Heavy metal removal and crude bio-oil upgrade from Sedum alfredii Hance harvest using hydrothermal upgrading.

In this study, heavy metals were removed and crude bio-oil was yielded from a heavy metal hyperaccumulator harvest, Sedum alfredii Hance, through hydrothermal upgrading process. This paper reports on the optimization of process parameters for the removal of heavy metals (zinc, lead, and copper) and for the upgrading of crude bio-oil from this biomass in an autoclave. Parameters such as granularity, temperature, pressure, and duration were examined for their effect on the removal efficiency of heavy metals and upgrading efficacy of crude bio-oil. Maximum heavy metal removal efficiency of >99% and crude bio-oil upgrading efficiency of >60% were attained with an 18 mesh (1 mm) granularity, and 22.1 MPa at 370 degrees C in the presence of 10 mg/L additives (K(2)CO(3)) for 60 s. Under these optimized conditions, an oil phase (mostly composed of phenolic hydrocarbons and derivatives), a water phase raffinate (containing Zn(2+) (0.39 g/L), Pb(2+) (0.10 g/L), Cu(2+) (0.15 g/L)), and a solid phase (the hydrothermal upgrading residue, which completely satisfies the limit set by China legislation related to biosolids disposal) were obtained.

Recovery of zinc from hyperaccumulator plants: Sedum plumbizincicola.

Hyperaccumulator biomass harvested after heavy-metal phytoremediation must be considered as hazardous waste that should be contained or treated appropriately before disposal or reuse. As a potential method to detoxify the biomass and to convert this material to a suitable fertilizer or mulch, leaching of heavy metals from Sedum plumbizincicola biomass was studied by using ammonia-ammonium chloride solution as a leaching agent. The research was carried out in two phases: (i) a leaching study to determine the heavy metal:zinc extraction efficiency of this leaching agent and (ii) a thermodynamic analysis to identify the likely reactions and stable Zn(II) species formed in the leaching systems. Experimentally, a Taguchi orthogonal experiment with four variable parameter elements: leaching temperature, nNH4Cl:nNH3 ratio, leaching time and solid-liquid ratio, each at three levels, was used to optimize the experimental parameters by the analysis of variances. Application of the Taguchi technique significantly reduced the time and cost required for the experimental investigation. The findings indicate that leaching temperature had the most dominant effect on metal extraction performance, followed by nNH4Cl:nNH3 ratio, solid-liquid ratio and leaching time. Accordingly, the optimum leaching conditions were determined as temperature: 60 degrees C, nNH4Cl:nNH3 = 0.6, leaching time: 2 h and solid/liquid ratio: 5:1. The total zinc removal after leaching under the optimum conditions reached 97.95%. The thermodynamic study indicated that the dominant species produced by the leaching process should be the soluble species Zn(NH3)4(2+).