where qe is the amount of solute adsorbed at equilibrium per unit
weight of adsorbent (mg/g), q the amount of solute adsorbed at
time t per unit weight of adsorbent (mg/g) and k1 and k2 are
constants. The following linearised time dependent functions
can be obtained by integrating and rearranging Eqs. (1) and (2)
for the boundary conditions t = 0 to >0 and q = 0 to >0 [13]