CN111468073B

CN111468073B - Dephosphorization reagent for air floatation and preparation method thereof

Info

Publication number: CN111468073B
Application number: CN202010259431.5A
Authority: CN
Inventors: 詹旭; 何剑伟; 赵鹏; 唐伟; 孙连军; 黄俊波
Original assignee: Jiangnan University
Current assignee: Wuxi Gongyuan Environmental Technology Co Ltd; Jiangnan University
Priority date: 2020-04-03
Filing date: 2020-04-03
Publication date: 2021-06-25
Anticipated expiration: 2040-04-03
Also published as: CN111468073A

Abstract

The invention discloses a dephosphorization reagent for air flotation and a preparation method thereof, belonging to the technical field of environmental protection. The bentonite is compositely modified by adopting an amphoteric surfactant of dodecyl Dimethyl Sulfopropyl Betaine (DSB) and a cationic surfactant of bromocetyl pyridine (CPB). The capacity of the DSB + CPB composite modified bentonite for adsorbing phosphate is superior to that of the DSB and CPB independently modified bentonite, the DSB and CPB have synergistic effect, the optimal adsorption capacity of the optimal modification ratio (1.0DSB +1.5CPB) can respectively reach 8.19 times and 1.79 times of that of the original soil and 1.0DSB amphoteric modified bentonite, and the adsorption capacity of the bentonite to the phosphate can be obviously improved through composite modification.

Description

Dephosphorization reagent for air floatation and preparation method thereof

Technical Field

The invention relates to a dephosphorization reagent for air flotation and a preparation method thereof, belonging to the technical field of environmental protection.

Background

With the rapid development of economy, the industrial and agricultural production activities of people are increased, a large amount of phosphorus-containing wastewater is discharged into the environment, so that the water quality of rivers and lakes is rapidly deteriorated, algae are erupted in a plurality of watersheds, the phenomenon of black and odorous water is generated, and the ecological function of the water is partially or completely lost. Research has shown that excess phosphorus content is a more critical factor in causing algal mass propagation in freshwater systems. Therefore, the development of an economical and efficient phosphorus removal technology becomes the current research focus. The main techniques currently used for removing phosphorus from sewage include chemical precipitation, ion exchange, microbiological, hydrobiological, soil treatment, and adsorption. The adsorption method has the advantages of wide material source, high removal efficiency, good economic benefit, reusability and the like, and is widely applied to sewage dephosphorization. Therefore, the development of highly efficient adsorbent materials is of great importance.

Disclosure of Invention

In order to solve the problems, the bentonite is modified by compounding an amphoteric surfactant dodecyl Dimethyl Sulfopropyl Betaine (DSB) and a cationic surfactant bromo Cetyl Pyridine (CPB), and when the amphoteric surfactant DSB is added to modify the bentonite, a quaternary ammonium hydrophilic group N with positive charges in the molecular structure of the DSB is added⁺The end can be combined with the negative charge site on the surface of the bentonite, meanwhile, the dodecyl hydrophobic long carbon chain in the DSB molecular structure forms an organic phase on the surface of the bentonite, so that the hydrophobicity is enhanced, and the positive charge group on the outer surface can form electric attraction with phosphate, so that the adsorption effect of the DSB is better than that of the original soil. Further, after the cationic surfactant CPB is added for composite modification, the quaternary ammonium group with positive charge in the CPB molecular structure can be combined with the negative charge sulfopropyl group in the DSB molecular structure and the negative charge site of the surface of the bentonite which is not combined by the DSB. Meanwhile, an organic phase is formed on the surface of the bentonite through the hydrophobic effect of the hydrophobic long carbon chains in the molecular structures of the CPB and the DSB, the surface hydrophobicity of the bentonite is enhanced, and the adsorption energy of the composite modified bentonite on phosphate is further improved by the outward positive charge end of the organic phase. Therefore, the phosphate adsorption capacity of the DSB + CPB composite modified bentonite is better than that of the DSB amphoteric modified bentonite, and the adsorption advantage is more obvious along with the increase of the CPB modification ratio.

The first purpose of the invention is to provide a method for modifying bentonite, which adopts dodecyl dimethyl sulfopropyl betaine DSB and cationic surfactant bromocetyl pyridine CPB to compound and modify bentonite.

