Preparing high opacity precipitated calcium carbonate using the causticizing reaction

The causticizing reaction, also known as the soda ash-lime (SAL) reaction, was investigated to determine if it could produce a precipitated calcium carbonate (PCC) with high opacifying characteristics. A high opacity PCC was achieved with the SAL reaction in the laboratory using a 6.4 liter reactor: Key process variables identified included a slow addition of Na2CO3 solution to the Ca(OH)(2) slurry, reaction temperatures less than 50 degrees C, and uniform mixing using an axial flow type impeller. Findings from the laboratory reactor were used to successfully scale up to a 450 liter pilot reactor and then to a 42 m(3) commercial reactor: PCC opacifying ability was estimated by determining the PCC scattering coefficients in handsheets prepared with PCC samples. The SAL reaction demonstrated PCC scattering coefficients ranging from 2700-3000 cm(2)/g, which is comparable to other commercial high opacify PCC products. Approximately 1800 kg of PCC produced by the SAL reaction in the commercial reactor were used to produce a lightweight printing grade of paper on a commercial paper machine. Salable paper was produced.