JP7198172B2 - Method for treating solution containing selenosulfuric acid - Google Patents

Description

The present invention relates to a method for treating solutions containing selenosulfuric acid.

Selenium is mostly produced as a by-product of copper smelting. In copper pyrometallurgical refining, copper concentrate is melted, converted into 99% or higher blister copper in a converter and a refining furnace, and then refined copper with a purity of 99.99% or higher is produced in an electrolytic refining process. Selenium precipitates as slime during electrorefining.

Noble metals and rare metals are also concentrated in this slime at the same time. These elements are separately separated and recovered as copper smelting by-products. In the hydrometallurgical process, gold and silver are first separated by dissolving them in acid. Thereafter, selenium is recovered as a precipitate as elemental selenium using a suitable reducing agent (Patent Document 1).

It is known that elemental selenium reacts with sulfurous acid and dissolves as selenosulfuric acid (Non-Patent Document 1). By removing the elemental selenium contained in the recovered precipitate, the contents of platinum group elements and tellurium are increased, and the load of the refining process is reduced. However, an industrial treatment method for the removed selenosulfuric acid has not been established.

JP-A-2001-316735 JP-A-9-75954

Seiji Takagi "Qualitative Analytical Chemistry Part 2 Ion Reaction" Nankodo Kazuya Koyama, Mikio Kobayashi, Hiroshi Sakamoto "Resources and Materials '97 Autumn Conference Abstracts" p104

The selenosulfuric acid solution is treated by solid-liquid separation after decomposition into elemental selenium. Patent Literature 2 discloses a method of adjusting selenium in wastewater to pH 1.2 or less and heating and aerating the wastewater. In addition, Non-Patent Document 2 discloses a precipitation removal method using pH adjustment and barium salt. This method utilizes thermal decomposition and equilibrium reaction, and is intended for solutions with a concentration of selenosulfuric acid of 0.3 g/L or less. Therefore, when the concentration of selenosulfuric acid becomes high, for example, when a liquid having a concentration of 10 g/L or more is used, it is difficult to reduce the concentration of selenium to below the discharge standard by an equilibrium reaction.

The sulfite ion precipitation by barium salt shown in Non-Patent Document 2 is also an equilibrium reaction, and the effect is high because the equilibrium constant is small, but it is difficult to reduce the selenium concentration to below the reference concentration. Also, when a high-concentration selenosulfuric acid solution is targeted, the cost of barium ions increases. Furthermore, in a system in which sulfate ions and carbonate ions are mixed, barium ions precipitate, so a huge amount of barium chloride is required.

The detailed properties of selenosulfuric acid are not known, and there is room for development in its proper treatment.

Accordingly, an object of the present invention is to provide a method for treating a solution containing selenosulfuric acid, which is capable of precipitating and separating elemental selenium from a solution containing selenosulfuric acid at low cost.

Embodiments of the invention are specified as follows.
(1) A method for treating a solution containing selenosulfuric acid, comprising the steps of adding an acid to a solution containing selenosulfuric acid to precipitate selenium, and further adding a reducing agent to precipitate selenium.
(2) The solution containing selenosulfuric acid according to (1), wherein the amount of acid added when precipitating the selenium is such that the pH of the final solution after the precipitation of selenium is 0.5 or less. Processing method.
(3) The method of (1) or (2), wherein the acid added to the solution containing selenosulfuric acid is hydrochloric acid or sulfuric acid, and the acid concentration of the solution after adding the acid is adjusted to 1 N or more. A method for treating a solution containing selenosulfuric acid.
(4) Selenium is precipitated as black selenium by adding the acid and the reducing agent while the solution containing selenosulfuric acid is heated to 70° C. or higher (1 A method for treating a solution containing selenosulfuric acid according to any one of ) to (3).
(5) Selenium is precipitated as red selenium by adding the acid and the reducing agent while the solution containing selenosulfuric acid is adjusted to 50° C. or lower (1) A method for treating a solution containing selenosulfuric acid according to any one of (3).
(6) The reducing agent contains at least one selected from the group consisting of sulfur dioxide, sodium sulfite, sodium hydrogen sulfite, iron (II) salt, thiourea, acetone and base metals (1)- A method for treating a solution containing selenosulfuric acid according to any one of (5).
(7) The method for treating a solution containing selenosulfuric acid according to any one of (1) to (6), wherein the solution containing selenosulfuric acid contains 0.1 g/L or more of selenium.
(8) Before adding the reducing agent, the selenosulfuric acid-containing solution is adjusted to have an oxidation-reduction potential of 200 mV or more with silver/silver chloride as a reference electrode by adding the acid. A method for treating a solution containing selenosulfuric acid according to any one of (1) to (7).
(9) The solution containing selenosulfuric acid is a solution obtained by adding sodium sulfite to the solution containing selenium in the electrolytic slime treatment process in the copper smelting process (1) to (8) A method for treating a solution containing selenosulfuric acid according to any one of
(10) The solution containing selenosulfuric acid is put into a tank for reducing and recovering selenium from the selenous acid-containing liquid in the electrolytic slime treatment process in the copper smelting process, and the acid is added and the reducing agent is added. The method for treating a solution containing selenosulfuric acid according to any one of (1) to (9), characterized in that