In one embodiment of the invention, the amounts of DSB and CPB are 50% to 100% CEC and 25% to 150% CEC, respectively, based on the cation exchange capacity, CEC, of the bentonite.

In one embodiment of the present invention, the modification conditions are: the modification temperature is 50-70 ℃, and the reaction time is 3-5 h.

In one embodiment of the invention, the modification method comprises the steps of adding DSB and CPB solution into bentonite slurry, stirring at a constant temperature of 50-70 ℃ for 3-5h, standing, cooling, performing suction filtration separation, washing, drying and grinding to obtain the modified bentonite.

In one embodiment of the invention, a certain mass of bentonite is weighed to prepare bentonite slurry, and the mass ratio of water to soil is (5-15): 1, adding DSB and CPB solution prepared by taking cation exchange capacity CEC as a reference, stirring at the constant temperature of 50-70 ℃ for 3-5h, standing, cooling, performing suction filtration and separation, and washing until no Br is generated^-Drying at 50-70 deg.C, grinding, and sieving with 80-100 mesh sieve to obtain modified bentonite.

The second purpose of the invention is to provide modified bentonite prepared by the method.

The third purpose of the invention is to provide the application of the modified bentonite as a phosphorus removal agent.

In one embodiment of the invention, the reaction pH is controlled to 3-9 and the reaction temperature is controlled to 20-40 ℃ in said application.

The fourth purpose of the invention is to provide an application of the modified bentonite in an air floatation tank as a dephosphorization reagent.

The invention has the beneficial effects that:

1) the bentonite has a large amount of negative charges on the surface, and the adsorption effect of the bentonite on phosphate is not ideal due to the influence of electric repulsion. When the amphoteric surfactant DSB is added to modify the amphoteric surfactant DSB, the positively charged quaternary ammonium hydrophilic group N in the molecular structure of the DSB⁺The end can be combined with the negative charge site on the surface of the bentonite, meanwhile, the dodecyl hydrophobic long carbon chain in the DSB molecular structure forms an organic phase on the surface of the bentonite, so that the hydrophobicity is enhanced, and the positive charge group on the outer surface can form electric attraction with phosphate, so that the adsorption effect of the DSB is better than that of the original soil. Further, after the cationic surfactant CPB is added for composite modification, the quaternary ammonium group with positive charge in the CPB molecular structure can be combined with the negative charge sulfopropyl group in the DSB molecular structure and the negative charge site of the surface of the bentonite which is not combined by the DSB. Meanwhile, an organic phase is formed on the surface of the bentonite through hydrophobic effect of hydrophobic long carbon chains in molecular structures of CPB and DSB, so that the surface hydrophobicity of the bentonite is enhanced, and the outward positive charge end of the organic phase can further promote the complex positive charge endThe modified bentonite has the adsorption energy to phosphate. Therefore, the phosphate adsorption capacity of the DSB + CPB composite modified bentonite is superior to that of the DSB and CPB independently modified bentonite, and the DSB and CPB have synergistic effect; and the adsorption advantage is more obvious with the increase of the CPB modification ratio.

2) The adsorption process of the modified bentonite to the phosphate can be described by a pseudo second order kinetic equation (R2 is more than 0.9900) and a Langmuir adsorption isothermal model, the optimal adsorption quantity of the optimal modification proportion (1.0DSB +1.5CPB) can respectively reach 8.19 times and 1.79 times of that of the original soil and 1.0DSB amphiprotic modified bentonite, and the adsorption capacity of the bentonite to the phosphate can be obviously improved by composite modification.

3) The change of the pH value of the solution can affect the charge characteristics of the surface of the bentonite and the existing form of phosphate in water, and further affect the adsorption capacity of the bentonite to the phosphate. The modified bentonite has a downward trend of adsorbing phosphate along with the increase of the pH value of the solution.

4) The adsorption of the modified bentonite to phosphate is a spontaneous, endothermic and entropy increasing process which exists simultaneously in physical adsorption and chemical adsorption.

Drawings

FIG. 1 is XRD patterns of bentonite before and after modification.

FIG. 2 shows FT-IR spectra of each bentonite before and after modification.

FIG. 3 is SEM images of bentonite before and after modification; (a) sodium bentonite; (b)0.5 DSB; (c)0.5DSB +0.25 CPB; (d)0.5DSB +0.5 CPB; (e)0.5DSB +1.0 CPB; (f)0.5DSB +1.5 CPB.

