Author: Subir Kumar Das, from CSIR - Institute of Minerals and Materials Technology, Bhubaneswar, India

Abstract: Magnetic particles in silico-aluminous bottom ash samples (NT-BA and HR-BA samples) of two thermal power plants of Talcher area, Odisha, India have been studied for determination of their concentration, morphology, internal structure and phase mineral composition. The amounts of magnetic concentrates in NT-BA and HR-BA samples are 25.7 and 4.03% respectively and the former particles are relatively coarse grained. In NT-BA sample, most of the magnetic particles are ideal solid spheres (ferrosphere) with diverse morphological features: smooth, skeletal, dendritic, octahedral, polygonal, granular, and spotted. The magnetic particles of HR-BA sample are fine grained, irregular to angular, mostly associated with glass matrix

The magnetite crystals occur as fine streaks, laths, lamellae and needles. Examination of the inner structure of the ferrospheres and irregular magnetic particles of concentrates of both the samples revealed that the magnetite crystals have different geometric patterns and association with different mineral phases indicating variations in crystallisation conditions in the combustion chamber. The magnetite crystals of HR-BA sample are extensively martitised. The EDS results indicated that in the magnetite, Fe is the dominant element with small amounts of Mn, Mg, Ca and Ti. These elements occur as diadochic replacement of ferrous ion in the magnetite crystal structure.

The glass coexisting with magnetite has highly variable chemical compositions mainly with respect to Si, Al and Fe; few glass particles are enriched in Fe. Detrital quartz grains are occasionally observed within the magnetic particles. The magnetite oxide crystallites in ferrospheres are derived from the decomposition and oxidation of iron-bearing minerals such as pyrite and clays minerals in feed coal during combustion in the thermal power plants.

The full-text of the paper may be viewed/downloaded at the Coal Combustion and Gasification Products journal website:

The CCGP journal is jointly published by the University of Kentucky Center for Applied Energy Research (UKCAER) and the American Coal Ash Association (ACAA).