Processo para separar impurezas em relação a cal e lama de cal e um processo de causticação de líquido que contém impurezas tais como silício em dois estágios

摘要

PCT No. PCT/FI96/00406 Sec. 371 Date Jan. 9, 1998 Sec. 102(e) Date Jan. 9, 1998 PCT Filed Jul. 10, 1996 PCT Pub. No. WO97/03245 PCT Pub. Date Jan. 30, 1997A method of separating impurities from lime or the calcium carbonate or the lime sludge produced in the chemical recovery system of a pulp mill so that lime sludge or lime is dissolved in a solution containing carbonate or hydrocarbonate in order to dissolve impurities. Subsequently the lime sludge or lime is separated from the solution containing dissolved impurities. A method of causticizing green liquor containing impurities, such as silicon, in two stages. In the first stage green liquor is causticized with such an amount of lime that impurities substantially remain in the liquor. The lime produced in this stage is removed from the liquor and the rest of the lime required in the causticizing is added to this liquor, so that impurities precipitate with the lime sludge produced in the second stage and at least a portion of the lime sludge rich in impurities is discharged from the process.