FIG. 4 is a graph showing the measurement of contact angle of bentonite before and after modification; (a) is sodium bentonite; (b) it was 0.5DSB +1.5 CPB.

FIG. 5 is a graph of 0.5DSB +1.5CPB composite modified bentonite TG.

FIG. 6 is a graph of bentonite versus phosphate adsorption kinetics before and after modification.

FIG. 7 is an adsorption isotherm of phosphate by each bentonite before and after modification.

FIG. 8 is a graph showing the effect of different pH values on the adsorption of phosphate by 0.5DSB +1.5CPB and 1.0DSB +1.5 CPB.

FIG. 9 is a graph showing the effect of different temperatures on phosphate adsorption by (a)0.5DSB +1.5CPB and (b)1.0DSB +1.5 CPB.

Detailed Description

The following description of the preferred embodiments of the present invention is provided for the purpose of better illustrating the invention and is not intended to limit the invention thereto.

1. Sodium bentonite, purchased from Anji, Zhejiang, and its basic physicochemical properties are shown in Table 1.

TABLE 1 physicochemical Properties of Bentonite

The Cation Exchange Capacity (CEC) is determined with reference to GB/T20973-2007.

2. Characterization of modified Bentonite

The crystal structure of the modified bentonite is analyzed by adopting a PANALYTICAL X' Pert PRO type X-ray diffractometer produced by the Panland PANALYTICAL company; carrying out Fourier infrared spectrum analysis by adopting an infrared spectrum instrument of Nicolet iS10 of Thermo scientific company in the United states; observing the surface morphology of the modified bentonite by using a Hitachi SU5000 thermal field type transmission scanning electron microscope; the hydrophilicity and hydrophobicity of the modified bentonite are analyzed by adopting a static contact angle instrument with the model of XG-CAMA, which is produced by Shanghai Xuan accurate instrument Co., Ltd; the thermal stability of the modified bentonite was analyzed using a thermogravimetric analyzer model SDT-Q600, manufactured by watshi corporation, usa.

3. Preparation of phosphorus-containing wastewater

Preparing 50 mg.L according to the requirement of ammonium molybdate spectrophotometry (GB11893-89)^-1Simulated standard stock solution of phosphorus-containing wastewater.

4. Adsorption experiments

0.25g of soil sample is weighed into a 250mL conical flask with a plug, 50mL of simulated phosphorus-containing wastewater is added, and the mixture is heated at 150 r.min^-1Oscillating for 5h at constant temperature, standing and centrifuging, measuring the mass concentration of phosphate in the supernatant by adopting an ammonium molybdate spectrophotometry (GB11893-89), and calculating the equilibrium adsorption quantity Q of the reaction according to the formula (1)_e。

In the formula: q_eThe equilibrium adsorption amount of the soil sample to phosphate is mg.g^-1；C₀And C_eRespectively the initial concentration and the equilibrium concentration of phosphate in the solution, mg.L^-1(ii) a m is the soil sample mass, g; v is the volume of the simulated phosphorus-containing wastewater added, mL.

Each experimental treatment was set to 3 replicates and the experimental results averaged.

5. Kinetics of adsorption

Selecting raw soil, amphoteric modified bentonite (0.5DSB), and composite modified bentonite (0.5DSB +1.5CPB), and adjusting pH to 7, temperature to 30 deg.C, and initial concentration to 50 mg.L^-1Under the condition, the reaction time is controlled to be 0-5h, and the change relation of the bentonite adsorption quantity along with time is measured.

6. Adsorption isotherm

Setting

1, 2, 4, 6, 8, 12, 20, 30, 40, 50 mg.L^-1The relationship between the adsorption amount of bentonite and the initial concentration was measured at 10 initial concentrations under the conditions of pH 7, temperature 30 ℃ and reaction time 5 h.

Example 1: DSB + CPB composite modified bentonite

Weighing a certain mass of bentonite, preparing bentonite slurry (water-soil ratio is 10: 1), adding DSB and CPB solutions prepared by taking the bentonite cation exchange capacity (CEC is 82.5mmol/100g) as the reference, and setting two proportions of 50% and 150% respectively, and marking as 0.5DSB +1.5 CPB; stirring at 60 deg.C for 4 hr, standing, cooling, vacuum filtering, separating, and washing until no Br is present^-(AgNO₃Detection), drying at 60 ℃, grinding and sieving with a 100-mesh sieve to obtain the modified bentonite.

