Direct immobilization of Se(IV) from acidic Se(IV)-rich wastewater via ferric selenite Co-precipitation
Zidan YuanRui SuXu MaLe YuYuanming PanNing ChenRoman ChernikovLeo Ka Long CheungReza DeevsalarAyetullah TuncLiang WangXiangfeng ZengJinru LinYongfeng Jia
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Keywords:
Schwertmannite
Ferrihydrite
Schwertmannite
Ferrihydrite
Acid Mine Drainage
Coprecipitation
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Ferrihydrite
Schwertmannite
Metalloid
Jarosite
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Ferrihydrite
Schwertmannite
Maghemite
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The precipitation of Fe-compounds from acid mine drainage (AMD) and stream water polluted by AMD plays a crucial role in regulating pollutant migration and determining the impacts of AMD on aquatic ecosystems. It is thus essential to identify the nature of precipitates that form and to understand their stabilities in order to assess their environmental impact. This is a necessary prerequisite before an appropriate treatment program can be prepared. Various kinds of Fe-compounds have been found to precipitate from AMD, but not all of them have been investigated in detail. Schwertmannite is one of the Fe-compounds which need more investigation. Its stability constant was reported only once (Bigham et al., 1996). The purpose of this study is to determine the stability of schwertmannite and ferrihydrite as a function of the composition of the stream water from which they precipitate. Schwertmannite and ferrihydrite have been found to precipitate respectively from the stream waters of Imgok Creek and Osheep Creek in Kangwon-Do, Korea (Yu, 1996; Yu et al., 1996). Although Imgok and Osheep Creeks both drain what were once very actively operated mining areas and are polluted by AMD from the abandoned coal mines, their compositions are very different.
Schwertmannite
Ferrihydrite
Acid Mine Drainage
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Schwertmannite, 2-line ferrihydrite, and 6-line ferrihydrite were synthesized at 25°C in the laboratory to determine their solubilities. Chemical and thermal analyses of the synthesized minerals show that schwertmannite has the chemical formula Fe2O3-x(SO4)x·nH2O (0.41 ≤ x ≤ 0.49, 1.51 ≤ n ≤ 2.81) and ferrihydrite Fe2O3-0.5y(OH)y·nH2O (0 ≤ y ≤ 1.96, 0.82 ≤ n ≤ 1.14). The solubility products (K) of the minerals were estimated from the activities of the corresponding species calculated with the computer program PHREEQC. The estimated log K values are 2.01 ± 0.30 for schwertmannite, 8.46 ± 1.40 for 2-line ferrihydrite, and 10.12 ± 0.74 for 6-line ferrihydrite. The solubility of schwertmannite seems to vary depending on the sulfate content, but more investigation is needed to quantify the relationship. The solubility of ferrihydrite does not show any significant correlation with the water content. The stability boundary between schwertmannite and ferrihydrite predicted in this study is biased to higher pH than that observed in nature, which also need further investigation.
Ferrihydrite
Schwertmannite
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Schwertmannite
Ferrihydrite
Acid Mine Drainage
Solubility equilibrium
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