KR20100013112A - Soil covering materials comprising lime, used gypsum, alumina, and sludge and preprration method of the same - Google Patents

Abstract

PURPOSE: A material for covering landfill including a quicklime, a waste gypsum, and an alumina and a sewage sludge and a manufacturing method is provided to fulfill the heavy metal elution rate to the environmental standard which is lower than Pb 3.0 mg/L, Cu 3.0 mg/L, Cd 0.3 mg/L and to facilitate the work of landfill bulldozer. CONSTITUTION: A material for covering landfill comprises: 100 parts by weight of a sewage sludge having 75~85wt% of water, a quicklime 10~15 parts by weight, a waste gypsum 2~7 parts by weight, and alumina 2~7 parts by weight, and mixed and dried solid substance. The content of water of the material for covering landfill is 40~50wt% and the amount of uniaxial pressure is 2.0 kgf/cm^2~2.5 kgf/cm^2. For the 100 parts by weight of the sewage sludge, the content of the waste gypsum is 3~5 parts by weight and the content of the alumina is 3~5 parts by weight.

Description

SOIL COVERING MATERIALS COMPRISING LIME, USED GYPSUM, ALUMINA, AND SLUDGE AND PREPRRATION METHOD OF THE SAME}

The present invention relates to a cover material having a low water content and a high uniaxial compressive strength and a method for producing the same.

In general, sewage sludge (sludge) refers to a mud state generated by sedimentation of water pollutants generated in the process of treating water (water and sewage). Among them, sewage sludge is used in sewage treatment at sewage treatment plants. Sewage sludge generated. Conventionally, such sewage sludge has been treated by landfill disposal or ocean dumping. However, when the landfill treatment has a water content of 70 to 80%, there is a problem that high concentrations of leachate and odor are generated when the sewage sludge is directly landfilled. This is expected to be difficult, and treatment of sewage sludge from water and sewage is in a very serious situation.

Therefore, in order to utilize such sewage sludge, it was used as some cover material after mixing with Mimihanama sewage sludge and general earth and left to air dry for several days, and partially developed and sewage sludge and incineration ash having a water content of 70 to 80%. (FLY ASH) and simple hardeners (quick lime, cement) were mixed in an appropriate amount and left to dry in the yard for 3 to 5 days to be used as a finished cover material.

However, due to the limitation of the hydration reaction of the simple solidifying agent and the natural drying method after curing, the drying effect of water content of 40 to 50% or less is impossible, and even if the hazard is not discussed, the uniaxial compressive strength is 0.4 kgf / cm ^2. The minimum uniaxial compressive strength of cover material and hardener is 0.4 kgf / cm ² As a result of the final treatment and disposal plan of sewage sludge issued by Seoul Metropolitan Government (cited III-81 page in December 1992), the workability of the cover equipment was not secured.

Therefore, in order to use sewage sludge as a landfill material or cover material, physical and chemical improvement of sewage sludge cake properties is necessary. In recent years, researches have been conducted to improve the properties of sewage sludge cakes in order to use sewage sludge as a cover material.

Korean Unexamined Patent Publication No. 2000-025028 is a special solidifying agent in water and sewage sludge which is mixed with gypsum, quicklime, cement, incineration ash, and Cary alum and heated to 500 ℃ or less for reclamation for landfill and filling for landfill. The technology for recycling to ash has been described.

In addition, Korean Laid-Open Patent Publication No. 1999-025028 intends to use organic waste having high water content with waste wood, and solidifying agent and moisture control agent to ferment into aerobic microorganisms and then dry it to use as a cover material of landfills.

However, Korean Patent Laid-Open Publication No. 2000-025028 uses expensive gypsum, quicklime, cement and incineration ash, and alum alum as a special additive solidifying agent, and has a disadvantage of solidifying at a high temperature of 500 ° C or lower. In addition, the Republic of Korea Patent Publication No. 1999-052626 is because the waste is mixed with waste wood and manufactured as cover material through the solidifying agent, moisture control agent and microbial fermentation step, the manufacturing process is complicated and the manufacturing cost increases. have.

