一般社団法人資源・素材学会 平成30(2018)年度春季大会

講演情報(2018年2月23日付 確定版)

一般講演

環境・リサイクル

2018年3月29日(木) 09:00 〜 12:00 第4会場 (3号館4F, 35号講義室)

司会:和嶋 隆昌(千葉大学),晴山 渉(岩手大学)

09:45 〜 10:00

[3401-11-04] XAFS解析による硫酸型グリーンラストへのCr(VI)収着機構のpH特性の解明

○Mamun Abdullah Al1、小野口 愛奈1、Granata Giuseppe1、所 千晴1 (1. 早稲田大学)

司会:和嶋 隆昌(千葉大学)

キーワード:クロム、グリーンラスト、pH、硫酸イオン交換、表面不活性

Green rust (GR) is an iron oxide consisting of FeII and FeIII hydroxide units intercalated with water molecules and anions such as Cl-, CO32- or SO42-. Since GR has a good ability towards the immobilization toxic metal anions like CrO42- and SeO42-, many researches focused on its formation and reaction kinetics. However, the reaction mechanism and its dependence on the pH requires further elucidation. In this work, we investigated the effect of pH on the preparation of sulfate-GR and its removal properties towards chromate. We prepared two types of GR at two different pH, namely pH 8.75 (GR8.75) and 7.50 (GR7.50) and we conducted the chromate removal experiments at pH 5 and 9. During the preparation of GR, increase of pH from 7.50 to 8.75 in confirmed a larger inclusion of SO42- and Na+ within the GR interlayer and almost doubled surface area. The higher pH also determined the enlargement of the crystal lattice and the increase of single corner Fe-Fe coordination via oxygen. The chromate removal by GR8.75 was found to be 1.7 times more efficient than GR7.50. At pH 5, GR8.75 oxidized significantly to goethite whereas magnetite was the predominant product at pH 9. The surface passivation of GR8.75 as a consequence of a surface reduction of the chromate ion confirmed by XPS. Instead, the GR7.50 removed the chromate mostly via replacement of the sulfate in the interlayer. For both GRs, the EXAFS results confirmed the change of the Cr-Cr bond to chromite-like bidentate mononuclear Cr-Fe bonding. For GR8.75, the increase of Fe-Fe edge sharing and double corner sharing coordination numbers confirmed the surface-based redox reaction. On the other hand, the increase of single corner sharing Fe-Fe coordination via oxygen for GR7.50 was a confirmation of the lateral insertion of Cr in the interlayer of GR.

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