JP2006142228A - Solid waste disposal method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid waste disposal method for easily extracting and separating metals in the solid waste, easily, safely and efficiently treating the solid waste after extracting the metals, and easily recovering and reusing the extracted and separated metals and easily reusing a metal extracting agent. <P>SOLUTION: The solid waste disposal method is provided in which the metal extracting agent having at least one per one molecule, of at least one of an alkaline metal salt of phosphoric acid bonded to a carbon atom and an alkaline salt of carboxylic acid is brought into contact with the solid waste in the presence of a solvent, to extract and separate the metals in the solid waste by the metal extracting agent into the solvent. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention makes it possible to safely separate solid waste by extracting and separating harmful metals present in solid waste such as incineration ash, dust, slag, sludge, soil, and shredder dust from solid waste. The present invention relates to a method for treating solid waste that can be treated and reused, and can be easily recovered and reused for extracted and separated metal, and further reuse of a metal extractant.

  Solid waste such as dust generated at garbage incinerators, slag discharged from mines, activated sludge used in wastewater treatment, contaminated soil, etc. contains various metals, such as mercury and cadmium. In many cases, heavy metals harmful to the human body such as lead, zinc, copper and chromium are contained in large quantities. If metal is eluted from these solid wastes, there is a risk of contamination of groundwater, rivers, seawater, and the like.

  For this reason, in the past, solid waste was solidified with cement, and then landfilled and treated. However, when it comes into contact with seawater or rainwater, metals may elute into seawater or soil through the cement wall. Therefore, this method is not always a safe treatment method. In order to solve such problems, in recent years, a method of immobilizing metal in solid waste using a metal scavenger has been adopted.

  The method of processing solid waste by immobilizing metal in solid waste with a metal scavenger is an excellent method for treating solid waste containing metal. When a strongly acidic substance is contained, or when solid waste after treatment with a metal scavenger is exposed to acid rain, etc., the metal immobilization power of the metal scavenger used for the treatment is insufficient. Then, the metal may be eluted from the solid waste. Also, in the method of fixing solid metal with a metal scavenger and treating the solid waste, the metal is discarded together with the solid waste, but useful metal is not included in the solid waste. In many cases, it is contained in a large amount, and the method of fixing and discarding the metal in the solid waste with the metal scavenger wastes useful metal resources. Therefore, when processing a solid waste containing a large amount of useful metals, it is preferable from the viewpoint of effective utilization of limited resources to recover and reuse the metal contained therein. As a method for extracting and separating a metal in a solid, a method is known in which a mineral acid is added and a metal in the solid is extracted and separated into a mineral acid (Non-patent Document 1).

Atomic Library: Atomic Encyclopedia “Atomica”: Title List: Nuclear Fuel Recycling: Crude Uranium, [online], [November 19, 2004 Search], Internet <URL: http: // mext-atm. jst. go. jp / atomica / 040040101_1. html>

  However, when the metal in the solid waste is extracted and separated by the mineral acid, a large amount of mineral acid remains in the solid waste. For this reason, it is necessary to neutralize the residual mineral acid when final disposal or reuse of the solid waste, but in order to neutralize the mineral acid remaining in the solid waste, a large amount of There is a problem that alkali is required and the processing cost is high. Furthermore, there is a possibility that the salt generated by neutralization remains in the solid waste, and this salt may be dissolved from the solid waste and contaminate the groundwater. The method of extracting and recovering the metal inside has many problems.

The present invention has been made in view of the above points, and by using a specific compound, the metal in the solid waste can be easily extracted and separated, and the solid waste after the metal extraction can be easily treated. An object of the present invention is to provide a solid waste treatment method capable of processing solid waste safely and efficiently, and easily recovering and reusing extracted and separated metals and reusing metal extractants. And

  That is, the present invention is to bring a metal extractant having at least one of a phosphate group salt and a carboxylic acid group salt bonded to a carbon atom into contact with a solid waste in the presence of a solvent. The gist of the present invention is a method for treating solid waste, characterized in that a metal in solid waste is extracted and separated into a solvent by a metal extractant.

  The method of the present invention employs a method in which a specific metal extractant is added to solid waste and the metal in the solid waste is extracted and separated by the metal extractant. Contains almost no harmful metals, so even if the solid waste treated by the method of the present invention is exposed to acid rain etc., there is no risk of toxic metals leaching, and safe disposal of solid waste Things can be finally disposed of or reused. In addition, the metal extracted and separated from the solid waste by the metal extractant can be easily recovered, and the useful metal contained in the solid waste can be effectively used, and the metal extraction can be performed. The agent can be reused and is economical. Further, unlike the method of extracting and separating metals by adding acid to solid waste, a large amount of acid does not remain in the solid waste. When disposing or reusing, there is no need for labor and costs such as neutralizing residual acid with alkali, and salt generated by neutralization elutes from solid waste and causes recontamination. In addition, there are various advantages such as being able to safely treat solid waste.

