Researchers testing environmentally friendly tin extraction

A mineral that is difficult to crack meets a raw material that is increasingly in demand in the electronics and semiconductor industry: In multi-stage smelting and refining processes, raw tin is processed from a concentrate of the mineral cassiterite (tin oxide) with the addition of carbon.

In a new research project, a team from TU Bergakademie Freiberg is testing how the metal 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.

In their recent publication in the Journal of Sustainable Metallurgy, the researchers propose a new process in which the direct CO₂ emissions from tin production are close to zero. In contrast, up to 2.5 metric tons of CO₂ are currently emitted to produce 1 metric ton of tin, according to the Federal Institute for Geosciences and Natural Resources. The new two-stage process could save these emissions, as a small amount of hydrogen is used instead of carbon in the first step.

Pretreated with hydrogen, about half of the tin concentrate (tin dioxide) is converted directly into pure tin. Water vapor and a tin-containing slag are also produced. "Cassiterite is difficult to crack, i.e., it cannot be leached, but the slag produced can. The residual tin can then be extracted from the slag by chemical leaching at low temperatures," says project leader Professor Alexandros Charitos.

"We were able to confirm in laboratory tests what our computer models predicted: In the first step, instead of carbon, a very small amount of hydrogen is sufficiently used—yet 50% of the cassiterite already becomes raw tin, without any direct CO₂ emissions."

The team and other working groups at the Institute of Nonferrous Metallurgy and High-Purity Materials are now investigating in more detail how the remaining tin can be purified using environmentally friendly methods after the chemical leaching of the slag and extracted by electrolysis in the final step.

The team's findings could be of particular relevance to the Free State of Saxony, as exploration projects for tin-bearing ores are underway in Geyer, Gottesberg and Tellerhäuser, for example.

"The new process harbors great potential for environmentally friendly extraction in Saxony and Europe, but also for the recycling of tin. After all, almost all of the world's tin is currently produced in countries with weak governance and often with rarely recorded environmental impacts," Charitos says.