Abstract
The removal, and its mechanism, of arsenate from aqueous solutions was investigated using Yunnan red soil. A series of adsorption experiments was designed to disclose the effect of key factors (soil types, soil/solution rates, initial arsenate concentrations, and shaking speeds) on the adsorption capacity of Yunnan red soil for arsenate. The soil/solution ratio was optimized as 0.05 g/100 mL to balance the adsorption capacity and removal efficiency. The optimal shaking speed (225 rpm) not only ensured enough contact frequency between the Yunnan red soil and the arsenate, but also reduced the mass transfer resistance. The results from applying an orthogonal array method showed that the most significant factor affecting arsenate removal efficiency was soil type, followed by the soil/solution ratio, contact time, and shaking speed. The IR spectra of the precipitates further confirmed that the metal arsenide was settled by the Yunnan red soil, indicating that the arsenate ion existed on the red soil surface in the form of protonated bidentate surface complexation of –FeO2As(O)(OH)− and FeO2As(O)2−. These results indicate that Yunnan red soil is promising for the removal of arsenate from aqueous solutions; it may thus be suitable as a new adsorbent for arsenate removal during water treatment.
Highlights
Arsenic is a metalloid that is considered to be a dangerous water pollutant throughout the world
Arsenic has been listed as a Class A carcinogen by the US Environmental Protection Agency (US EPA) due to its high toxic effects [2], and the US EPA in 2001 adopted a new standard for arsenic in drinking water at 10 μg/L, replacing the old standard of 50 μg/L
Raman and Fourier transform infrared (FTIR) spectroscopic methods, combined with sorption techniques, electrophoretic mobility measurements, and surface complexation modeling, were used by Goldberg [28] to study the interaction of As(III) and As(V) with amorphous oxide surfaces, and the results showed that arsenate formed inner-sphere surface complexes on both amorphous Al and Fe oxides
Summary
Arsenic is a metalloid that is considered to be a dangerous water pollutant throughout the world. It occurs in natural waters in both inorganic and organic forms, with the inorganic form being more toxic than the organic form. Considering its health and toxicological effects, the World Health Organization has revised the maximum contaminant level (MCL) for arsenic in drinking water from 50 to μg/L [3]. In 2008, the average value of arsenic concentrations in Yangzonghai Lake, Yunnan Province, reached 0.121 mg/L. Datunhai Lake in Honghe Prefecture, Yunnan Province, was found to have several times the pollution of Yangzonghai Lake, with an arsenic concentration exceeding 96 times the national standards. There are substantial data showing that more than 50% of the lakes in Honghe Prefecture are seriously contaminated by arsenic, and require urgent contamination control
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