In Situ Evaluation of Inorganic Matrix Effects on the Partitioning of Three Trace Elements (As, Sb, Se) at the Outset of Coal Combustion

摘要

A direct method of assessing the partitioning of semivolatile trace elements (TEs), such as As, Sb, and Se, between the gas and solid phases in the microenvironment of the burning char can be used to gain insight into TE partitioning in coal-fired furnaces. Such a method was developed using a graphite furnace atomic absorption spectrometer (GFAAS) to perform three separate functions simultaneously at high temperature (up to 2800 °C): in situ pyrolysis simulation, sample collection, and analysis. The current study focuses on further developing this method to study the vaporization of TEs entrapped in inorganic inclusions within coal. TEs were introduced into the GFAAS in their water-soluble form, using coal-relevant matrix/TE ratios. This allowed a homogeneous TE distribution within the matrix, which simulated various inclusion forms. Activation energies of the TE atomization were determined with and without these matrices to assess the chemical matrix effects. Several inorganic matrices were shown to alter the concentration and occurrence of TEs in the gas phase, suggesting plausible molecular mechanisms for their evaporation and atomization. By comparison, two matrices, Ca(CH_3CO_2)_2 and Fe(NO_3)_3, significantly increased atomization/vaporization activation energies, indicating an increased TE retention in the solid phase. NaAlO_2 did not alter the activation energies for these TEs. The other anionic matrix, K_2SiO_3, decreased the atomization/vaporization activation energy for Se and reduced its atomic absorption signal, apparently as a result of the nonspecific blocking of TE access to the surrounding carbon. These observations were attributed to specific interactions of anionic TE species with cationic matrices.