JP2018109207A - Method of recovering selenium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method in which selenium is efficiently separated from an acidic aqueous solution by precipitation for recovery.SOLUTION: A method of recovering selenium includes the steps of adding a ketone to an acidic aqueous solution containing selenium oxonium, to yield precipitate containing selenium.SELECTED DRAWING: None

Description

  The present invention relates to a method for recovering selenium.

  Selenium belongs to the chalcogen element and is used in optical instruments because it has various glass industries and semiconductor properties. Most of its production is produced as a by-product of copper dry smelting.

  In copper dry smelting, copper concentrate is melted and made into 99% or more of crude copper in a converter and refining furnace, and then electrolytic copper with a purity of 99.99% or more is produced in the electrolytic purification process. Valuables other than copper precipitate as slime during electrolytic purification.

  In addition to gold, silver, platinum and palladium, this slime is also enriched with rare metals such as ruthenium, rhodium and iridium, and selenium and tellurium contained in copper concentrate. These elements are separated and recovered separately as byproducts of copper smelting.

  A hydrometallurgical process is often applied to the treatment of this slime. For example, Patent Document 1 discloses a method in which silver is recovered with hydrochloric acid-hydrogen peroxide and slime is recovered by solvent extraction, and then other valuable materials are sequentially reduced and recovered with sulfur dioxide. Patent Document 2 discloses a method of concentrating noble metals by recovering gold and silver by the same method, reducing and precipitating valuables with sulfur dioxide, and distilling and removing only selenium.

  The solution after recovering the precious metal contains tellurium and selenium, and it is necessary to recover these valuable materials. As a recovery method, there are known a method of recovering a precipitate generated by a reducing agent, and a method of mixing the solution together with copper concentrate, drying it with a dryer and repeating it in a smelting furnace.

  In particular, as shown in Patent Document 1, a method for recovering a precipitate caused by sulfur dioxide has many advantages in terms of cost and production scale. In addition, since each element precipitates sequentially, it is effective for separation and purification.

JP 2001-316735 A JP 2004-190134 A

  When sulfur dioxide, sulfurous acid, or a salt thereof is used for recovery of selenium, the reaction is carried out to recover black selenium by raising the liquid temperature in order to prevent the adhering amorphous selenium from sticking or clogging. However, when the liquid temperature is high, the reduction rate of selenium is slow. Although a method of reducing the temperature by raising the liquid temperature in two stages is conceivable, selenium precipitated in the solution has the property of adhering to the reaction vessel when heated from a low temperature to a high temperature.

  Sulfur dioxide can be produced at low cost by roasting various sulfide ores in dry smelting of metals, but if it is purchased as gas, it does not meet the recovery cost when the reaction time is long. When sulfur dioxide is used in large quantities, it is necessary to install gas treatment equipment because of its pungent odor, toxicity, and environmental standards. Therefore, the capital investment becomes large.

  Although it is effective to add a base metal as a reducing agent, in an acidic solution, hydrogen is generated as a side reaction, which causes a safety problem. Moreover, there is a safety problem even if hydrazine or aldehydes are used.

  In view of such conventional circumstances, the present invention provides a method for efficiently separating and recovering selenium from an acidic aqueous solution.

  As a result of intensive studies to solve the above problems, the present inventors have found that selenium oxonium in acidic aqueous solution can be precipitated and separated as selenium by using ketones as a reducing agent. The present invention has been completed based on such findings.

  The present invention completed on the basis of the above knowledge is, in one aspect, a method for recovering selenium characterized by adding a ketone to an acidic aqueous solution containing selenium oxonium to cause precipitation containing selenium.

  In one embodiment of the method for recovering selenium according to the present invention, the ketones are added 1 to 8 moles of selenium oxonium.

  In another embodiment of the method for recovering selenium according to the present invention, in addition to the ketones, at least one of sulfur dioxide, sulfite and sulfite is added to the acidic aqueous solution to precipitate selenium and other valuable substances. Give rise to

  In still another embodiment of the method for recovering selenium of the present invention, the ketones are water-soluble ketones.

  In still another embodiment of the method for recovering selenium of the present invention, the water-soluble ketones are acetone or 2-butanone.

