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Where Goes the Missing Mercury?

As U.S. mercury controls tighten, attention focuses on mercury-cell chlor-alkali plants

by Jeff Johnson
March 15, 2004 | A version of this story appeared in Volume 82, Issue 11

Credit: Pioneer Americas
A typical mercury-cell chlor-alkali plant's cell room holds 50 to 100 mercury cells, more than a mile of pipes, hundreds of pumps and flanges, and a multitude of opportunities to misplace mercury.
Credit: Pioneer Americas
A typical mercury-cell chlor-alkali plant's cell room holds 50 to 100 mercury cells, more than a mile of pipes, hundreds of pumps and flanges, and a multitude of opportunities to misplace mercury.

A federal regulation intended to reduce mercury emissions from nine chlor-alkali plants is forcing a sharp examination of the plants' handling and use of the element, which is neurologically toxic and can lead to developmental impairment in children.

The plants are the remnants of a U.S. industry that once numbered about 35 facilities. They are operated by six companies and use a 50-year-old mercury-cell technology to produce chlorine and sodium hydroxide or caustic soda from sodium chloride.

The plants contain a sea of mercury. Industry officials estimate some 3,000 tons of mercury is in use at the nine plants. The mercury-cell technology is the least significant of three primary chlor-alkali manufacturing technologies. It produces only 10% of the nation's chlorine and is the only one that uses mercury.

Increasingly, regulators' attention has shifted to these plants and their use of mercury, as states and the Environmental Protection Agency try to ratchet down mercury emissions to air from power plants, municipal solid-waste incinerators, and other sources. EPA's regulations are driven by an ever-growing body of evidence of mercury's toxicity. The agency recently estimated that some 630,000 children are born each year in the U.S. with unsafe levels of mercury in their blood.

Credit: Chlorine Institute
Credit: Chlorine Institute

These nine chlor-alkali plants report air emissions of about 5 tons of mercury per year, a small amount when compared with coal-fired power plants that put about 50 tons of mercury into the air annually. In all, these chemical plants filed Toxics Release Inventory (TRI) reports showing about 15 tons of mercury exits the facilities each year, most going to off-site treatment of some sort.

However, these numbers don't tell the whole story. Industry officials acknowledge that at least twice this level of mercury is "consumed" annually by these plants in the production process. Although using up 30 tons may seem large, the amount lost in manufacturing has fallen dramatically in recent years through voluntary industry efforts.

Credit: Jeff Johnson
Credit: Jeff Johnson

Indeed, a successful program run by the Chlorine Institute has cut mercury consumption from 222 tons in 1990 to the current level, says Arthur E. Dungan, the institute's vice president for safety, health, and the environment.

Also declining over the years was replacement mercury tonnage purchased annually, which is also voluntarily reported by the industry. However, in 2002, purchases suddenly shot up to 130 tons, 100 tons above consumption, the Chlorine Institute reports.

Industry critics and some EPA regulators have quizzed the industry about where this large tonnage is going. Working out the numbers, the difference between the amount reported by the plants as legal TRI transfers and emission (15 tons) and the amount consumed in manufacture (30 tons) is a large amount, 15 tons. But the difference between the TRI amount and purchases is a huge figure, 115 tons. This tonnage dwarfs levels emitted to air by coal-fired power plants, which has been EPA's main interest, notes Jon P. Devine Jr., an attorney with the Natural Resources Defense Council (NRDC).

DEVINE WORRIES that the purchased amount signals a return to the bad old days of high use and high consumption.

"There is very little transparency to the industry numbers," Devine says. "I've seen no data showing that these purchases aren't for replacing mercury that has previously escaped from the process."

He points out that even EPA acknowledged the confusion in the wording of the recently released regulation for this industry, writing that "the fate of all the mercury consumed at mercury-cell plants remains somewhat of an enigma."

When the final regulation was issued last December, NRDC and several environmental groups objected, saying it was too weak and would lead to more emissions as well as more unaccounted-for mercury.

But EPA argued that the regulation would cut mercury emissions by 94% from current levels once compliance is required in 2006. Despite repeated phone calls, EPA officials were unwilling to comment on the rule, citing the litigation.

The regulation is based on a combination of emissions limits for point sources and work practices requirements. The regulation also will end use of an enforceable standard and will replace it with new housekeeping requirements, which guts the regulation, NRDC and Sierra Club attorneys say.

These groups sued the agency in mid-February over the regulation and petitioned EPA to reconsider how it is setting mercury emissions standards for this industry. They also charged that the rule fails to address the fundamental question of mercury lost during production.

Dungan counters, "We support the new standard, and if NRDC was being honest they would see it is much more stringent than the current one." The reductions are "very significant," he continues, but hard to quantify.

In fact, most agree it is quite difficult to quantify, as well as control, mercury emissions from cells in a football-field-sized building that must be left relatively open simply to offer a respite to workers facing an onslaught of heat and chemicals.

