Adsorption of polymers onto iron oxides: Equilibrium isotherms

The interactions of polymers (corn starch, dextrin from maize starch, humic acid sodium salt and sodium carboxymethyl cellulose) with iron oxides (hematite and magnetite) have been investigated by measuring adsorption isotherms and by electrophoresis. According to the electrophoresis measurements at pH 7 both iron oxides present negative surface charge and positive at pH 5. The equilibrium adsorption isotherms were then determined at pH 7 for all the adsorbates except for humic acid which was studied at pH 5, due to its anionic characteristics. The equilibrium data of both iron oxides were studied using Freundlich and Langmuir models and it was found to best fit to the Freundlich one. The values for Freundlich constants indicate that the mechanism that contributes most to the adsorption process in all experiments was the hydrogen bonding. However, the coexistence of more than one adsorption mechanism is what best explains the process itself, in addition to explaining the differences found amongst theories over the years. (C) 2019 The Authors. Published by Elsevier B.V.