Quantitative Phase Analysis Based on Rietveld Structure Refinement for Carbonate Rocks

Abstract

QPA (Quantitative Phase Analysis) of carbonate rocks bearing calcite and dolomite using X-ray diffractometry (XRD) can be performed using the combined Rietveld Structure Refinement (RSR) and semiquantitative Reference Intensity Ratio (RIR) methods, providing an estimation of crystalline phase in a mixture. Different ratios of five samples were prepared by mixing these crystal minerals with high sensitively. The scan speeds, adequate to determine mineral phases in rock samples, were used as 6 degrees per minute with 0.08 steps. The XRD analysis with commercial TOPAS 3.0 program, defined by a new generation of profile and structure analysis software, based on RSR provides Bragg reflection profiles and the dimension of the unit cell of a phase. The weight fractions of each phase were found by Le Bail and Pawley methods in RSR using a pseudo-Voigt peak shape model. The samples were also characterized by using X-ray fluorescence (XRF) and atomic absorption spectrometer (AAS). These analyses were conducted to compare these results with those obtained from the RSR. In addition to these, RSR of phases is very important to improve the goodness of fit (GOF). Therefore, the discussions of refinement of the carbonate mixing were made and a refinement procedure was given for these mixing in detail. Taking advantage of the RSR with the addition of an internal standard, the phase fraction of all the crystalline phases as well as the amorphous component, has been accurately determined. RSR technique offers a valid support for the characterization of marble in the light of industrial products.