Montana Earth Science Picture of the Week

Slag piled high in East Helena

If you've traveled through East Helena, you probably noticed the huge pile of black material at the ASARCO Smelter along the highway. The material, called "slag", is waste product produced as ASARCO removed lead from the ore.

Getting the lead out . . .
For more than a century, crushed ores containing galena (PbS) were brought to East Helena from as far away as Chile and Korea. Once at the smelter, the ores were "roasted" in order to remove the sulfur. The sulfur combined with oxygen to form a gas called sulfur dioxide, a pollutant that contributes to acid rain. A law called the Clean Air Act, which went into effect in the early 1970s, required that industries like the smelter remove this emission. A pollution-control device called a "scrubber" had to be installed to do this.

The roasting formed a material called "sinter," which was a mixture of lead oxide (PbO) and other rock materials. Next the sinter had to be melted. Crushed limestone and quartz were added to make it easier to melt the mixture. Once the material was melted, the heaviest stuff (lead) would sink to the bottom of the tank. The molten lead was then drained out through openings in the bottom into molds where it solidified.

Separation by melting . . .
This separation by melting is called smelting. The rest of the molten material, which had been floating above the layer of lead, also solidified, forming the black waste product called slag. For years the slag was disposed of by dumping it along the edge of the smelter property.

Other metals too . . .
Until its closure in the spring of 2001, the ASARCO Smelter shipped 10-ton pieces of lead by rail to a refinery back east. The refinery was able to separate trace amounts of other valuable metals such as gold and silver. In a typical year (early 1990s) the smelter's bullion yielded the following:

69,000 tons of lead
3,500 tons of copper
690 tons of arsenic
150 tons of bismuth
20,000,000 oz. of silver
200,000 oz. of gold

Anaconda also has piles of slag . . .
The smelter in Anaconda was designed to extract copper from the ores mined in Butte. The texture of Anaconda's slag (CLICK HERE to see aerial photo.) is much different than the slag in East Helena. East Helena's slag is very "blocky," with pieces varying from fist-size to much larger. In Anaconda the slag is more like sand because the molten slag was spilled into water, causing it to harden and shatter into sand-sized pieces. In fact Anaconda's slag has been used in sand traps at the famous Old Works Golf Course.

Trivia . . .
Country Music Hall of Fame singer, Charlie Pride, once worked at East Helena's smelter and starred on the Smelterite baseball team.

Below: A closer view of the slag (looking toward Helena)

Below: A view from the south (looking over the Helena Valley)

Terms: ore, flux


*East Helena is now a Superfund Site
*East Helena gets cleaned up
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By Rod Benson
Earth Science Teacher at Helena High School

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