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I have spent some time researching basic magnesium chemistry. Not anything synthetic but more safety and thermochemically related. I am not able to give a lot of particulars motivating the study, but I can say that one should consider that nitrogen over activated magnesium may not be as innocent as you think. While lithium is widely known to react with nitrogen gas to form a passivating nitride layer, the reaction of dinitrogen with magnesium is rarely encountered.

Activated magnesium residues from a Grignard or other magnesium metallation reaction may self-heat to incandescence under a nitrogen atmosphere in the right circumstances. Activated residues left isolated on the reactor wall or other features in a nitrogen blanketed reactor during an aqueous quenching procedure may self-heat to incandescence. In the presence of reactive gas-phase components like water vapor in nitrogen, activated metals can self-heat over an induction period of minutes to hours or longer.

Many metals, including magnesium and aluminum, can be rendered kinetically stable to air or humidity by the formation of a protective oxide layer. Once heated to some onset temperature by a low activation reaction, penetration of the protective layer by reactive gas composition can occur, leading to an exothermic reaction.

Performing a “kill reaction” or a quench of a reactive metal at the bench or at scale is always problematic and requires the skill and close attention of the process chemists and operators. I guess what I’d like to pass on is that nitrogen is not an innocent spectator in the presence of finely divided, activated magnesium. Humid nitrogen can support a combustion reaction to produce nitrided magnesium once preheated to an onset temperature.

If you mean to kill any reactive residues, it is important to apply the quenching agent in such a manner that the heat generated can be readily absorbed in the quenching medium itself. A good example of a quenching agent is water. Often a reactive must be killed slowly due to gas generation or some particular. Adding a quenching agent to a solution or slurry by slow feed or titration may be your best bet. If you have another vessel available, a feed to a chilled quenching agent will also work.  Dribs and drabs of water on a neat reactive material will lead to hotspots that may be incendive.

After a weekend in the Alma, CO, mining district, I have come around a bit on the merits of gold mining. Oh sure, I have always known that it was a dirty business, what with the mercury, the cyanide, the acidic tailings piles, and the blighted landscapes. But for God sakes man, it’s GOLD!

Last weekend was different. It wasn’t a dispassionate examination of mining history. I could see miles of blighted landscape heaped with spent alluvium along the road from Fairplay to Alma. To the north, over Hoosier Pass, are the McMansions of Breckenridge where new and old wealth mingle.  To the south of Fairplay is a sizeable expanse of gravel and cobble heaps from past placer mining.

Placer mining north of Fairplay 6-14-14

The photo shows just a short stretch of the creek bed undergoing placer mining on the north end of Fairplay. Granted, the mining company is using gravity separation by way of the sluice to recover the gold. The stones are all rounded and well weathered, so one might expect the tailings to release little in the way of toxic leachate. But what a colossal mess they have made of the landscape. Perhaps they have put up a bond assuring that restoration of the landscape will happen when the mining ceases. I don’t know. That does not seem to be the way of past mining in the district.

My point is this. Isn’t there some madness in gold mining? At best a handful of people get wealthy from putting more gold on the market. I would argue that gold does not have the utility of iron, aluminum, or copper for instance. It does not go into items that advance civilization and economics like tractors, bridges, ships or wires. Gold does not go on to enable the growth of industry in the manner a base metal. Some of it adorns our fingers but most falls into the hands of anonymous individuals and governments who hoard vast caches of the metal. Granted, a bit of the annual production goes into electronics and a few other applications.

The madness in gold mining is that people are willing to go to any length or bankrupt themselves to obtain a metal that in the end benefits approximately no one. Most of the metal will quietly sit in a vault somewhere producing nothing. It won’t support a building or a roadway over a river. It won’t produce goods or services, nor will it bring a silent heart back to life. It can only support abstractions like the notion of value. We’re willing to put up with scarred landscapes, mercury pollution and acidic runoff produced by other people for an abstraction. That is pretty funny.


