Rust Phase Transformation in the Presence of Mangrove Tannins

Abstract

The transformation of rust in the presence of 5 g L-1 tannins extractedfrom mangrove barks was studied. Pre-rusted samples prepared resulted inthe formation of predominantly lepidocrocite and magnetite. Partialtransformation of rust components, particularly lepidocrocite in thepresence of mangrove tannins was found to occur when observed viainfrared spectroscopy, X-ray diffraction and SEM analysis. Theanti-corrosive properties of the mangrove bark extracts seem to berelated to the tannins which are capable of chelating with Fe3+ giving ahighly stable, and insoluble ferric-tannate complexes. A molecularmodeling study of the reaction of catechin, a flavanoid of mangrovetannins with Fe3+ to form a ferrictannate complex was performed toexplain the adsorption mechanism of tannins on iron. The correlationbetween the electronic density of the catechin molecule and theinhibiting properties is reported.