JP2019214485A - Method of recovering selenium - Google Patents

Abstract

To provide a method of efficiently precipitating/separating selenium from an acidic aqueous solution containing selenious acid and recovering selenium therefrom.SOLUTION: The method of recovering selenium is characterized by adding 0.1 to 1 mL of acetone relative to 1 g of selenium to an acidic aqueous solution containing selenious acid, and controlling the liquid temperature of the acidic aqueous solution at 65°C or higher to generate sediment containing selenium.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for recovering selenium.

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

  In copper dry smelting, copper concentrate is melted and converted into coarse copper of 99% or more in a converter and a refining furnace, and then electrolytic copper having a purity of 99.99% or more is produced in an electrolytic refining process. Valuables other than copper precipitate as slime during electrolytic refining.

  In addition to gold, silver, platinum and palladium, rare metals such as ruthenium, rhodium and iridium, and selenium and tellurium contained in copper concentrates are simultaneously enriched in the slime. These elements are separately separated and recovered as by-products of copper smelting.

  In many cases, a hydrometallurgical method is applied to the treatment of the slime. For example, Patent Document 1 discloses a method in which silver is recovered from slime with hydrochloric acid-hydrogen peroxide, dissolved gold is recovered by solvent extraction, and other valuable substances are sequentially reduced and recovered with sulfur dioxide. Patent Document 2 discloses a method in which gold and silver are recovered by a similar method, and then valuables are reduced and precipitated with sulfur dioxide, and only selenium is removed by distillation to concentrate noble metals.

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

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

JP 2001-316735 A JP-A-2004-190134

  When sulfur dioxide, sulfurous acid or a salt thereof is used to recover selenium, the reaction is to raise the liquid temperature and recover black selenium in order to prevent sticking and clogging of amorphous selenium that precipitates. However, when the liquid temperature is high, the reduction rate of selenium becomes slow. A method of reducing by raising the liquid temperature in two stages is also conceivable, but selenium precipitated in the solution has a property of sticking to the reaction tank when heated from a low temperature to a high temperature.

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

  Sulfur dioxide generated when roasting sulfide ores and sulfur is a by-product. The supply of sulfur dioxide is stopped when the roasting equipment is regularly maintained or when a catastrophic failure occurs in the production process of the main product. In order to stably reduce and recover selenium, a recovery method using sulfur dioxide gas or another reducing agent is applied as a backup, but an effective reducing agent has not yet been known.

  Although it is effective to add a base metal as a reducing agent, hydrogen is generated as a side reaction in an acidic solution, which poses a safety problem. In addition, there is a safety problem even when hydrazine or aldehyde is used.

  The present invention has been made in view of such conventional circumstances, and provides a method of efficiently separating and recovering selenium from an acidic aqueous solution containing selenous acid.

  The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that selenous acid in an acidic aqueous solution can be precipitated and separated as selenium by using acetone as a reducing agent. The present invention has been completed based on such findings.

That is, the present invention is specified as follows.
(1) Addition of 0.1 to 1 mL of acetone to 1 g of selenium to an acidic aqueous solution containing selenous acid, and adjusting the liquid temperature of the acidic aqueous solution to 65 ° C. or more to generate a precipitate containing selenium. Characteristic method of recovering selenium.
(2) The method for recovering selenium according to (1), wherein the liquid temperature of the acidic aqueous solution is adjusted to 80 ° C. or higher to generate a precipitate containing black selenium.
(3) The method for recovering selenium according to (1) or (2), wherein the acetone is diluted with water and then added to the acidic aqueous solution.
(4) The method for recovering selenium according to (3), wherein the acetone and water are mixed at a volume ratio of 1: 1 to 3: 1 when the acetone is diluted with water.
(5) The method for recovering selenium according to any one of (1) to (4), wherein air is not supplied when the selenium-containing precipitate is generated.
(6) The method for recovering selenium according to any one of (1) to (5), wherein the acidic aqueous solution containing selenous acid is a solution of a copper electrolytic precipitate.

  ADVANTAGE OF THE INVENTION According to this invention, the method of precipitating and separating selenium efficiently from acidic aqueous solution containing selenous acid can be provided.

It is a figure which shows the time-dependent change of the addition amount of acetone and the selenium concentration.

  Electrolytic slime generated in the electrolytic refining process of nonferrous metal smelting, particularly copper smelting, contains a large amount of chalcogen elements and precious 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 5 to 15 wt%.

  When this electrolytic slime is dissolved by adding hydrochloric acid and hydrogen peroxide, a solution of a copper electrolytic precipitate is obtained, 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, noble metals can be dissolved and silver can be separated as silver chloride. Since it is a chloride bath, a noble metal element, a rare metal element, selenium, and tellurium are distributed to a leached precious solution (hereinafter also referred to as PLS). Selenium is contained as selenium oxonium in the acidic aqueous solution, but is mostly selenous acid.

