Characterization of Power Plant Residue Using Various Spectroscopic Techniques for Recycling Valuable Metals

Abstract

We successfully developed an optimized fast detection system based on an orthogonal double-pulse laser-induced plasma spectroscopy (ODPLIPS) system for quantitative analysis of valuable heavy metals like vanadium (V) and nickel (Ni) content in fuel power plant residue (PPR). The goal of this study was to investigate the existence of precious elements locally found in nine different kinds of fuel power plant residues and to pay attention to the mining industry towards exploration recycling of these reserves. Those metals were taken from the PPR as a solid waste residue for industrial recycling. The investigated composition analysis by employing the calibration of the LIPS scheme is established on the registered collection spectra of the plasma flare generated by the laser beam in air pressure. We prepared standard matrices in a known concentration in the PPR sample to draw the standard calibration curves for each element, as well as by utilizing a tactic based on the intense lines emission of the elements of interest as quantitative analysis. Those precious elements that exist in the PPR were exactly identified using the energy dispersive X-ray (EDX) and an orthogonal double-pulse-LIPS (ODPLIPS) systems. A combination of UV-NIR lasers of our double-pulse (DP-LIPS) system was employed under a similar adjustment condition to raise the signal-to-noise (SNR) ratio relative to the single-pulse (SP-LIPS) scheme. Several measurements were widely adjusted to elongate the plasma lifetime and to improve the sensitivity of the 266–1064 nm spectra. To overcome the difficulty of insufficient sensitivity in the SP-LIPS or CFLIPS manner for identification of the sample and to achieve a larger atomized mass, larger emitting volume, higher plasma temperature, and a lower detection limit, a double-pulse variant for vaporization of the sample were applied in our study. By using the ODPLIPS excitation technique, the intensity of both spectral lines Ni(II) 221.65 and V(II) 294.45 nm were enhanced by nearly 4 and 5 times, respectively at laser pulse energy (LPE) ratio (E2/E1 = 3) as compared to the SP signal that could help the analytical performance of the LIPS system in terms of increasing sensitivity and reducing self-absorption effects for PPR pellets. The preferable of the ODPLIPS scheme over the SP-LIPS scheme results from the suppression of molecular bands and improving the relative intensity of the spectral lines, which makes it favorable for enhancing the sensitivity of the LIPS determination in PPR. Several experimental parameters of ODPLIPS geometry like the periodic interval between the data acquisition and the excitation pulse laser (ICCD gate delay, td = 200 ns), the LPE ratio (E2 = 3 times E1) and the inter-pulse separation between the couple laser pulses (Δt = 800 ns) have been optimized to improve the SNR and sensitivity of our detection system and to achieve the best detection limit. For better understanding, the basis of the measured LIPS signal enlargement, the spatial evolution of the plasma temperature and density along the direction of the plasma plume expansion of the separated distance from the pressed sample surface was also measured for both SP-LIPS and ODPLIPS schemes. The calibration curves were employed to quantify the Ni and V concentration that exists in the PPR samples. Furthermore, the LIPS outcome accuracy in evaluating the V and Ni concentration in PPR was validated using an inductively coupled plasma-optical emission spectrometry (ICP-OES) system. The predicted LIPS outcomes were found in complete harmony with the ICP-OES outcomes. The predictable limit of detection of our ODPLIPS system for V and Ni heavy metals was observed to be about 12.58, and 14.75 mg/kg, respectively. The proposed protocols elucidated that the brilliant profit of ODPLIPS for identifying valuable V and Ni metals present in the PPR sample and for examining the quality and purity of recovering metal manufactures.