The removal capacity in the basic medium

The adsorption of MB on the
CFFS adsorbent is greatly influenced by the initial pH of the solution. In
order to optimize the pH, adsorption of MB was carried out over the pH range
from 3 to 10 at room temperature (30°C). The result indicated that there is a steep increase in the adsorption of MB from 3
to 8 and no significant change occur
after pH 8. Similar findings were reported by many authors (Pathania et al., 2017)(Njoya et al., 2017)(Cont, 2015).

The pH curve obtained explains
that the maximum adsorption takes place
at both natural and slightly basic pH. This is due to the electrostatic
interaction of MB which has a cationic structure with the negative charge of
the adsorbent. On the contrary, at lower pH value, the development of positive
charge on the adsorbent might occur and
causes the surface area of the adsorbent become gradually protonated and
competitive adsorption occurred between the H+ ions and the free MB
ions on the active sites thus decrease the adsorption of MB (Jirekar et al., 2014). So, it can be concluded that
CFFS adsorbent showed good removal capacity in the basic medium than in acid medium. The effect of MB concentration
on the adsorption of MB was investigated in the concentration range from 25-150
mg/L at room temperature without changing the pH of the MB and adsorbent
dosage. In this study, the removal of MB was represented in Figure 4.5 where
the percentage of dye uptake decreased with increasing initial dye
concentration. The adsorption of the dye was
constant at the initial stage and reach
equilibrium between 25 mg/L to 75 mg/L. the adsorption was high at the
beginning due to higher availability of actives sites on the adsorbent surface.

We Will Write a Custom Essay about The removal capacity in the basic medium
For You For Only $13.90/page!

order now


However, the uptake of MB dye
become lower at higher concentration due to an increased ratio of initial
adsorption number of moles of dyes to the available surface area. So, high
number of ions competing for the available sites on the surface of adsorbent at
higher dye concentration. Similar result was also reported by other researcher (García et al., 2014).The effect of temperature on
the adsorption of MB is shown in Figure 4.6. In the present study, the effect
of temperature of the adsorption of MB was studied at 303K, 313K, 323K and 333K
respectively. The result indicated that the adsorption of MB increase when the
temperature rose. This showed that the system was endothermic in nature. Other
researcher also reported the increase of MB uptake with increases of
temperature (Ehrampoosh, 2011).

Adsorption processes are
typically exothermic in nature, but some cases are endothermic adsorption (Pathania et al., 2017). At high temperature, the
adsorption capacity increase due to the swelling of adsorbent which
facilitating the adsorption of dye molecule on the surface of adsorbent. This
phenomenon leads to an increase of surface sites availability and porosity of
the adsorbent (Lopez-Nuñez et al., 2014). In adsorption studies, effect
of contact time plays an important role. From Figure 4.6, it clearly depicted
that at initial stage, the percentage removal of MB dyes was rapid due to the
fast transfer of metal ion on the vacant adsorption site. Afterwards, the
adsorption become slow and get stagnated from 60 min up to 100 min due to the
saturation of the actives site with Mb molecules. There was no significant
increase in the removal of MB after 100 minutes which indicated that
equilibrium condition has been reached. this is because the remaining empty
site on the adsorbent has been occupied (Berrazoum et al., 2015).