JP2013078711A - Method for removing selenium from wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove selenium from wastewater with high efficiency while suppressing an operation cost low.SOLUTION: In a method for removing the selenium from the wastewater, a rare earth compound-containing adsorbent is brought into contact with selenium-containing wastewater at pH of ≥1.0 and <4.5. As the rare earth compound, one or more kinds among oxide and hydroxide of yttrium, lantern, cerium and ytterbium can be chosen. Preferably a porous inorganic material or a porous organic material carrying the rare earth compound is used as the adsorbent.

Description

  The present invention relates to a method for removing selenium from waste water by bringing waste water containing selenium into contact with an adsorbent containing a rare earth compound.

Conventionally, for removing selenium contained in waste water, for example, a method of performing a coagulation precipitation process using ferrous chloride (FeCl ₂ ) as a reducing agent is known.

  Further, Patent Document 1 discloses a method in which an adsorbent containing a rare earth compound and wastewater containing selenium are brought into contact without performing pretreatment such as pH adjustment, and selenium in the wastewater is adsorbed and removed by a simple process. Proposed.

JP 2007-326077 A

  However, in the method of coagulating and precipitating using ferrous chloride as the reducing agent, a large amount of ferrous chloride as the reducing agent is consumed to remove the selenium concentration in the wastewater to a safe level. There was a problem that the operating cost would rise.

  On the other hand, the method for treating selenium-containing water described in Patent Document 1 has the advantage that pretreatment such as pH adjustment is unnecessary and can be treated in a simple process, but there is room for improvement in terms of the selenium removal rate. .

  Then, this invention is made | formed in view of the problem in the said prior art, Comprising: It aims at removing tetravalent and hexavalent selenium from waste_water | drain at a high rate, keeping operating cost low. .

  In order to achieve the above object, the present invention is a method for removing selenium from wastewater, characterized in that an adsorbent containing a rare earth compound is brought into contact with wastewater containing selenium at a pH of 1.0 or more and less than 4.5. To do.

  According to the present invention, it is possible to remove both tetravalent selenium and hexavalent selenium by adsorbing selenium to an adsorbent containing a rare earth compound by adjusting the pH to 1 or more and less than 4.5. Thus, a selenium removal rate of about 40 to 80% can be achieved, and selenium can be removed from the waste water at a high rate while keeping operating costs low. The pH is more preferably 3 or more and less than 4, and a selenium removal rate of 70% or more can be achieved. The selenium removal rate can be further increased by increasing the amount of adsorbent added.

  In the method for removing selenium from the waste water, the rare earth compound may include one or more rare earth compounds selected from oxides of yttrium, lanthanum, cerium, or ytterbium, or hydroxides.

  Further, in the method for removing selenium from the waste water, a material in which the rare earth compound is supported on a porous inorganic material or organic material can be used as the adsorbent, and the surface area used for adsorption of selenium is increased. Selenium can be efficiently removed by adsorption.

  As described above, according to the present invention, tetravalent and hexavalent selenium can be removed from waste water at a high rate while keeping operating costs low.

It is a graph which shows the relationship between the pH of waste_water | drain, and the selenium density | concentration of treated water at the time of throwing cerium hydroxide as an adsorbent into the waste_water | drain containing tetravalent and hexavalent selenium. It is a graph which shows the relationship between the pH of waste_water | drain, and a selenium removal rate at the time of throwing cerium hydroxide into the waste_water | drain containing tetravalent and hexavalent selenium as an adsorption agent.

  The method for removing selenium from wastewater according to the present invention is characterized in that an adsorbent containing a rare earth compound is brought into contact with wastewater containing selenium at a pH of 1.0 or more and less than 4.5. Rare earth compounds, especially yttrium, lanthanum, cerium, ytterbium oxide, or one or more rare earth compounds selected from hydroxides effectively absorb and remove tetravalent and hexavalent selenium. Even when tetravalent selenium and hexavalent selenium coexist in the wastewater, it is possible to remove selenium only by adjusting the pH of the wastewater to 1 or more and less than 4. The rare earth compounds used as the adsorbent are preferably those listed above, but are not limited thereto.

  As the rare earth compound, a powdery compound may be directly put into waste water, but it is preferable to use the rare earth compound supported on a porous inorganic material or organic material. Since the surface area of the adsorbent used for adsorption of selenium can be increased, selenium can be efficiently adsorbed and removed with the addition of a small amount of rare earth compound.

Na ₂ SeO ₃ was dissolved in distilled water to prepare an aqueous solution containing 5.1 mg / l of tetravalent selenium. Further, Na ₂ SeO ₄ was dissolved in distilled water to prepare an aqueous solution containing 5.7 mg / l of hexavalent selenium. An aqueous solution in which equal amounts of these aqueous solutions are mixed is diluted 10-fold with distilled water to contain 0.26 mg / l of tetravalent selenium and 0.29 mg / l of hexavalent selenium. A 6.3 aqueous solution was prepared and used as a test solution.

  900 g of the test solution was collected, and HCl and NaOH aqueous solution were added to adjust to a predetermined pH. A resin carrying 0.34 g of a cerium hydroxide reagent was added thereto and stirred for 30 minutes. When the selenium concentration contained in the treated water was measured, the results shown in FIG. 1 were obtained. In the treated water at pH = 13.5 to 4.5 and the treated water at pH = 2.5 to 1.0, the concentration of selenium contained in the treated water decreased as the pH was lowered. The selenium concentration contained in the treated water at pH = 2.5 to 4.5 draws a downwardly convex curve, and the treated water selenium concentration at pH = 3.0 and pH = 3.9 is 0.134 mg each. / L and 0.085 mg / l. FIG. 2 shows the selenium removal rate calculated from the selenium concentration contained in the treated water shown in FIG. 1, and shows a high removal rate at pH 1.0 to 4.5.

Claims (3)

  A method for removing selenium from wastewater, comprising contacting an adsorbent containing a rare earth compound with wastewater containing selenium at a pH of 1.0 or more and less than 4.5.   2. The wastewater according to claim 1, wherein the rare earth compound contains one or more rare earth compounds selected from oxides of yttrium, lanthanum, cerium, ytterbium, or hydroxides. Selenium removal method.   The method for removing selenium from waste water according to claim 1 or 2, wherein a material in which the rare earth compound is supported on a porous inorganic material or organic material is used as the adsorbent.

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