Adsorption of Co(II) from aqueous solutions by water treatment residuals.

A study on the removal of Co(II) from aqueous solutions by water treatment residuals (WTR) was conducted in batch conditions. The sorption process of Co(II) followed pseudosecond-order kinetics, with 30hr required to reach equilibrium. Using the Langmuir adsorption isotherm model, a relatively high maximum sorption capacity of 17.31mg/g Co(II) was determined. The adsorption of Co(II) was dependent on pH values and was affected by the ionic strength. Results show that Co(II) adsorption was a spontaneous endothermic process and was favorable at high temperature. Most of the adsorbed Co(II) stayed on the WTR permanently, whereas only small amounts of adsorbed Co(II) were desorbed. The shifting of peaks in FT-IR spectra indicated that Co(II) interacted with the WTR surface through strong covalent bond formation with Fe(Al)-O functional groups. It was concluded that WTR can be a suitable material from which to develop an efficient adsorbent for the removal of Co(II) from wastewater.