Calcite mineral has several properties that the researchers find useful: Elements such as strontium-90 can replace the calcium in the mineral, calcite is formed in water-based environments with high pH, and it is stable in the arid desert soil at INEEL.
Calcite mineral is made when calcium carbonate precipitates from the water in the aquifer (like when deposits form on your water pipes) when the pH of the water in which calcium carbonate is dissolved is high. While calcite forms naturally in arid environments, the researchers want to speed up the process by locally increasing the pH in regions rich in Strontium-90.
One efficient way to do this underground is to get the resident bacteria to do it. Many species of bacteria are quite happy to degrade urea in a process called urea hydrolysis, which results in an increase in pH.
"We're already experimenting with organisms from the aquifer that might hydrolyze urea," said Colwell. "We are looking for the specific ones that can be stimulated or are responsible for urea hydrolysis. We also have to determine if we need to add, in addition to the urea, a carbon source for food or other nutrients."
The crystallized mineral will stay put if the environmental conditions are right, as they are under the INEEL site in the arid Idaho desert. "The strontium gets taken up because it takes the place of calcium in the mineral," said Smith. "After the strontium is removed, more layers of calcium carbonate form on the mineral. As time goes on, the strontium gets buried inside the crystal and it's no longer accessible to the water."
Colwell and Ferris need to determine precise conditions for optimal urea
hydrolysis. Colwell said, "Some organisms won't hydrolyze urea unless they are
growing. If those are the organisms under INEEL, we may need to feed them an
energy source and nu
Contact: Mary Beckman
DOE/Idaho National Laboratory