Recovery of sodium sulphate, from solid fly ash obtained by incinerating paper treatment black liquor

摘要

Sodium sulphate is recovered from the solid particle product of paper pulp treatment black liquor incineration by: (a) dissolving (4) the particles in water; (b) decarbonating (20) the resulting solution by sulphuric acid treatment combined with concentration and temperature adjustment to avoid solid particles in the produced liquid stream; and (c) cooling and adding water to crystallise (48) sodium sulphate decahydrate (Na2SO4.10 H2O) which is then separated and recovered, the remaining liquid stream being partially recycled to step (b) and partially purged. Also claimed is a plant for carrying out the process.