The Bureau of Mines is conducting research to identify highly selective chemical lixiviants for in situ leach mining of critical and strategic minerals from domestic low-grade ores. This report presents part of that effort by (1) reviewing chemical lixiviants for manganese, (2) describing mineral dissolution models, and (3) presenting a geochemical approach to lixiviant selection and optimization called geochemical characterization. Geochemical characterization logically follows ore petrology by focusing on leaching chemistry at mineral surfaces. It consists of interrelated theoretical modeling and laboratory experimentation that lead to lixiviant systems specifically suited for a given ore body. This report focuses on the theoretical modeling necessary to develop selective lixiviants. This modeling consists of thermodynamic and kinetic evaluations of prospective lixiviant-ore combinations that favor commodity metal leaching over gangue leaching. Kinetic evaluation uses a number of predictive methods for leaching reactivity, including inorganic solution chemistry and molecular orbital theory. This evaluation process is illustrated in a study of selective so2 leaching of domestic manganese minerals. Geochemical reasons exist for observed leaching rate differences among manganese oxide minerals. Molecular orbital theory reveals that so2 has an ideal structure to directly bond and reduce mn4+ to water-soluble mn2+ more rapidly than mn3+.