Modificação no método do Thorin para determinação quantitativa rápida de tório em minérios brasileiros

摘要

The minerals controlled by CNEN have in its composition, moreover than uranium and thorium, other elements, as rare earths, bismuth, tantalum, niobium and iron. Most of these elements are a great obstacle to the analytical quantitative determination of Thorium, when modern and non-destructive techniques as Energy Dispersive X Ray Fluorescence – EDXRF, cannot be used. The present work is successful in satisfying all the CNEN parameters, and executing the job in a secure and optimized way. Through the planned and studied modifications, executed in well-know and consecrated analytical methods we hit the objective to reduce the total time of the analysis process to 3 hours. The new procedure is also versatile: it can be used in all the brazilian minerals which is responsibility to CNEN such as: ilmenite, anatase, columbite, tantalite, caldasite, zirconite, thorianite, monazite and pirochlorine with the same accurate and fast results although they have diverse chemical compositions. The foremost, modifications included in the process was the fusion with ammonium and potassium bifluorides, promoting the quantitative precipitation of thorium and allowing it's separation from uranium. So, the slowly step of precipitation with oxalate used in former processes can be eliminated. The results of the separation can be confirmed by FRX analysis. After, the thorium is separated from the rare-earth using mesytilium oxide. The thorium quantifying can be done just after, by epectrophotometry in 545 nm using thorin in a 0,24 mol L-1 HCl medium. The methodology developed and presented in this writing was compared with the classic method using the statistical test of the t pair used in the determination of Th in certified material of reference (monazite), not having been found difference between the two methodologies. The new methodology also was applied to some ores with values of concentration of Th certified presenting compatible agreement enters the results for a reliable level of 95%.