Waste gypsum is a by-product of the manufacturing process of phosphate fertilizers. Phosphate fertilizers used in most farms in Korea are mainly made by processing phosphate ore. The phosphate ore is imported 1.5 million tons and $ 80 million annually, and when the phosphate fertilizer production process is completed, the waste gypsum is accumulated, and the amount of waste gypsum accumulated this year is 4.5 million tons.

Waste gypsum can be used as a building material, chemicals, and cement subsidiary materials. However, waste gypsum made of phosphate fertilizer has so many impurities such as cadmium and lead that it is harmful to the human body.

Accordingly, the present inventors mixed waste gypsum and alumina (Al ₂ O ₃ ) with sewage sludge, quicklime, and auxiliary additives at a predetermined weight ratio, and after drying naturally, the uniaxial compressive strength is more than twice that of conventional cover materials, and the heavy metal dissolution concentration is A method for preparing sewage sludge for cover materials that meets the heavy metal leaching concentration environmental standard of solids, and the invention of the cover material produced thereby have been completed.

Therefore, the inventors of the present invention have completed the present invention while repeatedly researching a cover material which is easy to manufacture while exhibiting a low heavy metal elution amount, low water content and high uniaxial compressive strength.

The present invention is to satisfy the heavy metal dissolution concentration environmental standards of Pb 3.0 mg / L, Cu 3.0 mg / L, Cd 0.3 mg / L or less, and to provide a cover material that is expected to facilitate the operation of landfill bulldozer.

In addition, the present invention is to provide a method for producing a cover material that is easy to manufacture without working at high temperatures.

The present invention includes a dry solidified by mixing 100 parts by weight of sewage sludge with water content of 75 to 85% by weight, 10 to 15 parts by weight of quicklime, 2 to 7 parts by weight of waste gypsum, and 2 to 7 parts by weight of alumina, and the elution concentration of Pb It is to provide a cover material that the elution concentration of 0.01 to 3.0 mg / L, Cu, 0.01 to 3.0 mg / L, the elution concentration of Cd satisfies 0.001 to 0.3 mg / L.

The cover material of the present invention has a water content of 40 to 50% by weight and a uniaxial compressive strength of 2.0 kgf / cm ² to 2.5 kgf / cm ² , far exceeding 0.5 kg / cm ² or more, which is the minimum value required for ordinary cover material. By satisfying the physical properties, it is possible to improve the workability of the landfill, reduce the elution amount of harmful substances, Pb 3.0 mg / L, Cu 3.0 mg / L, Cd 0.3 mg / L or less is satisfied. Specifically, in the cover material of the present invention, the elution concentration of Pb is in the range of 0.01 to 3.0 mg / L, the elution concentration of Cu is 0.01 to 3.0 mg / L, and the elution concentration of Cd is in the range of 0.001 to 0.3 mg / L.

In the case of cover material having a uniaxial compressive strength in the range of 2.0 to 2.5 kgf / cm ² , the particle binding force of the cover material is increased to facilitate the workability of operating facilities in a landfill such as a bulldozer, and the amount of harmful substances released is reduced. (Poon, CS “Critical Review of Evaluation Procedures for Stabilization / Solidification Process” Environmental Aspect of Stabilization and Solidification of Hazardous and Radioactive Wastes, ASTM STP 1033, PL Cote) and TM Gillan, Eds., American Society for Testing and Materials.Philadelphia, 1989, pp114 ~ 124). The higher the uniaxial compressive strength, the lower the elution of harmful substances.

Quicklime is added to solidify sewage sludge. The addition of quicklime causes high heat and exothermic reactions to dry sewage sludge and enhance the strength and permeability coefficient due to the solidification reaction. Quicklime is added in an amount of 10 to 15 parts by weight based on 100 parts by weight of sewage sludge, for proper function control. When the weight ratio of quicklime mixed is less than 10 parts by weight of sewage sludge, the strength of the solidified product is weakened and the water content is increased, and when it is added more than 15 parts by weight, the effect of increasing the amount of quicklime is hardly observed. .

