title: Recovery of zinc from hyperaccumulator plants: Sedum plumbizincicola.
abstract: 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+).
authors.affiliation: Department of Metallurgical Science and Engineering, Central South University, China. Jianguang_yang@hotmail.com
authors.forename: Jian-Guang
authors.initials: JG
authors.lastname: Yang
authors.forename: Jian-Ying
authors.initials: JY
authors.lastname: Yang
authors.forename: Chang-Hong
authors.initials: CH
authors.lastname: Peng
authors.forename: Chao-Bo
authors.initials: CB
authors.lastname: Tang
authors.forename: Ke-Cao
authors.initials: KC
authors.lastname: Zhou
mesh_terms: D000641:Ammonia / Q000737:chemistry; D000643:Ammonium Chloride / Q000737:chemistry; D000704:Analysis of Variance; D001673:Biodegradation, Environmental; D018533:Biomass; D006863:Hydrogen-Ion Concentration; D008670:Metals / Q000032:analysis; D015203:Reproducibility of Results; D031963:Sedum / Q000737:chemistry* / Q000378:metabolism; D012989:Soil Pollutants / Q000737:chemistry / Q000302:isolation & purification* / Q000493:pharmacokinetics; D013696:Temperature; D013816:Thermodynamics; D015032:Zinc / Q000737:chemistry / Q000302:isolation & purification* / Q000493:pharmacokinetics
chemical_list: D008670:Metals; D012989:Soil Pollutants; D000643:Ammonium Chloride; D000641:Ammonia; D015032:Zinc