JP6233177B2 - Method for producing rhenium sulfide - Google Patents

Description

  The present invention relates to a method for producing high-purity rhenium sulfide from a sulfide containing rhenium, cadmium, arsenic and the like recovered in a non-ferrous metal smelting process.

Rhenium is a rare metal used as an additive element and catalyst for special alloys, and is naturally contained in molybdenite (MoS ₂ ), which is a raw material of molybdenum. In the smelting process of molybdenum, oxidation roasting of molybdenite is performed to solubilize molybdenum. At the time of this oxidation roasting, rhenium contained in molybdenite is separated from molybdenite as a volatile oxide Re ₂ O ₇ , recovered in a cleaning process such as a scrubber, and then purified.

In addition, it is known that pyroxenite coexists with copper minerals such as chalcopyrite (CuFeS ₂ ), but these hydropyrite and chalcopyrite are separated by a general method such as flotation. It is difficult. For this reason, when copper is obtained from chalcopyrite by dry smelting using a furnace such as a blast furnace located at the subsequent stage of flotation, pyroxenite is also charged into the furnace at the same time. As a result, volatilized rhenium is mixed in the exhaust gas mainly composed of sulfurous acid gas discharged from the furnace.

  In addition to the above rhenium, the exhaust gas sent to the sulfuric acid production plant contains arsenic contained in copper ore, volatilized or scattered copper, zinc, cadmium, and other solid or liquid fine particles (also called fumes). Floating). In order to remove these impurities, the exhaust gas is subjected to a cleaning process using a scrubber or the like as a pretreatment in the sulfuric acid production process. Since rhenium contained in the exhaust gas is also separated by this cleaning process, it is necessary to selectively recover only rhenium from the above-described many types of elements.

  As a method for selectively recovering only rhenium from a solution in which a plurality of elements coexist, a separation method using an anion exchange resin has been proposed. For example, in Patent Document 1, hydrogen sulfide gas is blown in a state in which the sulfuric acid concentration is maintained at 70 g / L or more with respect to the cleaning waste liquid generated when the exhaust gas containing sulfurous acid gas generated in the nonferrous metal smelting process is washed with water. Or a soluble sulfide is added, and a sulfide containing rhenium is precipitated under the condition of an oxidation-reduction potential of 120 to 150 mV (vs. silver-silver chloride electrode), and the resulting sulfide precipitate is dissolved in an acidic aqueous solution. Rhenium from a non-ferrous metal smelting process in which an aqueous solution containing rhenium is mixed with copper sulfate, and the aqueous solution containing rhenium is brought into contact with a quaternary ammonium salt anion exchange material to selectively adsorb and recover rhenium. A recovery method is disclosed.

  However, the method disclosed in Patent Document 1 has a problem that an aqueous solution of ammonium thiocyanate is required for elution of rhenium adsorbed on the anion exchange resin. In other words, when ammonium thiocyanate is decomposed, toxic cyanide ions are generated, so special considerations are required in the working environment. Wastewater containing a compound in which ammonium thiocyanate is decomposed must be treated with chemical oxygen demand (COD) and nitrogen. Since the concentration increases, there is a problem that the wastewater treatment cost increases. Also, ion exchange resins are not preferred in that the equipment cost is high.

  Therefore, a method for precipitating impurities other than rhenium using an alkali has been proposed instead of the above method using an anion exchange resin. For example, in Patent Document 2, oxidation leaching is performed on sulfide containing at least rhenium and arsenic obtained by sulfiding the exhaust gas containing sulfurous acid gas, and the obtained leachate is neutralized with alkali. A method for obtaining rhenium sulfide having a low arsenic quality by separating and removing arsenic as an impurity in a stable form is disclosed.

  Specifically, cleaning wastewater containing various impurity elements such as rhenium, cadmium, and arsenic discharged from the cleaning process of washing exhaust gas from the smelting process of a non-ferrous metal smelting plant containing sulfurous acid gas. After the impurity element is recovered as sulfided starch by sulfidation treatment, the sulfided starch is treated in the following leaching process, neutralization liquid purification process, rhenium recovery process, and starch treatment process to obtain rhenium. Is recovered as rhenium sulfide.

(Leaching process)
In the leaching step, repulping is performed by adding a liquid containing sulfuric acid as a main component to the sulfide starch. Oxidation leaching is performed by blowing high-temperature air into the slurry obtained by repulping. Thus, a leachate having a pH of about 0 containing rhenium and some other various elements is obtained. At the same time, elements that were not leached by the oxidative leaching are concentrated to obtain a leaching residue.

(Neutralization and purification process)
In the neutralization liquid purification step, for example, caustic soda is added to the leachate as a neutralizing agent, and neutralized at about pH 7. Thereby, the neutralized filtrate which rhenium was concentrated is obtained. At that time, elements other than rhenium are recovered as neutralized starch and repeated in the smelting process.

