Investigation of the decrepitation phenomenon of polymorphic materials: A theoretical and experimental study

Fine generation during thermal processing (basically roasting) of oxide materials is an unattained issue due to lack of knowledge on the mechanism of particle breakage. An important quality parameter to quantify fine generation for lumpy oxide materials is decrepitation. In this research article, primary reasons for decrepitation of polyformic materials like manganese oxides are addressed by characterization and experiments followed by a theoretical model for particle breakage. Herein, the physical, chemical and mineralogical characterizations of low grade manganese ore lumps from Indian mines are presented. Particle breakage has been correlated with the heat profile in the porous bed for three different packing geometries by variation of parameters: heating rate, time, and temperature. Optimization analysis was performed using response surface methodology to estimate the effect of interaction parameters on fine generation and to estimate the optimum parameter setting with a maximum of 5% fine generation. Secondly, a mathematical model was developed to simulate the heat transfer behavior in a single particle of 6 mm diameter with the objective of moisture evaporation and to estimate the heat distribution in porous bed geometries. Finally, a thermo-mechanical stress model has been developed to support the mechanism of particle breakage. Heat transfer analysis shows that cylindrical bed geometry has better heat distribution due to less bed permeability and larger contact area between the particles. The optimized condition for roasting of low grade manganese ores to achieve transformation of manganese dioxide & up to 5% decrepitation is as follows: temperature:700 degrees C, heating rate: 10 degrees C/min, and roasting time: 70 min. (C) 2016 Elsevier B.V. All rights reserved.