Determination of trace metals by ICP-OES in petroleum cokes using a novel microwave assisted digestion method

Abstract

Trace metals must be strictly controlled in petroleum coke when it is used as anode, as the function of electrodes depends on their concentration, being detrimental in process operations affecting the purity of the final product.In this research, the determination of Si, Fe, V, Ni, Ca, Na, P, Al, Ti, Mg, K, Zn, Mo, Ba, and Co at trace level in green and calcined petroleum cokes using a new digestion method was performed. The method involved microwave-assisted digestion of the sample using a single-reaction chamber (SRC) followed by ICP-OES measurement. This method aimed for a low sample preparation time and a quantitative extraction of the analytes.After optimization of the digestion process it was found that the best condition to digest green and calcined cokes was mixing 9 g HNO3 and 3 g HCl, heating at a temperature of 260 °C for 55 min, and taking 0.5 g of sample, leading to a recovery higher than 98% for all the elements analyzed. In addition, the developed method allowed the determination of the elements in 1.5 h versus the standard method, which takes about 8 h. The validation of the developed methodology was carried out analyzing certified reference materials and using independent methods, such as, wavelength dispersive X-ray fluorescence spectrometry (WD-XRF).The developed methodology is faster, more accurate and more environmentally friendly than other available methodologies as it does not require the decomposition process involving high temperatures and waste generation is minimized. In addition, low limits of quantification and low uncertainties have been reached enabling this method to be used as a control method.