where kad (g/mmol min) is the rate constant of adsorption, qe
(mmol/g) is the equilibrium adsorption capacity, qt (mmol/g) is the
amounts of metal adsorbed at time t.
The intraparticle diffusion rate was defined as [25,26]:
where q is the amount of heavy metals removed, kid stands for the
intraparticle diffusion constant.