Selective Separation and Preconcentration of Arsenite from Arsenic Enriched Natural Waters with Three Different Adsorbents

Arsenite (AsO₃^3-) is the dominant arsenic (As) oxyanion in most of As rich groundwaters, generating serious health problems worldwide. It is assumable that the isotopic composition of the associated oxygen may broaden our understanding about the causes, which led to the appearance of this kind of contamination. The aim of this study was to work out an efficient method for the selective extraction of arsenite from natural water samples, in a form adequate for isotopic measurements. Three adsorbents,

i. basic yttrium carbonate (BYC),

ii. porous polymer beads loaded with monoclinic hydrous zirconium oxide (MHZR), and

iii. nanoparticlate Fe₂O₃ (NFO) were tested for their suitability to separating AsO₃^3- from coexisting anions that may interfere with the isotopic measurement.

Results show that 95.1%, 99.3%, and 98.2% of AsO₃^3- were adsorbed selectively and separated from SO₄^2- and Cl^- in water by BYC, MHZR, and NFO, respectively. Using different desorption agents, 95.0% and 87.5% of AsO₃^3- were stripped from BYC in 0.05 M HNO₃ and NFO in 2 M NaOH, respectively, but only 27.5% from MHZR. By adding AgNO₃ in excess to these solutions, 98.3 ± 1.28% (n = 4) and 95.7 ± 4.81% (n = 4) of the AsO₃^3-, desorbed from the BYC and NFO, were precipitated as Ag₃AsO₃, respectively. The purity of the precipitates was checked with SEM-EDX.