Electrochemical study of gold recovery from ammoniacal thiosulfate, simulating the PCBs leaching of mobile phones

[EN] The high volume of sales and the high degree of obsolescence of mobile phones, together with the reduction of the natural reserves of the metals used in the composition of their printed circuit boards (PCBs), makes the recycling of these devices economically and environmentally attractive. Moreover, the search for the reduction of toxicity levels inherent to the gold leaching processes with alternatives to cyanide, such as thiosulfate is a priority. Thus, it is necessary to search for efficient alternatives for the recovery of gold from solutions containing thiosulfate, in the presence of copper, used in the leaching of PCBs of mobile phones. One of these alternatives could be the electrochemical recovery of the metals present in solution. Thus, this study aimed to verify some variables involved in the process of recovery of gold and copper and to determine the electrochemical yield obtained for these solutions. Initially, cyclic scanning voltammetry with a rotating disk electrode (RDE) was performed to verify the electrochemical behavior of gold and copper in solution. Then, electrowinning tests were used to determine the recovery rates of these metals and to calculate the yield obtained in the process. The results showed that this electrochemical reaction is mass transport controlled, which allowed the calculation of the diffusion coefficients of the metal in solution. In real solutions, the gold fraction recovered reached a 94%, and the copper fraction recovered was 95%, applying electrode potential values of -500 mV(Ag/AgCl) and -700 mV(Ag/AgCl), respectively. The current efficiency for the gold electrowinning achieved in the experiments was lower than 3%. (c) 2017 Elsevier Ltd. All rights reserved.The authors would like to thank the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES) and Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) from Brazil for financial support.Kasper, AC.; Veit, HM.; García Gabaldón, M.; Pérez-Herranz, V. (2018). Electrochemical study of gold recovery from ammoniacal thiosulfate, simulating the PCBs leaching of mobile phones. Electrochimica Acta. 259:500-509. https://doi.org/10.1016/j.electacta.2017.10.161S50050925

Kinetic Study of the Dissolution of Metallic Nickel in Sulphuric Acid Solutions in the Presence of Different Oxidants

The dissolution of metallic nickel particles in sulphuric acid solutions has been studied in this work. The effect of temperature, sulphuric acid concentration, and oxidant type has been assessed. In the presence of hydrogen peroxide or dissolved oxygen the dissolution of nickel was fast. A shrinking particle model was used to fit the experimental data and estimate kinetic parameters. The apparent reaction rate constants calculated at 55°C when dissolved oxygen, ferric sulphate, and hydrogen peroxide were used as oxidants were, respectively, 0.17, 0.02, and 7.13 ms-₁. The dissolution of Ni in the presence of ferric sulphate occurred under surface chemical control, with an activation energy of 82.3 kJ/mol, while in the presence of hydrogen peroxide and dissolved oxygen the reaction seemed to have been mass transfer controlled. The dissolution of Ni in ferric sulphate solutions was also pH sensitive, possibly due to the formation of NiFe₂O-₄ or NiO that was prevented when sulphuric acid concentration was 1 mol/L. The dissolution rate in ferric sulphate-free solutions was affected negatively by temperature due to a decrease in O₂ solubility.Applied Science, Faculty ofMaterials Engineering, Department ofReviewedFacultyPostdoctora

Aqueous metal recovery techniques from e-scrap: Hydrometallurgy in recycling

Waste of electric-electronic equipment (WEEE) with an annual growth rate of about 3-5% is the fastest growing waste stream in municipal wastes. Notwithstanding their environmental pollution potential, waste of electrical and electronic equipment (WEEE) with their high content of base and precious metals, in particular, are regarded as a potential secondary resource when compared with ores. For the recovery of metals from WEEE, various treatment options based on conventional physical, hydrometallurgical and pyrometallurgical processes are available. These process options with particular reference to hydrometallurgical processes were reviewed in this study. With their relatively low capital cost, reduced environmental impact (e.g. no hazardous gases/dusts), potential for high metal recoveries and suitability for small scale applications, hydrometallurgical processes are promising options for the treatment of WEEE. Since the metals are present in native form and/or as alloys, an oxidative leaching process is required for the effective extraction of base and precious metals of interest. A two-stage process based on oxidative acid leaching of base metals (Cu in particular) followed by leaching of precious metals using cyanide, thiosulfate, thiourea or halide as lixiviant(s) can be suitably developed for the hydrometallurgical treatment of WEEE. However, further research is required to develop new, cost effective and environmentally friendly processes and/or refine existing ones for leaching and, in particular, downstream processes. © 2011 Elsevier Ltd. All rights reserved

Reclamation of Precious Metals from Small Electronic Components of Computer Hard Disks

Present research work focuses on the recovery of precious metals (Ag, Au, Pd, and Pt) from the leach liquor of small populated chips present in the hard disk of computers. Initially, the hard disks were dismantled to separate the printed circuit boards (PCBs) followed by its depopulation to liberate the mounted small electronic components. The liberated black chips were pulverized to *100 mesh and chemically analysed. The powdered black chips containing *0.6% Ag, *0.3% Au, *0.01% Pd, *0.0003% Pt, and 20% Cu on mass basis were first leached in nitrate medium for maximum dissolution of non-ferrous metals along with Ag leaving Au, Pd, and Pt in the residue. About 99.99% of precious metals were leached out from the residue using suitable lixiviant. The obtained leach liquor was purified using advanced separation techniques (solvent extraction/ion-exchange/ precipitation) from which marketable products (metals/salts) could be produced

Characteristics of End-of-Life Printed Wiring Boards Processed by Electrodynamic Fragmentation

peer reviewedThe ElectroDynamic Fragmentation (EDF) is an innovative technique which enables selective fragmentation of material. Its inherent selective breakage principles enable liberation while avoiding fine grinding. In this study, the specific effects of the EDF on End-of-Life Printed Wiring Boards have been assessed. A novel methodology for their EDF processing has been developed and compared with hammer mill shredding. Various energy inputs and treatment stages have resulted in fragmentation degrees ranging from removal of components to structure delamination and subsequent size reduction