Method for catalytically reducing selenium

Abstract

Provided is a method for catalytically reducing selenium. Hydrogen peroxide is used as a catalyst, and a reducer is added to a hexavalent-selenium-containing solution for reaction so as to reduce the selenium to elemental selenium, wherein the standard oxidation-reduction potential of the reducer is lower than the standard oxidation-reduction potential of the conversion of the hexavalent selenium to elemental selenium. The present method can further reduce a hexavalent-selenium element-containing selenic acid or selenate solution to an elemental selenium product in one step. In the present method, the hydrogen peroxide effectively lowers the descending speed of the reduction potential of the solution while having a catalytic effect, so that the reduction reaction process is carried out gently, thereby effectively preventing the selenium in the solution from overreducing to generate negatively bivalent selenium ions or compounds thereof, and solving problems such as a low recovery rate caused by selenium overreduction.

Claims

1. A method for catalytically reducing hexavalent selenium present in a hexavalent-selenium-containing solution directly to elemental selenium, comprising: (a) adding hydrogen peroxide into the hexavalent-selenium-containing solution to be reduced, wherein the hexavalent-selenium-containing solution is a selenic acid or selenate solution generated in chemical or metallurgical scientific research or industrial production, and the selenium present in the hexavalent-selenium-containing solution has a valence of positive hexavalent; and (b) adding a reductant into a mixture obtained from step (a) to reduce the hexavalent selenium directly to the elemental selenium; wherein the hydrogen peroxide is used as a catalyst without oxidizing the hexavalent-selenium-containing solution, which decreases an activation energy in a reduction process of hexavalent selenium, and thus effectively reduce the hexavalent selenium directly to the elemental selenium, and wherein a ratio of a volume of the hydrogen peroxide to a concentration of hexavalent selenium in the hexavalent-selenium-containing solution is not lower than 10 mL:1 g/L.

2. The method according to claim 1, wherein a standard oxidation-reduction potential of the reductant is lower than a standard oxidation-reduction potential of a conversion of hexavalent selenium to elemental selenium.

3. The method according to claim 2, wherein the reductant is one or more of hydrazine hydrate, sulfur dioxide, sulfite and sodium borohydride.

4. The method according to claim 3, wherein a temperature of the hexavalent-selenium-containing solution in a reaction process is controlled at 0-100 C.

5. The method according to claim 2, wherein a temperature of the hexavalent-selenium-containing solution in a reaction process is controlled at 0-100 C.

6. The method according to claim 1, wherein a temperature of the hexavalent-selenium-containing solution in a reaction process is controlled at 0-100 C.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a diagram illustrating an X-ray diffraction detection of a reduced product according to Example 1 of the disclosure.

(2) FIG. 2 is diagram illustrating an X-ray diffraction detection of a reduced product according to Example 2 of the disclosure.

DETAILED DESCRIPTION

(3) Unless otherwise defined, all terminologies used hereinafter have the same meaning generally comprehended by those skilled in the art. The terminologies used herein are only for illustrating the specific examples and not intended to limit the protection scope of the disclosure.

(4) Unless otherwise specified, various agents and raw materials used herein all are commodities purchased from a market or products that may be prepared using a well-known method.

(5) For a better understanding of the disclosure, the disclosure will be described more comprehensively in detail with reference to the drawings of the description and preferred examples hereinafter. However, the protection scope of the disclosure is not limited to the following specific examples.

Example 1

(6) According to an embodiment, a method for catalytically reducing selenium may include the following specific steps.

(7) Sodium selenate (Na.sub.2SeO.sub.4) was dissolved with ultrapure water to be prepared into a sodium selenate solution, in which the selenium content in the solution was 1 g/L and the initial pH of the solution was adjusted to 2. 100 mL of the solution was taken, and added with 15 mL of analytical hydrogen peroxide by a constant flow pump. After being uniformly mixed, the resulting solution was charged with an industrial sulfur dioxide gas (with a gas flow rate of 1 L/min), meanwhile, a water bath was used to control a temperature of a reaction system at 60 C., and the reaction lasted for 2 h. After the obtained solution was filtered, the remained selenium content in the solution was detected, and the final selenium reduction rate was 99.97%. The reduction solid product was detected by X-ray diffraction (as shown in FIG. 1), scanning electron microscopy and inductively coupled plasma atomic emission spectrometry (the results are as shown in table 1). The table 1 shows that the reduction product was elemental selenium with a relatively high purity of 99.91%. As can be seen from FIG. 1, the product is a trigonal black elemental selenium.

Example 2

(8) According to another embodiment, a method for catalytically reducing selenium may include the following specific steps.

(9) Sodium selenate (Na.sub.2SeO.sub.4) was dissolved with ultrapure water to be prepared into a sodium selenate solution, in which the selenium content was 1 g/L and the initial pH of the solution was adjusted to 2. 100 mL of the solution was taken, and added with 15 mL of analytical hydrogen peroxide by a constant flow pump. After being uniformly mixed, the resulting solution was charged with an industrial sulfur dioxide gas (with a gas flow rate of 1 L/min), meanwhile, an ice-water bath was used to control a temperature of a reaction system at 0 C., and the reaction lasted for 2 h. After the obtained solution was filtered, the remained selenium content in the solution was detected, and the calculated selenium reduction rate was 99.89%. The solid product was detected by X-ray diffraction (as shown in FIG. 2), scanning electron microscopy and inductively coupled plasma atomic emission spectrometry (the results are as shown in table 1). The table 1 shows that the reduction product was an elemental selenium with a relatively high purity. As can be seen from FIG. 2, this elemental selenium is an amorphous red elemental selenium.

