Effect of calcination temperature on phase transformation and microstructural evolution of red gypsum
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Author |
Fatin ‘Aqilah Binti Mazlan, Mohd Al Amin Bin Muhamad Nor, Mohd Faiz Bin Hassan and Mazidah Binti Mamat
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e-ISSN |
1819-6608 |
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On Pages
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571-578
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Volume No. |
21
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Issue No. |
9
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Issue Date |
July 10, 2026
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DOI |
https://doi.org/10.59018/052664
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Keywords |
red gypsum, calcination, thermal stabilization, phase transformation, industrial waste valorization.
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Abstract
Red gypsum (RG) is a major byproduct of titanium dioxide production through the sulphate process, and its limited utilization poses significant accumulation challenges. One promising treatment method is thermal modification, particularly calcination, to achieve phase transformation and material stabilization. This study examines the impact of calcination temperatures ranging from 900℃ to 1300℃ on RG on the phase transformations and structural stability of RG. The raw RG and calcined RG samples were thoroughly characterized using thermogravimetric analysis (TGA), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM). TGA results for raw RG revealed weight loss of 19.3% between 100℃ and 200℃, attributed to the dehydration of calcium sulphate dihydrate (CaSO4∙2H2O), followed by a minor weight loss which goethite dihydroxylation between 250℃ to 300℃. XRF analysis revealed RG primarily consists of Ca (20-21%), S (11-12%), and Fe (10-11%), with trace amounts of other elements. FTIR spectra of raw RG indicated the presence of H-OH and -OH stretching vibrations, which disappeared after calcination, confirming dehydration. XRD analysis identified CaSO4∙2H2O and goethite (α-FeOOH) in raw RG, while anhydrite (CaSO4) and hematite (Fe2O3) were dominant after calcination. SEM analysis demonstrated that calcination at 900℃ achieved substantial dehydration while limiting excessive sintering, whereas temperatures ≥1200℃ resulted in pronounced sintering and structural degradation. Based on phase stability, morphology, and energy efficiency, 900℃ is recommended as the optimal calcination temperature. This demonstrates that calcination enhances RG's stability, making it a potentially suitable secondary raw material for use in cement, ceramics, and fertilizers.
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