  In yet another embodiment of the method for recovering selenium according to the present invention, before adding the ketones, at least one of sulfur dioxide, sulfurous acid and sulfite is added to the acidic aqueous solution in advance to add the acidic aqueous solution. An oxidant that can oxidize simple selenium present in the catalyst is decomposed.

  In yet another embodiment of the method for recovering selenium of the present invention, the liquid temperature of the acidic aqueous solution when the ketones are added to cause precipitation containing selenium is 65 ° C. or higher, whereby black selenium is obtained. This produces a precipitate containing.

  In still another embodiment of the method for recovering selenium of the present invention, the ketones are added to an acidic aqueous solution containing selenium oxonium to oxidize hydrogen at the α-position of the ketone group of the ketones.

  ADVANTAGE OF THE INVENTION According to this invention, the method of carrying out the precipitation separation | separation efficiently from acidic aqueous solution and collect | recovering can be provided.

  Electrolytic slime generated in the electrolytic refining process of nonferrous metal smelting, especially copper smelting, contains a lot of chalcogen elements and noble metals. As an example, gold contains 10 to 30 kg / t, silver 100 to 250 kg / t, palladium 1 to 3 kg / t, platinum 200 to 500 g / t, and selenium about 5 to 15 wt%.

  Hydrochloric acid and hydrogen peroxide are added to dissolve the electrolytic slime, but silver forms an insoluble silver chloride precipitate with chloride ions immediately after dissolution. In the case of a solution containing an oxidizing agent and chlorine, such as aqua regia or chlorine water, noble metals can be dissolved to separate silver as silver chloride. Since it is a chloride bath, noble metal elements, rare metal elements, selenium, and tellurium are distributed in the leached noble liquid (PLS). Selenium is contained as selenium oxonium in the acidic aqueous solution.

  Selenium is reduced and recovered after recovering the precious metals. At this time, a method of recovering by using sulfur dioxide is common. However, selenium undergoes reduction when sulfur dioxide is once dissolved in water and converted into sulfurous acid. Due to the solubility of sulfur dioxide, selenium is efficient when reduced at low temperatures.

  In the acidic aqueous solution containing selenium oxonium, the method of heating and reducing selenium in two steps causes red selenium deposited earlier to be modified by heating and to be fixed to the wall surface. The fixed selenium may cause problems in recovery and operability in the subsequent process. For this reason, it is preferable to collect selenium as black selenium by one-stage heating (heating at a single temperature) without heating in two stages.

  In the present invention, by using ketones as a reducing agent, it is possible to effectively reduce and precipitate selenous acid as selenium with the temperature of the acidic aqueous solution as a single temperature. The liquid temperature may be any as long as the residual selenium in the liquid is reduced and does not stick to the reaction vessel. That is, the temperature is 50 ° C. or lower at which red selenium precipitates and 65 ° C. or higher at which black selenium is precipitated.

  In the method for recovering selenium according to the present invention, a ketone is added to an acidic aqueous solution containing selenium oxonium as described above to cause precipitation containing selenium. For this reason, the reduction rate of selenium does not become slow as in the case of using sulfur dioxide, sulfurous acid or a salt thereof for the recovery of selenium, and the liquid temperature does not have to be increased in two stages. Moreover, since sulfur dioxide, sulfurous acid, or a salt thereof is not used, there is no need to install gas treatment equipment for irritating odor, toxicity, and environmental standards, and the treatment can be performed safely.

  Among ketones, acetone and 2-butanone are water-soluble ketones and are suitable for reduction of selenious acid in an aqueous solution. Ketones are partly present as enols due to keto-enol tautomerism. It is thought that reduction occurs when the π electron of enol moves to selenium oxonium.

  The amount of ketone to be added is preferably 1 to 8 mol times the total molar amount of selenium oxonium. If too much, the load of drainage is large. Furthermore, when heated, an aldol reaction occurs, and there is a possibility that it will be less than the effective concentration due to self-consumption before reacting with selenium oxonium. On the other hand, if the amount added is too small, the reaction rate may decrease.

