Lead miner Doe Run Co. hasn't turned lead into gold quite
yet. But Dave Olkkonen, manager of research and technical
development, has come close, helping to successfully adapt the
electrowinning refining process to lead concentrates.
"The technology we're talking about is very similar to what
microchips have meant to telecommunications and computers. It's
that significant of a technological advance for the lead
industry," Olkkonen said.
Traditional lead smelting can be a dirty business. Lead
concentrates are mixed with coke and various other raw
materials, like silica, limestone or soda ash, and fed into a
red-hot furnace where lighter impurities like sulfur are burned
off. The energy-intensive process is not fully efficient, as it
doesn't draw 100 percent of the lead out of the concentrate
mixture and allows lead particles to escape into the air.
More importantly, traditional lead refining is
environmentally hostile. Sulfur dioxide is released in large
quantities and must be converted to sulfuric acid, and lead
emissions leak into the atmosphere-lead particles can escape
even the most high-tech installations-pollute land and water.
Then there is the slag, a glass-like by-product that's a mix of
silica and heavy metal compounds that is hazardous to release
into the environment, forcing lead refiners to simply store
With that in mind, St. Louis-based Doe Run has been looking
for a more environmentally friendly alternative to its
Herculaneum furnaces, and began work on lead electrowinning in
1997. The process, widely used in copper and zinc refining,
involves electroplating pure metal directly from a concentrated
acid solution. The technology was never successfully applied to
lead, but in the late 1990s Engitec Technologies SpA, an
Italian technology firm, cracked the puzzle. It found that
fluorboric acid successfully dissolved lead from concentrates
and then allowed the metal to be plated out of the
"What Engitec gave us was the prospect of a commercial wet
chemical process to extract lead from lead sulfides," Olkkonen
said. But while the technology worked in a laboratory setting,
Doe Run faced a variety of problems when it tried to scale it
up. "When you're dealing with beakers and lab-sized equipment
and scaling it up to using large tanks and large-scale
electroplating cells, there are always, always issues and
growing pains," Olkkonen said. The project required the team to
design everything from the process and operational procedures
to equipment like the electrowinning cells and tanks.
The blank slate provided by the scale-up efforts gave Doe
Run the leeway to develop a variety of patented processes and
technologies along the way. One of the proprietary features of
Doe Run's technology is the reverse current leaching tanks, a
three-step system that selectively absorbs the lead sulfates
from concentrates into the fluorboric acid solution.
Lead concentrates arrive at the plant containing around
80-percent metal and enter the first leach tank to mix with the
acid, which dissolves some of the lead out of the lead sulfur
particles. The weaker concentrates are then transferred to a
second tank where the process is repeated, and the now
lead-poor solids and solution are then placed in the third tank
to leach out the remaining lead.
What's left behind is basically lead-free sulfur, which has
been separated from the lead using a wet chemical process
instead of being incinerated in traditional fire smelting and
can be used in sellable co-products, Olkkonen said. "We're
looking at higher lead metal recoveries from our concentrate.
What we've seen is that we can recover 99 percent of our lead
from concentrates. I'm not sure what fire-based operations are
doing on average, but we're getting anywhere from 2 to 4
percent better recovery."
The leaching solution starts off as lead-free anolyte and
travels through the tanks in reverse order, meeting the most
lead-poor material when it is strongest and absorbing lead to
become catholyte. "We want our richest, highest-potential
leaching solution in contact with the weakest lead-poor
material," Olkkonen said.
When the lead-bearing catholyte is ready to leave the first
leach tank, it is fed into the electrowinning cells where the
real magic takes place. The electrowinning tank is divided into
cells for lead cathode starter sheets and inert carbon anodes.
The lead-rich catholyte is poured into the cathode compartments
while the lead-free leach solution, or anolyte, surrounds the
carbon anodes. "There's a permeable membrane between the
cathodic and anodic compartments that allows the current to
pass, and the solution, once it changes its form, to pass as
well," Olkkonen said.
Once the cells are filled, the operator flips a switch and
an electric current plates pure lead from the solution onto the
cathode. The whole process takes around 24 hours, or "very
similar to what commercial plating times would be," Olkkonen
said. The result is a 150-pound lead cathode (including the
45-pound starter sheet).
Doe Run's demonstration facility in southeast Mo. runs two
commercial-sized tanks, each producing 64 cathodes at a time.
If operated continuously throughout the year, the facility
could generate about 2,450 tons of lead annually, exclusive of
"The beauty of this advance is that we have a sustainable
technology for our lead industry here in North America, and
potentially a global game changer. It means a better, safer
work environment, less exposures, cleaner communities,"
The new technology comes at a timely moment for Doe Run. The
U.S. Environmental Protection Agency is rolling out new
national ambient air quality regulations for lead in 2017 that
will force the company to stop traditional lead refining at its
Herculaneum smelter in Missouri. "We have several options that
we are exploring for the plant," said Jose Hansen, vice
president of marketing and sales. "We know primary smelting
using our current technology at this location will have to
cease by 2017 due to sulfur dioxide emission standards. Our
desire is to make the transition to the new technology even
earlier than that."
Taking the project from demonstration plant scale to a
commercial-sized operation is expected to require investments
of more than $150 million. Doe Run officials said earlier this
year that they were actively pursuing funding and loan
guarantees to help bring the new technology to fruition.