New technology for environmentally sound tin extraction

Researchers at TU Bergakademie Freiberg are investigating how tin can be extracted without carbon and therefore without direct CO2 emissions. The team’s method could be of particular relevance for the local extraction of tin in Europe.

A mineral that is hard to crack meets a raw material that is increasingly in demand in the electronics and semiconductor industry: during the course of multi-stage smelting and refining processes, raw tin is processed from a concentrate of the mineral cassiterite (tin oxide) through the addition of carbon. In a research project funded by the Dr Erich Krüger Foundation, a team from TU Bergakademie Freiberg is now testing how the metal can be extracted without the use of carbon, thus eliminating direct CO2 emissions. The team’s method could be of particular relevance for the local extraction of tin in Europe.
In a recent scientific article published in the Journal of Sustainable Metallurgy, the researchers propose a new process in which the direct CO₂ emissions from tin production are reduced to practically zero. In contrast, according to Germany’s Federal Society for Geosciences and Natural Resources, up to 2.5 tonnes of CO2 are currently emitted to produce one tonne of tin. The new two-stage process could reduce these emissions since, in the first stage, a small amount of hydrogen is used in place of carbon.
Pretreated with hydrogen, around half of the tin concentrate (tin dioxide) is converted directly into pure tin. Water vapour and slag containing tin are also produced. “Cassiterite is difficult to crack, meaning it cannot be leached, but the slag that is produced can be. The residual tin can then be extracted from the slag by means of chemical leaching at low temperatures,” explains project manager Prof. Alexandros Charitos.

From computer modelling to laboratory tests

“We were able to confirm what our computer models predicted in laboratory tests: in the first step, a very small amount of hydrogen suffices instead of carbon – even so, 50 per cent of the cassiterite becomes raw tin, without any direct CO2 emissions whatsoever.” The team is now investigating in more depth how the remaining tin can be purified using eco-friendly methods after the chemical leaching of the slag, before being extracted by electrolysis in the final step.
Source: TU Bergakademie Freiberg