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. 2021 Apr 30;6(18):12063-12071.
doi: 10.1021/acsomega.1c00724. eCollection 2021 May 11.

Leaching of Metals from e-Waste: From Its Thermodynamic Analysis and Design to Its Implementation and Optimization

Jose Angel Barragan  1 , Juan Roberto Alemán Castro  1 , Alejandro Aarón Peregrina-Lucano  2 , Moises Sánchez-Amaya  1 , Eligio P Rivero  3 , Erika Roxana Larios-Durán  1
Affiliations

Leaching of Metals from e-Waste: From Its Thermodynamic Analysis and Design to Its Implementation and Optimization

Jose Angel Barragan et al. ACS Omega. .

Abstract

The aim of this study is to design and develop an efficient leaching process based on a fundamental and theoretical thermodynamic analysis and the optimization of the operation parameters via the response surface methodology (RSM). Using this methodology, the design of a leaching process for the recovery of copper, silver, and lead from highly metal-concentrated fractions of e-waste is presented. Thermodynamic predictions were performed through the construction and analysis of Pourbaix diagrams for the specific conditions of the leaching system. From this analysis, it was possible to determine the values of potential (E vs NHE) and pH at which the leaching reactions occur spontaneously. Additionally, RSM was useful to deduce a quadratic semiempirical model that predicts the copper leaching efficiencies as a function of two parameters involved in the leaching procedure, the stirring speed and the solid/liquid ratio, by which the response variable, the leaching efficiency, can be optimized.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Diagram process for size reduction and concentration of e-waste. Reprinted (adapted) with permission from [ACS Omega2020,5, 21, 12355–12363]. Copyright [2020/American Chemical Society] [ACS Omega/American Chemical Society].
Figure 2
Figure 2
Pourbaix diagrams, E vs pH, of copper in the leaching system. Conditions: 2 mol dm–3 HNO3 as the leaching solution; (a) 2.57 M copper, (b) 0.16 mM silver, (c) 9.54 mM lead, (d) 0.24 M iron, (e) 0.32 M aluminum, and (f) 0.24 M nickel at 25 °C. The red line indicates the pH restriction, and the blue line indicates the potential (E vs NHE) restriction for the leaching process.
Figure 3
Figure 3
Actual values of the leaching efficiency (experimental) vs values predicted by the response surface quadratic model.
Figure 4
Figure 4
Response surface of the leaching copper efficiency vs solid/liquid ratio (g dm–3) and stirring speed (rpm).
Figure 5
Figure 5
Leaching test of stream D at the optimized parameters in the leaching reactor and the thermodynamic restrictions. Conditions: e-waste stream D; nitric acid concentration: 2 mol dm–3; stirring speed: 540 rpm; solid/liquid ratio: 80 g dm–3. (a) Concentration of Fe, Ni, and Cu vs time. (b) Concentration of Al, Ag, Pb, and Au vs time. (c) E vs NHE; pH and temperature vs time.
Figure 6
Figure 6
Leaching test of stream E at the optimized parameters in the leaching reactor and the thermodynamic restrictions. Conditions: e-waste stream E; nitric acid concentration: 2 mol dm–3; stirring speed: 540 rpm; solid/liquid ratio: 80 g dm–3. (a) Concentration of Fe, Ni, and Cu vs time. (b) Concentration of Al, Ag, Pb, and Nd vs time. (c) E vs NHE; pH and temperature vs time.
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