Journal of Thermal Analysis, Vol. 50 (1997) 393-400 CHEMICAL EFFECTS OF HEAVY METALS ON THE HYDRATION OF CALCIUM SULPHOALUMINATE 4CaO-3AI2OySO3 R. Berardi ~, R. Cioffi 2 and L. Santoro ~ 1Dipartimento di Chimica, Universitf di Napoli 'Federico II', via Mezzocannone 4 80134 Napoli 2Dipartimento di Ingegneria dei Materiali e della Produzione, Universitf di Napoli 'Federico II', Piazzale Tecchio 80, 80125 Napoli, Italy (Received March 27, 1996; in revised form September 26, 1996) Abstract The sYstem 4CaO.3AI203.SO3-CaSO4.2H20-Ca(OH)2 was hydrated in the presence of ten dopants, specifically soluble salts of heavy metals. When added in 10% amount, the effect of each salt is strongly evident at shorter curing times, the hydration kinetics being more favoured in the order Pb(NO3)2<K2CrO4< Cd(NO3)2< Zn(NO3)2=Mn(NO3)3=K2MoO4<Ni(NO3)z<Cu(NO3)z<Cr(NO3)3<Fe(NO3)3 . At longer curing times the differences among the systems decrease Significantly. The 28-day compressive strength is almost the same for all the systems except those con- taining Pb(NO3)2,K2MoO 4and K2CrO 4. Keywords: calcium sulphoaluminate, ettringite, hazardous wastes, heavy metals, solidification/ stabilization Introduction Many industrial processes generate solid inorganic hazardous wastes contain- ing heavy metals. Unsafe disposal of these wastes may result in environmental contamination due to possible release of metal species into waters and soil. So- lidification/stabilization (S/S) processes give the opportunity to avoid harmful effects by physical containment and/or chemical fixation of pollutants [1]. Most commonly practised inorganic S/S processes are cement or pozzolanic based. They owe their effectiveness to the formation of a calcium silicate hy- drate matrix. In these systems heavy metals may interact in a number of ways, that is adsorption, chemisorption, chemical precipitation, ion exchange, surface complexation, microencapsulation, chemical incorporation in the hydrated neoformed phases, diodochy and isomorphic substitution. The last two phe- nomena may preferentially take place when calcium trisulphoaluminate hy- drate 6CaO.AI203.3SO3.32H20 (ettringite) is among the hydration products. This is proved by the occurrence of ettringite-like minerals 0368-4466/97/$ 5.00 9 1997 Akad~miai Kiad6, Budapest John Wiley & Sons Limited Chichester