KR20150076582A - Cleaning Method of Contaminated Soils - Google Patents

Abstract

The present invention provides a method for purifying heavy metal contaminated soil by adjusting the bubble size by changing the amount of air. Specifically, the contaminated soil is crushed through a crusher in a state where contaminated soil and water are mixed and is present on the surface of the contaminated soil A surface grinding step of separating the contaminants from the soil; And a floating sorting step of removing the contaminants contained in the bubbles by removing air bubbles by generating air bubbles by injecting air into the mixture of water and contaminated soil after the surface grinding process, A method for purifying contaminated soil is provided.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cleaning method for contaminated heavy metals,

The present invention relates to a method for purifying soil contaminated with heavy metals or other harmful substances, and more particularly, to a method for purifying soil contaminated with a heavy metal by using a surface grinding process and a floating sorting process, To a method for purifying heavy metal contaminated soil which can efficiently remove the heavy metal contaminated soil.

 The interest in the soil environment is growing worldwide, and the technology and experience are accumulating in Korea as the large-scale soil pollution clean-up project proceeds. Over the past two decades since the Soil Environmental Conservation Act came into force in 1996, most of the 20 years have been concerned with the treatment of oil contaminated soils. In case of soils polluted with oil, it is relatively easy to confirm the pollution situation by smell and naked eye. Therefore, it seems that there is much interest in the treatment of such oil contaminated soil.

Unlike such oil pollution, when the soil is contaminated with heavy metals, the pollution situation can not easily be confirmed by smell or naked eye. Therefore, in case of soil, it is difficult to recognize the pollution situation relatively as compared with oil pollution. However, soil contamination by heavy metals is a major threat to human health over a long period of time. The agricultural land around the abandoned abandoned mines scattered all over the country is often contaminated by heavy metals, and the heavy industrial pollution of the soil is very serious.

Conventional methods for treating soils contaminated with heavy metals (heavy metal contaminated soil) include soil washing, solidification and stabilization, and electrodynamic purification. Among them, solidification and stabilization methods are the most widely used in the world. Since Korea is currently regulating the heavy metal contamination of soils based on the heavy metal content in the soil, even if the solidification and stabilization method is applied, the concentration of total heavy metals in the soil is not reduced. Therefore, the conventional solidification / stabilization method , It is possible that the soil may not meet legal regulations when it is used for the purification treatment of heavy metal contaminated soil.

Korean Patent Laid-Open Publication No. 10-2006-78779 discloses a soil washing method as a conventional technique for purifying contaminated soil. Such a conventional soil washing method uses a cleaning agent to remove the soil that has been adsorbed on the solid material of the soil It is a method to remove contaminants by moving them to liquid phase. Specifically, in the soil washing method, a surfactant, an acidic solution or an alkaline solution is mixed with a soil to remove contaminants such as heavy metals from the soil and brought to an aqueous solution to remove contaminants such as heavy metals from the soil. Such a soil washing method is currently in the spotlight because the equipment required for the soil purification is relatively simple and the purification treatment speed is fast. However, in the case of micro-contaminated soils with fine soil particles, a large amount of chemicals and facility costs are consumed in the course of soil washing so that the concentration of heavy metals after the purification satisfies the statutory standard value, , Conventional soil washing methods are not suitable for fine soil contaminated with heavy metals.

Korean Patent Publication No. 10-2006-78779 (published on June 7, 2006).

It is an object of the present invention to provide a technique capable of efficiently removing and purifying contaminants such as heavy metals from contaminated soil.

According to an aspect of the present invention, there is provided a surface grinding process for grinding a contaminated soil through a grinder in a state where contaminated soil and water are mixed, thereby separating contaminants present on the surface of the contaminated soil from the soil; And a floating sorting step of removing the contaminants contained in the bubbles by removing air bubbles by generating air bubbles by injecting air into the mixture of water and contaminated soil after the surface grinding process, A method for purifying contaminated soil is provided.

In the float-sorting step of the present invention as described above, potassium amyl xanthate is added as a trapping agent to a mixture of water and contaminated soil subjected to the surface grinding step, When the contaminated soil is crushed through the crusher in the surface crushing process, the crusher of the crusher containing water and the contaminated soil is crushed to 75 to 80% of the critical rotating speed, As shown in FIG.

Furthermore, in the present invention, when the air bubbles are generated by injecting air in the floating sorting process, air can be adjusted to adjust the average size of bubbles to a size suitable for separating contaminants from the soil .

