The Twelve Principles of Circular Hydrometallurgy

Abstract

In this academic position paper, we propose the 12 Principles of a novel and more sustainable approach to hydrometallurgy that we call “circular hydrometallurgy.” The paper intends to set a basis for identifying future areas of research in the field of hydrometallurgy, while providing a “sustainability” benchmark for assessing existing processes and technological developments. Circular hydrometallurgy refers to the designing of energy-efficient and resource-efficient flowsheets or unit processes that consume the minimum quantities of reagents and result in minimum waste. The application of a circular approach involves new ways of thinking about how hydrometallurgy is applied for both primary and secondary resources. In either case, the emphasis must be on the regeneration and reuse of every reagent in the process. This refers not only to the acids and bases employed for leaching or pH control, but also any reducing agents, oxidizing agents, and other auxiliary reagents. Likewise, the consumption of water and energy must be reduced to an absolute minimum. To consolidate the concept of circular hydrometallurgical flowsheets, we present the 12 Principles that will boost sustainability: (1) regenerate reagents, (2) close water loops, (3) prevent waste, (4) maximize mass, energy, space, and time efficiency, (5) integrate materials and energy flows, (6) safely dispose of potentially harmful elements, (7) decrease activation energy, (8) electrify processes wherever possible, (9) use benign chemicals, (10) reduce chemical diversity, (11) implement real-time analysis and digital process control, and (12) combine circular hydrometallurgy with zero-waste mining. Although we realize that the choice of these principles is somewhat arbitrary and that other principles could be imagined or some principles could be merged, we are nevertheless convinced that the present framework of these 12 Principles, as put forward in this position paper, provides a powerful tool to show the direction of future research and innovation in hydrometallurgy, both in industry and in academia. Graphical Abstract

Removal of Nickel from Nickel Sulfite-Fire Assay Dissolution Filtrate Through Precipitation

“…There have been various techniques reported in previous studies for the removal of Ni from different types of waste. Two different approaches can be applied to solid wastes: (i) hydrometallurgy, a method that involves solvent extraction (SX), leaching waste metal into a solution and recovering the target metal; (ii) pyrometallurgy, this method involves treating waste metal with heat to recover the target metal. , Herein, we address the environmental and economic aspects of Ni removal from nickel sulfide (NiS) collection from the novel fire assay fusion for precious group element (PGE) filtrate dissolution waste. NiS is a widely used method to collect PGEs .…”

Ionic Liquids and Deep-Eutectic Solvents in Extractive Metallurgy: Mismatch Between Academic Research and Industrial Applicability

“…We propose that this expertise should be re-channelled to the study of speciation and the chemical thermodynamics of hydrometallurgical solutions. In this way the problem-solving abilities of the many IL/DES researchers could play a crucial role in the on-going transition from linear to low-energy-input, circular hydrometallurgy [110].…”

“…Similar claims can be found for DESs, where the same tuneability of chemical and physical properties is possible with the proper choice of the hydrogen-bond donor and hydrogenbond acceptor. Apart from doubts about the actual tuneability of new solvents (because optimizing an IL for a single property could lead to other physicochemical properties being less favorable), the promotion of an infinite number of different ILs and DESs is in conflict with one of the principles of circular hydrometallurgy: i.e., "Reduce chemical diversity" [110]. Moreover, this approach also overlooks the fact that there is strict legislation for the introduction of new chemicals on the market.…”

A toolbox for improved recycling of critical metals and materials in low-carbon technologies

“…Limitations of these methods are the high consumption of chemicals (particularly water) and the generation of wastes, which emphasises the need for circular processes, where chemicals and water are re-used over several (typically >10) cycles. 3…”