JP2013159821A - Method for recovering palladium from palladium-containing selenium powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for selectively separating and recovering palladium from palladium-containing selenium powder.SOLUTION: Palladium-containing selenium powder is dissolved at a liquid temperature of 55°C or lower by adding hydrochloric acid and an oxidizer to the palladium-containing selenium powder (dissolution step); an organic solvent, preferably, containing 20-25 vol.% of dihexyl sulfide is brought into contact with the resulting solution to extract only palladium to the organic solvent (extraction step); and an ammonium water is brought into contact with the organic solvent including the extracted palladium to reversely extract the palladium to an aqueous phase (reverse extraction step), whereby palladium is separated and recovered from the selenium powder.

Description

  More particularly, the present invention relates to a method of recovering valuable palladium contained in the selenium powder by treating selenium powder generated as an intermediate in the process of treating copper electrolytic slime. About.

  In the treatment of copper electrolytic slime (also referred to as anode slime) generated in the copper refining electrolytic refining process, both the dry method and the wet method have been put to practical use. However, considering the equipment cost and environmental load, etc. The method is considered more useful.

  For example, Patent Document 1 discloses a method for treating copper electrolytic slime by a wet method. In this treatment method, water is first added to copper electrolytic slime to form a slurry, and then treated with chlorine to leach valuable metals such as gold, platinum group, selenium and tellurium, and the obtained leachate is bismuthed. Contact with (2-butoxyethyl) ether to extract and separate the gold in the leachate into the organic phase.

  Next, the platinum group element is extracted from the extracted residue after gold extraction using a mixture of trioctylammonium chloride and tributyl phosphate. Furthermore, after adding sulfur dioxide to the extraction residual liquid after extraction of the platinum group element, the oxidation-reduction potential is maintained at 400 to 500 mV, and selenium is selectively maintained by maintaining the liquid temperature at 50 to 80 ° C. Reduce. Thereby, selenium is recovered as selenium powder. Finally, tellurium is reduced and recovered by maintaining the redox potential of the liquid after selenium reduction at 290 to 380 mV.

  However, the copper electrolytic slime contains various elements such as barium, lead, bismuth, iron, copper, arsenic, tin, antimony, and silver in addition to the above-described gold, platinum group, selenium, and tellurium. And when chlorine gas is blown and leached into the slurry of copper electrolytic slime, copper, arsenic, antimony, bismuth, etc. are also leached in addition to the above-mentioned soluble gold and platinum group elements, as well as selenium and tellurium. It is contained in platinum group elements as impurities.

  The types and grades of impurities contained vary depending on the raw materials used for copper smelting, but in recent years, the increase in arsenic is particularly significant, and the amount of arsenic contained in the copper electrolytic slime is increasing accordingly. Therefore, the arsenic concentration in the leachate obtained by leaching with chlorine also tends to increase gradually. Therefore, as shown in Patent Document 2, a method for separating and recovering a platinum group using a polyamine type anion exchange resin from a chloride solution in which an impurity element coexists at a high concentration has been proposed.

JP 2001-207223 A JP 2004-131745 A

  However, in the platinum group separation using the above polyamine type anion exchange resin, the value at which the arsenic concentration of the slurry is 5.5 g / L is set as a threshold value. A phenomenon in which the palladium adsorption rate decreases may occur.

  As a result, the separation of palladium was insufficient, and palladium was sometimes contained in a high concentration in the selenium powder recovered by reducing the liquid that passed through the polyamine-type anion exchange resin. Increasing the palladium quality is not preferable because the commercial value of selenium powder decreases. Therefore, a treatment has been performed in which a small amount of sodium bisulfite or the like is added to the liquid after the platinum group is adsorbed by the polyamine type anion exchange resin, and palladium is coprecipitated together with a part of selenium to separate it.

