Cobalt is recovered from a variety of materials such as scrap cemented carbides by conversion to the hexammine cobalt (III) chloride or by digestion in hydrochloric acid followed by conversion to the hexamminecobalt (III) chloride. This process is disclosed in U.S. Pat. No. 4,218,240.
However, materials such as stellites which are a class of alloys used as hard-facing material for tools and which can contain up to about 65% cobalt with varying amounts of chromium, nickel, iron, tungsten, and silicon and are therefore oxidation resistant materials by virtue of their chromium content, do not lend themselves to any simple method of recovering cobalt.
Direct conversion to hexamminecobalt (III) chloride is not possible with stellites due to their resistance to oxidation.
Conversion of the chloride mixture obtained from the hydrochloric acid digestion of the stellite material to hexammmine cobalt (III) chloride has also proved unsuccessful. At the pH necessary for converting cobalt chloride to the hexammine cobalt (III) chloride that is a pH from about 9.0 to about 9.7, both chromium and iron precipitate and poor yields result, presumably because the cobalt is trapped in the precipitate and is not oxidized. Removal of the iron and chromium by adjusting the pH of the chloride mixture to about 3.5 and filtering has also proved unsuccessful. Cobalt is either co-precipitating with iron and chromium or is being occluded resulting in the loss of cobalt during this step.
A process in which cobalt can be recovered from impure material including stellites would be an advancement in the art.