Minimizing water pollution via removal of hazardous organics onto biomass-activated carbons

ABSTRACT

Liquid-phase adsorption of phenol [P], para-nitrophenol [PNP], 2, 4-dinitrophenol [DNP], 4-aminophenol [PAP] and 2,4-dichlorophenol [DCP] onto a series or activated carbons were measured under equilibrium conditions, at room temperature. Three carbon samples were obtained from maize stalks by impregnation with different concentrations of H3PO4. One activated carbon sample was obtained by the one-step steam pyrolysis at 700°C, the last fifth carbon sample was the non activated carbon and was prepared by carbonizing the raw material at 500°C for 3 hr. The adsorption capacity of mthelyene blue [MB], rhodamine B [RB] and Congo red [CR] dyes onto the investigated adsorbents was determined via one point bottle test as mg/g. The raw material and their carbon adsorbents showed high adsorption capacity towards both categories of pollutants, phenolics and dyes. Linear form or Langmuir and Freundlich equations were employed to analyze the equilibrium adsorption data which show a satisfactory fit in most cases. The results indicate that Langmuir isotherm was more favorable for the removal of these phenolic derivatives in most cases whereas the Freundlich isotherm is better for the high porosity sample of medium acid concentration which adsorbed the biggest amounts of these pollutants. The sequence of phenolic uptake was DCP>DNP> PNP>P> PAP and was found to be related to both nature or the carbon-surface and porosity besides the solubility and molecular dimensions of the solutes. Low affinity towards phenol may be associated with its competition with water molecules which are more favorably attracted to the acidic surface that are charged with oxygen functional groups. The dye uptake onto the studied sorbents follows the order MB>RB>CR which was attributed to the fact that MB are more accessible to a significant fraction of the pore system which is not available for both others bulky molecules of RB and CR. Dye uptake was found to be controlled by surface chemical nature rater than porosity. The adsorption or both phenolic derivatives and dyes from their aqueous solutions were found to be controlled by both the surface chemical nature and porosity besides the solute nature