CN107353034A - A kind of method for preparing haydite using microwave sintering curing heavy metal chromium - Google Patents

Abstract

The invention relates to a method for preparing ceramsite by using microwave sintering to solidify heavy metal chromium. The specific steps are: adding graphite powder, iron oxide, aluminum powder and potassium feldspar to chromium-contaminated soil, making it into a spherical shape, and then heating it by microwave sintering method. Ceramsite. The present invention uses chromium-contaminated soil as the main raw material to prepare ceramsite, which can effectively control the polluted land and realize the effective utilization of waste resources. In addition, graphite powder is added to the raw material, which can be used as a pore-forming agent and a reducing agent at the same time. Toxic hexavalent chromium is converted into trivalent chromium to achieve non-toxic treatment of chromium. The microwave sintering technology adopted in the present invention heats more evenly, not only the sintering atmosphere is controllable, the sintering speed is fast, the sintering quality is good, and the hexavalent chromium can be fully The reaction is trivalent chromium.

Description

A method for preparing ceramsite by solidifying heavy metal chromium by microwave sintering

technical field

The invention belongs to the technical field of solid waste treatment and resource utilization, and relates to a method for preparing ceramsite by using microwave sintering and solidifying heavy metal chromium.

Background technique

Soil heavy metal pollution refers to human activities, the content of trace metal elements in the soil exceeds the background value, and the excessive content caused by excessive deposition is collectively referred to as soil heavy metal pollution. Soil is the most important natural resource of a country, and it is the material basis of agricultural development. But in recent years, with the process of industrialization, more and more land has been used to build factories, which in turn causes heavy metal pollution in the soil. At present, the problem of soil pollution in my country is very serious. Heavy metals have become the most common source of soil pollution. Once heavy metals enter the soil, it will be difficult to remove them. How to deal with heavy metals in polluted soil has become a technical problem to be solved urgently in the field of domestic soil environment.

Chromium exists widely in nature in various valence states, and its toxicity to the human body is related to its valence state. Trivalent chromium is an essential trace element for the human body, while hexavalent chromium easily enters cells and is reduced to trivalent, producing pentavalent chromium at the same time. Valence chromium intermediates and a variety of oxygen free radicals, so it has strong toxicity. Trivalent chromium has little toxicity, is not carcinogenic or has low chronic toxicity. At present, the treatment of chromium-contaminated soil is mainly divided into physical remediation, chemical remediation, and biological remediation. Physical remediation is generally incompletely solidified and difficult to eradicate; chemical remediation projects often need to invest more reducing agents than the theoretical value, causing secondary pollution; bioremediation is the use of plants or microorganisms to absorb, transform, and remove pollutants. Bioremediation is a remediation technology that removes pollutants in soil by degradation. Bioremediation is safe and inexpensive, but it has disadvantages such as long effective time and incomplete treatment.

In recent years, some achievements have been made in the research on the control and treatment of chromium-contaminated soil at home and abroad. For example, Chinese invention patent 201110206407.6 provides a method for producing ceramsite by sintering high-chromium-contaminated soil, but it uses conventional sintering methods to consume energy Larger, the sintering rate is slower, and the chromium in the product ceramsite is still hexavalent chromium, which does not fundamentally reduce its toxicity.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for preparing ceramsite by using microwave sintering chromium-containing contaminated soil for the above-mentioned shortcomings in the prior art.

In order to solve the problems of the technologies described above, the technical solution provided by the invention is:

Provided is a method for preparing ceramsite by using microwave sintering to solidify heavy metal chromium: adding graphite powder, iron oxide, aluminum powder and potassium feldspar to chromium-contaminated soil, making it into a spherical shape, and heating by microwave sintering method to prepare ceramsite.

According to the above scheme, the content of chromium-contaminated soil, graphite powder, iron oxide, aluminum powder and potassium feldspar in terms of mass percentage is: 80-85% of chromium-contaminated soil, 2-5% of graphite powder, and 3-10% of iron oxide , aluminum powder 2-4%, potassium feldspar 1-7%.