  The compound used as a metal extractant in the present invention is a compound having a phosphate group salt or a carboxylic acid group salt bonded to a carbon atom. Examples of the compound having a carboxylic acid group salt include fatty acid salts, alkylpolycarboxylates, and maleic acid- (alkyl) acrylates. As a fatty acid salt, the salt of a C1-C22 fatty acid is preferable. Alkyl polycarboxylates can be obtained, for example, by polymerization or copolymerization of alkyl (meth) acrylates, and maleic acid- (alkyl) acrylates can be prepared, for example, with maleate and alkyl (meth) acrylates. Can be obtained by copolymerization.

  On the other hand, examples of the compound having a phosphate group salt bonded to a carbon atom include alkyl phosphates. For example, a compound having an α-olefin or a double bond and a hypophosphite are present in the presence of a peroxide. It can be obtained by reacting below. As said alpha olefin and a compound which has a double bond, a C2-C30 thing is preferable. The metal extractant used in the present invention is either a compound having only a salt of a carboxylic acid group bonded to a carbon atom or a compound having only a salt of a phosphate group bonded to a carbon atom. It can be used in combination.

  In the present invention, the salt of the carboxylic acid group and the salt of the phosphoric acid group include lithium salt, sodium salt, potassium, ammonium salt and the like, and sodium salt and potassium salt are preferable. In the case of a compound having two or more carboxylic acid groups or two or more phosphoric acid groups in the molecule, 10% or more, more preferably 15% or more of the total active hydrogen derived from the carboxylic acid group or phosphoric acid group is a salt. It only has to be.

  In the method of the present invention, the metal in the solid waste is extracted and removed by the metal scavenger by bringing the metal extractant into contact with the solid waste in the presence of a solvent. As the solvent, any of an aqueous solvent and a hydrophobic solvent can be used, and it is selected according to the properties of the metal complex to be used and the metal complex formed by the reaction between the metal extractant and the metal.

  That is, for example, when the metal complex that forms the metal extractant is also hydrophilic, an aqueous solvent is used as the solvent, the aqueous solvent containing the metal extractant is brought into contact with the solid waste, and the metal extractant and the metal react with each other. The hydrophilic metal complex thus formed can be extracted and separated in an aqueous solvent. When both the metal extractant and the metal complex to be formed are hydrophobic, a hydrophobic solvent is used as the solvent, and the hydrophobic solvent containing the metal extractant is brought into contact with the solid waste to form the hydrophobic The metal complex can be extracted and separated in a hydrophobic solvent. Further, when the metal extractant is hydrophilic and the formed metal complex is hydrophobic, the metal extractant is added to the aqueous solvent, and the hydrophobic solvent is added together with the aqueous solvent containing the metal extractant, An aqueous solvent and a hydrophobic solvent containing a metal extractant are brought into contact with a solid waste, and the formed hydrophobic metal complex can be extracted and separated in the hydrophobic solvent.

  Examples of the aqueous solvent include water, alcohol, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrohydrofuran (THF), hydrophilic organic solvents such as acetone, and mixtures thereof. Uses water. Examples of the hydrophobic solvent include benzene, toluene, xylene, n-hexane, cyclohexane, heptane, diethyl ether, petroleum ether, and the like.

  As a method of bringing solid waste and metal extractant into contact with each other in the presence of a solvent, a method in which a metal extractant and a solvent are added to solid waste and stirred, or a metal extractant is added to solid waste from above. A method of adding a solution obtained by dissolving the lysate and recovering from the lower part can be mentioned.

  The solid waste treated by the method of the present invention can be safely disposed of because the metal contained in the solid waste is extracted and separated by the metal extractant, and can be safely used as a concrete aggregate. It can be reused. In addition, when the metal complex is extracted into an aqueous solvent, the metal extracted by the metal extractant is adjusted by adjusting the pH of the aqueous solvent, and when the metal complex is extracted into a hydrophobic solvent, it is hydrophobic. By contacting the acidic solvent with the acid aqueous solution, the metal is liberated from the metal extractant, and the metal and the metal extractant can be recovered.

  More specifically, the metal complex formed as well as the metal extractant is hydrophilic, and when the metal complex is extracted and separated in an aqueous solvent, the pH of the aqueous solvent is adjusted to near the isoelectric point of the metal extractant. , The metal is released as ions from the metal complex and the metal extractant is precipitated. Next, by separating the precipitated extractant and reducing metal ions in the solution, the metal and the metal extractant can be recovered, respectively. In addition, both the metal complex that forms the metal extractant is hydrophobic, and when the metal complex is extracted and separated in a hydrophobic solvent, the acid complex can be obtained by contacting the hydrophobic solvent containing the metal complex with an aqueous acid solution. Metal ions are eluted from the metal complex in the aqueous solution, and the metal extractant remains in the hydrophobic solvent. Thereafter, the metal extractant and the metal can be respectively recovered by concentrating the hydrophobic solvent or neutralizing and reducing the aqueous acid solution. Furthermore, when the metal extractant is hydrophilic and the formed metal complex is hydrophobic, and the metal complex is extracted and separated in a hydrophobic solvent, the hydrophobic solvent containing the metal complex can be used as a metal extractant, etc. By contacting with an acid aqueous solution having a pH near the electric point, metal ions are eluted in the acid aqueous solution and the metal extractant is precipitated in the acid aqueous solution phase. The precipitated metal extractant is then separated and the metal can be recovered by neutralizing and reducing the acidic solution. The solvent remaining in the solid waste is recovered by heating or decompression.