Wherein the amount of the surfactant is calculated by formula (2):

W＝m×CEC×M×10-6×R/b (2)

in the formula: w is the weight of the weighed surfactant, g; m is the soil sample mass, g; CEC is cation exchange amount of modified soil sample, mmol/kg^-1(ii) a M is the molar mass of the corresponding surfactant, g.mol^-1(ii) a R is the modification ratio of the surfactant; and b is the content (mass fraction) of the modifier product.

Example 2: influence of modification ratio on performance of composite modified bentonite

The proportion of DSB modification in the experiment is based on CEC, two proportions of 50% and 100% (0.5DSB and 1.0DSB) are set, the proportion of composite modification added with CPB is based on bentonite CEC, and 4 proportions of 25%, 50%, 100% and 150% (0.5DSB +0.25CPB, 0.5DSB +0.5CPB, 0.5DSB +1.0CPB, 0.5DSB +1.5CPB, 1.0DSB +0.25CPB, 1.0DSB +0.5CPB, 1.0DSB +1.0CPB and 1.0DSB +1.5CPB) are set on the basis of DSB modification.

FIG. 1 is XRD patterns of bentonite before and after modification. From the figure, the diffraction peak of 0.5DSB amphiprotic modified bentonite is shifted to a small angle compared with the original soil; for the composite modified bentonite, as the proportion of CPB modification is increased, the amount of the modifier entering between layers of the bentonite is increased, and the diffraction peak continuously shifts towards a small angle; when the CPB modification ratio was the same (1.5CEC), the 1.0DSB +1.5CPB modified bentonite diffraction angle was less than 0.5DSB +1.5 CPB. The interlayer spacing can be calculated by taking the Bragg equation lambda as 2dsin theta, and the bentonite interlayer spacing d₍₀₀₁₎The original soil is changed from 1.278nm to 1.452 nm, 1.523 nm, 2.471 nm, 2.903 nm, 3.766 nm and 3.939nm, and the size change relationship corresponds to the change of the diffraction angle. It can be seen that as the modification ratio increases, the distance between each bentonite layer gradually increases, indicating that the modifier intercalates successfully.

FIG. 2 shows FT-IR spectra of each bentonite before and after modification. As can be seen from the figure, all the soil samples are 1037cm^-1～1041cm^-1The vibration peak of Si-O-Si stretching occurs at 518cm^-1And a Si-O-Al stretching vibration peak appears nearby, which indicates that the bentonite phyllosilicate structure is not changed by modification, and the basic framework is not damaged. Compared with the original soil, the modified bentonite is 2852cm^-1～2927cm^-1C-H stretching vibration peaks appear, which indicates that the bentonite is successfully modified.

FIG. 3 is SEM images of bentonite before and after modification. As can be seen, the raw soil of sodium bentonite has a large particle size, a compact surface structure, a thick wafer layer and relatively few pores. With the insertion of the modifier, the layered structure of the sodium bentonite begins to peel off, an obviously irregular loose flaky structure appears, edges and corners of the sheet layer are sharp, and gaps between the layers become larger, which shows that the modifier partially adheres to the surface of the bentonite while entering the bentonite layers to prop the sheet layers open, and the morphological characteristics of the bentonite are changed. When the modification ratio is continuously increased, the sheet structure becomes looser and fluffier, the interlayer gaps are also larger and larger, and meanwhile, some fine particles existing between the sheet layers further prop open the bentonite sheet layers to increase the interlayer distance, which is consistent with the XRD analysis result.

FIG. 4(a) is a diagram showing the measurement of the contact angle of raw sodium bentonite, and the contact angle is 33.04 ° <90 °, which shows that the surface of sodium bentonite is hydrophilic; fig. 4(b) is a graph showing the measurement of the contact angle of 0.5DSB +1.5CPB composite-modified bentonite, and the contact angle thereof was 121.96 ° >90 °, showing hydrophobicity. This shows that the addition of the modifier can obviously reduce the surface polarity of the sodium bentonite and change the surface property of the sodium bentonite.

