**1. Introduction and Scope**

In 2015, 193 governments agreed to act on climate change by drastically reducing carbon dioxide (CO2) emissions as envisaged in the sustainable development goal (SDG) number 13 [1]. The high consumption of metals during the period of industrialization (i.e., since 1900) and the global call for cutting down on CO<sup>2</sup> emissions have led to high demand for metals such as cobalt (Co), copper (Cu), gold (Au), zinc (Zn), lead (Pb), lithium (Li), nickel (Ni), tin (Sn), vanadium (V), rare earth metals, etc. [2]. These metals are critical as the world moves to low-carbon technologies based on renewable energy sources (RESs) and electric vehicles (EVs), and away from the heavy use of fossil fuels. To meet the high forecasted demand, unconventional sources of metals such as low-grade complex ores, seafloor massive sulphides (SMSs), and wastes (e.g., tailings, metallurgical residues, and electronic wastes (e-wastes)) have become very important sources of metals [3,4]. Moreover, these metals should be extracted in a sustainable manner without negatively impacting the environment.

The sustainable extraction of these critical metals begins with studies on the advancements in the beneficiation (i.e., gravity separation, magnetic separation, flotation, etc.) of valuable minerals from unconventional sources. The concentrated minerals are then subjected to advanced extractive metallurgy where unconventional methods (e.g., unconventional hydrometallurgical processes, pyrometallurgical processes, or the combination of the two) are used to obtain metal with lesser or no negative impacts on the environment.
