Removal of Arsenic in Drinking Water by Iron Oxide-Coated Sand and Ferrihydrite — Batch Studies

Abstract

Arsenic, a common toxic element is mainly transported in the environment by water. Arsenic in drinking water is of major concern to many of the water utilities in the world. Numerous studies have examined the removal of arsenic from drinking water through treatment processes such as coagulation-precipitation, reverse osmosis and ion exchange. The focus of research has now shifted to solve the problems using suitable adsorbents to achieve low level As in drinking water for communities with high raw water arsenic concentration. The determination of arsenic species is also essential for a better understanding and prediction of the toxic and carcinogenic nature of the species present in natural water systems. It is generally known that As(III) is more toxic than As(V) and inorganic arsenicals are more toxic than organic derivatives. The objective of this study was to study the arsenic adsorption behaviour on iron oxide-coated sand (IOCS) and ferrihydrite (FH). Batch studies were conducted using these adsorbents with natural water containing 325 μg/L arsenic, and the removal of approximately 90% was obtained. The adsorption capacity of the IOCS and FH used in this study for arsenic was estimated as 18.3 and 285 μg/g, respectively. The experimental data fitted well with the well-known isotherms, namely, Freundlich, Langmuir and BET, indicating a favourable adsorption by these adsorbents. Speciation studies were also conducted with natural water containing arsenic. Particulate and soluble arsenic in water were determined, and As(III) in the sample was determined by passing the sample containing arsenic through anion exchange resin (Dowex 1X8-100; acetate form) packed in the column. Speciation studies with natural water showed that the particulate and soluble arsenic contributed 11.4 and 88.6% of the total arsenic present in the natural water, respectively. In the case of soluble arsenic, As(III) and As(V) were 47.3 and 52.7%, respectively.

Modelling arsenic(III) adsorption from water by sulfate‐modified iron oxide‐coated sand (SMIOCS)

“…Also in the acidic pH range the net release of H þ ions blocks the surface sites available for sorption as iron-based sorbents have shown high sorption capacity for cations. 6 At near neutral pH values (7)(8)(9), slow dissociation of weak arsenic acid (H 3 AsO 3 ) produces arsenite ion (H 2 AsO 3 À ). This partially neutral and partially negative charged arsenite ion is attracted to the positively charged (below pH 8.2) surface of SMIOCS, resulting in high As(III) removal in this range.…”

“…7 Arsenic was removed from groundwater in laboratoryscale studies using iron oxide-coated sand by various researchers. [8][9][10] Arsenate forms stable solids (ie BaHAsO 4 and Ba 3 (AsO 4 ) 2 ) in the presence of Ba 2þ at near neutral pH values in aqueous systems.…”

Solvent Extraction of Arsenic(V) with Dispersed Ultrafine Magnetite Particles

“…This capacity was higher than the reported value for granulated Fe(OH)3 (4 -8 mg/g) 36 and goethite (3 -4 mg/g), 21 probably due to the small diameter and larger surface area of the ultrafine particles. On the other hand, the value was lower than the capacity of ferrihydrite (285 mg/g), 22 which suggests that adsorption is effective only on the surface of the particles.…”

“…Especially, hydrous metal oxides of iron(III), [21][22] zirconium(IV), [23][24] titanium(IV), 25 aluminum(III) 25 and rare earth elements(III), 26 etc. have been examined as selective adsorbents of arsenic(V) ion.…”

Adsorption of arsenic(V) from aqueous solutions by goethite/silica nanocomposite

“…In natural waters, arsenic exists predominantly in inorganic form as arsenite, As(III), and arsenate, As(V) (Thirunavukkarasu et al 2001). In aerobic environments, As(III) is thermodynamically unstable and easily converted to As(V) by oxidizing agents (Van Halem et al 2009).…”