The reaction between various forms of manganese dioxide and halide ions has been investigated. Analytical techniques for the study of this heterogeneous liquid-solid reaction have been developed. The appearance of the reaction products, I₂ and Mn²⁺, was monitored in the aqueous phase of the reaction mixture. I₂ was monitored using amperometry. Mn²⁺ was monitored by a novel application of flow injection analysis. A molecular mechanism was postulated which accounts for the complex pH dependence of the reaction and the inhibition of the reaction under conditions of lower hydrogen ion concentration. The potential of the manganese dioxide-iodide reaction for the metallurgical processing of ferromanganese nodules has been demonstrated. Studies show that there is a preferential dissolution of the manganese portion of the nodules by the action of iodide in acidic conditions. The use of deconvolution techniques for obtaining information from overlapping flow injection analysis peaks has been shown to be feasible. Deconvolution techniques allow an increase in the sampling rates which will broaden the application of flow injection analysis in kinetic studies.