Synthesis of copper and silver nanoparticles from the recycling of PCBs

The amount of waste electrical and electronic equipment (WEEE) discarded increases each year. Several factors may contribute to this growth, such as technological advances, changes in the population’s lifestyle, the development of society, economic growth and the very diversification and programmed obsolescence of these products. About 20 to 50 million tons of this waste is produced per year, with an annual increase of 3-5%.

Printed circuit boards (PCBs) are present in all WEEE and they represent about 5% of its total. These boards are substrates on which the electronic components are assembled and the circuits are interconnected. Elements in its composition may have economic value, such as copper, silver, gold, and nickel, in addition to elements that are harmful to the environment and health, such as lead, mercury, and cadmium. Studies estimate that metals represent more than 95% of the total intrinsic value of the plate. Hence, in addition to environmental concerns, the depletion of mineral reserves and the need for sources for secondary recovery of value-added metals are important factors for the study of metal recovery from electronic scrap.

Through recycling PCIs, recovering and reusing chemical elements in new production processes can provide economic, environmental and social benefits. An example is the production of metallic nanoparticles, which may increase the added value of this residue. Thus, after the recovery and purification of the extraction solution, the metal can be used as a precursor in the synthesis of nanoparticles, such as silver and/or copper, for example. These nanoparticles have the potential for application in several sectors of the industry, which justifies their added value, such as in catalysis, electronics, optics, in fabrics and packaging and in medicine.

In this context, this line of research aims to apply hydrometallurgical routes for the extraction and purification of copper and silver from PCBs of obsolete electrical and electronic equipments, later, synthesis and characterization of nanoparticles.

Initially, the PCIs of electrical and electronic equipment go through several processes of unitary operations (dismantling, comminution, the concentration of metals by magnetic, electrostatic or gravity separation) and characterization (particle size analysis, chemical characterization and loss on ignition).

Then, the hydrometallurgical processing is carried out, in which parameters such as the appropriate leaching agent (acid), concentration, solid-liquid ratio, solution potential, temperature, agitation, heating time, oxidant agent, and leaching steps are studied. After the recovery of the metals of interest, the leaching solution can be purified through solvent extraction, chelating resins, selective precipitation or electrorefining. Finally, after the recovery of silver and copper, the nanoparticles of these metals are synthesized.

The nanoparticles formed are characterized by UV-visible absorbance spectroscopy (UV-Vis), X-ray diffraction (DRX), energy-dispersive X-ray spectroscopy (EDS), Zeta potential, dynamic light scattering (DLS) and transmission electron microscopy (TEM).