Partitioning And Speciation Of Heavey Metals During The Thermal Disposal Of Phytoremediation Plant

With the wildly use of phytoextraction for controlling soil heavy metal pollution,the disposal of accumulators has become an important problem.Because of the advantages of small space occupation and high volume reduction rate,thermal method has attracted considerable interest.The disposal of Sedum plumbizincicola-cadmium(Cd)and zinc(Zn)hyperacc?mulator by incineration and pyrolysis in lab-scale tube furnace and pilot-scale fluidized bed furnace were studied.Thermal characteristics and fate of heavy metals of S.plumbizincicola were studied.The composition of bio oil from pyrolysis process was also determined for renewable energy.Thermal characteristics and fate of heavy metals of S.plumbizincicola harvested from farmland and mine area were studied druing the combustion process in the lab-scale tube furnace.The minim?m Gibbs free energy calculation method of heavy metals during the thermal process were studied.More than 99%of Zn,Cd and lead(Pb)found in fly ash and bottom ash during the comustion of S.plumbizincicola from farmland and mine area.Recovery of heavy metals in fly ash from mine area of Sed?m plumbizincicola was higher than that from farmland at high temperature;higher recovery of Zn,Cd and Pb from fly ash with higher temperature.Under reducing atmosphere,The volatilization of heavy metals were inhibited by sulfur or sulfide.But in oxidizing atmosphere,Zn,Cd and Pb are found as pure metal,crystalline oxides without reaction with S,Cl,SiO2 and Al2O3.Incineration of S.plumbizincicola was studied in pilot-scale fluidized bed furnace with different temperature and bed materials.The concentration of Pb increased and Zn discreased in ashes with the increasing temperature,but the concentration of Cd slight fluctuated with the increasing temperature.The recovery rate of Zn and Pb from ashes is highest by using attapulgite as bed material and highest of Cd from bottom ash by using bauxite as bed material.Most of Zn and some of Pb emitted with uncombusted ashes.Some of Pb vapored and then condensated in KCl crystals.Most of vapored Cd was found as renucleation with CaO and S.The formation of PMi,PM2.5 and PM10 particles was affected by the type of the bed materials and temperature.Zn enriched in PM10 and PM2.5,Pb enriched in PM2.5,while Cd enriched in PMi.Highest content of PM1,PM2.5 and PM10 particles was found when using quartz as bed material at 850?.Based on the Eulerain-Eulerian model for S.plumbizincicola incineration process,the combustration characteristics in fluidized bed and volatilization of heavy metals were studied.More than 78%of Cd vapored,and just a little of Pb and Zn vapored in the furnace at 823K.The volatilization rate of Pb and Zn increased with increasing temperature.The simulated date of evaporation rate of heavy metals are higher than that of the experimental,that may due to the ignore of some factor which limited the vapor of heavy metals(captured by fly ash and bed material,nonvolatile substance of heavy metals were synthesized,and so on).Overall,the simulation process of incineration of S.plumbizincicola can be better described by the volatilization of heavy metals in furnace and provide a theoretical basis for controlling of heavy metals in the incineration process in the future researches.The fate of heavy metals and the composition of bio oil of S.plumbizincicola harvested from farmland and mine area were studied druing the pyrolysis process.The yield of gas increased and char decreased with the increase of temperature.More heavy metals vapored at higher temperature.Higher recovery rate of heavy metals were found in bio-oil of S.plumbizincicola harvested from mine area than that from farmland.Main components of the bio oil were acids at 450? and alkanes at 650?.Pyrolysis of S.plumbizincicola in pilot-scale fluidized bed pyrolysis process was studied.The yield of gas increased and char decreased with the increasing temperature.The yield of bio oil was fluctuated with increasing temperature between 39.9?46.3wt%,and the highest yield was found at 550 ?.Pyrolysis of S.plumbizincicola at 550? with attapulgite as bed material can obtain high yield rate of bio-oil with low concentration of heavy metals.Most of heavy metals were found in char,the concentration of heavy metals in oil from second condencer higher than that from first one.The concentration of Cd,Pb,and Zn from first condencer were 0.014?0.045 mg/kg,0.14?0.53 and 53.6?142.2 mg/kg?respectively.