Coal usually contains high levels of selenium, particularly from sources that are also high in sulfur. This results in waste streams from coal-fired power plants having selenium concentrations that far exceed industrial discharge limits.
Removal of selenium from these wastewater streams can present a significant challenge since the effectiveness of most treatment processes depends on the forms (or species) of selenium present. Different plant operating conditions and treatment additives are well-known to impact selenium speciation in flue gas desulfurization (FGD) wastewaters. Monitoring which forms of selenium are present at various stages and over time, particularly as changes are made to plant operations, is critical for ensuring that wastewater treatment systems are functioning properly.
Brooks Applied Labs (BAL) offers advanced analytical services for the determination selenium species by a variety of hyphenated techniques, the most common of which is IC-ICP-CRC-MS. Coupling ion chromatography (IC) separation methods to inductively coupled plasma – mass spectrometry (ICP-MS) instruments equipped with collision reaction cell (CRC) technology allows for high sensitivity and accuracy in even the most complex matrices. Over a dozen different selenium species can be measured with these methods, including selenite [Se(IV)], selenate [Se(VI)], selenocyanate [SeCN], selenosulfate [SeSO32-], selenomethionine [SeMet], selenomethionine oxide [SeMetO], methylseleninic acid [MeSe(IV)], and methaneselenonic acid [MeSe(VI)]. An example chromatogram for selenium speciation by IC-ICP-CRC-MS is shown below:
Should these routine methods indicate the presence of “missing” forms of Se, BAL has both the expertise and other developed methods to close the selenium mass balance. For example, reverse phase high performance liquid chromatography ICP-CRC-MS (RP-HPLC-ICP-CRC-MS), can be used for measurement of non-ionic forms of selenium like dimethylselenide [DMSe] and dimethyldiselenide [DMDSe]. The latter two species can be formed in biological treatment systems that are often used for selenium removal.
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