And it has even been used to sand roads in the winter. This might not be such a good idea, however, since slag produced in refining copper, zinc, cadmium and other base metals can contain significant concentrations of a number of potentially toxic elements, including arsenic, lead, cadmium, barium, zinc and copper, Michael Parsons, a graduate student in geological and environmental sciences at Stanford, has found. He also has shown that slag can release these elements into the environment under natural weathering conditions and cause pollution of soils, surface waters and groundwater. Parsons presented the results of his work in a poster paper presented on Wednesday, Dec. 9, at the American Geophysical Union meeting in San Francisco. Collaborators include Professor Marco T. Einaudi and Associate Professor Dennis K. Bird in Stanford's department of geological and environmental sciences and Charles N. Alpers of the U.S. Geological Survey.
Parsons draws a distinction between two main kinds of slag.
The type produced in making steel does not contain high levels of toxic elements, but slag produced by smelters that refine copper, lead, cadmium and other base metals contains higher levels of potentially hazardous elements. That is particularly true of smelters that were operating at the turn of the century and before, Parsons says. He has been studying one such site, the Penn Mine in Calaveras County, Calif. that operated intermittently from the early 1860s to the late 1950s. During that time, the refinery operators drained slag off the molten metal and poured it into bathtub-shaped molds. When it cooled and hardened, they dumped the waste material along the banks of the nearby Mokelumne River.