According to an embodiment of the present invention, it is possible to provide a method for treating a solution containing selenosulfuric acid, which is capable of precipitating and separating elemental selenium from a solution containing selenosulfuric acid at low cost.

[Solution containing selenosulfuric acid]
Electrolytic slime generated in the electrorefining process of non-ferrous metal smelting, especially copper smelting, contains about 5 to 15 wt % of selenium. Some of the selenium in the electrolytic slime is elemental selenium, but most of it forms compounds with metals. Hydrochloric acid and hydrogen peroxide are added to dissolve this electrolytic slime, and precious metal elements, rare metal elements, selenium, and tellurium are distributed in the pregnant leach liquor (PLS).

Precious leach liquor (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. A widely used extractant for gold is dibutyl carbitol (DBC).

Valuables can be precipitated and recovered by reducing PLS after extracting gold, but the order of precipitation is naturally determined because the oxidation-reduction potential differs depending on the element. That is, first platinum metals, then chalcogens such as selenium and tellurium, and then inert noble metals are precipitated.

Water-soluble sulfur oxides such as sulfurous acid, sulfites, and sulfur dioxide are used as reducing agents because of their cost and efficiency. In particular, sulfur dioxide can be supplied in large quantities and at low cost through converter gas and roasting of sulfide ore. optimal.

When the solution after gold extraction is reduced with sulfur dioxide, platinum group compounds are first precipitated, but a large amount of selenium is mixed. Depending on the content, about 0.8 to 2 times the weight of selenium of the platinum group is mixed. There is a dilemma in that if the amount of sulfur dioxide supplied is reduced in order to suppress the contamination of selenium, the recovery amount of platinum group compounds will decrease. Selenium contamination is unavoidable even when other reducing agents are used to varying degrees.

After separation of the platinum group, selenium is reduced and precipitated as elemental selenium by sulfur dioxide. At this time, the reduction is stopped when 3 to 5 g/L of selenium is reached at the expense of the selenium recovery rate in order to selectively recover only selenium. The collected elemental selenium is distilled and refined to high-purity selenium.

Sulfur dioxide is supplied again to the residual liquid to recover residual selenium, tellurium and other rare metals. The selenium in the precipitate recovered here is as high as 0.5 to 3 times the weight of tellurium.

As a method for separating platinum group metals, tellurium, and elemental selenium, there is a method for separating selenosulfuric acid by reacting sulfite ions with selenium. Since tellurium and platinum group metals hardly react with sulfite ions, they remain dissolved as residues. When tellurium is contained as tellurium dioxide, only tellurium can be recovered by elution with an alkaline solution before contact with sulfite ions.

Platinum group metals and tellurium concentrated as residues are further purified by acid dissolution. Preliminary separation of elemental selenium greatly reduces the amount of reagents used for this acid dissolution. In addition, since the concentration of platinum group metals and tellurium contained in the solution is increased, the process load is reduced.

[Method for treating solution containing selenosulfuric acid]
The selenosulfuric acid-containing solution separated as described above contains 0.1 g/L or more of selenium, typically several g/L to several tens of g/L of selenium. This selenosulfuric acid is a liquid containing selenium at high concentration and high purity, and is treated to recover selenium. Even if it is discharged, it is required to reduce the selenium concentration to below the discharge standard.

A solution containing selenosulfuric acid exhibits an alkaline pH of 8.5 or higher. Selenosulfuric acid is stable in alkalinity. This is explained by the equilibrium shown in Equation 1 below.

SeSO ₃ ^2- +2H ⁺ <-> _H2SO3 +Se <-> _{H2O +} SO2 ₊ Se (Formula 1)

First, acid is added to push this equilibrium to the right. The oxidizing acid oxidizes the generated selenium to selenous acid and dissolves it. Sulfuric acid or hydrochloric acid is therefore preferred. Patent Document 2 states that the amount of acid added is until the pH reaches 1.2 or less. More preferably, the acid is added until the acid concentration reaches 1N or higher. Thus, in the method of treating a solution containing selenosulfuric acid according to the present invention, first, the acid concentration is increased to decompose selenosulfuric acid into elemental selenium and selenous acid. The selenous acid is then reacted with a reducing agent. In this reaction, the acid concentration in the decomposition of selenous acid in the first stage is important, and as described above, selenium is well precipitated if the acid concentration is finally pH 0.5 or less.

