Improvements in precipitation of zinc compounds

摘要

Zinc is removed as carbonate or basic carbonate from solutions of zinc ammonium carbonate which contains at least one additional non-ferrous metal capable of forming a soluble ammonia complex, particularly copper, by heating the solution to a temperature between 30 and 85 DEG C. to reduce the total ammonia content to an extent insufficient to hold all of the zinc in solution but sufficient to hold the additional non-ferrous metal in solution upon cooling the solution, and thereafter cooling the solution to precipitate the zinc as a zinc carbonate. The solutions employed are particularly those resulting from ammoniacal leaching of copper and zinc containing scrap but solutions containing zinc with nickel or cobalt may also be employed. The heating of the solution is preferably effected under vacuum and air may be bubbled through the solution being treated or alternatively steam may be admitted to heat the liquor. After heating the liquor to reduce the ammonia content and cooling to 20 to 25 DEG C. the solution may be carbonated to hasten zinc precipitation. The solutions treated may be recycled solutions from the ammoniacal ammonium carbonate leaching of a material containing zinc and copper a portion of the copper having been precipitated as metallic copper by gas reduction with carbon or hydrogen monoxide and it is preferred that the zinc content in such solutions be permitted to rise to about 30 grams or more of zinc per litre before precipitation; in such a case it is preferable that from 10 to 20 grams per litre of zinc be allowed to remain in the solution after precipitation, such solution being recycled back to the leach tank. Both the zinc and the copper ammonium carbonate hydrolyse on heating after which the ammonia and carbon dioxide come off. The copper appears to hydrolyse to a soluble basic carbonate of the azurite type. According to a typical example a leach recycle liquor was heated to about 60 DEG C. and agitated by air bubbled through it. After heating for 1 hour the solution was cooled to 25 DEG C. and carbon dioxide gas was bubbled through for 1 hour after which the precipitate of zinc carbonate was filtered and dried. The zinc carbonate precipitate may be dried or calcined, or redissolved in an ammonia-ammonium carbonate solution, metallic zinc added to cement out impurities to leave a zinc ammonium carbonate solution from which zinc carbonate may be obtained as above described.