Extractive metallurgy

Last updated July 14, 2024

Extractive metallurgy is a branch of metallurgical engineering wherein process and methods of extraction of metals from their natural mineral deposits are studied. The field is a materials science, covering all aspects of the types of ore, washing, concentration, separation, chemical processes and extraction of pure metal and their alloying to suit various applications, sometimes for direct use as a finished product, but more often in a form that requires further working to achieve the given properties to suit the applications.^[1]

The field of ferrous and non-ferrous extractive metallurgy have specialties that are generically grouped into the categories of mineral processing, hydrometallurgy, pyrometallurgy, and electrometallurgy based on the process adopted to extract the metal. Several processes are used for extraction of the same metal depending on occurrence and chemical requirements.

Mineral processing

Mineral processing begins with beneficiation, consisting of initially breaking down the ore to required sizes depending on the concentration process to be followed, by crushing, grinding, sieving etc. Thereafter, the ore is physically separated from any unwanted impurity, depending on the form of occurrence and or further process involved. Separation processes take advantage of physical properties of the materials. These physical properties can include density, particle size and shape, electrical and magnetic properties, and surface properties. Major physical and chemical methods include magnetic separation, froth flotation, leaching etc., whereby the impurities and unwanted materials are removed from the ore and the base ore of the metal is concentrated, meaning the percentage of metal in the ore is increased. This concentrate is then either processed to remove moisture or else used as is for extraction of the metal or made into shapes and forms that can undergo further processing, with ease of handling.

Ore bodies often contain more than one valuable metal. Tailings of a previous process may be used as a feed in another process to extract a secondary product from the original ore. Additionally, a concentrate may contain more than one valuable metal. That concentrate would then be processed to separate the valuable metals into individual constituents.

Hydrometallurgy

Hydrometallurgy is concerned with processes involving aqueous solutions to extract metals from ores. The first step in the hydrometallurgical process is leaching, which involves dissolution of the valuable metals into the aqueous solution and or a suitable solvent. After the solution is separated from the ore solids, the extract is often subjected to various processes of purification and concentration before the valuable metal is recovered either in its metallic state or as a chemical compound. This may include precipitation, distillation, adsorption, and solvent extraction. The final recovery step may involve precipitation, cementation, or an electrometallurgical process. Sometimes, hydrometallurgical processes may be carried out directly on the ore material without any pretreatment steps. More often, the ore must be pretreated by various mineral processing steps, and sometimes by pyrometallurgical processes.^[2]

Pyrometallurgy

Ellingham diagram for high temperature oxidation Ellingham-Richardson.svg — Ellingham diagram for high temperature oxidation

Pyrometallurgy involves high temperature processes where chemical reactions take place among gases, solids, and molten materials. Solids containing valuable metals are treated to form intermediate compounds for further processing or converted into their elemental or metallic state. Pyrometallurgical processes that involve gases and solids are typified by calcining and roasting operations. Processes that produce molten products are collectively referred to as smelting operations. The energy required to sustain the high temperature pyrometallurgical processes may derive from the exothermic nature of the chemical reactions taking place. Typically, these reactions are oxidation, e.g. of sulfide to sulfur dioxide . Often, however, energy must be added to the process by combustion of fuel or, in the case of some smelting processes, by the direct application of electrical energy.

Ellingham diagrams are a useful way of analysing the possible reactions, and so predicting their outcome.

Electrometallurgy

Electrometallurgy involves metallurgical processes that take place in some form of electrolytic cell. The most common types of electrometallurgical processes are electrowinning and electro-refining. Electrowinning is an electrolysis process used to recover metals in aqueous solution, usually as the result of an ore having undergone one or more hydrometallurgical processes. The metal of interest is plated onto the cathode, while the anode is an inert electrical conductor. Electro-refining is used to dissolve an impure metallic anode (typically from a smelting process) and produce a high purity cathode. Fused salt electrolysis is another electrometallurgical process whereby the valuable metal has been dissolved into a molten salt which acts as the electrolyte, and the valuable metal collects on the cathode of the cell. The fused salt electrolysis process is conducted at temperatures sufficient to keep both the electrolyte and the metal being produced in the molten state. The scope of electrometallurgy has significant overlap with the areas of hydrometallurgy and (in the case of fused salt electrolysis) pyrometallurgy. Additionally, electrochemical phenomena play a considerable role in many mineral processing and hydrometallurgical processes.

