JP2015063434A - Arsenic exudation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exude pentavalent arsenic.SOLUTION: Sodium carbonate is added to slurry comprising sulfide precipitate comprising basic copper arsenate, and pentavalent arsenic is exuded in the slurry for separation.

Description

  The present invention relates to an arsenic leaching method for leaching arsenic from a sulfided starch containing basic copper arsenate.

  Copper ore contains arsenic as an impurity. As a method for smelting copper from copper ore, for example, there is a dry method using a flash smelting furnace. When copper is smelted by a dry process, arsenic is distributed to mats and slag, but part of it is volatilized and distributed to exhaust gas.

  Arsenic distributed to the mat is transferred to copper-free slime generated in the liquid purification process in the electrolytic purification.

  On the other hand, arsenic distributed to the exhaust gas is transported to the sulfuric acid production process and transferred to waste acid generated in the gas purification process during sulfuric acid production. Furthermore, arsenic in the waste acid is contained in the sulfided starch by sulfidation treatment for removing heavy metals.

  In addition to arsenic, valuable copper is included in decopperized slime and sulfide starch. Therefore, in copper smelting, the produced decoppered slime and sulfide starch are again input into the copper smelting process, and valuable materials are recovered. In copper smelting, arsenic should be separated from decoppered slime and sulfide before re-injection so that arsenic, an impurity, does not accumulate in the copper smelting process by reintroducing decoppered slime and sulfide. Is desired.

  Furthermore, the separated arsenic may be harmful or toxic in the form of compounds such as oxides and chlorides. For this reason, it is desirable that arsenic is insoluble and has good cleaning properties in consideration of long-term storage management.

Generally, crystalline scorodite (FeAsO ₄ .2H ₂ O), which is iron arsenate, is a stable compound, and is known to be excellent in insolubility and detergency and suitable for long-term storage.

  Crystalline scorodite can be produced by leaching arsenic from a raw copper-free slime or sulfide starch with an acid or alkali, and then adding iron (for example, iron sulfate) to the obtained arsenic-containing liquid.

Since crystalline scorodite arsenic has a pentavalent valence, the arsenic valence in the arsenic-containing liquid needs to be pentavalent. However, when a sulfide starch is used as a raw material, arsenic is trivalent because it is contained as arsenic sulfide and is in the form of As ₂ S ₃ . Therefore, it is necessary to make pentavalent after leaching out arsenic in As ₂ S ₃ .

First, in order to leach arsenic from arsenic sulfide, first, copper sulfate is added to the slurry containing sulfide starch, and a substitution reaction is performed in which arsenic is a arsenous acid (HAsO ₂ ) solution and copper is copper sulfide. Next, the leached arsenous acid is oxidized to arsenic acid (H ₃ AsO ₄ ), and the valence of arsenic is made pentavalent. Here, in order to facilitate the oxidation of arsenic, it is preferable to increase the pH (see, for example, Patent Document 1). When the pH is increased, arsenic is precipitated as basic copper arsenate (Cu ₂ (AsO ₄ ) (OH)) by copper ions of copper sulfide.

  Arsenic in basic copper arsenate is pentavalent. Therefore, a raw material solution of crystalline scorodite can be obtained by releaching arsenic from this basic copper arsenate. There is a method of leaching arsenic using acid or alkali.

  In the case of re-leaching with an acid, a large amount of copper is also leached simultaneously with arsenic, and a raw material solution that can produce good crystalline scorodite cannot be obtained.

  On the other hand, since basic copper arsenate dissolves in an alkali, it can be re-leached using sodium hydroxide which is often used industrially. Furthermore, it is preferable to increase the pH because the arsenic valence can be maintained at pentavalent. Basic copper arsenate is contained in the sulfurized starch remaining without reacting. Therefore, sulfurized starch containing basic copper arsenate will be leached with sodium hydroxide, but when sulfurized starch was leached with alkali, sulfur contained in the sulfided starch was leached and leached. Sulfur and sodium hydroxide react to produce sodium thiosulfate.

