Research On The Fate Of Heavy Metals Of Hyperaccumulator During Pyrolysis And Supercritical Water Gasification

Soil heavy metal contamination has become serious in our country,the phyto re mediation technology matures gradually,and the wide application of phyto re mediation technology in the future will bring the disposal problem of hyperaccumulator after repair.Therefore,there is an urgent need to carry out the study on energy recycle and pollution control in disposal process.This paper summarizes the research progress of disposal technology of hyperaccumulator at home and abroad,analyzes the current situation and characteristics of traditional disposal,compared with supercritical water gasification(SCWG)technology,reflects the characteristics and advantages of SCWQ demonstrates the significance of the research and application prospects.Secondly,selects the Pteris vittata L.,which is a kind of hyperaccumulator after soil remediation,to pyrolysis in tube furnace.The results showed that a higher temperature was effective for the evaporation of heavy metal and their evaporation rates were ordered as Pb?-Cd>Zn>Cr>Cu?Ni;The pyrolysis was beneficial for the enrichment of heavy metals in solid residue,subsequently made it easier for recovery to improve the economic efficiency;The leaching rate decreased with the increase of temperature,indicating that the pyrolysis transfer the heavy metals to more stable forms.The SCWG experiments of Pteris vittata L.were carried out in the intermittent supercritical experimental bench,the results showed that a higher temperature was effective for the deposition of Cu?Pb and Zn,and the migration of Cd to liquid phase;More As?Cd?Cu transfered to residual fraction(F4)and Zn transfered to oxidizable fraction(F3)from reducible fraction(F2)with the raise of temperature;A higher pressure was effective for the deposition of Cu?As?Zn,more Cd transfered to F3 and F4 from acid extractable fraction(F1)and F2,more Pb transfered to F4 from F3,and more Zn transfered to F3 with the increase of pressure;More As?Cd and Zn dissolved in liquid and more Pb?Cu precipitated from liquid phase with the increase of residence time;A longer residence time promoted As?Zn?Pb transfer to F4 and Cd?Cutransfer to F3.Cu and As stayed in residual mainly,and Cd?Pb?Zn dissolved after SCWQ but the migration would change because of the reaction condition;Heavy metals existed in residual fraction mainly,the form fraction were ordered as F4>F3>F2>F1.By comparing the leaching toxicity of residual of pyrolysis and SCWG,and the condition parameters,the technology of SCWG had obvious advantages.Finally,this paper discussed the mechanism of the migration and speciation distribution of heavy metals in SCWQ established a dynamics experience model with experimental data,and made an outlook to the experimental study of the next step.