Study on the adsorption and mechanism of divalent iron and manganese ions by Eichhornia crassipes
凤眼莲对二价铁锰离子的吸附及机理研究

In this paper, dry powders of root, stem and leaf of Eichhornia crassipes were used to adsorb divalent iron and manganese ions from aqueous solution. With batch experiments, the optimum adsorbing conditions were determined. Also, the adsorption characteristics were studied by Isothermal Adsorption Model (IAM) and Kinetic Model (KM). According to the results, the dry powders of root and stem were the best for removing Fe2+ and Mn2+, respectively. The maximum adsorption capacity of Fe2+ and Mn2+ was observed at initial concentration of Fe2+ as 45 mg·L-1 and Mn2+ as 75 mg·L-1, respectively. The optimum pH was 4.0 for Fe2+ and 5.0 for Mn2+. Besides, an enhanced metal adsorption on 0.4 g of biomass with an agitation time of 120 min for Fe2+ and 60 min for Mn2+ was recorded. The optimum rotate speed for removing Fe2+ and Mn2+ was both confirmed at 180 r·min-1. It was also observed that the adsorptions of two metal ions correlated with temperature. Maximum adsorption of Fe2+(21.73±0.38) mg·g-1] and Mn2+ (15.55±0.58) mg·g-1] were obtained under the above optimum conditions, with the removal rate of 96.58% for Fe2+ and 82.93% for Mn2+. The adsorption process fit well with Langmuir model and pseudo-second order kinetic model, and activation energy of adsorption and FT-IR experiments confirmed that the adsorption of Fe2+ by root and Mn2+ by stem were a physiochemical process. Compared with the existing biomass for removing Fe2+ and Mn2+, the powder of E. crassipes is a good adsorption material to remove heavy metals from aqueous solution.