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Stabilization/solidification on chromium (III) wastes by C3A and C3A hydrated matrix

Li, Xiangguo, He, Chao, Bai, Yun, Ma, Baoguo, Wang, Guandong, Tan, Hongbo
Journal of hazardous materials 2014 v.268 pp. 61-67
X-ray diffraction, X-ray photoelectron spectroscopy, aluminum oxide, cement, chromium, energy, energy-dispersive X-ray analysis, heavy metals, leaching, nitric acid, scanning electron microscopy, solidification, sulfuric acid, toxic substances, wastes
Hazardous wastes are usually used in the Portland cement production in order to save energy, costs and/or stabilize toxic substances and heavy metals inside the clinker. This work focus on the stabilization/solidification on chromium (III) wastes by C3A and C3A hydrated matrix. The immobilization rate of chromium in C3A and the leaching characteristics of the C3A hydrated matrixes containing chromium were investigated by ICP-AES. The results indicated that C3A had a good solidifying effect on chromium using the clinkering process, however, the Cr leaching content of Cr-doped C3A was higher than that of hydrated C3A matrix in Cr(NO3)3 solution and was lower than that of the hydrated C3A matrix in K2CrO4 solution, no matter the leachant was sulphuric acid & nitric acid or water. To explain this, C3A formation, chemical valence states of chromium in C3A, hydration products and Cr distribution in the C3A-gypsum hydrated matrixes were studied by XRD, XPS and FESEM-EDS. The investigation showed that part of Cr3+ was oxidized to Cr6+ in the clinkering process and identified as the chromium compounds Ca4Al6O12CrO4 (3CaO·Al2O3·CaCrO4), which resulted in the higher leaching of hydrated matrix of Cr-doped C3A.