The waste gypsum is added in an amount of 2 to 7 parts by weight based on 100 parts by weight of sewage sludge. If the weight of the mixed waste gypsum is less than 2, the uniaxial compressive strength meets the conditions as a general cover material, but the strength of the solids is weakened and the water content is increased. When mixed with more than 7 parts by weight, the concentration of heavy metals contained in the waste gypsum does not meet the environmental standards of the heavy metal elution concentration of the solids.

Quicklime added in the present invention is characterized in that it is added in more parts by weight than waste gypsum. As described above, quicklime is added to solidify sewage sludge, and waste gypsum is also added to increase the uniaxial compressive strength of the sludge, but in the case of waste gypsum, when a predetermined amount or more is added, heavy metal is eluted. Therefore, in order to satisfy the uniaxial compressive strength and the heavy metal elution concentration environmental standard of the solids, which are satisfied as the cover material, it is preferable to add it in the above ratio.

Alumina is added in an amount of 2 to 7 parts by weight based on 100 parts by weight of sewage sludge, and the added alumina makes the sewage sludge solids more dense, further increasing the uniaxial compressive strength.

In the present invention, in order to have a good uniaxial compressive strength and low water content, the heavy metal elution content to meet the environmental standards, the content of quicklime is higher than the content of waste gypsum and alumina. The waste gypsum can be easily obtained, but the sewage sludge solids can be hardened. However, as the above-described addition of the waste gypsum has a problem in that heavy metals are eluted, the content is less than that of quicklime. Alumina was also added to densify the texture of solids, and the content was less than that of quicklime.

Hereinafter, the cover material according to the specific embodiment of the present invention will be described.

The cover material of the present invention is mixed with 100 parts by weight of sewage sludge having a water content of 75 to 85% by weight, 10 to 15 parts by weight of quicklime, 2 to 7 parts by weight of waste gypsum, 2 to 7 parts by weight of alumina, and elution of Pb. The concentration is 0.01 to 3.0 mg / L, the elution concentration of Cu is 0.01 to 3.0 mg / L, and the elution concentration of Cd satisfies 0.001 to 0.3 mg / L.

Preferably, 100 parts by weight of sewage sludge having a water content of 75 to 85% by weight includes 10 to 15 parts by weight of quicklime, 3 to 5 parts by weight of waste gypsum, and 3 to 5 parts by weight of alumina and dried solids.

The waste gypsum used in the cover material of the present invention can be used without particular limitation, but waste gypsum, which is a by-product of a chemical fertilizer process that is readily available in terms of waste recycling, is used.

The cover material according to the present invention has a water content of 40 to 50% by weight, and the uniaxial compressive strength satisfies 2.0 kgf / cm ² to 2.5 kgf / cm ² .

In addition, the cover material of the present invention is a size suitable for use in landfills 1 ~ 10 mm in diameter, the length of the pallet is 1.5 times the particle size, the size of the pallet should be in the form of a pallet, in addition to handling and transport, bulldozer work in the landfill is easy Do.

In addition, the present invention provides a method for producing a cover material. Hereinafter, the manufacturing method of the cover material according to a specific embodiment of the present invention will be described. Method for producing a cover material of the present invention is a step of mixing 10 to 15 parts by weight of quicklime, 2 to 7 parts by weight of waste gypsum and 2 to 7 parts by weight of alumina and 100% by weight of sewage sludge and the mixture is dried in outdoor natural conditions Curing step.

Preferably, the mixing ratio of the waste gypsum is 3 to 5 parts by weight, and the mixing ratio of the alumina is 3 to 5 parts by weight based on 100 parts by weight of sewage sludge. The mixing ratio of the waste gypsum and alumina can be adjusted within the above range for higher uniaxial compressive strength.

Drying and curing of the mixture are carried out under outdoor natural conditions, and the dry cured solids satisfy a water content of 40-50% and a uniaxial compressive strength of 2.0 kgf / cm ² to 2.5 kgf / cm ² .

