Synthesis of Cr(VI)-Ettringite in Portlandite Suspensions as a Function of pH

Abstract

The synthesis of CrVI-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 molL solutions, which were mixed with portlandite suspensions and stirred for 3 h at room temperature in CO 2 -free synthetic air. CaAl atomic ratios were varied from 1.0 to 5.0 against the CrAl atomic ratios 1.0, 1.5 and 2.0. Run products were evaluated by XRD, XRF and FE-SEM. The results showed that CrVI-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 CaOH 2 during drying in ambient air. The calculated yields of CrVI-ettringite generally exceeded 80 massಚ, and 85.6 massಚ was reached for the stoichiometric mixture. In the run products obtained at pH lower than 10.9, no CrVI-ettringite was identified, and the XRF analysis showed free-CaO and free-Al 2 O 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.

Atomic spectrometry update. X-ray fluorescence spectrometry

“…Developments in the production of SRMs included the issue of fresh-frozen biological materials and of jet-milled natural matrix materials with improved homogeneity, such as a highly homogeneous air particulate matter and sediment SRMs for small sample analytical techniques. Terai et al 208 reported the synthesis of Cr VI in portlandite, Ca(OH) 2 , suspensions for the immobilisation of hazardous hexavalent Cr. Solutions of 0.1 mol L À1 of NaAlO 2 and CrO 3 were prepared in deionised water which were then mixed with portlandite suspensions and stirred for 3 h in a CO 2 free synthetic air.…”