Hydrothermal Conversion of Cd-Enriched Rice Straw and Cu-Enriched Elsholtzia splendens with the Aims of Harmless Treatment and Resource Reuse

Abstract

In the present work, we report a greener and efficient process of hydrothermal conversion of rice straw (Cd low accumulated crop) and Elsholtzia splendens (Cu accumulated plant) to recover the metals and simultaneously produce biofuel for harmless treatment and resource reuse. The impacts of different types of additives, raw materials/solvent ratios, reaction times, and temperatures are investigated, and the composition of solid phase left is also studied for future efficient use. As the results suggest, almost all enriched metals (95 ± 2% of Cu in E. splendens and almost all Cd in rice straw) are concentrated in solid phase after hydrothermal conversion with a considerable amount of carbohydrates contained, making the solid residue an excellent material for producing metal carbide catalysts. During the hydrothermal conversion, the additives have little impact on the metals recovery, and higher raw material/solvent ratios have higher yields of Cu/Cd. Finally, 22.0–25.0% yields of bio-oils without any meta...