Environmentally friendly processes for the recovery of gold fromwaste electrical and electronic equipment (WEEE): A review

The recovery of gold from waste is more attracting with respect to other metals. Base on the data of World Gold Council, the request for gold had an increasing trend during the last decade. Gold is commonly extracted from mines by mercury amalgamation and more refined techniques such as, cyanidization, flotation and smelting. These are processes which have high impact on the environment, for example, mercury is a common by-product; beside from mercury amalgam based processes, which are obsolete. In the last years many efforts were made in order to design alternative environmentally acceptable procedures. Besides the obtainment of gold from ores, nowadays it is particularly important the extraction of gold from secondary sources such as electronic and electric waste (WEEE). By considering the great amount of precious metals contained in electronic devices, the recovery process of such waste seems economically sustainable and recovery of precious metals, including gold from e-waste, is necessary in order to save the natural raw materials. Hydrometallurgical process has been exploited more often than the pyro-metallurgical process. The basic hydrometallurgy processing steps include extraction, concentration/purification, and recovery. The extraction consists of acid or alkaline leaching attacks of material containing gold. In the Chapter many leachants are reported belonging to two families: chloride and sulfur-based