Sulfide minerals are the principal primary sources of copper, lead, zinc, nickel, molybdenum, and antimony, and copper in particular has been identified as a critical resource for the energy transition [1]. Their industrial treatment is dominated by conventional hydrometallurgical and pyrometallurgical routes applied to flotation products [2,3]. Progressive declines in head grade and increasing mineralogical complexity have intensified the technical demands on these routes and raised environmental concerns associated with processing low-grade materials [4]. Gangue mineralogy itself can also depress recovery in low-grade copper ores to an extent that conventional leaching does not overcome [5]. In parallel, intermediate and secondary sulfide-bearing materials have attracted attention as complements to primary production; examples include the iron precipitation residues generated during hydrometallurgical zinc production, in which substantial quantities of valuable elements are currently lost to disposal [6,7]. These converging pressures have sustained research into alternative processing media capable of treating feeds that are difficult to process by conventional means.

The limitations of established sulfide processing routes are specific rather than generic. Conventional copper production is energy-intensive, and pyrometallurgical smelting and refining contribute substantially to life-cycle energy demand and greenhouse gas emissions [8]; the environmental burden of these routes grows as the grade of the material processed declines [4]. Aqueous leaching of primary sulfides, chalcopyrite in particular, is constrained by slow kinetics and by surface passivation phenomena that limit dissolution under mild conditions, a problem that has motivated the search for non-aqueous media for several decades [9]. Aqueous systems also impose a water demand that alternative media can substantially reduce or eliminate [1,10]. These constraints have prompted research on low-water and non-aqueous media in which dissolution chemistry, redox behavior, and metal speciation differ from those of conventional aqueous systems. The rationale for exploring such media is therefore mechanistic and feed-specific; it does not assume that any alternative solvent will outperform established technology.

Deep eutectic solvents (DES) are mixtures of a hydrogen-bond acceptor, commonly a quaternary ammonium salt such as choline chloride, and a hydrogen-bond donor, such as urea, ethylene glycol, glycerol, or a carboxylic acid, whose melting point is depressed relative to that of the individual components owing to extensive hydrogen bonding [11–13]. The magnitude and origin of this depression continue to be debated, and the boundary between a simple eutectic mixture and a genuinely deep eutectic has been examined thermodynamically [14,15]. Their appeal for extractive applications derives from tunable properties: low volatility, electrochemical windows wider than that of water, the ability to modify metal speciation through coordinating anions, and a demonstrated capacity to dissolve metal oxides that are sparingly soluble in aqueous media [13,16]. Formulations such as ethaline, reline, and glyceline have become reference systems precisely because their composition can be varied systematically while retaining a common hydrogen-bond acceptor. DES are frequently described as green or sustainable solvents [17], but this designation applies to specific formulations evaluated against specific criteria rather than being an intrinsic attribute of the solvent class. Whole mixtures can be more toxic than their individual components [18], dedicated testing protocols are required to characterize their environmental effects [19], and the environmental origin and end-of-life fate of DES have been described as a two-edged sword for sustainability claims [20]. The relevant question for metallurgy is therefore not whether DES are green in principle, but what a given formulation does to a given sulfide under defined operating conditions.

The application of DES to mineral processing was demonstrated early for the dissolution and recovery of precious metals and associated sulfide-bearing assemblages [2], and was subsequently broadened into a recognized branch of hydrometallurgical and solvometallurgical metal recovery [10]. Within sulfide metallurgy, research has followed several distinct approaches. Chemical dissolution studies examine the solubilization of sulfide phases in the solvent itself, which acts simultaneously as a reaction medium and as a source of coordinating ligands [9]. Oxidative dissolution introduces chemical oxidants or oxidizing additives to drive the anodic half-reaction when the solvent alone does not mobilize the sulfide [10]. Electrochemical approaches exploit the dual function of DES as solvents and electrolytes [2]; they encompass anodic electrodissolution of sulfide phases, cathodic electroreduction, and direct electrolysis configurations in which sulfide conversion and metal deposition are coupled [10]. A further line of work addresses selective separation, seeking conditions under which one sulfide phase or one metal is mobilized preferentially from a multiphase assemblage, together with the downstream recovery of dissolved metals by electrodeposition, precipitation, or related operations [10]. These approaches differ not only in chemistry but also in the outcomes they are designed to demonstrate, which directly affects how the resulting evidence can be compared.

The literature on DES-based sulfide processing is fragmented along several axes simultaneously, and this fragmentation defines the gap addressed here. Studies differ in the sulfide investigated, spanning chemically defined model sulfides, natural mineral specimens, flotation concentrates, and industrial mattes. Because reactivity is mineral-specific, findings obtained for one phase do not transfer to another: the selective dissolution of copper sulfide minerals remains understudied even in conventional media [21], and leaching studies frequently lack the mineral-based resolution needed to attribute an outcome to a specific phase [3]. DES formulations differ in hydrogen-bond donor identity, molar ratio, water content, and the presence of oxidants or additives, while operating conditions differ in temperature, residence time, solid-to-liquid ratio, pretreatment, and electrochemical parameters. Reported outcomes are expressed through heterogeneous metrics with inconsistent definitions and units, so dissolution extent, selectivity, and recovered metal yield are not consistently distinguished. Downstream questions that determine process viability are reported unevenly: solvent regeneration is constrained by proton depletion and hydration-induced chemical drift that accumulate over repeated cycles [22], and techno-economic feasibility has been described as the missing piece in the assessment of DES processes [23]. A narrative review of DES for sulfide ore dissolution has recently appeared [9], and the broader mismatch between academic research on ionic liquids and DES and their industrial applicability in extractive metallurgy has been argued explicitly [24]. What has been lacking, however, is a synthesis that uses prespecified eligibility criteria, reproducible screening, and structured extraction to organize the experimental evidence by mineral species and processing route while preserving the distinction between dissolution, selectivity, metal recovery, and documented sustainability indicators.

This work therefore reports a systematic review addressing the following question: in sulfide minerals, ores, concentrates, industrial mattes, and explicitly defined model sulfides, how do mineral species, deep eutectic solvent composition, and chemical, oxidative, and electrochemical operating conditions influence mineral-specific dissolution, selectivity, metal recovery, and documented indicators of process sustainability? This review was conducted and reported in accordance with PRISMA 2020 [25]. Scopus and the Web of Science Core Collection were searched for journal articles published between 2010 and 7 September 2026, with a supplementary search that added mineral names to the sulfide terms. Two reviewers independently assessed records against predefined inclusion, exclusion, and uncertainty criteria using separate decision fields, and disagreements were reconciled by consensus. One reviewer extracted structured data into separate study-characteristic, DES-system, and performance-result datasets, and the evidence was combined through a descriptive and narrative synthesis, without meta-analysis or statistical pooling. The contribution is to consolidate an evidence base currently dispersed across mineralogies, solvent formulations, and process configurations; to identify which patterns are supported across studies and which rest on isolated observations; and to maintain, throughout, the analytical separation between dissolving a sulfide, dissolving it selectively, recovering the metal, and demonstrating that the process is sustainable. In doing so, the review identifies where the evidence is thin or absent, indicates the reporting practices that would make future studies comparable, and provides a structured basis for evaluating DES-based routes in sulfide metallurgy.