Extraction of Metals From Disposed Mining Sludge in Folldal, Norway

Funded by the Norwegian Directorate of Mining (DIRMIN), Nordic Sustainable Minerals (NSM) Project.

Acid mine drainage (AMD) from the former Folldal mine has, since operations ceased, continued to pollute the river Folla with dissolved heavy metals, while also representing an untapped source of valuable metals such as copper, zinc, iron, and aluminium. This project explored how these metals could be recovered from Folldal's AMD, turning an environmental liability into a resource recovery opportunity.

The work was carried out in three stages. The first stage reviewed existing characterization data on the Folldal AMD and assessed a broad range of established treatment technologies — including hydroxide and sulfide precipitation, ion exchange, liquid-liquid extraction, and membrane filtration — alongside case studies of similar mine water treatment plants in Norway, Sweden, and Serbia, to identify the most promising approach for Folldal's specific water chemistry.

Building on this, the second stage experimentally tested neutralization and precipitation using sodium hydroxide and calcium hydroxide across a range of pH values, in both batch and semi-batch reactor setups. The resulting sludge was characterized for metal content, settling behavior, and filterability. Calcium hydroxide was found to offer faster settling and better filtration performance than sodium hydroxide, despite producing more sulfate-rich sludge, making it the preferred precipitant for this application.

The third stage focused on recovering the valuable metals remaining in solution after iron removal. Selective precipitation first removed iron at pH 4 with minimal loss of copper, zinc, and aluminium. The remaining metals were then concentrated using ion exchange, increasing their concentration more than tenfold in the resulting eluate, before solvent extraction was used to separate copper from zinc and aluminium with high selectivity and over 98% recovery efficiency.

Together, these results demonstrated a viable, staged process — combining precipitation, ion exchange, and solvent extraction — for both treating Folldal's acid mine drainage and recovering valuable metals from it, offering a promising route toward more sustainable management of legacy mine sites.