JP2013150963A - Method for removing selenium from chlorine bypass dust flushing wastewater - Google Patents

Abstract

[PROBLEMS] To remove selenium at a high rate from waste water generated when chlorine bypass dust is washed with water while keeping operating costs low.
A method for removing selenium by adjusting waste water generated when chlorine bypass dust is washed with water to a pH of 3.0 or more and less than 7.0 and contacting with an adsorbent containing a rare earth compound. The rare earth compound can include one or a mixture of two or more rare earth compounds selected from yttrium, lanthanum, cerium, ytterbium oxide, or hydroxide. It is preferable to use a material in which a rare earth compound is supported on a porous inorganic material or organic material as an adsorbent. Drainage generated when the chlorine bypass dust was washed with water, drainage obtained by sequentially adding NaSH solution, hydrochloric acid and slaked lime to the wastewater, and chlorine bypass recovered by the chlorine bypass system attached to the cement manufacturing facility Wet exhaust gas desulfurization treatment wastewater using calcium contained in dust can be targeted.
[Selection] Figure 1

Description

  The present invention relates to a method for removing selenium from waste water generated when a chlorine bypass dust collected by a chlorine bypass system attached to a cement manufacturing facility is washed with water.

Conventionally, for removing selenium contained in the waste water of the chlorine bypass system, for example, a method of performing coagulation precipitation using ferrous chloride (FeCl ₂ ) as a reducing agent has been described (for example, Patent Document 1). reference).

  Further, in the method for treating selenium-containing water described in Patent Document 2, an adsorbent containing a rare earth compound and wastewater containing selenium are brought into contact with each other without performing pretreatment such as pH adjustment, thereby simplifying selenium in the wastewater. A method of adsorbing and removing in a simple process has been proposed.

JP 2004-330148 A 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, in the method for treating selenium-containing water described in Patent Document 2, there is an advantage that pretreatment such as pH adjustment is unnecessary and treatment can be performed in a simple process, but specific individual items generated in various production facilities and the like are available. It is unclear whether it can be applied to wastewater, and it has been considered that the removal rate of selenium varies depending on the pH of each wastewater, for example.

  Then, this invention is made | formed in view of said point, Comprising: It aims at removing tetravalent and hexavalent selenium from waste water 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 generated when chlorine bypass dust is washed with water, and the wastewater generated when chlorine bypass dust is washed with water has a pH of 3.0 or more and 7 It is characterized by being adjusted to less than 0.0 and contacting with an adsorbent containing a rare earth compound.

  Here, chlorine bypass dust refers to chlorine discharged from a chlorine bypass facility that extracts chlorine from a kiln exhaust gas passage from the bottom of the kiln of the cement kiln to the bottom cyclone to remove chlorine. The waste water generated when the chlorine bypass dust is washed with water is slurried by adding water to the dust, and then the liquid obtained by solid-liquid separation. Etc.

  According to the present invention, both tetravalent selenium and hexavalent selenium are removed by adjusting the pH to 3.0 or more and less than 7.0 and adsorbing selenium on an adsorbent containing a rare earth compound. And a high selenium removal rate can be achieved, and selenium can be removed from the waste water at a high rate while keeping operating costs low.

  In the method for removing selenium from the waste water, the rare earth compound may include one or a mixture of two or more rare earth compounds selected from yttrium, lanthanum, cerium, ytterbium oxide, or hydroxide. .

  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 at a high rate from the wastewater generated when the chlorine bypass dust is washed with water while keeping the operating cost low.

It is a graph which shows the relationship between the pH of the 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 produced | generated when the chlorine bypass dust was washed with water. 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 as adsorption agent into the waste_water | drain produced | generated when the chlorine bypass dust was washed with water.