FIG. 5 is a TG curve of 0.5DSB +1.5CPB composite modified bentonite. As can be seen from the figure, the change of the soil sample mass with the increase of the temperature is divided into three stages. In the first stage, when the temperature is lower than 200 ℃, the mass loss (loss on ignition) is about 2.98 percent, and the first stage mainly shows that free water and interlayer water are lost; the temperature of the second stage is 200-400 ℃, the mass loss of the second stage is about 22.56%, mainly because the organic modifier in the bentonite is decomposed at high temperature; the temperature is 400-800 ℃ and is the third stage, the mass loss of the third stage is about 9.98%, and the third stage is mainly caused by the collapse of the lattice layers of the bentonite. The stepwise change in the TG curve further indicates the success of the modification.

Example 4: application of DSB + CPB composite modified bentonite as phosphorus removal agent

The composite modified bentonite prepared in the example 1-2 is used as a phosphorus removal agent, a standard stock solution of simulated phosphorus-containing wastewater of 50 mg.L < -1 > is prepared according to the requirement of ammonium molybdate spectrophotometry (GB11893-89), and the phosphorus removal effect of the composite modified bentonite is examined. The method comprises the following steps: 0.25g of soil sample is weighed into a 250mL conical flask with a plug, 50mL of simulated phosphorus-containing wastewater is added, and the initial concentration is 50 mg.L at the temperature of 30 ℃ and the pH value of 7^-1Under the condition of 150 r.min^-1Oscillating for 5h at constant temperature, standing and centrifuging, and adopting molybdic acidAmmonium spectrophotometry (GB11893-89) measures the mass concentration of phosphate in the supernatant.

FIG. 6 is a graph showing the adsorption kinetics of phosphate by various soil samples. As can be seen from the figure, the 0.5DSB +1.5CPB composite modified bentonite reaches 97.92% of the equilibrium adsorption amount in 60min, while the adsorption capacities of the 0.5DSB modified bentonite and the original clay are only 87.64% and 70.99% of the equilibrium adsorption amount, and the corresponding equilibrium adsorption amounts are 2.78, 1.04 and 0.32mg g^-1This indicates that both the adsorption rate and the equilibrium adsorption capacity of the 0.5DSB + CPB composite modified bentonite are greater than those of the 0.5DSB modified bentonite and the raw soil. The adsorption of phosphate by various soil samples is changed into three stages along with time: fast adsorption, rate change and adsorption equilibrium. This is because the bentonite has a large number of adsorption sites on its surface which are rapidly occupied by phosphate at the start of adsorption, which is manifested by a high adsorption rate. As the adsorption reaction proceeds, the surface adsorption sites gradually decrease and the adsorption of phosphate by bentonite becomes difficult, as indicated by a slower adsorption rate.

In order to further explore the phosphate adsorption and diffusion conditions of the composite modified bentonite, the data in FIG. 6 are subjected to fitting analysis by using a pseudo first-order kinetic equation (3) and a pseudo second-order kinetic equation (4), and fitting parameters are shown in Table 2.

ln(Q_e-Q_t)＝lnQ_e-k₁t (3)

In the formula: q_tDenotes the amount of adsorption at time t, mg. g^-1；k₁Is a pseudo first order kinetic constant, min^-1(ii) a t is reaction time, min, k₂Is a pseudo second order kinetic constant, g (mg min)^-1。

TABLE 2 kinetic fitting parameters

Note: q_e(exp) presentation testTo obtain equilibrium adsorption capacity of mg.g^-1；Q_e(cal) is the fitted equilibrium adsorption quantity, mg. g^-1。

As can be seen from the table, the fitting effect of the pseudo-second order kinetic model of each bentonite sample is superior to that of the pseudo-first order kinetic model (R)²>0.9900), and the fitting equilibrium adsorption capacity is closer to the actual equilibrium adsorption capacity, which shows that the pseudo-second-stage adsorption kinetic model can better describe the adsorption process of the modified bentonite on the phosphate, and the chemical adsorption is the rate-limiting step.

FIG. 7 is a graph showing the adsorption isotherms of phosphate by various soil samples. As can be seen from the figure, the adsorption amount of phosphate of each soil sample increases with the increase of the equilibrium concentration of phosphate, gradually approaches to equilibrium, and the isotherms are all nonlinear, which indicates that the adsorption mode is mainly surface adsorption, and is consistent with the description of adsorption kinetics in the foregoing.