Example 3

(10) According to yet another embodiment, a method for catalytically reducing selenium may include the following specific steps.

(11) 1 L of hexavalent-selenium-containing wastewater was taken from a smeltery, in which the selenium concentration was 5.5 g/L, and impurities are arsenic ion, sodium ion, chromium ion, organic matter and the like. After the common processes of neutralization, impurity removal and the like, the concentration of selenium ion was 3.6 g/L. After 500 mL of excessive hydrogen peroxide was added to decompose the impurities such as organic matter, 30 g of sodium sulfite was added, and the temperature was controlled at 50 C. by a water bath. After 2 h of reaction, the resulting solution was filtered, the remained selenium content in the solution was detected, and the calculated selenium reduction rate was 97.87%. The X-ray detection result of the elemental selenium is the same as that in Example 1, and the detection result of the inductively coupled plasma atomic emission spectrometry is as shown in table 1.

Example 4

(12) According to a further embodiment, a method for catalytically reducing selenium may include the following specific steps.

(13) A selenium-tellurium containing waste material was treated by pressurized oxidizing acid leaching. Upon detection of ion chromatography, it contained 2.1 g/L of hexavalent selenium radical ions and 5 g/L selenite radical ions. 200 mL of the solution was taken, and added with 25 mL of hydrogen peroxide. The reaction temperature was controlled at 50 C. by a water bath, 5 g of sodium borohydride was added. After 2 h of reaction, the resulting solution was filtered, the remained selenium content in the solution was detected, and the calculated selenium reduction rate was 99.35%. The X-ray detection result of the elemental selenium is the same as that in Example 1, and the detection result of the inductively coupled plasma atomic emission spectrometry is as shown in table 1.

Example 5

(14) According to another further embodiment, a method for catalytically reducing selenium may include the following specific steps.

(15) A selenium-tellurium mixture was treated by acidic oxidizing leaching. After insoluble substances were filtered, the solution was detected, and contained 5.2 g/L hexavalent selenium ions and 18.9 g/L tetravalent selenium ions. After the solution was reduced by conventional sulfur dioxide, there remained 5.1 g/L hexavalent selenium ions. 200 mL of the solution was taken, and added with 55 mL of hydrogen peroxide. The reaction temperature was controlled at 90 C. by a water bath, and industrial sulfur dioxide (with a gas flow rate of 1.5 L/min) was charged. After 1 h of reaction, the resulting solution was filtered, the remained selenium content in the solution was detected, and the calculated selenium reduction rate was 99.53%. The X-ray detection result of the elemental selenium is the same as that in Example 1, and the detection result of the inductively coupled plasma atomic emission spectrometry is as shown in table 1.

Example 6

(16) According to yet another further embodiment, a method for catalytically reducing selenium may include the following specific steps.

(17) Similar to the above Example 5, 200 mL of a hexavalent selenium solution was taken, and added with 50 mL of hydrogen peroxide. The reaction temperature was controlled at 20 C. by a water bath, and industrial sulfur dioxide (with a gas flow rate of 1.5 L/min) was charged. After 1 h of reaction, the resulting solution was filtered, the remained selenium content in the solution was detected, and the calculated selenium reduction rate was 99.49%. The X-ray detection result of the elemental selenium is the same as that in Example 2, and the detection result of the inductively coupled plasma atomic emission spectrometry is as shown in table 1.

Example 7

(18) According to yet further embodiment, a method for catalytically reducing selenium may include the following specific steps.

(19) A selenium-tellurium containing acid slime was treated by sodium hydroxide-hydrogen peroxide oxidizing leaching. After the leaching, the pH was adjusted to be neutral to precipitate tellurium. After filtration, the solution was detected, and contained 2.2 g/L hexavalent selenium ions. 200 mL of the solution was taken, and added with 25 mL of hydrogen peroxide. After being uniformly mixed, the resulting solution was slowly added with 50 mL of a hydrazine hydrate solution with a concentration of 40%. After 2 h of reaction, the resulting solution was filtered, the remained selenium content in the solution was detected, and the calculated selenium reduction rate was 97.89%. The X-ray detection result of the elemental selenium is the same as that in Example 1, and the detection result of the inductively coupled plasma atomic emission spectrometry is as shown in table 1.

(20) TABLE-US-00001 TABLE 1 Detection results of reduction products in Examples 1~7 by inductively coupled plasma atomic emission spectrometry. Examples Selenium Content (%) Impurity Content (%) Example 1 99.91 0.09 Example 2 99.87 0.13 Example 3 98.35 1.65 Example 4 96.92 3.08 Example 5 97.93 2.07 Example 6 98.01 1.99 Example 7 92.35 7.65