Arsenic Removal from Aqueous Solution via Ferrihydrite Crystallization Control

Abstract

Removal of arsenate anion from aqueous solution by coprecipitation with ferrihydrite has been studied under conditions in which the Fe/As ratio is maintained at a constant level, while the degree of supersaturation with respect to the iron oxide precipitate is varied. An Fe/As ratio of 12 was chosen, and supersaturation was controlled by varying the iron concentration or the pH. The relationship between supersaturation and arsenic removal was found to follow an exponential curve, with greater arsenic removal occurring at higher supersaturation ratios for each of the pH values tested. Higher supersaturation ratios were required to achieve a given level of arsenic removal at pH 7 than would be required to achieve the same level of removal at pH 3.5. The results provide important guidelines for selection of appropriate concentrations of iron(III) required for arsenic removal under various circumstances. Powder XRD analysis of the arsenate-ferrihydrite precipitates showed an increasing degree of structural order with decreasing levels of supersaturation. TEM images of the precipitates revealed that aggregates with a morphology similar to that of schwertmannite are formed in some samples at low supersaturation levels. The results described in this paper indicate that the overall efficiency of arsenic removal involves a combination of both supersaturation and pH effects, with pH controlling the affinity of arsenate for the ferrihydrite surface, and supersaturation controlling the surface area and physical properties of the ferrihydrite product.

Arsenic removal from aqueous solution using ferrous based red mud sludge

“…Importantly, there is no evidence to suggest the formation of the more mobile As(III) species after the addition of ferrous [28]. After the formation of ferric, the coagulation and adsorption process will contribute to arsenic removal, and it is commonly regarded that arsenate is adsorbed via surface complex formation on ferrihydrite [29].…”

Mineral weathering and element cycling in soil-microorganism-plant system

“…The mobility of heavy metals was reduced by co-precipitated Fe(II) oxidation (Richmond et al, 2004) or absorbed on the surface of secondary iron minerals. Recent studies have confirmed the coupled mechanism of nitrateiron-arsenic reaction (Chen et al, 2008;Hohmann et al, 2009).…”

Study on arsenic removal process from water

“…Ferrihydrite readily adsorbs arsenic (V) in the form of arsenate anion (AsO 4 3-), but probably the most effective method of removal of arsenic from aqueous solutions is through coprecipitation of arsenic with ferrihydrite. (1) The main arsenic removal techniques from drinking water are: oxidation, precipitation/co precipitation, coagulation, sorption, ionexchange and reverse osmosis. Although these methods have been widely employed, they have several drawbacks: high operating and waste treatment costs, high consumption of reagents and large volume of sludge formation.…”