Uses of H2 and CO2 gases in hydrometallurgical processes: Potential towards sustainable pretreatment, metal production and carbon neutrality

Hydrometallurgical practices represent a vital area of focus within the metallurgical sector, and it is critical that these practices are carried out in an environmentally friendly manner in order to promote sustainability and responsible processing. One promising approach is the use of hydrogen gas (H 2 ), known for its ‘green’ properties, along with the pollutant carbon dioxide (CO 2 ), at various stages within the unit operations relevant to hydrometallurgical processes. This review provides a detailed overview of the utilization of H 2 and CO 2 gases, encompassing key stages including pretreatment, leaching, and metal recovery. Theoretical underpinnings are also provided for each stage, along with an overview of cutting-edge approaches such as application of supercritical CO 2 . Challenges and future directions associated with H 2 and CO 2 utilization are also discussed. This review serves an important step towards advancing sustainable hydrometallurgical processes promoting carbon neutrality. • Carbon neutrality in the hydrometallurgical field by utilizing H 2 and CO 2 . • H 2 as a green reductant in the hydrometallurgical processes. • CO 2 utilizations reduce carbon footprint and augment the metal recovery. • Supercritical CO 2 as an advanced CO 2 utilization in the hydrometallurgical field.