JP2019073767A - Method of recovering selenium - Google Patents

Abstract

To provide a method for recovering selenium quickly from aqueous solution with a reductive sulfur compound as a reductant, in an electrolytic slime treatment step for non-ferrous metal refining.SOLUTION: A method of recovering selenium from aqueous solution containing selenium, is characterized by adding an inorganic iodine compound in supplying the aqueous solution containing selenium with a reductive sulfur compound to supply precipitate the selenium.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for recovering selenium from an acidic solution generated in a copper smelting and electrolytic slime treatment process.

  In copper smelting and refining, copper concentrate is melted and made into crude 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. In recent years, metal scraps containing noble metals derived from electronic parts have been introduced as recycling raw materials in converters, and valuable materials other than copper contained in these metal scraps are precipitated as slime during electrolytic refining.

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

  Wet smelting is often applied to the processing of this slime. For example, Patent Document 1 discloses a method of recovering slime by hydrochloric acid-hydrogen peroxide, recovering dissolved gold by solvent extraction, and sequentially reducing and recovering other valuable materials by sulfur dioxide. Patent Document 2 discloses a method of recovering gold and silver in the same manner, reducing the value by sulfur dioxide to precipitate, and distilling and removing only selenium to concentrate noble metals.

  Selenium is used for various materials such as photosensitive materials and semiconductors, and its demand is increasing in recent years. The main production is copper smelting by-products, which are produced by the above-mentioned method, and it is necessary to keep the manufacturing cost low because versatility is required.

  Among the prior art methods for recovering selenium, a method for recovering a precipitate generated by sulfur dioxide, which is disclosed in Patent Document 1 in particular, has many advantages in terms of cost and production scale. In the case where a metal smelter and smelter is installed, the exhaust gas generated from the smoldering furnace contains sulfur dioxide, which can reduce the production cost.

  Furthermore, since it supplies as a gas, it becomes possible to charge a raw material liquid to the upper limit of the reaction tank volume. When a liquid or solid is used as the reducing agent, the volume is increased by the addition, so that the amount processed at one time is smaller than that of the gas.

JP 2001-316735 A Japanese Patent Application Publication No. 2004-190134

  The problem with using sulfur dioxide as a reducing agent is the low reaction efficiency. Since sulfur dioxide is a gas, when bubbling into a solution, only a part of it dissolves and causes a reduction reaction, and another part directly reacts at the gas-liquid interface, but a certain amount of gas is exhausted as bubbles. It will be released to the gas treatment process. When not only sulfur dioxide but also approximately reducing inorganic sulfur compounds are used, they are easily decomposed and gasified under acidic conditions, and the reaction rate is low.

Therefore, if the reaction vessel is sealed, the reaction efficiency can be increased, but a reaction vessel that can withstand pressure is required, but under the present circumstances, the smelting exhaust gas is often continuously supplied to the pressure reaction vessel. The reaction time due to the normally required 5 hours or more to 15 m ³ process selenium 30 g / L solution request. Therefore, this selenium recovery step takes the most time, and the electrolytic slime processing amount per unit time is determined.

  Furthermore, the maintenance of the smelting facility or a sudden failure may reduce or stop the smelting exhaust gas emissions. In this case, sodium sulfite or high purity sulfur dioxide gas is used as a backup for smelting exhaust gas, but since it is an industrial reagent, the production cost is increased. On the other hand, although the smelting exhaust gas is almost inexpensive, in any case the amount of sulfur dioxide used should be suppressed as much as possible, and it is required to improve the reaction efficiency and to terminate selenium recovery promptly.

  SUMMARY OF THE INVENTION In view of such conventional circumstances, the present invention provides a method for rapidly recovering selenium from an aqueous solution using a reducing sulfur compound as a reducing agent.

  As a result of intensive studies to solve the above problems, the present inventors have found that selenium can be rapidly recovered from an aqueous solution by using a reducing sulfur compound as a reducing agent with iodine as a catalyst. The present invention has been completed based on such findings.