According to the above scheme, the specific steps of the above method are as follows:

1) Grind the chromium-containing contaminated soil to a 100-mesh sieve with a residue of ≤15%, then mix it with graphite powder, iron oxide, aluminum powder, and potassium feldspar, add water and mix evenly, and make a ceramsite billet after aging for 24 hours;

2) The ceramsite blank obtained in step 1) is placed in a microwave sintering furnace, and microwave heating and sintering is carried out under an inert atmosphere or a reducing atmosphere (such as CO) to obtain ceramsite.

Preferably, the amount of water added in step 1) is 7-10% of the total solid mass.

Preferably, the output frequency of the microwave sintering furnace in step 2) is 2450±50MHz, and the output power is less than or equal to 15KW.

According to the above scheme, the microwave heating and sintering process in step 2) is as follows: microwave heating to 550°C for preheating, the preheating time is 30 minutes, then the temperature is raised to 950-1050°C, and the temperature is kept for 10-30 minutes.

The present invention also includes the ceramsite prepared by the above method, the ceramsite has a water absorption rate of 9.3-11.0%, a density of 1.73-1.85g/cm ³ , and a solidification rate of heavy metal chromium of 99.36-99.97%.

This application adopts microwave sintering technology. When microwave is heated, all parts of the object can evenly penetrate microwaves to generate heat, so the uniformity is greatly improved. The heating rate of microwave sintering is much higher than that of conventional sintering, which can avoid uneven heating and sintering progress of various parts of ceramsite. Different phenomena improve product quality, are conducive to the production of high-quality ceramsite, and are conducive to industrial production. At the same time, during microwave sintering, the sintering atmosphere is easy to control, so that the sintering atmosphere is in an inert atmosphere or a reducing atmosphere, which is conducive to the conversion of highly soluble and highly toxic hexavalent chromium to trivalent chromium, and improves the solidification efficiency of chromium.

The invention uses chromium-contaminated soil as the main raw material to prepare ceramsite, which can effectively control the pollution and realize the effective utilization of waste resources; at the same time, the addition of potassium feldspar can effectively reduce the sintering temperature and energy consumption, and can also increase the high temperature. The liquid phase viscosity during sintering is conducive to gas pore formation.

An appropriate amount of graphite powder is added to the raw materials, which can be used as a pore-forming agent for ceramsite to improve the pore structure of ceramsite, and can also be used as a reducing agent to promote the conversion of hexavalent chromium into trivalent chromium and realize the non-toxic treatment of chromium.

The aluminum powder in the raw material of the present invention can undergo thermite reaction with iron oxide at high temperature, prevent iron oxide from decomposing at high temperature and release oxygen chromium oxide, which is beneficial to the reduction of hexavalent chromium, and at the same time, the aluminotherm reaction can generate a large amount of heat for Sintering provides part of the energy, which is conducive to energy saving and emission reduction.

The beneficial effect of the present invention is that: the microwave sintering technology adopted in the present invention is more uniform in heating, not only the sintering atmosphere is controllable, the sintering rate is fast, and the sintering quality is good, but also the hexavalent chromium can be fully reacted into trivalent chromium, and graphite powder and Aluminum powder promotes the full conversion of hexavalent chromium into trivalent chromium; the ceramsite prepared by the present invention takes chromium-contaminated soil as the main raw material, has low water absorption (9.3% to 11.0% water absorption) and low density (1.73% to 1.85% density) g/cm ³ ), low cost, non-toxic (curing rate of 99.36-99.97% for heavy metal chromium), and has multiple uses.

detailed description

In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with examples.

Graphite powder, iron oxide, aluminum powder, and potassium feldspar used in the embodiments of the present invention are all commercially available materials, and wherein the content of iron oxide in iron oxide is greater than or equal to 85wt%; Or equal to 15%, and the fineness of the potassium feldspar is less than or equal to 15 wt% when passing through a 100-mesh sieve. The fineness of the aluminum powder is less than or equal to 15% when passing through a 100-mesh sieve.

