On the Climate Impact of the Local Circulation in the Itaipu Lake Area

The impact of the Itaipu Lake on the climate and local circulation is investigated here using the meteorological information available in the area. The Itaipu Lake is an artificial water reservoir of 1460 km² (approximately 170 km by 7.5 km), formed in 1982 as part of the Itaipu Power Plant. It is situated on the Brazil-Paraguay frontier, in the central portion of Parana River Valley. The analysis of the available meteorological data (air and water temperatures, air relative humidity, precipitation and radiosonde soundings) provides observational evidences supporting the hypothesis that the Itaipu Lake presence has an important impact in the local circulation, inducing a local circulation with lake breeze characteristics showing horizontal wind divergence over the lake during daytime and convergence during nighttime. From the regional point of view, the Itaipu Lake formation has reduced the thermal amplitude of the diurnal air temperature cycle. The precipitation data, investigated here, has not indicated any systematic effect associated to the lake formation. The reason for the apparent inconsistency is that others phenomena (e.g., valley-mountain circulation and El Niño events) could be masking the impact of the lake formation on the rain deficit in the region.     

Hydrofluoric Acid‐Free Digestion of Geological Samples for the Quantification of Rare Earth Elements by Inductively Coupled Plasma‐Optical Emission Spectrometry

Rare earth elements (REEs) are very important to technological development as well as to geochemical and environmental studies. In this work, hydrofluoric acid (HF) was replaced by condensed phosphoric acid (CPA) in the digestion of geological samples, and the quantification of REEs was performed by inductively coupled plasma‐optical emission spectrometry (ICP‐OES). Six international reference materials (RMs), named DC86318, CGL 111, CGL 124, CGL 126, OKA‐2 and COQ‐1 and three Brazilian ore samples, named Araxá, Catalão and Pitinga were analysed. Only zircon and xenotime, which are potential REE‐bearing minerals, were not completely dissolved. Nevertheless, no REE associated with zircon was detected. The investigated digestion method presented many advantages: It was relatively fast (3 h), avoided fluoride precipitation, it was less hazardous because handling diluted H₃PO₄ is safer than HF, NH₄F or NH₄HF₂ aqueous solutions, it preserved the quartz fittings of the measurement equipment and the final solution contained lower levels of total dissolved solids than those produced by the fusion method.     

Comparison of Fused Glass Beads and Pressed Powder Pellets for the Quantitative Measurement of Al,Fe, Si and Ti in Bauxite by Laser‐Induced Breakdown Spectroscopy

Due to matrix interference and sample particle size effects, some of the most important and difficult issues in laser‐induced breakdown spectroscopy (LIBS) analysis are the calibration and quantitative measurement of a complex matrix. This study proposes the use of borate fusion as an alternative sample preparation procedure for the quantitative measurement of Al, Fe, Si and Ti in bauxite by LIBS. Analytical calibration curves were made using bauxite certified reference materials (CRM), and the precision and accuracy of the methods were evaluated by analysing an additional bauxite CRM, using two different approaches: pressed powder pellets and fused glass beads. The borate fusion method was the most suitable sample preparation technique, since particle size effects and matrix interference could be minimised, obtaining better linearity on the analytical calibration curves (r²), and more accurate and more precise results for bauxite analysis.