That is, the present invention includes the following inventions.
(1) A method for recovering selenium from an aqueous solution containing selenium, which comprises adding an inorganic iodine compound in order to precipitate selenium by supplying a reducing sulfur compound to the aqueous solution containing selenium. How to recover selenium.
(2) The method for recovering selenium according to (1), wherein the inorganic iodine compound is any of potassium iodide, sodium iodide, periodate, and elemental iodine.
(3) The method for recovering selenium according to (1) or (2), wherein the reducing sulfur compound is any one or more of sulfur dioxide, sulfite and sulfite.
(4) The method for recovering selenium according to any one of (1) to (3), wherein the inorganic iodine compound is added as iodide ion to have a concentration of 50 mg / L or more.
(5) The method for recovering selenium according to any one of (1) to (4), wherein the aqueous solution containing selenium has a pH of 10 or less, and further contains arsenous acid.
(6) The method for recovering selenium according to any one of (1) to (5), wherein the aqueous solution containing selenium is hydrochloric acid.
(7) The aqueous solution containing selenium maintains the selenium concentration at 1.5 g / L or more, stops the supply of reducing sulfur compounds when reaching 3.0 g / L, and solid-liquid separates to precipitate selenium The method for recovering selenium according to any one of (1) to (6), characterized in that
(8) The method for recovering selenium according to any one of (1) to (7), wherein the aqueous solution containing selenium precipitates selenium after the solution is heated to 70 ° C. or higher.
(9) The aqueous solution containing selenium is a solution obtained by oxidizing and dissolving electrolytic slime produced in the electrolytic refining step of copper smelting and removing gold, platinum, palladium and rhodium until the total content thereof reaches 100 mg / L or less The method for recovering selenium according to any one of (1) to (8), which is characterized in that

  According to the present invention, selenium can be rapidly recovered from an aqueous solution using a reducing sulfur compound as a reducing agent.

It is a figure which shows the reaction pathway of the iodide ion in the aqueous solution containing selenium. It is a figure which shows a time-dependent change of the selenium reduction reaction in each iodide ion concentration.

  The electrolytic slime produced in the electrolytic refining process of nonferrous metal smelting, especially copper smelting contains a large amount of chalcogen elements and precious metals. As an example, 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, 15 to 25 kg / t of tellurium, 5 to 15 wt% of selenium Contains some.

  Hydrochloric acid and hydrogen peroxide are added to dissolve the electrolytic slime, but silver forms insoluble silver chloride precipitates 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. Because it is a chloride bath, precious metal elements, rare metal elements, selenium and tellurium are distributed in the leached precious liquid (PLS).

  The leached noble liquid (PLS) is cooled once to precipitate and separate chlorides of base metals such as lead and antimony. The gold is then separated into the organic phase by solvent extraction. Dibutyl carbitol (DBC) is widely used as a gold extractant.

  Valuables can be precipitated and recovered by reducing PLS after gold extraction, but since the redox potential differs depending on the element, the order of precipitation is naturally determined. Platinum groups first, then chalcogens such as selenium and tellurium, and inert noble metals are precipitated.

  The platinum group is separately solid-liquid separated for separation and purification. The platinum group separated in this step is mainly palladium, platinum, rhodium or the like. At this point, most of the oxidation numbers in the solution of selenium and tellurium are tetravalent. For example, selenium is mainly present as selenium acid.

  Selenium is reduced and recovered after the platinum group is separated. The reducing agent used is preferable because reducing sulfur compounds are used from the viewpoint of price and efficiency, and especially sulfur dioxide can be supplied in large quantities and inexpensively by roasting converter gas and sulfide ore.

  However, in order to reduce and precipitate selenium with sulfur dioxide, it is known that the acid concentration must be adjusted to 3% or more by acidification with hydrochloric acid. Therefore, at an acid concentration of 1 N or less, reduction of selenium with sulfur dioxide lowers the reaction efficiency.

