| Abstract
| - Boron, chromium, molybdenum, and selenium often occurin high concentrations in fly ash leachates. During theleaching of fly ash in alkaline environments, hydrocalumite(Ca4Al2(OH)12(OH)2·6H2O) and ettringite (Ca6Al2(OH)12(SO4)3·26H2O) form as secondary precipitates. In this study,the removal of B, Cr, Mo, and Se oxyanions from high pHwaters by incorporation into hydrocalumite and ettringitewas examined. Experiments were performed by precipitatingthese minerals in solutions containing B, Cr, Mo, and Seoxyanions at conditions relevant to lime-leaching of fly ashas well as to fly ash containing concrete. The uptake ofall four anions by hydrocalumite and ettringite was high.Anion uptake by hydrocalumite was larger than that byettringite, and hydrocalumite was able to reduce anionconcentrations to below drinking water standards. Ettringiteshowed an anion preference in the order of B(OH)4->SeO42-> CrO42-> MoO42-. In contrast, borate was leastpreferred by hydrocalumite. Coordination, size, andelectronegativity are likely the factors that result in theobserved differences among the oxyanions.
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