| 摘要 |
Na2SO4 and (NH4)2SO4 are separated from an aqueous solution containing them by crystallizing the solution at a temperature greater than 60 DEG C. to give a crystal mixture in which the crystals of each salt have differing size and density properties, separating the crystals to give one fraction consisting mainly of Na2SO4 crystals and another consisting mainly of (NH4)2SO4 crystals, washing each fraction separately at a temperature greater than 60 DEG C. to dissolve away the sulphate in the least quantity and leave the other substantially pure. The crystallization may be effected by concentration by evaporation, which may be in a single or multiple stages, e.g. at temperatures between 125 DEG and 65 DEG C. The washing may be with water or an unsaturated solution of the sulphates, e.g. the initial aqueous solution. The washing may be recycled to the initial aqueous solution. The crystals may be separated by decantation, flotation, dry or wet screening or by differential entrainment in a gas flow. All wet separation steps must be effected at a temperature above 60 DEG C. The larger crystals of (NH4)2SO4 may be washed on the screen. When screening is used to separate the crystals the crystallization of Na2SO4 may be controlled by finely ground seed crystals, e.g. 150-200 mesh. The washed crystals may be centrifuged, filtered or dried. The Na2SO4 mainly has a size <0.3 mm and a density of 2.7gm/cc. The (NH4)2SO4 mainly has a size from 0.5 to 1.0 mm and a density of 1.7-1.8 gm/cc.
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