A surface grinding step of grinding the contaminated soil through the grinder in a state where the contaminated soil and the water are mixed and separating the pollutants present on the surface of the contaminated soil from the soil; A floating separation process is performed in which bubbles are generated by injecting air into a mixture of water and contaminated soil after the surface grinding process and only contaminants contained in the bubbles are removed by removing only the generated bubbles, The effect of effectively removing contaminants such as heavy metals can be exerted on the soil contaminated with heavy metals.

Particularly, in the present invention, by using PAX as a trapping agent in the floating sorting process, the efficiency of collecting contaminants by bubbles is greatly improved, and contaminants can be removed more efficiently.

Particularly, according to the prior art, the purification efficiency for micro-soil having a particle size of 1 mm or less is very low, but the present invention has an advantage of showing a very high purification efficiency even for micro-soil having a size of 0.075 mm or less.

1 is a schematic flow chart showing each step of a contaminated soil purification method according to the present invention.
FIGS. 2, 3, and 4 are graphs showing the measurement results of the particle generation rate according to the progressing time of the surface grinding process when the rotating speed of the grinder is different according to the present invention.
FIGS. 5, 6, and 7 are graphs showing concentrations of heavy metals (arsenic concentrations) according to soil particle sizes according to the rotating speed of the pulverizer used in the surface grinding process in the present invention.
8 is a graph showing the result of measuring the concentration of heavy metals in the air bubbles generated in the flotation screening process according to the passage of time when PAX is used as a trapping agent.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Although the present invention has been described with reference to the embodiments shown in the drawings, it is to be understood that the technical idea of the present invention and its essential structure and operation are not limited thereby.

The method for purifying contaminated soil according to the present invention is a method for purifying contaminated soil (hereinafter abbreviated as "surface grinding process") and a process for removing contaminants by floating separation (hereinafter abbreviated as "float sorting process") ). FIG. 1 is a schematic flow chart showing each step of the method for purifying contaminated soil according to the present invention.

In the surface grinding process, the pollutants present on the surface of the contaminated soil are physically separated from the soil. Even if the pollutants such as heavy metals, which are difficult to chemically separate from the surface of the soil, can be separated very effectively through the surface grinding process do. Specifically, in the surface grinding process, a soil contaminated with heavy metals is put into a grinding container of a grinder containing grinding balls together with water, and then the grinding container is rotated to exist on the surface of the soil by friction between the grinding balls and the soil So that contaminants such as heavy metals are separated from the soil. As the pulverizer used in such a surface grinding process, a pot mill using a steel ball or a ceramic ball as a grinding ball can be used. For example, about 3 kg (66.7 g / Number, total number of use: about 45) can be used in the crushing vessel together with water and contaminated soil.

When the pot mill is rotated at an excessively high speed in the surface milling step, the crushing bowl is rotated in a state of closely contacting the inner wall surface of the crushing vessel, so that the process of removing contaminants from the surface of the soil is not performed , The soil particles are broken and the pollutant removal efficiency is reduced. Therefore, in carrying out the surface grinding process, it is preferable to rotate the pot mill to a critical rotation speed or less so as not to lower the removal efficiency of the contaminants. In order to efficiently crush the surface of the soil particles, the critical rotation speed of the pot mill is determined in the present invention, and the optimum rotation speed of the pot mill is determined while changing the rotation speed of the pot mill within a range below the critical rotation speed.

On the other hand, in order to determine the optimal rotation speed of the pot mill, the present inventors rotated the pot mill at the rotation speeds of 50%, 75% and 100% of the critical rotation speed, respectively, The concentration of heavy metals was measured and the rotation speed of the pot mill when the highest heavy metal concentration was measured was determined as "optimum rotation speed ".

According to the present invention, the pollutant is separated from the surface of the soil through the surface grinding process, and then the floating sorting process is performed in which separated pollutants are floated on the water by using a collecting agent and a foaming agent. Specifically, the soil subjected to the surface grinding process is in a slurry state because it contains water. In the present invention, a mixture of water and contaminated soil prepared in the slurry state through the surface grinding process is put into a flotation machine, Air is continuously injected into the chamber to generate air bubbles. In this way, when air bubbles are generated on the flotator, the contaminants separated from the soil are trapped in the air bubbles and floated on the water. Removal of air bubbles floating on the water removes contaminants separated from the soil, that is, heavy metals, along with air bubbles, thereby purifying the contaminated soil. That is, in the float sorting process, the contaminants separated from the soil particles after the surface grinding are floated on the water using the trapping agent and the foam agent to remove contaminants.