  This makes it possible to ensure the quality of the selenium powder, while the selenium co-precipitated with palladium and separated is repeated at the beginning of the process. Then, after leaching with chlorine gas again, a process of separating the palladium and selenium by passing through a polyamine-type anion exchange resin and recovering each is performed. That is, the coprecipitated palladium requires extra processing time to recover as a noble metal, and there is a problem that the cost increases accordingly.

  The present invention has been made in view of such conventional problems, and provides a method for selectively separating and recovering palladium from selenium powder containing palladium.

In order to solve the above problems, the method for separating palladium and selenium of the present invention is characterized by comprising the following three steps.
1) Dissolution step of dissolving the palladium-containing selenium powder at a liquid temperature of 55 ° C. or less by adding hydrochloric acid and an oxidizing agent to the palladium-containing selenium powder. 2) Dihexyl sulfide is added to the solution obtained in the dissolution step. Extraction step for extracting palladium into an organic solvent by contacting with an organic solvent 3) Back extraction step for recovering palladium by extracting it into an aqueous phase by contacting ammonia water with the organic solvent from which palladium has been extracted

  In the method for separating palladium and selenium according to the present invention, the concentration of hydrochloric acid is in the range of 6 mol / L or more and 9 mol / L or less, and the solution temperature when dissolved is in the range of 20 ° C. or more and less than 40 ° C. It is preferable. In addition, a reducing step of adding a reducing agent to the dissolving solution and adjusting the redox potential of the dissolving solution to a range of 630 mV or less with a silver-silver chloride electrode as a reference electrode between the dissolving step and the extracting step. Furthermore, it is preferable to have. Furthermore, it is preferable that a nonpolar diluent is added to the organic solvent used in the extraction step so that the concentration of the dihexyl sulfide is 20 to 25% by volume.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to process the selenium powder containing palladium safely and low-cost, and to collect | recover selenium powder and palladium separately.

  There is an oxidation roasting method as a method of separating selenium powder and palladium by treating selenium powder containing palladium. In this method, selenium powder containing palladium is oxidized and roasted to volatilize selenium as selenium oxide, thereby separating selenium from non-volatile palladium. Volatilized selenium is captured in water to form a solution, and sulfur dioxide gas is blown into the solution to be purified as selenium powder. On the other hand, palladium that has not volatilized can be recovered as a roasting furnace residue, so that it can be roasted and recovered as palladium.

  However, this method has a problem that the number of facilities for oxidation roasting treatment of selenium powder containing palladium is increased, such as a roasting furnace and an exhaust gas facility, and costs and labor are required. Further, since volatile selenium oxide is highly toxic, it is difficult to say that it is preferable in terms of environmental and safety considerations.

  On the other hand, in the method for separating selenium powder and palladium of the present invention, hydrochloric acid and an oxidizing agent are added to selenium powder containing palladium, and the selenium powder containing palladium is dissolved at a liquid temperature of 55 ° C. or less ( Dissolution step), the obtained solution is contacted with an organic solvent containing dihexyl sulfide (also referred to as dihexyl sulfide or DHS), preferably 20 to 25% by volume to extract only palladium into the organic solvent (extraction step), Ammonia water is brought into contact with the organic solvent from which palladium has been extracted, and palladium is back-extracted into the aqueous phase and recovered (back-extraction step).

  In this invention, it is preferable to make the density | concentration of hydrochloric acid used for melt | dissolution of the said selenium powder containing palladium into the range of 6 mol / L or more and 9 mol / L or less. When the hydrochloric acid concentration is less than 6 mol / L, it takes time to dissolve the selenium powder, and the efficiency is industrially low. On the other hand, if the hydrochloric acid concentration exceeds 9 mol / L, hydrogen chloride is excessively reacted when the temperature rises, which increases the risk of bumping and the like, which is not preferable.

