In 1973, the Freeport-McMoRan Copper and Gold ("Freeport") smelter at Miami, Arizona, installed a 51 MW electric furnace at its Miami smelter. The decision was based on a long-term electrical power contract with the Salt River Project that provided the company with a very low rate for electricity. This contract expired in 1990 and the resulting increase in electricity prices prompted the owners of the smelter, Cyprus Miami Mining Corporation ("Cyprus"), to seek alternative smelting technologies for lower operating costs.
The technologies evaluated included:
* Contop flame cyclone reactor
* Inco flash furnace
* ISASMELT
* Mitsubishi furnace
* Noranda reactor
* Outokumpu flash furnace
* Teniente furnace.
The Contop, Inco, Mitsubishi and Outokumpu processes "were all eliminated primarily because of their high dust levels, high capital costs and poor adaptability to the existing facility". The Teniente converter was ruled out because it required the use of the electric furnace for partial smelting. The Noranda reactor was not selected "because of its high refractory wear and its poor adaptability to the existing plant due to the handling of the reactor slag". ISASMELT was chosen as the preferred technology and a licence agreement was signed with MIM in October 1990. The major factor in the decision to select the ISASMELT technology was the ability to fit it into the existing plant and to maximise the use of existing equipment and infrastructure, while the major disadvantage was seen to be the risks associated with scaling up the technology from the Mount Isa demonstration plant.
The Miami copper ISASMELT furnace was designed to treat 590,000 t/y (650,000 short tons per year) of copper concentrate, a treatment rate that was constrained by the capacity of the sulfuric acid plant used to capture the sulfur dioxide from the smelter's waste gases. The existing electric furnace was converted from smelting duties to a slag cleaning furnace and providing matte surge capacity for the converters. The ISASMELT furnace was commissioned on 11 June 1992 and in 2002 treated over 700,000 t/y of concentrate. The modernisation of the Miami smelter cost an estimated US$95 million.
In 1993, the Cyprus Minerals Company merged with AMAX to form the Cyprus Amax Minerals company, which was in turn taken over by the Phelps Dodge Corporation in late 1999. After the take-over, Phelps Dodge closed its Hidalgo and Chino smelters. Phelps Dodge was acquired by Freeport in 2006.
The Miami smelter is one of only two remaining operating copper smelters in the United States, down from 16 in 1979.