In addition, the cover material manufacturing method of the present invention further comprises the step of cutting the dried cured cover material in the form of a pallet having a particle diameter of 1 ~ 10 mm and a length 1.5 times the particle diameter. The particle diameter ranges from 1 to 10 mm and the length should be 1.5 times the particle diameter, which facilitates bulldozer operation in landfills in addition to handling and transport.

The characteristics of quicklime, waste gypsum, and alumina added together with sewage sewage sludge and their role in solidification are as follows.

Quicklime [Calcium Oxide; CaO] is a powder of measurement system such as white, which absorbs moisture and CO ₂ in the air to produce Ca (OH) ₂ and CaCO ₃ , and reacts with water to generate a large amount of heat to produce Ca (OH) ₂ . That is, a phenomenon in which the crystal phase structure is firmly hardened such as CaO + CO ₂ + H ₂ O-> CaCO ₃ + H ₂ O occurs.

CaO + H ₂ O-> Ca (OH) ₂ + 15.2 Kcal When it meets CO ₂ in air and water with exothermic reaction, Ca (OH) ₂ + CO _2- > Ca (HCO) ₃ ) ₂ + CaCO ₃ + H ₂ O is a process of solidification stabilization of alkaline.

Waste gypsum is usually a by-product of the manufacturing process of phosphate fertilizers, which increases the uniaxial compressive strength by densifying the crystal structure of the hydrated product in the manufacture of solids. As the particles of the curing proceeds by the injection of alumina increases the colloidal silica, colloidal alumina dissolution in the water from the clay component to form a Ca ^{2 +} and reaction to a new compound of the lime. In addition, when cement is hydrated, it slowly reacts with free Ca (OH) ₂ to form insoluble calcium aluminate hydrate gel (calcium aluminate hydrate) to further increase the uniaxial compressive strength. Sewage sludge, quicklime, waste gypsum, and alumina of the present invention are mixed to produce sewage sludge solids for cover materials as follows.

(1) hydration reaction

When analyzing the mineral composition of sewage sludge, it is formed of a composite compound of silica such as SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ (3Al ₂ O ₃ · 2SiO ₂ ). Thus, the calcium ions in the lime of the hardeners coalesce with the siliceous in the sewage sludge, and some produce a large amount of pine needle-like material called Ettringite. This lowers the water content of the sewage sludge and constrains the movement of the granules, making the hydration reaction easier.

(2) ion exchange reaction

The calcium hydroxide (Ca (OH) ₂₎ produced by the hydration of calcium (Ca ^{2 +)} and hydroxyl ions 2 (OH) in the water gap in the soil ^- are ionized by ^one ordinary soil particle surface is electrically negative (-) And the cations (Na ⁺ , H ⁺ , K ⁺ ) are adsorbed on the surface, and the newly ionized (Ca ^{2 +} ), (OH ^-1 ) exchanges with the cations, resulting in weak charge on the earth particle. It is isolated by the action of attraction between each other. As a result, the plasticity of the soil is reduced, the physical properties are also improved, and harmful substances are insoluble by ion exchange.

(3) pozzolanic reaction

In the gap water, which has high alkalinity due to the dissolution of lime, silica or alumina components in clay minerals are ionized to cause a chemical reaction between calcium in the gap water and gels such as silicate lime hydrate and aluminate lime hydrate (GEL). Generates hydrate of phase. The resulting compound becomes a binder and sewage sludge is solidified. By the initial POSSOLANIC REACTION, the hydrate is further supplied with calcium ions to produce crystalline minerals in the long term, which increases in strength in the long term as the solidification progresses.

(4) carbonation reaction

In sewage sludge, carbon dioxide generated by decomposition of organic matter is often dissolved in the gap water. A carbonation reaction occurs between carbonate and lime to form calcium carbonate. Calcium carbonate not only functions as intergranular solidification or gap filler, but also combines with aluminate lime hydrate to form more stable crystalline minerals.

