ZINC DIVISION: Where There is Zinc, There is Lead: The Brunswick Smelter

What is a lead smelter doing in a “zinc” business unit? The idea is not so far-fetched when one considers that lead and zinc mineralization are usually found in the same deposits. Noranda built its lead smelter at Belledune, N.B., to complement production from the Bathurst mine, 60 km away.

Located on a year-round port, the smelter accepts as feed lead-precious metals concentrates, secondary materials, lead-acid batteries, and recyclable materials that are environmentally sensitive. It produces refined lead, custom lead alloys, precious metals dor, and sulphuric acid. The dor is further refined at CCR in Montreal.

The Brunswick smelter strives to be the cleanest and most productive of such facilities in the world. It sets the world standard when it comes to employee health and hygiene, and has the lowest ‘lead in blood’ levels of any primary lead smelter. Sulphur from the feed is captured and turned into sulphuric acid sold to several industries. Effluent is treated and other potential sources of pollution controlled.

The Brunswick smelter relies on conventional processing. Lead-containing feed is mixed with limestone and sand, and then sintered. Sintering drives off the sulphur from the feed creating SO2 gas, which passes though the acid plant to make H2SO4 acid. The blast furnace is top-charged with a mixture of sinter and coke. Oxygen-enriched air is blown into the bottom of the furnace, and as material drops down through it, temperatures of 1,250C are reached in the smelting zone at the bottom. Iron-rich slag is drawn off and granulated by high-pressure water. Lead bullion is tapped and sent to the refinery.

The lead refinery consists of a series of 21 kettles. As the bullion passes through them, trace elements such as bismuth and antimony are removed. High-silver dross is drawn off the seventh kettle and sent to the silver refinery. Refined lead is cast into 25-kg ingots or 1,100-kg jumbos. These shapes may consist of high purity lead (99.99%), pure lead (99.97%) or any of a number of custom lead alloys. Besides silver dor, Pb-Bi alloy, antimony bullion, copper matte, and copper speiss are produced as co-products. Products are sent to customers by rail, ship or truck.

The silver plant was modernized last year so that the smelter could handle more complex feeds. Capacity was increased to 450 tonnes per year from 250 tonnes. Improvements in safety, hygiene and environmental performance were made at the same time.

To begin, silver and gold are removed from lead bullion using the Parkes process, adding zinc to form intermetallic compounds. These crystalline compounds rise to the surface where they are drawn off and cast into blocks of crust. The crust is melted to remove lead, and passed through a vacuum induction retort to remove zinc. Then the metal is treated in a bottom-blown oxygen cupel to remove copper and traces of lead. The bullion recovered contains 99.3% Ag, 0.20% Au and tiny amounts of lead and copper. The silver bullion is shipped to CCR for final refining.

Recycling forms a growing portion of the Brunswick smelter’s throughput. Feeds not suitable for sintering and blast furnace treatment are sent to a pair of short rotary furnaces. These furnaces produce a semi-refined lead bullion, which may be returned to the supplier, sold to a third party, or further purified in the lead refinery.

Knowing that the largest market for lead is the automotive battery industry, the Brunswick smelter includes a lead-acid battery recycling circuit, installed in 1996. Virtually all scrap batteries available in the Maritimes, 10,000 tonnes per year, pass through this plant. They are crushed and washed to separate the plastic and metal. The plastic is dried and shipped to recyclers. Lead is treated according to its form. Lead paste is included in feed for the sintering plant. Lead parts are melted in the short rotary furnaces and cast into 2,000-kg blocks of battery plate bullion. The battery acid is diluted by the wash water, but it still has enough strength to fill the needs of the effluent treatment plant.

On-Going Commitment to Excellence

“If you want a thumbnail sketch, the zinc business is historically a very tough, competitive business. We are a low cost producer, but that’s not adequate in tomorrow’s world,” Jones told CMJ. “Our objective is to double our profitability. And that will mean new thinking.”

The application of new thinking has made Noranda’s zinc business a world leader. In every aspect the company has proved its excellence. No one can doubt that tomorrow’s gains belong to this forward-thinking and innovative Canadian enterprise.