The Big Tantalum Recovery
One of Mark Gussack’s fondest stories that he tells at Exotech, is of the ingenuity to recover Tantalum from a difficult source. The story goes back over 20 years ago.
In the late 1970’s, DuPont had built a new facility to produce Carbon Tetrachloride, a common cleaning fluid at the time. Shortly after the facility was completed, Carbon Tetrachloride was deemed a carcinogen: https://www.atsdr.cdc.gov/PHS/PHS.asp?id=194&tid=35 .
So DuPont never commissioned the facility. Most of the various parts of the facility were taken down and sold.
Part of that DuPont facility were two very large and very expensive distillation columns. Each column measured 20 meters long and 3 meters in diameter weighing about 100 metric tons. The columns were constructed of 25 mm thick steel. The columns were lined with 1.8 mm thick Copper and 1 mm thick Tantalum that had been explosion bonded to the inside which provided the corrosion barrier for the hot Sulfuric Acid. Each column cost US$12 million to produce in 1970’s dollars.
The Question That Resulted in Tantalum Oxide
For over 14 years, DuPont tried to sell the columns as distillation units and then later for recovery of the Tantalum units. We personally became involved when we were asked by a trader “Can’t you just melt the steel off?” In that very question was the answer. We determined that by raising the temperature up high enough, we could actually “burn” the Tantalum and recover it as an oxide. While the price of Tantalum Oxide was certainly less than the price of Tantalum metal, the value of the Tantalum Oxide we would recover certainly made this a worth while project.
This was no easy task, but we deemed it do-able. First we had to find a furnace big enough to accommodate the columns. We found a company that was heat treating the hulls of Navy oil tanker ships. By building the right fixtures we were able to heat both columns at the same time.
We then had to build special air heaters that could deliver a controlled amount of super-heated air sufficient to oxidize the Tantalum on the inside without cooling the columns. The hot air flow system we built could carefully monitor the amount of air, and thus the Oxygen, that was delivered to each column.
The process was repeated four times. After each run, the columns would take 3 days to cool enough to allow a person to go inside and collect the Tantalum Oxide. When the 4 month long project was completed, we recovered almost 9 MT of Tantalum Oxide.
The bonus? Not only was the remaining 100 tons of steel sold for scrap, but the recovery of hundreds of gold welds that were used to seal the sheets of Tantalum!