Passivity of iron in red mud's water solutions

Red mud suspensions are studied as passivating agents for iron in alkaline chloride media. Red mud particles in alkaline media are negatively charged, and can absorb considerable amounts of protons without significant changes in pH. These particles adhere easily to an iron surface forming aggregates of heterogeneous shape, smaller than 10 mum x 10 mum. These adhered particles recrystallise on potential cycling, and hinder metal dissolution and magnetite formation. Carbon steel samples passivated in red mud suspensions become resistant to corrosion in alkaline chloride media. Corrosion potential versus time records and impedance spectroscopy measurements allow formulating some hypotheses about the inhibiting mechanism. (C) 2004 Elsevier Ltd. All rights reserved.