Application of In Situ Calcium Carbonate Process for Producing Papermaking Fillers from Lime Mud.

A portion of the lime mud formed during the causticizing process in the recovery process of kraft pulping should be purged from the calcium cycle as waste before it is fed to the lime kiln; this ensures that the quality of the pulp and pulping chemicals is maintained. The discharged greenish-gray lime mud, which is often disposed as an industrial waste, has been transformed herein into a high-quality papermaking filler via the hybrid calcium carbonate (HCC) and post-HCC (pHCC) technology. Initially, the lime mud was heat-treated and then ground to small-size particles. The ground lime mud was preflocculated with calcium oxide by ionic polymers, and carbon dioxide was injected to the flocs to produce lime mud HCC (LHCC). To produce lime mud pHCC (pLHCC), only the ground lime mud was preflocculated first, calcium oxide was added next, and finally, carbon dioxide was injected to the flocs. The resultant products, LHCC and pLHCC, gave brightness as high as that of the ground calcium carbonate (GCC) in paper while a little higher brightness for pLHCC than for LHCC. They also enabled to increase bulk, stiffness, and tensile strength. Application of the LHCC and pLHCC technology to the lime mud could save waste disposal expenses and produce better-quality paper.

Development of Deformable Calcium Carbonate for High Filler Paper.

Controlling the size and rigidity of calcium carbonate became possible. HCCs were developed and manufactured by the in situ reaction of carbon dioxide and calcium oxide, which were already preflocculated together with GCC using ionic polymers before the reaction. HCC is deformable under pressure during the papermaking process, and its degree of rigidity can be controlled by adjusting the fraction of calcium oxide. The size of HCC can be further controlled by adjusting shearing force. The more the fraction of calcium oxide, the more rigid the HCC and the smaller the diameter of the HCC. When used in papermaking, HCC increased the tensile strength and bulk of paper simultaneously without lowering other essential paper properties, and its deformable nature under pressure improved paper smoothness. Saving chemical pulp by 10% by replacing it with HCC, which is 3-4 times less expensive than the chemical pulp, was demonstrated successfully without lowering the essential properties of paper. Implementation of HCC in the paper mill may result in saving chemical pulp, drying energy, and production cost. The paper mill may utilize the carbon dioxide from the mill stack after purification for HCC preparation.