The review work is completed with an overview of the different approaches to use renewable energies and valorize residual heat in pyrometallurgical units. A complete discussion about the alternatives to carbon-based reduction is constructed around the use of hydrogen, metallo-reduction as well as inert anode electrometallurgy. It also identifies all recycled streams that are available (such as steel and aluminum scraps, electronic waste and Li-ion batteries) as well as the technological challenges associated with their integration in primary metal processes.

This paper explores the possibility to use greener reactants such as bio-fuels, bio-char, hydrogen and ammonia in different pyrometallurgical units. Therefore, there are still many opportunities to lower the environmental footprint of key pyrometallurgical operations. Many unit operations also generate hazardous gaseous species on top of large CO 2 emissions which require gas-scrubbing and capture strategies for the future. Even though primary metal production industries are mature and operate optimized pyrometallurgical processes, they extensively rely on cheap and abundant carbonaceous reactants (fossil fuels, coke), require high power heating units (which are also typically powered by fossil fuels) to calcine, roast, smelt and refine, and they generate many output streams with high residual energy content. They allow the transportation of energy over great distances and are exploited in critical parts of renewable energy technologies. They are the most common structural materials used in cars, airplanes and buildings, and constitute the technological core of most electronic devices. Metals and alloys are among the most technologically important materials for our industrialized societies.

Submerge arc furnace