Control of Heavy Metals in Emission Streams

Abstract

Heavy metals are elements that are located in the periodic table from groups III to VI and periods 4 or greater. The elements have high atomic weight greater than sodium and high specific gravity (i.e., usually greater than 5.0 g/cm3). In addition, the elements have high thermal conductivity and are characterized by malleability and ductility. There are 65 elements listed in the periodic table that can be defined as heavy metals based on the above definitions. Approximately 30 metals, either in elemental forms, in salts, or in organometallic compounds, have been used by industry. Heavy metals in the wastes will not be directly exposed to the atmosphere. Thermal or vaporization processes enhance heavy metal exposure into the atmosphere. Unlike organic compounds, metals cannot be completely destroyed by the thermal process. The thermal process can only oxidize the majority of metals to particulate matter. Only a small amount of volatile metals having a boiling point lower than the thermal/combustion operation temperature will be vaporized. Metals, such as arsenic, barium, beryllium, chromium, cadmium, lead, mercury, nickel, and zinc, are of great concern in waste incineration and coal combustion because of their presence in many wastes and because of possible adverse health effects from human exposure to emissions 1.