Each cell, Dungan notes, is around 30 to 40 feet long by 10 feet wide, and a cell room may hold from 25 to 100 cells. The cells are sealed except during maintenance, he adds.

To produce chlorine gas and sodium hydroxide, the plants pass a brine solution through the closed cell, exposing the sodium chloride to electrical current. A fixed anode rests above the brine, and a flowing cathode, the mercury, moves below it.

Chlorine gas forms at the anode and is captured and removed from the cell. A sodium amalgam forms at the mercury cathode, and it also exits the cell but on a different path. The amalgam is further processed by the addition of deionized water and more electrolysis. The sodium amalgam and water create hydrogen gas and sodium hydroxide, which are captured and exit the system. The mercury held in the amalgam returns to the cell.

The process provides ample opportunity for mercury to get tied up in pumps, equipment, or thousands of feet of piping, Dungan notes. But, Devine says, it also offers great potential for mercury to exit the plant and enter the environment through regular cell maintenance as well as fugitive emission sources.

Dungan argues that much of the unaccounted-for mercury remains within the plants' pipes and vessels and adds that it is but a small amount of the 3,000 tons in mercury inventory at the nine plants.

"There is no scientific basis for the assertion that the difference between purchase and use equals environmental releases," he says, noting that a ton of mercury can be held in a 17.5-gal trash can.

He adds that it is dangerous for workers to open equipment and account for every last pound of mercury. But dozens of plants have been shut down over the years, providing a ready opportunity to determine how much mercury is tied up in the system.

"Yes," Dungan says, "there is anecdotal information on shut-down plants, but no one has been willing to report on it. Mercury is found throughout the system, but we have no specific information on where it goes."

Concerning the 130 tons of new mercury purchases in 2002, Dungan says, they are in support of a new technology that is showing dramatic evidence that a one-time addition of mercury to the cells results in improved cell performance, more time between maintenance shutdowns, and greater efficiency.

Of 2002 purchases, about 100 tons went to four facilities that are installing new technologies, he says. The Chlorine Institute estimates that 80 tons was bought in 2003 and another 50 tons will be purchased in 2004 for new technologies. Dungan believes that eventually all nine plants may retrofit. In the end, the result will be fewer emissions and more efficiency, he says.

But Devine says, "All we see is the aggregate numbers from the Chlorine Institute and its blanket assertion that it is a one-time addition to increase efficiency."

STRESSING THE NEED for litigation, he adds, "until industry comes forward with a clear explanation, it is incumbent on EPA to find out what is actually going on." He worries that the purchased amount may climb back up to the levels in the past or will at least be cyclical, going up and down in future years without any controls.

One of the companies that has installed this new technology is Pioneer Americas LLC, a chlor-alkali facility in Saint Gabriel, La.

Energy savings, not mercury emissions, is the driver, says Gary Sellers, Pioneer's engineering and maintenance manager. He estimates the company has reduced energy use by 15%, saving 85 million kWh of electricity per year since the renovation was made in 2001. Mercury emissions are also reduced, he says, but that is not the primary justification.

The company added about 103 tons of mercury to its system over two years to raise the level of mercury in each cell, Plant Manager David Gasper explains. The additional mercury raised the level in the cell and closed the gap between the anode and mercury cathode to less than a millimeter, he says. This saves electricity in two ways: The reduced distance cuts the amount of energy needed to move electrons from anode to cathode, and the higher level of mercury helps smooth the mercury's surface, allowing a more efficient electron transfer.

Anodes normally last about a year, he says, but with the new technology, they last three to five years, so the company doesn't have to open cells as frequently and there is less mercury loss from maintenance. He estimates that less frequent anode repairs results in a 25% reduction in cell openings.

Pioneer, however, makes no estimate of what this may mean in terms of mercury emissions reduction. "We know that if a cell is not opened, we reduce emissions," Seller says, "but measuring exact emissions from a cell house is very difficult."

The two officials say the company will meet the new mercury emissions standard through better housekeeping in the cell house and better sealed pumps and piping throughout the system, not through this technology modification.

Gasper says many modifications to comply with the rule have already been made at Pioneer, and he provides a rough estimate that about 5,300 lb of mercury left the plant last year--60 lb in product and the rest legally emitted to water, waste, and air. About 300 lb on top of this was "unaccounted" mercury, he says, and remains in the plant, tied up in piping.

Sellers says the new technology costs about $9 million to install and will save about $2 million annually in electricity bills. The changes make the company more competitive with newer chlor-alkali technologies that don't use mercury, he says. The changes will give the 35-year-old plant a new lease on life, which troubles NRDC's Devine.

"We think what industry ought to do is voluntarily phase out this antiquated process," he says. "Instead, EPA's regulation will give it a license to continue indefinitely into the future, which is exactly the wrong thing to do."


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