  In order to reduce the amount of ketone used, it is preferable to convert hexavalent selenium to tetravalent with an inexpensive reducing agent in advance. In addition, the cost can be reduced by reducing hexavalent tellurium and high oxidation number metal ions. Inexpensive reducing agents include reducing sulfur, chloride ions, base metals, and the like.

  Reduction occurs when ketones are added to an acidic aqueous solution and heated to 60 ° C. or higher. If nitrate solution is contained in the acidic aqueous solution, the precipitate is re-dissolved and removed beforehand. For removal of nitrate ions, reducing sulfur and various metals can be used. Nitrate ions can also be removed by heating the solution to be acidic.

  Selenium oxonium is tetravalent or hexavalent, and reduction with only acetone increases the reagent cost. Cost can be suppressed by making acetone act only as a reduction trigger and simultaneously supplying reducing sulfur. Examples of reducing sulfur include sulfur dioxide, sulfurous acid, sulfite, and hydrogen sulfide. Any compound is known to reduce selenium oxonium to zero valence if conditions are adjusted.

  In addition to ketones, at least one of sulfur dioxide, sulfurous acid and sulfite may be added to the acidic aqueous solution to cause precipitation of selenium and other valuable substances.

  When sulfur dioxide is used in combination, the addition amount of acetone may be 0.3 to 40 ml with respect to 1 L of the treatment liquid. Although it depends on the composition of the reaction solution, the effect of acetone is 1 mol times or more with respect to selenium, and the effect is remarkable if it is 2 mol times or more.

  Before adding ketones, at least one of sulfur dioxide, sulfurous acid and sulfite is added to the acidic aqueous solution in advance to decompose the oxidizing agent capable of oxidizing the simple selenium present in the acidic aqueous solution. Is preferred. According to such a structure, it can suppress favorably that single selenium will be oxidized. Here, examples of the “oxidizing agent capable of oxidizing single selenium present in an acidic aqueous solution” include nitric acid, hydrogen peroxide, hypochlorous acid, perchloric acid, and the like.

  The deposited precipitate is solid-liquid separated by a filter press or the like. Depending on the composition of the target solution, the precipitate contains precious metals in addition to the chalcogen elements of selenium and tellurium.

  This method can be applied not only to the selenium refining process but also to removing selenium from selenium-containing wastewater.

  In the present invention, ketones can be added to an acidic aqueous solution containing selenium oxonium to oxidize hydrogen at the α-position of the ketone group of the ketones. According to such a configuration, for example, the oxidation of ketones such as acetone can be performed using an acidic aqueous solution containing selenium oxonium produced by copper smelting or the like, which is advantageous in terms of cost.

  Hereinafter, the present invention will be described more specifically by experimental examples. However, the present invention is not limited to these.

(Experimental example 1)
The electrolytic slime recovered from the copper smelting was leached with sulfuric acid to remove the copper. Concentrated hydrochloric acid and 60% aqueous hydrogen peroxide were added and dissolved, and solid-liquid separation was performed to obtain a precipitating leached solution (hereinafter also referred to as PLS).
PLS after removing gold by solvent extraction was heated with stirring, and when it reached 70 ° C., a mixed gas of sulfur dioxide and air (sulfur dioxide concentration 5 to 20%) was blown at 0.1 L / min. Platinum, palladium and selenium precipitated after 1 hour 30 minutes were separated from the solution. Table 1 shows the main components of the liquid after separation.
After separation, the liquid was adjusted to a predetermined temperature, and 1 mL of acetone was added. Approximately 10 mL of the sample was taken as a slurry at regular intervals.
The obtained slurry was subjected to solid-liquid separation with 5C filter paper. The solution was diluted 25 times with dilute hydrochloric acid, and various component concentrations were measured by ICP-OES (SEPS SPS-3100) using yttrium as an internal standard. The experimental results are shown in Table 2.

  In Table 2, at 60 ° C. or higher, the concentration after 3 hours increases due to concentration by liquid evaporation. Selenium showed a reducing effect at any temperature range. It can be seen that the effect is particularly high at 60 ° C. or higher.