As described above, the cover material according to the present invention has a water content of 40 to 50% and a uniaxial compressive strength of 2.0 kgf / cm ² to 2.5 kgf / cm ² , and a dissolution concentration of Pb of 0.01 to 3.0 mg / L and Cu. Elution concentrations of 0.01 to 3.0 mg / L and Cd dissolution concentrations satisfying 0.001 to 0.3 mg / L, and Pb 3.0 mg / L, Cu 3.0 mg / L and Cd 0.3 mg / L or less Satisfies. In addition, by using waste gypsum, which is a by-product of sewage sludge and chemical fertilizer process, which is disposed of by landfill and ocean dumping, there is an advantage that it is possible to obtain a replacement effect of waste resources.

Preferred embodiments of the present invention will be described in detail. However, the invention is not limited to the embodiments described herein and may be embodied in other forms.

<Example>

Sewage sludge was collected from a certain amount of sewage sludge (water content 75 ~ 85% by weight) at Seongnam Sewage Treatment Plant and immediately refrigerated to prevent moisture drying. Quicklime purchased CaO powder and waste gypsum was a by-product of the phosphate fertilizer manufacturing process. With respect to 100 parts by weight of sewage sludge 100 parts by weight of quicklime, 4 parts by weight of waste gypsum, 4 parts by weight of alumina, and mixed in a stirring tank, the mixture was naturally dried by outdoor drying for 5 days.

The physical properties of the solids obtained by drying were measured in the following manner.

Weight ratio analysis before solidification

The weight ratio to the solidification before shown in Figure 1 was expressed by the following formula.

% By weight compared to solidification = (weight of solids / weight of mixture before solidification) ⅹ100

Contrast before solidification Volume ratio  analysis

The volume ratio to the solidification before shown in Figure 2 was expressed by the following equation.

Volume ratio before solidification (%) = (volume of solids / volume of mixture before solidification) ⅹ100

The volume is calculated by filling the cylindrical frame with the material to be measured and measuring the area and height assuming a cylinder.

Solid  Moisture content measurement

The water content of the solid shown in FIG. 3 is represented by the following formula.

Solid matter moisture content (%) = [solid weight before drying 화물 solid weight after drying (4 hours at 110 ° C.)] / Weight weight before dryingⅹ100

Solid Uniaxial compressive strength  exam

The uniaxial compressive strength test is a method of determining the shear strength by forming a cohesive sample into a conical specimen (φ5cm × 10cm) and applying a congratulation in the absence of lateral pressure to determine the shear strength of KS F 2314. The stress gauge and the strain amount were measured using MARITO) and calculated by Equation 1. The results are shown in FIG.

[Equation 1]

Where P is the load (kgf) applied to the specimen when the compressive strain is ΔL, D _avg is the average diameter of the solid (cm), L is the length of the solid (cm), and ΔL is the maximum load of the solidifying agent. Displacement (cm), provided 1.1 cm unless maximum load is given.

Dissolution test of heavy metal

Heavy metal dissolution test according to the content of waste gypsum was carried out in the following procedure. A dissolution test was performed on the sample prepared according to KS F 2301 by the waste process test method, and the results are shown in FIG. 5. (For reference, the 1997 heavy metals concentration standard domestic waste management Cu: 3.0mg / L, Cd: 0.3 mg / L, Cr 6 +: 1.5 mg / L, Pb: a 3.0 mg / L.)

Comparative Example 1: Manufacture of Blank

The sewage sludge having a water content of 84.2% obtained from the Seongnam sewage treatment plant was mixed with nothing, and dried by solidification by outdoor natural drying for 5 days. In the same manner as in the above embodiment, the weight ratio analysis before solidification, the volume ratio analysis before solidification, the solid water content measurement, the uniaxial compressive strength measurement of solids, and the dissolution test of heavy metals were shown in FIGS. 1 to 5, respectively. .

Comparative Example 2

The quicklime was mixed in a proportion of 12 parts by weight based on 100 parts of the same sewage sludge used in Comparative Example 1, and then dried by outdoor natural drying for 5 days under the same conditions as in Comparative Example 1. The quicklime used the same one used in the examples. In the same manner as in Example 1 and Comparative Example 1, the weight ratio analysis before the solidification, the volume ratio analysis before the solidification, the measurement of the moisture content of the solids, the uniaxial compressive strength of the solids and the dissolution test of the heavy metals were respectively performed. 5 is shown.

