Adsorption of antimony(V) on kaolinite as a function of pH, ionic strength and humic acid

School of Chemistry and Chemical Engineering, Shanxi Datong University, 037009 Datong, China
Environmental earth sciences (Impact Factor: 1.45). 60(4):715-722. DOI: 10.1007/s12665-009-0209-z

ABSTRACT The present work investigated the adsorption and mobility (desorption) of Sb(V) on kaolinite using batch experiments. The
adsorption of Sb(V) on kaolinite was studied as a function of contact time, pH, ionic strength, humic acid (HA), initial Sb(V)
concentration and temperature. Kinetic studies suggest that the equilibrium is achieved within 24h. The adsorption of Sb(V)
was strongly affected by changes in I at low ionic strength and unaffected at high ionic strength. The adsorption is weakly
dependent on the presence of humic acid, but is strongly dependent on pH. Within the range tested, the optimal pH for Sb(V)
adsorption is 3.6, and close to 75% removal can be achieved. Desorption is dependent on the original suspension pH. The addition
sequence of Sb(V)/HA do not influence the adsorption of Sb(V) on kaolinite. The adsorption data fit both the Freundlich and
Langmuir isotherm. The thermodynamic parameters (ΔH
0, ΔS
0 and ΔG
0) were calculated from the temperature dependence, and the results suggest the endothermic and spontaneous nature of the process.


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    ABSTRACT: The Kantishna Hills mining district of interior Alaska, USA, located within Denali National Park and Preserve, contains a number of antimony lode deposits, including Alaska's historically largest antimony producer, the Stampede mine. Oxidative weathering of sulfidic tailings and waste rock associated with historic mining operations has impacted water quality in the region. In the Stampede and Slate Creek watersheds, antimony and arsenic concentrations in stream waters were as high as 720 μg/L and 239 μg/L, respectively. Antimony in all water samples is predominantly present as Sb(V), whereas arsenic was detected in varying ratios of As(III) and As(V). Based on X-ray absorption spectroscopy (XAS) measurements reduced As(III) and Sb(III) were identified in mine waste materials, whereas predominantly oxidized forms, As(V) and Sb(V), were found in downstream sediments. Elevated antimony concentrations extend for more than 8 km downstream from the antimony lodes, whereas arsenic quickly attenuates within 1.5 km. The difference between antimony and arsenic aqueous phase speciation suggests that antimony oxidation is more rapid than arsenic within this system. A high correlation is observed between antimony, arsenic, and iron concentrations in fine-fraction streambed sediments downstream of the source lodes. This suggests that sorption and co-precipitation with iron (hydr)oxides are important pathways for the attenuation of antimony and arsenic in these interior Alaska watersheds. Further XAS characterization of the downstream sediments corroborates these observations and indicates that antimony is adsorbed to Fe-oxide phases as inner-sphere bi-dentate edge and corner sharing complexes. The trace element redox states, as well as downstream partitioning, are mainly controlled by iron speciation based on the strong correlation between redox potentials calculated from iron (Fe(II)/Fe(III)) and arsenic (As(III)/As(V)).
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    ABSTRACT: Antimony (Sb) is extensively used in flame retardants, lead-acid batteries, solder, cable coverings, ammunition, fireworks, ceramic and porcelain glazes and semiconductors. However, the geochemical fate of antimony (Sb) remained largely unexplored. Among the different Sb species, Sb (V) is the dominant form in the soil environment in a very wide redox range. Although earlier studies have examined the fate of Sb in the presence of iron oxides such as goethite and hematite, few studies till date reported the interaction of Sb (V) with gibbsite, a common soil Al-oxide mineral. The objective of this study was to understand the sorption behavior of Sb (V) on gibbsite as a function of various solution properties such as pH, ionic strength (I), and initial Sb concentrations, and to interpret the sorption-edge data using a surface complexation model. A batch sorption study with 20 g L(-1) gibbsite was conducted using initial Sb concentrations range of 2.03-16.43 μM, pH values between 2 and 10, and ionic strengths (I) between 0.001 and 0.1M. The results suggest that Sb (V) sorbs strongly to the gibbsite surface, possibly via inner-sphere type mechanism with the formation of a binuclear monodentate surface complex. Weak I effect was noticed in sorption-edge data or in the isotherm data at a low surface coverage. Sorption of Sb (V) on gibbsite was highest in the pH range of 2-4, and negligible at pH 10. Our results suggest that gibbsite will likely play an important role in immobilizing Sb (V) in the soil environment.
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