where k1 is the pseudo-first-order rate constant (min1), k2 is the
pseudo-second-order rate constant (g min1 mg1), qt is the
amount of ammonium nitrogen adsorbed at time t (mg g1), qe is
the adsorption capacity at equilibrium (mg g1), and t is the contact
time (min). kp is the diffusion coefficient of intraparticle diffusion
model (mg min1/2 g1), and C is the intercept.