CN116037116B - A Fenton sludge magnetic iron-based catalyst and its preparation method and application - Google Patents

Abstract

The invention discloses a Fenton sludge magnetic iron-based catalyst and a preparation method and application thereof. The catalyst comprises the following steps: mixing Fenton sludge and organic sludge in proportion and crushing them to obtain organic iron sludge, wherein the mass ratio of iron oxide to organic matter in the organic iron sludge is 8-10:1; adding water to the organic iron sludge, placing the organic iron sludge in a high-pressure reactor, introducing an inert gas, and performing hydrothermal carbonization, wherein the hydrothermal carbonization temperature is 150-170 DEG C, and the hydrothermal carbonization time is 100-140 min; after the hydrothermal carbonization is completed, performing solid-liquid separation and drying on the hydrothermal product to obtain dry sludge hydrothermal carbon; performing microwave heating on the dry sludge hydrothermal carbon in an inert atmosphere, and when the temperature is increased to 500-600 DEG C at a rate of 110-130 DEG C/min, stopping the microwave heating, cooling naturally and drying to obtain the magnetic iron-based catalyst.

Description

A Fenton sludge magnetic iron-based catalyst and its preparation method and application

Technical Field

The invention belongs to the technical field of solid waste utilization, and specifically relates to a Fenton sludge magnetic iron-based catalyst and a preparation method and application thereof.

Background technique

The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

The Fenton process is an efficient and economical wastewater treatment technology, which is widely used in the textile, pharmaceutical, chemical and other industries. The sludge produced by the Fenton process in treating wastewater is called Fenton sludge, which contains a large amount of iron ions, organic matter and heavy metals. At present, the main methods for disposing Fenton sludge in my country are landfill, incineration, cement making, etc., which causes a large amount of iron resources waste and easily causes secondary pollution.

Microwave heating has the advantages of high heating efficiency, volume heating, simple equipment, and fast start and stop, and is a common method for sludge disposal. However, microwave heating is selective, and the microwave heating characteristics of a substance in a microwave field depend on its dielectric loss coefficient. The iron oxide and macromolecular organic matter contained in Fenton sludge have poor microwave heating characteristics, and direct microwave heating has the disadvantages of slow heating and low efficiency.

Summary of the invention

In view of the deficiencies in the prior art, the present invention aims to provide a Fenton sludge magnetic iron-based catalyst and a preparation method and application thereof.

In order to achieve the above object, the present invention is implemented through the following technical solutions:

In a first aspect, the present invention provides a method for preparing a Fenton sludge magnetic iron-based catalyst, comprising the following steps:

The Fenton sludge and the organic sludge are mixed and crushed in proportion to obtain organic iron sludge, in which the mass ratio of iron oxide to organic matter is 8-10:1;

After adding water to the organic iron sludge, the organic iron sludge is placed in a high-pressure reactor and introduced with inert gas for hydrothermal carbonization at a temperature of 150-170°C and a time of 100-140 minutes. After the hydrothermal carbonization is completed, the hydrothermal product is subjected to solid-liquid separation and drying to obtain dry sludge hydrothermal carbon.

The dry sludge hydrothermal carbon is subjected to microwave heating in an inert atmosphere, and when the temperature is raised to 500-600°C at 110-130°C/min, the microwave heating is stopped, and the product is naturally cooled and dried to obtain a magnetic iron-based catalyst.

The inventors have found through experiments that hydrothermal carbonization in an inert environment can pre-crackle the organic matter in Fenton sludge to generate some charcoal, and use the charcoal to partially reduce the iron oxide in the Fenton sludge to ferroferric oxide with better microwave heating characteristics. However, due to the limited content of organic matter in Fenton sludge, it is difficult to fully reduce the iron oxide in the sludge, resulting in fewer microwave active sites in the sludge matrix, making it difficult to in situ solidify the heavy metals in the Fenton sludge.

