A new process to prodnce high-quality PCC by the causticising process in a kraft pulp mill

摘要

Growing market demand for lower grammage papers and higher machine speeds, require paper fillers with high opacifying ability and lower plastic wire abrasion. Because of its contribution to opacity and brightness and its low cost, precipitated calcium carbonate (PCC) has come to be used extensively as a filler. PCC is generally produced by "bubbling boiler exhaust gas through a calcium hydroxide slurry in an agitated vessel and a number of mills have installed on-site PCC plants. However, in the conversion of green liquor to white liquor in the kraft pulping process causticised calcium carbonate (CCC) is produced as a by-product, which is generally calcined and recirculated. If this CCC could be extracted and replaced by quicklime from an external source, it could be used as a filler and lime kiln operation would become redundant. CCC, however, includes large non-uniform particles making it unsuitable for papermaking. This paper describes development of a process for the production of needle-like CCC crystals suitable for use as a filler in papermaking.