  The method for removing selenium from wastewater generated when the chlorine bypass dust according to the present invention is washed with water (hereinafter, abbreviated as “drainage” where appropriate) adjusts the wastewater to pH 3.0 or more and less than 7.0. It is characterized by contacting with an adsorbent containing a compound. Rare earth compounds, especially yttrium, lanthanum, cerium, ytterbium oxide, or a mixture of one or more rare earth compounds selected from hydroxides effectively adsorb tetravalent and hexavalent selenium. Even when tetravalent selenium and hexavalent selenium coexist in the wastewater, the selenium can be removed only by adjusting the pH of the wastewater to 3.0 or more and less than 7.0. The rare earth compounds used as the adsorbent are preferably those listed above, but are not limited thereto.

  The rare earth compound may be powdered and put directly into the wastewater, and stirred to adsorb selenium, but the rare earth compound is supported on a porous inorganic or organic material to increase the surface area for selenium adsorption. It is preferable to use the adsorbent as an adsorbent because the selenium removal rate can be further increased.

  The wastewater generated when the chlorine bypass dust was washed with water was not only the wastewater itself generated when the chlorine bypass dust collected by the chlorine bypass system attached to the cement manufacturing facility was washed with water, but also the wastewater. In addition, wastewater obtained by sequentially adding a NaSH solution, hydrochloric acid, and slaked lime for the purpose of removing heavy metals is included.

  Another example of the wastewater generated when the chlorine bypass dust is washed with water is wet exhaust gas desulfurization treatment wastewater using calcium contained in the chlorine bypass dust. Since this desulfurization process is a wet process, HCl gas contained in the exhaust gas is also processed.

  Drainage generated when the chlorine bypass dust collected by the chlorine bypass system attached to the cement production facility was washed was used as a test solution. This test solution contained 1.2 ppm of selenium, and its pH was 12.7. In addition, pH in this method can take the numerical range of 12.0-13.5.

  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 6.8 g of 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 = 1.0 to 3.0, the concentration of selenium contained in the treated water decreased as the pH was raised. The selenium concentration contained in the treated water at pH = 3.0 to 7.0 did not change greatly and was a low value of 0.18 to 0.29 ppm. On the other hand, the selenium concentration contained in the treated water at pH = 12.7 was higher than this range and was 0.45 ppm. FIG. 2 shows the selenium removal rate calculated from the selenium concentration contained in the treated water shown in FIG. 1, and the removal rate was high at pH 3.0 to 7.0.

  The wastewater obtained by sequentially adding NaSH solution, hydrochloric acid and slaked lime to the wastewater generated when the chlorine bypass dust collected by the chlorine bypass system attached to the cement production facility was washed with water was used as a test solution. This test solution contained 0.24 ppm of selenium, and its pH was 6.5. In addition, pH in this method can take the numerical range of 6.5-8.5.

  900 g of a test solution was collected, and a resin carrying 6.8 g of a cerium hydroxide reagent was added thereto, followed by stirring for 30 minutes. When the concentration of selenium contained in the treated water was measured, it was 0.096 ppm and the removal rate was 60%.

  Wet exhaust gas desulfurization treatment wastewater using calcium contained in chlorine bypass dust collected by a chlorine bypass system attached to a cement production facility was used as a test solution. This test solution contained 1.1 ppm of selenium, and its pH was 5.0. In addition, pH in this method can take the numerical range of 4.0-7.0.

  900 g of a test solution was collected, and a resin carrying 6.8 g of a cerium hydroxide reagent was added thereto, followed by stirring for 30 minutes. When the concentration of selenium contained in the treated water was measured, it was 0.20 ppm and the removal rate was 82%.

Claims (3)

  A method for removing selenium from waste water, characterized in that waste water generated when chlorine bypass dust is washed with water is adjusted to a pH of 3.0 or more and less than 7.0 and brought into contact with an adsorbent containing a rare earth compound.   The wastewater according to claim 1, wherein the rare earth compound includes one kind or a mixture of two or more kinds of rare earth compounds selected from yttrium, lanthanum, cerium, ytterbium oxide, or hydroxide. To remove selenium from the surface.   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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