JPH108155A - Method for recovering palladium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently recover palladium to a high grade by dissolving the palladium in a strong acid, such as aqua regia, and adding iodine to form palladium iodide and separating the palladium iodide. SOLUTION: After the palladium is dissolved in the strongly acidic liquid, such as aqua regia, the iodine or iodide is added to the liquid and the palladium is separated in the form of the palladium iodide. Potassium iodide, sodium iodide, calcium iodide, hydroiodic hydrogen acid, etc., are used as the iodide. The amt. of the iodine or iodine ions to be added is confined up to about 1.5 times the equiv. derived from the reaction formula. The separated palladium iodide is dissolved in an aq. alkaline iodide soln. and is then reduced by using reducing agents, such as sodium baron hydride, hydrazine, hydrazine sulfate and sulfite, by which the palladium is recovered. The filtrate after the recovery is repetitively used as the iodine ion-contg. liquid. The concn. of the aq. alkaline iodide soln. is preferably specified to 10wt.% to satd. concn.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dissolving and recovering palladium using a strongly acidic liquid such as aqua regia, and includes, for example, waste catalysts, waste industrial products and the like. And a method for dissolving and recovering palladium. 2. Description of the Related Art A conventionally known method for recovering palladium is to dissolve palladium in an inorganic acid such as aqua regia and then add ammonium chloride, ammonia or the like to form dichloroammine palladium, and after separation. A method of recovering palladium by reduction in a stream of hydrogen. Alternatively, a solvent extraction method is known. However, aqua regia has a great expense for drainage management because its drainage is strongly acidic. In addition, since harmful gas is generated in the firing of dichloroammine palladium, a great deal of expense is required for its management. In addition, the solvent extraction method has been pointed out with problems such as the efficiency of back extraction, deterioration of expensive extractants, and complicated operability. DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks, in which a strong acid solution used for dissolving and recovering palladium from spent catalysts, waste industrial products and the like is used repeatedly without discarding. It is an object of the present invention to provide a new economical method for recovering palladium, which makes it possible to reduce wastewater as much as possible. One of the features of the present invention is that when recovering palladium, up to 1.5 times the theoretical amount of iodine or iodide derived from the reaction formula is added to convert palladium into iodine. Is to separate as palladium chloride. At that time, the contaminating base metal may be slightly produced as a base metal iodide, but has good solubility and is dissolved in the dissolving solution, so that it can be easily separated from palladium iodide, and the base metal is contaminated. Not recovered as high-grade palladium iodide. Palladium obtained by reducing high-grade palladium iodide becomes highly purified high-grade palladium. Another feature of the present invention is that the strongly acidic solution used for dissolution can be used repeatedly.
After separation as palladium iodide, the amount of palladium remaining in the solution is only a few ppm. The strongly acidic liquid is repeatedly used without any problem in dissolving the contaminating base metal. Further, a feature of the present invention is that the separated palladium iodide is reduced by adding a reducing agent thereto, and is recovered as high-grade palladium, and then the by-produced iodide is again used for producing palladium iodide, and is used repeatedly. . That is, a feature of the present invention is that a strongly acidic solution such as aqua regia and iodide can be used repeatedly. The present invention will be described in detail with reference to the following examples. Example 1 0.3890 g (approximately 3.890 g) of 99.9% grade palladium.
After dissolving 0.0948 g (about 3.5 × 10 ⁻³ mol) of aluminum of 7 × 10 ⁻³ mol and 99.9% in 12 ml of aqua regia, 1.3929 g (about 5.5 ×) of iodine was dissolved. 10 ⁻³ mol) was added to produce 1.32 g of palladium iodide. The residual palladium concentration in the filtrate was 0.7 ppm. Palladium iodide was dissolved in 10 ml of an aqueous potassium iodide solution (1 mol / l), reduced by adding 0.25 g of formic acid, and 0.38 g of palladium was recovered. The grade of the recovered palladium was 99.9%. Example 2 To about 10 ml of aqua regia used in Example 1, 2 ml of nitric acid was added, and 0.3912 g of 99.9% grade palladium was added.
(3.7 × 10 ⁻³ mol) and 0.0921 g (approximately 3.4 × 10 ⁻³ mol) of aluminum having a grade of 99.9% were dissolved, and 2.1011 g (approximately 1.3) of potassium iodide was dissolved.
× 10 ^-2 mol), and after separating the generated palladium iodide, the reduced iodine ion-containing liquid 10 of Example 1 was added.
in 0.2 ml, reduced by adding 0.25 g of formic acid,
About 0.39 g of palladium was recovered. The grade of the recovered palladium was 99.9%. The same operation was repeated four times, but the quality of the recovered palladium was maintained at 99.9%, and it was confirmed that the palladium could withstand five repetitions. As shown in the above examples, according to the method of the present invention, palladium iodide is once separated, so that palladium can be recovered efficiently and with high quality. In addition, since aqua regia used to dissolve palladium can be used repeatedly, it is possible to remarkably reduce strongly acidic wastewater, and the burden of neutralization treatment and the like is significantly reduced as compared with the conventional method. In addition, there is no generation of harmful gas due to firing, the recovery operation is simplified, and an economically advantageous effect is obtained.

Claims (1)

Claims: 1. A method for recovering palladium, comprising dissolving palladium in a strongly acidic liquid such as aqua regia and then adding iodine (I).
₍₂ ) A method for recovering palladium, which comprises adding palladium to produce palladium iodide and then separating. 2. A method for recovering palladium, which comprises dissolving palladium in a strongly acidic solution such as aqua regia and then adding iodide ions such as potassium iodide, sodium iodide, calcium iodide, and hydroiodic acid. Separating palladium iodide after its production. 3. A method for recovering palladium wherein the amount of iodine or iodine ion added in the above [claim 1] and [claim 2] is up to 1.5 times the equivalent derived from the reaction formula. 4. A method for recovering palladium, comprising separating palladium iodide from a strongly acidic solution such as aqua regia and repeatedly using a strongly acidic solution such as aqua regia for dissolving palladium. 5. A method for recovering palladium, wherein the concentration of the aqueous solution of alkali iodide is from 10% by weight to the saturation concentration when the separated palladium iodide is dissolved in the aqueous solution of alkali iodide. 6. A palladium iodide is dissolved in an aqueous alkali iodide solution and then reduced with a reducing agent such as sodium borohydride, hydrazine, hydrazine sulfate, hydrazine hydrochloride, sulfurous acid, bisulfite, formic acid, oxalic acid and the like. A method for recovering palladium, characterized in that the filtrate obtained after recovering palladium by filtration is used again as an iodine ion-containing liquid in the above [Claim 2] and [Claim 5].