“Alumina” Demystified: Hungary Is Awash in Liquid Rubies

Did I miss some episode of Schoolhouse Rock about metallurgy when I was growing up? In the coverage of this week’s Hungarian sludge disaster, reports keep saying that the caustic red material is waste from a plant refining “alumina.”

And what is alumina? It is the stuff the plant was refining.

Far down in one of its mud-spill stories , the New York Times cited the Aluminum Association describing it as “the basic material for manufacturing aluminum.” “Basic” here seems to mean “elementary,” rather than “having a high pH,” (though the sludge did have a scarily high pH). But what is more elementary than an element? Aluminum is aluminum, No. 13* on your periodic table.

Alumina, for a news audience that’s not in the metals trade, is aluminum oxide . Here’s a case where two words are less confusing than one. Two aluminum atoms, three oxygen atoms. In one of its crystalline forms, it makes rubies and sapphires . Or sandpaper. When refined from bauxite ore, according to Alcoa’s website, it is “a white granular material, a little finer than table salt.” That material can be smelted into metal.

But it can also be used for other things. The industry blog MetalMiner reports that the Hungarian plant was not producing raw materials for your soda can or iPad case, but alumina products that would be ingredients in other industrial chemical processes:

This is not, nowadays anyway, a plant for producing alumina for aluminum smelting.

MetalMiner also has a breakdown of the composition of a similar sludge from a Turkish plant*. Mostly it is iron oxide—hence the red color—aluminum oxide, and silica, but, despite its official nontoxic status, there are plenty of less pleasant chemicals in there:

More disturbingly the report goes on to say the waste can contain thorium and uranium and confirms it can be highly caustic. The majority of the constituents are relatively harmless, iron oxide, aluminum oxide, silica and sodium, titanium and calcium oxides. It’s the minor constituents and caustic ph of this sludge that could prove to be the most dangerous contaminants.

* Corrections: I initially wrote that the breakdown was of the Hungarian sludge, and put aluminum one box out of place on the periodic table.