3.4. Breakthrough curves
Fig. 6 illustrates the breakthrough curves of Ni2+ and Fe3+ at a short
column bed of 1.1 mL volume. The flow rate was 1 mL/min and the feed
metal ion concentration was 10 mg/L. When the breakthrough point
was determined as c/c0 = 0.1 (the effluent metal ion concentration
attained one-tenth of the feed concentration), the related breakthrough
volumes were 75 bed volume for Ni2+ and 90 bed volume for Fe3+, respectively.
The dynamic adsorption performance of Fe3+ at a low feed
concentration was better than Ni2+, which agrees well with the batch
results in Figs. 4 and 5. In the study using Ponkan peel as adsorbent
[12], the maximum adsorption capacity for Ni2+ was 1.92 mmol/g
and the associated breakthrough volume was 110 bed volume (1 bed
volume = 5 mL and flow rate = 3.5 mL/min). The Ni2+ breakthrough
performance of the water bamboo particles prepared in this study was
comparable to that of Ponkan peel biosorbent.
Comparing to the static adsorption capacities in Fig. 5, the dynamic
capacities of metal ions obtained at breakthrough points in Fig. 6 are
2 fold (for Fe3+) or 3 fold (for Ni2+) higher. This phenomenon may
be attributed to the mass transfer effect in packed-bed process which
forced the metal ions to flow through the intraparticle mesopores and