where qeq is the amount of metal adsorbed per unit weight
of the adsorbent at equilibrium (mg g -1), qmax is the
maximum metal uptake per unit mass of the adsorbent
(mg g -1), b is the Langmuir constant (L mg -1) related to
energy of sorption which quantitatively reflects the affinity
between the sorbent and the sorbate and Ceq is the
equilibrium concentration of the adsorbate (mg L-1).