Category Archives: Chemistry

Homestake Mine Visit

2 Replies

The town of Lead, SD, pronounced “leed”, is home to the Homestake gold mine. The mine was purchased and subsequently developed by George Hearst, father of William Randolph Hearst, and partners ca 1876.

Homestake Open Cut from Yates Hoist House

 The photo above shows one ground view of the large open cut found on the north end of town. The pit is approximately 1/2 mile across and 1200 ft in depth from the highest elevation.

The pit exposes the ore body which is comprised of inhomogeneous igneous rock with gold bearing veins. In the photo below the vein structure can be seen. The buff colored rhyolite bands seen below are not associated with value.

Homestake Open Cut, Lead, SD.

Gold was discovered at a surface exposure, called a “lead”, which became the namesake for the town of Lead. Mining activity was halted in 2002, in part due to the low price of gold at the time. By that time the underground workings had reached a depth of 8000 ft, which puts it at ca 3000 ft below sea level. The rock temperature at the 8000 ft level was reported to be 130 degrees F, requiring substantial air conditioning for the workers and equipment.

Hoist Cable

The (poor quality) photo above shows the hoist equipment in the Yates head works. Of interest is the conical cable spool used to provide lift for hoisting operations at the Homestake mine. The purpose of the variable diameter feature of the hoist was to provide maximum mechanical advantage when the cable was at the end of its reach, presumably when it was ready to lift a heavy load of ore from the bottom of the shaft.

Homestake Honey Wagon

The “ore cart” in the photo above was the toilet facility for the miners. It featured a seat on top which could be sealed, a thoughtfully placed foot platform, and railings so the user could hang on for those rough rides.

The surface tour of the mine consists of a trolly ride around town with a stop at the Yates hoist. Warning: It is quite superficial in content, but is the only type of tour available. Our tour guide was student on summer break with near-zero knowledge of the geology or the engineering. He was accustomed to entertaining the barely interested.  If you are keen on the particulars of Homestake history, I recommend Nuggets to Neutrinos, by Steven T. Mitchell.

Homestake was one of the very richest loads of gold in the western hemisphere. Reportedly, some 40 million oz of gold were extracted from the mine.

Today, the Homestake mine is being converted to an underground nuclear physics lab facility under a program called DUSEL. On a side note, it is interesting to listen to the townsfolk talk about the new labs. I could tell they are trying to be enthusiastic, but the reality of neutrinos is very hard to get your arms around.

A bit of sympathy for BP

6 Replies

I can’t help but have some sympathy for the folks at BP just now. They are not the evil empire and despite their poor safety history, say, the recent Texas City refinery explosion, they do in fact rack up a good many safe operating hours doing very hazardous work. They handle and process flammable materials on the gigantic scale.  And, they respond to market pull for petroleum products.

I have been to meetings in their facilities in the UK and discussed new technology platforms that they wanted to bring on stream. I have listen to a few of their scientists describe their technology and marveled at the new things they have found for molecules to do. They are smart, competent, and well meaning people and we should not lose sight of this.

BP helps to provide the petroleum that we use to conduct out busy modern lives.  We gladly consume every bit of their output. In fact, their contribution to the supply picture helps to keep hydrocarbon prices low. The same is true of all the producers.

The now famous spill in the gulf is clearly a bad thing and it happened to them for several reasons.  But consumers have not responded to this in what you might call a philosophical manner. Nobody seems to be jolted into wakefulness by the depth that producers have to drill to find oil or the fact that these guys are resorting to drilling way out on the continental shelf.  We just plug along expecting demanding that they keep producing at the same price.

If the critics of BP can drill better or operate distillation towers or cat crackers better than BP, then they should get off their duffs and do it. Put up or shut up. The chronic condition we are all subject to is the truism that we can do better.  If you think you can be a better driller, then try it. It’s harder than it looks and it doesn’t look easy.

Needlessly invoking clathrates. BP’s underwater ice machine.

