THE APPLICATION OF HOLLOW FIBER SUPPORTED LIQUID MEMBRANE TO SEPARATE LEAD, MERCURY AND ARSENIC IONS FROM SYNTHETIC WATER AND MATHEMATICAL MODEL FOR PREDICTION

Abstract

This study investigated the separation of lead, mercury and arsenic ions from feed solution, i.e., produced water and synthetic water across hollow fiber supported liquid membrane (HFSLM). The influences of types of extractants (D2EHPA, TOA, Aliquat 336, Bromo-PADAP, Cyanex 471 and Cyanex 923), concentration of the extractants, types of stripping solutions (distilled water, HNO3, H2SO4, HCl, NaOH and thiourea), concentration of the stripping solutions, concentration of H2SO4 in feed solution, flow patterns of feed and stripping solutions, types of lead complexes in the feed solution, types of extractans and stripping solutions in the HFSLM series, operating time, and flow rates of feed and stripping solutions were investigated. For the separation of mercury and arsenic ions from produced water, the superior performance in the extraction of mercury compared with arsenic was observed. Remarkably, the synergistic extraction of arsenic was discovered by using the mixture of Aliquat 336 and Cyanex 471 at the synergistic coefficient of 2.8. Thiourea of 0.1 M was found to be the suitable stripping solution. The concentrations of discharged mercury and arsenic ions complied with the regulatory discharge standards by using the mixture of 0.22 M Aliquat 336 and 0.06 M Cyanex 471 with 0.2 M H2SO4 in feed solution at 1 and 3 cycle separations, respectively. In the case of the separation of Pb(II) and Hg(II) from synthetic water, it was found that by using a double-module HFSLM in series could extract lead and mercury ions below their regulatory discharge standards in 80 min. The concentrations of lead and mercury ions in the stripping solutions were higher than those in the inlet feed solution of about 2.7 and 1.2 times. The optimum conditions were achieved by using 0.03 M D2EHPA as the extractant and 0.9 M HCl as the stripping solution in the first module, and 0.06 M Aliquat 336 as the extractant and 0.1 M thiourea as the stripping solution in the second module. A single-pass flow pattern of feed solution and circulating flow pattern of the stripping solution of 100 mL/min were found to be the most suitable. In addition, a mathematical model to predict the separation of lead and mercury ions was developed by considering the material balance concept in terms of convection and accumulation of metal ions, and the reactions at the liquid-membrane interfaces. Consequently, the concentrations of lead and mercury ions in feed and stripping solutions predicted by the model agreed well with the experimental results. It indicated that the rates of lead and mercury ions transport from feed solution to the stripping solution corresponded to the convection and accumulation of lead and mercury ions and the reactions at the liquid-membrane interfaces.