Earlier in this series, we made the case for copper being “the metal that built technology.” Some readers took issue with that statement, noting correctly that meteoric iron and gold were worked long before our ancestors were able to locate and exploit natural copper outcroppings, therefore beating copper to the historical punch. That seems to miss the point, though; figuring out how to fashion gold decorations and iron trinkets doesn’t seem like building the foundations for industry. Learning to make tools from copper, either pure or alloyed with tin to make bronze? Now that’s how you build an industrial base.
So now comes the time for us to make the case for our most recent addition to humanity’s stable of industrial metals: titanium. Despite having been discovered in 1791, titanium remained locked away inside abundantly distributed ores until the 1940s, when the technological demands of a World War coupled with a growing chemical prowess and command of sufficient energy allowed us to finally wrest the “element of the gods” from its minerals. The suddenness of it all is breathtaking, too; in 1945, titanium was still a fantastically expensive laboratory oddity, but just a decade later, we were producing it by the (still very expensive) ton and building an entirely new aerospace industry around the metal.
In this installment of “Mining and Refining,” we’ll take a look at titanium and see why it took us over 11,000 years to figure out how to put it to work for us.
Starting With Sand
For something that has been commercially exploited for less than a century, titanium is surprisingly abundant. It’s the ninth most abundant element in Earth’s crust, making up more than half a percent by mass. Titanium is never found in the metallic state in nature, but rather as oxides like titanium dioxide (TiO2), and as such is widely distributed around the world.
The chief mineral ores of titanium are rutile and ilmenite. Rutile is basically pure TiO2 in crystal form that occurs in many types of rocks including quartz, gneiss, and schist. Ilmenite is a titanium oxide complexed with iron (FeTiO3), and while sometimes found in its pure form, it’s more often found mixed with manganese and magnesium. Ilmenite is mostly found in heavy mineral sands that have weathered out of solid rock deposits, which has the effect of making it relatively easy to harvest using standard open-cast mining techniques.
There are large ilmenite deposits in South Africa, Australia, Canada, China, and Ukraine. Commercially viable rutile deposits are harder to come by, with most of the mineral coming from Australia, countries around the southern tip of Africa, and Ukraine. Something like 80% of the world’s supply of titanium comes from ilmenite, with a mere 5% sourced from rutile; the rest comes from “titaniferous slags,” which are essentially iron- and titanium-containing waste products from titanium refining processes.
Like aluminum, titanium is an element that forms thermally and chemically stable oxides, so liberating it from its minerals is a complex and energy-intensive process. Processing begins with mining, which for certain ilmenite deposits can be as simple as scooping up sand with loaders or eroding it with high-pressure water and pumping up the resulting slurry. Rutile is also sometimes recovered directly from weathered sands, but when either mineral occurs embedded in other rocks, more extreme measures such as blasting and crushing may be required to get the ore into grains fine enough to be conveniently moved around the processing plant.
Concentration of the ore and removal of non-ore material (gangue) and other valuable minerals come next. Ore feedstocks with a lot of iron in them, such as ilmenite, undergo a magnetic separation step, with powerful spinning magnets that remove magnetic particles from ground ore carried by a conveyor belt. Electrostatic separation, where electrostatically charged ore particles pass through strong electric fields to remove titanium oxide particles from gangue, is also used. Spiral concentrators, which are also used in graphite refining, are often used to separate the dense gangue particles in an ore slurry from less dense titanium oxides.
Source: Hackaday
