Abstract:
The selective enhancement of mercuric ions (Hg(II)) recovered from the natural gas well water by hollow fiber supported liquid membrane was investigated. Emulsion liquid membrane was applied to select types of the extractants and solvents, and the selectivity of the extractant for further experiments by hollow fiber supported liquid membrane due to a lower amount of extractant and shorter operating time. The parameters studied by using hollow fiber supported liquid membrane were pH of feed solution, the concentration of extractant in the liquid membrane, the concentration of sodium hydroxide as a stripping solution, the volumetric flow rates of feed and stripping solutions, the numbers of columns or liquid membrane modules, and life time of hollow fiber supported liquid membrane. From the experimental results, tri-n-octylamine (TOA) in toluene found to be the most suitable extractant. The increase in liquid membrane modules had almost no significance on the extraction and recovery of mercuric ions. By using 4 modules within 3.5 h, the percentages of extraction and recovery of mercuric ions achieved 98% and 60%, respectively. These values obtained at the pH of feed solution of 2.5, the TOA concentration of 2% (v/v), the concentration of sodium hydroxide at 0.5 M, and the flow rates of the feed and stripping solutions of 100 ml/min. The life time at high performance extraction lasted until 120 min. The mass transfer coefficients of the aqueous phase (k[subscript i]) and organic phase (k[subscript m]) were 0.011 and 1.028 cm/s. The mass transfer coefficient of the organic phase was higher than that of the aqueous phase, that means the rate controlling step was the diffusion of mercuric ions through the film layer between feed solution and liquid membrane.