The present invention relates to a process for recovering silver oxide and metals from spent silver oxide button cells, and particularly to a physical process to separate its shell and content to recover silver oxide, silver, zinc, iron and nickel.
Generally, button cells are divided into four groups, i.e., silver oxide cells, mercury cells, lithium cells and alkali-manganese cells. A silver oxide cell's content is silver oxide and silver metal, and the shell is made of zinc, iron and nickel. Therefore, it is necessary to recover silver oxide, silver and other metals from spent silver oxide button cell so as to reuse the metals therefrom.
When conventional chemical process is used to recover the silver oxide and silver from spent silver oxide button cells, however, other valuable metals such as iron, zinc and nickel are disposed of without recovery.
In the conventional chemical process, aqua regia, a composition of concentrated nitric acid and hydrochloric acid, is used to dissolve the shell of the cell, and a protective film of silver chloride is formed on the surface of the silver metal by a reaction with hydrochloric acid. The silver oxide and silver are recovered, and the rest is disposed as an effluent. However, the effluent contains some highly contaminating substances, i.e., the aqua regia which contains strong acid may produce waste water and waste gas such as NO.sub.x. Consequently, it is difficult to treat these pollutants to meet effluent standards and also this process becomes accordingly more complicated and costly.
After a pyrometallurgic purification of the silver oxide and silver (by Na.sub.2 CO.sub.3 +C, at 1000.degree. C.) to 95% crude silver, the crude silver is further refined to silver ingot with a purity of 99.99% by a conventional process. Then the silver ingot can be sold and reused (see FIG. 1).