| 摘要 |
The waste liquor from a sodium sulphite process of preparing wood pulp is concentrated, burned and smelted, sodium is extracted, predominently as sodium sulphide, in aqueous solution, and then adsorbed from the solution with a weakly acidic ion exchange material in the hydrogen form, whereupon the exchange material is regenerated with a sulphurous acid solution to produce a solution of sodium bisulphite and sulphurous acid for reuse in the pulping process. Chloride ions which may be present in the wood as sodium chloride are thus eliminated from the cycle. In carrying out the process wood chips are pulped with the recycled solution and fresh sulphurous acid, the processed pulp is removed and the liquors passed to evaporators. Salt cake or sodium carbonate is added to compensate for loss of sodium, and the concentrated liquor passed to a furnace wherein a sodium sulphide smelt is formed under reducing conditions. The pH of the solution of the smelt passing to the ion exchange columns is preferably above 6, and that of the regenerating sulphurous acid solution is less than 4. Hydrogen sulphide evolved during the adsorption process is burned with added sulphur to produce sulphur dioxide from which the regenerating sulphurous acid solution is obtained. If desired, sodium losses can be replaced by adsorbing in the ion exchange column sodium from other solutions, e.g. from the waste liquors used in the purification of unbleached pulps. Specification 469,051, [Group IV], is referred to. Reference has been directed by the Comptroller to Specification 684,224.
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