3.4. Effect of initial metal ion concentration and contact time on temperature-dependent adsorption
The rate of adsorption is a function of the initial metal ion concentration, which makes it an important factor to be considered for effective biosorption [14]. Temperature of the medium is also an effective parameter on adsorption efficiency [15]. The effects of initial metal ion concentration and contact time were determined within the range of 50–200 mg/L and contact time range of 30–240 min at 20, 30 and 40 °C. The results are shown in Fig. 4. The adsorbed amount was increased as the initial metal concentrations and contact time increased. Large amounts of metal ions were removed within 150 min for both Ni(II) and Co(II). After that the capacity of adsorption remained constant. In general, the data revealed that sorption capacity increased with increase in initial metal ion concentrations for Ni(II) and Co(II) on adsorbent. Moreover, the experimental results showed that adsorbed amount was increased as temperature increased. The increase in adsorption with temperature may be attributed to either increase in the number of active surface sites available for adsorption on the adsorbent [16]. At higher temperatures the energy of the system seems to facilitate Ni(II) and Co(II) attachment onto the cell surface.