  When producing crystalline scorodite, it is necessary to lower the pH to 2 or less using sulfuric acid. At the time of pH adjustment, sodium thiosulfate and sulfuric acid react, sulfur is leached, and sulfur dioxide gas is generated (see, for example, Non-Patent Document 1).

  Since the produced sulfur dioxide acts as a reducing agent, pentavalent arsenic is reduced to trivalent, and is no longer suitable as a raw material liquid for crystalline scorodite.

  Therefore, if the temperature and pH during leaching are lowered in order to suppress sulfur leaching when leaching arsenic again, sufficient arsenic leaching will not be performed. Therefore, when leaching of arsenic is performed using sodium hydroxide, which is often used industrially, it is difficult to simultaneously satisfy the suppression of sulfur leaching and the increase of the arsenic leaching rate.

  Therefore, there is a need for a method that can simultaneously suppress sulfur leaching and increase the arsenic leaching rate.

JP 2005-000823 A

Edited by Seiji Takagi, 41st edition of “New Revised Qualitative Analytical Chemistry”, Nankodo Co., Ltd., April 1, 1991, p273-274

  Therefore, the present invention has been proposed in view of such circumstances, suppressing the leaching of copper which hinders the production of crystalline scorodite, and leaching arsenic from sulfided starch containing basic copper sulfate under alkaline conditions. It is an object of the present invention to provide an arsenic leaching method that can suppress sulfur leaching and increase the arsenic leaching rate.

  In the arsenic leaching method according to the present invention that achieves the above-mentioned object, sodium carbonate is added to a slurry containing a sulfurized starch containing basic copper arsenate, and arsenic is leached into the slurry to separate it from the sulfided starch. .

  In the present invention, leaching of copper can be suppressed, and even if arsenic is leached from a sulfided starch containing basic copper sulfate under alkaline conditions, the leaching of sulfur can be suppressed and the arsenic leaching rate can be increased.

  The arsenic leaching method to which the present invention is applied will be described below. Note that the present invention is not limited to the following detailed description unless otherwise specified.

The arsenic leaching method is a method in which sodium carbonate is added to a slurry containing a sulfided starch containing basic copper arsenate, and arsenic is leached into the slurry and separated from the sulfided starch. This arsenic leaching method is, for example, when leaching arsenic from sulfide starch generated in a sulfuric acid production process using exhaust gas incorporated in a copper smelting process for smelting copper from copper ore using a flash furnace. Can be used. This arsenic leaching method can leach pentavalent arsenic that can produce stable crystalline scorodite (FeAsO ₄ .2H ₂ O) at a high leaching rate.

<Arsenic leaching from arsenic sulfide>
Arsenic contained in the exhaust gas shifts to waste acid generated during the production of sulfuric acid. Furthermore, arsenic in the waste acid is contained in the form of arsenic sulfide (As ₂ S ₃ ) in the sulfurized starch produced by the sulfiding treatment for removing heavy metals. Therefore, arsenic is leached from this arsenic sulfide.

In the method of leaching arsenic from arsenic sulfide, first, a copper source such as copper sulfate or copper powder is added to the slurry of the sulfide starch. When copper sulfate or copper powder is added to the slurry, arsenic is leached by the substitution reaction shown in the following formula 1. Arsenous acid (HAsO ₂ ) obtained by the substitution reaction has a valence of arsenic of three.
As ₂ S ₃ + 4H ₂ O + 3CuSO ₄ ⇒ 3H ₂ SO ₄ + 2HAsO ₂ + 3CuS
... (Formula 1)