This is an excerpt from a writing project I’m working on.

The impulse to find and extract gold and silver was one of the drivers of 19th century westward expansion in North America.  The discovery of gold in a California stream bed in 1849 and the subsequent discovery of gold and silver in other territories eastward to Pikes Peak and the Black Hills resulted in waves of migration of prospectors, merchants, investors, and swindlers from all directions, including Europe.

The staking of mineral claims in the American west by people who were engaged in the extraction of mineral wealth lead to an inevitable avalanche of settlers interested in tapping some of the wealth of the miners themselves. The open territory created a void that was filled by industrialists, merchants, government, and perhaps most importantly, the railroad. Miners needed supplies and their ore concentrates required transportation and beneficiation.

As claims were made on valuable mineral deposits, the outline of the geographical distribution of mineral value in a region eventually defined what came to be known as a district. The expansion of the railroad, sweetened by land grants, added permanence to the settlement of many regions around and en route to the mining districts.  The simple logistical requirement of frequent stops to fill the steam locomotive with water lead to the establishment of towns along the railway. This expanding transportation network, along with liberal access to land, lead to settlement by farmers and ranchers who then created a demand for goods exported from long distances by rail.

The history of man’s fascination with gold and other metals is well documented and there is no need to reiterate that saga in the present work. The mania for gold and silver in the west is legendary. Indeed, clues to the history of gold and silver mining in the American west are quite apparent even to the casual observer today. A drive to Cripple Creek or Central City in Colorado will take the motorist past a great many long abandoned mine dumps, prospect holes, adits, and antiquated mineshaft head works. These quiet features of the landscape mark the location of what was in times past a great and bustling industry.

Throughout the American west today there are many “tourist mines” and mining museums operated by individuals and organizations who recognize the importance of keeping this part of our cultural heritage alive. Through their efforts, visitors can view 19th century mining technology on site and experience the dark and eerily silent realm of the miner. Visitors can see for themselves the intense and sustained effort required in hard rock mining and the occupational hazards miners were exposed to.

The tourist mines and museums often focus on the activity of mining itself as well as the specialized equipment needed to blast the rock and muck it out of the mine. This is only natural. The gold and silver rushes left behind a large number of artifacts. These items are of general interest to all.

The technology that is often glossed over relates the matter of getting the pay out of the pay dirt. Indeed, this is a central challenge to gold and silver extraction. Once the streams have been depleted of placer gold and the vein or lode has been discovered somewhere up the mountainside, the business of extracting gold or silver from hard rock becomes technically much more challenging and capital intensive.

The panning and sluicing of placer or alluvial gold, while labor intensive, is conceptually easy to grasp. High density gold particles can be transported by suspension in a water slurry of the water is moving sufficiently fast. Gold particles will tend to settle at low points in a crevice or a gold pan where the stream velocity slows. A gold pan or the bend in a stream for that matter will have a flow gradient that will tend to collect the gold particles where the stream velocity slows.  A sluice or a Wilfley table are just devices designed to trip laminar fluid flow by inducing turbulence to encourage the denser gold particles to settle. Riffles or channels serve to concentrate the gold particles.

While gravity and clever tricks with fluid flow can be used to collect placer gold, isolating gold or silver from a hard rock ore body is quite a different challenge.  Gold and silver may exist in reduced form within the ore. They may also be found alloyed with one another or otherwise combined with other heavy elements. While gold tends to be inert even under oxygenated conditions near the surface, silver is subject to more facile oxidation and may be found in ionic form with several anionic species. Thus technology for the isolation of gold may not serve as an exact template for silver extraction and isolation.

Gold or silver may exist in the metallic form as bodies visible to the naked eye within the solid rock. Or they may be dispersed in microscopic elemental form throughout the ore body. Gold ore may be rich in elements that complicate its isolation even though the gold is in reduced form.  Silver ore is commonly found in ionic form and with numerous ionic base metals present.

