Primary production and recycling of critical metals

Metals are important engineering materials, and are produced from non-renewable natural resources. This chapter starts with the criticality and scarcity issue of metals and metal resources. Then various available extraction and refining technologies and processes are introduced for primary production and recycling of metals. The principles of pyrometallurgy, hydrometallurgy and electro-metallurgy (electrowinning and electro-refining) are described for primary production of metals. The applications of metallurgical technologies to metals recovery from secondary resources (metal scrap and waste residues), i.e. recycling of metals, are discussed. As the last part, the extraction and recycling of cobalt, one of the most critical metals, is given as an example to illustrate how different metallurgical technologies are used and combined to extract a metal from different types of raw materials.