Assessment of microwave-induced combustion in disposable vessels as a low-cost approach for sulfur determination in coal

Abstract

The determination and removal of sulfur from coal has become important to the industry and the environment for the pollution control. Therefore, the microwave-induced combustion in disposable vessels (MIC-DV) for sulfur determination in coal by inductively coupled plasma optical emission spectrometry (ICP-OES) was proposed. The parameters that could influence in the combustion, such as sample mass (5 to 30 mg), influence of pressurization (1.0 to 1.8 bar), and type (H2O and HNO3), concentration (1.0 to 14.4 mol L−1) and volume (2.5 to 12.5 mL) of absorbing solution were evaluated. The proposed method was compared with microwave-assisted digestion (MAD), microwave-induced combustion (MIC) and direct solid sampling elemental analysis (DSS-EA) and the agreement was better than 91, 82 and 91%, respectively. The limits of detection and quantification for sulfur in coal after optimized MIC-DV and determination by ICP-OES were 11 and 37 µg g−1. It is important to mention, that the MIC-DV employs low cost and environmental friendly materials and instrumentation. Moreover, the speed of the sample preparation process was increased comparing to MAD, MIC and DSS-EA, since sample combustion was achieved in less than 30 s in a rotor containing 5 positions. Last, but not least, the MIC-DV method is based on the single vessel principle, using the same vessel comprising the sample preparation and quantification, avoiding the use of additional vessels for dilution, reducing the risk of contamination by excessive handling.