous for adsorbing heavy metals, so that the study selects the modified Al-CSH to perform an adsorption experiment on lead ions.
TABLE 1 specific surface area, pore size and pore volume measurement data for CSH and Al-CSH samples
The infrared spectrum characterization results of xonotlite (CSH) and aluminum-doped xonotlite (Al-CSH) are shown in figure 1, and the infrared spectrum shows that the structure of the modified material is not damaged and the basic skeleton is still preserved. 3300--1Band is stretching vibration absorption peak of-OH, 714.4cm-1And 1081.7cm-1The band has a symmetrical stretching vibration absorption peak and an asymmetrical stretching vibration absorption peak of Si-O-Si bond, the two peaks of Si-O-Si bond are shifted to different degrees, and the intensities of the two peaks are weakened to a certain degree because of AlO2 -Replaces part of SiO in xonotlite3 2-Causing it to be.
As shown in a scanning electron microscope atlas of Al-CSH in figure 2, the sample is similar to a needle-like fiber, the surface is extremely rough due to the needle-like development of the surface, and adsorbates in a solution are favorably and rapidly contacted with active sites on the surface of the Al-CSH to be adsorbed, so that the material is a good adsorbing material.
As can be seen from the energy spectrum (EDX) of FIG. 3, the synthesized xonotlite sample material contains Ca, Si and O as main components, the energy spectrum of the aluminum-doped xonotlite obviously increases the Al element peak, and the Si element peak is slightly weakened, which indicates that AlO is present2 -Successfully doped in the CSH lattice, which is a substitute for part of SiO3 2-Forming new xonotlite derivatives.
Further, the crystal structure of Al-CSH was analyzed by X-ray diffraction, and the results are shown in FIG. 4. XRD pattern of Al-CSH particle at 2θDiffraction peaks around 20.8 °, 26.7 °, and 29.4 ° were shown, which substantially coincided with the standard diffraction pattern of xonotlite. While in figure 2θAlO appears at 23.0 degrees, 36.0 degrees and 36.5 degrees2 -Characteristic absorption peak, which indicates partial AlO2 -Into crystal lattice of xonotlite to replace SiO3 2-So that the crystallinity of the particles is reduced and the agglomeration phenomenon is weakened.
2. Influence of pH value on adsorption Effect
As can be seen from fig. 5 and 6, inThe pH value is 1.5-5.5, the Pb removal rate and the adsorption capacity of the Al-CSH are increased continuously along with the increase of the pH value, and the main reason is that a large amount of H exists in strong acidity of the solution+With Pb2+Form competitive adsorption due to H+Is easy to be adsorbed and quickly occupies the surface adsorption sites of the Al-CSH adsorbent, so that the positive charge on the surface of the adsorbent is increased, and the same-property Pb is mixed with the same-property Pb2+Generate rejection and inhibit Pb2+Is exchanged and surface complexed, thereby leading to Al-CSH to Pb2+The adsorption efficiency of (a) decreases significantly with decreasing pH. The removal rate reached a maximum of 95.58% when the pH was 5.5. The removal rate and adsorption capacity are gradually reduced by continuously increasing the pH value of the solution, because when the pH value is increased>At 5.5, OH in solution-Increase and easily make Pb (II)+Becomes strong in hydrolysis, resulting in Pb2+Rapid conversion to Pb (OH)3+、Pb(OH)+、Pb4(OH)4 4+Iso-conversion of these positively charged ionic lead hydroxide compounds with Pb2+The same charge generates repulsion, and the Pb is inhibited2+Reaches the surface of the Al-CSH to be adsorbed, thereby reducing the adsorption capacity of the Al-CSH to Pb (II). Further increase of pH resulted in the appearance of Pb (OH)2Precipitation, which is more unfavorable for adsorbing Pb (II). Therefore, the pH value of the invention is controlled to be 4.5-5.5, and the optimal pH value is 5.5.
