Arsenate and Arsenite Adsorption and Desorption Behavior on Coprecipitated Aluminum:Iron Hydroxides

Abstract

Although arsenic adsorption/desorption behavior on aluminum and iron (oxyhydr)oxides has been extensively studied, little is known about arsenic adsorption/desorption behavior by bimetal Al:Fe hydroxides. In this study, influence of the Al:Fe molar ratio, pH, and counterion (Ca2+ versus Na+) on arsenic adsorption/desorption by preformed coprecipitated Al:Fe hydroxides was investigated. Adsorbents were formed by initial hydrolysis of mixed Al3+/ Fe3+ salts to form coprecipitated Al:Fe hydroxide products. At Al:Fe molar ratios < or = 1:4, Al3+ was largely incorporated into the iron hydroxide structure to form a poorly crystalline bimetal hydroxide; however, at higher Al:Fe molar ratios, crystalline aluminum hydroxides (bayerite and gibbsite) were formed. Although approximately equal As(V) adsorption maxima were observed for 0:1 and 1:4 Al:Fe hydroxides, the As(III) adsorption maximum was greater with the 0:1 Al: Fe hydroxide. As(V) and As(III) adsorption decreased with further increases in Al:Fe molar ratio. As(V) exhibited strong affinity to 0:1 and 1:4 Al:Fe hydroxides at pH 3-6. Adsorption decreased at pH > 6.5; however, the presence of Ca2+ compared to Na+ as the counterion enhanced As( retention by both hydroxides. There was more As(V) and especially As(III) desorption by phosphate with an increase in Al:Fe molar ratio.

Adsorption and co-precipitation behavior of arsenate, chromate, selenate and boric acid with synthetic allophane-like materials

“…that allophane has a strong affinity for As(V) and supports the fact that arsenic mobility in soils is limited by its capacity to be sorbed on soil components particularly by metal oxides, short-ranged ordered aluminosilicates [25] and Al and Fe hydroxides [26].…”

Recent progress of arsenic adsorption on TiO 2 in the presence of coexisting ions: A review

“…Hu et al (2015a) studied the interference of Ca toward As(V) molecular structures absorbed on TiO 2 , and the results suggested the formation of a Ca-As(V)-TiO 2 ternary surface complex. The formation of a ternary complex can significantly increase the synergetic uptake of As(V) and Ca (Masue et al, 2007), and promote As attenuation in groundwater (Zhang et al, 2014). Though the coexisting Mg concentration (104.3 mg/L) was much higher than Ca (39.1 mg/L) in groundwater, the Ca adsorption density was higher than Mg (311 mg/g vs. 171 mg/g) in a study by Cui et al (2015a).…”

Natural Arsenic in Global Groundwaters: Distribution and Geochemical Triggers for Mobilization

“…The As(III) inner-and outer-sphere adsorption coexists, whereas for As(V), inner-sphere complexes are predominant [123]. Chemical models also confirmed that arsenate adsorption occurs over a pH range of 4.5 to 9 on gibbsite and amorphous Al hydroxide [51,118]. The degree of crystallinity of Al oxides and hydroxides also is important for As adsorption.…”

“…One of the most important key parameters that may affect the adsorption of As(III) and As(V) is pH. The greatest adsorption of As(V) usually occurs at low pH values (pH 3-6) and decreases with increasing pH (pH >6) [118,119]. Greater adsorption of As(V) at low pH is attributable to more favorable adsorption energies between the more positively charged surface and negatively charged H 2 AsO 4 − , which is the predominant As(V) species between pH 2 and 6.…”