Example 1

Using microwave sintering to solidify heavy metal chromium to prepare ceramsite, the method is as follows:

1) Chromium-contaminated soil sample: take the polluted soil near a chemical plant, the chromium content in this soil is 1453.44mg/kg;

2) Treatment of chromium-contaminated soil: Weigh the chromium-contaminated soil sample and dry it in a drying oven for 3 hours, then cool the chromium-contaminated soil to room temperature, and put the powder into a ceramic ball mill for 30 minutes until the 100-mesh sieve remains ≤ 15%;

3) Mixed aging: add water to the treated soil in step 2) with graphite powder, iron oxide, aluminum powder, and potassium feldspar in a mass ratio of 82:5:5:2:5 (the mass of water is 10% of the total mass of solids) ) mixed evenly, and aged for 24 hours to make ceramsite blank;

4) Sintering: Put the ceramsite blank obtained in step 3) into a microwave sintering furnace (output frequency is 2450±50MHz, output power 12KW), and carry out microwave heating and sintering under a nitrogen atmosphere to obtain ceramsite. The microwave heating and sintering process is as follows: Microwave heating to 550°C for preheating, the preheating time is 30min, then the temperature is raised to 1050°C, and the temperature is kept for 30min.

Using GB/T17431.2-2010 "Light Aggregate and Its Test Method Part 2: Light Aggregate Test Method" to test the sample obtained in this example, the water absorption of the sintered sample is 9.3%, and the density is 1.85g/ ^cm3 . The content of heavy metal chromium (total chromium content) in the leaching solution was detected by the horizontal oscillation method (HJ 557-2010), which is a toxic leaching method for solid waste leaching. The chromium solidification rate of ceramsite was measured to be 99.97%.

Example 2

Using microwave sintering to solidify heavy metal chromium to prepare ceramsite, the method is as follows:

1) Chromium-contaminated soil sample: take the polluted soil near a chemical plant, the chromium content in this soil is 1453.44mg/kg;

2) Treatment of chromium-contaminated soil: Weigh the chromium-contaminated soil sample and dry it in a drying box for 3 hours, then cool the contaminated soil to room temperature, and put the powder in a ceramic ball mill for 30 minutes until the 100-mesh sieve remains ≤ 15%;

3) Mixed aging: add water to the treated soil in step 2) with graphite powder, iron oxide, aluminum powder, and potassium feldspar at a mass ratio of 80:5:3:2:7 (the mass of water is 8% of the total solid mass) ) mixed evenly, and aged for 24 hours to make ceramsite blank;

4) Sintering: Put the ceramsite blank obtained in step 3) into a microwave sintering furnace (output frequency is 2450±50MHz, output power 12KW), and carry out microwave heating and sintering under a nitrogen atmosphere to obtain ceramsite. The microwave heating and sintering process is as follows: Microwave heating to 550°C for preheating, the preheating time is 30min, and then the temperature is raised to 1000°C and kept for 10min.

The sample obtained in this example was tested by the same method as in Example 1, and the water absorption of the sintered sample was 10.5%, and the density was 1.76g/cm ³ . The content of heavy metal chromium (total chromium content) in the leaching solution was detected by horizontal oscillation method (HJ 557-2010), which is a toxic leaching method for solid waste leaching. The chromium solidification rate of ceramsite was measured to be 99.41%.

Example 3

Using microwave sintering to solidify heavy metal chromium to prepare ceramsite, the method is as follows:

1) Chromium-contaminated soil sample: take the polluted soil near a chemical plant, the chromium content in this soil is 1453.44mg/kg;

2) Treatment of chromium-contaminated soil: Weigh 100 g of chromium-contaminated soil sample and dry it in a drying oven for 3 hours, then cool the contaminated soil to room temperature, and put the powder in a ceramic ball mill for 30 minutes until the residue on a 100-mesh sieve is ≤15%;

3) Mixed aging: add water to the treated soil in step 2) with graphite powder, iron oxide, aluminum powder and potassium feldspar according to the mass ratio of 84:3:3:3:7 (the mass of water is 8% of the total solid mass) Mix evenly, and make ceramsite blank after aging for 24 hours;

4) Sintering: Put the ceramsite blank obtained in step 3) into a microwave sintering furnace (output frequency is 2450±50MHz, output power 12KW), and carry out microwave heating and sintering under a nitrogen atmosphere to obtain ceramsite. The microwave heating and sintering process is as follows: Microwave heating to 550°C for preheating, the preheating time is 30min, and then the temperature is raised to 950°C and kept for 20min.

