where k is rate constant of pseudo-

where k is rate constant of pseudo-second-order
kinetic model (g/mg/min), Ea
is the activation energy
(kJ/mol), A the Arrhenius factor, R the gas constant
(8.314 J/mol K) and T is the solution absolute
temperature (K). The linear plot of ln k versus 1/T gives
a straight line with slope –Ea
/R. The magnitude of Ea
gives an opinion about the mechanism adsorption (Fan
et al., 2011; Rahchamani et al., 2011; Wang et al., 2013).
Physical adsorption typically has activation energy of
5-40 kJ/mol and chemical adsorption has activation
energy of 40-800 kJ/mol (Fan et al., 2011; Rahchamani
et al., 2011; Wang et al., 2013). The activation energy
obtained in this study was 23.23 kJ/mol (Table 6)
indicating that humic acid adsorption onto CSC
corresponded to physisorption. The positive value of
Ea
suggests that an increase in temperature favors the
adsorption of humic acid on SCS and the adsorption
process is endothermic in nature (Lin and Zhan, 2012).
A comparative evaluation of the adsorbent capacities
of various types of adsorbents for the adsorption of
humic acid is listed in Table 7. The adsorption capacities
of the adsorbents used in this study were not among
the highest available but a relatively high uptake
capacity of the humic acid could be obtained which
makes the adsorbents suitable for humic acid removal
from peat water.