Although by 1990 mercury was “banned” from alkaline batteries, they still contain a small amount of mercury. Apparently this is an unavoidable part of the manufacturing and mining processes. When the other metals in alkaline batteries, like zinc and manganese, are mined, small amounts of mercury are included in the raw ore. The good news is that the process Toxco uses to recycle alkalines also reclaims the mercury.

http://willtaft.com/environment/yes-we-do-need-to-recycle-alkaline-batteries/