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,
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
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.”