TABLE OF CONTENTS 7.10.1. Cadmium has low volatilization temperature, which is taken advantage of in separating and recycling this metal from its alloys by distillation and subsequent condensation. The distillate is acid leached and impurities are selectively precipitated and cadmium recovered by electrolysis.
Cadmium is also recycled from electric arc furnace (EAF) dust and from discarded nickel-cadmium batteries. These topics will be discussed in Chapters 8, 9 and 10..
7.10.2. Mercury is found in solid wastes in elemental form and as amalgams, organic mercury and mercury salts. It is recovered from electronic devices such as rectifiers, relays, switches and thermostats; and on a smaller scale from dental amalgams, batteries, lamps and broken thermometers. As it is a volatile element, mercury is recovered by distillation in steel retorts, followed by condensation. The product is then redistilled to remove base metal and other impurities. Triple distillation is done for obtaining a high purity product.
A vacuum retort system to recover mercury from broken or discarded mercury containing devices has been developed (Boyle, 1995). The retort unit is a batch system The scrap received is first sorted to obtain a uniform material; This requires crushing to break the higher strength glass containing mercury to allow the metal to be vaporized, The method is based on taking advantage of the liquid nature of mercury at room temperature and with boiling point of 357 C. A vacuum equivalent of 25 inches of mercury column is maintained in the retort. By heating...
