JP6948910B2 - How to collect selenium - Google Patents

Description

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

In the copper pyrometallurgy, copper concentrate is melted to obtain 99% or more blister copper in a converter and a purification furnace, and then electrolytic copper having a purity of 99.99% or more is produced in the electrolytic refining process. In recent years, metal scraps containing precious metals derived from electronic parts have been introduced as recycling raw materials in converters, and valuable resources 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 individually separated and recovered as copper smelting by-products.

A wet smelting 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 with hydrochloric acid-hydrogen peroxide, the dissolved gold is recovered by solvent extraction, and then other valuable resources are sequentially reduced and recovered with 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.

Selenium is used in various materials such as photosensitive materials and semiconductors, and its demand has been increasing in recent years. Its main production is copper smelting by-product, which is produced by the above-mentioned method and requires versatility, so it is necessary to keep the production cost low.

Among the prior arts relating to the method for recovering selenium, the method for recovering the precipitate formed by sulfur dioxide, which is shown in Patent Document 1, has many advantages in terms of cost and production scale. In particular, when a metal dry smelter is installed, the exhaust gas generated from the roasting furnace contains sulfur dioxide, which can be used to keep the manufacturing cost low.

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

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

Therefore, if the reaction vessel is sealed, the reaction efficiency is improved, but a reaction vessel that can withstand the pressure is required. However, at present, the smelted exhaust gas is often continuously supplied to the normal pressure reaction vessel. The reaction time depends on the requirement, but it usually takes 5 hours or more to treat ^{15 m 3 of the selenium 30 g / L solution.} Therefore, this selenium recovery step takes the longest time, and determines the amount of electrolytic slime processed per unit time.

Furthermore, smelting exhaust gas emissions may decrease or stop due to maintenance of smelting equipment or sudden failure. In this case, sodium sulfite or high-purity sulfur dioxide gas is used as a backup for the smelted exhaust gas, but the production cost increases because it is an industrial reagent. On the other hand, although the smelted exhaust gas costs almost no cost, the amount of sulfur dioxide used should be suppressed as much as possible, and it is required to improve the reaction efficiency and finish the selenium recovery promptly.

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 diligent research to solve the above problems, the present inventors have found that selenium can be efficiently and quickly recovered from an aqueous solution by adding an iron salt and using a reducing sulfur compound as a reducing agent. 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 iron salt when supplying a reducing sulfur compound to the aqueous solution containing selenium to precipitate selenium. How to collect.
(2) The method for recovering selenium according to (1), wherein the iron salt is either ferrous sulfate or ferrous sulfate hydrate.
(3) The method for recovering selenium according to (1) or (2), wherein the reducing sulfur compound is at least one of sulfur dioxide, sulfites, and sulfurous acid.
(4) The method for recovering selenium according to any one of (1) to (3), wherein the iron salt is added so as to be 80 mg / L or more in terms of iron.
(5) The method for recovering selenium according to any one of (1) to (4), wherein the iron salt is added when the amount of selenium in the aqueous solution containing the selenium reaches 20 g / L or less.
(6) The selenium-containing aqueous solution is a solution obtained by oxidizing and dissolving the electrolytic slime produced in the electrolytic refining step of copper refining, and then removing gold, platinum, palladium, and rhodium until the total content reaches 100 mg / L or less. The method for recovering selenium according to any one of (1) to (5).
(7) The method for recovering selenium according to any one of (1) to (6), wherein the aqueous solution containing selenium is acidic with hydrochloric acid, and selenium is contained as selenous acid.
(8) The method for recovering selenium according to any one of (1) to (7), wherein the iron salt is added so as to be 10 g / L or more as iron.
(9) The method for recovering selenium according to any one of (1) to (8), wherein the aqueous solution containing selenium heats the solution to 70 ° C. or higher and then precipitates the selenium.
(10) When the sulfur dioxide is supplied to precipitate selenium, the supply of sulfur dioxide is stopped when the selenium concentration reaches 3 g / L, and the selenium is ^{reduced with Fe 2+} (3) to ( The method for recovering selenium according to any one of 9).

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 iron salt in the aqueous solution containing selenium. It is a figure which shows the time-dependent change of the selenium reduction reaction with each iron salt input amount.

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. For example, gold is 10 to 30 kg / t, silver is 100 to 250 kg / t, palladium is 1 to 3 kg / t, platinum is 200 to 500 g / t, tellurium is 15 to 25 kg / t, and selenium is 5 to 15 wt%. Contains to some extent.