(Rhenium recovery process)
In the rhenium recovery step, sulfuric acid is added to the neutralized filtrate to adjust the pH to almost zero, and sodium hydrosulfide is added to perform sulfuration treatment. Thereby, rhenium in the neutralized filtrate is recovered as rhenium sulfide. The waste liquid after the recovery of rhenium sulfide is treated in the wastewater treatment process.

(Starch processing step)
The leaching residue obtained in the aforementioned leaching step is divided into a residue and a waste liquid in the starch treatment step. The residue is repeated in the smelting process, and the waste liquid is treated in the wastewater treatment process.

  However, in the method of Patent Document 2 described above, when the cadmium grade of sulfide ore such as chalcopyrite, which is a raw material for non-ferrous metal smelting, increases, the cadmium concentration in the cleaning effluent from the exhaust gas cleaning process increases accordingly. In some cases, the cadmium quality in rhenium sulfide may not satisfy the general management regulation value of 0.2% by mass or less. As a result, there is a problem that the actual yield when rhenium is obtained from rhenium sulfide is lowered.

JP 7-286221 A International Publication No. 2013/129130

  The present invention has been made in view of the above-described conventional situation, and the cadmium grade of sulfide ore such as chalcopyrite, which is a raw material for non-ferrous metal smelting, is increased, and cadmium in the cleaning effluent from the exhaust gas cleaning process is increased. It is an object of the present invention to provide a method for producing rhenium sulfide capable of suppressing the cadmium quality in rhenium sulfide recovered from the washing waste liquid to a desired control regulation value or less even when the concentration becomes high.

In order to achieve the above object, the rhenium sulfide production method of the present invention includes a leaching step of obtaining an leaching solution by oxidizing and leaching a raw material containing at least rhenium, cadmium, and arsenic; A method for producing rhenium sulfide, comprising: a neutralization purification step for obtaining a neutralized precipitate containing and a neutralized filtrate containing rhenium; and a rhenium recovery step for recovering rhenium sulfide from the neutralized filtrate, In the neutralization and purification step, caustic soda is first added to the leachate as an alkali and neutralized at pH 6.6 to 7.2, and then a calcium-based neutralizing agent is added as an alkali to pH 7. It is characterized by neutralizing at 5 to 8.5 .

  According to the present invention, the cadmium quality of sulfide ore such as chalcopyrite as a raw material for the nonferrous metal smelting process is increased, and the cadmium concentration in the cleaning effluent in the cleaning process of the exhaust gas from the nonferrous metal smelting process is high. Even so, the cadmium quality in the rhenium sulfide recovered from the washing waste liquid can be suppressed to a desired control regulation value or less.

1 is a schematic block flow diagram showing a method for producing rhenium sulfide according to an embodiment of the present invention.

  Hereinafter, a method for producing rhenium sulfide according to an embodiment of the present invention will be described with reference to FIG. The method for producing rhenium sulfide according to one embodiment of the present invention includes a leaching step 1 in which a raw material containing at least rhenium, cadmium, and arsenic is oxidized and leached to obtain a leachate, and an alkali is added to the leachate to add cadmium and arsenic. It consists of a neutralization purification process 2 for obtaining a neutralized precipitate containing and a neutralized filtrate containing rhenium, and a rhenium recovery process 3 for recovering rhenium sulfide from the neutralized filtrate. And the leaching residue remaining after obtaining the leaching solution in the leaching step 1 is processed in the starch treatment step 4 and divided into a residue and a waste solution. The residue is repeated in the smelting process, and the waste liquid is treated in the wastewater treatment process.

  Among these steps, in the neutralization and purification step 2, the leachate is neutralized at about pH 7 and solid-liquid separation is performed to obtain a neutralized filtrate enriched with rhenium. Conventionally, cadmium in the raw material is used. If the quality is high, the concentration of cadmium remaining in the neutralized filtrate also increases. For example, the cadmium concentration of the neutralized filtrate sometimes exceeds 40 mg / L. As a result, the cadmium quality in the rhenium sulfide obtained in the subsequent rhenium recovery step may exceed the general management regulation value of 0.2% by mass.

  Therefore, in the method for producing rhenium sulfide according to one specific example of the present invention, the neutralization purification step 2 is divided into a first neutralization purification step 2a and a first neutralization purification step 2b. In the liquid step 2a, neutralization is performed by adding caustic soda as an alkali to the leachate, and then neutralizing at a higher pH by adding a calcium-based neutralizing agent such as slaked lime as an alkali in the first neutralization liquid purification step 2b. To do.

  More specifically, first, caustic soda as an alkali is added to the leachate in the first neutralization purification step 2a, and neutralization is preferably performed at a pH of 6.6 or more and 7.2 or less. As a result, the pH of the leachate can be raised to some extent using caustic soda with little scaling to the equipment, and the first neutralization purification step 2b from 7.5 to 8.5, which is a desirable pH range for removing impurities. The amount of calcium-based neutralizing agent such as slaked lime required to increase the pH of the leachate can be reduced.

  If the pH when the caustic soda is added is less than 6.6, the amount of calcium-based neutralizing agent such as slaked lime increases, which may cause scaling of the equipment. If scaling occurs in the equipment, for example, the slurry feeding pipe generated by the reaction may be blocked and the operation may be interrupted, or the substantial capacity of the reaction tank may decrease and the reaction may become uneven. May occur. On the other hand, when the pH when caustic soda is added exceeds 7.2, it becomes difficult to raise the pH while suppressing re-dissolution of arsenic.

  Next, in the 2nd neutralization liquid purification process 2b, calcium-type neutralizing agents, such as slaked lime, are added as an alkali, and it neutralizes suitably at pH 7.5 or more and 8.5 or less. Thus, cadmium can be efficiently removed by coprecipitation with calcium by adding a calcium-based neutralizing agent and raising the pH to the above range. As a result, in the conventional method, even if the cadmium concentration in the neutralized filtrate obtained in the neutralization liquid purification step exceeds 40 mg / L, the cadmium concentration in the neutralized filtrate is 10 mg / L or less. It becomes possible to. Thus, if the cadmium concentration in the neutralized filtrate is 10 mg / L or less, the cadmium quality in rhenium sulfide can be suppressed to 0.2 mass% or less in the subsequent rhenium recovery step 3.

  As described above, in the method for producing rhenium sulfide according to one specific example of the present invention, the cadmium concentration in the neutralized filtrate is reduced by utilizing coprecipitation with calcium contained in a calcium-based neutralizing agent such as slaked lime. Yes. This makes it possible to efficiently perform cadmium hydroxide precipitate formation at a pH lower than the theoretical value. If the pH at the time of neutralization in the first neutralization / purification step 2b is less than 7.5, the cadmium precipitate may be insufficient. On the other hand, if the pH at the time of neutralization in the first neutralization and purification step 2b exceeds 8.5, re-dissolution of arsenic may not be suppressed even if a calcium-based neutralizing agent such as slaked lime is added.

  In the above-described method for producing rhenium sulfide according to one embodiment of the present invention, when caustic soda is added as an alkali in the first neutralization liquid purification step 2a, an iron compound such as a divalent water-soluble iron compound, air, etc. It is preferable to add an oxidizing agent. As a result, the arsenic quality in rhenium sulfide can be kept at a low value, in contrast to the conventional method. Specifically, the arsenic concentration in the neutralized filtrate can be suppressed to 10 mg / L or less, and as a result, the arsenic quality in rhenium sulfide can be reduced to 1.0 mass% or less.

  Thus, the arsenic concentration in the neutralized filtrate is reduced because the arsenic in the leachate is fixed as arsenate by the neutralization reaction of the following reaction formula 1, and then the arsenate obtained is divalent. This is because a water-soluble iron compound and an oxidizing agent can be reacted to precipitate and remove as iron arsenate. In the reaction example of the following reaction formula 1, arsenate was formed with copper ions, but arsenate is similarly formed with other metal ions.

[Reaction Formula 1]
2H ₃ AsO ₄ + 3CuSO ₄ + 6NaOH
→ Cu ₃ (AsO ₄ ) ₂ + 3Na ₂ SO ₄ + 6H ₂ O

  However, when the pH is raised to pH 7.5 to 8.5 suitable for cadmium removal as described above, the arsenate produced by the reaction formula 1 may start to redissolve. The degree of re-dissolution varies depending on the type of alkali added, and arsenic re-dissolution can be suppressed by increasing the pH by adding a calcium-based neutralizing agent such as slaked lime rather than adding caustic soda. This is presumably because calcium arsenate produced by the addition of a calcium-based neutralizing agent such as slaked lime has lower solubility and is less likely to be redissolved than sodium arsenate produced by the addition of caustic soda.

  For the above reasons, a calcium-based neutralizer such as slaked lime is used for the alkali added after the addition of caustic soda. Thereby, cadmium can be removed while suppressing re-dissolution of arsenic. That is, rhenium sulfide having low cadmium quality and arsenic quality can be obtained. As the calcium-based neutralizing agent added after the addition of caustic soda, a calcium-based neutralizing agent containing at least one of calcium oxide (quick lime), calcium carbonate (lime carbonate), and calcium hydroxide (slaked lime) is preferable. . Among these, calcium hydroxide (slaked lime) is more preferable because it is easily available and inexpensive.

