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Fukushi, Keisuke*; Sato, Tsutomu*; Yanase, Nobuyuki; Minato, Junichi*; Yamada, Hirohisa*
American Mineralogist, 89(11-12), p.1728 - 1734, 2004/11
The sorption mechanism of As(V) on schwertmannite was investigated by both a batch sorption experiment and crystallographic considerations. The batch experiment was carried out as a function of As(V) concentration in acidic solution at 25 
C. Crystallographic considerations indicate surface sites of schwertmannite comprise varied surface oxygen (hydroxyl) and SO
groups. Sorption experiments showed reactive surface sites for As(V) sorption are surface SO groups. As(V) sorption mechanism involves ligand exchange with solid phase SO. Results also suggest monodentate As(V) coordination with surface adsorbed SO sites and bidentate As(V) coordination in structural originated SO sites. Estimated equilibrium constant for ligand exchange reaction describes the observed As(V) sorption behavior. The surface structure approach in this study reveals reactive surface sites in As(V) sorption on schwertmannite comprise surface SO group instead of surface hydroxyl groups identified by former views.
Fukushi, Keisuke*; Sasaki, Miwa*; Sato, Tsutomu*; Yanase, Nobuyuki; Amano, Hikaru; Ikeda, Hodaka*
Applied Geochemistry, 18(8), p.1267 - 1278, 2003/08
Times Cited Count：220 Percentile：95.91(Geochemistry & Geophysics)At Nishinomaki abandoned mine district, the water is acidic and contains much amounts of arsenic. However, arsenic concentration decreases downward without any artificial treatment. To understand the mechanism of the natural attenuation, the acid mine drainage and the ochreous precipitates were collected. The samples were analyzed by XRD, IR, ICP-MS and ion-chromatograph. The precipitates were investigated by selective extraction procedure. These results were interpreted with those calculated by the geochemical code. The contamination of water has been result from oxidation of pyrite and realgar and subsequent release of iron. The released ferrous iron transforms to ferric form by bacterial oxidation and then schwertmannite forms immediately. While the arsenic concentrations in the stream are lowered to background level at downstream, these in the ochreous precipitates are up to 60 mg/g. The iron hydroxide has been known to exhibit the high sorption affinity to arsenate. Hence, arsenic is effectively removed by the schwertmannite from the contaminated water and attenuated naturally.
Fukushi, Keisuke*; Sato, Tsutomu*; Yanase, Nobuyuki
Environmental Science & Technology, 37(16), p.3581 - 3586, 2003/07
Times Cited Count：71 Percentile：79.84(Engineering, Environmental)The mechanism of As(V) sorption on schwertmannite was investigated by a batch sorption experiment as a function of solution As(V) concentration under acidic conditions (pH 3.3 
0.1) at 25 C. The reacted solution chemistry and mineralogy showed that the mechanism of As(V) sorption was ligand exchange with solid phase SO in schwertmannite. Two processes presumably occur simultaneously within the reaction period. i.e., ligand exchange of As(V) with surface site SO and subsequent transfer of As(V) to the structure and ligand exchange with tunnel site SO. The exchange ratio between As(V) sorption and SO release, and the SO coordination environment in schwertmannite indicates that monodentate As(V) coordination occurs in surface sites while bidentate binuclear As(V) coordination occurs in tunnel sites. Sorption modeling that considers the different types of reactive sites successfully described the observed As(V) sorption behavior.
