Stabilization of Cr(III) wastes by C3S and C3S hydrated matrix : comparison of two incorporation methods

摘要

In the present study, the influence of Cr(III) on the properties of C3S and its stabilization in C3S hydrates was investigated by either direct incorporation as Cr2O3 during C3S preparation or introduced as nitrate salt during hydration. Levels of Cr used were from 0.1 to 3.0 wt% of C3S. The effect of Cr on the polymorph and hydration of C3S and its immobilization in the hydrates was detected by means of DTA/TG, XRD, isothermal calorimeter and ICP-AES, etc. When doped during sintering process, Cr caused a C3S polymorph transformation from T1 to T2 and led a decomposition of C3S into C2S and CaO resulting in high f-CaO content. Cr doping showed an obvious promotion effect on the hydration properties. The promotion effect decreased when the Cr addition increased to 3.0 wt%. When Cr was added as nitrate salt, Cr showed a retardation effect on the hydration of C3S due to the formation of Ca2Cr(OH)7 center dot 3H(2)O, which resulted in a high degree of Cr stabilization.