The higher the temperature of the solution, the better. Patent Document 2 also has a description of 60° C. or higher. As can be seen from Eq. 1 above, increasing the temperature to decrease the solubility of sulfur dioxide will help push the equilibrium to the right. If the rate of decrease in the solubility of sulfur dioxide exceeds 60°C, there is no significant change, so it is preferable to set the solubility to 60°C or higher.

Volatilizing the sulfur dioxide dissolved in the liquid by aeration increases the precipitation efficiency of elemental selenium. Aeration also has the effect of oxidizing sulfurous acid. No particular air supply speed is specified.

It is difficult to lower the concentration of selenosulfuric acid to below the emission standards for selenium only by acid decomposition. An excess of acid must be added due to the equilibrium of formula 1 above, and the excess acid must be treated. Second, selenite is produced as a side reaction of selenosulfuric acid decomposition is.

Selenosulfuric acid is represented by the chemical formula H ₂ SeSO ₃ , where Se is (-II) valence and S is (VI) valence, but no spectroscopic evidence is given. From a different point of view, it can be seen that Se and H ₂ O are coordinated on the sulfur atom of SO ₂ .

_In the SO2 molecule, the sulfur element is partially positively charged and under acidic conditions pulls electrons from the selenium atom. Furthermore, if this selenium atom undergoes hydrolysis, it is possible to be oxidized to selenous acid. If a part of selenosulfuric acid undergoes this side reaction, the final decomposition form of selenosulfuric acid becomes elemental selenium and selenous acid.

To reduce selenous acid to elemental selenium, a reducing agent is added under the acidic conditions described above. Reducing agents include sulfur dioxide, sulfurous acid and its salts, ketones, base metals, iron (II) salts, hydrogen sulfide, thiourea, thiocyanate, and the like. Sulfur dioxide, sulfurous acid and its salts (sodium sulfite, sodium hydrogen sulfite, etc.), acetone, and iron (II) sulfate heptahydrate are preferred in terms of price.

According to the above formula 1, sulfur dioxide is produced during selenosulfate acid decomposition. A portion of this reduces selenite to yield elemental selenium. In order to suppress the amount of the reducing agent to be used, it is preferable to add the reducing agent after the acid decomposition. In addition, if the sulfite-based reducing agent is added early, there is a possibility that the concentration of sulfur dioxide will increase and the reaction efficiency will decrease due to the equilibrium of the above equation (1).

As described above, the selenosulfuric acid treatment is preferably performed at 60° C. or higher. However, at 60° C., the selenium produced becomes amorphous selenium and may adhere to the reaction vessel or stirrer. Therefore, it is preferable to carry out the acid decomposition and the addition of the reducing agent while heating to 70° C. or higher. At this time, elemental selenium can be recovered by converting selenium into black selenium.

Single selenium can be recovered as red selenium by acid decomposition and addition of a reducing agent at 50°C or less.

The acid decomposition of selenosulfuric acid can be terminated by ORP (oxidation-reduction potential, reference electrode Ag/AgCl). The solution containing selenosulfuric acid is preferably adjusted to have a redox electrode potential of 200 mV or more with Ag/AgCl as a reference electrode by addition of acid. When it shows 440 mV or more, selenous acid becomes the dominant species and the addition of acid becomes almost ineffective. If a reducing agent is added at this time, simple selenium can be effectively precipitated. Various metals, sulfurous acid and its salts, sulfur dioxide, hydrogen sulfide, iron (II) salts, thiourea, etc. are known as reagents for reducing selenous acid.

When selenium is incompletely removed even with the addition of a reducing agent, a known selenite precipitation method can be used as a selenium removal method. Specific examples include iron coprecipitation, metal cementation, and resin adsorption.

Embodiments of the present invention are particularly suitable for solutions containing selenosulfuric acid obtained from selenium-containing material generated in the slime treatment process generated in the electrorefining process in copper smelting. That is, the selenosulfuric acid-containing solution may be a solution obtained by adding sodium sulfite to a selenium-containing solution in the electrolytic slime treatment process during the copper smelting process. Alternatively, a solution containing selenosulfuric acid may be introduced into a tank for reducing and recovering selenium from a selenous acid-containing liquid in the electrolytic slime treatment process in the copper smelting process, and the acid and the reducing agent may be added. can.

