Non-enhanced ultrafiltration of iron(III) with commercial ceramic membranes

Membranes are nowadays being developed as a mature technology to deal with polluted waters containing heavy metals. Nanofiltration membranes have classically been employed for this purpose. However, it was recently shown that a 5 kDa ceramic ultrafiltration membrane could be successfully used to recover iron(III) from aqueous solutions even at acidic pH, although the mechanisms associated with the retention of iron were not clearly established. This paper aims to highlight the phenomena associated with the retention of iron(III) species by commercial ceramic ultrafiltration membranes. The results show that iron(III) retention by ceramic membranes is strongly influenced by the molecular weight cut-off of the membranes and their material, although even 50 kDa molecular weight cut-off membranes are capable to efficiently retain iron species. A retention mechanism based on iron-membrane adsorption seems to be the most likely for explaining iron rejection when using UF membranes. However, charge repulsion phenomena and sieving effects may also contribute to the rejection of iron(III). The occurrence of mononuclear hydrolysed iron species, which can result in the formation of polynuclear species in the neighbourhood of the membrane surface could definitively contribute to the high retention of iron(III) shown by ceramic ultrafiltration membranes.