3.7. Kinetics studies
In order to explain the mechanism of adsorption of Ni(II) and Zn
(II), pseudo-first-order and pseudo-second-order are used to explain
sorption kinetics of the reaction.
The pseudo-first-order Lagergren model [48] for solid/liquid
systems of adsorption states that the rate is proportional to the
number of unoccupied sites. It is expressed as:
log qe–qt ð Þ= logqe–k1t=2:303 ð6Þ
where qe and qt (mg/g) are the amounts of metal ions adsorbed on
the adsorbent at equilibrium and at any time t, in mg/g, respectively.
k1 (/min) is the rate constant of pseudo-first-order adsorption. The
graph was plotted between log (qe–qt) versus t. From the slopes and
intercepts of the graph, the constant values of pseudo-first-order were
calculated.
The pseudo-second-order [49] assumes that the rate of sorption is
proportional to the square of the number of unoccupied sites. It is
expressed as
t=qt = 1=k2q2e
+ t=qe ð7Þ