When organic sludge is added to Fenton sludge, the organic matter content in the organic sludge is high. This part of the organic matter is pre-cracked during the hydrothermal carbonization process. On the one hand, the pre-cracked product can reduce the iron oxide in the Fenton sludge and promote the formation of ferroferric oxide; on the other hand, it can serve as an active site, which is beneficial to improve the microwave heating characteristics of the sludge mixture, and then it is beneficial to achieve the in-situ solidification of heavy metals in the Fenton sludge. Thirdly, the organic matter content in the organic sludge is high. After hydrothermal pre-cracked and further microwave pyrolysis, it is beneficial to increase the specific surface area of the catalyst, and then it is beneficial to improve the catalytic performance of the catalyst (the catalytic performance of the catalyst is the result of the dual effects of adsorption performance and catalytic performance).

When studying the hydrothermal reaction, the inventors found that when the temperature of the hydrothermal reaction is high, the pore structure of the solid product is unstable and easy to collapse, resulting in a sharp decrease in the specific surface area. In addition, the high hydrothermal reaction temperature causes the iron oxide to be reduced excessively to ferroferric oxide, resulting in the microwave heating stage being difficult to control and partial generation of elemental iron. On the one hand, elemental iron has basically no catalytic performance, and the excessive generation of elemental iron reduces the content of active ingredients in the catalyst, thereby reducing the catalytic performance of the catalyst to a certain extent; on the other hand, the generated elemental iron is easy to agglomerate, resulting in a significant decrease in the specific surface area of the catalyst, further reducing the catalytic performance of the catalyst.

After further experiments, it was found that when the hydrothermal reaction temperature is around 165°C, both the pre-cracking process of organic matter and the generation process of ferroferric oxide can be controlled, making the temperature of the subsequent microwave process controllable, and thus making the reaction of the microwave process controllable.

In the present invention, the amount of organic sludge added is controlled to be less, and the char formed in the hydrothermal carbonization and microwave cracking process is mainly used to reduce iron oxide to ferroferric oxide, while avoiding excessive reduction of iron oxide to elemental iron. In addition, since there are organic matter cracking to form char (carbon formation, i.e., formation of microwave active sites) and char reducing iron oxide to ferroferric oxide (carbon consumption and ferroferric oxide generation) in the microwave treatment process, by adjusting the amount of organic sludge added, the amount of char and ferroferric oxide in the whole sludge system is in a relatively balanced state during the microwave treatment, so that the microwave treatment process is always in a temperature-controllable state to avoid temperature runaway and violent reaction to generate elemental iron.

In addition, the inventors also explored the microwave heating process. When the heating rate is 110-130℃/min, the temperature of the mixed sludge can be quickly heated up, thereby achieving in-situ solidification of heavy metals. When the temperature reaches 500-600℃, the heating is stopped. In this process, the microwave treatment time is relatively short, which can effectively control the proper reduction of iron oxide in the sludge, thereby avoiding excessive reduction to elemental iron.

Finally, the hydrothermal carbonization reaction is a high-pressure reaction carried out in a reactor, which can promote the redox reaction and reduce the temperature required for the cracking of organic matter. In addition, the hydrothermal carbonization method can be used to treat sludge without pre-dehydration, and the dehydration of the solid product after the hydrothermal reaction is enhanced, the mass is reduced, and the comprehensive dehydration energy consumption is reduced.

In some embodiments, the moisture content of the Fenton sludge is 30%-80%, and the iron oxide content is 40-65%, where % is mass percentage.

In some embodiments, the organic sludge has a moisture content of 30%-80%, an organic matter content of 30-50%, and % is mass percentage. Organic sludge includes domestic sludge, food processing sludge, leather sludge, papermaking sludge, printing and dyeing sludge, and petrochemical sludge.

In some embodiments, the mass ratio of organic iron sludge to water is 1:4-6.

Preferably, the mass ratio of iron oxide to organic matter in the organic iron mud is 8.5-9.5:1.

In some embodiments, the heating rate of the hydrothermal carbonization process is 3-7° C./min.

Preferably, the hydrothermal carbonization temperature is 163-167° C., and the hydrothermal carbonization time is 110-130 min.

Preferably, stirring is continued during the hydrothermal carbonization process.

