Preparation of anhydrite from eggshell via pyrolysis

Abstract

Calcium sulfate dihydrate (CaSO4·2H2O) was prepared from the chemical reaction between calcium carbonate from duck eggshell and sulfuric acid at 25°C. The CaSO4·2H2O was dried in an oven at 110°C and transformed into calcium sulfate hemihydrate or plaster of Paris (CaSO4·0.5H2O). The CaSO4·0.5H2O was calcined at 700, 800 and 900°C and transformed into anhydrite or anhydrous calcium sulfate (CaSO4). The raw material used in this research was the duck eggshell, the waste eggshell generated from food processing industries. The obtained anhydrous calcium sulfate or anhydrite has true density, color, specific surface area, pore diameter and particle size equal to 2.95 g/cm3, white powder, 3.57 m2/g, 96.98 Å and 3.983 μm, respectively. In addition, other characteristics, microstructures, phase transformation and physical properties of raw materials and calcium sulfates were investigated and reported here using X-ray fluorescencemeter, Fourier transform infrared spectrometer, differential thermal analyzer, thermogravimetric analysis, scanning electron microscope, X-ray diffractometer, pycnometer method and Brunauer-Emmett-Teller.

Keywords

• anhydrite
• calcium sulfate
• duck eggshell
• phase transformation
• pyrolysis