chemistry

Chemistry Rocks Webinar

chemistryrocksacs

The American Chemical Society is hosting a live webinar called “Chemistry Rocks! – Exploring the Chemistry of Rocks and Minerals” on Tue, Oct 24, 2017 from 6:00 PM – 7:00 PM CDT. We are surrounded by rocks and minerals everywhere…in the ground we walk on, the places we work and live, and even in the food we eat. How are chemists experimenting with these fundamental materials to help the world and make our lives better? Ask questions live to the experts regarding the amazing work that is being done in rock and mineral science.

To see the webinar, sign up at GoToWebinar and fill out the form. They will send you an email to confirm. Then, on Tuesday at 6PM Central Time, follow the link in the email, make sure you have your computer’s sound turned on, and enjoy!

Chemistry in Mining

During Earth Science WeekTM, we went to a lecture by Dr. Innocent Pumure from UCM called “Sonochemical Extraction of Arsenic and Selenium from Pulverized Rocks Associated with Mountaintop Removal Valley Fill (MTR/VF) Method of Coal Mining”.

You may be wondering, what is Mountaintop Removal Valley Fill Mining? First, the excavation company blows up (or strips) the top part of the mountain to remove vegetation and expose the coal seams. The coal seams are then mined through the open cast/strip method, and the extra rock and soil is dumped in nearby valleys called valley fills. It is cheaper and easier to do than regular mining, where they dig a vertical shaft down and do everything through the tunnel, but it blasts the mountain apart and looks ugly. Since 30% of electricity in the USA comes from coal, valley fill mining is still pretty popular.

In 2002, the EPA found too much selenium downstream of a certain mine in West Virginia (we’re not going to say which one). It was over 5 ng/mL, which was the limit back then.[*] 7 years later, there was still an active mine there and the water still had too much selenium. Even worse, the surrounding sediment had 10.7 mg/kg selenium. This could cause problems for the environment later. Due to bioaccumulation, you could say once it’s in there, it’s really in there.

So now we get to the topic of Dr. Pumure’s talk, in which he and his colleagues discovered a way to quickly find out how much selenium and arsenic were in the ground around this mine in West Virginia. When you do a chemical analysis, you usually have to break down the samples in order to measure what is in them. One method to do this would be to take some core samples and do an acid extraction, but that takes a long time and uses a lot of reagents. Sonochemical extraction uses ultrasound energy to accelerate the leaching process that would naturally happen as rocks become weathered. Since it is ultrasound, it does not directly touch the sample, is minimally invasive, and does not need any reagents except water.

Next, he explained the methodology, which means a description of exactly how they did it in the lab: the size of the extraction cells, how much water and power were used (200W/cm3), how long the samples were sonicated, and all the other pertinent information for chemists. Pumure actually spent quite a lot of time finding out the optimal sonicating time to get the best extraction. It turned out the best times for his sample sizes were 20 minutes for Se and 25 minutes for As. That’s really fast![**] Then, he did a comparison to a chemical sequential extraction to make sure that the sonochemical extraction method was getting everything. To summarize, yes it was. Finally, he did a principal component analysis of core samples from different places all over the mountain using this same technique. They found some really interesting trends and correlations, for example, it appears that there is more arsenic in illite clay than other types of clay.

This research has many useful applications. If you were running a mine, you could take samples more frequently to see if your mine is polluting the surrounding environment, and then you could do something about it before the EPA finds out. The method could probably be used for other analytes, too. For other research needs, you could now quickly analyze large batches of mineral samples to get lots of data that would otherwise be too expensive or time consuming to obtain.

[*]The EPA has since lowered the limit and now it is 3.1 ng/mL.
[**]For comparison, some of my colleagues do chemical extractions that take 2 days.

Minerals in Fireworks

The 4th of July fireworks that we saw last night would not be possible without minerals. Fireworks mainly contain gunpowder, which is a combination of charcoal, sulfur, and the mineral potassium nitrate. In order to create the pretty colors we are used to seeing in fireworks, mineral salts are added. This infographic from Compound Interest explains which mineral salts create which colors. If you go to the website, you can read a lot more about the chemistry of fireworks and a brief explanation of why different minerals make different colored flames.

I learned that blue fireworks are very difficult to produce because copper chloride breaks down at high temperatures, so they have to somehow keep the temperature hot enough to ignite but not so hot that the blue color vanishes. Thus, you almost never see purple fireworks because it is a combination of red and blue.

Andradite Garnet
andradite garnet

Credit: Aaron Palke/Gemological Institute of America

Since it’s January, it’s a good time to read about this garnet originally posted by Chemistry in Pictures.

“This gemstone isn’t pure andradite garnet [Ca₃Fe₂(SiO₄)₃], but its flaws produce its mesmerizing colors. Some gemologists think that this rainbow explosion arises because the garnet’s different elements aren’t regularly spaced from the core of the gemstone to the outside. For example, in some regions, aluminum atoms might have worked their way into the structure and replaced the iron atoms. These irregularities create mismatched sheets of atoms that then bend and stretch. This makes the stone birefringent, meaning that light travels through it at two different speeds. Under cross-polarized lighting conditions, rays of light that enter get misaligned by the time they exit, so they then interfere with each other and highlight some colors in certain spots, producing the spectrum seen here. The black flecks are tiny pieces of magnetite that were enveloped by the crystal as it grew.”

Chemical Composition of Gemstones

Here’s a neat infographic from Compound Interest (one of my favorite websites) that describes 16 different gemstones and why they have different colors. It also includes their chemical formulas and hardness on the Mohs scale.

Many gemstones would be colorless or a different color if not for the presence of small amounts of transition metals such as chromium or titanium. For example, you can see that aquamarine and emerald both have the same chemical formula Be3Al2(SiO3)6, but emeralds are green because of chromium ions replacing some of the aluminum ions and aquamarines are blue because of iron 2+ or 3+ ions replacing some of the aluminum ions. Click through to read the whole article, because there are many other ways that gems and minerals get their colors!

What color were the dinosaurs?
A dinosaur fossil of anchiomis huxleyi

Johan Lindgren/Sci. Rep.

In this article from Chemical & Engineering News, researchers use chemistry to find out what colors the dinosaurs were.

Researchers led by Johan Lindgren of Lund University, in Sweden, used a battery of analytical techniques to scrutinize the molecular makeup of a fossilized Anchiornis huxleyi specimen. This dinosaur is a distant relative of today’s birds, and its remnants were preserved for about 150 million years in what is now northeastern China.

The researchers’ thorough analyses have allowed them to conclude that some of the dinosaur’s melanin, or pigment molecules, and melanin-producing organelles have also survived the intervening epochs (Sci. Rep. 2015, DOI: 10.1038/srep13520).

Scientists have previously observed signs of similar biomaterials in fossils, but studies have lacked sufficient evidence to rule out the idea that these materials come from bacteria or other microbial intruders.

Using methods including infrared spectroscopy and time-of-flight secondary ion mass spectrometry, Lindgren and his colleagues have shown that the sample’s fossilized feathers contain substances that closely resemble modern animal—not bacterial—eumelanin, the pigments responsible for brown and black coloration.

Click here to read the whole article.