 In performing the float sorting process, a foaming agent may be used so that the foaming agent is floated on the water without using a trapping agent for selectively attaching the contaminant to the foam. In the use of such a trapping agent, foaming agent and the like Thereby further improving the removal efficiency of contaminants.

In the present invention, as a surfactant, Potassium Amyl Xanthate (PAX) is used as a surfactant in the form of an aqueous solution having a critical micelle concentration or less. That is, after the above-described collecting agent is added to the mixture of water and contaminated soil after the surface grinding process, air is injected to generate bubbles. Pine-oil may be used as the foaming agent.

  Meanwhile, in the present invention, when performing the floating sorting process using the flotation device, the amount of air to be injected into the flotation device is determined according to the particle size of the surface ground soils, thereby adjusting the size of the air bubble. If the size of the bubbles generated in the barge by the air injection is not appropriate, not only the pollutant but also the general soil will be blown into bubbles together, which reduces the purification efficiency. Therefore, in the present invention, the amount of air is decreased to reduce the size of the bubbles generated by the air inflow as the size of the soil particles is smaller, and in the opposite case, the size of the bubbles is increased by increasing the amount of air. Particularly, in the present invention, the air bubble size is controlled by adjusting the air amount. In this case, the average bubble size is 0.04 mm at 200 L / min, 0.1 mm at 400 L / min, and 0.2 mm at 600 L / min .

In the following, a specific experimental example in which contaminants such as heavy metals are removed from contaminated soil using the contaminated soil remediation method of the present invention will be described.

<Experimental Example>

(1) Contaminated soil used in the experiment

In this experiment, the soil collected from the field near the Janghang smelter was separated into sandy clay and clayey by wet granular separation, and sandy soil was used as contaminated soil for the experiment. In wet granular separation, the soil was separated by using a standard, and the soil was separated by 0.075mm. The soil with a size of 0.075mm or less was classified into clay (fine soil), and the soil with a size of 0.075mm or more was classified into sand.

As a result of the heavy metal analysis, the content of arsenic was 101.208 mg / kg.

(2) Experimental configuration and experimental method

In the experiment of the contaminated soil purification method according to the present invention, a well-known pot mill having a capacity of 4 L was used for performing the surface grinding process. Experimental use of the pot mill inner diameter used in the experiment, Experiments were conducted on the rotation speeds of the pot mills corresponding to 50%, 75% and 100% of the critical rotation speed, respectively, in order to confirm the optimum efficiency of surface grinding. Tap water was used for the experiment. The ratio of contaminated soil to water was 1: 2.5 by weight.

The conditions of the present invention in which the surface grinding process was carried out according to the present invention are summarized in Table 1 below.

After the surface grinding process was carried out, a floating sorting process was performed. Table 2 shows the conditions of the present experiment in which the flotation screening process according to the present invention was carried out. For each of the specimens shown in Table 1, "Run 1" and "Run 2" The floating sorting process was performed according to the conditions.

In the float sorting process, tap water was added to the slurry soil prepared in the pot mill in the surface grinding step, and the mixture was added to the flotation machine. The weight ratio of the contaminated soil in the slurry state to the newly added tap water was about 1: 3. In order to adhere the contaminants to the foam in the float sorting process, the soil remediation efficiency was evaluated by adding a surfactant, potassium amyl zantate (PAX) as a trapping agent. Each of the surfactants was added at a concentration of 150 g / ton, 200 g / ton and 250 g / ton. 0.04 ml of pine oil was used as foaming agent so that the generated bubbles float above the water surface without breaking.

To verify the efficiency of the barge according to the size of the generated bubbles, the average size of the bubbles was adjusted to be 0.04 mm, 0.1 mm and 0.2 mm, respectively. The bubble size was measured using a bubble diameter Respectively. Airborne sorting was carried out continuously for 20 minutes. Bubbles were collected and their weights and concentrations were measured. For reference, the concentration "g / ton" of the sorbent in Table 2 below means the mass of the sorbent per ton of soil.

As described above, the soil subjected to the surface grinding process according to the present invention, the bubbles generated in the flotation machine of the flotation screening process, and the soil remaining in the flotation machine are sieved with a standard, and analyzed for heavy metal concentration by the known soil contamination process test method Respectively.

(3) Experimental results

FIGS. 2, 3 and 4 are graphs showing the measurement results of the particle generation rate according to the progressing time of the surface grinding process when the rotating speed of the grinder is different. FIG. 2 shows a case where the speed of the pulverizer is 10 rpm, FIG. 3 shows the case where the speed of the pulverizer is 15 rpm, and FIG. 4 shows the case where the speed of the pulverizer is 20 rpm. In the legend for each graph shown in Figs. 2 to 4, the numerical value expressed in mm means the size of the soil particle.

