Effect of Dye Concentration on Batch Adsorption Process

In the present work, the initial RR158 concentration was varied from 40 to 120 mg/L while maintaining the adsorbent dosage at 7.5, 10, 12.5, 15, 17.5 and 20 g/L. In batch adsorption, the initial concentration of the dye molecules in the solution plays a key role as a driving force to overcome the mass transfer resistance between the aqueous and solid phases. Therefore, the amount of dye particles adsorbed is expected to be higher with a higher initial concentration [3]. This was indeed the case (Fig. 10) for dosages of CAC's of 7.500 and 10.000 ± 0.001 g/L that showed an increase in removal of RR158 as the initial dye concentration increased from 40 to 80 mg/L until an optimum value was reached. However, the dye removal decreased from 57.18 to 36.44% when the dye concentration

Fig. 10 Dye removal with initial dye concentration variation at constant dosages of adsorbent. Experimental conditions: room temperature, agitation: 200 rpm

increased from 40 to 120 mg/L with the same contact time and adsorption temperature for a constant dosage of 20 g/L of CAC's while, for a dosage of 17.500 g/L the dye removal decreased from 55.00 to 22.08% and from 27.5 to 15.29% when the dosage was 12.500 ± 0.001 g/L. This decrease in dye uptake with an increase in initial dye concentration may be due to an increase in the number of RR158 particles for the fixed amount of adsorbent and may be due to the complete utilization of adsorption surface and active sites available which was not possible in low concentration [2].

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