Abstract
The presence of inorganic and organic substances may alter the physicochemical properties of iron (Fe) salt precipitates, thereby stabilizing the antimony (Sb) oxyanions in potable water during the chemical treatment process. Therefore, the present study aimed to examine the surface characteristics, size of Fe flocs and coagulation performance of Sb oxyanions under different aqueous matrices. The results showed that surface properties of Fe flocs significantly varies with pH in both Sb(III, V) suspensions, thereby increasing the mobility of Sb(V) ions in alkaline conditions. The negligible change in surface characteristics of Fe flocs was observed in pure water and Sb(III, V) suspension at pH 7. The key role of Van der Waals forces of attraction as well as hydration force in the aggregation of early formed flocs were found, with greater agglomeration capability at higher more ferric chloride dosage. The higher Sb(V) loading decreased the size of Fe flocs and reversed the surface charge of precipitates, resulting in a significant reduction in Sb(V) removal efficiency. The competitive inhibition effect on Sb(III, V) removal was noticed in the presence of phosphate anions, owing to lowering of ζ-potential values towards more negative trajectory. The presence of hydrophobic organic matter (humic acid) significantly altered the surface characteristics of Fe flocs, thereby affecting the coagulation behavior of Sb in water as compared to the hydrophilic (salicylic acid). Overall, the findings of this research may provide a new insight into the variation in physicochemical characteristics of Fe flocs and Sb removal behavior in the presence of inorganic and organic compounds during the drinking water treatment process.
Highlights
In the past decade, heavy metal pollution in potable water supplies have received serious attention at a global level because of their potential health risks to humans and the ecosystem
It was noteworthy that the isoelectric points of Fe precipitates were observed under circumneutral pH environment in both stabilizing the antimony (Sb)(III, V) suspensions and pure water (Figures 1A and S1A)
Such observation may be attributable to the strong interaction of Fe(OH)2+ with neutral Sb(III) species [Sb(OH)3] and negatively charged Sb(V) ions [Sb(OH)6−] under neutral pH environment (Figure S1C,D)
Summary
Heavy metal pollution in potable water supplies have received serious attention at a global level because of their potential health risks to humans and the ecosystem. It has been reported that the agglomeration process of Fe precipitates may be hindered in the presence of inorganic and organic compounds in water [9,13,14] The organic compounds such as humic acid (HA) and fulvic acid (FA) may form various complexes with Sb and Fe species, thereby affecting the overall systems’ performance [9,14]. The presence of hydrophobic organic compounds such as HA may alter the surface properties of Fe flocs, thereby affecting the overall performance of the coagulation process [7,17]. Available literature addressing the impact of anions and hydrophobic/hydrophilic organics on the electrical characteristics and aggregation behavior of Fe flocs, as well as their effect on the coagulation of Sb(III, V) oxyanions in water, seems insufficient. Present study systematically examined the surface characteristics of Fe flocs and removal efficiency of Sb(III, V) oxyanions in water during the coagulation process. The influence of pH, ferric chloride (FC) dosages, contaminant loading, phosphate and hydrophobic/hydrophilic organic compounds were investigated under heterogeneous aqueous environments
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