Questions About Mercury's Fate

THE EXCELLENT ARTICLE "Getting Rid of Mercury" by Marc Reisch raises many unaddressed issues (C&EN, Nov. 24, 2008, page 22). The article states in the second paragraph that "electricity-generating utilities in the U.S. burn so much coal that they send 48 tons of mercury up and out their chimneys each year." In paragraph four, "Utilities are adopting activated carbon to control mercury emissions." Then in paragraph five, "When injected into power plant flue gas, activated carbon adsorbs mercury and then gets captured in the plant's waste fly ash."

As a concerned citizen, I have several questions. What happens to the fly ash? Is the "waste fly ash" just collected and dumped in a landfill somewhere, allowing the mercury to desorb into the environment over time anyway? Does capturing the mercury from the flue gas only change the avenue to the environment to meet shortsighted agency regulations rather than solving the problem?

Is subsequent processing of the "waste fly ash" for various commercial purposes hindered chemically by the mercury/activated carbon content?

Is the incorporation of power plant fly ash in cement formulations (now a common industry practice) affected by the mercury? Does the processing of fly ash into cement/concrete create a toxicity problem for workers by releasing the mercury and exposing workers either at the cement-making step or at the final placement of the concrete mix? What happens in a concrete tank, a concrete-lined reservoir, or a concrete pipe conveying drinking water when the tank or reservoir or pipe is made with concrete containing mercury-laden fly ash?

The list of questions continues indefinitely. As chemists, we need to address the whole picture. I have asked friends in the cement industry, and they respond that nobody yet knows the answers to these questions. It is quite likely that most other approaches to the mercury problem cited in the article will encounter similar issues.

Richard L. Talbott
Scottsdale, Ariz.