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Removal of phenol from industrial wastewaters using lignitic coals
Phenol adsorption capacity of lignitic coals which were obtained from Soma and Yataan / Turkey was investigated under different operational conditions such as solid-liquid ratio (S/L), reaction time, initial phenol concentration and temperature. Based on batch adsorption studies, it was observed that the phenol was completely adsorbed by coal depending on time of adsorption and the S/L ratio. From these results, the maximum adsorption values on the time axis at various S/L ratios were used and the fractions of phenol receptive adsorption sites on coal surfaces were calculated as 60 % and 43 % for Soma and Yataan coals, respectively. Freundlich adsorption isotherm was found to describe the adsorption of phenol on lignitic coals well. The Langmuir model did not describe the system as good as Freundlich model most probably due to the monolayer coverage assumption on this model. Activation energy and the maximum heat of adsorption calculated using adsorption data at different temperatures by the Arrhenious and Van.t Hoff equations were 10.3 and -20.2 kJ/mol, respectively. The low energies suggest that the adsorption of phenol on these lignitic coals were through physical interactions. An adsorption mechanism of phenol on lignite was discussed based on these findings. Residual water quality following adsorption in terms of major elements and heavy metals was within acceptable limits defined for wastewaters. The amount of organic matters dissolved from coals were also negligable. The presence of heavy metals as Cu, Zn etc. in water as a contaminant was also found to affect the removal of phenol by about 10-20 %.