JP2008155105A - Removal method of arsenic from arsenic-containing aqueous solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for simply, efficiently and inexpensively removing arsenic from an arsenic-including aqueous solution of every kind such as industrial wastewater, an aqueous solution of nickel sulfate being an intermediate raw material of a nickel chemical forming compound becoming an electronic material, etc. <P>SOLUTION: A metal iron powder is added to the arsenic-including aqueous solution to be mixed with it under stirring or the arsenic-including aqueous solution is passed through a column or the like filled with the metal iron powder to react arsenic with the metal iron powder on its surface. Thereafter, the metal iron powder having arsenic adsorbed thereon as an iron compound is recovered by solid-liquid separation. The particle size of the metal iron powder is adjusted to 1 mm or below, preferably 10 μm-1 mm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for easily removing arsenic from wastewater containing arsenic or an aqueous metal salt solution to a low concentration.

  In recent years, arsenic (As) is toxic to the human body, and even a small amount causes chronic poisoning symptoms in the long term. Therefore, it is required to reduce the concentration of As in drinking water or waste water. . Also, industrially, it is desired to remove As from nickel sulfate, which is an intermediate raw material, in order to prevent As from being mixed not only in wastewater but also in nickel chemical products as various electronic materials. .

  Removal of As from aqueous solutions containing various chemical forms of As has been studied in many industrial fields, for example, a coagulation precipitation method, an adsorption method, a sulfurization method and the like have been proposed. For example, as described in JP-A-2003-19404, the coagulation sedimentation method is a method in which an aggregation floc is formed by adding an aggregating agent such as an aluminum salt or an iron salt, and As is precipitated together with the aggregation floc. It is. The coagulation sedimentation method is widely adopted because it can remove As simultaneously with the turbidity in the raw water, but in the case of raw water containing many metal elements other than As, a large amount of precipitate is generated by aggregation. There is a problem in that post-processing of the aggregated floc requires a lot of labor and cost.

  The adsorption method is a method of selectively removing As using activated clay or a chelating material as described in, for example, JP-A-2005-000747. However, the cost of the adsorbent itself, the cost of the drug used as the eluent, and the processing cost of the As eluent are high, and this is not a particularly excellent method in terms of cost.

  Further, as described in, for example, JP-A-2005-224686, the sulfurization method is performed by adding a water-soluble sulfide or hydrogen sulfide gas to an As-containing aqueous solution to insolubilize As as arsenic sulfide, and then perform solid-liquid separation. It is a method to do. However, in the case of a dilute As-containing solution with an As concentration of 10 mg / l or less, arsenic sulfide crystal formation is extremely slow, and it takes a relatively long time to remove As to a certain concentration or less. There are difficulties. In addition, in the case of raw water containing a metal element that easily becomes sulfide other than As, there is also a problem that a large amount of sulfide precipitate is generated.

Japanese Patent Laid-Open No. 2003-19404 JP 2005-000747 A JP 2005-224686A

  In view of the above-described conventional problems, an object of the present invention is to provide a method for removing arsenic from an aqueous solution containing arsenic efficiently and at low cost.

  In order to achieve the above object, the present invention provides a method for removing arsenic from an arsenic-containing aqueous solution by bringing a metallic iron powder having a particle size of 1 mm or less into contact with the aqueous solution containing arsenic, and After the reaction, the metal iron powder in which arsenic is adsorbed as an iron compound is recovered by solid-liquid separation.

  According to the present invention, various types of arsenic such as industrial waste water and nickel sulfate aqueous solution that is an intermediate raw material for nickel chemical products to be used as electronic materials can be obtained by a simple method of contacting and reacting metallic iron powder with an aqueous solution containing arsenic. Arsenic in the aqueous solution can be removed efficiently and at low cost.

  In the method of the present invention, in order to remove arsenic (As) contained in the aqueous solution, metallic iron powder is brought into contact with the arsenic-containing aqueous solution. As a method of contacting the arsenic-containing aqueous solution with the metallic iron powder, there are a method of adding the metallic iron powder to the arsenic-containing aqueous solution and stirring and mixing, and a method of passing the arsenic-containing aqueous solution through a column filled with the metallic iron powder. .

Arsenic in the aqueous solution is considered to have been removed from the aqueous solution by causing a reduction / adsorption reaction on the surface of the metallic iron powder, for example, as shown in the chemical formula below. Moreover, As produced | generated by the following chemical formula forms iron compounds, such as a FeAs alloy, and it is estimated that it adsorb | sucks to the surface of metal iron powder.
[Chemical formula]
2HAsO ₂ + 3Fe ⁰ + H ₂ SO ₄
→ 2As ⁰ + 3FeSO ₄ + 4H ₂ O

  After the reduction / adsorption reaction, solid-liquid separation is performed by means such as suction filtration. As described above, since arsenic is adsorbed on the surface of the metal iron powder as an iron compound such as an FeAs alloy, the arsenic can be removed from the aqueous solution by collecting the metal iron powder by solid-liquid separation.