To further explore the adsorption mechanism and maximum adsorption capacity, experimental data were fitted using Langmuir and Freundlich adsorption isotherm equations, and the results of the fitting parameters are shown in table 3. The mathematical expressions for Langmuir and Freundlich isothermal models are shown in equations (5) and (6), respectively:

in the formula: q_mThe maximum adsorption capacity of the modified bentonite to phosphate in water is mg.g^-1；K_LIs Langmuir constant, L.mg^-1；K_FAnd 1/n are both Freundlich parameters.

TABLE 3 adsorption isotherm model fitting parameters

Through comparison, the two adsorption isothermal equations can be well fitted to experimental data, but the correlation coefficient of the Langmuir equation is better than that of the Freundlich equation, so that the adsorption of phosphate by bentonite in the method is more consistent with the Langmuir adsorption model.

As can be seen from Table 3, the maximum adsorption amount of 1.0DSB was higher than 0.5DSB for the DSB amphoteric modified bentonite. For the composite modified bentonite, when the DSB modification proportion is the same, the maximum adsorption capacity of the composite modified bentonite is sequentially increased along with the increase of the CPB modification proportion, namely DSB +0.25CPB < DSB +0.5CPB < DSB +1.0CPB < DSB +1.5 CPB; when the CPB modification ratio was the same, the maximum adsorption amount exhibited a case where it increased as the DSB modification ratio increased, that is, 0.5DSB + CPB <1.0DSB + CPB. The variation trend of the maximum adsorption capacity of each soil sample is consistent with the variation condition of the interlayer spacing of the XRD pattern in characterization and analysis.

The adsorption capacity of the modified bentonite is obviously improved compared with that of the original soil. The maximum adsorption capacity of 0.5DSB and 1.0DSB amphoteric modified bentonite to phosphate is 3.08 times and 4.57 times of that of the original soil respectively; the maximum adsorption capacity of the 0.5DSB +0.25CPB, 0.5DSB +0.5CPB, 0.5DSB +1.0CPB and 0.5DSB +1.5CPB composite modified bentonite to phosphate is respectively 1.25 times, 1.68 times, 2.17 times and 2.54 times of that of the 0.5DSB amphiprotic modified bentonite; the maximum adsorption capacity of the 1.0DSB +0.25CPB, 1.0DSB +0.5CPB, 1.0DSB +1.0CPB and 1.0DSB +1.5CPB composite modified bentonite to phosphate is respectively 1.14 times, 1.31 times, 1.59 times and 1.79 times of that of the 1.0DSB amphoteric modified bentonite. The DSB modification can improve the adsorption capacity of bentonite to phosphate, and the compounding of CPB can obviously promote the adsorption of DSB amphoteric modified bentonite to phosphate.

As can be seen from fig. 7 and table 3, the adsorption effect of the bentonite raw soil on the phosphate is not ideal, mainly because the bentonite surface has a large amount of negative charges, which affect the adsorption of the phosphate due to the electric repulsion. When the amphoteric surfactant DSB is added to modify the amphoteric surfactant DSB, the positively charged quaternary ammonium hydrophilic group N in the molecular structure of the DSB⁺The end can be combined with the negative charge site on the surface of the bentonite, meanwhile, the dodecyl hydrophobic long carbon chain in the DSB molecular structure forms an organic phase on the surface of the bentonite, so that the hydrophobicity is enhanced, and the positive charge group on the outer surface can form electric attraction with phosphate, so that the adsorption effect of the DSB is better than that of the original soil.

When the cationic surfactant CPB is added for composite modification, the quaternary ammonium group with positive charge in the CPB molecular structure can be combined with the negative charge sulfopropyl group in the DSB molecular structure and the negative charge site of the bentonite surface which is not combined by the DSB. Meanwhile, an organic phase is formed on the surface of the bentonite through the hydrophobic effect of the hydrophobic long carbon chains in the molecular structures of the CPB and the DSB, the surface hydrophobicity of the bentonite is enhanced, and the adsorption capacity of the composite modified bentonite on phosphate is further improved by the outward positive charge end of the organic phase. Therefore, the phosphate adsorption capacity of the DSB + CPB composite modified bentonite is better than that of the DSB amphoteric modified bentonite, and the adsorption advantage is more obvious along with the increase of the CPB modification ratio.