The reaction at the time of dissolving selenium powder by adding hydrochloric acid and an oxidizing agent is considered that selenium reacts with chlorine gas to generate selenium chloride as shown in the following formula 1. When the oxidation-reduction potential (ORP) at the end of the reaction is high, selenium takes a hexavalent form and stabilizes.
[Formula 1]
2Cl ₂ + Se⇒SeCl ₄ (or SeCl ₆ )

  Accordingly, an oxidizing agent that is added together with hydrochloric acid is suitable for generating chlorine gas by reacting with hydrochloric acid. Specific examples include aqueous hydrogen peroxide, sodium hypochlorite, sodium chlorite, sodium chlorate, and chlorine gas. Among these, sodium chlorite or chlorine gas is particularly preferable because of its good reactivity and easy handling.

For example, when sodium chlorite is used as the oxidizing agent, the reaction between the sodium chlorite and hydrochloric acid is represented by the following formula 2.
[Formula 2]
4HCl + NaClO ₂ ⇒2Cl ₂ ↑ + 2H ₂ O + NaCl

  The liquid temperature when the hydrochloric acid and the oxidizing agent are added to dissolve the selenium powder containing palladium is preferably within a range of 20 ° C. or higher and 55 ° C. or lower, and more preferably less than 40 ° C. This is because selenium shows the form shown in Table 1 below depending on the temperature range when it is produced by reduction, and a powdery form with a large surface area is suitable for dissolution and is preferable. That is, in the case of crystal (monoclinic system), when the temperature rises due to melting, it changes into an amorphous form and becomes unfavorable because it becomes a coarse rubbery and the dissolution reaction is lowered. The following is suitable.

  An organic solvent is brought into contact with the solution obtained in the dissolution step to extract palladium into the organic solvent. At that time, dihexyl sulfide (DHS) diluted with a nonpolar solvent such as kerosene or light oil is used as the organic solvent. DHS is highly selective with respect to palladium, while it does not extract selenium. Furthermore, since DHS is easily dissolved in a diluent such as kerosene and light oil and can be back extracted with aqueous ammonia as described later, it is convenient for purifying palladium in a subsequent step. In addition, selenium is recovered by performing a reduction treatment with sodium sulfite, sodium bisulfite, sulfite gas, or the like on the extraction liquid after extraction of palladium with an organic solvent.

  The concentration of DHS contained in the organic solvent is preferably in the range of 20 to 25% by volume. If it is less than 20% by volume, the extraction rate of palladium from the solution becomes insufficient, and a long time is required for extraction. On the other hand, if it exceeds 25% by volume, the amount of palladium extracted into DHS becomes too large. That is, when the volume concentration of DHS is 100%, there is an ability to support 150 g / L of palladium. Therefore, 25% by volume can sufficiently support palladium.

  The organic solvent from which palladium has been extracted is then brought into contact with aqueous ammonia to back-extract palladium into the aqueous phase. And palladium (diammine palladium chloride) is collect | recovered by adding hydrochloric acid to the ammonia water containing this palladium, and neutralizing PH to <= 2.

  It should be noted that the oxidation-reduction potential (ORP) of the solution is maintained at 630 mV or less as measured using a silver-silver chloride electrode as a reference electrode between the dissolution step and the extraction step, that is, before contacting the organic solvent with the solution. It is preferable to do this. This is because DHS is easily oxidized to dihexyl sulfoxide (DHSO). Specifically, it is preferable that the redox potential of the solution is adjusted in advance by adding a reducing agent such as hydrazine to the solution before the DHS contacts the solution by mixing.

  Hereinafter, the method for separating palladium and selenium of the present invention will be described in more detail by way of examples. First, 10 g of wet selenium powder containing palladium was placed in a 1 liter beaker, and 200 mL of pure water and 200 mL of 35% hydrochloric acid were added and suspended therein. While stirring the obtained suspension with a stirrer, 25 mL of 25% sodium chlorite was added to the suspension in small portions over about 10 minutes.

