The effect of the amount of adsorbent dosage was determined byvarying the amount of adsorbent dosage added at a particular MB concentration,pH and temperature. This present study observed that with an increase of the amountof adsorbent, the percentage removal of MB dyes also increases until reaching an equilibrium value after 0.16g whichcorresponded to 96.6% of dye adsorption. The increase of adsorption due to theadsorbent dosage can be attributed to a greatersurface area and more availability on the adsorption sites.
However, at dosage beyond 0.16g, the surface ofadsorbent becomes fully covered with MB molecules due to the aggregation oroverlapping on the adsorption site so the residual concentration in thesolution becomes high. This causing theremoval efficiency become constant and the incremental of MB removal becomevery low as the concentration of MB on the adsorbent surface and in thesolution become equilibrium to each other. This finding agreed with otherresearchers (Edokpayi et al., 2015)(Rahman et al., 2012)(Kose etal., 2014)The adsorption of MB on theCFFS adsorbent is greatly influenced by the initial pH of the solution. Inorder to optimize the pH, adsorption of MB was carried out over the pH rangefrom 3 to 10 at room temperature (30°C).
The result indicated that there is a steep increase in the adsorption of MB from 3to 8 and no significant change occurafter pH 8. Similar findings were reported by many authors (Pathania et al., 2017)(Njoya et al.
, 2017)(Cont, 2015).The pH curve obtained explainsthat the maximum adsorption takes placeat both natural and slightly basic pH. This is due to the electrostaticinteraction of MB which has a cationic structure with the negative charge ofthe adsorbent. On the contrary, at lower pH value, the development of positivecharge on the adsorbent might occur andcauses the surface area of the adsorbent become gradually protonated andcompetitive adsorption occurred between the H+ ions and the free MBions on the active sites thus decrease the adsorption of MB (Jirekar et al., 2014). So, it can be concluded thatCFFS adsorbent showed good removal capacity in the basic medium than in acid medium.
The effect of MB concentrationon the adsorption of MB was investigated in the concentration range from 25-150mg/L at room temperature without changing the pH of the MB and adsorbentdosage. In this study, the removal of MB was represented in Figure 4.5 wherethe percentage of dye uptake decreased with increasing initial dyeconcentration. The adsorption of the dye wasconstant at the initial stage and reachequilibrium between 25 mg/L to 75 mg/L. the adsorption was high at thebeginning due to higher availability of actives sites on the adsorbent surface. However, the uptake of MB dyebecome lower at higher concentration due to an increased ratio of initialadsorption number of moles of dyes to the available surface area.
So, highnumber of ions competing for the available sites on the surface of adsorbent athigher dye concentration. Similar result was also reported by other researcher (García et al., 2014).