Description of adsorption interactions of lead ions with functional groups of pectin-containing substances

Pectin-containing substances extracted from flax fiber and commercial preparations of apple and citrus pectins have been modified to obtain model samples of pectic acid, pectinate and pectate. The IR-spectroscopy method has been used to estimate the ratio of galacturonate units with the unsubstituted carboxyl group and those in the methoxylated and calcium pectate forms in the polymer. Correlation ratios have been obtained for describing the dependence between the changes in the state of pectin functional groups, kinetic and thermodynamic parameters of lead cation sorption within the temperature range of 298-318 K. The adsorption process and the equilibrium have been adequately described by the Weber-Morris diffusion model, the pseudo-second order kinetic model and the Langmuir adsorption model. It has been confirmed and quantitatively characterized that lead binding is driven by the mechanisms of ion exchange with COOH groups, cation substitution with COOCa1/2 groups and coordination bonding with OH groups of methoxylated units. (C) 2019 Elsevier B.V. All rights reserved.