Formation of Fe(iii)–As(v) complexes: effect on the solubility of ferric hydroxide precipitates and molecular structural identification. Issue 5 (27th April 2020)

• Record Type: Journal Article
• Authors: Shi, Qiantao; Sterbinsky, George E.; Zhang, Shujuan; Christodoulatos, Christos; Korfiatis, George P.; Meng, Xiaoguang
• Is Part Of: Environmental science. Volume 7:Issue 5(2020)
• Page Start: 1388
• Page End: 1398
• Publication Date: 2020-04-27
• Subjects: Environmental sciences -- Periodicals; Nanotechnology -- Periodicals; 620.505
• DOI: 10.1039/d0en00024h
• Languages: English
• ISSNs: 2051-8153

Abstract

Abstract : Soluble Fe(iii )–As(v ) complexes were found at both acidic and neutral conditions, which significantly change the solubility of ferric oxides. Abstract : Ferric iron (Fe(iii )) and arsenate (As(v )) generally co-exist in natural waters. Also, Fe(iii ) chemicals are widely used for treatment of As(v ) in water. This paper reported the existence of Fe(iii )–As(v ) complexes, which are molecular clusters containing only one iron atom with sizes of less than 1 nm, typically considered as soluble species. The formation of Fe(iii )–As(v ) complexes varies with the change of pH. Specifically, the soluble Fe(iii )–As(v ) complex formed at acidic conditions (pH <2) with a Fe : As mole ratio of 1 : 1. When the pH increased to 2–5, Fe(iii ) and As(v ) formed precipitate rather than a soluble complex, which led to a reduced solubility of Fe(iii ) at pH 2–5. The soluble Fe(iii )–As(v ) complex again appeared at pH >5 with the Fe : As mole ratio of 1 : 2. DFT calculation identified that these soluble Fe(iii )–As(v ) complexes were in a monodentate configuration. The chloride was found to be coordinated with the Fe(iii )–As(v ) complexes, which improved their thermodynamic stability. The existence of these soluble complexes promoted the solubility of Fe(iii ) at neutral pH ( i.e., total soluble Fe(iii ) increased to 0.73 mM (∼41 mg L −1 ) with an initial 0.1 M Fe(iii )). The findings in this study shed new light on the understanding of the transport and fate of Fe(iii ) and As(v ) in natural water systems, as well as the As(v ) leaching from the sludge produced in the Fe(iii )-based As(v ) removal techniques.