Batch biosorption experiments onto the litter of natural trembling poplar (Populus tremula) forest (LNTPF) were investigated for the biosorption of chromium(VI) ions from aqueous solutions. The influence of different experimental parameters such as initial pH, particle size, agitating speed, initial Cr(VI) concentration (C0), adsorbent concentration (m), and temperature on chromium(VI) ion removal were evaluated. The efficiency of chromium(VI) removal increases with a rise of adsorbent concentration, agitating speed, temperature, and with a fall of solution pH, particle size, and initial Cr(VI) concentration. The optimum biosorption conditions were determined as pH = 2.0, particle size ≤0.15 mm, agitating speed = 300 rpm, C0 = 30 mg L−1, m = 10 g L−1, and T = 45°C. The equilibrium was reached at around 150 min. The biosorption kinetics showed the pseudo-second-order model better than the pseudo-first-order model. Kinetic studies showed that the biosorption process was an endothermic process. The experimental biosorption data were fitted to the Freundlich biosorption model. The maximum biosorption capacity was found to be 16.97 mg g−1 removed by raw adsorbent. Electron paramagnetic resonance studies combined with FTIR spectroscopy were used to represent the biosorption mechanism. These studies display new remarkable findings. © 2010 American Institute of Chemical Engineers Environ Prog, 2010
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