COPPER DIVISION: Horne Smelter

Three flags on poles in front of the Horne smelter office building announce the nationality of the visitors to the smelter each day, and they are ever-changing. Customers and vendors are constantly dropping by to see how this unique smelter treats complex concentrate and recycled copper- and precious-metal-bearing materials, or to the check out the world’s first installations of the innovative smelter furnaces: the Noranda reactor and the Noranda converter.

A quarter century ago, the Horne copper-gold mine closed in Rouyn-Noranda, northwest Quebec, leaving behind an out-of-date smelter with a small custom feed operation. The Horne smelter today is a very modern, 100%-custom smelter, and is the world’s largest processor of precious metals recyclables, with 850 employees.

“Technically we have become world-class in terms of flexibility and being able to treat a wide variety of materials, physically and chemically,” says Mario Chapados, general manager of the smelter. The innovative technologies that have allowed this are concentrate injection (introduced in 1991) and continuous smelting in the Noranda reactor (started up in 1973). The acid plant (built in 1989) and the Noranda converter (commissioned in 1998) have caused big environmental gains.

Feed and Function

The Horne smelter has a base annual feed of 400,000 tonnes of “green concentrate” (low impurity levels). This is drawn mainly from the Louvicourt Cu-Zn-Au mine and other base metal producers in northwest Quebec as well as imported feeds from Europe and elsewhere. The recycling business provides about 100,000 tonnes of the feed, but a larger amount of the value because of its precious metal content. About 350,000 tonnes comes from complex mine concentrates, ores and reverts.

Senior metallurgist Yves Prvost gave CMJ a tour of the operations in April.

There have been many changes to Horne this decade, including the retirement of all the reverberatory furnaces. Most of the feed is routed through the $30-million Noranda reactor, which was built to handle 800 tonnes but now receives 3,200 tonnes of material per day. The reactor has three main advantages: very high energy efficiency, the ability to handle a great variety of feed compositions and physical characteristics, and a high level of precious metal recovery.

Over 85% of the feed (all of the recycled materials and some of the concentrate) is introduced into the 21.3-m-long x 5.1-m-diameter reactor. There the charge is heated to 1,250C and injected with oxygen-enriched air to produce a copper matte containing 72-75% Cu. The matte from the reactor is tapped into ladles and sent to the Noranda converter and the four Pierce-Smith converters. The SO2 off-gas is sent to the acid plant.

Up to 15% of the concentrate feed can be treated by concentrate injection: the concentrate is dried and injected directly into the Pierce-Smith converters through tuyeres, bypassing the reactor.

The $53-million Noranda converter is a cylindrical furnace 4.5 metres in diameter and almost 20 metres long. It works on a semi-continuous basis, maintaining liquid in fusion at a temperature of 1,225C. The converter produces a semi-blister containing 97.5% Cu and fixes virtually all the remaining sulphur. It has the advantages of highly effective sulphur fixation, flexibility and low operating costs. The Noranda converter will soon replace the Pierce-Smith converters.

Three oxygen plants supply the 730 tonnes of oxygen used each day by the reactor and converters.

Molten matte from the reactor and semi-blister copper from the Noranda converter is sent to the Pierce-Smith converters, operating at 1,200C for several cycles of air injection and slag-skimming to produce 98%-pure blister copper containing precious metals. Soda and lime are injected to eliminate impurities (such as antimony and arsenic) in the slag, which is recycled to the reactor.

The blister is refined in the anode furnaces for purification to 99.1% Cu, before being cast to form 300-kg copper anodes. These are cooled and then sent by rail and truck to the CCR refinery in Montreal East.

Slag from the reactor and the converters is sent to the concentrator to recover the copper. This concentrate is fed back into the reactor, and the slag tails go to the tailings pond.

The acid plant production is currently 525,000 tonnes sulphuric acid per year, and comprises the largest gas-cleaning installation of any acid plant in the world. The acid is shipped via rail to market.

Environmental Improvements

Mining operations have been generating tailings around the Horne since 1929. The 70 million tonnes of tails-mostly sulphide plus some slag-are stored in seven sites, all of which have been completely or partially reclaimed.

“Noranda is a leader in tailings reclamation and acid mine drainage control,” says Peter Godbehere, superintendent of business development. “Every plant is obliged to have a very good environmental management system in place. Over the last year we have been over 99% in compliance in our tailings areas. We have incorporated two acid mine drainage streams into the Horne’s water treatment plant, so we can use the metals in solution as reagents to treat effluent from the acid plant,” says Godbehere.

Much effort has gone into reducing the environmental effect of the smelter’s operation. “The Noranda converter is allowing us to fix more sulphur,” says Chapados. “Last year we fixed about 78% sulphur, and we reduced dust emissions by 30% compared with the previous year. By the end of 2002 we expect to fix more than 90% of the sulphur and to reduce the particulate emissions by 60% of present levels. We will invest about $30 million in the next two years to achieve this: to increase the capacity of the acid plant and to modify the Pierce-Smith converters to capture more sulphur dioxide and particulates.”

Despite improvements, the smelter still depends on the markets. “The last couple of years we have been in a trough of treatment charges and metal prices,” says Godbehere, “but there’s always a cycle-we have to be there for the better periods.”