Researchers have developed a more efficient and sustainable silicon recovery process
Spotted: The number of US solar panels due to retire by 2050, would cover an area the size of 3,000 american football fields. The bulk of these old solar panels is made up of high-purity silicon, a material that has many applications, including in lithium-ion batteries, where it can be added to the anode to improve energy density. But recovering silicon from old solar cells has so far proved difficult, as it is hard to separate the element from other components such as plastic, aluminium, copper, lead, and silver.
Now researchers at Nanyang Technological University, Singapore, have developed a new method of extracting silicon using phosphoric acid. The old solar cells are soaked in the hot acid, which is commonly used in the food and beverage industry, and, in around 30 minutes, the metals are removed from their surface. The process is then repeated with a fresh batch of the acid to obtain pure silicon wafers.
One of the key benefits of this approach is that it only uses one reagent. Existing approaches, by contrast, use at least two types of highly acidic or highly alkaline chemical, and using only one chemical reduces the time spent on post-treatment of the chemical waste.
What is more, the researcher’s method proved to have a higher recovery rate than existing methods, which means that a higher proportion of the waste material was recovered for further use. The resulting silicon also had a higher purity than silicon produced using alternative approaches.
When the upcycled silicon was added to a lithium-ion battery anode to test for efficiency, it was found to perform similarly to fresh commercially sourced silicon.
Other recycling innovations tackling the waste created by the new clean economy include a more sustainable process for lithium-ion battery recycling, fully circular solar PV cells, and state-of-the art recycling for solar panels.
Written By: Matthew Hempstead