Study On The Migration And Transformation Characteristics Of Heavy Metals In Sludge Hydrothermal Liquefaction Treatment

As a kind of biomass conversion technology with low energy consumption and safe operation,the preparation of bio oil by sludge hydrothermal liquefaction technology also has the problem of heavy metal pollution.The migration and transformation of heavy metals in hydrothermal liquefaction should also be paid more attention.In this paper,the behavior of heavy metals was discussed by the migration and transformation of heavy metals in the process of hydrothermal liquefaction under different temperature and reaction time.Combined with inductively coupled plasma mass spectrometry（ICP-MS）,it was found that different heavy metals exhibited different migration characteristics during hydrothermal process.With the increase of temperature and reaction time,heavy metals turned into more stable forms.The concentration of heavy metals in solid phase increased,but the environmental risk decreased by 95.7%.The organic matter in sludge were extracted by cetyltrimethyl ammonium bromide（CTAB）,and soybean protein was used as model compound.The interaction between organic matter and heavy metals in hydrothermal process was studied by ICP-MS,XPS,FT-IR and GC-MS.The results show that CTAB can effectively extract protein,polysaccharide and other organic matters from sludge.In the low temperature stage（less than 200°C）,the combination of heavy metal and organic matter was not destroyed.The addition of heavy metals increased the proportion of C and N on the surface of solid-phase products.Heavy metals and nitrogen formed the covalent bonds of-N:?M²⁺.The addition of Zn and Cr increased the content of carbon oxygen to double bond,while the ion exchange reacted by Cu,Cd,Pb and carboxyl groups.In the aqueous phase,Cu can reduce aromatic compounds by 50%,and other heavy metals can significantly reduce the content of oxyheterocyclic compounds.Except Cr,the other heavy metals decreased the content of acids.When the reaction temperature rises to 280°C,the heavy metals stored in the sludge in the form of organic binding state were greatly reduced,and the proportion of oxygen on solid surface was greatly increased.The covalent bond between heavy metal and nitrogen disappeared and pyridine-n was formed.Zn,Cu,Cd and Pb were reacted with carboxyl group to form the metal oxide.In the aqueous phase,aromatic compounds and nitrogen-containing heterocyclic compounds are the main components of the liquid phase,and different kinds of heavy metals have little effect on them.