The Florence In-Situ Mine
The copper mine being developed in Florence, Arizona will leave hardly a trace after it has come and gone. The before and after photos of this desert and farmland area, will be almost the same.
How? Doesn't copper mining mean a big hole in the ground, hundreds of acres of tailings and huge waste piles, or shafts sunk deep into the earth with towering head frames?
Not if it is an in-situ mine at Florence. BHP Copper is developing the first standalone in-situ copper mine in the world. It will create jobs, protect the environment, and prove a new technology that may open up many low grade orebodies, allowing them to be mined at low cost with minimum disturbance.
So, What Is an In-situ Mine and How Does It Work?
In-situ means "in the natural or original position." An in-situ mine would obtain the desired material without disturbing the location. With conventional mining, large amounts of rock are moved to expose the ore, which then has to be mined so the copper can be extracted. The in-situ process avoids almost all this work; ore is leached right where it is.
The in-situ mine consists of a series of injection wells and recovery wells. The wells, built with acid-resistant casings and cemented from the top of the ore zone to the surface, penetrate the copper-bearing rock. A weak acid leach solution is pumped, through perforations in the casing, into the ore. As the leach solution passes through the cracks in the ore, the copper is dissolved into the solution. This copper-rich solution is pumped up through the recovery wells for processing. A ring of recovery wells always surrounds the active leach area. This creates a flow that moves inward toward the leaching zone, preventing the leach solution from escaping.
The copper-rich solution is then sent to a solvent extraction/electrowinning (SX/EW) plant, where an organic reagent is added to the solution to draw out the copper. The copper is removed from the reagent, creating a liquid that contains enough copper for "electrowinning." Electrowinning is a process in which an electrical charge is passed through the solution and forces the copper to deposit as a metal. In a few days, 100-pound sheets of pure copper can be shipped for manufacturing into wire and cable. Finally, when the ore body is depleted of copper, the ore zone is cleaned of any hazardous components by pumping and rinsing with fresh water. The wells are then filled with cement, and the land is returned to its original use. In Florence, this means farming.
BHP Copper Sets The Standard
BHP Copper has worked with the government to develop the Best Available Demonstrated Control Technology (BADCT) for in-situ leaching. It will become the standard for this kind of mining and demonstrates the best known methods for protecting the environment. The Florence operation will meet or exceed the Arizona Department of Environmental Quality (ADEQ) recommended BADCT guidelines. This hydrological control has three main components:
Primary hydraulic control: All the solutions introduced into the ground are retrieved. This is important not only for protection of the environment, but also because lost solutions means lost copper and less revenue. Good environmental control means copper resource conservation.
Secondary hydraulic control: A series of pump-out wells surround the leach system to draw water inward and downward into the mining system. This method has been effective in environmental clean-ups at other sites.
BHP borrowed and improved on that technology.
"Close-as-we-go": As copper is extracted, the land will be cleaned up in the mining area and the wells closed. Most open-pit mines cannot close until all of the ore is mined. In the case of in-situ mining, closure and reclamation of the land will be on-going throughout the life of the mine.
The Aquifer Protection Permit (APP) requires monitoring of area groundwater, contingency plans in case of operating problems, and an approved closure and reclamation plan before the mine can start production. The permit is required by ADEQ and Florence received the Notice of Intent to Permit and the technical review of the Florence Aquifer Protection Permit application in mid-December. At the time of writing this article, ADEQ intended to go to public notice on January 10, with the public notice period running for 30 days until February 10. The public hearing would be held on that date and notwithstanding any objection from the public, the permit would be issued shortly thereafter.
Protecting The Environment
The Aquifer Protection Permit is designed to protect Arizonas drinking water resources. It is a comprehensive program covering mining and processing operations on the surface of the land and discharges into the land.
Its hard to imagine putting a sulfuric acid solution into the ground, and protecting the environment. But the permitting process makes sure the environment is protected. Besides the APP, an Underground Injection Control (UIC) permit is required by the US Environmental Protection Agency. The UIC is not only designed to protect groundwater, but also looks at endangered or threatened species, archaeological assets, and evaluates the socioeconomic impacts of the mining operations.
A Lesson in Community Relations
No matter how good the project is technically, it is critical to have public support. A research company was hired in 1995 to survey a portion of the Florence community. Of the 3,600 permanent residents, 250 people were questioned to determine how much they knew about Magma, copper mining, the in-situ leaching process and their familiarity with other forms of mining.
BHP then held more than 35 public meetings where presentations were made on the Florence project and the in-situ leaching process. Stories appeared on the local television station and in the Tri Valley Dispatch, the local newspaper. The goal was to make everyone aware of the project and to help them see the positive impact that this mine would have on Florence.
A Visitor Center was built at the BHP Florence office complete with displays on in-situ leaching, a history of mining in the area, and answers to questions about BHP and copper mining. Many local residents, as well as tourists, have visited the center.
http://www.copper.org/environment/casestudies/cottonfield.html
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