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The green chemical synthesis of copper nanoparticles (CuNPs) is an alternative which uses chemicals and processes that reduce or eliminate the use and generation of toxic substances, such as ascorbic acid, cyclodextrin, plant extracts, chitosan and gelatine. In this study, precursor solutions of copper sulfate pentahydrate and ascorbic acid were used. The synthesized CuNPs were characterized by UV-visible (UV-vis) absorption spectroscopy, scanning electron microscope coupled to an energy dispersive X-ray spectrometry (SEM-EDS) and X-ray diffraction (XRD). The presence of Cu oxide particles and Cu nanoparticles was inferred through UV-vis. In the images and compositions of the SEM-EDS, oxygen and Cu were found as well as particles of non-uniform size and morphology. The results showed that at pH 5, agglomerated CuNPs were found. XRD verification was performed on the particulate at pH 5 in which diffraction peaks were attributed to copper structure planes (with dimensions of 1042–3.34 nm) and other CuO and Cu2O diffraction peaks that overlapped with Cu phases.

Printed circuit boards represent a source of urban mining for the reuse of resources in a circular economy. The number of metals in these boards can vary according to the model, year of manufacture, and function, making these scraps a complex residue for the application of recovery routes. In the present study, the leaching process was evaluated as an alternative to the magnetic separation step of the current hydrometallurgical routes for the recovery of iron and copper in these waste in which recovery of the metals present was carried out. The first stage of the hydrometallurgical route was leaching in sulfuric acid, for the recovery of iron. Subsequently, the copper recovery study was carried out, through the second stage of acid leaching in an oxidizing medium. The third stage was carried out in a nitric medium for the solubilization of the remaining metals. After using the same solid/liquid ratio for the solubilization of the metals present in the two types of boards, it was found that for the board with the highest concentration of metals that this ratio should be changed for greater extraction results. The percentage of leaching for the motherboard samples increased (to about 98 wt%) together with the residue/acid ratio, and this showed that for each type of waste, according to its composition, the metal/acid ratio must be established for complete solubilization of the metals of interest. The recovery of this waste, depending on the type of scrap, can reach at least US$ 1,230,000.00 /t waste.

The amount of waste from electrical and electronic equipment has been growing every year. The printed circuit boards contained in this waste include metals that can be recovered through urban mining, adding value to this waste and minimizing environmental impacts with its incorrect disposal or treatment. In this work, memory boards obsolete with 0.053 wt.% Ag were used. The extraction of all metals studied (Ag, Al, Cu, Fe, Ni, Sn, and Zn) involved the evaluation of the Pourbaix and speciation diagrams to identify the pH and redox potential conditions, considering the possible species formed with leaching agents: sulfuric, nitric, and hydrochloric medium. After the definition of the leaching agent, the extraction routes by hydrometallurgical processing were proposed from the parameters of temperature, s/l ratio, and reaction time previously studied. Route A was composed of sequential stages (the first leaching in a sulfuric medium and the second in an oxidizing sulfuric medium) and obtained 100% of Ag recovery. Route B consisted only of leaching in an oxidizing sulfuric medium, obtained about 94% of the Ag recovery, and could not contribute to the subsequent purification steps (if necessary) of this solution, as all metals would also be in the solution. These two routes showed that Ag can only be recovered in an oxidizing sulfuric acid medium, according to the conditions studied. Ag recovered in the leach liquor of the second stage of Route A was purified by chemical precipitation with NaCl, and the AgCl was solubilized in an NH4OH solution. This solution was used to synthesize silver nanoparticles by the Turkevich method in 25 minutes. The spherical nanoparticles synthesized an average size distribution of 67 nm.