  Since the reduction / adsorption reaction is a solid-liquid reaction, it is advantageous that the contact frequency between the metal iron powder and the arsenic-containing aqueous solution is higher, that is, the particle diameter of the metal iron powder is smaller. Therefore, in the present invention, it is possible to efficiently remove arsenic contained in the aqueous liquid by using metallic iron powder having a particle size of 1 mm or less. However, if the particle size of the metal iron powder is too small, there is a possibility of clogging during solid-liquid separation or column water flow, so that the particle size of the metal iron powder should be adjusted to about 10 μm to 1 mm. preferable.

  In the above reduction / adsorption reaction, the reaction temperature and reaction time are not particularly limited, and it is possible to remove arsenic even at room temperature, without heating, or in a relatively short time within 60 minutes. . In addition, the pH of the target As-containing aqueous solution is not particularly limited, and industrially, a neutral drainage of pH 7 to 8 or a weakly acidic nickel sulfate aqueous solution of about pH 2 to 7 is generally used. However, since the metallic iron powder dissolves when the pH of the aqueous solution is lower than 2, the lower limit of the pH is preferably about pH 2.

[Example 1]
To 100 ml of nickel sulfate solution with an As concentration of 2.6 mg / l (Ni concentration of 90 g / l, initial pH of 5.6), 10 g of metallic iron powder was added, and the pH was reached at 20 ° C. using a synthetic resin peller. Stirring was performed for 60 minutes. After the reaction, the final solution (pH 6.2) was subjected to solid-liquid separation by suction filtration using a 5C filter cloth. The As concentration of the obtained filtrate was 0.1 mg / l or less.

  The metal iron powder used had chemical components of total Fe: 96.7%, metal Fe: 92.5%, and FeO: 5.4%. The particle size distribution is +425 μm: 0.0%, ˜300 μm: 0.7%, ˜250 μm: 5.2%, ˜150 μm: 30.5%, ˜106 μm: 22.3%, ˜75 μm: 18. 5%, −75 μm: 22.8.

[Example 2]
To 100 ml of nickel sulfate solution with an As concentration of 2.6 mg / l (Ni concentration of 90 g / l, initial pH of 5.6), 10 g of the above metal iron powder is added, and at 40 ° C. according to the pH, using a synthetic resin peller. For 60 minutes. After the reaction, the final liquid (pH 5.7) was subjected to solid-liquid separation by suction filtration using a 5C filter cloth. The As concentration of the obtained filtrate was 0.1 mg / l or less.

[Example 3]
While adding 10 g of the above metal iron powder to 100 ml of nickel sulfate solution with an As concentration of 2.6 mg / l (Ni concentration of 90 g / l, initial pH of 5.6), adjusting the pH to 2.0 with sulfuric acid at 40 ° C. The mixture was stirred for 60 minutes using a synthetic resin peller. After the reaction, the final liquid was subjected to solid-liquid separation by suction filtration using a 5C filter cloth. The As concentration of the obtained filtrate was 0.1 mg / l or less.

[Comparative Example 1]
To 100 ml of nickel sulfate solution with an As concentration of 2.6 mg / l (Ni concentration of 90 g / l, initial pH of 5.6), 10 g of metal copper powder (reagent grade 1) is added instead of the above metal iron powder, and the pH is reached. The mixture was stirred at 20 ° C. for 60 minutes using a synthetic resin peller. After the reaction, the final liquid was subjected to solid-liquid separation by suction filtration using a 5C filter cloth. The As concentration of the obtained filtrate was 1.7 mg / l.

[Comparative Example 2]
To 100 ml of nickel sulfate solution with an As concentration of 2.6 mg / l (Ni concentration of 90 g / l, initial pH of 5.6), 2 g of activated clay powder was added, and at 20 ° C according to the pH, using a synthetic resin peller. Stirring was performed for 60 minutes. Thereafter, the final liquid was subjected to solid-liquid separation by suction filtration using a 5C filter cloth. The As concentration of the obtained filtrate was 0.8 mg / l.

[Comparative Example 3]
To 100 ml of nickel sulfate solution with an As concentration of 2.6 mg / l (Ni concentration of 90 g / l, initial pH of 5.6), 2 ml of sodium sulfide solution was added, and a synthetic resin peller was placed at 40 ° C. at pH 2.5. And stirred for 60 minutes. Thereafter, the final liquid was subjected to solid-liquid separation by suction filtration using a 5C filter cloth. The As concentration of the obtained filtrate was 0.3 mg / l.

Claims (2)

  A method for removing arsenic from an aqueous solution containing arsenic, wherein a metal iron powder having a particle size of 1 mm or less is brought into contact with the aqueous solution containing arsenic, and arsenic is reacted on the surface of the metal iron powder, followed by solid-liquid separation. A method for removing arsenic from an arsenic-containing aqueous solution, characterized in that metallic iron powder in which arsenic is adsorbed as an iron compound is recovered.   The method for removing arsenic from an arsenic-containing aqueous solution according to claim 1, wherein the aqueous solution containing arsenic is an aqueous nickel sulfate solution.