Investigation of Fe, Mn oxides and organic material in surface coatings and Pb, Cd adsorption to surface coatings developed in different natural waters

Surface coatings (biofilms and associated minerals) were developed on glass slides in five natural waters in Jilin Province, PR China and were used to evaluate Pb and Cd adsorption after they were analyzed for their iron, man ganese oxides and organic material content. Pb and Cd adsorption to the sur face coatings was measured under controlled laboratory conditions (mineral salt solution with defined speciation, ionic strength 0.05 mol/l, 25 degree sC and pH 6.0). The classical Langmuir and Freundlich adsorption isotherms were applied to estimate equilibrium coefficients of Pb and Cd adsorption t o the surface coatings. The results show that the former is more suitable t han the latter as a model to describe Pb and Cd adsorption to natural surfa ce coatings. Correlation analyses between the maximum adsorption of Pb and Cd and components in the surface coatings indicate that the adsorption of P b to Mn oxides and the adsorption of Cd to Fe oxides are statistically high er than the adsorption of Pb and Cd to other components. Moreover, the adso rption of Pb and Cd to organic material is insignificant, highlighting the relative importance of the metal oxide fraction for Pb and Cd adsorption to the surface coatings developed in five natural waters. (C) 2001 Elsevier S cience B.V. All rights reserved.