March/April 2007

New copper concentrate and leaching facility at Morenci

By H. Ednie

Construction is well underway of a new copper concentrate leaching and direct electrowinning facility at the Morenci, Arizona, mine of Phelps Dodge Mining Co., a part of Freeport-McMoRan Copper & Gold Inc.This concentrate leaching plant, scheduled to start up in the third quarter of this year, will be capable of treating about 217,000 tonnes of copper concentrate a year while producing acid for the leaching facilities on site.

The facility will employ proprietary technology the company developed and demonstrated at its copper mine in Bagdad, Arizona, to process mixed primary and secondary copper ores. The new concentrate leaching facilities will be incorporated into the existing leaching and electrowinning complex at Morenci, which is the world’s largest. Production from these facilities will replace an expected decline in Morenci’s heap leach output later this decade.

At a total capital cost in excess of US$100 million, this project is an example of the technology development work that is a cornerstone of the company’s success.

“Our primary objective for the application of this technology is to produce copper at a lower cost,” said John Marsden, senior vice president, technology and product development, Phelps Dodge. “We will continue to evaluate potential applications of this technology at several sites and projects.”

The Morenci facility will use medium-temperature pressure leaching with direct electrowinning to process the copper concentrate. It’s one example of a suite of technologies developed by the former Phelps Dodge for pressure leaching of copper.

In general,Marsden said there are two types of pressure leaching for copper they have commercialized.The first, high-temperature pressure leaching, has been in operation at the company’s Bagdad mine since 2003. In 2005 the facility converted to operating medium-temperature pressure leaching with direct electrowinning for a period of eight months, as a demonstration plant to support the decision to use this process at Morenci, then converted back to high-temperature.

The main difference,Marsden explained, is the two processes produce different amounts of sulphuric acid as a byproduct. In high-temperature pressure leaching, almost 100 per cent of the sulphur is converted to sulphuric acid, used in the leaching process. In medium-temperature, a significant portion of the sulphide sulphur is converted to elemental sulphur, which remains in the residue as a stable product. A smaller amount converts to acid, for leaching.

“We select the process that meets the acid requirements at site,” Marsden said. “Ore mineralogy, ore grade, and configuration of the circuit all determine what mode to utilize for a particular application.” The Morenci mine operation is cutting into an area of the deposit which contains a greater proportion of chalcopyrite, making it less effective to leach on heaps and stockpiles, as traditionally done onsite. The new facility will be used to treat this portion of the ore, and has an expected life of greater than seven years.

To implement the new facility, a preexisting mill, shutdown in 2001, will be restarted in essentially its original configuration, of crushing to ball milling, to flotation. “Startup of the mill is a refurbishing job, including some equipment replacement, the reconditioning of some equipment, and general maintenance work on the rest,”Marsden said.

Aker Kvaerner Metals Inc was awarded the engineering and procurement services agreement for the development of the facility at Morenci.

A brief history of Morenci

The existing Morenci mill and concentrator began operation in 1942, then doubled in size two years later to support the World War II effort. It ceased operation in 2001, and in 2006 resumed limited operation. Until completion of the concentrate leach facility later this year, concentrate is shipped to the company’s smelter in Miami, Arizona.

In 1998, Phelps Dodge launched a program to investigate alternative technology for the extraction and recovery of copper, and other metal values, from copper concentrates. The drivers included increasing capital and operating costs for smelting and refining in recent year; the need to drive copper production costs down; and the need to provide safe and environmentally sound alternatives for processing of concentrates. The result—the world’s first commercial application of high temperature pressure leaching of chalcopyrite concentrate was at Baghdad in 2003.

Last year Morenci copper production reached 16.5 thousand tons (33 million pounds) concentrate; 391.3 thousand tons (782.6 million pounds) electrowin; for a total of 407.8 thousands tons (815.6 million pounds) of product.

A number of companies and organizations are active in the development and implementation of new concentrate leaching technology for copper, but “it’s fair to say we’re at the forefront of development and implementation of this technology,”Marsden added. “It is important to stress that this technology is site specific, and not a universal replacement for smelting globally. It has to provide a good fit with an application and the technology must be integrated into the site; however, we see it as a very important step change for the copper industry.”

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