Phytoextraction potential of Manihot esculenta Crantz. (cassava) grown in mercury- and gold-containing biosolids and mine tailings

- Cassava was grown successfully for the 1st time on biosolids-amended mine tailings.
- The best substrate contained 75% biosolids and 25% Au mine tailings.
- Fibrous roots accumulated up to 12.59 g kg−1 Hg and 18.99 mg kg−1 Au.
- The phytoextraction of Au was suppressed at higher Hg concentrations.

The potential of Manihot esculenta Crantz (cassava) to phytoextract Hg and Au from Hg- and Au-containing biosolids and mine tailings was successfully demonstrated for the first time. Removal of Hg by a hyperaccumulating plant species offers new options to clean up Hg-contaminated sites and at the same time harvest trace amounts of Au. Pre-rooted cassava cuttings with 5-7 nodes were grown in different combinations of biosolids-amended mine tailings to evaluate the best combination that will support optimum plant growth. The 75% biosolids - 25% mine tailings combination produced the best growth in cassava. Plant cuttings were also grown in hydroponics solutions amended with Hg and/or Au to determine root uptake of the two metals. Metals uptake was found to be greatest in the fibrous roots, accumulating up to 12.59 g kg−1 Hg and 18.99 mg kg−1 Au. Given its ease of cultivation and harvesting as well as the high accumulation of Hg and Au in its roots, cassava can be considered as a suitable candidate for Hg remediation and Au recovery from biosolids and mine tailings containing these metals.