Intensification of Ni(II) adsorption in a fixed bed column through subcritical conditions

Abstract

Adsorption for environmental applications is normally studied in gas and liquid phases. For the first time in the literature, Ni(II) was adsorbed from a subcritical water stream in a fixed column using activated carbon as an adsorbent. Several breakthrough curves were constructed at different conditions of pressure (from 5 to 25 MPa) and temperature (from 100 to 200 °C), so that, the effects of these variables on the adsorption operation were evaluated using an experimental design. The results were also compared with an adsorption in normal conditions. The fixed bed performance was largely improved when subcritical conditions were used, mainly at 25 MPa and 200 °C. The values of stoichiometric adsorption capacity (Qeq), breakthrough time (tr) and length of mass transfer zone (MTZ) were, respectively, 1.54 mg g–1, 5 min and 28.31 cm for the operation in normal conditions. Under subcritical conditions, Qeq was 6.30 mg g–1, tr was 166 min and the MTZ decreased around 10 cm. These results show that a fixed bed column containing activated carbon has better performance when adsorption take place using subcritical water instead of water under ambient conditions.