The uptake of MB onto RPR and APR as a function of dye concentration is shown in Figs. 2a and 2b. It can be seen that the amount of MB adsorbed per unit mass of adsorbent increased with increasing dye concentration (25-200 ppm), although percentage removal decreased with increase in initial dye concentration. This may be attributed to an increase in the driving force of the concentration gradient with the increase in the initial dye concentration [19].