Ionometallurgy

Mineral processing and extraction of metals are very energy-intensive processes, which are not exempted of producing large volumes of solid residues and wastewater, which also require energy to be further treated and disposed. Moreover, as the demand for metals increases, the metallurgical industry must rely on sources of materials with lower metal contents both from a primary (e.g., mineral ores) and/or secondary (e.g., slags, tailings, municipal waste) raw materials. Consequently, mining activities and waste recycling must evolve towards the development of more selective, efficient and environmentally friendly mineral and metal processing routes.

Mineral processing operations are needed firstly to concentrate the mineral phases of interest and reject the unwanted material physical or chemically associated to a defined raw material. The process, however, demand about 30 GJ/tonne of metal, which accounts about 29% of the total energy spent on mining in the USA.^[3] Meanwhile, pyrometallurgy is a significant producer of greenhouse gas emissions and harmful flue dust. Hydrometallurgy entails the consumption of large volumes of lixiviants such as H₂SO₄, HCl, KCN, NaCN which have poor selectivity.^[4] Moreover, despite the environmental concern and the use restriction imposed by some countries, cyanidation is still considered the prime process technology to recover gold from ores. Mercury is also used by artisanal miners in less economically developed countries to concentrate gold and silver from minerals, despite its obvious toxicity. Bio-hydro-metallurgy make use of living organisms, such as bacteria and fungi, and although this method demands only the input of O₂ and CO₂ from the atmosphere, it requires low solid-to-liquid ratios and long contact times, which significantly reduces space-time yields.

Ionometallurgy makes use of non-aqueous ionic solvents such ionic liquids (ILs) and deep eutectic solvents (DESs), which allows the development of closed-loop flow sheet to effectively recover metals by, for instance, integrating the metallurgical unit operations of leaching and electrowinning. It allows to process metals at moderate temperatures in a non-aqueous environment which allows controlling metal speciation, tolerates impurities and at the same time exhibits suitable solubilities and current efficiencies. This simplify conventional processing routes and allows a substantial reduction in the size of a metal processing plant.

Metal extraction with ionic fluids

DESs are fluids generally composed of two or three cheap and safe components that are capable of self-association, often through hydrogen bond interactions, to form eutectic mixtures with a melting point lower than that of each individual component. DESs are generally liquid at temperatures lower than 100 °C, and they exhibit similar physico-chemical properties to traditional ILs, while being much cheaper and environmentally friendlier. Most of them are mixtures of choline chloride (ChCl) and a hydrogen-bond donor (e.g., urea, ethylene glycol, malonic acid) or mixtures of choline chloride with a hydrated metal salt. Other choline salts (e.g. acetate, citrate, nitrate) have a much higher costs or need to be synthesised,^[5] and the DES formulated from these anions are typically much more viscous and can have higher conductivities than for choline chloride.^[6] This results in lower plating rates and poorer throwing power and for this reason chloride-based DES systems are still favoured. For instance, Reline (a 1:2 mixture of choline chloride and urea) has been used to selectively recover Zn and Pb from a mixed metal oxide matrix.^[7] Similarly, Ethaline (a 1: 2 mixture of choline chloride and ethylene glycol) facilitates metal dissolution in electropolishing of steels.^[8] DESs have also demonstrated promising results to recover metals from complex mixtures such Cu/Zn and Ga/As,^[9] and precious metals from minerals.^[10] It has also been demonstrated that metals can be recovered from complex mixtures by electrocatalysis using a combination of DESs as lixiviants and an oxidising agent,^[11] while metal ions can be simultaneously separated from the solution by electrowinning.^[12]