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).

The leachate noble liquid (PLS) is cooled once to precipitate and separate chlorides of base metals such as lead and antimony. After that, the gold is separated into an 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 extracting gold, but the order of precipitation is naturally determined because the redox potential differs depending on the element. First, platinum groups, then chalcogens such as selenium and tellurium, and then the inert noble metals are precipitated.

Platinum groups are separately solid-liquid separated for separation and purification. Palladium, platinum, rhodium and the like are the main elements of the platinum group separated in this step. At this point, most of the selenium and tellurium solutions in solution are tetravalent. For example, selenium exists primarily as selenite.

After separating the platinum groups, selenium is reduced and recovered. Reducing agents used are reducing sulfur compounds in terms of price and efficiency. Specifically, sulfur dioxide, sulfites, and sulfurous acid, especially sulfur dioxide, are produced in large quantities by roasting furnace gas and sulfide ore. It is preferable because it can be supplied at low cost. The reducing sulfur compound refers to a sulfur compound having an oxidation-reduction potential lower than 0.77 V, which is the redox standard electrode potential of ^{Fe 3+} , due to the reaction mechanism due to the addition of iron salt, which will be described later.

When reducing selenium in a liquid with sulfur dioxide, the selenium is reduced after the sulfur dioxide is dissolved in the solution. Therefore, the lower the temperature of the solution, the more advantageous it is in terms of solubility, but selenium exists as red selenium or amorphous selenium below 70 ° C. In this state, problems such as a high water content and a slow filtration rate occur, so the liquid temperature is preferably 70 ° C. or higher.

If the solubility of sulfur dioxide is low, the reaction efficiency will decrease. This is because the sulfur dioxide supplied as a gas is discharged before it is sufficiently dissolved in the solution. In the first place, selenous acid tends to receive electrons from once dissolved sulfite ion or sulfur dioxide hydrate rather than directly receiving electrons from gaseous sulfur dioxide. Even if it is supplied as a solid such as sodium sulfite, it is immediately vaporized as sulfur dioxide and lost under strongly acidic conditions.

Therefore, in the present invention, an iron salt is added in order to increase the reaction efficiency. Iron salts function in the pathway shown in FIG. Especially in the case of ferrous iron, it also has the effect of directly reducing selenium. Even when the selenium concentration is low, iron (III) ions receive electrons from sulfur dioxide and sulfite ions, and the generated iron (II) ions reduce selenium. Iron (III) efficiently accepts electrons from both gaseous sulfur dioxide and sulfur dioxide in aqueous solution. Therefore, the iron salt may be divalent or trivalent. The timing of adding the iron salt may be before, at the start, or after the start of the supply of the reducing sulfur compound.

The reason why the iron salt promotes the reduction reaction is presumed as follows.
That is, selenous acid is a relatively soft acid. In contrast, iron (III) ions are hard acids. Therefore, when reducing with intermediate soft sulfur dioxide or sulfite ion, the effect of adding an iron salt is small if sufficient selenous acid is present. However, when the selenium concentration is 20 g / L or less, the amount of selenium directly reduced from the gaseous sulfur dioxide decreases, and the reduction via iron (III) ions becomes conspicuous.

It is not noticeable when the absolute amount of selenium is large, but reduction via iron ions is efficient. In particular, when the selenium concentration is 20 g / L or less, the reduction via iron ions becomes conspicuous. Therefore, the reduction rate does not decrease but also increases in the latter stage of the reaction.

This improvement in the reduction rate of selenium becomes noticeable. When the selenium concentration reaches 20 g / L or less, iron salts, especially ferrous sulfate or ferrous sulfate hydrate, which are divalent iron salts, are added. You may. In particular, ferrous sulfate heptahydrate is very inexpensive and therefore effective in terms of cost. Furthermore, there is also the effect that the reduction of selenous acid by iron (II) occurs at the moment of injection.
When the iron salt is added so as to be 80 mg / L or more in terms of iron, the effect is remarkable.

When the selenium-containing aqueous solution contains precious metals such as palladium (II), rhodium (III), gold (III), and platinum (IV), the iron (II) ion is palladium (II), rhodium (III), Since gold (III) and platinum (IV) are also reduced to form a precipitate of these metals and become an impurity of selenium to be recovered, it is preferable to remove ions of these precious metals in advance. The total amount of precious metal ions is preferably 100 mg / L or less.

