Arsenate co-precipitation with Fe(II) oxidation products and retention or release during precipitate aging

WATER RESEARCH

卷:131

Article

Senn, Anna-Caterina^1,2  Hug, Stephan J.¹  Kaegi, Ralf¹  Hering, Janet G.^1,2,3  Voegelin, Andreas¹ 

[1] Eawag, Swiss Fed Inst Aquat Sci & Technol, Ueberlandstr 133, CH-8600 Dubendorf, Switzerland

[2] ETH, Inst Biogeochem & Pollutant Dynam, Dept Environm Sci, Swiss Fed Inst Technol, Zurich, Switzerland

[3] Ecole Polytech Fed Lausanne, Sch Architecture Civil & Environm Engn, Lausanne, Switzerland

关键词: Arsenic removal;    Phosphate removal;    Iron precipitates;    Precipitate aging;    Water treatment;   

DOI  :  10.1016/j.watres.2017.12.038

来源: Elsevier

【 摘 要 】

The co-precipitation of arsenate (As(V)) with Fe(III)-precipitates is of great importance in water treatment and critically affects the fate of As in environmental systems. We studied the effects of dissolved phosphate (P; 0-1 mM), silicate (Si; 0 or 0.5 mM) and Ca (0, 0.5 and 4 mM) on the sequestration of 7 mu M As(V) by Fe(III)-precipitates formed by the oxidation of 0.5 mM Fe(II) in aerated bicarbonate-buffered solutions with an initial pH of 7.0 as well as the retention or release of As(V) after precipitate aging for 30 d at 40 degrees C. Dissolved As(V) concentrations in fresh precipitate suspensions greatly varied as a function of the initial dissolved P/Fe ratio ((P/Fe)(init)) and the concentrations of Ca and Si. Limited As(V) removal was observed at (P/Fe)(init) that exceeded the critical ratio (P/Fe)(crit) above which exclusively (Ca-) Fe(III)-phosphate forms. Effective As(V) removal was observed at (P/Fe)(init) < (P/Fe)(crit), where initial formation of (Ca-)Fe(III)-phosphate is followed by the formation of Si-ferrihydrite in Si-containing electrolytes and of poorly-crystalline lepidocrocite and hydrous ferric oxide in the Si-free electrolytes. The retention of As(V) and P by fresh Fe(III)-precipitates was most effective in systems containing both Ca and Si. In the Si- and Ca-free electrolytes at (P/Fe)(init) of similar to 0.2-0.6, the rapid onset of precipitate aging with conversion of Fe(III)-phosphate to ferrihydrite resulted in a substantial remobilization of As(V) (up to 55% of initially precipitated As(V)). Ca reduced As remobilization during aging by stabilizing Ca-Fe(III)phosphate and promoting Ca-phosphate formation, and Si by stabilizing Si-ferrihydrite against transformation. Consequently, also after aging, the lowest dissolved As(V) and P fractions were observed in precipitate suspensions containing both Ca and Si. (C) 2017 Elsevier Ltd. All rights reserved.

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