EXTRACTION METHOD FOR A METALLIC, IRIDIUM AND/OR IRIDIUM OXIDE COMPRISING MIXTURE OF SOLID PARTICLES

A process for digestion of fine iridium includes (a) alkaline oxidative digestion of 1 part by weight fine iridium and 3 to 20 parts by weight of a combination comprising 40 to 70 parts by weight sodium hydroxide, 15 to 30 parts by weight sodium nitrate, and 10 to 40 parts by weight sodium peroxide in the melt, whereby the sum of the weight fractions equals 100 parts by weight; (b) cooling the digestion material formed in step (a) to 20 to 70° C.; (c) dissolving the acid-soluble fractions of the cooled digestion material in water/halogen hydracid until an acidic aqueous solution with a pH value of −1 to +1 is obtained; and (d) boiling the acidic aqueous solution obtained in step (c) until the formation of nitrous gases is completed. Insoluble ingredients can be separated from the acidic aqueous solution before or after step (d), if needed.