種々のpH条件で調製したポートランダイト懸濁液によるクロム(VI)エトリンガイトの合成

概要

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The synthesis of Cr (VI)-ettringite was attempted in portlandite suspensions for the immobilization of hazardous hexavalent Cr. The reagents NaAlO_2 and CrO_3 were used by dissolving them in deionized water to obtain 0.1 mol/L solutions, which were mixed with portlandite suspensions and stirred for 3 h at room temperature in CO_2-free synthetic air. Ca/Al atomic ratios were varied from 1.0 to 5.0 against the Cr/Al atomic ratios 1.0, 1.5 and 2.0. Run products were evaluated by XRD, XRF and FE-SEM. The results showed that Cr (VI)-ettringite formed under the conditions of pH 10.9 and more always associates with calcite. The calcite was also formed due to the carbonation of the remaining portlandite Ca(OH)_2 during drying in ambient air. The calculated yields of Cr (VI)-ettringite generally exceeded 80 mass%, and 85.6 mass% was reached for the stoichiometric mixture. In the run products obtained at pH lower than 10.9, no Cr (VI)-ettringite was identified, and the XRF analysis showed free-CaO and free-Al_2O_3 other than free-CrO_3 potentials each corresponding to calcite, ill-crystallized gibbsite (gibbsite gels) and the soluble chromatite CaCrO_4 adsorbed and trapped in the jelly gibbsite gels.
社団法人日本セラミックス協会の論文
2006-04-01