Cleaner Pre-concentration of Metals from Printed Circuit Board Waste Using Novel Dense Liquid Medium Based on Sodium Sil
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Cleaner Pre‑concentration of Metals from Printed Circuit Board Waste Using Novel Dense Liquid Medium Based on Sodium Silicate Éllen F. Rodrigues1 · Andreia De Rossi1 · Beatriz Rovaris1 · Alexsandra Valério1 · Débora de Oliveira1 · Dachamir Hotza1 Received: 30 June 2020 / Accepted: 30 September 2020 © Springer Nature B.V. 2020
Abstract Printed circuit boards (PCBs) are present in most electrical and electronic equipment and contain valuable metals such as Cu, Au, Ag, and Pd, being considered attractive sources of metals. In order to recover those metals from PCBs by metallurgical processes, a pre-concentration step is needed. In this study, the metallic components from waste PCBs have been pre-concentrated using a separation process with dense liquid medium based on sodium silicate, as an alternative to toxic chloroform, which is commonly used. After grinding, the waste PCBs presented a mean particle size of less than 0.56 mm. After dense medium separation, similar concentrations of Cu and precious metals were obtained using either sodium silicate solution or chloroform. Therefore, sodium silicate has a high potential to be applied as a cleaner dense liquid medium in gravity separation processes. Graphic Abstract
Keywords Sodium silicate · Electronic waste · Gravity separation · Precious metals * Éllen F. Rodrigues [email protected] 1
Department of Chemical and Food Engineering (EQA), Federal University of Santa Catarina (UFSC), Florianópolis, SC 88040‑900, Brazil
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Statement of Novelty This work evaluates the use of sodium silicate as a novel alternative to replacement of dense heavy liquids used in the pre-concentrate of metals from electronic wastes. In the traditional processes, gravity separation is applied using heavy organic liquids, such as chloroform, bromoform, tetrabromoethane. To the best of our knowledge, sodium silicate as a dense liquid in the gravity process has not been yet evaluated.
Introduction The increased use of electronic devices such as computers and cell phones represents new challenges and environmental impacts when they are inappropriately discarded [1]. About 20–50 million tons of electronic wastes are produced around the world every year with an annual increase of 3–5% [2]. These electronic wastes are a complex mixture of precious metals (Ag, Au, Pd, and Pt), common metals (Cu, Al, Ni, Si, Zn, and Fe), and toxic metals (Hg, Be, Cd, Cr, Sb, and Bi), along with halogens (Br, Cl) and combustible substances (plastics, additives) [3, 4]. The printed circuit board is an essential component of e-waste, in charge of 3% of the total mass [5]. It is possible to find metals in PCBs with concentrations up to 10 times higher than those typically observed in raw minerals [6]. The recovery of this type of material from PCB may be referred to as “urban mining”. Many studies are found in the literature on the mining of precious metals (Au, Ag, Pd, Pt) and high content metals (Cu, Al, Sn) from waste PCBs by physical, chemical and/or biologica
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