Solar thermal treatment of phosphogypsum and its impact on the mineralogical modification for effective utilization in cement production

Abstract

Gypsum is a key component in cement because it plays vital role in controlling the setting behavior of the cement. PG is a chemical gypsum, contains substantial amount of SO3 and has the potential to replace mineral gypsum in cement. PG acts as super retarder by extending cement setting process. The retardation property of PG calcinated at 250–550 °C was investigated by taking around 5% of resultant PG in cement. All the samples were characterized by chemical analysis, X-ray diffraction and isothermal calorimetry. No significant variation of phosphate content was observed in untreated and thermally treated samples. Mineralogical characterization showed that the phosphate was converted into inert form at and above 350 °C. The retardation behavior of PG in cement was studied by using isothermal calorimetry and observed that it was reduced in treated samples than untreated sample. Solar thermal treatment at optimized temperature of PG was performed and the resultant PG exhibited shorten setting time than the untreated PG in cement.