Removal of cobalt from aqueous solution by magnetic multiwalled carbon nanotube/iron oxide composites

The effects of contact time, pH, ionic strength, foreign ions, temperature, humic substances (HSs), and the addition sequences of Co(II)/HSs on Co(II) sorption on magnetic multiwalled carbon nanotube/iron oxide composites (magnetic MWCNT/IO composites) were investigated under ambient conditions. The results indicated that Co(II) sorption on the magnetic MWCNT/IO composites increased with increasing pH. The ionic strength and foreign ion dependent of Co(II) sorption suggested that ion exchange and outer-sphere surface complexation were the main sorption mechanism at low pH, whereas the ionic strength and foreign ion independent of Co(II) sorption at high pH values indicated that inner-sphere surface complexation was predominant sorption mechanism. The Langmuir model fitted Co(II) sorption isotherms better than the Freundlich model. The thermodynamic data calculated from the temperature dependent sorption isotherms suggested that Co(II) sorption on the magnetic MWCNT/IO composites was a spontaneous and endothermic process. The removal of Co(II) by the magnetic MWCNT/IO composites was affected evidently by the presence of HSs and by the addition sequences of Co(II)/HSs. This study highlights the interactions between Co(II) and HSs to determine the mutual effects of inorganic and organic matters on the removal of metal ions in environmental pollution management.

Humic substances increased Co(II) sorption on MWCNT/iron oxide composites at low pH, whereas decreased Co(II) sorption at high pH.Figure optionsDownload as PowerPoint slideHighlights
► MWCNT/iron oxide composites were used to remove Co(II) and humic substances.
► Humic substances affected Co(II) sorption on MWCNT/iron oxide composites.
► The Langmuir model fitted well Co(II) sorption isotherms.
► MWCNT/iron oxide composites can be used to remove the pollutants in large scale.