Laser-induced breakdown spectroscopy (LIBS) for analysis of precious metals in minerals

The use of LIBS to quantify naturally-occurring gold and silver was investigated with the purpose of exploring its future application as an in situ and online monitoring technique for the precious metal mining industry. Two types of samples were prepared as pressed pellets and analyzed with conventi...

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Autores:: Diaz Ordonez, Daniel Hernando

Tipo de recurso:: Doctoral thesis

Fecha de publicación:: 2017

Institución:: Universidad Nacional de Colombia

Repositorio:: Universidad Nacional de Colombia

Idioma:: spa

Description
Summary:	The use of LIBS to quantify naturally-occurring gold and silver was investigated with the purpose of exploring its future application as an in situ and online monitoring technique for the precious metal mining industry. Two types of samples were prepared as pressed pellets and analyzed with conventional LIBS setups: a) surrogate samples were prepared by doping gold-free matrices with Au and Ag standard solutions, and b) ore samples from a Colombian mine company containing naturally-occurring gold. The ore samples were extracted from underground locations and from a processing plant. The LIBS setups included Nd:YAG lasers (1064 and 355 nm), two Czerny-Turner spectrometers and ICCD detectors (1024×256 pixels). The net peak height, peak-to-base ratio and the background intensities were measured and compared to understand the influence of LIBS parameters on analytical results. From 100 to 5 000 sampling shots were fired over the pellets and an equal number of single-shot spectra were acquired. Single-shot as well as ensemble-averaged spectra were considered. LIBS performance was evaluated using calibration curves, limits of detection and quantification, relative standard deviation and coefficients of determination. Quantification of silver was achieved through conventional ensemble-average calculation and calibration curves. On the other hand, gold quantification was not possible with conventional LIBS spectra processing (ensemble-averaging). However, under specific conditions of sampling, spectra manipulation and the use of conditional analysis to improve gold detection and quantification, a semi-quantitative approach to quantify gold was developed. Finally, Principal Component Analysis was applied to the discrimination of single-shot spectra containing Au emission lines.

Laser-induced breakdown spectroscopy (LIBS) for analysis of precious metals in minerals

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