An improved process for working up the waste liquors of the cuprammonium silk stretch spinning process

摘要

In the recovery of copper from the precipitating liquid obtained in the cuprammonium silk stretch spinning process, the liquid is treated first with excess of alkali such as soda lye and then with a solution of a magnesium salt such as the sulphate, whereby a mud containing copper hydroxide and magnesium hydroxide is precipitated. The bucking lye obtained during the preparation of the cotton may be used as the source of the alkali. From the precipitated mud magnesium is dissolved out by acid, for instance by sulphuric acid, and the copper at the same time converted wholly or partially to an insoluble basic salt. For this step the copper-bearing sulphuric acid obtained during the acidification of the filaments may be used. The magnesium salt solution may be re-used for precipitation of more copper, and the basic copper salt be treated, as by washing with cuprammonium solution or by heating in air to say 400 DEG C., to remove or destroy cellulose degradation products. The purified basic salt, with or without further purification by solution in sulphuric acid and precipitation as basic sulphate by soda solution, may be again added to the cellulose solution. A statement of the art refers to absorption of the copper from precipitating liquids by means of carbohydrates, cellulose, or wood meal, and to its precipitation, after expelling ammonia, as hydroxide.