Example 5: influence of pH value on adsorption effect of DSB + CPB composite modified bentonite

Referring to the method of example 4 for adsorbing phosphate, 0.5DSB +1.5CPB and 1.0DSB +1.5CPB of composite modified bentonite are selected, the pH value of the solution is controlled to be 3, 5, 7 and 9 under the conditions of 30 ℃ and 5h of reaction time, and the relation of the adsorption capacity of the bentonite along with the change of the pH value is measured.

FIG. 8 is a graph showing the effect of pH on phosphate adsorption by 0.5DSB and 1.0DSB optimal complex modified soil samples (0.5DSB +1.5CPB, 1.0DSB +1.5 CPB). As can be seen from the graph, when the pH value of the solution is increased from 3 to 5, the adsorption amount of phosphate by the modified bentonite is remarkably reduced; when the pH value is 5-7, the change of the adsorption quantity of the modified bentonite to phosphate is small; when the pH value is increased to 9, the adsorption amount of phosphate by the modified bentonite is continuously reduced. The adsorption capacity of the modified bentonite to phosphate is in a descending trend along with the increase of the pH value of the solution. This is mainly because the change of pH affects the charge characteristics of the surface of bentonite and the existence of phosphate in water, and further affects the adsorption capacity of bentonite to phosphate.

Under acidic conditions, H in solution⁺Higher concentration, part H⁺The modified bentonite is attached to the surface of the bentonite, so that the positive charges on the surface of the modified bentonite are increased, and the adsorption capacity of the bentonite on phosphate is improved through the action of electrostatic attraction. The main existing form of phosphate in the acid solution is

And

when the pH value of the solution is increased from 3 to 7, the positive charge in the solution is reduced,

the content of the active carbon is reduced,

the content is increased because

Has an adsorption free energy of less than

Thereby causing the adsorption capacity of the modified bentonite to phosphate to decrease with increasing pH.

OH in solution under alkaline conditions with increasing pH^-The concentration is increased, so that the capacity of the bentonite to compete for active site adsorption on the surface of the bentonite is enhanced, partial groups on the amphoteric surfactant DSB are in negative charge due to the increase of the pH value, the electrostatic repulsion between phosphate and the surface of the modified bentonite is enhanced, and the adsorption capacity of the modified bentonite to the phosphate under an alkaline condition is obviously lower than that under an acidic condition.

Example 6: influence of temperature on adsorption effect of DSB + CPB composite modified bentonite

Referring to the method of example 4 for adsorbing phosphate, composite modified bentonite of 0.5DSB +1.5CPB and 1.0DSB +1.5CPB was selected, and the relationship of the adsorption amount of bentonite with temperature change was determined by controlling the reaction temperature at 20, 30 and 40 ℃ under the conditions of pH 7 and reaction time of 5 h. The changes of the adsorption amounts of the 0.5DSB and 1.0DSB to phosphate at 20, 30 and 40 ℃ corresponding to the optimum composite modified soil samples (0.5DSB +1.5CPB, 1.0DSB +1.5CPB) are shown in FIG. 9.

As can be seen from fig. 9, the adsorption amount of the composite modified soil sample to phosphate increases with the increase of temperature, and a positive temperature-increasing effect is shown, which is probably because the adsorption process is influenced by nonpolar interaction, so that the adsorption resistance to hydrophilic phosphate is enhanced to a certain extent, and thus energy needs to be absorbed to overcome the problem.

Thermodynamic parameters calculated by the formulae (8), (9) and (10) are shown in table 4, and the calculation formula of the adsorption thermodynamic parameters is as follows:

ΔG＝ΔH-TΔS (10)

in the formula: k is a radical of_dThe equilibrium adsorption partition coefficient is obtained; delta S is the standard adsorption entropy change, J (mol. K)^-1(ii) a Δ H is the standard adsorption enthalpy change, kJ. mol^-1(ii) a Δ G is the standard adsorption free energy change, kJ. mol^-1T is absolute temperature, K; r is a molar gas constant, 8.314J (mol. K)^-1。

TABLE 4 thermodynamic parameters of adsorption

As can be seen from table 4, the standard enthalpy change Δ H of the modified bentonite for phosphate adsorption is greater than 0, which is an endothermic reaction, and is consistent with the positive temperature-increasing effect mentioned above; and the standard entropy changes Delta S are both larger than 0, which is because the modification increases the adsorption point positions on the surface of the bentonite, so that the phosphate arrangement has multi-directionality in the adsorption reaction process of the bentonite, the chaos is increased, and the entropy change is increased.