Examples of the present invention are described below, but the examples are for illustrative purposes and are not intended to limit the invention.

Concentrated hydrochloric acid and 60% hydrogen peroxide solution were added to the electrolytic slime recovered from copper smelting to dissolve it, followed by solid-liquid separation to obtain PLS. The PLS was then cooled to 6° C. to precipitate and remove base metals. Next, gold was extracted by mixing DBC (dibutyl carbitol) and PLS.

The PLS after the gold extraction was heated to 70° C., and copper smelting converter exhaust gas was blown into the PLS to reduce the noble metals. A mixed gas of sulfur dioxide and air (5 to 20 vol %) was further blown into the liquid after noble metal separation at about 1.2 L/min to precipitate selenium and perform solid-liquid separation. A mixed gas of sulfur dioxide and air was further blown into the liquid after selenium separation to obtain a tellurium-containing residue.
An equal weight of sodium sulfite was added to the noble metal-containing slag, 200 ml of 1 g/L NaOH solution was poured and heated at 50° C. for 30 minutes. Next, it was filtered through a 5C filter paper to obtain an aqueous solution containing selenosulfuric acid derived from the slag containing precious metals.
Next, 100 ml of a 10 g/L NaOH solution was poured into 10 g of the tellurium-containing residue and stirred at 20° C. for 30 minutes. After filtering, the solid content was separated, an equal weight of sodium sulfite was added to the weighed tellurium-containing residue, 200 ml of 1 g/L NaOH solution was poured, and the mixture was heated at 50° C. for 30 minutes. Next, it was filtered through a 5C filter paper to obtain an aqueous solution containing selenosulfuric acid derived from the tellurium-containing slag.

(Experimental example 1)
An amount of 300 ml of the selenosulfuric acid-containing aqueous solution (Se concentration: 24.8 g/L, Te concentration: 6.2 g/L) derived from the tellurium-containing slag was collected. However, in some experiments, fractional amounts were changed as shown in Table 1.
Next, 15 ml of concentrated sulfuric acid was added, and a predetermined amount of the additive shown in Table 1 was added, and the conditions shown in Table 1 were set.

Next, the tellurium-containing slag-derived selenosulfuric acid-containing aqueous solution was prepared at the temperature shown in Table 1, and samples were taken every 15 minutes. Aeration described in Table 1 was performed with a pump for breeding tropical fish. After 1 hour, the reaction was stopped, and the pH was measured and filtered. The filter paper was washed with water and further washed with acetone. The acetone was then air-dried and then dried overnight at 50° C. and weighed.
A 2 ml sample was taken after filtration. It was placed in a 50 ml volumetric flask previously added with 2 ml of hydrogen peroxide and 1 ml of nitric acid, calibrated, and the concentration was determined by ICP-OES. Table 2 shows the results.

In Table 2, the time when the predetermined temperature was reached after the addition of sulfuric acid was defined as 0 minutes. That is, the starting point of the arrow is the concentration after addition of sulfuric acid, and the end point of the arrow is the concentration at the end of the reaction. In both cases, it can be seen that selenosulfuric acid was decomposed by acid decomposition. The lower the pH, the better, and the acid is added so that the final pH becomes 0.5 or less, preferably 0.4 or less.

A comparison of conditions 1 and 6 shows that aeration is effective. Also, from the results of conditions 2 and 3, it is inferred that selenous acid is partially reduced. The only thing that reduces selenite is sulfite, which would be the result of following the equilibrium reaction of Equation 1 above. The liquid after noble metal separation contains about 35 g/L of selenium as selenous acid.

(Experimental example 2)
A 100 ml portion of an aqueous solution containing selenosulfuric acid (Se concentration: 15.5 g/L, pH: 8.9, ORP: 183 mV) derived from slag containing precious metals was taken. The selenosulfuric acid-containing aqueous solution was adjusted to the temperature shown in Table 3, and the amount of sulfuric acid shown in Table 3 was added. When adding 10 ml or more of sulfuric acid, the sulfuric acid was added and stirred before reaching the temperature shown in Table 3. A sample was taken at 0 minutes after addition and further samples were taken at 15 and 30 minutes. After 30 minutes, the reaction was terminated and pH and ORP were measured. Acid concentrations were determined by titration with sodium hydroxide solution when the pH was below 0.1. After filtration, the sample was diluted and measured for selenium concentration by ICP-OES.

