Molecular Structures of Al/Si and Fe/Si Coprecipitates and the Implication for Selenite Removal.
Aluminum and iron oxides have been often used in the coagulation processes during water purification due to their unique surface properties toward anions. In the presence of silica, the coprecipitation of Al/Si or Fe/Si might decrease the efficiency of wastewater purification and reuse. In this study, surface properties and molecular structures of Al/Si and Fe/Si coprecipitates were characterized using spectroscopic techniques. Also, the selenite removal efficiency of Al/Si and Fe/Si coprecipitates in relation to their surface and structural properties was investigated. While dissolved silicate increased with increasing pH from Fe/Si coprecipitates, less than 7% of silicate was discernible from Al/Si samples over the range from acidic to alkaline conditions. Our spectroscopic results showed that the associations between Al and Si were relatively stronger than that between Fe and Si in coprecipitates. In Al/Si coprecipitates, core-shell structures were developed with AlO6/AlO4 domains as the shells and Si frameworks polymerized from the SiO2 as the cores. However, Si framework remained relatively unchanged upon coprecipitation with Fe hydroxides in Fe/Si samples. The Si core with Al shell structure of Al/Si coprecipitates shielded the negative charges from SiO2 and thereby resulted in a higher adsorption capacity of selenite than Fe/Si coprecipitates.
Department of Soil and Environmental Sciences, National Chung Hsing University, 250 Kuo Kuang Rd., Taichung 40227, Taiwan, R.O.C.
Ya-Ting
YT
Chan
Department of Safety, Health and Environmental Engineering, Ming-Chi University of Technology, New Taipei City 24301, Taiwan, R.O.C.
Wen-Hui
WH
Kuan
Department of Soil and Environmental Sciences, National Chung Hsing University, 250 Kuo Kuang Rd., Taichung 40227, Taiwan, R.O.C.
Yu-Min
YM
Tzou
Department of Engineering and System Sciences, National Tsing Hua University, Hsin-Chu 30043, Taiwan, R.O.C.
Tsan-Yao
TY
Chen
Department of Soil and Environmental Sciences, National Chung Hsing University, 250 Kuo Kuang Rd., Taichung 40227, Taiwan, R.O.C.
Yu-Ting
YT
Liu
Department of Agricultural Chemistry, National Taiwan University, Taipei 10617, Taiwan, R.O.C.
Ming-Kuang
MK
Wang
Division of Environmental Studies, Graduate School of Frontier Sciences, The University of Tokyo, 332 Building of Environmental Studies, 5-1-5 Kashiwanoha, Kashiwa City, Chiba 277-8563, Japan.
Heng-Yi
HY
Teah
D000327:Adsorption; D000535:Aluminum / Q000737:chemistry*; D011232:Chemical Precipitation; D007501:Iron / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular; D020887:Selenious Acid / Q000737:chemistry*; D012825:Silicon / Q000737:chemistry*; D012995:Solubility; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties
D000535:Aluminum; D007501:Iron; D020887:Selenious Acid; D012825:Silicon