3. Influence of Al-CSH dosage on Pb adsorption effect
According to the experimental method, the dosage of the adsorbent is adjusted to carry out a comparative experiment, the Pb (II) removal efficiency in the solution changes with the dosage of the adsorbent Al-CSH as shown in figure 7, and as seen from figure 7, the Pb (II) removal rate increases from rapid increase to slow increase with the dosage of the adsorbent Al-CSH, while the change trend of the adsorption capacity is opposite to rapid decrease to slow decrease, which is basically consistent with the adsorption rule of the similar adsorption material. The addition amount of Al-CSH is increased from 0.02g to 0.06g, the removal rate is improved from 83.77 percent to 95.58 percent, the adsorption capacity is reduced from 837.7mg/g to 318.48mg/g, and the weight loss is obvious. The dosage of Al-CSH is continuously increased to 0.12g, the removal rate and the adsorption capacity are respectively 98.07 percent and 163.44mg/g, and the removal rate of the adsorbent with the dosage of 0.06g is only increased by 2.52 percent, and the adsorption capacity is reduced by 155.04 mg/g. Compared comprehensively, on the premise of ensuring higher removal rate and relatively large adsorption capacity, the dosage of the adsorbent is preferably 0.06 g.
4. Influence of initial Pb concentration on adsorption Effect
According to the experimental method, the adsorption experiment temperature is controlled at 293, 303 and 313K, the initial concentration (60-300 mg/L) of Pb (II) is changed for carrying out the adsorption experiment, and the adsorption result of Pb (II) by Al-CSH is shown in figure 8. As can be seen from FIG. 8, as the initial concentration of Pb (II) increases, the removal rate of Pb (II) by Al-CSH decreases continuously at three temperatures, and the removal rate at a higher temperature is higher than that at a lower temperature, indicating that the increase in temperature is beneficial to the removal of Pb (II) by Al-CSH within a certain temperature range. It is also stated that the adsorption mechanism should be chemisorbed in addition to physisorption, promoting the bonding of Al-CSH to Pb (II) by the applied energy, thereby promoting the effective removal of Pb (II).
5. Influence of action time on Pb (II) adsorption effect
According to the experimental method, compared adsorption experiments of Al-CSH on Pb (II) are carried out at 293, 303 and 313k respectively, and the trend of the removal rate with the action time is shown in figure 9. As can be seen from FIG. 9, in the early stage of 5-60 min of adsorption, the Pb (II) removal rate by Al-CSH rises rapidly, and the removal rate is increased from 70% to over 90%, which indicates that the adsorption rate is quite rapid; and (3) continuing to prolong the adsorption time, wherein the removal rate and the adsorption capacity of the Al-CSH to Pb (II) are slowly increased from 60min to 300min in the later stage, the removal rates at the three temperatures are only increased by 1.5%, 1.67% and 2.28%, respectively, and the increase is not obvious, which shows that the effect of the Al-CSH to Pb (II) is close to adsorption balance after 60min, and the significance of prolonging the adsorption time to improving the adsorption effect is small. In the early stage of adsorption, most Pb (II) is adsorbed on the surface of Al-CSH due to electrostatic action, and partial lead ions and calcium ions are subjected to ion exchange and surface complexation; in the later stage of adsorption, the adsorption force is weakened due to the fact that most of adsorption sites on the surface of the adsorbent are occupied by Pb (II), and the adsorption rate is reduced. Therefore, the adsorption time in this study was preferably controlled to 60 min.
In addition, it should be noted that the study on the amount of Al-CSH, the acting time and the initial concentration of Pb is only to further illustrate the adsorption effect of the Al-CSH material, and in practical application, the concentration of heavy metals in the wastewater needs to be properly adjusted.
6. Study of adsorption mechanism
6.1 adsorption isotherm
The equilibrium adsorption isotherm is an important method for reflecting the adsorption characteristics of the adsorbent to the adsorbate, can be used for describing the adsorption capacity under different equilibrium concentrations, and can obtain the saturated adsorption capacity of the adsorbent by fitting the adsorption process. Common isothermal equations are the Langmuir isotherm (3), the Freundlich isotherm (4), and the Dubinin-Radushkevich (D-R) isotherm (5).