In some embodiments, when microwave heating is performed, the temperature is increased to 520-570° C. at a rate of 115-125° C./min, and then microwave heating is stopped, and the mixture is naturally cooled and dried.

In a second aspect, the present invention provides a Fenton sludge magnetic iron-based catalyst prepared by the preparation method.

In a third aspect, the present invention provides the use of the Fenton sludge magnetic iron-based catalyst in the catalytic oxidation of toluene.

In a fourth aspect, the present invention provides the use of the Fenton sludge magnetic iron-based catalyst for adsorbing pentavalent arsenic in a solution.

The beneficial effects achieved by one or more embodiments of the present invention are as follows:

The hydrothermal carbonization method is used to partially reduce the iron oxide to ferroferric oxide with good microwave heating characteristics, and the macromolecular organic matter is pre-cracked. The ferroferric oxide particles and pre-cracked carbon particles generated by hydrothermal carbonization are dispersed in the sludge matrix to form a large number of evenly dispersed microwave active sites, which solves the problem of poor microwave heating characteristics of Fenton sludge. During microwave heating, local high temperatures are formed near the microwave active sites, causing the heavy metals in the sludge to solidify in situ. This method can effectively prevent the leaching of heavy metals during use of the product.

By controlling the temperature of the hydrothermal carbonization reaction and the ratio of iron oxide to organic matter in the organic iron mud, poor microwave heating characteristics or thermal runaway to generate iron element during microwave heating can be avoided. In addition, microwave heating makes the pore structure of the solid product after the hydrothermal carbonization reaction more developed and more stable.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

FIG. 1 is a process flow chart of an embodiment of the present invention.

Detailed ways

It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

The present invention will be further described below in conjunction with the embodiments.

Embodiment 1:

50g of dehydrated Fenton sludge with a water content of 56.6wt% and an iron oxide content of 56.5wt% and 8g of dehydrated organic sludge with a water content of 59.6wt% and an organic matter content of 41.1wt% were mixed and crushed to obtain organic iron sludge. The mass ratio of iron oxide to organic matter in the organic iron sludge was measured to be 8.9:1.

Organic iron sludge and water were mixed in a mass ratio of 1:5, placed in a high-pressure reactor, sealed, and nitrogen was introduced to carry out hydrothermal carbonization reaction. During the reaction, stirring was continuous, the stirring speed was 60 rpm, the heating rate was 5 °C/min, the target temperature was 165 °C, and the target temperature was maintained for 120 min. Then the mixture was naturally cooled, and the product was separated into solid and liquid and dried to obtain dry sludge hydrothermal carbon.

The dry sludge hydrothermal carbon was placed in a microwave reactor, nitrogen was introduced into the reactor, microwave heating was performed, the heating rate was 120℃/min, the temperature was stopped when the target temperature was 550℃, and then naturally cooled to room temperature and dried to obtain a magnetic iron-based catalyst. The specific surface area of the magnetic iron-based catalyst was measured to be ^263m2 /g, and the saturation magnetization intensity was 12.47emu/g.

Embodiment 2:

50g of dehydrated Fenton sludge with a water content of 56.6wt% and an iron oxide content of 56.5wt% and 6g of dehydrated organic sludge with a water content of 57.1wt% and an organic matter content of 48.3wt% were mixed and crushed to obtain organic iron sludge. The mass ratio of iron oxide to organic matter in the organic iron sludge was measured to be 9.5:1.

Organic iron sludge and water were mixed in a mass ratio of 1:5, placed in a high-pressure reactor, sealed, and nitrogen was introduced to carry out hydrothermal carbonization reaction. During the reaction, stirring was continuous, the stirring speed was 60 rpm, the heating rate was 5 °C/min, the target temperature was 170 °C, and the target temperature was maintained for 120 min. Then the mixture was naturally cooled, and the product was separated into solid and liquid and dried to obtain dry sludge hydrothermal carbon.