The sample obtained in this example was tested by the same method as in Example 1. The water absorption of the sintered sample was 10.1%, and the density was 1.73g/cm ³ . The level oscillation method (HJ 557-2010) of solid waste leaching toxicity leaching method was used to detect the content of heavy metal chromium (total chromium content) in the leach solution was 0.934mg/L, and the chromium solidification rate of ceramsite was measured to be 99.36%.

Example 4

Using microwave sintering to solidify heavy metal chromium to prepare ceramsite, the method is as follows:

1) Chromium-contaminated soil sample: take the polluted soil near a chemical plant, the chromium content in this soil is 1453.44mg/kg;

2) Treatment of chromium-contaminated soil: Weigh 100 g of chromium-contaminated soil sample and dry it in a drying oven for 3 hours, then cool the contaminated soil to room temperature, and put the powder in a ceramic ball mill for 30 minutes until the residue on a 100-mesh sieve is ≤15%;

3) Mixed aging: add water to the treated soil in step 2) with graphite powder, iron oxide, aluminum powder, and potassium feldspar at a mass ratio of 80:3:6:4:7 (the mass of water is 10% of the total solid mass) ) mixed evenly, and aged for 24 hours to make ceramsite blank;

4) Sintering: Put the ceramsite blank obtained in step 3) into a microwave sintering furnace (output frequency is 2450±50MHz, output power 12KW), and conduct microwave heating and sintering under a CO atmosphere to obtain ceramsite. The microwave heating and sintering process is as follows: Microwave heating to 550°C for preheating, the preheating time is 30min, and then the temperature is raised to 1000°C and kept for 30min.

The sample obtained in this example was tested by the same method as in Example 1. The water absorption of the sintered sample was 11.0%, and the density was 1.81g/cm ³ . The content of heavy metal chromium (total chromium content) in the leaching solution was detected by the horizontal oscillation method (HJ 557-2010), which is a toxic leaching method for solid waste leaching. The chromium solidification rate of ceramsite was measured to be 99.81%.

Each raw material listed in the present invention, as well as the upper and lower limits and interval values of each raw material in the present invention, and the upper and lower limits and interval values of process parameters can all realize the present invention, and the embodiments are not enumerated here one by one.

Claims (7)

1. A method utilizing microwave sintering to solidify heavy metal chromium to prepare ceramsite is characterized in that: graphite powder, iron oxide, aluminum powder and potassium feldspar are added to chromium-contaminated soil, and microwave sintering method heating is used to prepare pottery after being made spherical grain. 2. the method according to claim 1 is characterized in that, by mass percentage, the content of chromium polluted soil, graphite powder, iron oxide, aluminum powder and potassium feldspar is: chromium polluted soil 80～85%, graphite powder 2-5%, iron oxide 3-10%, aluminum powder 2-4%, potassium feldspar 1-7%. 3. The method according to claim 1 or 2, wherein the specific steps are as follows: 1) Grind the chromium-containing contaminated soil to a 100-mesh sieve with a residue of ≤15%, then mix it with graphite powder, iron oxide, aluminum powder, and potassium feldspar, add water and mix evenly, and make ceramsite blank after aging for 24 hours; 2) The ceramsite blank obtained in step 1) is placed in a microwave sintering furnace, and microwave heating and sintering is carried out under an inert atmosphere or a reducing atmosphere to obtain ceramsite. 4. The method according to claim 3, characterized in that the amount of water added in step 1) is 7-10% of the total solid mass. 5. The method according to claim 3, characterized in that the output frequency of the microwave sintering furnace in step 2) is 2450±50MHz, and the output power is less than or equal to 15KW. 6. The method according to claim 3, characterized in that the microwave heating and sintering process in step 2) is: microwave heating to 550°C for preheating, the preheating time is 30min, then the temperature is raised to 950-1050°C, and the heat preservation time is 10 minutes. ~30min. 7. The ceramsite prepared by the method according to claims 1-6, characterized in that, the ceramsite has a water absorption rate of 9.3-11.0%, a density of 1.73-1.85g/cm ³ , and a curing rate of 99.36% for heavy metal chromium. ~99.97%.