Measurement of dissolved aluminium in waters: use of the tangential flow filtration technology

A comparison of tangential or cross flow filtration (TFF) and dead-end filtration (DEF) is presented with respect to the separation of particulate and dissolved forms of aluminium in natural and potable waters (from the Melbourne area, Australia) and synthetic suspensions of alumina in waters. It was found that 34 and 87% of the aluminium transmitted through 0.45 μm filters in DEF mode were not transmitted through 0.2 and 0.003 μm filters, respectively, both being operated in TFF mode. Spectroscopic and particle size analysis of suspended matter in a typical water sample from the Yarra River indicated the presence of quartz and aluminium bearing clay minerals with a modal size of 0.2 μm—below the pore size of filters (0.45 μm) commonly used to define dissolved and particulate forms of many elements. Results indicate that TFF produces filtrates whose composition is less dependent on the nature and concentration of solids in the sample being processed, and that the use of filters of 0.003 μm pore size effectively prevents particulate and colloidal forms passing into filtrates from their samples. Such filtrates therefore more accurately reflect the concentration of dissolved species of aluminium in natural waters.