Recovery of mercury from spent silver oxide button cells

The present work describes an investigation of a hydrometallurgical process for the recovery of mercury from spent silver oxide button cells. The cell paste was leached in nitric acid to solubilize silver, mercury and zinc. The optimum leaching conditions, in which mercury is entirely converted to Hg(2+) ions and, therefore, does not co-precipitate with silver chloride during treatment with potassium chloride solution, were 1.0 M HNO(3), 45 degrees C, 1 hour and 200 rpm. After the silver was removed from the solution, mercury was cemented out with zinc powder with an efficiency greater than 99%. In the cementation experiments, the amount of zinc powder, shaking rate, temperature and solution pH were investigated in detail. The mercury recovery (%) increased as the amounts of zinc powder and the temperature were increased. Zinc hydroxide was precipitated from the waste solution by the addition of sodium hydroxide. The Zn(OH)(2) precipitate was then converted to zinc oxide. The proposed process is proven to be simple, straightforward and environmentally friendly.