KR20040000585A - Method for Manufacturing Absorbent Capable of Stabilizing Heavy Metal in MSWI Fly Ash by Admixture and Absorbing Heavy Metal - Google Patents

Abstract

PURPOSE: Provided is a method for preparing adsorbent for heavy metals by adding sodium sulfate and water to fly ash as additives and heating it to stabilize hazardous material in fly ash, thereby preparing adsorbent with large specific surface area and high adsorbability at low cost. CONSTITUTION: The method comprises the steps of (a) mixing fly ash collected by a dust collector in an incinerator, sodium sulfate and water with a mixing ratio of 4 : 0.5 to 1.5 : 5 to 6, (b) molding the mixture of the step (a) in granular form, (c) heating the granular form of the mixture at temperature in the range of 700 to 900°C, and (d) cooling the granular form of mixture.

Description

Method for Manufacturing Absorbent Capable of Stabilizing Heavy Metal in MSWI Fly Ash by Admixture and Absorbing Heavy Metal}

The present invention relates to a method for stabilizing heavy metals and adsorbents for incineration fly ash using additives, and more particularly, to a method for producing an optimal adsorbent for recycling fly ash discharged from a dust collector to a heavy metal adsorbent when incineration of municipal waste.

In general, incineration ash generated after incineration of waste can be classified into floor ash and fly ash. Among them, fly ash must be classified as designated waste and treated at a specially managed landfill, but it is difficult to secure landfill for final disposal of designated waste in the future. to be.

Most of the incineration ash (80-85%) is a flooring material, but the flooring material contains a large amount of incombustibles such as iron and nails, and the overall particle size distribution is made up of 48 mesh [300 μm] or more to produce an adsorbent. This is big. Fly ash, on the other hand, mainly contains 10-20% by weight of silicon oxide (SiO ₂ ), 20-40% by weight of calcium oxide (CaO), 3-10% by weight of aluminum oxide (Al ₂ O ₃ ), 1-5 It is composed of iron (Fe) by weight, 4-12% by weight sodium oxide (Na ₂ O), 10-30% by weight of unburned powder, etc., and the particle size is mainly composed of 100 mesh [150㎛] or less have.

The fly ash has a small particle size and is easier to prepare as an adsorbent than a floor ash, and can be usefully prepared as an adsorbent using components of silicon, calcium and sodium mainly contained in the fly ash. However, fly ash contained more basic components than flooring and contained heavy metals such as chromium (Cr), copper (Cu), and lead (Pb). Therefore, in order to prepare the incineration fly ash as an adsorbent, it is necessary to stabilize the heavy metals contained in the fly ash and enhance the adsorption capacity.

Today, due to the development of the industry and the increase of consumption, the problem of environmental pollution caused by various by-products has been raised seriously, and the purification and removal of harmful substances such as heavy metals has become a key factor in determining the right to survival. The treatment of environmental pollutants is selected according to the characteristics of the pollutant. Generally, wastewater discharged from dye plants, steel mills, film manufacturing plants, alloy plants, synthesis plants, pigment plants and mines is biologically Since it contains unprocessable chemicals, heavy metals, etc., the wastewater is treated using an adsorption method, an ion exchange method, a precipitation method, or the like depending on the type.

Among the above methods, the adsorption method uses adsorption, which is a phenomenon in which molecules adhere to a solid surface by physical or chemical bonding force in a solution or gas phase, and an adsorption agent is required to provide a surface to which molecules can adhere for adsorption. Activated carbon, ion exchange resin, and synthetic zeolite are mainly used as adsorbents to remove heavy metal ions contained in wastewater and water, and activated carbon is activated at 800-1000 ℃ by steam or combustion gas or zinc chloride. Activated by (ZnCl ₂ ), heavy metal ions are adsorbed and removed in the micropores generated in the activation process.

Since the ion exchange resin adsorbs other ions coexisting with the heavy metal ions in the same manner, there is a problem in that heavy metal ions flow out when the heavy metal ions are removed in the wastewater and the water containing a large amount of co-ions. In addition, synthetic zeolites are manufactured using sodium aluminate (NaAl (OH) ₄ ), sodium silicate (Na ₂ SiO ₃ ) and sodium hydroxide (NaOH) or potassium hydroxide (KOH) as starting materials for special purposes. There is a problem that can not remove the whole ion when a lot of ions coexist.