Based on the results in Table 2, it is expected that most of the selenosulfuric acid will be decomposed to produce elemental selenium when the acid concentration reaches 1.6 N, but the results in Table 3 show that a large amount of selenium remained. This difference is due to the difference in the concentration of tellurite contained in the liquid, and while the liquid derived from tellurium slag contains tellurite, the liquid derived from noble metals does not have tellurite or other electron acceptors. Although the definite reaction mechanism is unknown, it is presumed that the amount of Lewis acid present has an effect.

In addition, in the system to which 5 ml or more of sulfuric acid was added, the ORP was as high as 440 mV or more. When thiourea was added to the post-decomposition liquid with an ORP of 440 mV or more, red selenium was produced. This is a reaction peculiar to selenous acid, and it can be seen that selenosulfuric acid produced selenous acid by acid decomposition.

(Experimental example 3)
A 200 ml portion of an aqueous solution containing selenosulfuric acid (Se concentration 20.5 g/L, pH 8.9, ORP-183 mV) derived from slag containing precious metals was collected. The amount of acid shown in Table 4 was added to the selenosulfuric acid-containing aqueous solution, and the temperature was adjusted to 70°C. A sample was taken after 30 minutes. Further, a reducing agent shown in Table 4 was added and stirred for 60 minutes. The reducing gas is a mixed gas of sulfur dioxide and air produced by mixing sulfite and sulfuric acid with sulfite water and aeration. After completion, samples were filtered and pH and ORP were measured. After diluting with dilute hydrochloric acid, the selenium concentration was measured by ICP-OES.

Effective selenium removal was observed in experimental conditions 20-23. By adjusting the acid concentration and heating, the selenium of selenosulfuric acid can be precipitated and recovered, but by adding a reducing agent, the selenium concentration can be greatly reduced.

Even when sulfuric acid is insufficiently added, the addition of a reducing agent is effective. However, adjusting the final acid concentration to pH 0.5 or less enhances the effect.

The resting potential of selenite is 480 mV as viewed by ORP. The ORP is about 200 mV as seen in Experimental Condition 18 when the predominant species in the system is selenosulfate ion in the acidic region. Therefore, in order to use the reducing agent efficiently, the acid is added until the ORP reaches 200 mV or more. More preferably, the reducing agent is added after reaching 480 mV or higher.

Claims (10)

A method for treating a solution containing selenosulfuric acid, comprising the steps of adding an acid to a solution containing selenosulfuric acid to precipitate selenium, and further adding a reducing agent to precipitate selenium. 2. The treatment of a solution containing selenosulfuric acid according to claim 1, wherein the amount of acid added when precipitating the selenium is such that the pH of the final solution after the precipitation of selenium is 0.5 or less. Method. 3. The selenosulfuric acid according to claim 1 or 2, wherein the acid added to the solution containing selenosulfuric acid is hydrochloric acid or sulfuric acid, and the acid concentration of the solution after adding the acid is adjusted to 1N or higher. How to treat the contained solution. 4. Selenium is precipitated as black selenium by adding the acid and the reducing agent while the solution containing selenosulfuric acid is heated to 70° C. or higher. A method for treating a solution containing selenosulfuric acid according to any one of . Selenium is precipitated as red selenium by adding the acid and the reducing agent while the solution containing selenosulfuric acid is adjusted to 50° C. or less. A method for treating a solution containing selenosulfuric acid according to any one of claims 1 to 3. Any one of claims 1 to 5, wherein the reducing agent comprises at least one selected from the group consisting of sulfur dioxide, sodium sulfite, sodium hydrogen sulfite, iron (II) salt, thiourea, acetone and base metals. A method for treating a solution containing selenosulfuric acid according to claim 1. The method for treating a solution containing selenosulfuric acid according to any one of claims 1 to 6, wherein the solution containing selenosulfuric acid contains 0.1 g/L or more of selenium. 3. The solution containing selenosulfuric acid is adjusted to have an oxidation-reduction potential of 200 mV or more with silver/silver chloride as a reference electrode by adding the acid before adding the reducing agent. A method for treating a solution containing selenosulfuric acid according to any one of 1 to 7. 9. The solution according to any one of claims 1 to 8, wherein the solution containing selenosulfuric acid is a solution obtained by adding sodium sulfite to a solution containing selenium in an electrolytic slime treatment step in a copper smelting process. A method for treating a solution containing selenosulfuric acid according to the above item. The solution containing selenosulfuric acid is put into a tank for reducing and recovering selenium from the selenous acid-containing liquid in the electrolytic slime treatment process in the copper smelting process, and the acid is added and the reducing agent is added. The method for treating a solution containing selenosulfuric acid according to any one of claims 1 to 9.