Qe＝QmKLCe/(1+KLCe) (3)
Qe＝KFCe 1/n (4)
In the formula, CeIs the concentration (mg/L) of Pb (II) in the solution at equilibrium of adsorption, QeIs the adsorption capacity (mg/g), Q, at which the adsorption reaches equilibriummIs the maximum adsorption (mg/g), KLIs the adsorption constant (L/mg), K, associated with the adsorption energyFAnd 1/n is the Freundlich constant.
lnQe＝lnXm－kε2 (5)
ε＝RTln(1+Ce -1) (6)
E＝(2k)-1 (7)
In the formula, CeFor the concentration (mol/L) of Pb (II) in the solution at adsorption equilibrium, k is a model constant related to free energy, XmThe adsorption amount (mol/g) of the single layer of the adsorbent is epsilon, the Polanyi potential energy (kJ/mol), R is the ordinary kJ/(mol.K) of the Purchase gas, T is the temperature (K), and E is the adsorption average free energy change (KJ/mol).
According to the isothermal adsorption experimental data, the process of Al-CSH adsorbing Pb is fitted by adopting Langmuir, Freundlich and D-R isothermal models, the fitting result schematic diagram is shown in figures 10-12, and the fitting parameter results are shown in Table 2. Comparing the fitting results of the three isothermal models, wherein the fitting correlation coefficients of all the isothermal models are higher than 0.9 in an experimental range, and the three isothermal models can reflect the adsorption behavior, wherein the Langmuir isothermal model has the highest correlation coefficient which is higher than that of all the isothermal models0.98, indicating that the Langmuir isothermal model is best suited to describe the adsorption process, revealed that the adsorption is monolayer adsorption. Freundlich isothermal constant KFThe larger value and the 1/n value less than 1 indicate that Al-CSH is preferential for Pb adsorption. The average change E values of adsorption free energy calculated by a D-R isothermal model are 128.21, 147.06 and 166.67kJ/mol respectively, which indicates that the adsorption effect of Al-CSH on Pb (II) has adsorption characteristics such as ion exchange and surface complexation.
TABLE 2 Table of isothermal adsorption parameters of Al-CSH to Pb (II) at different temperatures
Saturated adsorption capacity Q of Al-CSH to Pb (II) adsorption Langmiur model at different temperaturesmIt can be seen that the temperature is high and the corresponding Q ismLarge indicates that the temperature rise favors the adsorption reaction. The saturated adsorption capacity of Al-CSH to Pb (II) at 313K is up to 497.99mg/g, and compared with the saturated endothermic capacity of Pb (II) adsorbing materials reported in recent literatures, the results are shown in Table 3, and the Al-CSH adsorbing material has obvious advantages in the research.
TABLE 3 comparison of Al-CSH with other adsorbents for Pb (II) adsorption Capacity
6.2 kinetics of adsorption
In order to further examine the adsorption mechanism of Al-CSH on Pb (II) in the solution, kinetic models such as Lagergren quasi-first-stage (formula 8), Lagergren quasi-second-stage (formula 9), Weber-Morris diffusion (formula 10) and Elovich (formula 11) are respectively utilized.
Qt＝Qe(1-e-K1t) (8)
Qt＝Qe 2K2t/(1+QeK2t) (9)
Qt＝Kit1/2+C (10)
Qt＝1/βeln(αeβe)+1/βelnt (11)
In the formula, QtIs the amount of adsorption at time t (mg/g), K1Is the quasi first order adsorption rate constant (min)-1)，K2Is the quasi-second order adsorption rate constant [ mg/(g min)]；KiIs the internal diffusion adsorption rate constant (mg/g-min)1/2) C is a constant; alpha is alphae[mg/(g·min)]Is an initial adsorption rate constant, betae(g/mg) is the desorption rate constant.
The experimental data for Al-CSH adsorbing Pb (II) at 293, 303 and 313K are fitted as shown in FIGS. 13-16, and the fitting results are shown in Table 4.
TABLE 4 parameters of the fitted kinetic model
The adsorption experimental data were fitted and the results are shown in table 4. The results of comparing the four dynamics fitting parameters show that the quasi-secondary dynamics model has the best fitting effect and the correlation coefficient R2The theoretical adsorption capacity Q is more than 0.99 and is obtained by calculation of a quasi-second order kinetic equatione,calAnd the result value Q obtained by the experimente,expThe method is quite consistent with the principle that the adsorption of the Al-CSH to the Pb (II) can be well described, and the adsorption has the chemical adsorption behavior. Parameter intercept in a Weber-Morris diffusion fitting model is not equal to zero, and a straight line does not pass through an original point, so that the internal diffusion process is not a single control step of the adsorption rate, and the adsorption can be inferred to comprise a plurality of comprehensive control processes such as external liquid film diffusion, surface adsorption and particle internal diffusion; in addition, K of the internal diffusion equationiThe equilibrium adsorption capacity for Pb (II) is correspondingly increased along with the reduction of the temperature, which shows that the temperature rise in the adsorption process is favorable for the adsorption reaction and can effectively improve the removal of Pb (II). Elovich fittingThe obtained model has relatively large slope and intercept, which shows that the adsorption speed of the Al-CSH to the Pb (II) is high and the adsorption capacity is strong.
