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

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.

Copper and Antimony Recovery from Electronic Waste by Hydrometallurgical and Electrochemical Techniques.

A strategy for the efficient recovery of highly pure copper and antimony metals from electronic waste (e-waste) was implemented by the combination of hydrometallurgical and electrochemical processes. The focus is on copper recovery as the main component in the leached solution, whereas the antimony recovery process was established as a purification step in order to achieve a highly pure copper deposit. The strategy includes mechanical methods to reduce the size of the wasted printed circuit boards to enhance the efficiency of antimony and copper lixiviation via ferric chloride in acidic media (0.5 M HCl) followed by an electrowinning process. In order to establish the best parameters for copper electrowinning, the leached solution was characterized by cyclic voltammetry and cathodic polarization. Then, an electrochemical reactor with a rotating cylinder electrode was used to evaluate the copper concentration decay, the cathodic current efficiency, the specific energy consumption, and mass-transfer coefficient. Furthermore, antimony was recovered via precipitation by a pH modification in accordance with the Pourbaix diagram. Under this methodology, two valuable products from the e-waste were recovered: a 96 wt % pure copper deposit and 81 wt % pure antimony precipitate. The strategy for recovery of other metal ions, such as lead, present in the e-waste at high concentrations will be reported in further works.