Hydrothermal conversion of the hyperaccumulator Sedum alfredii Hance for efficiently recovering heavy metals and bio-oil

Recovering heavy metals from a hyperaccumulator is of significant interest; however, such metals are typically extracted in the liquid phase, which increases the cost of recovery. In this work, hydrothermal processing is used to extract Cd, Cu, Pb and Zn from enriched Sedum alfredii Hance in order to separate the heavy metals into the solid phase for easy recovery and the simultaneous production of bio–oil. The results show that almost all enriched Cd, Cu, Pb and Zn (87.8% Ce, 87.5% Cu, 90.2% Pd and 87.2% Zn) are concentrated in the solid phase at only 320 °C (30 min), which also contains considerable carbohydrates. Interestingly, the additives/H 2 O 2 do not affect the removal of metals during the hydrothermal process. The yield of bio-oil is 21.5% (38.1 MJ/kg of calorific value) and is obtained with almost no heavy metals. Finally, we use different ratios of metals ions to reducing sugars as well as the non-hyper accumulating ecotype Sedum alfredii Hance to study the behavior of metals’ recovery. It is showed that the heavy metals are recovered in the solid phase due to reducing substances in the biomass that convert metal ions to the metallic state.