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Separation of chromate and borate anions by polymer enhanced ultrafiltration from aqueous solutions employing specifically tailored polymers

Oktar Doğanay, Ceren
In this study two polychelatogens for borate and a polyelectrolyte for chromate retention (R) were designed for investigating the effect of pH and loading (g metal /g polymer) on the separation performances of the synthesized polymers using continuous polymer enhanced ultrafiltration. Increase in pH increased the retention of borate for all of the synthesized polymers. Decrease in the loading resulted in an enhancement in boron retention with PNSM and PNSL. When COP was utilized, retentions remained almost constant after a certain loading, probably due to possible adverse effects of high polymer concentrations on polymer conformation in aqueous solutions. Decrease in loading caused an increase in the retention of chromate until a loading of 0.01. After that a slight decrease was observed. Maximum Cr (VI) retention was obtained as 0.70 for a loading of 0.01 and a pH of 4. Effect of crowding on Cr(VI) retention was also investigated. It was observed that retention does not only depend on the loading but also on the concentrations of both Cr (VI) and PDAM. Effect of the presence of competing anions such as chloride and sulfate on the retention of chromate was investigated to see the effect of competing anion charge to the selectivity of the synthesized polyelectrolyte. Addition of both anions decreased the retention of Cr(VI) . Divalent sulfate decreased the retention more than monovalent chloride indicating that charge of the anion may be the predominant variable in the retention of chromate using PDAM. Finally, dynamic and static light scattering measurements were performed to investigate the conformational changes in the structure of the synthesized polymers at different pH values as well as in the presence of boron in the solution. In this study, it is shown that PEUF can be successfully applied to for boron and Cr (VI) retention with the synthesized polymers. Satisfactory retention values were obtained both for boron and Cr (VI). Even if the retention of Cr (VI) decreased with the addition of high amount of competing anions, significant Cr (VI) retentions could be obtained.