Recovery of precious metals by ionometallurgy

Precious metals are rare, naturally occurring metallic chemical elements of high economic value. Chemically, the precious metals tend to be less reactive than most elements. They include gold and silver, but also the so-called platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum (see precious metals). Extraction of these metals from their corresponding hosting minerals would typically require pyrometallurgy (e.g., roasting), hydrometallurgy (cyanidation), or both as processing routes. Early studies have demonstrated that gold dissolution rate in Ethaline compares very favourably to the cyanidation method, which is further enhanced by the addition of iodine as an oxidising agent. In an industrial process the iodine has the potential to be employed as an electrocatalyst, whereby it is continuously recovered in situ from the reduced iodide by electrochemical oxidation at the anode of an electrochemical cell. Dissolved metals can be selectively deposited at the cathode by adjusting the electrode potential. The method also allows better selectivity as part of the gangue (e.g., pyrite) tend to be dissolved more slowly.^[13]

Sperrylite (PtAs₂) and moncheite (PtTe₂), which are typically the more abundant platinum minerals in many orthomagmatic deposits, do not react under the same conditions in Ethaline because they are disulphide (pyrite), diarsenide (sperrylite) or ditellurides (calaverite and moncheite) minerals, which are particularly resistant to iodine oxidation. The reaction mechanism by which dissolution of platinum minerals is taking place is still under investigation.

Metal recovery from sulfide minerals with ionometallurgy

Metal sulfides (e.g., pyrite FeS₂, arsenopyrite FeAsS, chalcopyrite CuFeS₂) are normally processed by chemical oxidation either in aqueous media or at high temperatures. In fact, most base metals, e.g., aluminium, chromium, must be (electro)chemically reduced at high temperatures by which the process entails a high energy demand, and sometimes large volumes of aqueous waste is generated. In aqueous media chalcopyrite, for instance, is more difficult to dissolve chemically than covellite and chalcocite due to surface effects (formation of polysulfide species,^[14]^[15]). The presence of Cl⁻ ions has been suggested to alter the morphology of any sulfide surface formed, allowing the sulfide mineral to leach more easily by preventing passivation.^[16] DESs provide a high Cl⁻ ion concentration and low water content, whilst reducing the need for either high additional salt or acid concentrations, circumventing most oxide chemistry. Thus, the electrodissolution of sulfide minerals has demonstrated promising results in DES media in absence of passivation layers, with the release into the solution of metal ions which could be recovered from solution.

During extraction of copper from copper sulfide minerals with Ethaline, chalcocite (Cu₂S) and covellite (CuS) produce a yellow solution, indicating that [CuCl₄]²⁻ complex are formed. Meanwhile, in the solution formed from chalcopyrite, Cu²⁺ and Cu⁺ species co-exist in solution due to the generation of reducing Fe²⁺ species at the cathode. The best selective recovery of copper (>97%) from chalcopyrite can be obtained with a mixed DES of 20 wt.% ChCl-oxalic acid and 80 wt.% Ethaline.^[17]

Metal recovery from oxide compounds with Ionometallurgy

Recovery of metals from oxide matrixes is generally carried out using mineral acids. However, electrochemical dissolution of metal oxides in DES can allow to enhance the dissolution up to more than 10 000 times in pH neutral solutions.^[18]

Studies have shown that ionic oxides such as ZnO tend to have high solubility in ChCl:malonic acid, ChCl:urea and Ethaline, which can resemble the solubilities in aqueous acidic solutions, e.g., HCl. Covalent oxides such as TiO₂, however, exhibits almost no solubility. The electrochemical dissolution of metal oxides is strongly dependent on the proton activity from the HBD, i.e. capability of the protons to act as oxygen acceptors, and on the temperature. It has been reported that eutectic ionic fluids of lower pH-values, such as ChCl:oxalic acid and ChCl:lactic acid, allow a better solubility than that of higher pH (e.g., ChCl:acetic acid).^[19] Hence, different solubilities can be obtained by using, for instance, different carboxylic acids as HBD.^[20]

