| 摘要 |
The invention relates to a method and apparatus for recovering precipitated calcium carbonate, PCC, prepared by a causticizing reaction. According to the method PCC is separated from the reaction mixture of the causticizing reaction by filtration, and the PCC-containing precipitate collected onto a filter (3-5) is washed with water, in order to separate by-products from the PCC. According to the invention the PCC precipitate is washed with water into which carbon dioxide is dissolved to a sufficient extent to convert at least part of the hydroxy compounds in the precipitate into the corresponding carbonate compounds. Most suitably carbon dioxide is used in an amount that is at the most 20 % in excess in comparison to the hydroxy compounds. The apparatus of the invention comprises several pressure filtration units (3-5), with which calcium carbonate may be separated from the reaction mixture, and each of which has its own input line for adding the liquid to be filtered, the wash liquid for calcium carbonate and the neutralizing liquid for calcium carbonate into the filtration unit. |
