activated carbon increased with the increase of Ni(II) concentration
in equilibrium solution. When CIP was present in the solution,
Ni(II) adsorption on activated carbon was suppressed. Langmuir
model assumes monolayer adsorption with no lateral interaction
and steric hindrance between the adsorbed molecules, even on
adjacent sites. Adsorption occurs at identical and equivalent
localized sites [24]. While, Freundlich model (Eq.) is an empirical
equation, which assumes multilayer adsorption with non-uniform
distribution of adsorption heat and affinities on adsorbent surface
[25]. The equation can be expressed as: