Abstract
Iron-based nanomaterials have high technological impacts on various pro-environmental applications, including wastewater treatment using the co-precipitation method. The purpose of this research was to identify the changes of iron nanomaterial’s structure caused by the presence of selenium, a typical water contaminant, which might affect the removal when the iron co-precipitation method is used. Therefore, we have investigated the maturation of co-precipitated nanosized ferric oxyhydroxides under alkaline conditions and their thermal transformation into hematite in the presence of selenite and selenate with high concentrations. Since the association of selenium with precipitates surfaces has been proven to be weak, the mineralogy of the system was affected insignificantly, and the goethite was identified as an only ferric phase in all treatments. However, the morphology and the crystallinity of ferric oxyhydroxides was slightly altered. Selenium affected the structural order of precipitates, especially at the initial phase of co-precipitation. Still, the crystal integrity and homogeneity increased with time almost constantly, regardless of the treatment. The thermal transformation into well crystalized hematite was more pronounced in the presence of selenite, while selenate-treated and selenium-free samples indicated the presence of highly disordered fraction. This highlights that the aftermath of selenium release does not result in destabilization of ferric phases; however, since weak interactions of selenium are dominant at alkaline conditions with goethite’s surfaces, it still poses a high risk for the environment. The findings of this study should be applicable in waters affected by mining and metallurgical operations.
Highlights
Selenium naturally occurs in oxidation states of −II, 0, IV and VI, with selenites and selenates being prevalent in oxic environments [1,2,3]
This study highlights that the precipitation of ferric oxyhydroxides is a relatively fast process, where the initial kinetics depend on the chemical speciation of selenium
Selenite and selenate were most probably bound by weak physical interactions with goethite surfaces and, they do not manifest themselves in the mineralogy of the precipitates since goethite was observed as the only major phase
Summary
Selenium naturally occurs in oxidation states of −II, 0, IV and VI, with selenites and selenates being prevalent in oxic environments [1,2,3]. Since it usually occurs in a wide range of pHs as oxyanion, selenium is considered a highly mobile element. The main anthropogenic sources include excavated rocks from coal mining, tunnel construction and underground space development [11,12]. It includes coal combustion, nonferrous metal smelting, and agricultural runoff [13,14]
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