6.3 thermodynamic study of adsorption
The adsorption thermodynamics reflects the heat effect of the adsorption process under the isothermal and isobaric pressure, embodies the heat absorption or heat release characteristics, and indirectly reflects whether the adsorption process can be carried out spontaneously. The main parameters of the adsorption thermodynamics include Gibbs free energy (delta G), enthalpy change (delta H) and entropy change (delta S), wherein the positive or negative value of delta G can judge whether the reaction can spontaneously proceed, and the positive or negative value of delta H judges whether the reaction belongs to an endothermic or exothermic process. The thermodynamic parameter value is calculated by the following formula 12-15:
ΔG＝ΔH-TΔS (12)
ΔG＝-RTlnK0 (13)
lnK0＝1000*C0*lnKL (14)
lnK0＝-ΔH/(RT)+ΔS/R (15)
wherein R is a gas constant [ J/(mol. K)]T is the absolute temperature (K), K0To characterize the equilibrium constant (where K) of the Pb (II) partition between the adsorbent and the solution0is the equilibrium constant characterizing the distribution of lead ions between the solution phase and the phase of the adsorbent material)，KLLangmiur constant.
As lnK0Linear regression with 1/T, as shown in FIG. 17, the linear fit equation is Y-5212X +27.33, correlation coefficient R20.9890, gibbs free energy (Δ G), enthalpy change (Δ H), and entropy change (Δ S) in the actual state are calculated from equations (16) and (17), see table 5. As can be seen from Table 5, Δ G is negative in the thermodynamic parameters, indicating that the adsorption of Pb (II) in the solution by Al-CSH proceeds spontaneously; the enthalpy change value can be used to determine the type of adsorption, the enthalpy change of the chemisorption process is usually more than 60KJ/mol, and the enthalpy change of the physisorption process is usually less than 40 KJ/mol. The adsorption delta H of the Al-CSH to the Pb (II) is more than 40KJ/mol, the adsorption is an endothermic reaction process, the temperature is increased to be favorable for the adsorption reaction, and the adsorption mechanism of the Al-CSH to the Pb (II) is the comprehensive adsorption behavior of ion exchange, surface complexation and physical adsorption and the isothermal adsorption moduleThe pattern speculation results are substantially consistent. A positive entropy change indicates an increase in the irregularity of the adsorption process.
TABLE 5 thermodynamic parameters at different temperatures
7. Reproducibility of
50ml of 0.1mol/L hydrochloric acid is adopted to perform desorption treatment on the Al-CSH sample after adsorbing the Pb (II), the sample after desorption is washed and filtered by deionized water for 4 times, dried at 70 ℃, the Pb (II) adsorption experiment is continued according to the experimental method, the steps are repeated for 5 times in sequence, and the experimental result is shown in figure 18. As can be seen from the desorption-adsorption cycle experiment, after 5 times of regeneration, the adsorption of Al-CSH to Pb (II) still keeps higher removal rate of 88.67%, which is only reduced by 6.88%, which fully shows that the material has strong regeneration capability and impact resistance, and is a material with good adsorption performance.
In conclusion, the aluminum-doped xonotlite synthesized for the first time by combining the ultrasonic technology and the doping technology is applied to simulating the treatment of the lead-containing wastewater, and experiments prove that the removal effect is obvious and is obviously superior to the adsorption effect of similar materials reported recently, so that the method is worthy of great popularization and application.
Further, under the optimized experimental conditions of pH5.5, temperature 313K, action time 60min and the like, the removal rate of 100mL of 200mg/LPb (II) by using 0.06g of Al-CSH can reach 95.55%, and the equilibrium adsorption capacity can reach 318.48 mg/g.
