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Coal combustion is one of the main anthropogenic sources of toxic trace element emissions to the environment. Various species and oxidation states of the trace elements released from power stations may determine their ultimate environmental fate and health impacts. This study focuses on speciation of arsenic and selenium present in the coal combustion products. Speciation analysis in representative coal, bottom ash, and fly ash obtained from four different Australian power stations was carried out in this work. Laboratory ash and char were also produced by carrying out combustion and pyrolysis experiments in a laboratory based drop tube furnace. The synchrotron based nondestructive speciation analysis method X-ray absorption fine structure spectrometry (XAFS) was applied for arsenic and selenium speciation analysis of the selected coal, ash, and char samples. The semiquantitative analysis of arsenic revealed variations in arsenic species in the coal samples indicating the presence of As/pyrite, arsenite (As 3+ ), and arsenate (As 5+ ) with the latter as a dominant form. Arsenic in power station fly ash samples was found to be mainly in an arsenate form with little presence of arsenite (As 3+ ). Selenium speciation in coal samples indicated organic/reduced or elemental forms as dominant selenium species along with presence of selenite (Se 4+ )/selenate (Se 6+ ). Selenium in fly ash was mainly found to be selenite with a minor presence of selenate. Char produced by pyrolysis indicated different speciation behavior of arsenic and selenium compared to coal and ash samples, which might be due to their further reactions with other volatilized species produced during pyrolysis and/or retained mineral matter.

In this study, a sequential extraction procedure (SEP) and X-ray absorption near edge structure (XANES) spectroscopy were used to determine the solid-phase speciation and phytoavailability of arsenic (As) of historically contaminated soils from As containing pesticides and herbicides and soils spiked with As in the laboratory. Brassica juncea was grown in the contaminated soils to measure plant available As in a glasshouse experiment. Arsenic associated with amorphous Fe oxides was found to be the dominant phase using both SEP and XANES spectroscopy. Arsenic predominantly existed in arsenate (As(V)) form in the soils; in a few samples As was also present in arsenite (As(III)) form or in scorodite mineral. Arsenic concentration in shoots showed significant (p < 0.001-0.05) correlations with the exchangeable As (r = 0.85), and amorphous Fe oxides associated As evaluated by the SEP (r = 0.67), and As associated with amorphous Fe oxides as determined by XANES spectroscopy (r = 0.51). The results show that As in both fractions was readily available for plant uptake and may pose a potential risk to the environment. The combination of SEP and XANES spectroscopy allowed us the quantitative speciation of As in the contaminated soils and the identification of valence and mineral forms of As. Such detailed knowledge on As speciation and availability is vital for management and rehabilitation of As-contaminated soils.

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