The dry sludge hydrothermal carbon was placed in a microwave reactor, nitrogen was introduced into the reactor, microwave heating was performed, the heating rate was 110℃/min, and the target temperature was stopped when it was 580℃, and then naturally cooled to room temperature and dried to obtain a magnetic iron-based catalyst. The specific surface area of the magnetic iron-based catalyst was measured to be ^237m2 /g, and the saturation magnetization intensity was 11.89emu/g.

Embodiment 3:

50g of dehydrated Fenton sludge with a water content of 56.6wt% and an iron oxide content of 56.5wt% and 10g of dehydrated organic sludge with a water content of 63.5wt% and an organic matter content of 38.9wt% were mixed and crushed to obtain organic iron sludge. The mass ratio of iron oxide to organic matter in the organic iron sludge was measured to be 8.3:1.

Organic iron sludge and water were mixed in a mass ratio of 1:5, placed in a high-pressure reactor, sealed, and nitrogen was introduced to carry out hydrothermal carbonization reaction. During the reaction, stirring was continuous, the stirring speed was 60 rpm, the heating rate was 5 °C/min, the target temperature was 150 °C, and the target temperature was maintained for 120 min. Then it was naturally cooled, the product was separated from the solid and liquid, and dried to obtain dry sludge hydrothermal carbon.

The dry sludge hydrothermal carbon was placed in a microwave reactor, nitrogen was introduced into the reactor, microwave heating was performed, the heating rate was 125°C/min, and the target temperature was stopped when it was measured to be 510°C, and then naturally cooled to room temperature and dried to obtain a magnetic iron-based catalyst. The specific surface area of the magnetic iron-based catalyst was measured to be ^209m2 /g, and the saturation magnetization intensity was 10.73emu/g.

Comparative Example 1:

The difference from Example 1 is that the mass of organic sludge added is 7g, and the mass ratio of iron oxide to organic matter in the organic iron sludge is 10.2:1. Others are the same as Example 1. The specific surface area of the magnetic iron-based catalyst is ^135m2 /g, and the saturation magnetization is 7.29emu/g.

Comparative Example 2:

The difference from Example 1 is that the mass of organic sludge added is 9g, and the mass ratio of iron oxide to organic matter in the organic iron sludge is 7.9:1. Others are the same as Example 1. The specific surface area of the prepared magnetic iron-based catalyst is ^53m2 /g, and the saturation magnetization is 9.73emu/g.

Comparative Example 3:

The difference from Example 1 is that the target temperature of the hydrothermal carbonization reaction is 145°C, and the rest is the same as Example 1. The specific surface area of the magnetic iron-based catalyst is 93 m ² /g, and the saturation magnetization is 2.76 emu/g.

Comparative Example 4:

The difference from Example 1 is that the target temperature of the hydrothermal carbonization reaction is 175° C., and the rest is the same as Example 1. The specific surface area of the magnetic iron-based catalyst is 146 m ² /g, and the saturation magnetization is 5.75 emu/g.

Comparative Example 5:

The difference from Example 1 is that the target temperature of microwave heating is 490°C, and the rest is the same as Example 1. The specific surface area of the magnetic iron-based catalyst is 147 m ² /g, and the saturation magnetization is 4.21 emu/g.

Comparative Example 6:

The difference from Example 1 is that the target temperature of microwave heating is 610° C., and the rest is the same as Example 1. The specific surface area of the magnetic iron-based catalyst is 37 m ² /g, and the saturation magnetization is 7.96 emu/g.

Comparative Example 7:

The difference from Example 1 is that the heating rate of microwave heating is 105°C/min, and the rest is the same as Example 1. The specific surface area of the magnetic iron-based catalyst is 163 m ² /g, and the saturation magnetization is 9.73 emu/g.

Comparative Example 8:

The difference from Example 1 is that the heating rate of microwave heating is 135°C/min, and the rest is the same as Example 1. The specific surface area of the magnetic iron-based catalyst is 102 m ² /g, and the saturation magnetization is 6.29 emu/g.

