11 Aug 2022

Bioleaching offers potential for reclaiming PCB tin

More than one third of all tin is used in electronics every year. Although around of a third of all tin is recycled, more could be done to recover the metal from waste circuit boards. Traditionally the industry has mainly focused on recovering gold and copper, but tin has been attracting more attention.

Up to 3% of a circuit board’s weight is tin. With tin prices having doubled in the last year, incentives to develop new tin recycling processes are growing. E-waste is one of the most significant potential sources of new tin supply. More than 50,000 tonnes of tin could be recoverable every year if challenges such as collection and processing are tackled.

The Bioremediation Group, part of the Bioscience and Biotechnology Engineering research group at Coventry University, UK, is at the forefront of developing new e-waste recycling methods.

Along with others around the world, the Coventry team is designing improved processes for selectively recovering tin from the complex metallurgy of a circuit board. The International Tin Association (ITA) has been tracking this field over the last decade, including its own European-funded pilot-scale JV project Itrimex that processed more than 10 tonnes of waste circuit boards to recover tin.

Several traditional options are possible but bioleaching is a novel approach which offers a lower energy, sustainable route. However, key challenges, such as scalability and improving the reaction rate, remain.

Representatives of the ITA met the Coventry R&D team in November 2021 and discussed optimisation of bioleaching chemistries, using bacteria to dissolve tin solder from waste circuit boards. The team have already demonstrated 100% recovery of tin from gold-tin connectors after 11 days using bacteria at 30°C. Success in this field may open wider opportunities for tin recovery from other tin wastes.

The Coventry team is partnered with UK IT life-cycle service market leader N2S, with support from UK government department DEFRA as well as large electronics industry players. These links will be important in dealing with issues related to integration of any new process into the existing supply chain for e-waste metals recovery. Economics of such a process will have been improved by increased tin prices but viability will still need to demonstrated on the large-scale.