To explore the rate control steps of the physical and chemical adsorption process, the kinetic data were fitted by the pseudo-first-order and pseudo-second-order kinetic models. The solution pH was adjusted to pH 4, while the other conditions were the same as in the batch experiments, only changing the adsorption time (4–720 min). The adsorption Q (mg g−1) was calculated according to eqn (1) . The pseudo-first-order and pseudo-second-order kinetic models are shown in eqn (2) and (3) :
The pseudo-first-order kinetic model:
The pseudo-second-order kinetic model: where Q is the adsorption capacity of MCT (mg g−1) when adsorption reached equilibrium, Qt is the adsorption capacity of MCT (mg g−1) when adsorption reached time t, K1 is the rate constant of the first-order kinetic model, and K2 is the rate constant of the second-order kinetic model.
The pseudo-first-order kinetic model:
The pseudo-second-order kinetic model: where Q is the adsorption capacity of MCT (mg g−1) when adsorption reached equilibrium, Qt is the adsorption capacity of MCT (mg g−1) when adsorption reached time t, K1 is the rate constant of the first-order kinetic model, and K2 is the rate constant of the second-order kinetic model.