Test Example 1:

The magnetic iron-based catalysts prepared in Examples 1-3 and Comparative Examples 1-8 were tested for their catalytic oxidation performance of toluene, and the process was as follows:

The magnetic iron-based catalyst was placed in a sample tube in a tubular furnace, synthetic air with a toluene concentration of 500 ppm was introduced, the air velocity ratio was 20 L/(g·h), the heating rate of the tubular furnace was 2°C/min, and the toluene concentration of the outlet gas was measured using a high-precision gas chromatograph. The temperature at which the toluene degradation rate reached 90% was recorded as T90. After testing, the T90 temperature values corresponding to the magnetic iron-based catalysts prepared in Examples 1-3 and Comparative Examples 1-8 are shown in Table 1.

Test Example 2:

The magnetic iron-based catalysts prepared in Examples 1-3 and Comparative Examples 1-8 were tested for pentavalent arsenic adsorption performance in solution, and the process was as follows:

100 mL of a pentavalent arsenic solution with a concentration of 1 mg/L was prepared, 0.2 g of a magnetic iron-based catalyst was placed in the solution, the solution pH was adjusted to 7 using NaOH and HCl, and the solution was shaken at a constant temperature of 25°C for 24 hours, 5 mL of the solution was taken to measure the residual concentration of pentavalent arsenic, and the adsorption rate was calculated. After testing, the adsorption rates corresponding to the magnetic iron-based catalysts prepared in Examples 1-3 and Comparative Examples 1-8 are shown in Table 1.

After one cycle, the magnetic iron-based catalyst was separated by magnetic field to complete solid-liquid separation, washed, dried and tested again. After 5 cycles, the 24h adsorption rate of the magnetic iron-based catalyst prepared in Examples 1-3 was still maintained above 75%.

Table 1 Relevant performance parameters of magnetic iron-based catalysts prepared in various embodiments and comparative examples

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (9)

1. A method for preparing a Fenton sludge magnetic iron-based catalyst, characterized in that it comprises the following steps: The Fenton sludge and the organic sludge are mixed and crushed in proportion to obtain organic iron sludge, in which the mass ratio of iron oxide to organic matter is 8-10:1; After adding water to the organic iron sludge, the organic iron sludge is placed in a high-pressure reactor and introduced with inert gas for hydrothermal carbonization at a temperature of 150-170°C and a time of 100-140 minutes. After the hydrothermal carbonization is completed, the hydrothermal product is subjected to solid-liquid separation and drying to obtain dry sludge hydrothermal carbon. The dry sludge hydrothermal carbon is subjected to microwave heating in an inert atmosphere, and when the temperature is raised to 520-570°C at a rate of 115-125°C/min, microwave heating is stopped, and the mixture is naturally cooled and dried to obtain a magnetic iron-based catalyst; The iron oxide content of the Fenton sludge is 40%-65%, where % is the mass percentage; The organic matter content of the organic sludge is 30%-50%, where % is the mass percentage. 2. The method for preparing a Fenton sludge magnetic iron-based catalyst according to claim 1, wherein the moisture content of the Fenton sludge is 30%-80%, where % is the mass percentage. 3. The method for preparing a Fenton sludge magnetic iron-based catalyst according to claim 1, wherein the moisture content of the organic sludge is 30%-80%, where % is the mass percentage. 4. The method for preparing a Fenton sludge magnetic iron-based catalyst according to claim 1, wherein the mass ratio of iron oxide to organic matter in the organic iron sludge is 8.5-9.5:1. 5. The method for preparing the Fenton sludge magnetic iron-based catalyst according to claim 1, characterized in that the heating rate of the hydrothermal carbonization process is 3-7°C/min. 6. The method for preparing a Fenton sludge magnetic iron-based catalyst according to claim 5, characterized in that the hydrothermal carbonization temperature is 163-167°C and the hydrothermal carbonization time is 110-130 min. 7. A Fenton sludge magnetic iron-based catalyst, characterized in that it is prepared by the preparation method described in any one of claims 1-6. 8. Use of the Fenton sludge magnetic iron-based catalyst according to claim 7 in catalytic oxidation of toluene. 9. Use of the Fenton sludge magnetic iron-based catalyst according to claim 7 for adsorbing pentavalent arsenic in a solution.