  The noble metals are recovered using solvent extraction or oxidation-reduction potential difference. Thereafter, selenium is reduced and recovered, and at this time, a method of recovering using selenium dioxide is generally used. However, when sulfur dioxide cannot be used for the above reasons, selenous acid can be reduced with acetone.

  Selenous acid or selenium dioxide is known to cause a reaction called selenium oxidation on the aryl carbon-hydrogen bond. Since acetone reacts but 2-propanol does not react, it is considered that in the case of acetone, an enol generated by keto-enol tautomerism reacts.

  Acetone is converted to hydroxyacetone by the selenium oxidation reaction, and selenium is precipitated as selenium as a single substance. The precipitated selenium becomes red selenium or black selenium depending on the temperature. Since red selenium has a high water content and is difficult to separate into solid and liquid, it is preferable to recover it as black selenium. Generally, red selenium changes to black selenium at 65 ° C. or higher. Therefore, the liquid temperature is set to 65 ° C. or more to reduce selenium.

However, when selenium is recovered by adding acetone, red selenium may precipitate even at 70 ° C. or adhere to the wall surface as amorphous selenium. Although the reason is unknown, it is preferable to add acetone at 80 ° C. or higher in order to surely recover as black selenium and improve the effect of the present invention.

  Acetone is a water-soluble ketone and is suitable for reducing selenous acid in an aqueous solution. Acetone is suitable because it is inexpensive and has low toxicity.

  Acetone is oxidized to 1,3-dihydroxyacetone by selenium oxidation. 1,3-dihydroxyacetone is a monosaccharide, exhibits reducing properties, and can further reduce selenium. Dihydroxyacetone is harmless.

  There is a concern that the reduction of selenite with acetone will increase the COD (chemical oxygen demand) in the solution. It does not matter if dihydroxyacetone is further reacted and oxidized to carbon dioxide, but its use is preferably small.

  Thus, 1 mL of acetone can recover 1 to 3 g of selenium. Also, as the amount of acetone added is smaller than that of selenium, the amount of selenium recovered per unit amount tends to increase. However, when reducing selenous acid with ketones, an excessive amount of addition causes unreacted ketones or reaction products remaining in the wastewater to increase COD. Further, a phenomenon may occur in which a very small amount of selenium is hardly subjected to reduction by the addition of ketones. Therefore, the wastewater treatment load increases. Therefore, it is preferable to add 0.1 to 1 mL of acetone to be added to 1 g of selenium element in the solution. In addition, when adding acetone after mixing with water, the amount of the above-mentioned acetone indicates the amount before mixing with water.

  Selenium is obtained by subjecting the deposited precipitate to solid-liquid separation using a filter press or the like. Selenium recovered by solid-liquid separation can be further distilled to increase its purity.

  After the reaction, valuable substances such as tellurium, iridium, and ruthenium remain in the liquid after the reaction. These valuables are reduced and recovered with sulfur dioxide or sulfite. At this time, it is preferable that residual selenium is also removed and the final concentration of selenium is 1 mg / L or less.

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

(Experimental example 1)
The electrolytic slime recovered from copper smelting was leached with sulfuric acid to remove copper. Concentrated hydrochloric acid and 60% aqueous hydrogen peroxide were added to dissolve and solid-liquid separated to obtain a leached precious liquid (PLS).
The PLS from which gold had been removed by solvent extraction was heated while stirring, and when the temperature reached 70 ° C., a mixed gas of sulfur dioxide and air (sulfur dioxide concentration 5 to 20%) was blown at 0.1 L / min. After confirming that the concentrations of platinum and palladium were both 5 mg / L or less, the resulting precipitate was separated from the solution. The liquid after PMG (precious metal group) separation had a selenium concentration of 23 g / L and a tellurium concentration of 260 mg / L.
After the PMG separation, 300 mL of the liquid was separated (6.9 g of selenium), the temperature was adjusted to 70 to 75 ° C., and 0.5 to 15 mL of acetone was added and stirred. For comparison, 5 vol% to 20 vol% sulfur dioxide was blown into the same liquid without adding acetone for reduction. Approximately 10 mL samples were taken at regular intervals. After 2 hours, the precipitate was collected by filtration. After washing with water and drying at 60 ° C. overnight, the weight was measured.
The collected sample was subjected to solid-liquid separation with a 5C filter paper. The solution was diluted 25-fold with diluted hydrochloric acid, and the concentrations of various components were measured by ICP-OES (SPS-3100 manufactured by Seiko) using yttrium as an internal standard. The results are shown in Table 1 and FIG.

