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. 2016 Apr 27:5:542.
doi: 10.1186/s40064-016-2191-8. eCollection 2016.

Effects of bloom-forming cyanobacterial extracellular polymeric substances on the adsorption of cadmium onto kaolinite: behaviors and possible mechanisms

Xiaolin Kuang  1 , Jihai Shao  1 , Anwei Chen  1 , Si Luo  1 , Liang Peng  1 , Genyi Wu  1 , Ji-Dong Gu  2
Affiliations

Effects of bloom-forming cyanobacterial extracellular polymeric substances on the adsorption of cadmium onto kaolinite: behaviors and possible mechanisms

Xiaolin Kuang et al. Springerplus. .

Abstract

Cyanobacterial blooms result in high level of cyanobacterial extracellular polymeric substances (EPS) in water. The effects of bloom-forming cyanobacterial EPS on the distribution of Cd(II) in the interface between sediment and water is unknown. Clay is a main component in sediment. The effects of EPS, originated from a typical bloom-forming cyanobacterium Microcystis aeruginosa, on the adsorption and desorption characteristics of Cd(II) by kaolinite were investigated in this study. Results of XRD analysis indicated that cyanobacterial EPS bound on the surface of kaolinite. The composite of kaolinite + EPS showed higher adsorption capacity toward Cd(II) than pure kaolinite, and hydroxyl groups were involved in the adsorption processes. The data for the adsorption of Cd(II) by kaolinite are well fitted by both Langmuir model and Freundlich model, whereas only Freundlich model well describes the adsorption data of Cd(II) by the composite of kaolinite + EPS. The adsorption of Cd(II) onto kaolinite was an exothermic process, but it became an endothermic process after EPS incorporation. Results of desorption showed that EPS incorporation increased the adsorption of kaolinite toward Cd(II) through physical adsorption, ion exchange and complexation.

Keywords: Cadmium; Extracellular polymeric substances; Kaolinite; Microcystisaeruginosa.

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Figures

Fig. 1
Fig. 1
Effects of cyanobacterial EPS on the adsorption of Cd(II) by kaolinite. Data are presented as average value ± standard deviation (n = 3)
Fig. 2
Fig. 2
FT-IR spectra of kaolinite, EPS, and the composite of kaolinite + EPS before and after Cd(II) adsorption. Kao: Kaolinite; Kao + EPS: the composite of kaolinite + EPS before Cd(II) adsorption; Kao + EPS + Cd: the composite of kaolinite + EPS after Cd(II) adsorption
Fig. 3
Fig. 3
XRD patterns of kaolinite and the composite of kaolinite + EPS before and after Cd(II) adsorption
Fig. 4
Fig. 4
Effects of pH on the adsorption of Cd(II) by kaolinite and the composite of kaolinite + EPS. Data are presented as average value ± standard deviation
Fig. 5
Fig. 5
Effects of initial Cd(II) concentration on its adsorption onto kaolinite and the composite of kaolinite + EPS. Data are presented as average value ± standard deviation
Fig. 6
Fig. 6
Langmuir (a) and Freundlich (b) isotherm plots for Cd(II) adsorption by kaolinite and the composite of kaolinite + EPS
Fig. 7
Fig. 7
Effects of temperature on the adsorption of Cd(II) by kaolinite and the composite of kaolinite + EPS. Data are presented as average value ± standard deviation
Fig. 8
Fig. 8
Desorption ratio of Cd(II) from kaolinite and the composite of kaolinite + EPS using different desorbents. Data are presented as average value ± standard deviation
Fig. 9
Fig. 9
Schematic diagram for the adsorption of Cd(II) by kaolinite (a) and the composite of kaolinite + EPS (b)
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