1 Reply

In the news reporting on the BP oil spill, there is talk of methane/water forming a special ice composition that defeated the previous attempt to channel oil to the surface.  I think folks are referring to clathrate formation. This ice blocked the flow of petroleum from the concrete structure that was lowered over the well head.

But, here is the deal. Wouldn’t you expect cooling of a compressed gas as it exits the well pipe and into the sea water? Isn’t this just an example of the Joule-Thompson effect?  As the natural gas component of the petroleum discharge exits the pipe, it is going to expand somewhat, even at a one mile depth, and cool the surrounding water. If this occurs in unconfined, open water, the jet of petroleum will entrain water in the flow and be warmed by the continuous flow of heat from the water.

But, if the gas/oil mixture of petroleum is ejected in a confined space that interferes with heat transfer, then one would expect the expansion cooling of the gas phase to predominate and cool the water in the confining space, possibly to the freezing point. Clathrates may be formed, but the simplest explanation is from good old thermodynamics.

Minnesota’s fabulous Cu-Ni-Pt-Pd-Au Nokomis deposit

Leave a reply

A world class non-ferrous mineral deposit in Minnesota is on the cusp of opening.  Duluth Metals, a Canadian mining company, has been engaged since at least 2006 in developing its Nokomis property in northern Minnesota along the north shore of Lake Superior. The magnitude of the find is stunning and Minnesota will eventually be synonymous with non-ferrous metals like copper, nickel, platinum group metals, and Norwegian bachelor farmers.  The Duluth complex is part of the second largest mafic intrusion in the world, second only to the Bushveld complex in South Africa.

Mining people are accustomed to looking at these reports and the accompanying prospectus. But it is interesting for we sheltered, begloved, and begoggled chemists to view the birth of a new mining district from the protected confines of our air conditioned laboratories. Perhaps in a few years Minnesota palladium will catalyze your Suzuki coupling.

BP oil spill. What are the merits of using dispersants?

2 Replies

BP Oil Spill Image, May 4, 2010 (NASA Earth Observatory)

Oil Spill near Mississippi delta. Vegetation, red; Oil, silver. MA 24, 2010. (NASA Earth Observatory photo)

Eventually, BP will find a way to block the discharge of petroleum into the Gulf of Mexico.  And, eventually, the effectiveness of how the relevant parties responded to the incident will be analyzed and findings posted.

I hope that some effort will be put into an analysis of the merits of using dispersants in general and Corexit in particular. What sparks my comment is the finding that considerable subsurface petroleum has been found. This material is evidently close to neutral buoyancy and is drifting with the currents.

Question 1: Is there a connection between the dispersant use and the presence of this subsurface body of petroleum?  

Question 2: What is the desired outcome of dispersant use?  Where did the planners think the petroleum would go?

Question 3: Is there any advantage in encouraging petroleum to remain below the surface, if that is even possible?

At some point, a decision was made to use dispersants on this massive discharge. Is there a scientifically supported rationale for this, or was it palliative treatment intended to mask the surface effects of the release?

Whither Diethyl Ether?

5 Replies

Diethyl ether seems to be in short supply in North America these days. Suppliers have customers under allocation constraints.  Yes Virginia, people still use Et2O in certain kinds of chemical processing. Sometimes Et2O is prized for its solvent effects and sometimes for its volatility. Sometimes the only way to solubilize some  inorganic compounds is as the metal etherate.  Solvent residues in fine chemicals are often a problem and volatile process solvents can be a big help in ameliorating that issue.  You can purchase 5,000 gallon tanker loads of Et2O if the supplier has qualified you. Another reason not to swerve in front of trucks on the highway. 

Part of the problem with Et2O availability is the considerable reduced demand for it these days.  Many companies have banned the use of Et2O on their site for any purpose. It is easy to understand why. The insane vapor pressure and low autodecomposition temperature are problematic for plant safety. The low boiling point of Et2O means that plant utilities can heat a vessel of ethereal soln rapidly and blow a rupture disk at reasonably low pot temps.  Naturally, the safetly department gets surly about this kind of thing.

