Heating Changes Bio-Schwertmannite Microstructure and Arsenic(III) Removal Efficiency

Schwertmannite (Sch) is an efficient adsorbent for arsenic(III) removal from arsenic(III)-contaminated groundwater. In this study, bio-schertmannite was synthesized in the presence of dissolved ferrous ions and Acidithiobacillus ferrooxidans LX5 in a culture media. Bio-synthesized Sch characteristics, such as total organic carbon (TOC), morphology, chemical functional groups, mineral phase, specific surface area, and pore volume were systematically studied after it was dried at 105 degrees C and then heated at 250-550 degrees C. Differences in arsenic(III) removal efficiency between 105 degrees C dried-sch and 250-550 degrees C heated-sch also were investigated. The results showed that total organic carbon content in Sch and Sch weight gradually decreased when temperature increased from 105 degrees C to 350 degrees C. Sch partly transformed to another nanocrystalline or amorphous phase above 350 degrees C. The specific surface area of 250 degrees C heated-sch was 110.06 m(2)/g compared to 5.14 m(2)/g for the 105 degrees C dried-sch. Total pore volume of 105 degrees C dried-sch was 0.025 cm(3)/g with 32.0% mesopore and 68.0% macropore. However, total pore volume of 250 degrees C heated-mineral was 0.106 cm(3)/g with 23.6% micropore, 33.0% mesopore, and 43.4% macropore. The arsenic(III) removal efficiency from an initial 1 mg/L arsenic(III) solution (pH 7.5) was 25.1% when 0.25 g/L of 105 degrees C dried-sch was used as adsorbent. However, this efficiency increased to 93.0% when using 250 degrees C heated-sch as adsorbent. Finally, the highest efficiency for arsenic(III) removal was obtained with sch-250 degrees C due to high amounts of sorption sites in agreement with the high specific surface area (SSA) obtained for this sample.