Korean Patent Laid-Open No. 2000-049962 relates to a method for manufacturing fly ash discharged from a dust collecting device as an adsorbent for wastewater treatment when incineration of municipal waste, and the fly ash mixed with fly ash or slaked lime is reduced to 500 to 600 ° C. An adsorbent production method is disclosed that comprises a step of heat treatment for 1 to 2 hours and cooling the heat-treated fly ash to produce a powder adsorbent.

Since the above-described prior art uses the heat-treated fly ash itself as an adsorbent, it produces a powder adsorbent that is difficult to have a uniform particle size and pores. For example, when used in a continuous wastewater treatment system that continuously treats wastewater, it has a constant flow rate and flow rate. Since it does not guarantee the pressure drop problem is difficult to use, there is a problem that the stabilization and adsorption capacity is poor.

The present inventors have diligently studied to solve the problems of the prior art, and as a result, by adding an additive and water to the incineration fly ash, the particles are formed into a predetermined shape and then heat treated to stabilize the harmful substances contained in the fly ash, and molding The present invention completed the present invention by finding that the particles have a certain strength and size, and thus have excellent specific surface area and heavy metal adsorption capacity, and can be economically manufactured as an adsorbent for removing heavy metals even in a continuous facility.

The present invention has been proposed to solve the above problems of the prior art, and an object of the present invention is to add harmful sulfate and water as additives to incineration fly ash, which is rich in raw material and inexpensive, to heat the harmful substances contained in the fly ash. Stabilization and molding to have a certain strength and size is excellent in specific surface area and heavy metal adsorption capacity, and can be applied to continuous wastewater treatment facilities, and to provide an economical method for producing heavy metal removal adsorbent.

1 is a process flow diagram illustrating a method for preparing an adsorbent from an incineration fly ash according to the present invention.

In order to achieve the above object, the present invention comprises the steps of mixing the fly ash collected in the dust collector of the incinerator, sodium sulfate and water in a weight ratio of 4: 0.5 ~ 1.5: 5 ~ 6, and molding the mixture into a granular shape There is provided a method of stabilizing heavy metals and adsorbents for incineration fly ash using an additive, comprising the steps of, heat treating the molded body, and cooling the adsorbent formed by the heat treatment.

In general, the adsorbent should have the following conditions: That is, first, the adsorption force per unit weight should be excellent. Second, it must be acid and alkali resistant without dissolving in water. Third, playback should be possible. Fourth, it must be porous and have a large specific surface area for the particle size (volume). Fifth, it should not generate toxic substances in liquid or gas phase. Sixth, the particle size distribution should be uniform. Seventh, it should be easy to purchase and low price.

The mixture is preferably a mixture of fly ash and additives, sodium sulfate and water in a weight ratio of 4: 0.5 to 1.5: 5 to 6, when the weight ratio of sodium sulfate is less than 0.5 weight ratio of the lower limit, satisfactory performance of the adsorbent, that is, cation exchange capacity ( Cation Exchange Capacity) cannot be obtained sufficiently, and when the upper limit of 1.5 weight ratio is exceeded, a problem occurs that the heavy metal leaching amount is higher than the standard leaching amount.

In addition, the molded body preferably has a circular, polygonal cylinder type or spherical shape in cross section. In this case, the molded article is preferably a cylinder type of 3 ± 0.5 mm in diameter and 2.5 to 7 mm in length. The reason for this is that when the length of the molded article is less than 2.5 mm, the granules are too small and the strength is low. This is because it is difficult to maintain, and if the length exceeds 7 mm, the volatiles and moisture during the heat treatment are not evaporated in a short time, and thus the CEC value is lowered because voids are not formed.

In addition, the molded body is preferably heat-treated at 700 to 900 ° C with air at 1 L / min, because, when the heat treatment temperature is less than 700 ° C or more than 900 ° C heavy metals are not stabilized and the Because form is not maintained.

The present invention relates to a heavy metal stabilization of incineration fly ash using an additive that satisfies the above conditions and to a method for preparing an adsorbent, with reference to the accompanying drawings.

1 is a process flow diagram illustrating a method for preparing an adsorbent from an incineration fly ash according to the present invention.