  With the addition of sodium chlorite, the amount of selenium powder decreased, and finally the undissolved material disappeared and all the selenium powder was dissolved. In this way, a solution for Sample 1 was prepared. When sodium chlorite was added, generation of chlorine gas was observed. The temperature of the dissolved solution after dissolution was 46 ° C., and the oxidation-reduction potential was 1030 mV with a silver-silver chloride electrode as a reference electrode. Thereafter, the concentration of selenium and palladium in the solution of Sample 1 was analyzed with an ICP analyzer.

  A solution of Sample 2 was prepared in the same manner as above except that 20 g of wet selenium powder similar to the above was used instead of 10 g and 45 mL of 25% sodium chlorite was added instead of 25 mL. In the dissolution solution of Sample 2, when 45 mL of sodium chlorite was added, the undissolved material disappeared, and it was confirmed that all the selenium powder was dissolved. The temperature of the dissolved solution after dissolution was 50 ° C., and the oxidation-reduction potential was 1036 mV with a silver-silver chloride electrode as a reference electrode. Thereafter, the concentration of selenium and palladium in the solution of Sample 2 was analyzed with an ICP analyzer. The analysis results of the lysates of Sample 1 and Sample 2 are shown in Table 2 below.

  Next, several drops of hydrazine hydrate having a concentration of 6% were added to each solution, and the oxidation-reduction potential of each solution was adjusted to 550 mV using a silver-silver chloride electrode as a reference electrode. Then, the organic solvent adjusted with the light oil so that the density | concentration of dihexyl sulfide might be 25 volume% was prepared, 40 mL of this was added to each solution, and it stirred. This mixture was sampled at the start of stirring and every few hours after the start of stirring, and the concentrations of palladium and selenium were analyzed. The analysis results are shown in Table 3 below.

  As can be seen from the results of Table 3, palladium in the solution could be extracted into the organic solvent at an extraction rate of 95% or higher in about 3 to 5 hours after the start of stirring. . On the other hand, it can be seen that selenium in the solution is hardly extracted into the organic solvent. That is, palladium could be selectively recovered.

  For comparison, a suspension was prepared in the same manner as Sample 1. With respect to this suspension, the temperature was raised to 60 ° C. and maintained while stirring with a stirrer. Next, 25 mL of 25% sodium chlorite was added to the suspension in small portions over about 10 minutes. As a result, the suspended selenium powder gradually decreased with time, but a lump of undissolved material was formed at the bottom of the 1 liter beaker. Thereafter, for about 30 minutes, the redox potential of the liquid was adjusted with sodium chlorite so that the value using the silver-silver chloride electrode as a reference electrode was 1000 mV or more. Even after 5 hours from the start of stirring, the lump undissolved material remained as it was and could not be dissolved.

Claims (4)

A method for separating palladium and selenium comprising the following three steps.
1) Dissolution step of dissolving the palladium-containing selenium powder at a liquid temperature of 55 ° C. or less by adding hydrochloric acid and an oxidizing agent to the palladium-containing selenium powder. 2) Dihexyl sulfide is added to the solution obtained in the dissolution step. Extraction step for extracting palladium into an organic solvent by contacting with an organic solvent 3) Back extraction step for recovering palladium by extracting it into an aqueous phase by contacting ammonia water with the organic solvent from which palladium has been extracted   2. The palladium according to claim 1, wherein the concentration of the hydrochloric acid is in the range of 6 mol / L or more and 9 mol / L or less, and the liquid temperature after the dissolution is in the range of 20 ° C. or more and less than 50 ° C. 3. To separate selenium from selenium.   A reduction step of adding a reducing agent to the solution and adjusting the redox potential of the solution to a range of 630 mV or less with a silver-silver chloride electrode as a reference electrode between the dissolution step and the extraction step. The method for separating palladium and selenium according to claim 1 or 2, further comprising:   The organic solvent used in the extraction step is added with a nonpolar diluent so that the concentration of dihexyl sulfide is 20 to 25% by volume. Of separation of palladium and selenium.