This solution is then subjected to a process called solvent extraction (SX). The SX process concentrates and purifies the copper leach solution so the copper can be recovered at a high electrical current efficiency by the electrowinning cells. This is accomplished by adding a chemical reagent to the SX tanks, which selectively binds with and extracts the copper. This reagent is easily separated from the copper (stripped), as the operation looks to recover as much of the reagent as possible for re-use. The concentrated copper solution is dissolved in sulfuric acid and then sent to the electrolytic cells for recovery as copper plates (cathodes).
The Morenci operation has quite a large crusher, which can output at maximum approximately 63,000 tons of ore per day. This crusher pulverizes the ore and more conveyors send it to a nearby stump-leaching site called the Stargo leaching pad. This ore is agglomerated and made ready for spreading by two mobile stacking units. The actual leaching is bacterially assisted, with air blown into alternate lifts. This is currently the most efficient process for extracting the copper and other metals like lead out of the crushed ore.
Environmental Concerns and Impacts
The process of ore extraction by smelting is quite environmentally damaging. Many of the largest copper mines in the state of Arizona are designated as Superfund Clean-up Sites, or places where the Federal Government has placed restrictions on future operations while mandating clean-up of environmental toxins and contaminants. While the Morenci mine itself no longer has a smelter, one of the mine's most utilized smelters, called the Miami smelter, is currently on the Federal Government's list of Superfund sites due to toxic metals and contaminants that have leached through into the groundwater nearby.
The hydrometallurgical process of leaching copper ore also has many environmental concerns. This process often involves radioactive chemicals and other toxic chemicals. The Philips Dodge operations are regular recipients of Notices of Violation from the U.S. Attorney General. These notices reflect violations to environmental or other previously outlined health concerns associated with the mining operation. Some other major environmental concerns for this company, including the Morenci location are:
1) Phelps Dodge has pending water quality permits intended to stop the discharge of mining toxic waste into groundwater used for public and private drinking water.
2) Phelps Dodge has state and federal superfund and compliance programs now in place or pending.
3) Phelps Dodge has extensive environmental and reclamation costs at present and in the future.
These and other concerns come with mandatory permitting and regulation from the Federal Government. They have cost the Philips Dodge Company over $822 million dollars from the years 2002-2005 alone. But no amount of money can make up for the fact that million of gallons and thousands of tons of these toxic substances have been contaminating the area around the Morenci site for decades. It is extremely costly and time-consuming to remove these substances, which if left untouched, will remain in the soil and groundwater of the region for millions of years. The smelting operations in the early years of the mine's operation were much more environmentally harmful than those of later periods, and the Federal Government did not start regulating polluters until a few short decades ago.
The State of Arizona has also come down hard on the Philips Dodge Company for destroying migratory bird habitat and breeding grounds at the Morenci site as well as other sites across the state. The State of Arizona has mandated that the company pay millions in clean up and rehabilitation fees for these habitats. The Morenci mine currently estimates that it has over 250 million tons of copper ore in reserves and will likely operate for years to come. The region's resource-rich mountains and desert area make it one of the most profitable in the world.
Groundwater Awareness League Homepage. (2007). "Phelps Corporation Environmental
Liabilities." Accessed via web: < http://www.g-a-l.info/ComplaintOne.htm> on August 9th, 2010.