Outlook

Currently, the stability of most ionic liquids under practical electrochemical conditions is unknown, and the fundamental choice of ionic fluid is still empirical as there is almost no data on metal ion thermodynamics to feed into solubility and speciation models. Also, there are no Pourbaix diagrams available, no standard redox potentials, and bare knowledge of speciation or pH-values. It must be noticed that most processes reported in the literature involving ionic fluids have a Technology Readiness Level (TRL) 3 (experimental proof-of-concept) or 4 (technology validated in the lab), which is a disadvantage for short-term implementation. However, ionometallurgy has the potential to effectively recover metals in a more selective and sustainable way, as it considers environmentally benign solvents, reduction of greenhouse gas emissions and avoidance of corrosive and harmful reagents.

Related Research Articles

Bioleaching is the extraction or liberation of metals from their ores through the use of living organisms. Bioleaching is one of several applications within biohydrometallurgy and several methods are used to treat ores or concentrates containing copper, zinc, lead, arsenic, antimony, nickel, molybdenum, gold, silver, and cobalt.

Tantalum is a chemical element; it has symbol Ta and atomic number 73. Previously known as tantalium, it is named after Tantalus, a figure in Greek mythology. Tantalum is a very hard, ductile, lustrous, blue-gray transition metal that is highly corrosion-resistant. It is part of the refractory metals group, which are widely used as components of strong high-melting-point alloys. It is a group 5 element, along with vanadium and niobium, and it always occurs in geologic sources together with the chemically similar niobium, mainly in the mineral groups tantalite, columbite and coltan.

<span class="mw-page-title-main">Chalcopyrite</span> Copper iron sulfide mineral

Chalcopyrite ( KAL-kə-PY-ryte, -⁠koh-) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS₂ and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green-tinged black.

A noble metal is ordinarily regarded as a metallic chemical element that is generally resistant to corrosion and is usually found in nature in its raw form. Gold, platinum, and the other platinum group metals are most often so classified. Silver, copper, and mercury are sometimes included as noble metals, but each of these usually occurs in nature combined with sulfur.

Malachite is a copper carbonate hydroxide mineral, with the formula Cu₂CO₃(OH)₂. This opaque, green-banded mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses, in fractures and deep, underground spaces, where the water table and hydrothermal fluids provide the means for chemical precipitation. Individual crystals are rare, but occur as slender to acicular prisms. Pseudomorphs after more tabular or blocky azurite crystals also occur.

Copper extraction refers to the methods used to obtain copper from its ores. The conversion of copper ores consists of a series of physical, chemical and electrochemical processes. Methods have evolved and vary with country depending on the ore source, local environmental regulations, and other factors.

Neodymium(III) chloride or neodymium trichloride is a chemical compound of neodymium and chlorine with the formula NdCl₃. This anhydrous compound is a mauve-colored solid that rapidly absorbs water on exposure to air to form a purple-colored hexahydrate, NdCl₃·6H₂O. Neodymium(III) chloride is produced from minerals monazite and bastnäsite using a complex multistage extraction process. The chloride has several important applications as an intermediate chemical for production of neodymium metal and neodymium-based lasers and optical fibers. Other applications include a catalyst in organic synthesis and in decomposition of waste water contamination, corrosion protection of aluminium and its alloys, and fluorescent labeling of organic molecules (DNA).

Hydrometallurgy is a technique within the field of extractive metallurgy, the obtaining of metals from their ores. Hydrometallurgy involve the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual materials. Processing techniques that complement hydrometallurgy are pyrometallurgy, vapour metallurgy, and molten salt electrometallurgy. Hydrometallurgy is typically divided into three general areas:

<span class="mw-page-title-main">Liquid–liquid extraction</span> Method to separate compounds or metal complexes

Liquid–liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds or metal complexes, based on their relative solubilities in two different immiscible liquids, usually water (polar) and an organic solvent (non-polar). There is a net transfer of one or more species from one liquid into another liquid phase, generally from aqueous to organic. The transfer is driven by chemical potential, i.e. once the transfer is complete, the overall system of chemical components that make up the solutes and the solvents are in a more stable configuration. The solvent that is enriched in solute(s) is called extract. The feed solution that is depleted in solute(s) is called the raffinate. Liquid–liquid extraction is a basic technique in chemical laboratories, where it is performed using a variety of apparatus, from separatory funnels to countercurrent distribution equipment called as mixer settlers. This type of process is commonly performed after a chemical reaction as part of the work-up, often including an acidic work-up.

