Detection of Heavy Metals Contents in Sudanese Cement Using Laser Induced Breakdown Spectroscopy Technique

Abstract

In this work, Laser Induced Breakdown Spectroscopy (LIBS) was used to Investigate, and identify, the heavy metals in samples of cement collected from different local markets in Khartoum state. Four cement samples were used as study samples (Atbara, Barbar, Mas and Sakhr Al Sudan) cement. Optimal experimental conditions were evaluated using Nd: YAG laser in Q-switched mode with ability to deliver maximum pulse energy of one joule with a pulse width of 8 ns and operating at a 10 Hz was employed for production of plasma spark at the sample surface. A convex lens having focal length 30 mm was used to focus Nd-YAG laser pulse onto the surface of sample at 266 nm. With pulse energy 30 mj. The spectrometer used was Ocean Optics LIBS 2000+ system. Our LIBS 2000+ has four spectrometers modules to provide high resolution (FWHM 0.1 nm) in the (200 to 620) nm wavelength region. The detector has a gated CCD camera having 14,336 pixels. This makes it possible to measure a LIBS spectrum over broad spectral range (200 to 620) nm simultaneously with high spectral resolution (0.1 nm). The emission is observed at a 90° angle to the laser pulse. The recorded spectra of the samples were analyzed using NIST data. The analysis of the spectra showed considerable amounts of neutral atoms like (Ca, Fe, Si, Na, Ti, Cr, V, Sr, Zr, Kr, K and Cs) that were found in all samples. In addition to the ions: (Ca+1, Fe+, Si+1, Na+1, Ti+1, Cr+1, and K+1). The heavy metals like: metals (Cr, Fe, Ti, Mn, V, Xe, Y and Zn) were appeared in the four samples with nearly amounts, they are toxic metals harmful to human and environment. To identify the relationship between the laser pulsed energy and the intensity of the LIBS signal, the Mas cement sample was irradiated by different pulse laser V energies (10, 15, 20, 25, 30 and 32) mJ .respectively and 200 ns delay time. We observed when the laser pulse energy increase the line intensity was increase. LIBS were applied for the determination of plasma temperature and electron density of Cr in Mas cement sample. The plasma temperature and electron density were calculated at (10, 20, 25 and 30) mJ laser pulse energy using standard equations and well resolved spectral lines in the (428.97 ,430.117,435.17,and 435.96) nm region. These parameters were found to increase with increase in laser pulse energy. The Boltzmann distribution and experimentally measured line intensities support the assumption that the laser-induced plasma was in local thermal equilibrium. To identify the relationship between the laser delay time and the intensity of the LIBS signal, the Mas cement sample was irradiated by 32mj laser pulse energy and (200,300,400 ,500, 600, 700, 800, 1000, and 2000) ns delay times. We observed LIBS signal decreases with increase in laser delay times. The plasma temperature and electron density were calculated at (300,500, and 700) ns laser delay time at 32mj laser pulse energy using standard equations and well resolved spectral lines of Ca in the (422.67, 430.25and 430.774) nm region. It was observed that when the delay time increases the plasma temperature and electron density were decreased. Then the electron density increased with increased in plasma temperature.