As regards the removal efficiency, it decreased from 98% to 50%
as the initial MB concentration increased from 50 to 350 mg L
−1
(Fig. 3a). At constant adsorbent dosage and higher initial dye con-centrations, the available adsorption sites of adsorbent became
fewer, therefore a decrease in the removal efficiency occurs.
Fig. 4 shows the effect of contact time on the adsorption capacity
and removal efficiency evaluated at two different initial MB concen-tration of 50 and 250 mg L
−1
, at pH 6 and 20
◦
C, using an adsorbent
dosage of 1 g L
−1
. As shown, there was a rapid uptake in the first
60 min, afterwards a plateau was reached