Deep eutectic solvents or DESs are solutions of Lewis or Brønsted acids and bases which form a eutectic mixture. Deep eutectic solvents are highly tunable through varying the structure or relative ratio of parent components and thus have a wide variety of potential applications including catalytic, separation, and electrochemical processes. The parent components of deep eutectic solvents engage in a complex hydrogen bonding network which results in significant freezing point depression as compared to the parent compounds. The extent of freezing point depression observed in DESs is well illustrated by a mixture of choline chloride and urea in a 1:2 mole ratio. Choline chloride and urea are both solids at room temperature with melting points of 302 °C and 133 °C respectively, yet the combination of the two in a 1:2 molar ratio forms a liquid with a freezing point of 12 °C. DESs share similar properties to ionic liquids such as tunability and lack of flammability yet are distinct in that ionic liquids are neat salts composed exclusively of discrete ions. In contrast to ordinary solvents, such as Volatile Organic Compounds (VOC), DESs are non-flammable, and possess low vapour pressures and toxicity.

Mixer settlers are a class of mineral process equipment used in the solvent extraction process. A mixer settler consists of a first stage that mixes the phases together followed by a quiescent settling stage that allows the phases to separate by gravity.

Biohydrometallurgy is a technique in the world of metallurgy that utilizes biological agents (bacteria) to recover and treat metals such as copper. Modern biohydrometallurgy advances started with the bioleaching of copper more efficiently in the 1950s

Chloroauric acid is an inorganic compound with the chemical formula H[AuCl₄]. It forms hydrates H[AuCl₄]·nH₂O. Both the trihydrate and tetrahydrate are known. Both are orange-yellow solids consisting of the planar [AuCl₄]⁻ anion. Often chloroauric acid is handled as a solution, such as those obtained by dissolution of gold in aqua regia. These solutions can be converted to other gold complexes or reduced to metallic gold or gold nanoparticles.

Leaching is a process widely used in extractive metallurgy where ore is treated with chemicals to convert the valuable metals within the ore, into soluble salts while the impurity remains insoluble. These can then be washed out and processed to give the pure metal; the materials left over are commonly known as tailings. Compared to pyrometallurgy, leaching is easier to perform, requires less energy and is potentially less harmful as no gaseous pollution occurs. Drawbacks of leaching include its lower efficiency and the often significant quantities of waste effluent and tailings produced, which are usually either highly acidic or alkali as well as toxic.

The salt extraction process is an electrolytic method which may be used to extract valuable metals from slag, low-grade ores, or other materials by using molten salts. This method was developed by S. Seetharaman, O. Grinder, L. Teng and X. Ge at the Royal Institute of Technology in Sweden as part of a large Steel Eco-Cycle Project in 2005.

Di(2-ethylhexyl)phosphoric acid (DEHPA or HDEHP) is an organophosphorus compound with the formula (C₈H₁₇O)₂PO₂H. The colorless liquid is a diester of phosphoric acid and 2-ethylhexanol. It is used in the solvent extraction of uranium, vanadium and the rare-earth metals.

Non-ferrous extractive metallurgy is one of the two branches of extractive metallurgy which pertains to the processes of reducing valuable, non-iron metals from ores or raw material. Metals like zinc, copper, lead, aluminium as well as rare and noble metals are of particular interest in this field, while the more common metal, iron, is considered a major impurity. Like ferrous extraction, non-ferrous extraction primarily focuses on the economic optimization of extraction processes in separating qualitatively and quantitatively marketable metals from its impurities (gangue).

