Synthesis of peanut-like calcium carbonate intermediates in silica system containing partially hydrolyzed polyacrylamide and heavy alkyl-benzene sulfonate

Abstract

Calcium carbonate (CaCO3) crystals with various morphologies and polymorphs were synthesized from the aging calcium chloride (CaCl2) and sodium carbonate (Na2CO3) solution using inorganic silica as well as organic partially hydrolyzed polyacrylamide (HPAM) and surfactant heavy alkyl-benzene sulfonate (HABS) as effective crystal growth modifiers by the rapidly mixing method at 45°C. The effect of different additives on controlling calcium carbonate morphology has been investigated by field emission scanning electron microscopy (FESEM), fourier transform infrared (FT-IR) spectrometer and X-ray diffraction (XRD). Peanut-like CaCO3 particles were successfully obtained after the mixture system being aged for 6h at pH of 11.3±0.2, and the transition from sphere through peanut-like shape to cubic shape for CaCO3 particles occurred with increasing of aging time. All the CaCO3 particles were pure calcite when pH was unadjusted (pH=11.2±0.1), however, lower pH favored the formation of vaterite. The research results showed that the adsorption of HPAM and HABS on SiO2-coated CaCO3 surfaces played a crucial role in modifying the crystals morphologies. A hypothetical mechanism for the formation process of the peanut-like CaCO3 was presented.