Study On The Adsorption Characteristics Of Agrobacterium Tumefaciens Biosorbent To Low Concentrations Of Pb(?) And Cr(?)

The development of industrial economy promotes the improvement of public living standards,but it brings a series of environmental problems such as water environmental pollution,among which heavy metal pollution is an important aspect of water environmental pollution.Microbial adsorbents have special structure,contain a large number of functional groups which have good affinity with heavy metal ions,and have the characteristics of wide source,low cost of treatment of low concentration heavy metal wastewater,environment-friendly,etc.,which has attracted worldwide attention.Because the Ti plasmid of Agrobacterium tumefaciens contains T-DNA,which is essential for gene transfer,it has been widely used in the research of plant genetic engineering.However,there are few reports on its use as microbial adsorbent.In this paper,Agrobacterium tumefaciens,which was screened from a mine wastewater in Yunnan Province,was selected as the main body,It was first treated at high temperature,and then freeze-dried into a granular microbe adsorbent DB;using CTAB modified DB to make adsorbent CTAB-DB,which were respectively used to remove Pb(II)and Cr(?)in the wastewater.The research work and achievements were summarized as follows:(1)The effects of pH value of solution,amount of adsorbent,coexisting ions,adsorption time,initial concentration and reaction temperature on the adsorption of Pb(II)by DB were investigated.The results of adsorption kinetics and isotherms showed that the adsorption process of Pb(II)by DB fitted with pseudo-second-order kinetics and Langmuir adsorption isotherm model.That is,the adsorption processes with Pb(II)was chemical adsorption occurring on the monolayer.Under the optimal conditions,the maximum adsorption amount of Pb(II)by DB calculated by the Langmuir isotherm was 45.541 mg g^-1.The adsorption of Pb(II)by DB was a spontaneous,endothermic,entropy increasing process,and mainly chemical adsorption.The Zeta potential value of DB decreased with increasing p H,At p H>3.12,the material appeared negatively charged,which was conducive to the adsorption of most positively charged heavy metals.FTIR and XPS analysis showed that DB contains functional groups such as hydroxyl group,carbonyl group,amino group and organic phosphate groups,and they were maybe participated in the adsorption process through chelation,electrostatic action and other ways.(2)The effects of pH value of solution,amount of adsorbent,coexisting ions,adsorption time,initial concentration and reaction temperature on the adsorption of Cr(?)by CTAB-DB were investigated.In the presence of anion Cl^-,NO₃^-and SO₄^2-,can affect the adsorption of Cr(?)by CTAB-DB to varying degrees,but the removal rate can reach more than 78%,indicating that CTAB-DB was selective in Cr(?)adsorption.Through the establishment of adsorption kinetics and isotherm model,it could be concluded that the adsorption behavior of Cr(?)on CTAB-DB conformed to the pseudo-second-order kinetics and Langmuir isotherm model,the adsorption of Cr(?)on CTAB-DB was chemical adsorption on the homogeneous monolayer interface and the theoretical maximum adsorption amount was 30.572 mg g^-1.In addition,The adsorption of Cr(?)by CTAB-DB was a spontaneous,endothermic and entropy increasing process,mainly chemical adsorption.The physical and chemical properties of adsorbent before and after adsorption were characterized by Zeta potential,FTIR and XPS.The results showed that:The zeta potential of CTAB-DB decreased with the increase of p H,when p H<6.51,the surface of CTAB-DB was positively charged,which had better adsorption effect on anionic adsorbate in solution.The CTAB was successfully grafted on DB and adsorbent CTAB-DB was modified successfully.The hydroxyl,carbonyl group,amino and organic phosphate group in CTAB-DB may participate in the adsorption of Cr(?)through redox reaction,ion exchange and electrostatic attraction.