JP6964408B2 - How to collect selenium - Google Patents

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 pyrometallurgy.

In the copper pyrometallurgy, copper concentrate is melted to obtain 99% or more blister copper in a converter and a refining furnace, and then electrolytic copper having a purity of 99.99% or more is produced in the electrolytic refining process. Valuables other than copper precipitate as slime during electrolytic refining.

In addition to gold, silver, platinum and palladium, this slime is simultaneously enriched with rare metals such as ruthenium, rhodium and iridium, and selenium and tellurium contained in copper concentrate. These elements are individually separated and recovered as copper smelting by-products.

A hydrometallurgy method is often applied to the treatment of this slime. For example, Patent Document 1 discloses a method in which silver is recovered from slime by hydrochloric acid-hydrogen peroxide, dissolved gold is recovered by solvent extraction, and then other valuable resources are sequentially reduced and recovered by sulfur dioxide. Patent Document 2 discloses a method of recovering gold and silver by the same method, reducing valuable resources with sulfur dioxide to precipitate them, and distilling and removing only selenium to concentrate precious metals.

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

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

Japanese Unexamined Patent Publication No. 2001-316735 Japanese Unexamined Patent Publication No. 2004-190134

When sulfur dioxide, sulfurous acid, or a salt thereof is used to recover selenium, the reaction is to raise the liquid temperature to recover black selenium in order to prevent the precipitated amorphous selenium from sticking or clogging. However, when the liquid temperature is high, the reduction rate of selenium slows down. A method of raising the liquid temperature in two steps to reduce the liquid is also conceivable, but the selenium precipitated in the solution has the property of sticking to the reaction vessel when heated from a low temperature to a high temperature.

Sulfur dioxide can be produced inexpensively by roasting various sulfide ores in the pyrometallurgy of metals, but if purchased as gas, it is not worth the recovery cost if the reaction time is long. When a large amount of sulfur dioxide is used, it is necessary to install gas treatment equipment due to its pungent odor, toxicity, and environmental standards. Therefore, capital investment will be large.

It is effective to add a base metal as a reducing agent, but hydrogen is generated as a side reaction in an acidic solution, which poses a safety problem. In addition, 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 precipitating and separating selenium from an acidic aqueous solution and recovering it.

As a result of diligent research to solve the above problems, the present inventors have found that selenium oxonium in an 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, which has been completed based on the above findings, is a method for recovering selenium, which is characterized in that, on one aspect, ketones are added to an acidic aqueous solution containing selenium oxonium to form a precipitate containing selenium.

In one embodiment of the method for recovering selenium of the present invention, the ketones are added 1 to 8 mol times as much as selenium oxonium.

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

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

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

In still another embodiment of the method for recovering selenium of the present invention, at least one of sulfur dioxide, sulfurous acid and sulfite is added to the acidic aqueous solution in advance before adding the ketones, and the acidic aqueous solution is added. Decompose the oxidizing agent that can oxidize the single selenium present in.

In yet another embodiment of the method for recovering selenium of the present invention, black selenium is produced by raising the liquid temperature of the acidic aqueous solution to 65 ° C. or higher when the ketones are added to form a precipitate containing selenium. Produces a containing precipitate.

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

According to the present invention, it is possible to provide a method for efficiently precipitating and separating selenium from an acidic aqueous solution and recovering it.

Electrolytic slime produced in the electrolytic refining process of non-ferrous metal smelting, especially copper smelting, contains a large amount of chalcogen elements and precious metals. As an example, it contains 10 to 30 kg / t of gold, 100 to 250 kg / t of silver, 1 to 3 kg / t of palladium, 200 to 500 g / t of platinum, and 5 to 15 wt% of selenium.

Hydrochloric acid and hydrogen are added to dissolve this 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, for example, aqua regia or chlorine water, precious metals can be dissolved and silver can be separated as silver chloride. Since it is a chloride bath, noble metal elements, rare metal elements, selenium, and tellurium are distributed in the leachate noble liquid (PLS). Selenium is contained as selenium oxonium in the acidic aqueous solution.