Tetrahydrofuran is not always a suitable process stand-in for Et2O. Reactivity behaviors may be quite different from Et2O solns.  THF’s sensitivity to butyllithium, for instance, forces one to keep the processing conditions at low temp with a chiller. Lower pot temperatures increase the thermal margin of safety, but may have a deleterious effect on activation of a transformation once BuLi has done its job. 

I have studied the decomposition of methyl tetrahydrofuran with BuLi and have determined that it decomposes in the low 30’s °C range, somewhat higher than THF. MeTHF is not an exact stand-in for THF or Et2O either.  But it is definitely worth having in the stockroom for development work. It will surprise you in regard to how different it can be from THF.

While MeTHF is touted for its ability to phase separate with water, it will hold appreciable amounts of water.

Cripple Creek and Victor Gold Mine Tour

3 Replies

A vanload of members of the ACS, Colorado Section, were treated to an extensive tour of the Cripple Creek and Victor (CC&V) mine last Friday. The photo below shows a view of the mine from the abandoned American Eagle Mine above the CC&V pit operations. The mountains in the background are the Sangre de Cristo range.

View of Cripple Creek & Victor Mining Operations from the American Eagle Mine, May 2010.

A haul truck bed was converted to a scenic overlook platform (below).  A few section members take in the view.

CC&V Scenic overlook platform

From this high vantage point we could see blasting operations at work. Multiple sites may be prepared simultaneously. Blasting typically occurs at 1:00 pm. Holes are drilled on 20 ft centers for optimum coverage. Every blasting hole is sampled and analyzed by ICP to measure the gold value for that zone.  Zones with low value are hauled to the waste heap and the high value rock is taken to the crusher.

Preparation for blasting, CC&V, May 2010.

We visited the pit and watched haul trucks get loaded by a gigantic loader. For every one truckload of ore there are two truckloads of unproductive rock that have to be hauled to a separate location on site. The definition of unproductive rock depends entirely on the market price of gold.  In the photo below, drilling rigs for the blasting charges are in operation for the next round of blasting.

Loading area, CC&V Mine.

Later we watched the trucks unload into a crusher with a gyrating element that crushed the rock into football sized chunks. The resulting rock is conveyed to a screener and another crusher in order to further reduce the size to 0.75 inches. Every truckload of rock is treated with lime to help maintain a high pH for the aqueous cyanide leaching operation.  In the photo below, the white tank on the lower right contains the lime.

Heap leaching operations, CC&V May 2010.

The gold bearing rock is irrigated with a very dilute sodium cyanide solution which percolates to the bottom of the heap and is captured in a basin feature at the bottom of the heap. The “pregnant” solution of gold cyanide extract is pumped out from under the heap at 14,500 gal/min into a cascading series of charcoal filtration tanks in the extraction building (see photo).

Pregnant solution passing over charcoal filter bed. CC&V May 2010.

Once a specified loading of Au is sorbed onto the charcoal, the sorbent is treated with hot concentrated cyanide. This concentrate is then passed over steel wool where the gold precipitates. The precipitated gold is then smelted to produce bulk crude metal which is shipped off-site for further refinement.

Chemistry Field Trip!

2 Replies

So I decided to kick up my interest in the local metalliferous deposits and get more folks involved. As a member of the executive cmte of the ACS local section I’ve organized a seminar at a local university and arranged to have the lead exploration geologist from CC&V come to talk about the their gold mine in Cripple Creek.

The seminar is thursday night. Friday morning a few of us will board a van and drive the 5 h round trip to visit the open pit operation. We’ll stop at the nearby Molly Kathleen mine as well. I’m hoping we’ll be 1000 ft down the hole when the mine next door begins blasting. That’s an unforgettable experience.

Enthusiasm is contagious.  Especially with regard to gold colored precious metals. Unfortunately, bench chemists have few opportunities to take field trips. So the thinking here is that we’ll find a way to get members out and about to look at heavy industry. And gold mining is definitely a chemically related industry. Email blast notifications to rouse attendance are surprisingly ineffective- 1 or 2 % response at most. It is hard to get folks to participate in local section activities because everyone has a life.

