The Efficiency And Mechanism Of Cd/As Immobilization By Biochar And Iron-impregnated Biochar

Cadmium(Cd) and arsenic(As) sourced from large quantity of mining and industry pollutant discharge has been posing severe threatens to public health through water drinking and food consumption. Biochar could adsorb and immobilize heavy metal efficiently from solution and soil in consideration of its special physical and chemical properties.Biochar and iron-impregnated biochar was prepared to investigate the efficiency and mechanism toward Cd and As(V) removal from solution and further applied to the soil–rice system to reveal its influence and suppression on soil As bioavailability. The main results are as follows:(1) Biochar pyrolyzed from water hyacinth(BC) at 250-550 ℃.BC450 out-performed the other BCs at varying initial Cd concentrations with the max Cd sorbed amount at 70.3 mg g-1 based on Langmuir model.(2) Based on the balance analysis between cations released and Cd sorbed onto BC450 in combination with SEM-EDX and XPS data,ion-exchange followed by surface complexation is proposed as the dominant mechanism responsible for Cd immobilization by BC450. In parallel, XRD analysis also suggested the formation of insoluble Cd minerals(CdCO3, Cd3(PO4)2 Cd3P2, and K4CdCl6) loaded on the surface of BC450 after Cd sorption.(3) Magnetic biochars(MWs) was prepared by iron–modifying onwater hyacinth biomass followed by pyrolysis. MWs with injection initial1 M ferric solution subsequent pyrolysis at 250℃(MW2501)was superior other MWs and exhibited the highest As(V) sorption capacity which was estimated to be 7.4 mg g-1based on Langmuir-Freundlic model.(4) Solution pH(3-10) had less effect on the As(V) removal by MW2501. Besides, competition anions scarcely interfered As(V) sorption in the presence of P≤0.1 mM or Cr/Sb≤0.5 mM.(5) FTIR and XPS investigation revealed ligand exchange between As(V) anion and the hydroxylated surface of Fe3O4 as well as H bond was largely responsible for As(V) sorption with less redox reaction between Fe and As.(6) Iron-impregnated biochar(BCFe) prepared by biochar derived from rice straw dipped with Fe2+solution was applied to rice pot culture with As contaminated soil. This results show that BCFe reduces the rhizosphere soil pore water As concentration, increase of root iron plaque and DCB extract As amount and lower the As content in plant,especially, decreased ~70% As of brown rice.