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Swedish researchers have developed a method to recycle valuable metals from flexible copper, indium, gallium, diselenide (CIGS) thin-film solar cells under mild leaching conditions.
Scientists at Chalmers University of Technology (Sweden) have demonstrated how to recycle valuable metals such as silver (Ag) and indium (In) from flexible CIGS solar cells using mild leaching conditions. They used 15.6 cm2 x 15.6 cm2 flexible CIGS solar cells with an Ag conductive grid and stainless steel substrate from Swedish photovoltaic manufacturer Midsummer AB. Each cell was cut into eight identical pieces, and then each sample was cut in turn into a small and a large piece.
The academics placed the small pieces of the photovoltaic cells in perfectly sized digestion vessels to obtain the total amount of silver and indium per cell. They placed the large piece in leaching vessels and filled both types of vessels with a desired volume of nitric acid (HNO3) solution of a specified concentration. The ratio between the geometric surface and the liquid (A:L) also varied in the different experiments. The team performed all experiments at room temperature and with a stirring speed of 200 rpm.
After demonstrating that both silver and indium were completely dissolved during digestion, and therefore that leaching experiments would be performed with the full amount of each element in the cells, the scientists set out to test what concentration of nitric acid and what ratio of geometric surface to liquid gave rise to the highest leaching yields.
The results show that a nitric acid concentration of two moles and an A:L ratio of 1:3 lead to very high recovery rates for silver and indium. After four to six hours of leaching, about 90% of the silver is recovered, and after 24 hours the recovery rate reaches 100%. Between 20% and 25% of the indium is recovered in the first hour of leaching, and the highest yield, 85%, is reached after 28 hours.
"When comparing all the results of the different experimental conditions, it can be said that the high yields of Ag and In are always accompanied by high levels of contamination by many other elements, [Zinc] being always present," the scientists pointed out, adding that molybdenum contamination can also be problematic.
They then demonstrated that purer streams can be obtained with a selective leaching process. Using a nitric acid concentration of 0.5 mol and an A:L ratio of 1:3, the silver recovery rate reaches approximately 85% after 24 hours with lower contamination levels. However, the recovery rate of the Indian plummets to only 30%.
The scientists also noted that their method is not yet suitable for industrialization, as the concentrations of silver and indium are too low to be used directly in a viable purification process using more than 1 gram per liter. "For industrialization, the possibility of increasing the concentration should be considered, for example by reusing the same leachate in several cells," they conclude.
The team shared their findings in “ Valuable metal recycling from thin film CIGS solar cells by leaching under mild conditions ,” recently published in Solar Energy Materials and Solar Cells. . |