  Therefore, in the present invention, in order to increase the reaction efficiency, the reducing sulfur compound is supplied to an aqueous solution containing selenium to precipitate selenium, and an inorganic iodine compound is added as a catalyst. The iodide ion generated by the dissolution of the inorganic iodine compound functions by the following reaction formula (1) or the route shown in FIG. In the reaction, selenous acid can be reduced if protons are present, so the effect is high in the neutral to acidic region. Although there is a concern that protons may be reduced as the reaction proceeds, major problems do not occur when using sulfur dioxide or sulfurous acid because the protons and sulfuric acid are regenerated. Further, the timing of adding the inorganic iodine compound may be before, at, or after the start of the supply of the reducing sulfur compound.

The reason why iodide ion promotes the reduction reaction is presumed as follows.
That is, selenious acid is a relatively soft acid, so the reaction is faster if it is reduced with iodide ion, which is a softer base than the intermediate soft sulfur dioxide. The iodine produced by the reaction is rapidly reduced by sulfur dioxide or sulfurous acid. It can be seen that it acts as a catalyst since the amount of iodide ion does not change before and after the reaction.

  When the aqueous solution containing selenium contains noble metals such as palladium (II), rhodium (III), gold (III), platinum (IV), etc., the iodide ion can be palladium (II), rhodium (III), gold In order to form a hardly soluble precipitate with III) and platinum (IV) to form a stable complex ion with iodide ion, it is preferable to remove ions of these noble metals in advance. The total amount of precious metal ions is preferably 100 mg / L or less.

  In addition to iodide ions, inorganic iodine salts such as simple iodine and periodic acid are reduced by reducing sulfur compounds such as sulfur dioxide to form iodide ions, and when they are iodide ions, they function as catalysts. Therefore, the inorganic iodine compound in the present invention refers to one that generates iodide ion in an aqueous solution containing selenium. Specifically, potassium iodide, sodium iodide, periodate, simple iodine and the like can be mentioned.

  In addition to sulfur dioxide, reducing sulfur compounds and sulfurous acid and salts thereof can be used. Furthermore, any substance whose standard redox potential is lower than the standard redox potential of iodine (535 mV / standard hydrogen electrode) functions as a reducing agent. Therefore, the reducible sulfur compound in the present invention refers to a sulfur compound having a standard redox potential lower than 535 mV / standard hydrogen electrode. Specifically, sulfur dioxide, sulfite and sulfite are mentioned.

  Further, since arsenous acid is oxidized to arsenate by iodine at a weakly acidic region to pH 10, it functions as an alternative reducing agent for sulfur dioxide in this case. Therefore, when the aqueous solution containing selenium contains arsenous acid, the amount of the reducing sulfur compound supplied can be reduced. Hydrogen sulfide and thiosulfuric acid are also conceivable, but when reaction products such as sulfur precipitate, they become impurities of recovered selenium.

  By adding the inorganic iodine compound to be 50 mg / L or more as iodide ion, the effect of the present invention is more remarkable. From that point of view, the concentration of iodide ion in the solution is more preferably 80 mg / L, and even more preferably 150 mg / L or more. If the concentration of iodide ion is too low, volatilization of produced single iodine tends to lose the catalytic ability, and if too high, the cost of iodine increases.

  When the aqueous solution containing selenium contains tellurium or lead, iodine may form a precipitate with these elements due to the decrease in the concentration of selenium in the solution. Therefore, it is preferable to maintain the selenium concentration at 1.5 g / L or more. More preferably, it is 3.0 g / L or more. Then, when selenium reaches 3.0 g / L, it is preferable to stop the reaction and perform solid-liquid separation by an appropriate method to recover selenium.

  When the temperature of the solution at the time of reaction is less than 70 ° C., selenium becomes red selenium and amorphous selenium. These forms of selenium cause adhesion to the reaction vessel and clogging in the piping. Therefore, it is preferable to recover the reaction as black selenium while maintaining the liquid temperature at 70 ° C. or higher.

