3.5. Effect of time
The effect of contact time on the adsorption of Ni (50 mg/L) and Zn (30 mg/L) onto MBRC and MBAC is shown in Fig. 7. The maximum adsorption occurred within 60 min, after which there were no significant change in absorption. The equilibrium was reached at 360 min for Ni and Zn(II) adsorption onto MBRC and MBAC. Metal uptake by the sorbent surface is rapid initially up to 60 min and then decreases as time increases. This can be explained as: initially adsorption of metal ions is increased as contact time is increased due to the availability of more active sites. More and more functional groups participated in adsorption of the metal ions until it reached equilibrium. After it reached the equilibrium, there was no significance
changes in Ni(II) and Zn(II) concentrations in the solutions was
observed.