Next, the valence of arsenic contained in arsenous acid is changed from trivalent to pentavalent. Since arsenic of crystalline scorodite has a pentavalent valence, it is made pentavalent suitable for the production of crystalline scorodite. Arsenic oxidation is performed under alkaline conditions by adding an oxidizing agent such as air to the leachate after the substitution reaction. Arsenic is more easily oxidized from trivalent to pentavalent under alkaline conditions than under acidic conditions. For this reason, the oxidation reaction is performed under alkaline conditions. Arsenous acid is oxidized to arsenic acid as shown in the following formula 2, but reacts with copper sulfide contained in the leachate under alkaline conditions to react with basic copper arsenate (Cu ₂₎ having pentavalent arsenic. Precipitate as (AsO ₄ ) (OH)).
2HAsO ₂ + 2H ₂ O + O ₂ ⇒2H ₃ AsO ₄ (Formula 2)

<Leaching of pentavalent arsenic from basic copper arsenate>
Next, pentavalent arsenic is re-leached from basic copper arsenate. This re-leaching of pentavalent arsenic is performed using an alkaline agent. As the alkaline agent, sodium carbonate is used instead of sodium hydroxide.

When sodium carbonate is used as the alkaline agent, arsenic is leached as sodium arsenate as shown in the following formula 3, and pentavalent arsenic can be leached. Copper can be precipitated and removed as copper carbonate. Thereby, copper can be prevented from leaching together with arsenic. Most of the copper in basic copper arsenate precipitates as copper carbonate, but in the presence of excess sodium carbonate, a small amount of copper dissolves and exists as copper ions in the leachate.
2Cu ₂ (AsO ₄ ) (OH) + 3Na ₂ CO ₃ + H ₂ O
⇒2Na ₃ AsO ₄ + 2CuCO ₃ .Cu (OH) ₂ + CO ₂
... (Formula 3)

  Here, when sodium carbonate is added and arsenic is leached again under alkaline conditions, sulfur is dissolved from the sulfurized starch, and dissolved sulfur-derived sodium thiosulfate is produced. This sodium thiosulfate has sulfur having a valence of -2 in the molecule. -2-valent sulfur cannot coexist with copper ions in the liquid, and precipitates copper sulfide. That is, sulfur reacts with a trace amount of copper in the presence of excess sodium carbonate, precipitates as copper sulfide, and is removed from the re-leaching solution.

  Thereby, for example, when producing crystalline scorodite in the next step, generation of sulfur dioxide can be prevented even if the pH is adjusted to 2 or less with sulfuric acid or the like. Therefore, it is possible to prevent the generated pentavalent arsenic from being reduced to trivalent by sulfur dioxide.

  In the arsenic leaching method as described above, when arsenic is leached again from basic copper arsenate, the leaching of copper can be suppressed by using sodium carbonate as an alkaline agent without using an acid. In the arsenic leaching method, when arsenic is leached again from basic copper arsenate, leaching of pentavalent arsenic can be suppressed by using sodium carbonate instead of sodium hydroxide as an alkaline agent. The rate can be increased.

  Therefore, such an arsenic leaching method can recover arsenic at a high recovery rate from sulfides containing arsenic discharged in the sulfuric acid production process included in the copper smelting process. It is suitable for removing arsenic, which is an impurity, in advance when an object is reintroduced to recover valuable metals.

Further, in this arsenic leaching method, copper is not contained, and a large amount of pentavalent arsenic can be leached. Therefore, the arsenic leaching method is used for producing a raw material solution for producing good crystalline scorodite (FeAsO ₄ .2H ₂ O). be able to.

  Specific examples to which the present invention is applied will be described below, but the present invention is not limited to these examples.

(Example)
In Examples, 36 g by dry weight of sulfide starch having the composition shown in Table 1 below, 33 g of copper powder, and 9 g of copper sulfate pentahydrate were added to 300 ml of water to form a slurry.

  Next, the slurry was heated at 80 ° C., and stirred and mixed for 5 hours while blowing air. The pH during stirring and mixing was stable between 3.5 and 4.0. Arsenic in the obtained leachate was 3 mg / l. From the pH range, it was judged that arsenic was precipitated as basic copper arsenate.

  Next, re-leaching of arsenic from the obtained residue was performed. First, in re-leaching, 300 ml of water was added to 20 g of residue by dry weight, and the mixture was stirred and mixed to prepare a slurry.

