Sorption Behavior of Arsenate by Mg-Bearing Minerals at Hyperalkaline Condition: Implications for Oxyanions Sequestration During the Use and Disposal of Alkaline Wastes Einstine Opiso & Atsushi Asai & Tsutomu Sato & Tetsuro Yoneda & Xiaoji Liu Received: 21 October 2011 / Accepted: 23 February 2012 / Published online: 8 March 2012 # Springer Science+Business Media B.V. 2012 Abstract The utilization and disposal of alkaline waste materials such as slag and coal fly ash as cement aggregates and raw materials in cement manufacturing can pose environmental and health hazards because these waste materials usually contain elevated concen- tration of toxic elements. This study examined the possibility of controlling the pore water chemistry of these waste materials in order to induce the secondary mineral formation of Mg-bearing minerals as major sorbing solids for oxyanions during the utilization and disposal of alkaline wastes. The formation of Mg- bearing minerals was examined at ambient tempera- ture and alkaline pH conditions in the Mg–Si–Al system. The interaction of Mg-bearing minerals with oxyanions using arsenate as an analog was examined during and after mineral formation. The results revealed that the generated Mg-bearing mineral phases were smectite and brucite in Mg–Si system and hydro- talcite and serpentine in Mg–Si–Al system. Moreover, hydrotalcite, serpentine, brucite, and smectite phases formed under low Si ratio showed high sorption ca- pacity for arsenate, but only high Al content hydro- talcite and serpentine showed substantial irreversible fraction of sorbed arsenate. Hence, the generation of these kinds of hydrotalcite and serpentine phases as scavengers for oxyanions must be considered during the utilization and disposal of alkaline wastes. Keywords Oxyanions . Arsenate . Sorption . Slag . Coal fly ash 1 Introduction Alkaline waste materials such as coal fly ash and slag are currently recycled as cement aggregates, road base mate- rials, soil amendments, and building materials. However, the utilization and disposal of these waste materials have environmental and health drawbacks. Slag and coal fly ash usually contain elevated concentration of toxic ele- ments such as As, Se, Br, and Mo which can be released into the environment during weathering and internal dis- solution of these alkaline wastes. Slag and coal fly ash also contain large amount of CaO which could lead to the generation of hyperalkaline pore water during hydration wherein in such condition, toxic elements such as As and Se can exist as oxyanions with high mobility and solu- bility due to the predominantly negative surface charge Water Air Soil Pollut (2012) 223:3471–3483 DOI 10.1007/s11270-012-1125-5 E. Opiso : A. Asai : T. Sato : T. Yoneda : X. Liu Laboratory of Environmental Geology, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan Present Address: E. Opiso (*) Geo-environmental Engineering Group, College of Engineering, Central Mindanao University, Musuan, Bukidnon 8710, Philippines e-mail: einstineop@gmail.com Present Address: A. Asai ECO-SYSTEM OKAYAMA CO., Ltd. 3-1, 1-chome, Kaigandori, Minami-ku, Okayama-City, Okayama 702-8506, Japan