The adsorption isothermal model shows that the fitting correlation coefficient of the Langmuir model is as high as 0.99, the Al-CSH model is most suitable for describing the adsorption characteristics of Pb (II), the maximum adsorption capacity under 313K is 497.99mg/g respectively, and the strong adsorption capacity is fully embodied. The D-R isothermal model is fitted to 293, 303 and 313K experimental data, the corresponding activation energy E values are large, and the adsorption behaviors of ion exchange and surface complexation existing in the adsorption effect of Al-CSH on Pb (II) are reflected.
The quasi-second-order kinetic model is used for fitting the adsorption process of the Al-CSH to the Pb (II), the correlation coefficient is higher than 0.99, and the adsorption behavior of the Al-CSH to the Pb (II) can be reflected most effectively. Thermodynamic parameters show that the adsorption is spontaneous endothermic reaction, and the temperature rise is favorable for removing Pb (II) by Al-CSH.
Results of an isothermal adsorption model, a kinetic model and thermodynamic parameters are fitted to prove that the adsorption mechanism of the Al-CSH to the Pb (II) is mainly a comprehensive adsorption behavior combining ion exchange, surface complexation and physics.
In addition, the invention also makes the adsorption comparison of other heavy metals under the same conditions (the dosage of the adsorbent is 0.06g, the initial concentration of the heavy metal is 200mg/L, the volume is 100ml, the reaction time is 60min, the temperature is 313K, and the pH is 5.5), such as wastewater of cadmium (the removal rate is 88.54 percent, the adsorption capacity is 135.9mg/g), copper (the removal rate is 89.63 percent, the adsorption capacity is 149.38mg/g), zinc (the removal rate is 89.35 percent, the adsorption capacity is 138.92mg/g), chromium (the removal rate is 85.47 percent, the adsorption capacity is 127.45mg/g) and the like, wherein the maximum removal rate and the adsorption capacity of lead wastewater under the same conditions are realized
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (6)
1. The application of the aluminum-doped xonotlite material in treating lead wastewater is characterized in that the preparation method of the aluminum-doped xonotlite material specifically comprises the following steps:
1) preparation of highly dispersed suspension a: reacting Ca (OH)2Powder is added toUniformly mixing in ionized water to obtain a high-dispersion suspension A;
2) preparation of highly dispersed suspension B: mixing SiO2Adding the powder into KOH, then adding deionized water, and uniformly mixing to obtain a high-dispersion suspension B;
3) preparing an aluminum-doped xonotlite material: slowly dripping the high-dispersion suspension B into the high-dispersion suspension A under the continuous action of ultrasonic waves, and then slowly adding NaAlO2Adding a foaming agent into the solution, carrying out ultrasonic reaction for 30-35min, then aging for 24-26h, washing, drying, grinding and sieving the obtained product to obtain the aluminum-doped xonotlite powder.
2. The use of an aluminum-doped xonotlite material in the treatment of lead wastewater as claimed in claim 1, wherein said method of making said aluminum-doped xonotlite material comprises adding Ca (OH) in a stoichiometric ratio n (Ca)/n (Si + Al) of 1.0-2.0, n (Al)/n (Si + Al) of 5%2、SiO2、NaAlO2。
3. The application of the aluminum-doped xonotlite material in the treatment of lead wastewater as claimed in claim 1, wherein the high dispersion suspension B is slowly added dropwise to the high dispersion suspension A under the continuous action of ultrasonic waves at 50-60 ℃ in the step 3).
4. Use of an aluminium-doped xonotlite material as claimed in any one of claims 1 to 3 in the treatment of lead wastewater wherein said foaming agent is NH4HCO3Or urea.
5. The use of the aluminum-doped xonotlite material as claimed in claim 4 in the treatment of lead wastewater, wherein in step 3) dilute hydrochloric acid, deionized water and absolute ethanol are used for washing in sequence.
6. The application of the aluminum-doped xonotlite material in the treatment of lead wastewater as claimed in claim 1, wherein the aluminum-doped xonotlite material is added into wastewater to be treated to remove lead, cadmium, copper, zinc and chromium in the wastewater and maintain the pH value at 4.5-5.5.
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