A Process for the Utilization of Spent Nitric Acid used by Engravers and the Recovery of Copper therefrom.

摘要

15,087. Calico Printers' Association, and Warr, W. July 1. Lead nitrate; lead chromate.-In a process for utilizing spent nitric acid which has been used for etching on copper surfaces, the spent acid is diluted with boiling water. lead or lead oxide then being added, and the mixture vigorously stirred. When the action is finished, the temperature is raised to the boiling point, the mixture is allowed to settle, and the liquor is run off and allowed to crystallize. The crystals are dissolved in a boiling solution of lead nitrate, obtained from a previous operation, from which all the copper has been removed by metallic lead. The liquor is then again allowed to crystallize, and the mother liquor treated with lead to remove copper, thus rendering it available for treating another set of crystals. The mother liquor from the treatment of the spent acid is diluted and treated with lead to remove the copper. The clear liquor is run off and may be (1) treated by adding nitric acid and boiling down to obtain lead nitrate crystals, or (2) converted into a pigment of lead chromate. Or the spent nitric acid may be diluted, the copper removed by lead, and the liquor treated to obtain lead nitrate or chromate. The deposited copper is washed with boiling water, and again with water containing a little of the spent acid and then again in boiling water on a sieve or in a sieve drum. The copper is then covered with successive quantities of spent acid and allowed to stand until free from lead, and is then washed, dried, and cast into ingots.