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

In an acidic aqueous solution containing selenium oxonium, the method of heating selenium in two steps to reduce it causes the previously precipitated red selenium to be denatured by heating and adhere to the wall surface. Adhered selenium may cause problems in recovery and operability in the subsequent process. Therefore, it is preferable to recover selenium as black selenium by one-step heating (heating at a single temperature) without heating in two steps.

In the present invention, by using ketones as a reducing agent, it is possible to effectively reduce and precipitate selenous acid as selenium by setting the liquid temperature of the acidic aqueous solution to a single temperature. The liquid temperature may be any condition 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 is precipitated, and 65 ° C. or higher at which black selenium is precipitated.

In the method for recovering selenium of the present invention, ketones are added to an acidic aqueous solution containing selenium oxonium in this way to form a precipitate containing selenium. Therefore, unlike the case where sulfur dioxide, sulfurous acid or a salt thereof is used for the recovery of selenium, the reduction rate of selenium does not slow down, and the liquid temperature does not have to be raised in two steps to reduce the selenium. In addition, since sulfur dioxide, sulfurous acid, or a salt thereof is not used, there is no need to install gas treatment equipment for pungent odor, toxicity, and environmental standards, and treatment can be performed safely.

Among the ketones, acetone and 2-butanone are water-soluble ketones and are suitable for reducing selenous acid in an aqueous solution. A small part of ketones exists as enol due to keto-enol tequal modification. It is considered that reduction occurs when the π electron of the 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 it is too much, the load of drainage will be large. Furthermore, when heated, an aldol reaction may occur, and the concentration may drop below the effective concentration due to self-consumption before reacting with selenium oxonium. On the contrary, if the addition amount 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. Costs can be suppressed by reducing other metal ions such as hexavalent tellurium and high oxidation number. Examples of inexpensive reducing agents include reducing sulfur, chloride ions, and base metals.

Reduction occurs when ketones are added to an acidic aqueous solution and heated to 60 ° C. or higher. If nitrate ions are contained in the acidic aqueous solution, the precipitate will be redissolved, so this should be removed in advance. Reducing sulfur and various metals can be used to remove nitrate ions. Nitrate ions can also be removed by acidifying the solution and heating it.

Selenium oxonium is tetravalent or hexavalent, and reduction with acetone alone increases reagent cost. Costs can be reduced by allowing acetone to act only as a reducing trigger and at the same time supplying reducing sulfur. Examples of reducing sulfur include sulfur dioxide, sulfurous acid, sulfites, and hydrogen sulfide. It is known that all compounds reduce selenium oxonium to zero valence if the 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 resources.

When sulfur dioxide is used in combination, the amount of acetone added 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 observed at 1 mol times or more with respect to selenium, and the effect is remarkable at 2 mol times or more.

Before adding the ketones, at least one of sulfur dioxide, sulfurous acid and sulfite should be 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 preferable. According to such a configuration, it is possible to satisfactorily suppress the oxidation of elemental selenium. Here, examples of the "oxidizing agent capable of oxidizing a single selenium present in an acidic aqueous solution" include nitric acid, hydrogen peroxide, hypochlorous acid, and perchloric acid.

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

This method can be applied not only in the selenium purification step but also in the case of removing selenium from the selenium-containing wastewater.

Further, in the present invention, ketones can be added to an acidic aqueous solution containing selenium oxonium to oxidize the 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 carried out using an acidic aqueous solution containing selenium oxonium produced in copper smelting or the like, which is advantageous in terms of cost.

Hereinafter, the present invention will be described in more detail with reference to experimental examples. However, the present invention is not limited thereto.