As shown in the process flow diagram of FIG. 1 according to the present invention, first, a predetermined amount of water and an additive are added to an incineration fly ash to form a predetermined size and shape, and thus an adsorbent is prepared. That is, water and additives are added to the incineration fly ash and mixed well in a mixer, and then molded into, for example, a cylinder having a diameter of 3 mm and a length of 7 mm. The molded body is heat-treated at 700 to 900 ° C. for 1 hour under air conditions at 1 to 2 L / min, and then dried to 60 ° C. or less in a dryer.

In the present invention, the performance of the adsorbent was measured by the cation exchange capacity (CEC), and the cation exchange capacity (Cation Exchange Capacity) is a measure of the degree to which one ion can substitute for another ion to find out the possibility of the adsorbent. It is used as an indirect figure for viewing.

The adsorbent according to the present invention is alkaline, has a large number of micropores, has a large surface area, a high adsorption force, and can be used for various purposes. In addition, the adsorbent of the present invention is manufactured in a granule having a constant size and strength, which is easy to use and has excellent adsorption ability, without guaranteeing a constant flow rate and flow rate without generating a pressure drop that has conventionally occurred when using a powder adsorbent in a continuous processing system. It was possible.

(Example)

If the present invention will be described in detail based on the Examples as follows, the present invention is not limited to the Examples.

<Prior Example 1>

Conventional Example 1 obtained only a powder form sample by heat treatment of the incineration fly ash (ash) discharged from the incinerator, and measured by the value of CEC that can evaluate the adsorption capacity for this sample is shown in Table 1 below.

<Comparative Examples 1-2, Examples 3-4>

Comparative Examples 1 to 2 and Examples 3 to 4 show the effect of the addition of water to maintain strength and adsorption capacity, and change the amount of water in well-dried incineration fly ash to be molded into a cylinder type and then air 1L at 700 ° C. After heat treatment at the condition of / min and dried to 60 ℃ or less is shown in Table 1 by measuring the CEC value.

Reaction condition CEC (meq / 100g) Conventional Example 1 Heat treatment ash 4.6 Comparative Example 1 ash / water (4: 3) 4.6 Comparative Example 2 ash / water (4: 4) 5.9 Example 1 ash / water (4: 5) 8.4 Example 2 ash / water (4: 6) 8.4

As shown in Table 1, the conventional example 1 has a CEC value of about 4.6 meq / 100 g when only the incineration fly ash discharged from the incineration plant is heat-treated.In Comparative Examples 1 and 2, the amount of incineration fly ash is fixed and the amount of water added is increased. 3 to 4 mL, Examples 1 to 2 added 5 to 6 mL of water, and CEC values of Examples 1 to 2 according to the present invention added 5 to 6 mL of water were 8.4 (meq / 100g) showed the best adsorption efficiency.

<Examples 3-5, Comparative Examples 3-5>

In Examples 3 to 5 and Comparative Examples 3 to 5, the amount of fly ash and water was fixed and the amount of additive sodium sulfate was changed to reduce the amount of heavy metals contained in the fly ash and to enhance the adsorption capacity. After heat treatment at / min air condition and dried to 60 ℃ or less, the heavy metal elution amount and CEC value according to the concentration of the additive is measured and shown in Table 2.

Reaction condition CEC (meq / 100g) Pb elution amount (mg / L) Example 3 ash 4g + 0.5g Na ₂ SO ₄ + water 5mL 15.7 1.8 Example 4 ash 4g + 1.25g Na ₂ SO ₄ + water 5mL 25.1 1.9 Example 5 ash 4g + 1.5g Na ₂ SO ₄ + water 5mL 36.6 2.4 Comparative Example 3 ash 4g + 1.75g Na ₂ SO ₄ + water 5mL 54.2 4.2 Comparative Example 4 ash 4g + 2.0g Na ₂ SO ₄ + water 5mL 47.1 6.3 Comparative Example 5 ash 4g + 2.5g Na ₂ SO ₄ + water 5mL 15.6 3.9

As shown in Table 2, Examples 3 to 5 and Comparative Examples 3 to 5 were experiments by varying the amount of sodium sulfate as an additive, and the optimum conditions showing the best adsorption conditions and low heavy metal elution amount were scattered according to Example 5. The highest adsorption efficiency was obtained when 1.5 g Na ₂ SO ₄ was added to 5 mL of water in ₄ g of.

