Shibaura Institute of Technology successfully recovers hazardous selenium from waste solar panels using microorganisms

Senior Professor Mitsuo Yamashita from the Collaborative Research Programs for Metal Biotechnology at Shibaura Institute of Technology and K.F.C. Co., Ltd. (Minato City, Tokyo Prefecture) have achieved the world's first successful purification, recovery, and resource recycling of selenium. To achieve this success, the selenate-reducing microorganism Stutzerimonas stutzeri NT-I was used after dissolving rare metals including selenium from waste solar panels.

Mass disposal of solar panels is expected from the 2030s onward, but those made with glass, metal, and resin strongly bonded together are waste materials which are complex to recycle. Additionally, compound-type solar cells contain hazardous substances such as arsenic, selenium, and cadmium, raising concerns about environmental impacts from leachate contamination.

Selenium is a type of rare metal widely used in semiconductor materials and solar panels. Selenate and selenite are toxic, and wastewater standards and environmental standard values for soil contamination have been established, making them targets for purification. Meanwhile, with the accelerating introduction of renewable energy, production and sales of solar panels have gradually expanded since the 2000s. Large quantities of solar panels will be thrown away due to events such as natural disasters and deterioration caused by aging, and because of the potential for major social and environmental problems such as securing disposal sites, recycling is desirable.

In this study, the research group successfully dissolved CIGS (Cu, In, Ga, Se) from CIGS-type waste solar panels, a type of compound solar cell that contains selenium. After neutralization, the research group combined the dissolved CIGS with the selenate-reducing microorganism NT-I in a reaction environment, achieving the world's first successful selenium recovery and resource recycling.

NT-I reduces selenate to selenite and selenite to elemental selenium, making it insoluble to be transformed into a solid form. Subsequently, it generates dimethyl diselenide from elemental selenium and synthesizes vaporized selenium. In this experiment, selenium solidification and recovery were performed using a bioreactor and centrifuge. NT-I was added to 3 liters of simulated selenium wastewater and continuously stirred at a stirring speed of 250 rpm and 38℃. Selenium recovery was successfully achieved in 12 hours from an initial concentration of 87.8%. The recovered bio-selenium could be refined to 99.99% purity through simple purification, drying, and chemical reduction.

In the future, the researchers plan to scale up from lab scale to bench scale and ultimately to plant level, aiming to realize a recycling-based society.