Thread: What kind of mercury compound is found in batteries containing mercury?

What is the mercury compound used in batteries (eg AA, AAA, etc.) containing mercury (1 ppm)?
What about batteries that have a chemical system NOT containing mercury (such as Zn/MnO2) but are labeled as "low mercury" and having a mercury content of 1 ppm?

http://en.wikipedia.org/wiki/Mercury_battery

If the battery only contains 1ppm mercury, no mercury has been added to the battery. Instead, it's just occurring as an impurity in the components of the battery - the zinc anode, the manganese dioxide anode, the potassium hydroxide electrolyte, etc. Mercury occurs in trace amounts in most metal ore deposits, and potassium hydroxide is sometimes manufactured using a mercury electrode; either could be sources of the trace of Hg present. It could also be that the equipment used to detect Hg has a 1ppm limit of detection, so if no Hg was detected, the battery would be labeled "<1ppm Hg"

There are some types of batteries where mercury has been added intentionally. In mercuric oxide batteries, HgO serves as the cathode (oxidizing agent), with zinc as the anode (reducing agent). When the battery is used, the HgO gets reduced to metallic mercury.

Old alkaline and carbon-zinc batteries would sometimes also contain mercury - with these, metallic mercury was added to the zinc to form an amalgam (liquid alloy with mercury). Amalgamating the zinc removes the layer of zinc oxide from its surface, allowing it to react more easily in the battery, and also controls unwanted side reactions.