If the additive amount of sodium sulfate, which is the additive, is less than 0.5 weight ratio, satisfactory adsorbent performance, that is, the Cation Exchange Capacity value cannot be sufficiently obtained, and when the upper limit is 1.5 weight ratio, Comparative Examples 3 to 5 As shown in FIG. 2, it can be seen that there is a problem that the heavy metal elution amount is higher than the standard elution amount (domestic elution standard value (3 mg / L)).

<Example 6, Comparative Examples 6-10>

Example 6 and Comparative Examples 6 to 10 are mixed with each other additives in a weight ratio of 4: 0.5: 5 fly ash, additives and water, respectively, as shown in Table 3 in order to identify a suitable additive 1L / at a heat treatment temperature of 700 ℃ After heat treatment at min air condition and dried to 60 ℃ or less, the heavy metal elution amount and CEC value according to the type of additives were measured and shown in Table 3.

additive CEC (meq / 100g) Pb elution amount (mg / L) Example 6 Na ₂ SO ₄ 18.0 1.9 Comparative Example 6 MgCO ₃ 9.5 25.4 Comparative Example 7 PVA 9.8 9.7 Comparative Example 8 NAOH 12.8 27.0 Comparative Example 9 NaC1 12.6 18.0 Comparative Example 10 MgC12 23.6 10.1

As shown in Table 3, unlike other additives, Na ₂ SO ₄ was found to have the lowest elution of heavy metals and increase the adsorption capacity. MgCl ₂ showed the highest CEC value of 24 meq / 100 g, but the heavy metal elution amount was about 10 mg / L, which exceeded the domestic dissolution standard (3 mg / L). When MgCO ₃ , PVA, NaOH, and NaCl were used as additives, they showed similar CEC values but different values for heavy metal leaching amounts. All four additives showed heavy metal elution above the standard elution (3 mg / L), indicating that it was not suitable as an additive for incineration fly ash.

When Na ₂ SO ₄ is used as an additive to reduce the volume by reducing the melting temperature of coal ash or incineration ash, and to lower the dissolution rate or to make sodium-based crystals, the Na component is combined with the high melting point material at low temperature. Because it is good to stabilize the heavy metals in fly ash easily appeared and showed a high CEC value.

In addition, since sodium compounds have excellent binding to chlorine, they can convert chloride-type compounds, which are easily eluted into water, into oxides to prevent elution, and when reacted with water, they react with hydrogen first. It is judged that the occurrence of can be suppressed. In the sodium compound, the sulfur component easily forms a stable compound with other heavy metals at high temperature, thereby preventing the stabilization and volatilization of the heavy metals.

As described above, the present invention stabilizes the harmful substances contained in the fly ash by adding an additive to the incineration fly ash which will be increased in the future, and recycles the stabilized fly ash as an adsorbent having excellent adsorption capacity and economical efficiency. Not only can it be used, it can be used as a viable way to solve the problem of incineration of municipal solid waste.

Therefore, the adsorbent according to the present invention can be effectively used not only for livestock wastewater, dye, steelmaking, film production, alloy plant, wastewater treatment of mines, but also for improving contaminated paper contaminated with heavy metals. In addition, the adsorbent of the present invention can use infinite resources with low added value, adsorb heavy metals in the waste water to the adsorbent, separate the adsorbents and bury them in a fixed place, or extract the heavy metals adsorbed on the adsorbent with a strong inorganic acid solution and reuse it. It is economical.

Claims (3)

Mixing the fly ash collected in the dust collector of the incinerator, sodium sulfate and water in a weight ratio of 4: 0.5 to 1.5: 5 to 6, Shaping the mixed mixture into granules of a predetermined shape; Heat-treating the molded body, Method for producing a heavy metal stabilization and adsorbent of incineration fly ash using an additive comprising the step of cooling the adsorbent formed by the heat treatment. According to claim 1, wherein the molded body is formed of any one of a circular, polygonal cylinder type (cylinder type) and a sphere, the circular cylinder granularity is characterized in that the diameter of 3 ± 0.5mm, 2.5 ~ 7mm in length Method for preparing heavy metals and adsorbents for incineration fly ash using additives. The method of claim 1, wherein the molded body is heat treated at a temperature of 700 ~ 900 ℃ and air conditions of 1L / min using heavy additives stabilization and adsorbent manufacturing method of the incineration fly ash.