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Molecular Structures of Al/Si and Fe/Si Coprecipitates and the Implication for Selenite Removal.

Chan YT, Kuan WH, Tzou YM, Chen TY, Liu YT, Wang MK, Teah HY - Sci Rep (2016)

Bottom Line: In the presence of silica, the coprecipitation of Al/Si or Fe/Si might decrease the efficiency of wastewater purification and reuse.Our spectroscopic results showed that the associations between Al and Si were relatively stronger than that between Fe and Si in coprecipitates.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Soil and Environmental Sciences, National Chung Hsing University, 250 Kuo Kuang Rd., Taichung 40227, Taiwan, R.O.C.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus

Conceptualized structural development and removal mechanisms of selenite for (a) Al/Si and (b) Fe/Si coprecipitates.
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f8: Conceptualized structural development and removal mechanisms of selenite for (a) Al/Si and (b) Fe/Si coprecipitates.

Mentions: Taken together, our findings allow us to conceptualize the structural development for Al/Si and Fe/Si coprecipitates in Fig. 6. Here, AlO6 with minor amounts of AlO4 that hydrolyzed from Al3+ adhered onto SiO2 surfaces by forming the direct bonding of Si–O–Al (Fig. 8a). Such robust structural development suppressed the silicate dissolution. On the contrary, the octahedral Fe domains that grew from Fe3+ hydrolysis were loosely associated with SiO2 colloids. The relatively isolated SiO2 in Fe/Si samples, therefore, led to the more pronounced silicate release (Fig. 8b). The forgoing mechanisms of structural developments were also supported by our XPS data. The Al/Si ratios on the near surfaces of Al/Si coprecipitates were significantly greater than the Fe/Si ratios for Fe/Si samples. The enrichment of Al relative to Si implied that the SiO2 might serve as a core with Al attached at SiO2 surfaces. This was in line with the core-shell structure that plausible formed during the heterogeneous nucleation of Al hydroxide with SiO2 serving as a template5962. For Fe/Si samples, however, the trifle amount of Fe relative to Si on the near surfaces of coprecipitates implied the relatively independent phases formed between SiO2 and Fe hydroxides.


Molecular Structures of Al/Si and Fe/Si Coprecipitates and the Implication for Selenite Removal.

Chan YT, Kuan WH, Tzou YM, Chen TY, Liu YT, Wang MK, Teah HY - Sci Rep (2016)

Conceptualized structural development and removal mechanisms of selenite for (a) Al/Si and (b) Fe/Si coprecipitates.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837376&req=5

f8: Conceptualized structural development and removal mechanisms of selenite for (a) Al/Si and (b) Fe/Si coprecipitates.
Mentions: Taken together, our findings allow us to conceptualize the structural development for Al/Si and Fe/Si coprecipitates in Fig. 6. Here, AlO6 with minor amounts of AlO4 that hydrolyzed from Al3+ adhered onto SiO2 surfaces by forming the direct bonding of Si–O–Al (Fig. 8a). Such robust structural development suppressed the silicate dissolution. On the contrary, the octahedral Fe domains that grew from Fe3+ hydrolysis were loosely associated with SiO2 colloids. The relatively isolated SiO2 in Fe/Si samples, therefore, led to the more pronounced silicate release (Fig. 8b). The forgoing mechanisms of structural developments were also supported by our XPS data. The Al/Si ratios on the near surfaces of Al/Si coprecipitates were significantly greater than the Fe/Si ratios for Fe/Si samples. The enrichment of Al relative to Si implied that the SiO2 might serve as a core with Al attached at SiO2 surfaces. This was in line with the core-shell structure that plausible formed during the heterogeneous nucleation of Al hydroxide with SiO2 serving as a template5962. For Fe/Si samples, however, the trifle amount of Fe relative to Si on the near surfaces of coprecipitates implied the relatively independent phases formed between SiO2 and Fe hydroxides.

Bottom Line: In the presence of silica, the coprecipitation of Al/Si or Fe/Si might decrease the efficiency of wastewater purification and reuse.Our spectroscopic results showed that the associations between Al and Si were relatively stronger than that between Fe and Si in coprecipitates.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Soil and Environmental Sciences, National Chung Hsing University, 250 Kuo Kuang Rd., Taichung 40227, Taiwan, R.O.C.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus