150 years of the Periodic table

2019 marks the sesquicentennial of Dmitri Mendeleev’s Periodic Table of the elements, which was not just an effective organizational scheme based on the atomic nature of the elements, but also a predictive tool regarding elements that had not yet been discovered in 1869.

The validity of the Table was proven in 1875. Mendeleev had predicted the existence of several elements, including one he called eka-aluminum. “Eka” is Sanskrit for “one,” thus meaning the unknown element would be one period down from aluminum. French chemist Paul Emile Lecoq de Boisbaudran identified a new element spectroscopically (as Mendeleev had foretold) in a sample of the mineral sphalerite (zinc sulfide). He named Element 31 gallium for his native France (Gallia in Latin) in 1875.

Mendeleev’s predictive table even allowed him to estimate properties of the unknown elements. When de Boisbaudran reported eka-aluminum/gallium’s density as 4.7 grams per cubic centimeter, Mendeleev suggested to him that he should recalculate it. When the new measurement was made, gallium’s density was found to be 5.9 g/cc, almost exactly as Mendeleev predicted several years earlier on theoretical grounds alone. Today the density of gallium is taken as 5.904 g/cc.

As described in my book What Things Are Made Of, gallium is used in tiny but critical amounts in solid-state semi-conductors in lots of high-tech devices, from computers and radios to cell phones and televisions. Gallium also finds its way into wireless technology infrastructure, integrated circuits, LED manufacture, and solar cells.

As it was when it was discovered, gallium today is found mostly in zinc and aluminum minerals and is produced by refining those ores, which are dominantly sphalerite for zinc and bauxite for aluminum. There’s typically only 50 parts per million or less gallium in such ores, but refineries can often separate it economically. In terms of crustal abundance, gallium is about the same as lead – but while lead easily forms common minerals that can be exploited economically, gallium’s properties mean that the few minerals it forms are extraordinarily rare. Instead, gallium gets incorporated into the structures of those zinc and aluminum compounds.

The United States is 100% dependent on imports for gallium, mainly from China (32%), United Kingdom (28%), Germany (15%) and Ukraine (14%). China is overwhelmingly the 600-pound-gorilla in terms of gallium, with more than 95% of total world production.

The sphalerite in this photo probably has some gallium in it, a few molecules at least, but I haven’t had it analyzed. The mineralization is hosted in limestones and cherty rocks of Mississippian age, deposited about 345 million years ago. The mineralization came in at some later time.

—Richard I. Gibson

Episode 369: Gallium

On my What Things Are Made of blog, by far the most popular post is one on the element gallium. I don’t know why this is so, unless there are a lot of middle schools assigning homework on gallium. So I thought I’d update that post here for the podcast.

Gallium is an element isolated in 1875 by French chemist Paul Lecoq de Boisbaudran, who named it for his native France or Gaul, Gallia in Latin. It proved the predictive validity of Mendeleyev’s then new Periodic Table of the Elements, in which Mendeleyev had predicted the element in 1870. Gallium is extremely rare in terms of gallium minerals. There’s one, gallite, a copper gallium sulfide, but most gallium occurs as traces in other minerals, and most of it is recovered during processing of aluminum and zinc ores, bauxite and sphalerite, where it can occur at up to 50 parts per million. Not much, but enough to be economically recoverable.

So what? Well, virtually every American uses gallium virtually every day. Not much, but it’s critical in things like semi-conductors and integrated circuits in computers and televisions, cell phones, LEDs in street lights, solar panels, and more. About three-quarters of the gallium used in the United States goes to integrated circuits in the forms of gallium arsenide and gallium nitride. Most of the rest is in devices such as lasers, LEDs, telecommunications, and solar cells. Gallium has also been used as an additive to ski wax, where it helps reduce friction on the surface.

The United States hasn’t produced gallium since 1987, so it’s entirely dependent on imports. As with many mineral products, China is the world leader in gallium production with about 80% of the total, and they’ve really ramped up their production in recent years, leading to a decline in the price of gallium from almost $700 per kilogram in 2011 to $240 per kilogram in September 2014. Even though supply increased by 26% in 2014 over 2013, so did demand, especially as Asia increases its electronics usage. An increasing use for gallium is in thin-film solar cells, made with copper-indium-gallium diselenide, an alloy with photoelectric properties.

About a third of U.S. imports come from metal refineries in Germany, with another quarter from the U.K. and the same amount from China. Ukraine provides about 6% of U.S. gallium. Total U.S. consumption is about 40,000 kilograms a year, or about 88,000 pounds. Not much compared to, say, almost a million tons of zinc the U.S. consumes annually – but as I suggested earlier, gallium is pretty critical to the modern American lifestyle.

—Richard I. Gibson

Resource: USGS Mineral Commodities Summary – Gallium