**4. Conclusions**

This paper discusses for the first time, to the knowledge of the authors, the potential of cultivating annual plants in conventional MIBA in order to generate metal-enriched biomass fuel, which is to be used for metal recovery.

The results show that cultivation of rapeseed and sunflowers in conventional MIBA is challenging. The main explanations for this are the inhibited root development and low water- and nutrient-holding capacities caused by unsuitable properties such as the high fraction of large particles, the low TOC content, and the high density of MIBA. Rapeseed plants with more developed taproots grew better than sunflowers, but the addition of fertilizer was crucial.

There was an accumulation of numerous metals in both plant types, and the highest metal content was generally found in the roots. Calculations indicated ash from rapeseed root incineration contained 2% Zn, and the contents of Co, Cu, and Pb were comparable to those in workable ores. The metal reduction in MIBA after cultivation was limited.

The results indicate that to promote phytoextraction on MIBA, the material itself should be refined, but also the choice of plants is important. Perennials with roots that efficiently penetrate the compact MIBA material, e.g., members of the salix family, are theoretically suitable. This initial study shows that cultivation in and phytoextraction on MIBA is possible, but further research is needed.

**Author Contributions:** Conceptualization, K.K.F., V.E. and D.D.; Investigation, K.K.F.; Methodology, K.K.F., V.E. and D.D.; Resources, K.K.F., V.E. and D.D.; Visualization, K.K.F.; Writing—original draft, K.K.F. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by "the Ash program", managed by Energiforsk (2018-113) and Avfall Sverige (F226), gran<sup>t</sup> number (2018-113) and (F226).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Acknowledgments:** This work was supported by the "Ash program", managed by Energiforsk (2018-113) and Avfall Sverige (F226), which is gratefully acknowledged. Sandra Dassoum is recognized for her assistance with cultivation management.

**Conflicts of Interest:** The authors declare no conflict of interest.
