Quantitative and Qualitative Analysis of Heavy Trace Metals in Crude Oil from Southern Iraqi Oilfields Using LIBS

Abstract

The determination of heavy trace metals in crude oil is essential for evaluating environmental risks and refining efficiency. This study investigates the qualitative and quantitative distribution of heavy trace metals in crude oil from major southern Iraqi oilfields (North Rumaila, Majnoon, and Zubair) using Laser-Induced Breakdown Spectroscopy (LIBS). The liquid crude oil samples were thermally treated at 350 °C to produce a stable solid residue, which was then ground into a fine powder and compressed into pellets for LIBS analysis. To achieve efficient material ablation, the laser beam from a Q-switched Nd:YAG laser (1064 nm, 300 mJ, 8 ns) was focused onto the pellet surface using a 50 mm focal length lens. This setup created a focal spot diameter of approximately 0.4 mm, resulting in a calculated laser fluency of 238.8 J/ at the target surface. The generated plasma light was then collected and analyzed using an Ocean Optics HR4000CG-UV-NIR spectrometer, equipped with a Toshiba TCD1304AP linear CCD array detector (3648 pixels) covering a spectral range of 200–790 nm. Finally, elemental identification and spectral consistency were verified using the NIST atomic spectra database. A wide range of toxic and radioactive elements (Hg, Pb, Cd, U, Ra) along with transition and noble metals (W, Sn, Mo, Ag, Pt, Au, Ir, Rh) were successfully identified. Quantitative analysis showed strong linearity (R² up to 0.9961), low detection limits (as low as 0.001841% for Pb), and acceptable precision (RSD < 6%). Elemental distribution revealed significant variability, with Hg (6.03–9.65%) and Pb (2.26–6.87%) as dominant contaminants, and pronounced enrichment in the Zubair sample (W3). These findings confirm that LIBS is a rapid, sensitive, and reliable technique for multi-element analysis in crude oil. The observed distribution of heavy trace metals highlights their environmental and industrial significance, particularly in pollution monitoring and refining processes, and demonstrates the potential of LIBS as an effective tool for petroleum characterization and geochemical assessment.

DOI: https://doi.org/10.31257/2018/JKP/2023/v15.i02.13216