Identification of Fe, Si, Mg and Ni in Limestone Rocks Collected from Omdurman Area Using Laser Induced Breakdown Spectroscopy

Abstract

In this research were analyzed 20 samples collected water wells, where sedimentary rocks exists, were collected. The concentrations of Fe, Si, Mg and Ni were identified by laser induced breakdown spectroscopy (LIBS) and atomic absorption spectroscopy (AAS). The aim of the work is first to see the relative abundance of minerals especially Fe with respect to silicon, because minerals are assumed to be rare in sedimentary rocks. The second aim is to determine the degree of accuracy of LIBS in identifying and finding the concentration of these elements. In this research laser induced breakdown spectroscopy (LIBS) was assembled from Nd: YAG laser source, fiber optic and USB spectrometer. The laser beam of high energy, such as neodymium-doped yttrium aluminum garnet laser, Nd: YAG with wave length 1064 nm was focused to induce breakdown of the atoms in the medium under study, then electrons were excited from the ground level to the high level while material in the plasma state, then the material radiate spectrum of certain wave lengths of particular density. Each element can be determined in the sample by its specific wave length, thus one can therefore, call this technique laser induced plasma spectroscopy (LIPS) as well. laser induced breakdown spectroscopy (LIBS) is characterized by many advantages such as saving of time-no time required to prepare samples-and also very small amount of the sample about 0.1 µg is needed. More over, the assembled LIBS is less expensive regarding the prices of its component in the market. To ensure the efficiency of instrument half of samples have been analyzed by atomic absorption spectroscopy (AAS). The composition result of laser induced breakdown spectroscopy (LIBS) proved that the ability of the instrument to identify the elements under test is highly accurate. But the concentration determination is not at the same accuracy, which means that to measure concentration by laser induced breakdown spectroscopy need modification in its exposure time and homogenous sample in the future. The analysis of all sedimentary rock samples shows that the average abundance of minerals is 15.8 % ppm thus it is much less than the silicon abundance which is 40.8 % ppm. This indicates that the relative average abundance of minerals with respect to silicon can be utilized to differentiate sedimentary rocks from other rock types.