Characteristics of membrane filters in relation to aluminium studies in soil solutions and natural waters

Abstract

SUMMARYPotential vitiative effects of Millipore 0.45‐, 0.22‐, 0.05‐ and 0.025‐pm filter elements on aqueous samples were investigated. All the filter elements evaluated exhibited a cation exchange capacity (CEC); in the case of 0.025‐pm filter elements, the CEC increased with pH. Filtration of 20 μM AlCl3/1.65 mM CaCl2, solutions (I∼0.005 M) to 0.45, 0.22 and 0.05 pm resulted in no significant change in solution A1 concentration. Filtration through 0.025‐μm filter elements significantly reduced the total A1 present in solutions adjusted to pH 4.5 and 5.0; the A1 concentration of solution adjusted to pH 4.0 was not altered. The removal of A1 from pH 4.5 and pH 5.0 solutions was attributed to the retention of A1 hydroxide micro‐particulates formed during pH adjustment of the AlCl3/CaCI2, solution. Adsorption of A1 by the filter element was not significant.Soil solutions were analysed without filtering and after filtration to 0.45,0.22,0.05 and 0.025 pm. Filtration had no effect on the concentration of the major anions (Cl−, SO24 ‐, NO13) or cations (Ca++, Mg++, Na+, K+). However, filtration to 0.05 and 0.025 pm resulted in significant reductions in the concentration of Al, Fe, Si and organic C in some samples. In soil solutions for which filtration resulted in the removal of large amounts of particulate material, the solution appeared less coloured after filtration and exhibited lower absorbance in the visible spectrum (4O(MOO nm). However, the absence of colour did not preclude the presence of colloidal particles.