Solid Solutions between CrO^sub 4^- and SO^sub 4^-Ettringite Ca^sub 6^(Al(OH)^sub 6^)^sub 2^[(CrO^sub 4^)^sub x^(SO^sub 4^)^sub 1-x^]^sub 3^26 H^sub 2^O

• Published in: Environmental science & technology Vol. 44; no. 23; p. 8983
• Main Authors: Leisinger, Sabine M, Lothenbach, Barbara, Le Saout, Gwenn, Kägi, Ralf, Wehrli, Bernhard, Johnson, C Annette
• Format: Journal Article
• Language: English
• Published: Easton American Chemical Society 01.12.2010
• Subjects: Contamination; Diffraction; Solid solutions; Toxicology
• ISSN: 0013-936X

Chromate is a toxic contaminant of potential concern, as it is quite soluble in the alkaline pH range and could be released to the environment. In cementitous systems, ... is thought to be incorporated as a solid solution with ... in ettringite. The formation of a solid solution (SS) could lower the soluble ... concentrations. Ettringite containing ... or ... and mixtures thereof have been synthesized. The resulting solids and their solubility after an equilibration time of 3 months have been characterized. For ... -ettringite at 25 ...C, a solubility product log ... of --40.2 ± 0.4 was calculated: log ... = 6log{...} + 2log{Al(OH)4--} + 3log{...} + 4log{...} + 26log{...}. X-ray diffraction and the analysis of the solution indicated the formation of a regular solid solution between ...- and ...-ettringite with a miscibility gap between 0.4 ≤ ... ≤ 0.6. The miscibility gap of the ... and ...-ettringite solid solution could be reproduced with a dimensionless Guggenheim fitting parameter (...) of 2.03. The presence of a solid solution between ...- and ...-ettringite results in a stabilization of the solids compared to the pure ettringites and thus in an increased uptake of ... in cementitious systems. (ProQuest: ... denotes formulae/symbols omitted.)