Adsorption of Arsenate onto Ferrihydrite from Aqueous Solution:  Influence of Media (Sulfate vs Nitrate), Added Gypsum, and pH Alteration

Abstract

Mineral processing effluents generated in hydrometallurgical industrial operations are sulfate based; hence it is of interest to investigate the effect sulfate matrix solution ("sulfate media") has on arsenate adsorption onto ferrihydrite. In this work, in particular, the influence of media (SO4(2-) vs NO3-), added gypsum, and pH alteration on the adsorption of arsenate onto ferrihydrite has been studied. The ferrihydrite precipitated from sulfate solution incorporated a significant amount of sulfate ions and showed a much higher adsorption capacityfor arsenate compared to nitrateferrihydrite at pH 3-8 and initial Fe/As molar ratios of 2, 4, and 8. Adsorption of arsenate onto sulfate-ferrihydrite involved ligand exchange with SO4(2-) ions that were found to be more easily exchangeable with increasing pH. Added gypsum to the adsorption system significantly enhanced the uptake of arsenate by ferrihydrite at pH 8. Equilibration treatment at acidic pH and addition of gypsum markedly improved the stability of adsorbed arsenate on ferrihydrite when pH was elevated. Comparison of arsenate adsorption onto ferrihydrite to coprecipitation of arsenate with iron(III) showed the latter process to lead to higher arsenic removal.

Removal of arsenate from water by using an Fe–Ce oxide adsorbent: Effects of coexistent fluoride and phosphate

“…In our previous studies [6,7] the surface acidity and formation of surface hydroxyl groups of the Fe-Ce have been provide to the interpretation of the adsorption behaviors. At the same time, the exchange of surface sulfate groups has also been suggested to be an important mechanism for the removal of arsenate [31,32]. In the present study, sulfate was introduced in the Fe-Ce preparation process because of the use of Ce(SO 4 ) 2 ·4H 2 O.…”

Preparation, characterization and As(V) adsorption behaviour of CNT-ferrihydrite composites

“…Synthetic ferrihydrite and other iron oxides/hydroxides as well as those which occur naturally are known to play an important role in the sequestration of contaminants from ground water through adsorption (Schwertmann and Taylor, 1989). Ferrihydrite has previously been studied for its use in arsenic remediation from water (Raven et al, 1998;Jia and Demopoulos, 2005).…”

Adsorption of arsenic by iron rich precipitates from two coal mine drainage sites on the West Coast of New Zealand

“…Arsenic extraction from mine waters is commonly achieved by oxidation of As(III) to As(V) and co-precipitation of ferric arsenate with iron hydroxide (FeAsO 4 × Fe(OH) 3 ) in a high-density sludge process in active treatment systems (Lawrence & Higgs 1999;Leist et al 2000). Many workers have documented the removal of As from mine water by adsorption onto various iron compounds including ferric hydroxide (Dousova et al 2005;Ku¨chler et al 2005), zerovalent iron (Wildeman et al 2006), ferrihydrite (Jia & Demopoulos 2005), goethite (Fendorf et al 1997), red mud produced during the extraction of aluminium from bauxite (Altundogan et al 2000(Altundogan et al , 2002, and natural red earth (Vithanage et al 2007). Treatment of As-contaminated mine water through adsorption and coprecipitation in a water treatment plant is reliable and appropriate at active mine sites where power is available and personnel are on site to operate the plant.…”