A novel separation technique: Gas-assisted three-liquid-phase extraction for treatment of the phenolic wastewater

A novel technique, gas-assisted three-liquid-phase extraction (GATE), was proposed to improve three-liquid-phase separation of p-nitrophenol (p-NP) and o-nitrophenol (o-NP) from wastewater. The partition behavior of p-NP and o-NP into a three-liquid-phase system composed of hexane-PEG2000-(NH4)(2)SO4-H2O at the aid of gas bubbling was discussed. It was demonstrated that the process of gas bubbling was effective for the mass transfer of p-NP and o-NP into PEG phase and hexane phase, respectively. Influences of various parameters including the phase-forming salt concentrations, gas flow rate, gas bubbling time, initial volume of hexane and PEG phase on distribution behavior of p-NP and o-NP were investigated. Under the optimal conditions for GATE, the removal ratio of p-NP and o-NP from wastewater could reach 81% and 90%, respectively. While the mass fraction of p-NP into PEG phase and o-NP into hexane phase arrived at 75% and 74%, respectively. The distribution ratio and concentration factor were all higher than conventional three-liquid-phase extraction system. During GATE processes, the dispersed PEG and hexane in (NH4)(2)SO4 aqueous solution can be captured by ascending gas streams. GATE is demonstrated to be an effective method for the simultaneously extraction and separation of two or more organic chemicals in one-step's three-liquid-phase extraction, and also provides a technique to prevent loss of dispersed polymers and organic solvents in aqueous phase in extraction process for treatment of the phenolic wastewater. (C) 2010 Elsevier B.V. All rights reserved.