Here we report on the ability of two different water treatment residues, a Fe-based (Fe-WTR) and an Al-based (Al-WTR) ones, to accumulate Cd(II) and Zn(II) from aqueous solutions at different pH values (pH 4.5, 5.5 and 7.0). Fe-WTR showed a greater Zn(II) and Cd(II) sorption capacity than Al-WTR at all the pH values investigated, in particular at pH 7.0 (e.g. ~0.200 mmol•g-1 and ~0.100 mmol•g-1 of Me(II) sorbed by Fe- and Al-WTR at pH 7.0 respectively). The greater capacity of the Fe-WTR to accumulate Me(II) seems to be linked to its higher content of iron and manganese ions and to its higher CEC value compared to Al-WTR. The role of the inorganic and organic fractions of WTRs in metals sorption was also assessed. A higher affinity of Cd(II) with respect to Zn(II) towards functional groups of the organic matter of both WTRs was observed, while Zn(II) showed a stronger association with the inorganic phases. The sorption of both metal ions appeared mainly governed by the formation of inner-sphere surface complexes with the inorganic and organic phases of WTRs, as suggested by the sequential extraction data.
Sorption of Cadmium(II) and Zinc(II) from Aqueous Solution by Water Treatment Residuals at Different pH Values / Silvetti, Margherita; Castaldi, Paola; Garau, Giovanni; Demurtas, D; Deiana, Salvatore Andrea. - In: WATER AIR AND SOIL POLLUTION. - ISSN 0049-6979. - 226:9(2015), pp. 313.1-313.13. [10.1007/s11270-015-2578-0]