<span class="mw-page-title-main">Actinide chemistry</span> Branch of nuclear chemistry

Actinide chemistry is one of the main branches of nuclear chemistry that investigates the processes and molecular systems of the actinides. The actinides derive their name from the group 3 element actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide. All but one of the actinides are f-block elements, corresponding to the filling of the 5f electron shell; lawrencium, a d-block element, is also generally considered an actinide. In comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence. The actinide series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.

Mineral processing and extraction of metals are very energy-intensive processes, which are not exempted of producing large volumes of solid residues and wastewater, which also require energy to be further treated and disposed. Moreover, as the demand for metals increases, the metallurgical industry must rely on sources of materials with lower metal contents both from a primary and/or secondary raw materials. Consequently, mining activities and waste recycling must evolve towards the development of more selective, efficient and environmentally friendly mineral and metal processing routes.

Green solvents are environmentally friendly chemical solvents that are used as a part of green chemistry. They came to prominence in 2015, when the UN defined a new sustainability-focused development plan based on 17 sustainable development goals, recognizing the need for green chemistry and green solvents for a more sustainable future. Green solvents are developed as more environmentally friendly solvents, derived from the processing of agricultural crops or otherwise sustainable methods as alternatives to petrochemical solvents. Some of the expected characteristics of green solvents include ease of recycling, ease of biodegradation, and low toxicity.

