Castaldi, Paola and Mele, Elena and Silvetti, Margherita and Garau, Giovanni and Deiana, Salvatore Andrea (2014) Water treatment residues as accumulators of oxoanions in soil: sorption of arsenate and phosphate anions from an aqueous solution. Journal of Hazardous Materials, Vol. 264 , p. 144-152. ISSN 0304-3894. eISSN 1873-3336. Article.
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Here we report a survey addressed to determine, at different pH values (pH 4.0, 7.0 and 9.0), the ability of two different water treatment residues, a Fe-based (Fe-WTR) and an Al-based (Al-WTR), to accumulate arsenate and phosphate anions from an aqueous solution and to define the mechanism which regulate the sorption of these anions. Fe-WTR showed a greater As(V) and P(V) sorption capacity respect to Al-WTR at all the pH values investigated, in particular at pH 4.0. The greater capacity of the Fe-WTR to accumulate phosphate at pH 4.0 seems to be linked to the higher content of manganese ions compared to Al-WTR, which can give rise, with phosphate ions, to the formation of MnHPO4 precipitates. Sequential extraction of As(V)- or P(V)-WTRs suggested that the main mechanism governing the sorption of both two anions likely involve the formation of inner-sphere surface complexes [Fe/Al–O–As(P)]. Such a coordination mode was supported by the FT-IR spectra that exhibit well resolved band at 865 cm−1 and 1040 cm−1 attributable to ν(As–O) or ν(P–O) stretching vibration, respectively.
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