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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

Results of (a) pH-dependent and (b) isotherm sorption of selenite on Al/Si and Fe/Si coprecipitates synthesized at pH 5.0 and 8.0 (Al/Si-5.0, -8.0 and Fe/Si-5.0, -8.0) at 25 °C under a 0.01 M NaNO3 background. The Langmuir fitting results showed the maximum adsorption capacities for Al/Si and Fe/Si coprecipitates were 0.40 and 0.22 mmol g−1. The coefficients of determination for the fitting are 0.993 and 0.980 (P < 0.05, n = 5), respectively.
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f7: Results of (a) pH-dependent and (b) isotherm sorption of selenite on Al/Si and Fe/Si coprecipitates synthesized at pH 5.0 and 8.0 (Al/Si-5.0, -8.0 and Fe/Si-5.0, -8.0) at 25 °C under a 0.01 M NaNO3 background. The Langmuir fitting results showed the maximum adsorption capacities for Al/Si and Fe/Si coprecipitates were 0.40 and 0.22 mmol g−1. The coefficients of determination for the fitting are 0.993 and 0.980 (P < 0.05, n = 5), respectively.

Mentions: Given that the pH values for industry and domestic wastewater effluent are generally in the wide range between 1.5–8.55253, it is worthy to examine the pH-dependent removal efficiency of selenite by Al/Si and Fe/Si coprecipitates. As shown in Fig. 7a, for both Al/Si and Fe/Si coprecipitates, the proportion of sorbed selenite decreased as suspension pH was artificially increased. With the exception of Al/Si-8.0 samples, more than 80% of selenite was fixed at pH 4. At pH > 8, however, less than 20% of selenite was fixed on Al/Fe-Si coprecipitates. This observed trend in decreasing sorbed Se with increasing sorption pH could be attributed to the fewer protonated surface sites on coprecipitates that serve as binding sites for selenite5455. Given that the Al/Si-5.0 and Fe/Si-5.0 showed relatively greater efficiency for selenite removal than that of Al/Si- and Fe/Si-8.0 among all tasted pH, the samples coprecipitated at pH 5.0 was further used to conduct the isotherm experiments for selenite. As shown in Fig. 7b, the sorption capacity for Al/Si-5.0 (0.40 mmol g−1) was 81% higher than that of Fe/Si-5.0 (0.22 mmol g−1). As shown in Figure S2, the maximum adsorption capacities of selenite on pure Al(OH)3 and Fe(OH)3 are 0.41 and 0.28 mmol g−1 by Langmuir isothermal model, slightly greater than Al/Si (0.40 mmol g−1) and Fe/Si sample (0.22 mmol g−1). Given that SiO2 particles have almost no sorption capacity for selenite (data not shown), the association of SiO2 on Al/Fe hydroxides might decreased the selenite sorption capacity for the Al/Fe-Si coprecipitates. Wherein silica might occupy active sorption sites on Al hydroxides by formed the core-shell structures in Al/Si coprecipitates. In Fe/Si samples, the dissolved silicate might compete for sorption sites on Fe hydroxides with selenite.


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)

Results of (a) pH-dependent and (b) isotherm sorption of selenite on Al/Si and Fe/Si coprecipitates synthesized at pH 5.0 and 8.0 (Al/Si-5.0, -8.0 and Fe/Si-5.0, -8.0) at 25 °C under a 0.01 M NaNO3 background. The Langmuir fitting results showed the maximum adsorption capacities for Al/Si and Fe/Si coprecipitates were 0.40 and 0.22 mmol g−1. The coefficients of determination for the fitting are 0.993 and 0.980 (P < 0.05, n = 5), respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f7: Results of (a) pH-dependent and (b) isotherm sorption of selenite on Al/Si and Fe/Si coprecipitates synthesized at pH 5.0 and 8.0 (Al/Si-5.0, -8.0 and Fe/Si-5.0, -8.0) at 25 °C under a 0.01 M NaNO3 background. The Langmuir fitting results showed the maximum adsorption capacities for Al/Si and Fe/Si coprecipitates were 0.40 and 0.22 mmol g−1. The coefficients of determination for the fitting are 0.993 and 0.980 (P < 0.05, n = 5), respectively.
Mentions: Given that the pH values for industry and domestic wastewater effluent are generally in the wide range between 1.5–8.55253, it is worthy to examine the pH-dependent removal efficiency of selenite by Al/Si and Fe/Si coprecipitates. As shown in Fig. 7a, for both Al/Si and Fe/Si coprecipitates, the proportion of sorbed selenite decreased as suspension pH was artificially increased. With the exception of Al/Si-8.0 samples, more than 80% of selenite was fixed at pH 4. At pH > 8, however, less than 20% of selenite was fixed on Al/Fe-Si coprecipitates. This observed trend in decreasing sorbed Se with increasing sorption pH could be attributed to the fewer protonated surface sites on coprecipitates that serve as binding sites for selenite5455. Given that the Al/Si-5.0 and Fe/Si-5.0 showed relatively greater efficiency for selenite removal than that of Al/Si- and Fe/Si-8.0 among all tasted pH, the samples coprecipitated at pH 5.0 was further used to conduct the isotherm experiments for selenite. As shown in Fig. 7b, the sorption capacity for Al/Si-5.0 (0.40 mmol g−1) was 81% higher than that of Fe/Si-5.0 (0.22 mmol g−1). As shown in Figure S2, the maximum adsorption capacities of selenite on pure Al(OH)3 and Fe(OH)3 are 0.41 and 0.28 mmol g−1 by Langmuir isothermal model, slightly greater than Al/Si (0.40 mmol g−1) and Fe/Si sample (0.22 mmol g−1). Given that SiO2 particles have almost no sorption capacity for selenite (data not shown), the association of SiO2 on Al/Fe hydroxides might decreased the selenite sorption capacity for the Al/Fe-Si coprecipitates. Wherein silica might occupy active sorption sites on Al hydroxides by formed the core-shell structures in Al/Si coprecipitates. In Fe/Si samples, the dissolved silicate might compete for sorption sites on Fe hydroxides with selenite.

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