Cadmium: batteries, TVs, plastics

Greenockite from Tsumeb, Namibia. 

Nobody mines cadmium. It comes from metal refineries, mostly zinc processors, where it is recovered as a trace component. It’s toxic, and not much goes a long way—only about 228 tons in the US in 2009 (down from 700 tons in 2005), with nickel-cadmium batteries (NiCd) leading the way. As lithium ion batteries, with greater energy density, take over in many small devices, NiCd batteries have declined in use, but they may return as storage batteries for on-grid solar energy systems that store electricity during the day and make it available at night.

China produces about a quarter of the world’s cadmium, and while the US is a net exporter, it ranks #9 in world cadmium production with about 4% of the total. A lot of US cadmium is exported to Asia where batteries are made.

Cadmium’s minor uses include photovoltaic devices such as photocopiers, where cadmium sulfide coats drums. Traditional uses include yellow, orange, and red pigments: yellow no-passing stripes on highways once contained cadmium. It also stabilizes plastics, makes lasers, and in phosphors gave the bluish tint to black-and-white TV sets in the 1950s. Cadmium was also once a low-melting component of solder and Wood’s metal—an alloy of bismuth, lead, tin, and cadmium sometimes used in the fusible valves found in automatic sprinkler systems. Wood’s metal melts at 158°F; when fires reach that temperature, the metal melts to open the valve, allowing water to flow.

The only noteworthy cadmium mineral is greenockite, cadmium sulfide, which forms pretty honey-colored crystals shaped like hexagonal barrels.

Photo by Christian Rewitzer, via Wikipedia under creative commons license.

Barite helps find oil

Barite roses from Kansas. R.I. Gibson photo.

Barite is a fairly common mineral, barium sulfate, frequently represented in collections. Its noticeably high specific gravity, 4.5, together with interesting crystals and occasional fluorescence make it popular with mineral collectors. Iron-bearing red sand incorporated into its crystalline aggregates makes barite roses, the state rock of Oklahoma. Gypsum crystals with sand in their matrix make similar “desert roses.”

From 2005 through 2008, the US consumed more than three million tons of barite each year. This volume fell to under two million in 2009 thanks to the recession and its impact on oil and gas consumption because 95% of all the barite used goes into drilling fluids for oil and gas wells. Barite’s density helps control high subsurface pressures.

Barite finds its way into many other uses, volumetrically smaller than oil and gas drilling but more directly pertinent to consumers. It helps protect metal in brake linings and adds gloss to automobile paint. Truck mud flaps, auto tires, home carpet backings, and playing cards include barite for weight, strength, and stiffness.

As a radiation blocker, barite shields x-ray machines and nuclear reactors, and creates the x-ray-opaque contrast medium for intestinal soft-tissue scans. A use that is declining as flat-panel technology expands is in the glass of cathode-ray tubes, where barium carbonate reduces radiation from old-style televisions and computer monitors.

About 80% of US barite is imported, virtually all of it (93%) from China, world leader with more than half the production (India is #2 with about 15%). The 20% of US consumption mined domestically is mostly from Nevada; the US industry employs about 330 workers in a $20 million business, representing about 7% of the world’s barite.

Photo: Barite roses from Kansas. Photo by Richard Gibson. 

Arsenic

Orpiment (arsenic sulfide)

Arsenic is Bad Stuff. It may have contributed to Napoleon’s death (accidentally or otherwise) and its presence in water supplies is an ongoing concern. For many years the wood treatment industry in the US consumed most of the arsenic used here, because it is an excellent preservative and insecticide. But toxicity issues led the industry to voluntarily cease using chromated copper arsenate for human-contact lumber like decks and picnic tables in 2003. Total US arsenic consumption has fallen from more than 30,000 metric tons in 1998 to 3,600 tons in 2009.

But arsenic finds its way into a lot of other critical but low-volume uses. It strengthens grids in lead-acid batteries, combines with other metals in some ammunition, and is a vital component of semiconductors in solar cells, circuit boards, and telecommunication electronics. Light-emitting diodes (LEDs) in computers, CD players, and numerous other household electronic devices contain gallium arsenide phosphide in tiny amounts. Two pounds of gallium arsenide can make 500,000 LEDs.

There are some arsenic ore minerals, mostly arsenic sulfides like lemon-yellow orpiment and red-orange realgar, but the primary ore is arsenopyrite, iron arsenic sulfide. It is also common in other minerals mined for elements like copper, and arsenic contributes significantly to environmental problems in copper-mining regions.

All US arsenic is imported. 86% of arsenic metal comes to the United States from China, which produces about half the world’s arsenic.

Orpiment photo from USGS via Wikipedia (public domain).

Sapphires

I recently completed an article on Montana sapphires for Distinctly Montana Magazine, focused on beautiful gems from Yogo Gulch. But sapphires have practical uses too.

Because rubies (red) and sapphires (famously blue, but also pink, yellow, green, purple, and even colorless) are nothing more than corundum, aluminum oxide, with some interesting trace elements (mostly titanium and iron), they are very hard—number nine on the Mohs Hardness Scale, second only to diamond. Consequently they find their way into watch and clock bearings, and those that don’t make the cut as gems are sometimes used as high-quality abrasives.

The first lasers, in 1960, used synthetic rubies to focus light into a coherent beam. Solid-state integrated circuits sometimes use sapphires formed into small thin wafers as their insulating substrate. Larger sheets built from synthetic sapphire sometimes make tough windows in armored vehicles, as well as mundane surfaces such as grocery-store barcode scanners where scratch resistance is valued. High quality watches may have sapphire crystal faces in addition to gem-like bearings inside.

Even though Auguste Verneuil invented a process for making synthetic sapphires in 1902, natural sapphires were used for non-jewel applications for decades after that. Today about 250 tons of synthetic sapphires supply the world annually with watch bearings, abrasives, and specialty uses. The US and Russia manufacture most synthetic stones, while Madagascar is the leading gem sapphire producer.

Watch for the article on Montana’s Yogo sapphires in the Summer issue of Distinctly Montana.

Image: The 182-carat Star of Bombay star sapphire, via Wikipedia.