*3.3. Characterization of the Thermal Processing Products*

The recovered glass fiber was characterized utilizing SEM/EDS and its results are presented in Figure 12. It is possible to note that Si and Ca are the major metals in the fiberglass while oxygen is the major overall component. The preeminent levels of C also followed the carbon-black-deposition expectations. Some minor contents of Al, Ti and Cu were also detected. Some minor, bright, particulate material within the knitting pattern can be observed. Since such elements are heavier than C, and combined with the Backscattered Electrons detection mode, it is possible to affirm that some metallic powder is also being transported with the fiberglass.

**Figure 12.** SEM/EDS characterization of the fiberglass recovered after the size separation.

Figure 13 is associated with the copper sheets recovered in this study, presenting the SEM/EDS analysis as well as the chemical mapping for the same area. The morphological aspect of the image indicates some deposition of organic matter (dark scales) over the copper sheet (bright area). This is indicative that some fraction of the polymeric material is not being transferred to the gas phase in the thermal degradation. The qualitative chemical mapping clarifies that suggestion, as copper is the major component of this material while the scales have carbon and bromine in their composition. This context indicates that temperature and reaction time could also be optimized to separate copper from non-metals and flame-retardant elements.

Figure 14 presents the SEM/EDS analysis of the recovered magnetic connector. It was verified, through the EDS microanalysis, that the Cu, Ni and Au are being recovered in this material (Figure 14a). Without size reduction to powder, some non-magnetic metals remain linked to nickel providing its concentration being subjected to a magnetic field. These elements are the main constituents of the bright area of the connector that covers the inner layer of copper (Figure 14b). The presence of carbon is also perceptible, both in the EDS microanalysis as well as through the dark matter over the metallic phase.

**Figure 14.** SEM/EDS characterization of the metallic contacts recovered after the size separation and magnetic separation: (**a**) microanalysis of the surface layer; (**b**) microanalysis of the inner contact.

#### **4. Final Remarks**

In short, the proposed route was established as an alternative for processing PCB samples and to valorize them, concentrating metals, separating these from some pf the ceramic content and organic substances. The process produced a black liquid which condensates from the gas phase, therefore diminishing atmospheric emissions and possibly providing a source of materials in some technological applications.

The SEM/EDS analyses showed that the support for the alloy connectors was composed of carbon and oxygen, which indicates, as expected, a typical polymeric material. The presence of bromine, related to flame-retardant additives, was also observed, as were small fractions of metals. The chemical composition for this part of the PCBs samples does not change between varieties. Analyses also showed that the metal connectors have some compositional distinctions between the three types. It was observed that all three samples contain gold and nickel in the surface. The main difference is the relative amounts, with Au as the main metallic constituent for Types 1 and 2 while it is Ni for Type 3. The chemical

mapping indicated a clear presence of copper in the inner layers of the connectors. The distribution of chemical elements is also clear following the SEM/EDS approach.

The TGA analyses showed a mass loss of 30%. The observed degradation temperature of about 250 ◦C is related to the presence of thermoplastic materials. This behavior indicates that all three samples could be processed simultaneously to volatilize the organic fraction. The tubular reactor processing also showed a mass loss of around 30% in weight. The formation of black liquid under inert processing condition was also observed. The characterization of the produced fluid will be assessed in future developments.

It is interesting to observe that combing all metallic contacts in a single fraction in the magnetic separation step is a significant contribution and a simple alternative for metals separation. It should be noted that these characterization and processing experiments could contribute to future recycling route development, lowering environmental impacts associated with this type of WEEE.

**Author Contributions:** Conceptualization, F.J.M. and R.F.M.S.; methodology, J.S.S.O., R.R.H., F.J.M. and R.F.M.S.; formal analysis, J.S.S.O., R.R.H., F.S.d. and C.A.A.; investigation, J.S.S.O., F.S.d. and C.A.A.; resources, F.J.M., E.A.B. and R.F.M.S.; data curation, J.S.S.O.; writing—original draft preparation, F.J.M. and R.F.M.S.; writing—review and editing, F.S.d., C.A.A. and R.F.M.S.; supervision, F.J.M. and R.F.M.S.; project administration, F.J.M. and R.F.M.S.; funding acquisition, E.A.B. and R.F.M.S.; All authors have read and agreed to the published version of the manuscript.

**Funding:** The APC was funded by Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ)–Project "Apoio para publicações científicas em revistas qualificadas e de open access, priorizando a participação de alunos" (Edital 05/2020).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data will be made available based on request to the authors.

**Acknowledgments:** This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Financial Code 001. The authors are also grateful for the support throughout the research to VRAc/PUC-Rio (Vice-Reitoria para Assuntos Acadêmicos) and CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico).

**Conflicts of Interest:** The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

#### **References**

