Since the beginning of the industrial age, slag, the glassy material left over when metals are refined from ore, has been considered ugly but harmless. But research conducted at Stanford University has found that some kinds of this voluminous mining waste, which closely resembles volcanic rock, contain high levels of potentially toxic elements and can release them into the environment. Because it has been considered chemically inert, slag has been mixed with cement and used to construct roadways and railroad beds. It has been used for sand blasting. It has been added to roofing shingles. 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.