Biosorption Characteristics And Mechanism Of Typical Rare Earth Ionsin By Serratia Marcescens

The low concentration of rare earth ions in rare earth smelting wastewater is directly discharged due to the lack of economic and effective recovery methods,which not only causes a waste of rare earth resources,but also pollutes the environment.Compared with traditional water treatment methods,microbial adsorption has the advantages of low operating cost and fast adsorption and desorption rate.However,there are few studies on the treatment of rare earth wastewater by microbial adsorption,especially the adsorption mechanism,which limits its application in the treatment of rare earth wastewater.In this paper,the adsorption behaviors of Eu(?)and Dy(?)in rare earth wastewater by S.marcescens before and after modification were studied.The effects of p H,adsorption time,initial concentration of rare earth ions and adsorbent dosage on the adsorption capacity of S.marcescens for Eu(?)and Dy(?)were investigated.The adsorption mechanism was explored and proposed as well.This study can provide theoretical and technical support for the recovery and utilization of typical rare earth ions in rare earth wastewater by S.marcescens.The main research results are as follows:(1)The activity of S.marcescens has an important influence on the adsorption of rare earth ions.S.marcescens with high activity cultured for 48 h was selected as the adsorbent.The results showed that S.marcescens had high adsorption capacity for Eu(?)and Dy(?).Under the optimal adsorption conditions,the maximum adsorption capacity and removal rate were 115.36 mg·g^-1 and90.12%for Eu(?),and 95.81 mg·g^-1 and 95.86%for Dy(?),respectively.Adsorption kinetics and adsorption isotherm study showed that the biosorption process followed the pseudo-second-order-kinetics model and Langmuir adsorption model,indicating that the process was a monolayer chemical adsorption.The desorption experiments showed that EDTA had a good desorption efficiency on Eu(?)and Dy(?)with the desorption rates of 93.28%and 99.07%respectively,indicating that the EDTA can effectively recover rare earth.(2)In order to improve the adsorption performance of the non-active dry bacteria of S.marcescens,which was chemically modified by grafting polyamide.Zeta potential measurement and FTIR analysis showed that the polyamide acid was successfully grafted on the surface of S.marcescens.The results showed that the chemical modification significantly improved the adsorption capacity of S.marcescens for Eu(?)and Dy(?),and the maximum adsorption capacity and removal rate were 131mg·g^-1 and 99.31%for Eu(?),and 122 mg·g^-1 and 99.46%for Dy(?),respectively.The improvement of adsorption performance is attributed to that with the modification of bacteria by polyamide,the introduction of carboxyl group enhances the negative electric property of S.marcescens,which strengthens its electrostatic attraction to the rare earth ions.At the same time,there are more amino and amide groups produced on the surface of the modified S.marcescens,which increases the adsorption active sites for the coordination with rare earth ions,promoting the adsorption capacity of S.marcescens for Eu(?)and Dy(?)rare earth ions.The biosorption kinetics and thermodynamics were similar to that of S.marcescens before modification,which conformed to the pseudo-second-order-kinetics model and Langmuir adsorption model,indicating that the biosorption process was a monolayer chemical adsorption.(3)The mechanism of biosorption of Eu(?)and Dy(?)by Serratia marcescens was discussed and analyzed.Under appropriate conditions,the surface of S.marcescens shows negative charge,which can effectively attract the positively charged Eu(?)and Dy(?)ions through electrostatic attraction,and promote the adsorption of Eu(?)and Dy(?)ions on the surface of S.marcescens.Another way for the adsorption of Eu(?)and Dy(?)is through ions exchange with Na⁺,K⁺and other metal ions in the S.marcescens.In addition,S.marcescens contains a large number of active functional groups such as-NH₂,-CONH and-COOH,which can coordinate with Eu(?)and Dy(?)to promote the adsorption.Therefore,the adsorption of Eu(?)and Dy(?)ions by S.marcescens is a combination of electrostatic attraction,ions exchange and coordination.The results show that S.marcescens can be used as a potential biosorbent to recover rare earth elements from rare earth wastewater.