(Experimental Example 1)
The electrolytic slime recovered from the copper smelting was leached with sulfuric acid to remove copper. Concentrated hydrochloric acid and 60% hydrogen peroxide solution were added and dissolved, and solid-liquid separation was performed to obtain a pregnant leached solution (hereinafter also referred to as PLS).
The 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 and 30 minutes were separated from the solution. Table 1 shows each main component 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 solid-liquid separated with a 5C filter paper. The solution was diluted 25-fold with dilute hydrochloric acid, and the concentrations of various components were measured by ICP-OES (SPS-3100 manufactured by Seiko Co., Ltd.) 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 in all temperature ranges. It can be seen that the effect is particularly high at 60 ° C. or higher.

(Experimental Example 2)
A post-separation liquid having the composition shown in Table 1 was prepared by the same operation as in Experimental Example 1.
300 ml was dispensed, 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 maintained the initial temperature and continued reduction. Samples were taken as a slurry at regular intervals.
Various concentrations in the liquid were quantified by the same operation as in Experimental Example 1. The experimental results are shown in Table 3.

It can be seen that when the supply of sulfur dioxide is used in combination, the reduction precipitation of tellurium occurs rapidly in addition to selenium in any temperature range. In particular, it can be seen that the reduction rate of tellurium is high at 50 ° C. or higher. Acetone is a substance that easily vaporizes, but blowing sulfur dioxide gas does not cause any major problems.

By using acetone and sulfur dioxide together, the reduction of selenium achieved a significant reduction in reaction time. Furthermore, it can be seen that tellurium can be collected at the same time.

(Experimental Example 3)
An experimental target solution was prepared by dissolving 19.7 g of sodium selenite (manufactured by Wako Pure Chemical Industries, Ltd., first grade) in 3 L of 2.5 N hydrochloric acid.
500 mL was dispensed, 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 by the same operation as in Experimental Example 1. The experimental results are shown in Table 4.

It can be seen that selenium can be reduced if it is a water-soluble ketone. 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 considered to be that under acidic conditions, acetone reacts with each other by an aldol reaction before reacting with selenium oxonium.

The amount of selenium in the solution in which the reagent is dissolved is 38 mmol / L, and the amount of selenium actually reduced when 2 ml of acetone is added is 36 mmol / L. It reacts 1.5 mol times with selenium. Since there is an amount that is volatilized by heat, about twice the amount will be the same amount. Since selenium is tetravalent, it is inferred that acetone donates two electrons.

Excessive addition of acetone reduced the recovery rate of selenium, but did not completely impair the reducing ability. Although there is no particular upper limit to the amount of addition, it is preferable that the amount of addition is less than 20 mL / L because 20 mL per 1 L significantly impairs the reducing ability.

When butanone was added to reduce selenous acid, the post-reaction solution had a peculiar odor and was presumed 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 replaced with a hydroxyl group, indicating that it was selectively oxidized by the reaction with selenous acid.

Claims (8)

A method for recovering selenium, which comprises adding ketones to an acidic aqueous solution containing selenium oxonium to form a precipitate containing selenium. The method for recovering selenium according to claim 1, wherein the ketones are added 1 to 8 mol times as much as selenium oxonium. The invention according to claim 1 or 2, wherein at least one of sulfur dioxide, sulfurous acid and sulfite is added to the acidic aqueous solution in addition to the ketones to cause precipitation of selenium and other valuable resources. How to collect 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 oxidizing agent capable of oxidizing the single selenium present in the acidic aqueous solution. The method for recovering selenium according to any one of claims 1 to 5, which is characterized in that it is kept. Claims 1 to 6, wherein a precipitate containing black selenium is produced by raising the liquid temperature of the acidic aqueous solution to 65 ° C. or higher when the ketones are added to form a precipitate containing selenium. The method for recovering selenium according to any one item. The selenium according to any one of claims 1 to 7, wherein the ketones are added to the acidic aqueous solution containing selenium oxonium to oxidize the hydrogen at the α-position of the ketone group of the ketones. How to collect.