References

↑ Brent Hiskey "Metallurgy, Survey" in Kirk-Othmer Encyclopedia of Chemical Technology, 2000, Wiley-VCH, Weinheim. doi : 10.1002/0471238961.1921182208091911.a01
↑ "Boundless. "Extractive Metallurgy." Boundless Chemistry. Boundless, 21 Jul. 2015. Retrieved 18 Mar. 2016". Archived from the original on October 12, 2016. Retrieved March 18, 2016.
↑ Norgate (2010). "Energy and greenhouse gas impacts of mining and mineral processing operations". Journal of Cleaner Production. 18 (3): 266–274. doi:10.1016/j.jclepro.2009.09.020.
↑ Binnemans, Koen (2017). "Solvometallurgy: An Emerging Branch of Extractive Metallurgy". Journal of Sustainable Metallurgy. 3 (3): 571–600. Bibcode:2017JSusM...3..570B. doi: 10.1007/s40831-017-0128-2 . S2CID 52203805.
↑ Endres, F; MacFarlane, D; Abbott, A (2017). Electrodeposition from Ionic Liquids. Wiley-VCH.
↑ Bernasconi, R.; Zebarjadi, Z.; Magagnin, L. (2015). "Copper electrodeposition from a chloride free deep eutectic solvent". Journal of Electroanalytical Chemistry. 758 (1): 163–169. doi:10.1016/j.jelechem.2015.10.024. hdl: 11311/987216 .
↑ Abbott, A.; Collins, J.; Dalrymple, I.; Harris, R.C.; Mistry, R.; Qiu, F.; Scheirer, J.; Wise, W.R. (2009). "Processing of Electric Arc Furnace Dust using Deep Eutectic Solvents". Australian Journal of Chemistry. 62 (4): 341–347. doi:10.1071/CH08476.
↑ Abbott, A.; Capper, G.; McKenzie, K.J.; Glidle, A.; Ryder, K.S. (2006). "Electropolishing of stainless steels in a choline chloride based ionic liquid: an electrochemical study with surface characterisation using SEM and atomic force microscopy". Phys. Chem. Chem. Phys. 8 (36): 4214–4221. Bibcode:2006PCCP....8.4214A. doi:10.1039/B607763N. hdl: 2381/628 . PMID 16971989.
↑ Abbott, A.; Harris, R.C.; Holyoak, F.; Frisch, G.; Hartley, J.; Jenkin, G.R.T. (2015). "Electrocatalytic recovery of elements from complex mixtures using deep eutectic solvents". Green Chem. 17 (4): 2172–2179. doi:10.1039/C4GC02246G. hdl: 2381/31850 .
↑ Jenkin, G.R.T.; Al-Bassam, A.Z.M.; Harris, R.C.; Abbott, A.; Smith, D.J.; Holwell, D.A.; Chapman, R.J.; Stanley, C.J. (2016). "The application of deep eutectic solvent ionic liquids for environmentally-friendly dissolution and recovery of precious metals". Minerals Engineering. 87: 18–24. Bibcode:2016MiEng..87...18J. doi: 10.1016/j.mineng.2015.09.026 . hdl: 10141/603645 .
↑ Abbott, A.; Harris, R.C.; Holyoak, F.; Frisch, G.; Hartley, J.; Jenkin, G.R.T. (2015). "Electrocatalytic recovery of elements from complex mixtures using deep eutectic solvents". Green Chemistry. 17 (4): 2172–2179. doi:10.1039/C4GC02246G. hdl: 2381/31850 .
↑ Anggara, S.; Bevan, F.; Harris, R.C.; Hartley, J.; Frisch, G.; Jenkin, G.R.T.; Abbot, A. (2019). "Direct extraction of copper from copper sulfide minerals using deep eutectic solvents". Green Chemistry. 21 (23): 6502–6512. doi:10.1039/C9GC03213D. S2CID 209704861.
↑ Jenkin, G.R.T.; Al-Bassam, A.Z.M.; Harris, R.C.; Abbott, A.; Smith, D.J.; Holwell, D.A.; Chapman, R.J.; Stanley, C.J. (2016). "The application of deep eutectic solvent ionic liquids for environmentally-friendly dissolution and recovery of precious metals". Minerals Engineering. 87: 18–24. Bibcode:2016MiEng..87...18J. doi: 10.1016/j.mineng.2015.09.026 . hdl: 10141/603645 .
↑ Ghahremaninezhad, A.; Dixon, D.G.; Asselin, E. (2013). "Electrochemical and XPS analysis of chalcopyrite (CuFeS2) dissolution in sulfuric acid solution". Electrochimica Acta. 87: 97–112. doi:10.1016/j.electacta.2012.07.119.
↑ Dreisinger, D.; Abed, N. (2002). "A fundamental study of the reductive leaching of chalcopyrite using metallic iron part I: kinetic analysis". Hydrometallurgy. 60 (1–3): 293–296. Bibcode:2002HydMe..66...37D. doi:10.1016/S0304-386X(02)00079-8.
↑ Pikna, L.; Lux, L.; Grygar, T. (2006). "Electrochemical dissolution of chalcopyrite studied by voltammetry of immobilized microparticles". Chemical Papers. 60 (4): 293–296. doi:10.2478/s11696-006-0051-7. S2CID 95349687.
↑ Abbott, A.; Al-Bassam, A.Z.M.; Goddard, A.; Harris, R.C.; Jenkin, G.R.T.; Nisbet, J.; Wieland, M. (2017). "Dissolution of pyrite and other Fe – S – As minerals using deep eutectic solvents". Green Chemistry. 19 (9): 2225–2233. doi:10.1039/C7GC00334J. hdl: 2381/40192 .
↑ Pateli, I.M.; Abbott, A.; Hartley, J.; Jenkin, G.R.T (2020). "Electrochemical oxidation as alternative for dissolution of metal oxides in deep eutectic solvents". Green Chemistry. 22 (23): 8360–8368. doi:10.1039/D0GC03491F. S2CID 229243585.
↑ Pateli, I.M.; Thompson, D.; Alabdullah, S.S.M; Abbott, A.; Jenkin, G.R.T.; Hartley, J. (2020). "The effect of pH and hydrogen bond donor on the dissolution of metal oxides in deep eutectic solvents". Green Chemistry. 22 (16): 5476–5486. doi:10.1039/D0GC02023K. S2CID 225401121.
↑ Abbott, A.; Boothby, D.; Capper, G.; Davies, D.L.; Rasheed, R.K. (2004). "Deep Eutectic Solvents formed between choline chloride and carboxylic acids: Versatile alternatives to ionic liquids". J. Am. Chem. Soc. 126 (29): 9142–9147. doi:10.1021/ja048266j. PMID 15264850.