  As described above, the solid waste treated by the method of the present invention can be safely finalized or reused as concrete aggregate, brick, tile raw material, road pavement raw material, etc. The metal extractant can be easily recovered, and the recovered metal and the metal extractant can be effectively reused.

  Hereinafter, the present invention will be described in more detail with reference to examples. The metal extractant used in Examples and Comparative Examples is as follows.

(1) Metal extractant 1: Potassium oleate (2) Metal extractant 2: 30% sodium salt of copolymer of acrylic acid and maleic acid (3) Metal extractant 3: 60% potassium salt of lauryl phosphate ( 4) Metal extractant 4: 20% sodium salt of stearyl phosphate (5) Metal extractant 5: 1: 3 (weight ratio) mixture of metal extractant 1 and metal extractant 3 (6) Metal extractant 6: Metal 1: 1 (weight ratio) mixture of extractant 1 and metal extractant 4

Examples 1-6
After adding 200 g of a 1% by weight aqueous solution of the metal extractant shown in Table 1 to 100 g of mineral iron containing 450 mg / kg of nickel, 355 mg / kg of lead, 32 mg / kg of cadmium and 18 mg / kg of chromium, and stirring for 5 hours, The slag was allowed to settle and precipitate. The separated slag was washed with 100 ml of ion-exchanged water, then dried and the content of the metal remaining in the slag was measured by X-ray fluorescence analysis (Shimadzu Corporation X-ray fluorescence analyzer model: XRF-1800). Table 1 shows. As shown in Table 1, after contact with the metal extractant, the separated slag showed almost no harmful metal residue, and it could be discarded as it was or reused as a concrete aggregate or the like. Moreover, hydrochloric acid was added to the solution after separating and removing the slag and the pH was adjusted to 1 and allowed to stand for 30 minutes, followed by filtration to recover the metal extractant. The recovered metal extractant was neutralized with a predetermined amount of alkali, and the metal extraction test was repeated. As a result, the recovery rate was maintained at 90% or more.

(Table 1)

Comparative Example 1
After adding 8.6 g of hydrochloric acid to 100 g of the same iron slag as in Examples 1 to 6, the mixture was stirred for 5 hours, and then allowed to stand to precipitate and separate the slag. The separated slag was washed with 100 ml of ion-exchanged water, dried, and the content of the metal remaining in the slag was measured by fluorescent X-ray analysis. No harmful metal remained in the slag after treatment with acid, but a large amount of acid remains in the slag, so it is difficult to dispose of it without neutralization, and it remains in 100 g of slag. 2 g of sodium hydroxide was required to neutralize the acid.

Implementation 7-12
After adding 1 g of 2 wt% aqueous solution of metal extractant shown in Table 2 to 100 g of fly ash containing 1240 mg / kg of lead, 38 mg / kg of cadmium, 8 mg / kg of mercury, and 380 g / kg of calcium, and stirring for 1 hour The fly ash was allowed to settle and separated. The separated fly ash was washed with 100 ml of ion-exchanged water, dried, and the content of the metal remaining in the slag was measured by fluorescent X-ray analysis. As shown in Table 2, after contact with the metal extractant, the separated fly ash showed almost no harmful metal residue and could be discarded or reused as it was. Moreover, after diluting sulfuric acid was added to the solution after separating and removing the slag and the pH was adjusted to 1.5 and allowed to stand for 10 minutes, filtration was performed to recover the metal extractant. The recovered metal extractant was neutralized with a predetermined amount of alkali, and the metal extraction test was repeated. As a result, the recovery rate was maintained at 90% or more.

(Table 2)

Comparative Example 2
After adding 45 g of hydrochloric acid to 100 g of fly ash similar to Examples 7 to 12, the mixture was stirred for 1 hour, and then allowed to stand to precipitate and separate fly ash. Table 2 shows the results obtained by washing the separated fly ash with 100 ml of ion-exchanged water and then measuring the content of the metal remaining in the slag by fluorescent X-ray analysis. Although no harmful metal remained in the fly ash after treatment with acid, 3.8 g of sodium hydroxide was required to neutralize the acid remaining in 100 g of fly ash.

Claims (1)

A metal extractant having at least one of an alkali metal salt of a phosphate group bonded to a carbon atom and an alkali metal salt of a carboxylic acid group in one molecule is brought into contact with a solid waste in the presence of a solvent. A method for treating solid waste, characterized in that a metal in solid waste is extracted and separated into a solvent by a metal extractant.