For both sorbents, the removal is faster at the beginning of the
experiments, and slows down with the attainment of the plateau
value on CA. Such behaviour is explained by the large driving forces
to mass transfer that prevailed at the beginning of the sorption
process, since both CC and CS particles are initially free of Hg2+
ions. The results also show that the efficiency of the process can be
improved by keeping the CA,0 constant and increasing the amount
of sorbent used (Fig. 2). This procedure increases the external
surface area and consequently increases the number of active
sorption sites where the sorption of Hg2+ ions takes place. In some
cases, the 10 fold increase on CC or CS mass led to a significant
decrease on Hg2+ concentration in solution and to a substantial
increase on metal removal. This phenomenon is particularly
observable for the clam shells, for which, the increase of the
sorbent dose provoked an increased on Hg2+ removal from ca. 20%
to more than 80% for both CA,0 (Fig. 2)