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Korean researchers have used wet thermal and gravity separation to separate EVA from silicon powder recovered from end-of-life photovoltaic modules with “minimal” use of chemicals. The proposed technique provides silicon powder that could be reused as a feedstock for upcycling into silicon nitride, silicon oxide or silicon carbide.
Researchers at Gyeongsang Jinju National University in South Korea have developed a new method to separate ethylene vinyl acetate (EVA) encapsulant from recycled silicon energy in end-of-life (EoL) solar panels.
In typical mechanical recycling processes, EVA is mixed after crushing or grinding, while chemical and delamination methods are often time-consuming or generate hazardous waste. The new process uses thermal and wet gravity separation (WGS) to separate EVA from recovered Si powder with “minimal” use of chemicals, according to the researchers.
The wet gravity separation process uses an aqueous sodium chloride (NaCl) solution that takes advantage of the difference in gravity between silicon and EVA, and the WGS process uses the specific gravities of the two materials to facilitate centrifugation. “All recycling processes were carried out at the commercial facility except for the wet gravity separation to remove the ethylene vinyl acetate (EVA) encapsulant,” corresponding author of the research, Jongsung Park , explained to pv magazine .
The entire process begins with the disassembly of the modules aluminum frame and the removal of the sealant. A crushing process then removes the backsheet and a heating process separates the remaining layers. The next step is a crushing process to select the EVA-encapsulated solar cells, followed by a sorting process based on the particle size differences of the crushed materials. In addition, small particle-sized powder solar cells and metals are separated, and a thermal process removes the EVA contained in the silicon powder.
“The thermal process at 550°C effectively removed all polymeric components, particularly EVA, from the recovered silicon powder, as confirmed by various analytical techniques such as TGA, FT-IR, SEM and EDS,” the group explained. “Although effective, the thermal process has significant drawbacks, such as high energy consumption and significant carbon dioxide emissions, making it less environmentally friendly than WGS.”
Further analysis confirmed the effective removal of EVA and other polymers. “The recycling of the EoL PV modules was carried out at a commercial facility and an environmentally friendly process was used to recover high-purity silicon,” Park explained. “We recovered the silicon in powder form and will not reuse it to manufacture solar cells, but rather as raw material for upcycling into silicon nitride (SiNx), silicon oxide (SiOx) or silicon carbide (SiC).”
The scientists presented the novel technique in the study « Development of eco-friendly pretreatment processes for high-purity silicon recovery from end-of-life photovoltaic modules », recently published in the Royal Society of Chemistry . |