The standard free energy change delta G of the modified bentonite on phosphate adsorption at different temperatures is less than 0, which indicates that the adsorption process is spontaneous reaction, and the absolute value of delta G is increased along with the increase of the temperature, which indicates that the spontaneous degree is gradually enhanced, namely, the temperature rise is favorable for the reaction, and all the delta G is in the range of-20-0 kJ.mol^-1In the specification of adsorptionNo new chemical bond is generated, physical adsorption is the main, and the interaction force mainly comprises electrostatic force, hydrogen bond force, van der waals force and the like.

Example 7: application of DSB + CPB composite modified bentonite as phosphorus removal agent in air floatation tank

The composite modified bentonite prepared in example 1 is used as a phosphorus removal agent, 0.25g of soil sample is weighed into a 250mL conical flask with a plug, 50mL of simulated phosphorus-containing wastewater is added, and the initial concentration is 50 mg.L at the temperature of 30 ℃ and the pH value of 7^-1Under the condition of 150 r.min^-1And (5) oscillating at constant temperature for 5h, taking out the conical flask after the reaction from the constant-temperature oscillator, introducing a certain amount of dissolved air water generated by the air floatation machine into the conical flask, and standing for 10s to ensure that the adsorption material completely floats upwards. The DSB + CPB composite modified bentonite has hydrophobicity, and has better air floatation performance, so that solid-liquid separation can be realized.

Comparative example 1:

modified bentonite was prepared by the method of example 1 except that bentonite was modified with only 150% CPB and 1.5CPB modified bentonite was obtained under the same conditions as in example 1. The phosphate adsorption performance of 1.5 CPB-modified bentonite was measured with reference to the method of example 4.

The 0.5DSB +1.5CPB composite modified bentonite reaches 97.92 percent of the equilibrium adsorption capacity in 60min, while the adsorption capacities of the 0.5DSB modified bentonite, the 1.5CPB modified bentonite and the raw soil are only 87.64 percent, 78.75 percent and 70.99 percent of the equilibrium adsorption capacity, and the corresponding equilibrium adsorption capacities are 2.78, 1.04, 0.98 and 0.32mg g^-1This shows that the adsorption rate and equilibrium adsorption capacity of the 0.5DSB + CPB composite modified bentonite are superior to the sum of the adsorption effects of the 0.5DSB modified bentonite and the 1.5CPB modified bentonite, which indicates that the DSB and the CPB have a synergistic effect in enhancing the adsorption performance of the bentonite to phosphate.

Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. The method for modifying the bentonite is characterized in that the bentonite is modified by compounding dodecyl dimethyl sulfopropyl betaine DSB and cationic surfactant bromocetyl pyridine CPB; the dosage of the DSB and the CPB is based on the cation exchange capacity CEC of the bentonite, and is respectively 50% -100% CEC and 25% -150% CEC.

2. The method according to claim 1, wherein the modification conditions are: the modification temperature is 50-70 ℃, and the reaction time is 3-5 h.

3. The method according to claim 1 or 2, wherein the modification method comprises the steps of adding DSB and CPB solution into bentonite slurry, stirring at a constant temperature of 50-70 ℃ for 3-5h, standing, cooling, performing suction filtration separation, washing, drying and grinding to obtain the modified bentonite.

4. The method as claimed in claim 1, wherein bentonite slurry is prepared by weighing a mass of bentonite, wherein the mass ratio of water to soil is (5-15): 1, adding DSB and CPB solution prepared by taking cation exchange capacity CEC as a reference, stirring at the constant temperature of 50-70 ℃ for 3-5h, standing, cooling, performing suction filtration and separation, and washing until no Br is generated^-Drying at 50-70 deg.C, grinding, and sieving with 80-100 mesh sieve to obtain modified bentonite.

5. A modified bentonite prepared by the method of any one of claims 1 to 4.

6. Use of the modified bentonite of claim 5 as a phosphorous removal agent.

7. Use of the modified bentonite of claim 5 as a phosphorous removal agent in an air flotation tank.

8. Use according to claim 6 or 7, wherein the pH in use is between 3 and 9.

9. Use according to claim 6 or 7, wherein the in-use temperature is 20-40 ℃.