Behavior of calcium aluminate cement (CAC) in the presence of hexavalent chromium

Chromium forms part of numerous processes and its unsafe disposal increases the risk of pollution of soils and aquatic systems, especially hexavalent chromium. This paper deals with the behavior of calcium aluminate cement (CAC) in presence of Cr6+ (0.5, 1.0 and 2.5%) as potassium dichromate (K2Cr2O7). The efficiency of CAC to immobilize Cr6+ was studied using leaching tests. The hydration temperature, hydration products and compressive strength of CAC in presence of Cr6+ were also investigated. Analysis of the results showed that the presence of Cr6+ strongly reduced the rate of reactions, which was related to inhibition of the consumption of anhydrous phases (calcium aluminate). However, leaching tests showed the high efficiency of CAC regarding Cr6+ immobilization (>90%), better than that presented by Portland cement. CAC also presented both the capacity for hexavalent chromium retention and its reduction.