ENHANCED MINERAL DISSOLUTION (POPULATION BALANCE, MANGANESE)

A comprehensive study of the acid dissolution of a family of manganese oxides was undertaken and it was discovered that the rate of dissolution could be accelerated by up to five orders of magnitude (over the base rate in HCl) by the appropriate selection of the solvent. The work was divided into three major areas consisting of kinetic studies, analysis of particle attack morphology, and modeling the effects of polydispersity on the dissolution process. The kinetics of dissolution of the manganese oxides were studied using a slurry reactor and rate laws were obtained based on bulk solvent concentrations. In acidic solution, it was discovered that addition of iodide ions produced the greatest rate enhancement of any of the ions studied. Iodide ions produced dissolution rates approximately 100,000 times the rates observed with chloride ions in solution. The basis for these drastically accelerated rates was related to the band structure of the manganese oxides and the redox potential of the ions in solution.; The nature of the particle attack morphology was studied using scanning electron microscopy on partially dissolved particles. The types of surface attack fell into three basic modes: uniform; deep cylindrical holes or "needles"; and wide, shallow pock marks. The source of these surface instabilities can be explained in terms of a distribution of surface energies on the particles and varying degrees of solvent ion aggressiveness.; The effect of polydispersity on solid particle dissolution was modeled using population balance theory. Analytical solutions to the resulting partial differential equations were obtained. Standard lognormal and Rosin-Rammler particle size distributions were used to model the initial particle distributions. Limiting regime kinetics, mixed regime kinetics, and truncated distributions were incorporated into the population balance model which was used successfully to predict the changing physical characteristics of dissolving mineral slurries.; Of the many potential applications for this work, several of the most significant are new hydrometallurgical treatments for ores, semiconductor etching, prediction of the effectiveness of lake liming treatments, and controlled drug delivery modeling.