(Experimental example 2)
A post-separation solution having the composition shown in Table 1 was prepared in the same manner as in Experimental Example 1.
300 ml was collected and heated to a predetermined temperature, and 1 ml of acetone was added. Sulfur dioxide (purity 99.9%) was blown at 0.1 L / min with stirring. The liquid temperature was maintained at the initial temperature and the reduction was continued. Samples were taken as slurry at regular intervals.
Various concentrations in the liquid were quantified in the same manner as in Experimental Example 1. The experimental results are shown in Table 3.

  It can be seen that when sulfur dioxide supply is used in combination, tellurium is rapidly reduced and precipitated in addition to selenium in any temperature range. It can be seen that the reduction rate of tellurium is particularly fast at 50 ° C. or higher. Acetone is a substance that is easily vaporized, but even if sulfur dioxide gas is blown in, it does not cause a big problem.

  By using acetone and sulfur dioxide in combination, the reduction of selenium achieved a significant reduction in reaction time. It can also be seen that tellurium can be recovered simultaneously.

(Experimental example 3)
19.7 g of sodium selenite (manufactured by Wako Pure Chemical Industries, Ltd., first grade) was dissolved in 3 L of 2.5N hydrochloric acid to prepare a test solution.
500 mL was collected and heated to 70 to 75 ° C., and a predetermined amount of acetone or 2-butanone was added (both manufactured by Wako Pure Chemical Industries, Ltd., special grade). The liquid temperature was stirred while maintaining the initial temperature. Samples were taken at regular intervals.
Various concentrations in the liquid were quantified in the same manner as in Experimental Example 1. The experimental results are shown in Table 4.

  It can be seen that water-soluble ketones can reduce selenium. The effect was observed when the amount of acetone added was 2 ml (54 mmol) with respect to 500 ml of the target solution, and the reaction rate decreased as the amount added increased. The reason for this is thought to be that acetone reacts by an aldol reaction before reacting with selenium oxonium under acidic conditions.

  The selenium in the solution in which the reagent is dissolved is 38 mmol / L, and the selenium actually reduced when 2 ml of acetone is added is 36 mmol / L. It reacts 1.5 times as much as selenium. Since there is also a quantity that volatilizes with heat, approximately twice will be equivalent. Since selenium is tetravalent, it is assumed that acetone donates two electrons.

  When acetone was added excessively, the recovery rate of selenium was reduced, but the reduction ability was not completely impaired. There is no particular upper limit to the amount added, but the amount added is preferably less than 20 mL / L because the reducing ability is greatly impaired at 20 mL per 1 L.

  When butanone was added to reduce selenious acid, the post-reaction solution had a specific odor and was estimated to be 3-hydroxy-2-butanone by gas chromatography. 3-Hydroxy-2-butanone is a form in which the α-hydrogen of the original 2-butanone is substituted with a hydroxyl group, and is selectively oxidized by reaction with selenious acid.

Claims (8)

  A method for recovering selenium, comprising adding a ketone to an acidic aqueous solution containing selenium oxonium to cause precipitation containing selenium.   The method for recovering selenium according to claim 1, wherein the ketones are added in an amount of 1 to 8 moles of selenium oxonium.   3. The selenium and other valuable substances are precipitated by adding at least one of sulfur dioxide, sulfite and sulfite to the acidic aqueous solution in addition to the ketones. To recover selenium.   The method for recovering selenium according to any one of claims 1 to 3, wherein the ketones are water-soluble ketones.   The method for recovering selenium according to claim 4, wherein the water-soluble ketone is acetone or 2-butanone.   Before adding the ketones, at least one of sulfur dioxide, sulfurous acid, and sulfite is added to the acidic aqueous solution in advance to decompose an oxidant that can oxidize elemental selenium present in the acidic aqueous solution. The method for recovering selenium according to any one of claims 1 to 5, wherein   The precipitate containing black selenium is produced by setting the liquid temperature of the acidic aqueous solution when the ketones are added to cause precipitation containing selenium to 65 ° C or higher. The method for recovering selenium according to any one of the above.   The selenium according to any one of claims 1 to 7, wherein the ketone is added to an acidic aqueous solution containing the selenium oxonium to oxidize hydrogen at the α-position of the ketone group of the ketone. Recovery method.