Comparative Example 3

With respect to 100 parts of the same sewage sludge 100 parts used in Comparative Example 1 mixed quicklime 12 parts by weight, waste gypsum in the ratio of 4 parts, and then dried by outdoor natural drying for 5 days under the same conditions as Comparative Examples 1 and 2 Got it. The quicklime was used the same as used in the Example, the waste gypsum was obtained from Namhae Chemical. In the same manner as in Examples and Comparative Examples 1 and 2, the weight ratio analysis before solidification, the volume ratio analysis before solidification, the measurement of solid water content, the uniaxial compressive strength measurement of solids, and the dissolution test of heavy metals were respectively shown. 1 to 5 are shown.

<Comparative Example 4>

With respect to 100 parts of the same sewage sludge 100 parts used in Comparative Example 1 by mixing quicklime 12 parts by weight, waste gypsum in a ratio of 8 parts by weight, and then outdoor natural drying for 5 days under the same conditions as Comparative Examples 1 to 3 and solidified Got it. The quicklime used the same as used in the Example. In the same manner as in Examples and Comparative Examples 1 to 3, the weight ratio analysis before the solidification, the volume ratio analysis before the solidification, the measurement of the moisture content of the solids, the uniaxial compressive strength of the solids, and the dissolution test of the heavy metals were respectively shown. 1 to 5 are shown.

From the above results, quicklime, waste gypsum, and alumina, which are solidifying sewage sludge, have excellent solidification effect, and the mixture shows soil characteristics and landfill characteristics comparable to that of general cover materials, and particularly shows excellent uniaxial compressive strength and low water content. By using the waste gypsum as a by-product of the chemical fertilizer manufacturing process, there is an advantage that it is possible to obtain a replacement effect of waste resources.

1 is a graph showing the weight ratio (%) compared to the solidification of the solidified according to the waste gypsum input.

Figure 2 is a graph showing the volume ratio (%) compared to the solidification of the solidified according to the waste gypsum input.

Figure 3 is a graph showing the water content (%) of the solidified according to the waste gypsum input.

Figure 4 is a graph showing the uniaxial compressive strength (kgf / cm ² ) of the solid according to the waste gypsum input.

Figure 5 is a graph showing the heavy metal elution concentration (mg / L) of the solidified according to the waste gypsum input.

Claims (7)

100 parts by weight of sewage sludge having a water content of 75 to 85% by weight, 10 to 15 parts by weight of quicklime, 2 to 7 parts by weight of waste gypsum, and 2 to 7 parts by weight of alumina, and dried solidified material, wherein the moisture content of the cover material is 40 to 50% by weight, uniaxial compressive strength of 2.0 kgf / cm ² to 2.5 kgf / cm ² covering material. The cover material according to claim 1, wherein the waste gypsum content is 3 to 5 parts by weight and the alumina content is 3 to 5 parts by weight based on 100 parts by weight of the sewage sludge. The dissolution concentration of Pb of the cover material is obtained by preparing the cover material according to KS F 2301 and performing the dissolution test according to the waste process test method. A cover material having a dissolution concentration of 0.01 to 3.0 mg / L and a dissolution concentration of Cd of 0.001 to 0.3 mg / L. The cover material according to claim 1 or 2, wherein the solidified material has a pallet shape having a particle diameter of 1 to 10 mm and a length of 1.5 times the particle size. Mixing at a ratio of 10 to 15 parts by weight of quicklime, 2 to 7 parts by weight of waste gypsum and 2 to 7 parts by weight of alumina, relative to 100 parts by weight of sewage sludge having a water content of 75 to 85% by weight; And Covering the manufacturing method of the cover material comprising the step of curing the mixture. The method of claim 5, wherein the content of the waste gypsum is 3 to 5 parts by weight, and the content of the alumina is 3 to 5 parts by weight based on 100 parts by weight of the sewage sludge. The method of claim 5, further comprising the step of cutting the dried hardened cover material in the form of a pallet having a particle diameter of 1 to 10 mm and a length 1.5 times the particle size.

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