Characteristics of membrane filters in relation to aluminium studies in soil solutions and natural waters
1991
Menzies, N.W. | Bell, L.C. | Edwards, D.G.
Potential vitiative effects of Millipore 0.45-, 0.22-. 0.05- and 0.025-micrometer filter elements on aqueous samples were investigated. All the filter elements evaluated exhibited a cation exchange capacity (CEC); in the case of 0.025-micrometer filter elements, the CEC increased with pH. Filtration of 20 micrometer AlCl3/1.65 millimole CaCl2, solutions (I approximately 0.005 m) to 0.45. 0.22 and 0.05 micrometer resulted in no significant change in solution Al concentration. Filtration through 0.025-micrometer filter elements significantly reduced the total Al present in solutions adjusted to pH 4.5 and 5.0; the Al concentration of solution adjusted to pH 4.0 was not altered. The removal of Al from pH 4.5 and pH 5.0 solutions was attributed to the retention of Al hydroxide micro-particulates formed during pH adjustment of the AlCl3/CaCl solution. Adsorption of Al 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 micrometer. Filtration had no effect on the concentration of the major anions (Cl-, SO4(-2) NO3(-) or cations (Ca++, Mg++, Na+, K+). However. filtration to 0.05 and 0.025 micrometer 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 (400-600 nm). However, the absence of colour did not preclude the presence of colloidal particles.
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