Multivariate regression models for the simultaneous quantitative analysis of calcium and magnesium carbonates and magnesium oxide through drifts data

Abstract

Neste trabalho são apresentados modelos de regressão multivariada, empregando espectros por reflexão difusa no infravermelho com transformada de Fourier (DRIFTS), para análise quantitativa do sistema ternário formado pelos carbonatos de cálcio e magnésio e pelo óxido de magnésio. Através de um diagrama ternário, foram definidas as misturas para aquisição dos espectros por reflexão no infravermelho médio. Empregando-se a regressão por mínimos quadrados parciais (PLS), foram construídos modelos com os dados espectrais centrados na média e/ou escalados pela variância, utilizando o conjunto de espectros de calibração. Para selecionar os melhores modelos, foram comparados os valores de RMSEP (root mean square error of prediction). Os resultados comprovam que bons modelos de calibração multivariada para a determinação de carbonatos de cálcio e magnésio e de óxido de cálcio podem ser obtidos a partir dos espectros por reflexão no infravermelho. Estas determinações são particularmente úteis no estudo da decomposição térmica de rochas dolomíticas.In the present work multivariate regression models were developed for the quantitative analysis of ternary systems using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) to determine the concentration in weight of calcium carbonate, magnesium carbonate and magnesium oxide. Nineteen spectra of standard samples previously defined in ternary diagram by mixture design were prepared and mid-infrared diffuse reflectance spectra were recorded. The partial least squares (PLS) regression method was applied to the model. The spectra set was preprocessed by either mean-centered and variance-scaled (model 2) or mean-centered only (model 1). The results based on the prediction performance of the external validation set expressed by RMSEP (root mean square error of prediction) demonstrated that it is possible to develop good models to simultaneously determine calcium carbonate, magnesium carbonate and magnesium oxide content in powdered samples that can be used in the study of the thermal decomposition of dolomite rocks.Keywords: dolomite, DRIFTS, partial least squares, multivariate regression, ternary mixture design IntroductionThe reserves of carbonate rocks in the state of Rio Grande do Sul -Brazil, are mainly constituted by dolomitelike rocks (MgO content ≅ 18%), while calcite-like rocks (MgO content < 4%) occur in a smaller proportion. It is assumed that, in volume, only 18% of the calcareous rocks are calcite-like (used mainly in cement production) and 82% are dolomite-like and are used mainly in the correction of soil acidity and in the production of lime.The search for a solution to the suppressed demand of raw materials by turning dolomite into calcium-rich carbonate and magnesium oxide, which are thoroughly used in industrial processes impelled the development of a physical process of dissociation of dolomite-like rocks, in order to obtain these two different products. The basic idea of the process is a fractionated calcination of a dolomite-like rock, composed m...