where qe is the amount of adsorbate adsorbed (mg/kg of
adsorbent); Ce is the equilibrium concentration of adsorbate
(mg/L); Kl (L/mg) is the Langmuir adsorption constant, and Q0 (mg/
g) is the maximum adsorption amount; KF (mg/g(L/mg)1/n) and 1/n
are the constants that give estimates of the adsorptive capacity and
intensity. According to correlation coefficient (R2), both Langmuir
and Freundlich isotherms fit the experimental data well (see
Table 1). The maximum adsorption capacity (Q0) of Ni(II) varied
from 8.614 to 4.695 mg/g when 400 mg/L of CIP was present in
Ni(II) solution calculated by Langmuir model. The adsorption
process indicates favorable, moderately difficult and poor adsorption
if the values of n are in the range 2–10, 1–2 and 0–1. The n
values (greater than 1 without CIP and lower than 1 with CIP) and
KF values (0.2294 without CIP and 0.0978 with CIP) calculated from
the Freundlich model indicated that the Ni(II) adsorption could be
suppressed by CIP.