The next day I’ll be on a field trip with geologists to visit various sites showing ductile and brittle deformation as well as hydrothermal alteration of formations in the central front range. I’ll be a chemical science interloper, as usual. The key to many of the metalliferous features in the world is hydrothermal transport. Shallow magma intrusions energize a kind of heat engine that pumps water through metal-bearing rock and transports hot, pressurized mineral laden fluids through a large and cooler network of fissures and faults where minerals precipitate according to their solubility.  Hydrothermal alteration is an important feature to look for when prospecting for metals.

Force Majeure

Leave a reply

If you are in the business of buying or selling chemicals under contract, you probably understand the merit of a force majeure clause in the contract. Literally meaning “greater force”, force majeure is essentially a declaration that a term, usually delivery, is not going to be met in an agreement owing to an “act of god” or other influence that is well beyond control or prediction. It’s not unheard of for a force majeure clause to be omitted in a supply contract. Both buyer and seller can benefit from this escape hatch when the sky falls.

Companies declaring force majeure in 2010 include Chevron Phillips on US olefins (ethylene cracker outage), Ineos on certain polyolefins (outage due to agglomeration in the reactor), Shell Chemicals on is Moerdijk styrene (ethylene supply problems), AkzoNobel on its Perkadox 14 line in Belgium (explosion & fire), Dow on phenol in the Americas (broken heat exchanger), Domo on its nylon 6 (feedstock supply shortage), Sasol on chemicals out of its Germiston, SA, plant (fire), Olin Corp. on its McIntosh, Alabama, Chlor-Alkalai plant (equipment failure), Cristal Global on its Stallingborough, UK, TiO2 operations (unspecified malfunction), BASF on acrilonitrile-butadiene-styrene (ABS) at its Tamaulipas, Mexico, site (butadiene shortage). Diethyl ether is also in short supply, but I am aware of no specific reason.

A few of these force majeure interruptions have been lifted already. Point is, it is always good to have multiple suppliers on line to provide supply of feedstocks. In regard to the olefin/polyolefin force majeure declarations, I wouldn’t be surprised if there wasn’t a bit of foot dragging that lead to a shortfall in capacity. Why keep all of your crackers in operation during the Great Recession?

Depth of knowledge

5 Replies

It’s funny how you can deceive yourself into thinking that you understand a reaction. Then you do that last experiment and get a result that shows unexpected sensitivity to one thing or other.  Depth of knowledge comes from doing a lot of experiments, not hand waving. It is important to try to learn something from every experiment. If the rxn went south, what happened?  Can you do a mass balance?  What happens to the mass that doesn’t convert to product?  Consider every “poor” result as an opportunity to extend your understanding of the reaction.

If you want to claim true expertise in a process, you have to know what the reaction system is broadly sensitive to and what it may be insensitive to. In short, you need to know what affects the velocity of the reaction or what steers it to side product formation. Exactly what are the boundaries of “normal”? 

Running the same reaction a hundred times successfully by carefully following the directions confers proficiency, not expertise.  It is fine for most workers to have proficiency. But someone should take the trouble to acquire broad expertise for the inevitable off-normal event somewhere down the timeline.

An upset condition can stem from an off-normal engineering input or from some reactivity issue. How many watts per liter will your reaction generate?  How will your reaction mass behave if there is a solvent boil-off? Does the solvent boiling point fall below the maximum temperature of the reaction in an off-normal condition? In other words, can the reaction mass self-heat in a manner leading to a runaway condition?  If so, what layers of protection are in place to prevent this kind of event?

The ability to push electrons in a mechanism or facility with named reactions is not enough skill for process scale-up. A chemist has to walk over the entire acreage to thoroughly map out the hills and valleys of the process. The people who operate the big pots and pans, and their families, are depending on your thorough knowledge to keep them safe.

Acquiring expertise is going to annoy people. It necessarily slows things down. It will make you a colossal boor at parties. But never confuse motion for progress or data for knowledge. Over time, people will come to you for advice on things. Be patient.