Science: Strategic Metal No. 1

Science moved the U.S. closer to wartime self-sufficiency last week in the vital, imported metal manganese. Grey-white and brittle, manganese is a steelmaker’s necessity—paradoxically, to make their steel less brittle.

The U.S. has abundant manganese deposits, but nearly all of them are low-grade and many of them contain the mineral in the wrong form for easy separation: manganese dioxide. But two new processes developed by the U.S. Bureau of Mines are on the point of making low-grade manganese oxide ore a useful citizen of steel metallurgy. Last week in three new pilot plants at Boulder City, Nev., where oxide ore beds adjoin Boulder Dam’s cheap electricity, manganese’s first citizenship papers were being signed.

Seldom has the U.S. produced more than 1% of its manganese needs. High point was a war-inspired 300,000 tons in 1918, chiefly from now run-down oxide beds in Colorado. By 1934 ore production shriveled to 853 tons. It is now about 100,000 tons—10% of a year’s needs—mostly turned out from carbonate by an Anaconda Copper subsidiary in Butte, Mont.

Biggest foreign supplier (25% in 1940) has been Russia. Last month the Nazis captured the Nikopol manganese beds in the Ukraine, but the blockade has cut off Russian shipments anyway. Except for Cuba’s 10% contribution, most other U.S. manganese supplies come by long, dangerous hauls from the Gold Coast, South Africa, India, Brazil. Federal stockpile builders have accumulated enough warehoused manganese (some 2,000,000 tons) to last for two years of arms-making—but nobody knows how much will be needed before the war is over.

U.S. manganese carbonate ores, such as Montana’s, assay a mere 20-27% (as against 50% for imported ores), but they are easy enough to concentrate by methods developed soon after World War I. But low-grade oxide ores, like Nevada’s, evaded all ordinary flotation methods until the Bureau of Mines men hit on a new scheme: flotation in reverse with a new solvent.

In the flotation process, ores are first ground to powder and mixed with a frother. This is an oil or an acid which attaches itself to some powder particles but not to others. Then the ores are dumped into water and stirred (usually by compressed air).

In flotation of manganese carbonate, the sandy wastes sink and the desirable minerals float and are skimmed off. But this didn’t work with the oxide, so new reagents had to be developed which have an affinity for the wastes rather than for the minerals. Now the wastes are floated off, and the manganese oxide collects in fairly pure form in the bottom.

An additional process, now being perfected at Boulder City, is electrolysis. The oxide is put in water with a solvent and a current is passed through the solution. The metallic part of the dissolved compound becomes a positive ion which migrates to and accumulates on the negative electrode.

Manganese is used in small amounts by the copper, glass and dry-cell battery industries; but steel uses most of it; about 13 Ib. per ton. Its function in steelmaking is to collect the stray traces of sulfur which all carbon steels contain. The sulfur tends to combine with the iron to make iron sulfide, which collects in films among the crystals of hardening steel, prevents cohesion, makes it brittle, so that it cannot be forged and rolled. Manganese takes the sulfur away from the iron and the manganous sulfide which is formed collects in small globules throughout the metal without weakening it.

Bureau of Mines officials last week felt that their new reverse flotation and electrolytic processes promised to remove manganese from the list of U.S. wartime worries. But, they observed, only months of pilot plant operations will show whether low-grade U.S. manganese ores can compete in a peaceful, free-trading world with foreign ores which need neither concentrating nor refining.