As can be seen from Figs. 2 to 4, in the case of soil particles having a size of more than 0.075 mm, the particle generation rate decreased with the execution time of the surface grinding process, and the particle generation rate gradually increased in the case of soil below 0.075 mm Respectively. This is because the surface of the soil particles is gradually crushed by the crushing balls.

5, 6, and 7 are graphs each showing the concentration of heavy metal (concentration of arsenic) in the soil particle size according to the rotation speed of the pulverizer used in the surface grinding process. FIG. 5 shows the case where the speed of the pulverizer is 10 rpm, FIG. 6 shows the case where the speed of the pulverizer is 15 rpm, and FIG. 7 shows the case where the speed of the pulverizer is 20 rpm. In Figs. 5 to 7, numerical values in millimeters of the legend for each graph mean the size of the soil particles. As can be seen from FIGS. 5 to 7, when the crusher was operated at a rotation speed corresponding to 50% and 75% of the critical rotation speed, the soil of the size 0.075 mm or less had time from the start of operation of the crusher to 5 minutes The concentration of heavy metals gradually increased. However, the concentration of heavy metals gradually decreased after 5 minutes and after. Most of the heavy metals are present on the surface of the soil. In the early stage of the surface grinding process, the surface is ground by the grinding ball, and the concentration of the heavy metal is increased. However, when about 5 minutes elapses after grinding, It can be understood that the above results are measured because the concentration of the measured heavy metal decreases in point.

On the other hand, when the rotating speed of the pulverizer was operated at 100% of the critical rotating speed, there was no significant difference from the case of operating at 75% of the critical rotating speed. Therefore, when the surface grinding process is performed for the purification of heavy soil contaminated with heavy metals, it is preferable to operate the grinding machine at a rotational speed within 75 to 80% of the critical rotating speed in consideration of the operating energy consumption of the grinder.

FIG. 8 is a graph showing the results of measuring the concentration of heavy metals in the bubbles generated in the flotation screening process according to the passage of time, when PAX was used as a collecting agent. In the legend for each graph shown in FIG. 8, the numerical value in g / ton represents the concentration of the collecting agent, and the numerical value in mm represents the size of the bubble.

As the concentration of sorbent increased to 200g / ton, the concentration of heavy metal in the generated bubbles tended to increase. However, in the case of PAX, because of the high capture capacity of heavy metals, when an excessively large concentration of PAX is used, all of the soil not contaminated with heavy metals tends to be flaked. Therefore, 200 g or less, that is, 200 g / ton or less. As described above, in the present invention, by using PAX as a trapping agent in the floating sorting process, the efficiency of collecting contaminants by bubbles is greatly improved, and contaminants can be removed more efficiently.

On the other hand, as the barge time increases, the concentration of heavy metals in the bubble tends to decrease gradually. This result is because the large amount of soil particles including arsenic was removed by barge at the beginning of the barge. According to the result of the experiment on the barge efficiency according to the generated bubble size, the concentration of heavy metal in the generated bubble tends to increase as the bubble size increases. However, when the bubble size is 0.1 mm or more, The concentration was decreased. Most of the heavy metals are present in soil particles below 0.075mm when the surface is ground. Therefore, when the size of the bubble increases, the soil having a size of more than 0.075 mm and containing no heavy metal tends to be flogged together with the bubble. Therefore, it is most effective when the average size of the bubble is 0.1 mm.

If the contaminated soil with an initial arsenic concentration of 101.208 mg / kg is subjected to the soil pollution purification method according to the present invention, that is, the surface grinding process and the floating sorting process, the arsenic concentration is reduced by about 60% The results of this study are summarized as follows.

Claims (1)

A surface grinding step of grinding the contaminated soil through the grinder with the contaminated soil mixed with water to separate the pollutants present on the surface of the contaminated soil from the soil;
And a floating sorting step of removing air bubbles by injecting air into the mixture of water and contaminated soil after the surface grinding step and removing only the generated bubbles;
In the floating separation step, potassium amyl xanthate or sodium dodecyl sulfate is added as a trapping agent to a mixture of water and contaminated soil after the surface grinding step, Air is injected into a mixture of water and contaminated soil to generate air bubbles, and the average size of the air bubbles is controlled by changing the amount of air to be injected;
Characterized in that, when the contaminated soil is crushed through the crusher in the surface crushing process, the crusher of the crusher containing water and the contaminated soil is rotated at a speed corresponding to 75 to 80% of the critical rotating speed .

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