Reactive Behavior of Ferrihydrite and Aluminic Ferrihydrite Toward the Adsorption of Arsenate: Fid-Bau Portal

Reactive Behavior of Ferrihydrite and Aluminic Ferrihydrite Toward the Adsorption of Arsenate

Mohapatra, Debasish / Mishra, Debaraj / Chaudhury, G. Roy / Das, R. P. / Park, Kyung Ho

The adsorption of arsenate (As(V)) on “ferrihydrite” prepared by two different methods; “aluminic ferrihydrite” (Fe(III)/Al(III) molar ratio 1:1) and the stability of As(V) bearing materials were investigated. The parameters optimized for adsorption were pH, contact time, adsorbent and As(V) concentration. For leaching study four different leaching reagents (10 mg C/L dissolved organic matter, 0.1M phosphate, 0.1M citrate and 0.1M oxalate) were used. The kinetics of arsenic adsorption on both type of ferrihydrites were similar with an equilibrium time of 1h; whereas, in case of aluminic ferrihydrite the equilibrium time was 3h. For aluminic ferrihydrite, maximum adsorption was found at pH 6.0. Whereas, for ferrihydrites pH 7.0 was found to be the best for As(V) adsorption. The highest As(V) adsorption capacity was shown by aluminic ferrihydrite (21.8 mg/g), followed by ferrihydrite prepared by emulsion method and ferrihydrite prepared by ordinary method (14.9 and 9.8 mg/g, respectively). In case of As(V) extraction from the loaded materials, the pH had a significant effect. In all cases, except citrate for aluminic ferrihydrite, extraction decreased with increasing pH in the range 5.0–8.0. For oxalate the iron extraction and for citrate the aluminium extraction followed the same trend as that for arsenic as a function of pH, suggesting that dissolution of these metals and consequent release of the adsorbed arsenic is one of the main mechanisms for arsenic extraction. However, for phosphate and DOM, the As(V) extraction mechanism was competition between arsenic and those anions for adsorption sites.