Behaviour of calcium sulfoaluminate cement in presence of high concentrations of chromium salts

This paper deals with the behaviour of calcium sulfoaluminate cement hydrated in presence of high concentration of soluble chromium salts (65 g/kg): chromium nitrate and sodium chromate. Chromium nitrate was chosen to verify the good retention of Cr3+ by calcium sulfoaluminate cement. Sodium chromate was employed to assess the ability of calcium sulfoaluminate to immobilize Cr6+.Leaching tests were carried out on two types of calcium sulfoaluminate cement containing 20% and 30% phosphogypsum, respectively. The microstructure was also investigated at 28 and 90 days.The results obtained point two main findings: –the retention of Cr3+ is excellent (> 99%), regardless of the type of cement,–the retention of Cr6+ depends on the type of cement and, in this case, the U phase is detected and promotes some expansion leading to cracking of the matrix.