When tellurium also coexists in an aqueous solution containing selenium, tellurium begins to precipitate when the selenium concentration reaches about 3 g / L. Tellurium is an impurity in selenium, so mixing is not desirable. Therefore, when the selenium concentration reaches about 3 g / L, it is preferable to stop the supply of sulfur dioxide and precipitate selenium by reduction via iron ions in the system.

Tellurium is not reduced by iron (II) ions, so selenium is reduced until even lower concentrations are reached. Reduction proceeds until sulfur dioxide or sulfurous acid in the reaction system disappears, and the recovery efficiency of selenium is improved.

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

(Experimental Example 1)
Copper was removed from the electrolytic slime recovered from copper smelting with sulfuric acid. Concentrated hydrochloric acid and 60% hydrogen peroxide solution were added to this electrolytic slime to dissolve it, and solid-liquid separation was obtained 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, the 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 groups were removed to obtain the liquids shown in Table 1.
Next, 300 ml of the prepared liquid was taken. 0.5 to 30 g of ferrous sulfate heptahydrate (manufactured by Wako Pure Chemical Industries, Ltd., special grade) was added to this liquid at the same time as the supply of a mixed gas of sulfur dioxide and air (sulfur dioxide concentration 5 to 20%) was started. Then, reduction was carried out with a mixed gas of sulfur dioxide and air (sulfur dioxide content 8 to 20%). A 10 ml sample was taken every 20 minutes. Pure water was added as appropriate to keep the volume of the reaction solution constant.
The collected liquid was filtered, 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. Since the element concentration decreases due to sampling, the value is shown with the concentration corrected using arsenic, which is reduced and does not precipitate, as a tracer. The legend in the figure shows the amount of iron salt input.

The change over time in the selenium concentration is shown in FIG. It can be seen that the reduction rate was improved by adding ferrous sulfate heptahydrate. In particular, when the reduction reaction proceeds and the selenium concentration decreases, the addition effect is large.

When the concentration of selenium is 20 g / L or less, the reaction mechanism shown in FIG. 1 acts as the main reaction. Therefore, a divalent iron salt may be added when the selenium concentration reaches 20 g / L. If a divalent iron salt is added when the selenium concentration is difficult to reduce with sulfur dioxide, the effect of lowering the selenium concentration can be expected due to the reducing ability of the iron salt itself.

When the amount of iron salt to be added is large, the effect is recognized even if the amount of selenium is 20 g / L or more. A typical case was when 15 g of ferrous sulfate heptahydrate in FIG. 2 was added, and the iron concentration at that time was 10 g / L.

Claims (10)

A method for recovering selenium from an aqueous solution containing selenium, which comprises adding an iron salt when supplying a reducing sulfur compound to the aqueous solution containing selenium to precipitate selenium. .. The method for recovering selenium according to claim 1, wherein the iron salt is either ferrous sulfate or ferrous sulfate hydrate. The method for recovering selenium according to claim 1 or 2, wherein the reducing sulfur compound is one or more of sulfur dioxide, sulfites, and sulfurous acid. The method for recovering selenium according to any one of claims 1 to 3, wherein the iron salt is added so as to be 80 mg / L or more in terms of iron. The method for recovering selenium according to any one of claims 1 to 4, wherein the iron salt is added when the amount of selenium in the aqueous solution containing the selenium reaches 20 g / L or less. The selenium-containing aqueous solution is a solution obtained by oxidizing and dissolving the electrolytic slime produced in the electrolytic refining step of copper refining, and then removing gold, platinum, palladium, and rhodium until the total content reaches 100 mg / L or less. The method for recovering selenium according to any one of claims 1 to 5. The method for recovering selenium according to any one of claims 1 to 6, wherein the aqueous solution containing selenium is acidic with hydrochloric acid, and selenium is contained as selenous acid. The method for recovering selenium according to any one of claims 1 to 7, wherein the iron salt is added so as to be 10 g / L or more as iron. The method for recovering selenium according to any one of claims 1 to 8, wherein the aqueous solution containing selenium heats the solution to 70 ° C. or higher and then precipitates the selenium. Any of claims 3 to 9, wherein when the sulfur dioxide is supplied to precipitate selenium, the supply of sulfur dioxide is stopped and the selenium is ^{reduced with Fe 2+ when the selenium concentration reaches 3 g / L.} The method for recovering selenium described in 1.

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