Modification and Scale-Up Process of Citrogypsum to α-Calcium Sulfate Hemihydrate over Sodium Chloride Solution

It describes the development of a marketable citrogypsum which is also a by-product of citric acid production from laboratory scale to pilot scale. The modification of b-phase citrogypsum was carried out in different sodium chloride solution at 95oC for 7 hours under atmospheric pressure to α-calcium sulfate hemihydrate (α-CaSO 4 ∙0.5H 2 O, α-HH). This can be achieved in the laboratory scale experiment. The phase analysis of a citrogypsum was confirmed by XRD technique demonstrated that mostly made up of calcium sulfate dihydrate (CaSO 4 ∙2H 2 O, DH). The dehydration and phase transformation of citrogypsum to α-HH were conducted by DSC thermograms which were presented two endothermic peaks in the range 150-180oC of citrogypsum and an exothermic peak at 290 to 300oC, resulting that the product being α-HH when the 4M and 5M sodium chloride solutions were used. The outcome products were presented in a plate-like shape of citrogypsum but a hexagonal shape of α-HH. The experiment scaled up for modification of DH up to 100% in a batch reactor at the same condition with the 4M sodium chloride solution. The results showed that α-HH was obtained within 15 to 60 min after that calcium sulfate anhydrous (CaSO 4 , AH) had been formed. The non-isothermal of DSC was an adapted method to investigate kinetics study of DH to α-HH transformation under the optimum condition with a model fitting d α /d t = -3k (α 2 ) for predicting the process compared to the experiment values. In addition, the coefficient of determination (R 2 ) from estimation and experiment value was 0.9940. Hence, the model equation was completely represent data.