Determinação de enxofre em carvão mineral após preparo de amostra por MIC-DV

Abstract

The determination and removal of sulfur from coal has become important to the industry, as well as for the environmental pollution control. Microwave-induced combustion in disposable vessels (MIC-DV) was proposed for the subsequent sulfur determination in coal by inductively coupled plasma optical emission spectrometry (ICP-OES). The parameters that could influence the sample digestion by MIC-DV were evaluated, such as sample mass (5 to 30 mg), influence of oxygen pressurization (1.0 to 1.8 bar), as well as the type (H2O and HNO3), concentration (1.0 to 14.4 mol L-1) and volume of the absorbing solution (2.5 to 12.5 mL). As MIC-DV is an alternative to the conventional methods, it was compared with microwave-assisted digestion (MAD), microwave-induced combustion (MIC) and direct solid sampling elemental analysis (DSS-EA). The agreement ranged from 91 to 97%, 82 to 102% and 91 to 94%, 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. The sulfur concentration in the analyzed samples ranged from 8815 to 10370 μg g-1. It is important to mention that the MIC-DV uses low-cost and environmentally friendly materials and instrumentation. Moreover, the sample preparation time for MIC-DV method was shorter than other methods, 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 from the sample preparation up to quantification, avoiding the use of additional vessels for dilution and reducing the risk of contamination by excessive handling.