  As a method of adding a calcium-based neutralizing agent such as slaked lime to the leachate, for example, a calcium-based neutralizing agent such as slaked lime may be mixed with process water and added as a slurry, but calcium having a maximum particle size of 1 mm or less. If it is a system neutralizing agent, it may be added as it is without forming a slurry. Examples of such a calcium-based neutralizing agent having a maximum particle size of 1 mm or less include JIS standard special name slaked lime. Such a JIS standard special slaked lime powder is preferable because it can be easily obtained, for example, in a package of 20 kg per bag, and facilities such as an agitation tank and an agitation blade for preparing slurry are not necessary.

(Example)
Washed effluent discharged from a washing tower for washing exhaust gas containing sulfurous acid gas generated at a copper smelting plant was sulfurized using sodium hydrosulfide to recover sulfided starch containing rhenium. This sulfurized starch was repulped with a 100-200 g / L sulfuric acid aqueous solution, and steam was blown into the slurry so that the temperature of the resulting slurry was 70 ° C., and oxidative leaching was performed. As a result, a leachate having a pH of about 0 was obtained. When this leachate was analyzed using ICP, the cadmium concentration was 10.4 g / L and the arsenic concentration was 39.1 g / L. In the subsequent analysis, ICP was used for the concentration analysis of cadmium and arsenic.

  The leaching solution is neutralized at the first stage by adding 20% by mass of caustic soda so that the pH becomes 6.8 at 25 ° C., and then JIS standard special name so that the pH becomes 8.0. Of slaked lime was added and neutralized in the second stage to produce a neutralized starch. The neutralized starch was removed using a filter press to obtain a neutralized filtrate. When impurities in the neutralized filtrate were analyzed, the cadmium concentration was 1.93 mg / L and the arsenic concentration was 1.90 mg / L.

  Next, 200-300 g / L sulfuric acid aqueous solution and NaHS (manufactured by Sankyo Kasei Co., Ltd., flake sodium hydrosulfide) were added to the neutralized filtrate to recover rhenium as rhenium sulfide. When the impurity quality of the obtained rhenium sulfide was analyzed, the cadmium quality was 0.07% by mass, and the arsenic quality was 0.73% by mass. Furthermore, when the operation was performed for one month under the above treatment conditions, no cadmium grade of rhenium sulfide as a product exceeded 0.2% by mass.

(Comparative example)
An leaching solution was obtained by oxidative leaching in the same manner as in the above example. This leaching solution had a cadmium concentration of 10.7 g / L and an arsenic concentration of 33.5 g / L. The leachate was neutralized by adding 20% by mass of caustic soda to a pH of 7.1 at 25 ° C. to produce neutralized starch. Thereafter, neutralized starch was removed in the same manner as in the Examples, and rhenium sulfide was recovered from the obtained neutralized filtrate.

  As a result, the impurities in the neutralized filtrate had a cadmium concentration of 45.0 mg / L and an arsenic concentration of 1.10 mg / L. The impurity grade of rhenium sulfide was 0.65% by mass for cadmium grade and 0.22% by mass for arsenic grade. As described above, the arsenic quality was 1.0% by mass or less, but the cadmium quality was 0.2% by mass or more. Furthermore, when one month operation was carried out under the above processing conditions, all the rhenium sulfide products exceeded 0.2% by mass of cadmium quality.

Claims (4)

A leaching step of obtaining a leachate by oxidatively leaching a raw material containing at least rhenium, cadmium and arsenic, and a neutralized precipitate containing cadmium and arsenic by adding alkali to the leachate and a neutralized filtrate containing rhenium A rhenium sulfide production method comprising a neutralizing and purifying step for obtaining and a rhenium collecting step for recovering rhenium sulfide from the neutralized filtrate, wherein in the neutralizing and purifying step, caustic soda is first added as an alkali to the leachate. After neutralizing at pH 6.6 to 7.2, a calcium-based neutralizing agent is subsequently added as an alkali and neutralized at a higher pH of pH 7.5 to 8.5 . Production method. 2. The rhenium sulfide according to claim 1, wherein the calcium-based neutralizer includes at least one of calcium oxide (quick lime), calcium carbonate (lime carbonate), and calcium hydroxide (slaked lime). Production method. The method for producing rhenium sulfide according to claim 1 or 2 , wherein the calcium-based neutralizing agent is in a powder form having a maximum particle size of 1 mm or less. The raw material containing at least rhenium, cadmium, and arsenic is recovered from a cleaning effluent discharged from a cleaning step of washing exhaust gas containing sulfurous acid gas generated from a non-ferrous metal smelting plant, The manufacturing method of rhenium sulfide in any one of Claims 1-3 .

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