Property optimization of calcium carbonate precipitated in a high shear, circulation reactor

Precipitated calcium carbonate (PCC) is a widely used mineral in a range of different applications. Its properties, such as morphology, particle size and surface area, determine its functionality and will have a large impact on the properties of the end product. This study examines the effect of different parameters in the PCC process on the pigment properties and the end-use properties in a paper filler application. The applicability of high shear, rapid solid/liquid mixing machine in lime slaking was examined and the properties of slaked lime prepared at different temperatures and concentrations were measured. For precipitation, a novel lab-scale reactor with a high shear mixer and circulation system was constructed. The precipitations were conducted at varying temperatures, slaked lime concentrations, carbon dioxide (CO2) flow rates and mixing shear rates. The reactor had the rotational mixer in the CO2 feeding zone, which broke up gas bubbles into different sizes by adjusting the rotation speed. This gave an additional parameter to control the particle size and specific surface area of the PCC particles. High precipitation temperature and calcium-to-carbonate ratio were found to favor the formation of scalenohedral PCC, which gave good optical performance and very low air permeability to paper. The rotation speed of 14,600rpm was found to be optimal resulting in high optical properties together with good paper bulk. The use of a high shear mixer in the PCC process allowed an additional degree of freedom for engineering pigments with advantageous end-use properties. The set-up of the PCC reactor and the effect of the mixer rotation speed on the properties of PCC particles. [Display omitted] •A reactor with a high shear mixer was designed for calcium carbonate precipitation.•The high shear mixer in the CO2 feeding zone enabled the breakage of gas bubbles.•Properties of PCC could be controlled by adjusting the rotation speed of mixer.•The produced PCC gave unique properties to paper when applied as a filler.