Improved process for the recovery of chemical products from viscose rayon spinning baths

摘要

Chemical products, from viscose rayon spinning baths containing sulphuric acid, sodium sulphate and less than 2 per cent. of zinc sulphate in solution, are recovered by evaporating water from said bath while maintaining the temperature above 32 DEG C. so as to precipitate crystals of anhydrous sodium sulphate associated with complex salts containing sodium, zinc and hydrogen sulphates, separating the crystals from the mother liquor at a temperature above 32 DEG C. and then submitting the crystals to countercurrent lixiviation with an aqueous sodium sulphate solution at a temperature above 32 DEG C., the amount of water in said solution being insufficient to dissolve all the sodium sulphate contained in the crystals but sufficient to decompose the complex salts and dissolve substantially all the sulphuric acid and zinc sulphate contained therein. The lixiviation may be effected in two stages, in the first of which sodium sulphate collected as drippings from freshly spun threads may be used, and a hot saturated solution of pure sodium sulphate for the last washing stage. The acid mother liquor removed from the crystals and the washing liquor containing sulphuric acid and zinc sulphate may be returned to the spinning bath, while the crystals of sodium sulphate may be dried. Specifications 298,639, [Class 1 (ii)], 384,726, U.S.A. Specifications 1,863,172, 2,374,004 and German Specification 356,103 are referred to.