  In the next step, the slurry was heated to 80 ° C., and 50 g of sodium carbonate (purity 99.8%: manufactured by Kanto Chemical Co., Ltd .: special grade) was added. After the addition, the mixture was stirred for 1 hour while maintaining the temperature at 80 ° C. The pH in the re-leaching solution was 10.2, the arsenic concentration was 2.5 g / l, the sulfur concentration was 2.4 g / l, and the copper concentration was 0.6 g / l. Concentration was performed using ICP emission spectrometry.

  Next, 58 ml of a 64% by weight aqueous sulfuric acid solution was added to the re-leaching solution and the pH was adjusted to be between 0 and 1. Sulfur precipitation and generation of sulfur dioxide could not be confirmed. As a result of analysis of the arsenic valence in the re-leaching solution, the existence ratio of pentavalent arsenic, that is, the leaching rate was 95%. The valence analysis was performed using a solvent extraction method using diethyldithiocarbamine diethylammonium and ICP (Inductively Coupled Plasma) mass spectrometry.

  In the above examples, it is understood that even when arsenic re-leaching is performed under alkaline conditions, sulfur leaching and sulfur dioxide generation are suppressed, and pentavalent arsenic can be leached at a high leaching rate. Further, in the examples, since leaching of arsenic is not performed using an acid, copper leaching can be suppressed. When leaching of arsenic is performed using an acid, copper of several tens of g / l is leached, and in comparison with the example, the leaching of copper is 0.6 g / l. Yes.

(Comparative example)
In a comparative example, 90 g by dry weight of a sulfide starch having the composition shown in Table 1, 33 g of copper powder, and 9 g of copper sulfate pentahydrate were added to 300 ml of pure water to form a slurry.

  Next, the slurry was heated at 80 ° C., and stirred and mixed for 5 hours while blowing air. The pH during stirring and mixing was stable between 3.5 and 4.0. Arsenic in the obtained leachate was 3 mg / l. From the pH range, it was judged that arsenic was precipitated as basic copper arsenate.

  Next, re-leaching of arsenic from the obtained residue was performed. First, in re-leaching, 300 ml of water was added to 20 g of residue by dry weight, and the mixture was stirred and mixed to prepare a slurry.

  In the next step, the slurry was heated to 80 ° C., and then 9 ml of an aqueous sodium hydroxide solution (concentration 8 mol / l: manufactured by Wako Pure Chemical Industries, Ltd .: for volumetric analysis) was added. After the addition, the mixture was stirred for 1 hour while maintaining the temperature at 80 ° C. The pH in the leaching solution was 10.3, the arsenic concentration was 1.1 g / l, the sulfur concentration was 3.7 g / l, and the copper concentration was 0.03 g / l. Concentration was performed using ICP emission spectrometry.

  Next, 58 ml of sulfuric acid aqueous solution having a concentration of 64% by weight was added to the re-leaching solution to adjust the pH between 0 and 1, and sulfur precipitation and generation of sulfur dioxide were confirmed. As a result of analysis of the valence of arsenic in the re-leaching solution, the presence ratio of pentavalent arsenic, that is, the leaching rate was 1%. For the analysis of the valence, a solvent extraction method using diethyldithiocarbamine diethylammonium and ICP mass spectrometry were used.

  In the comparative example, since the leaching of arsenic was performed under alkaline conditions, the leaching of copper was suppressed, but sulfur and sulfur dioxide were generated, and pentavalent arsenic was hardly leached. Therefore, it can be seen that the method of the comparative example cannot re-extract pentavalent arsenic from the sulfided starch containing basic copper arsenate.

Claims (2)

  A method for leaching arsenic in which sodium carbonate is added to a slurry containing a sulfide sulfide containing basic copper arsenate, and pentavalent arsenic is leached into the slurry and separated from the sulfide starch.   The arsenic leaching method according to claim 1, wherein the sulfided starch is a sulfided starch generated in a sulfuric acid production process included in a copper smelting process using a flash smelting furnace.