  It can be seen that selenium was precipitated by the addition of acetone at any amount. Also, excluding the result of 8 mL or more added in excess, it can be seen that the amount of selenium precipitated with respect to the amount of acetone added was acetone (mL): selenium (g) = 1: (1 to 1.5).

(Experimental example 2)
300 mL (6.9 g of selenium) of the same liquid after PMG separation as in Experimental Example 1 was fractionated and heated to 75 to 93 ° C. 5 mL of acetone was added. A system in which 5 mL of water and 5 mL of acetone (mixing volume ratio 1: 1) were mixed and added was also tried. The liquid temperature was kept at the initial temperature and the reduction was continued. A sample was taken as a slurry at regular intervals.
Various concentrations in the liquid were determined by the same operation as in Experimental Example 1. Table 2 shows the experimental results.

  In Experimental Example 1, selenium reduced with acetone was mostly recovered as red selenium. Red selenium has a high moisture content and must be subsequently dried before distillation in the purification process. In addition, a phenomenon was observed in which red selenium became amorphous selenium and stuck to the walls of the stirrer and the reaction vessel. On the other hand, in Experimental Example 2, when selenium was recovered by adding acetone at 80 ° C. or higher, black selenium could be recovered.

  Generally, selenium is considered to precipitate as black selenium when reduced at a temperature exceeding 65 ° C. However, when acetone is used as a reducing agent, black selenium may be partially obtained by adjusting the liquid temperature to 65 ° C. or higher. It has been found that reduction is preferable.

  The boiling point of acetone is 56 ° C. Therefore, it is considered that if the liquid temperature is high, the amount of acetone vaporized before the reaction increases and the reaction efficiency decreases. This shows that acetone is preferably added after being mixed with water and diluted to increase the reaction efficiency of acetone. The effect was seen at a mixing volume ratio of 1: 1. The vapor-liquid equilibrium curve of acetone and water can be expected to have an effect from dilution of acetone: water at a mixing volume ratio of about 3: 1 in consideration of a large boiling point when the mole fraction of acetone is 0.2 or less.

  In addition, although increasing the amount of water to lower the acetone ratio is effective, it is not preferable because it causes an increase in the amount of the added liquid. This is because an increase in the amount of the added liquid requires a reaction tank having a larger capacity. Therefore, the mixing ratio of acetone and water is preferably as small as possible.

  Comparing the results of Experimental Example 2 with the acetone 5 ml addition system of Experimental Example 1, it can be seen that the selenium concentration after 90 minutes is much lower when acetone is diluted with water and added. When mixed with water, the reaction efficiency of acetone is clearly increased. Further, at a liquid temperature of 80 ° C. or higher, the concentration of selenium is low, and the reduction of selenium by acetone is promoted. In particular, it was found that the temperature greatly changed around 80 ° C.

(Experimental example 3)
A plurality of 300 mL (6.9 g of selenium) liquids after the same PMG separation as in Experimental Example 1 were taken and heated to 75 ° C. or 80 ° C., respectively. 5 mL of acetone or 2-butanone was added. After one hour, aeration (blowing air) was performed as shown in Table 3. After stirring was continued for another 30 minutes, the reaction was stopped. The liquid temperature was kept at the initial temperature and the reduction was continued. A sample was taken as a slurry at regular intervals.
Next, the concentrations of various components in the liquid were determined by the same operation as in Experimental Example 1. The COD of the solution was quantified according to JIS-K0102-17. The COD of the stock solution was 3 g / L. Table 3 shows the experimental results.

  From the results in Table 3, it was found that the use of acetone did not raise the COD in the wastewater. In addition, it was found that in the reduction with acetone, the absence of aeration was advantageous for the precipitation of selenium. Therefore, it is preferable not to supply air when precipitating selenium.

Claims (6)

  0.1 to 1 mL of acetone is added to 1 g of selenium to an acidic aqueous solution containing selenous acid, and the liquid temperature of the acidic aqueous solution is adjusted to 65 ° C. or more to cause precipitation containing selenium. How to collect selenium.   The method for recovering selenium according to claim 1, wherein the temperature of the acidic aqueous solution is adjusted to 80 ° C. or higher to generate a precipitate containing black selenium.   The method for recovering selenium according to claim 1 or 2, wherein the acetone is diluted with water and then added to the acidic aqueous solution.   The method for recovering selenium according to claim 3, wherein the acetone and water are mixed at a volume ratio of 1: 1 to 3: 1 when diluting the acetone with water.   The method for recovering selenium according to any one of claims 1 to 4, wherein air is not supplied when the selenium-containing precipitate is generated.   The method for recovering selenium according to any one of claims 1 to 5, wherein the acidic aqueous solution containing selenous acid is a solution of a copper electrolytic precipitate.