Micellar enhanced ultrafiltration (MEUF) of metal cations with oleylethoxycarboxylate

The technical grade nonaoxyethylene oleylether carboxylic acid RO90 is investigated as surfactant for heavy metal ion removal via micellar enhanced ultrafiltration (MEUF). In contrast to sodium dodecylsulfate (SIDS), which is a standard surfactant for this purpose, RO90 has a much lower cmc (similar to 0.014 g L-1) and forms larger aggregates (similar to 8 nm). These properties render RO90 a much more efficient surfactant for MELT than SIDS. The surfactant can be filtered out very efficiently using a membrane with a MWCO <= 10 kDa and the gel layer concentration is about 170 g L-1 For a molar [RO90]/[Me2+] ratio of about 10, metal ion removal efficiency is > 95% for the investigated divalent cations Mg2+, Ni2+, Cd2+, Cu2+, Fe2+, and Zn2+. The simultaneous removal results in the following order: Fe2+ similar to Cu2+ > Cd2+ > Zn2+ > Ni2+ > Mg2+, which is a result of the different complex binding constants as shown earlier by Bunting and Thong for different alkylcarboxylates. This shows that RO90 in MEUF is a selectively binding surfactant with superior properties compared to so far employed surfactants. (C) 2015 Elsevier B.V. All rights reserved.