Effect of ultrasound on the morphology of the CaCO3 precipitated from CaSO4-NH3-CO2-H2O system

Micron-grade calcium carbonate (CaCO3) crystals are by-products in the preparation of (NH4)2SO4 fertilizer using CaSO4·2H2O, NH3, and CO2. Since ultrasound can make crystals smaller and their morphology quite complex, the morphological change rules need to be studied to make meaningful use of them. In the present work, the morphologies of CaCO3 crystals precipitated from the ultrasound CaSO4-NH3-CO2-H2O system were analyzed in different conditions. It was found that ultrasound can make the crystals smaller in nucleation or the early growth stage, or it can make the shapes diversified and dispersed by influencing the solution property and in the aging process. In an ultrasound environment, crystals may be square, spheroidal, ellipsoidal, pisciform (spindle), hexagonal, carambola-like, or scattered particles. High-concentrations of NH3 and CO2 facilitate CaCO3 crystals becoming smooth balls, while high-intensity ultrasound and a high-concentration of foreign Na+ ions help to turn CaCO3 into tiny square particles or a clustered aggregate of tiny particles with rough surfaces. •The effect of ultrasound on morphology of precipitated CaCO3 was investigated.•Ultrasound makes CaCO3 crystals smaller in nucleation or early growth stages.•Pretreatment and post-treatment by ultrasound cause diverse morphologies.•Effects of NH3 and CO2 on morphology are opposite to those of ultrasound and Na+.•Crystals may be square, spheroidal, ellipsoidal, pisciform, hexagonal, etc.