ABSTRACT
Mercury is one of two elements that occur as a liquid at normal room temperature and pressure. It is a silvery-white metal that is naturally present in the environment at low concentration. It can exist in various forms in air, water, sediments, soil, and rocks. The metal is produced from primary sources via the thermal extraction of mercury from ore containing cinnabar (mercuric sulfide, HgS). Approximately 4100 metric tons were produced worldwide in 1990. Seven years later, the production had dropped to 3200 metric tons. The last dedicated mercury mine in the United States closed in 1990; since then, mercury has been produced only from primary sources as a by-product of gold mining (Plachy, 1996). In 1997, only five mines were producing mercury as a by-product of gold recovery (Reese, 1997). Because of its toxicity, discarded products containing significant amounts of mercury are usually reprocessed and the mercury is recovered.
