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A research group in the United States has developed a process to recover lead in its metallic form and be able to reuse it in the photovoltaic industry. The process relies on a leaching solution made from a combination of acetic acid (CH3COOH) and hydrogen peroxide (H2O2) which, according to the researchers, leaches lead “in a matter of minutes”.
Scientists at Arizona State University have developed a new two-step process to recycle lead (Pb) from photovoltaic modules at the end of their life cycle.
“No recycler talks about lead recovery because it doesnt generate a lot of income, but rather increases the cost of recycling,” the corresponding author of the research, Meng Tao, told pv magazine . “In the long term, it is a drag on recyclers, as it is toxic and sooner or later it will leak out of the photovoltaic panels. We are considering lead recovery as part of the global recycling process that we are developing."
The process uses a leaching solution based on a combination of acetic acid (CH3COOH) and hydrogen peroxide (H2O2), which the researchers say works as an effective leaching agent for Pb “within minutes.” They specified that each solar cell used in photovoltaic panels contains, on average, about 0.2 grams of Pb.
The metal is recovered by dissolving it in the leach solution. After leaching, the resulting Pb powders are rinsed and dried on highly absorbent paper to minimize the formation of lead acetate compounds, which the team says introduce errors during weight measurements. "It is preferable to recover it in its metallic form to be able to sell it again to the solar industry for new welds," says the US group.
The second step in the process is electrowinning, a technique often used to recover metals from solution through an electrolytic chemical reaction. The scientists conducted nine electrowinning experiments with different combinations of CH3COOH concentrations. They achieved the highest recovery rates, greater than 99%, with a 10% CH3COOH solution.
“These high recovery rates were determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES) for post-electrowinning leachates,” they explained. “The 0% CH3COOH solution presents the lowest Pb recovery rates for each applied potential, suggesting that CH3COOH aids in Pb electrowinning.”
The scientists noted that the total amount of Pb in the solution is approximately 16 mg or 0.05% of the total mass of dust. Assuming that 0.2% of the silicon cell weight is represented by Pb, the total amount of Pb in the 1.3 g silicon cells should be 26 mg, they said.
The technique is fully described in the study “ Lead leaching and electrowinning in acetic acid for solar module recycling”, published in Solar Energy Materials and Solar Cells . “Overall, the CH3COOH leaching and electrowinning process holds promise as a viable and safe method for lead recovery from silicon solar modules,” the researchers conclude. |
