In order to determine the rate constants, the pseudo-secondorder
kinetic model was applied to our experimental result. The
linear form of pseudo second-order model can be expressed as Eq.
(1):
t
qt
= 1
kq2e
+ t
qe
(1)
where qe and qt are the amounts of metal ions adsorbed at
equilibrium and any time t (mmol g−1), respectively, k is the
rate constant of pseudo-second-order kinetics (gmmol−1 h−1). The
second-order rate constant k and qe can be determined from
the intercept and slope of the plot obtained by plotting t/qt
versus t.
Table S1 lists the results of applying pseudo second-order model
to our experiment data. A linear relationship with high correlation
coefficient (R2 = 0.9999 for both Cd2+ and Zn2+) between
t/qt and t was obtained which indicated the applicability of
the pseudo second-order model to describe the adsorption
process. In previous papers, the pseudo-second-order kinetic
model was found to be appropriate for describing kinetics of
metal sorption by different apatite materials, such as: Cr3+
by animal bones [35], Cd2+ by bone char [36], Pb2+ by soi amended with HAP [37], and uranium by low-cost rock phosphate