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Recovery Processes and Utilisation of Valuable Materials from Acid Mine Drainage
Published in Geoffrey S. Simate, Sehliselo Ndlovu, Acid Mine Drainage, 2021
Electrowinning, as a form of electrodeposition, is the deposition of a metal from solution due to an applied electrical potential. The dissolved metals migrate towards the cathode where they are reduced and deposit on the cathode. In general, the anode composition (effectively inert) is selected to limit its oxidation and thus promote the oxidation of water at the anode (Figueroa and Wolkersdorfer, 2014). Most importantly, electrochemical recovery processes, particularly electrowinning, have been applied primarily to high metal concentration solutions (≫1000 mg/L) at low pH (<1) in waste streams where competitive metals tend to be at much lower concentrations than the target metal (e.g., electroplating waste) (Figueroa and Wolkersdorfer, 2014). Nordstrom et al. (2017) also reiterate that electrowinning for Cu is generally not done on AMD because concentrations of nearly 1000 mg/L are necessary.
Some applications of electrochemistry
Published in W. John Rankin, Chemical Thermodynamics, 2019
In electrowinning, the metal compound is dissolved in solution or melted (molten salt systems) to form metallic cations, and these are reduced to the atomic state and deposited on the cathode by passage of a current. Metals that lie below hydrogen in Table 16.3 can be reduced from aqueous solutions since water is then stable. However, in practice, many metals above hydrogen can also be reduced due to the hydrogen overpotential effect. Table 17.1 lists common metals which can be produced electrochemically from aqueous solutions. Metals which cannot be produced electrochemically from aqueous solutions can be produced by electrochemical reduction of their molten salts, and a list of the metals in this category is also given in Table 17.1. In most cases the metal chloride has been found to be a suitable salt because chlorides have moderate melting points and high molar conductivities. Other halides can be used, but chlorine is the cheapest of the halogens and, therefore, preferred for the halogenation of metals that occur naturally as oxides using reactions of the type:MO(s)+C(s)+Cl2(g)=MCl2(s,lorg)+CO(g)
Electrometallurgy
Published in C. K. Gupta, Extractive Metallurgy of Molybdenum, 2017
In molten-salt electro winning, the commonly used feed materials are halides of the metal to be electrodeposited. Molten inorganic materials having a common anion have a very high miscibility. Since halides are the commonly used solvents, it is possible to maintain a high concentration of the metal in the electrowinning system. In most cases, concentrated solutions are advantageous for the enhancement of mass transfer rates. Dilute solutions, on the other hand, are advantageous from the point of view of thermal stability. Other types of feed materials like oxides, sulfides, carbides, and nitrides are also used. Electrowinning of metals directly from their natural minerals is commercially very desirable, since feed preparations can then be minimized. Although oxides form the most important group of ore minerals, their use as feed material in molten-salt electrolysis is often limited by their low solubilities. The oxide, however, has good solubility in all fluoride or fluoride-containing molten baths. As an example of an all-fluoride bath, mention may be made of the case of alumina dissolved in a cryolite (Na3AlF6) and fluorspar (CaF2) mixed melt from which aluminum is electrowon. Likewise, mention may be made of tantalum oxide dissolved in a potassium tantalum fluoride (K2TaF7) and alkali halide mixed melt (from which tantalum metal is industrially electrowon) as an example of a fluoride-containing molten bath.
Copper removal from a cyanidation liquor by electrowinning using batch and continuous flow cells.
Published in Canadian Metallurgical Quarterly, 2020
G. I. Dávila-Pulido, J. M. Flores-Álvarez, A. Uribe-Salas, F. López-Saucedo
The electrowinning of solutions containing cuprocyanide complexes has several advantages: high deposit adhesion, relatively uniform deposit thickness, and fine-grained morphology [11]. Although electrochemistry may require a higher investment cost, avoiding the need for chemicals could lower operating costs; therefore, it is of interest to study, understand and optimise the electrochemical processes that occur during electrowinning, by analyzing parameters such as pH, applied potential, temperature, recirculation rate and the stirring of the solution. Considering the above, the objective of this study was to develop a continuous electrowinning cell to remove part of the copper present in the exhausted solution from Merrill Crowe cementation of aurocyanide complexes, as well as to define the operating conditions for process optimisation.
Recent advances on hydrometallurgical recovery of critical and precious elements from end of life electronic wastes - a review
Published in Critical Reviews in Environmental Science and Technology, 2019
Manivannan Sethurajan, Eric D. van Hullebusch, Danilo Fontana, Ata Akcil, Haci Deveci, Bojan Batinic, João P. Leal, Teresa A. Gasche, Mehmet Ali Kucuker, Kerstin Kuchta, Isabel F. F. Neto, Helena M. V. M. Soares, Andrzej Chmielarz
Electrowinning (EW) is also one of the efficient technologies that helps to recover metals from the metal containing solutions or leachates. Selective recovery of the target metal is one of the main advantages of electrowinning. EW has some other merits such as (1) less or no secondary waste generation, (2) no hazardous chemical usage and (3) comparatively lesser investment cost. EW technology was successfully applied to electronic scraps for the selective recovery of base metals such as Cu and Pb (Mecucci & Scott, 2002; Madenoğlu, 2005). However, EW technology application on the selective recovery of critical and precious metals is still in its early stages. Selective separation of precious metals (Au) by EW is challenging especially in presence of Cu (Grosse, Dicinoski, Shaw, & Haddad, 2003). However, Chehade et al. (2012) demonstrated on the selective separation of pure Cu, Ag, Au and Pd from the PCBs (containing (wt %) Cu 18.49%, Au 0.04%, Ag 0.16%, Pd 0.01%, Cu 0.06 g·L−1, Cd 0.04 g·L−1). The PCBs were first digested using aqua-regia and then electrowinning was applied to the leachate. Four sequential EW chambers were used and in each chambers one metal was electro deposited on the cathode. Copper was the first to selectively recover by this technology, followed by gold, palladium and finally silver. A maximum of 0.04 kg of Au, 0.18 kg of Ag, 0.01 kg of Pd and 21.00 kg of Cu was recovered from 125 kg of PCBs (Chehade et al., 2012).
Improving the recovery of copper from electric cable waste derived from automotive industry by corona-electrostatic separation
Published in Particulate Science and Technology, 2021
Andrei Catinean, Lucian Dascalescu, Mihai Lungu, Laurentiu Marius Dumitran, Adrian Samuila
The chemical methods are based on copper cementation onto less noble metals (iron, aluminium), and electrowinning (Fouad and Abdel Basir 2005). Cementation is a chemical process that has been used to precipitate and recover an ionized metal from solution by spontaneous electrochemical reduction to its elemental metallic state, with consequent oxidation of a sacrificial metal. In electrowinning, a current is passed from an inert anode through a liquid solution containing the metal so that the metal is extracted as it is deposited in an electroplating process onto the cathode.