Separation properties of surface modified silica supported liquid membranes for divalent metal removal/recovery

The synthesis and separation properties of a mesoporous silica supported liquid membrane (SLM) were studied. The membranes consisted of a silica layer, from dip-coated colloidal silica, on an α-alumina support, modified with dichlorodimethyl silane (DCDMS) to add surface methyl groups to the silica layer. 2-Hydroxy-5-nonylacetophenome oxime (LIX-84) was entrapped within the pores of the silica due to hydrophobic interactions between the surface methyl groups and the long hydrocarbon chain from the LIX-84. The goal of synthesizing the membrane in this manner was to enhance the stability of SLMs. The membranes made after two-time dip-coating demonstrated good stability (no sign of LIX loss after 12 days) and uphill Cu2+ transport against the concentration gradient. Regardless of operating conditions, of the six metals studied (Ca, Cd, Cu, Pb, Zn, and Ni), only Cu2+ showed any flux except for some experiments in which Ca2+ flux could be attributed to imperfections in the membrane. Cu2+ fluxes as high as 2.3×10−10 mol/cm2 s (with 40 mmol/L (40 ppm) Cu2+ feed) and permeability coefficients as high as 8.0×10−4 cm/s were obtained for these mesoporous inorganic SLMs.