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

(Experimental example 1)
The electrolytic slime recovered from copper smelting was stripped of copper with sulfuric acid. Concentrated hydrochloric acid and 60% hydrogen peroxide water were added to the electrolytic slime and dissolved, and solid-liquid separation was performed to obtain PLS. The PLS was cooled to 6 ° C. to precipitate and remove base metals such as lead. Next, DBC (dibutyl carbitol) and PLS were mixed to extract gold.
Next, PLS after gold extraction was heated to 70 to 75 ° C., and a mixed gas of sulfur dioxide and air (sulfur dioxide concentration 5 to 20%) was blown until the palladium concentration became 20 mg / L or less. The supply of gas was stopped and the precipitated platinum group was removed to obtain a liquid shown in Table 1.
Next, 300 ml of the prepared solution was taken. In this solution, simultaneously with the start of supply of mixed gas of sulfur dioxide and air (sulfur dioxide concentration 5 to 20%), potassium iodide (made by Wako Pure Chemical Industries, special grade) to 0 to 600 mg / L as shown in Table 2. It added so that it might become and it reduced. 10 ml samples were taken every 20 minutes.
The collected solution was filtered and then diluted 25-fold with dilute hydrochloric acid, and the concentrations of various components were measured by ICP-OES (SPS-3100 manufactured by Seiko Instruments Inc.). The measurement was performed using yttrium as an internal standard element. The results are shown in FIG. The legend in the figure indicates the concentration of iodide ion. Each reaction rate was calculated from the slope of an approximate straight line drawn from the graph of FIG. The first half for 140 minutes and the second half for 140 minutes to a selenium concentration of 0.1 g / L or less. The slope is shown in Table 2. Since the element concentration is lowered by sampling, the concentration is corrected by using arsenic which does not precipitate due to reduction as a tracer.

  From the results in Table 2, it can be seen that the addition of potassium iodide accelerates the reduction rate of selenium. 200 mg / L of potassium iodide is about 150 mg / L in terms of iodine. The rate in the second half of Table 2 is improved by 0.09 (g / L) / min at 400 mg / L of potassium iodide. Therefore, it is surmised that about 50 mg / L in iodine conversion is sufficient to improve from no addition to 0.12 (g / L) / min.

Claims (9)

  A method of recovering selenium from an aqueous solution containing selenium, the method comprising adding an inorganic iodine compound to precipitate selenium by supplying a reducing sulfur compound to the aqueous solution containing selenium. Method.   The method for recovering selenium according to claim 1, wherein the inorganic iodine compound is any one of potassium iodide, sodium iodide, periodate and simple iodine.   The method for recovering selenium according to claim 1 or 2, wherein the reducing sulfur compound is any one or more of sulfur dioxide, sulfite and sulfite.   The method for recovering selenium according to any one of claims 1 to 3, wherein the inorganic iodine compound is added as iodide ion to have a concentration of 50 mg / L or more.   The method for recovering selenium according to any one of claims 1 to 4, wherein the aqueous solution containing selenium has a pH of 10 or less, and further contains arsenous acid.   The method for recovering selenium according to any one of claims 1 to 5, wherein the aqueous solution containing selenium is hydrochloric acid acid.   The aqueous solution containing selenium maintains the selenium concentration at 1.5 g / L or more, stops the supply of reducing sulfur compounds when reaching 3.0 g / L, and solid-liquid separates to recover the selenium precipitate The method for recovering selenium according to any one of claims 1 to 6, wherein   The method for recovering selenium according to any one of claims 1 to 7, wherein the aqueous solution containing selenium precipitates selenium after the solution is heated to 70 ° C or higher.   The aqueous solution containing selenium is a solution in which gold, platinum, palladium and rhodium are removed until the total content reaches 100 mg / L or less after oxidation dissolution of the electrolytic slime generated in the electrolytic refining step of copper smelting. The method for recovering selenium according to any one of claims 1 to 8, wherein