Researchers at the Gyeongsang National University Jinju in South Korea have developed a new method for separating ethylene vinyl acetate (EVA) encapsulant from recycled silicon power in end-of-life (EoL) solar panels.
In common mechanical recycling processes, EVA is mixed after the crushing or grinding, while chemical and delamination methods are generally time-consuming or create dangerous waste products. The new process utilizes thermal and wet gravity separation (WGS) to separate EVA from reclaimed Si powder with “minimal.” chemical usage, according to the researchers.
The wet gravity separation process uses an aqueous sodium chloride (NaCl) solution that exploits the gravity difference between silicon and EVA and the WGS process uses specific gravities of the two materials to facilitate their centrifugation. “All recycling processes were performed in the commercial facility except for wet gravity separation to remove ethylene vinyl acetate (EVA) encapsulant,” the research's corresponding author, Jongsung Park, told pv magazine.
The entire process begins with dismantling the module aluminum frame and removing the sealant. Then, a grinding process removes the backsheet and a heating process separates the remaining layers. The following step consists of a shredding process to select solar cells encapsulated in EVA, which is followed by a sorting process based on particle size differences of shredded materials. In addition, small particle-size powder-type solar cells and metals are separated and a thermal process eliminates the EVA contained in silicon powder.
“The thermal process at 550 C effectively removed all polymer components, specifically EVA, from the reclaimed silicon powder, as confirmed by various analytical techniques such as TGA, FT-IR, SEM, and EDS,” the group explained. “While effective, the thermal process has notable drawbacks, including high energy consumption and significant carbon dioxide emissions, making it less environmentally friendly than the WGS.”
Further analysis confirmed the effective removal of EVA and other polymers. “The recycling of EoL PV modules was carried out in 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 use it for solar cell manufacturing again, but as a 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,” which was recently published in the Royal Society of Chemistry.
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