Chapter 7 - Oxidation and Reduction Mechanisms

Abstract

This chapter deals with the thermodynamic basics behind the oxidation and reduction mechanisms. The solubility of oxides decreases with the oxidation state. Monovalent alkali metal oxides are highly soluble, and most of the divalent oxides are sparsely soluble. Trivalent oxides such as alumina and hematite (Fe2O3) exhibit very low solubility, but are more soluble than quadrivalent oxides containing titanium, lanthanides, and actinides. Fortunately, some of the metals have more than one oxidation state. The reduction approach is also useful in stabilization of hazardous metal oxides of high oxidation states. Because of these reasons, a good understanding of the reduction mechanism of oxides within high oxidation states is needed. The basic concepts of thermodynamics in a chemical reaction can be used to predict formation of new products and to predict the direction of a reaction, and the same can be said for an electrochemical reaction also. An important oxide used in the reduction mechanisms is Fe2O3. This oxide is one of the most common and low cost raw materials used in forming inexpensive CBPCs. This oxide is very stable and cannot be dissolved sufficiently in an acid solution to produce Fe2+(aq) or Fe3+(aq) to form CBPC by the conventional dissolution method. The chapter concludes that the reduction may be achieved simply by adding a small amount of elemental iron. Reduction process is also very useful in stabilization of most difficult contaminants such as radioactive technetium in CBPCs.