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Student mine remediation project now full-fledged research

What began as a student team project for an environmental design competition has blossomed into a funded research project with global potential for remediation of mine tailings.

Graduate student Mohamad Murshed and faculty member David Rockstraw prepare a mine tailing slurry mixture for treatment to remove contaminants. (Photo courtesy Tom A. Freelove)

In 1998, NMSU chemical engineer David Rockstraw mentored a student team in the WERC Environmental Design Contest, an annual event at NMSU that challenges university students from around the world to tackle environmental problems.

Rockstraw's students developed a technology that would collect and transport mine tailings in a slurry mixture and recover and reuse the water used in the process, while enhancing the removal of residual copper. The task was sponsored by Phelps-Dodge, the world's second-largest copper producer.

The NMSU team competed against 14 others and although it didn't win first prize, it was recognized for developing the most innovative process.

"We got some good results from that project," Rockstraw said. "Later, one of my students, Mohamad Murshed, adopted it for further research as part of his master's thesis. Now he is a Ph.D. candidate and is continuing this research."

WERC: A Consortium for Environmental Education and Technology Development recently awarded a $60,000 technology development grant to support the project.

The high concentration of metal in mine tailings reacts with rain water and oxygen in the atmosphere, producing sulfuric acid that contaminates surface and ground water. Mining operations must contain and treat the water runoff, even when the mines are no longer active.

The students incorporated the use of potassium ferrate, a form of iron that has the ability to oxidize the residual metal in the tailings, while also preventing the production of sulfuric acid by converting sulfides in the tailings to sulfates that can be removed easily in a liquid process. The solid tailing that remains is benign and has no potential to further leach sulfuric acid.

"We confirmed the chemistry," Rockstraw said. "Now we are studying the fundamental mechanisms of the process: how fast it works, how different temperatures and concentrations affect the process. We need to determine how effective it is and get a better picture of the cost of implementing the process."

The expense involved in the creation of potassium ferrate has been a barrier to its commercial manufacture. However, a recently patented technology developed by Michael Johnson of NMSU's Chemistry and Biochemistry Department shows promise for less expensive laboratory production of the material. Johnson's process will be further refined to produce the potassium ferrate used in the mine tailings research.

Further increasing expense, when potassium ferrate is introduced into a slurry mixture, it reacts not only with the metals, but also with the water, reducing its efficiency. Rockstraw and Murshed will experiment with a new solid phase process in which tailings, potassium ferrate and ball bearings are placed in a device called a ball mill that spins at a high speed and allows the chemicals to react without the water.

The ball mill has been used predominantly to grind solid materials, but in this application, Rockstraw intends to use it as a solid phase reactor. Elimination of water from the reaction mass is expected to significantly improve the efficiency of the process.

"The process is a long way from being economically feasible for widespread use, but the potential is enormous because all mines have this problem," Rockstraw said. "And there are other applications for potassium ferrate in waste-water treatment and in medicine."

"It is very fulfilling to see something spawned by our Environmental Design Contest grow into something that has the potential to address a serious worldwide environmental problem," said WERC Executive Director Abbas Ghassemi. "This is what it's all about."

The WERC consortium consists of New Mexico State University, the University of New Mexico, the New Mexico Institute of Mining and Technology, Dine College and Los Alamos and Sandia National Laboratories.

For more information about WERC, visit www.werc.net or call (505) 646-2038. For more information about this technology, contact Rockstraw through NMSU's Department of Chemical Engineering, chemeng@nmsu.edu.