Técnicas de análises de densidade e porosidade de minério de ferro por cálculo normativo mineralógico, microtomografia computadorizada, permoporosimetria e picnometria clássica : um estudo comparativo entre os métodos

Abstract

During the mineral resources estimation process the apparent density of the rock material is of great relevance because it is a multiplier factor of the modeled volumes. Mistakes caused by low numbers of samples, low reliability of information and the representativeness of this parameter can cause significant financial losses in the mineral projects.

Difficulties related to the collect of bulk density samples for iron ore led to the development of the indirect bulk density determination methodology through the Mineralogical Normative Calculation Method. In this methodology the chemistry of the samples is converted to mineral composition and in turn the absolute mineralogical density is determined. The application of correlation equations and assumptions related to humidity allows to obtain the natural apparent density.

The use of the Mineralogical Normative Calculation methodology has brought gains regarding the apparent density regionalization evidenced by the increased adherence in reconciliation data, however the absence of detailed characterization of the apparent density, absolute mineralogical density and iron ore porosity has limited the application. this technique more broadly.

The present work characterized the parameters concerning the apparent density of iron ore (Itabirites) and waste (Ferrous Breccia and Dolomites) of the Iron Quadrangle and compared it with the indirect determination methodology by normative mineralogical calculation through the collection of 262 samples, in three drilling stratigraphic holes in Aboboras mine.

The natural apparent density tests were performed by the volume displacement technique. Absolute mineralogical density was also determined by Helium picnometry, alcohol picnometry and water picnometry, direct measurements of porosity by computerized microtomography and Boyle's law, electron microscopy, distribution of the particle size and chemistry of samples. The obtained results allowed to quantify the errors associated with the measurement of natural bulk density, the impact caused by the expansion of the samples and the best porosimetry for iron ore. A model of chemical evolution of iron ore deposits and a model of porosity was achieved.

This set of information indicated the presence of bias in the methodology of indirect bulk density determination through normative mineralogical calculation, however, they did not neglect the use of the technique.