Reiner Neumann

Raman spectroscopic analysis of real samples: Brazilian bauxite mineralogy

In this investigation, Raman spectroscopy with 1064 and 632.8 nm excitation was used to investigate real mineral samples of bauxite ore from mines of Northern Brazil, together with Raman mapping and X-rays diffraction. The obtained results show clearly that the use of microRaman spectroscopy is a powerful tool for the identification of all the minerals usually found in bauxites: gibbsite, kaolinite, goethite, hematite, anatase and quartz. Bulk samples can also be analysed, and FT-Raman is more adequate due to better signal-to-noise ratio and representativity, although not efficient for kaolinite. The identification of fingerprinting vibrations for all the minerals allows the acquisition of Raman-based chemical maps, potentially powerful tools for process mineralogy applied to bauxite ores.

Powdered microporous glasses: changing porosity through aging

Recently, we have reported the production of a microporous high purity silica powder from the acid leaching of glasses with average pore size around 2.5nm and specific surface area of 420m2/g (BET). The employed glasses derived from the melting of two types of waste from the industrial processing of Brazilian oil shale (retorted oil shale and the top fraction of the intermediate layer of Irati Formation). Depending on the proportion of the two wastes employed in the formulation of the glasses, either a silica gel or a powdered one is obtained, after leaching. The acid leaching of those glasses with hydrochloric acid, at 90 °C, was used to produce powdered microporous silica. In the present work it is studied the effect of aging time and temperature on the morphology and structure of the obtained powdered silica. Aging studies were performed in two different media, an acidic (hydrochloric acid) and a basic one (ammonium hydroxide) for different periods of time and temperatures. XRD, SEM/EDX, TEM, specific surface area measurements and DTA/TGA were used to characterize these materials. The results have shown a decrease of specific surface area with increasing time and temperature. Apparently, this behavior may be associated with dissolution and re-precipitation mechanisms.

Back-scattered electron imaging of a lateritic iron ore and its applications in process mineralogy

Abstract A hydrocyclone treating an itabirite iron ore was sampled, characterized in detail using modern image analysis techniques and modeled. Some of the most interesting results from this investigation were: the itabirite studied is highly porous; this property may be advantageous in direct reduction applications; two types of porosity are present; one is macroscopic and the other microscopic; the micro-pores in this itabirite are interconnected. Porosity liberation in the size range studied is associated to the macro pores; the process of liberation in this itabirite is quick, probably aided by liberation by detachment; the regimen inside the hydrocyclone is closer to turbulent than it is to laminar regimen; the density of the slurry in the separation zone must be used instead of the density of the liquid. It is anticipated that lateritic iron ores in general may present significant porosity, and this must be taken into consideration when evaluating image analysis results from this type of ores.