Recovering Rare Earth Elements from leftovers of biogas production

Important results from the project

Rare Earth Elements (REEs) can be found in leftovers (digestates) from biogas production. The results show that if the goal is to recover as much of the total REEs as possible, sewage sludge should be the substrate of the digestate used. If the goal, on the other hand, is to recover as much Cerium (Sc) as possible, digestate composed of co-digested agricultural waste should be used. The highest percentage of the found REEs in digestate are present in the solid phase of the digestate.

Expected long term effects

The results presented are of great importance for companies interested of extracting REEs from digestate. That would be beneficial for the society in large since it could lead to less conventional mining of REEs which would mean reduced pollution, less wastewater and decreased depletion of natural resources. Recovering REEs from digestate would increasing the value of digestate and could therefore increase the overall interest in biogas production and therefore increase the usage of renewable energy.

Approach and implementation

The results reported have not been compared to the measurement uncertainty of the method. This is not seen as a necessity since the method used is considered steady and gives consistent results. Moreover, this project is explorative and therefore a limit of a “acceptable” concentration is not determined. Consequently, all calculated concentrations were presented.