Lode gold or lode silver, that is, gold and silver found dispersed in an ore body, were subject to considerable variation in mineral composition. As a result, differences in isolation techniques and process economics arose among the various operations.

In the 19th century a considerable body of chemical knowledge evolved as the gold and silver rushes progressed. This chemical knowledge was put into practice largely through the efforts of mining engineers.  It was not uncommon for the mining engineer to conceive of what today would be considered a process chemistry change, draw up plans, press the ownership for funding, and put the change into operation.

Twenty-first century chemists may recognize much of the nomenclature from this period as well as the intended inorganic transformations. However, the older literature is filled with obsolete nomenclature or that which is confined to the mining industry.  What should be apparent to the observant reader is the level of sophistication possessed by 19th century metallurgists and engineers in what chemists today might refer to as the “workup”.  That is, the series of isolation steps used to remove undesired components to afford a reasonably clean metal product. Mining engineers refer to this as beneficiation or as extractive metallurgy. Beneficiation of lode gold and lode silver involved chemical transformation in batch or continuous processing.

The story of the development of extractive metallurgy is in part the story of redox chemistry on complex compositions like rock. In the mid 16th century Europe, key individuals like Biringuccio, Agricola, and Ercker began to capture mining and extractive metallurgical technology in print. Vannoccio Biringuccio (1480-1539) published his De la pirotechnia in 1540, detailing economical methods of metallurgy and assaying. In 1556, the work of Georg Bauer (“Agricola”, 1494-1555) was published posthumously. His De re metallica is regarded as a classic of metallurgy. Agricola’s book describes the practical issues related to mining, smelting, and assay work and is illustrated with remarkable woodcuts.

By the year 1520, do-it-yourself books like Ein nützlich Bergbüchlein and Probierbüchlein were beginning to appear in Europe describing basic mining and metallurgy techniques.[1] By this time methods of cupellation and the separation of gold and silver were committed to print.

Cupellation is an assay technique wherein crucibles made of bone ash were used to fire prepared gold ore samples with an oxidizer, affording base metal oxides which then separated from the gold and absorbed into the crucible to afford an isolated button of gold.

[1] Aaron J. Ihde, The Development of Modern Chemistry, 1964, pp 22-24; Dover Reprint 1984, QD11.I44, ISBN 0-486-64235-6.

I’m a fan of Gold Rush on the Discovery Channel and have been since the beginning. Aside from the producers constant over-dramatization and spreading the content a little too thin over the time block, I’d have to say that my main criticism would be with the miners themselves.

What I would throw on the table is the observation that there is a troublesome lack of analytical data supporting the miner’s choices of where to dig a cut. The few episodes where core samples have been taken, useful data was obtained and decisions made therefrom. But the holes were paid for grudgingly and the range covered too miserly. A sufficiently capitalized operation would be sure to survey the ore body and make the decision to bring in the heavy equipment on the basis of data.

Obviously they have been chronically short of capital for their operations. Fortunately for them, over the last 2 seasons they have been able to upgrade their wash plants, trommels, and earth moving equipment. Must be the TV connection.

But I suppose it is the very lack of capitalization that forms the dramatic basis of the show. Without scarcity there would be no drama. Without the conflicting personalities and dubious decision making there would be only a documentary on gold mining.

I have to imagine that the recent collapse in gold prices will get folded into the dramatic context in the next season.

I truly wish Parker Schnabel, the Hoffman crew, and the Dakota boys the best of luck in their efforts. What the viewers can’t see are the 10,000 details and problems that remain on the editing room floor.

It is a crying shame that we (the rest of the world) did not think to encourage Iran and other states to develop thorium-based nuclear power many years ago. The thorium fuel cycle provides nuclear-powered steam generation, but is largely absent the use of fissile isotopes in the cycle which may be used for nuclear proliferation.  Thorium-232 is more abundant that uranium-(235 + 238) isotopes and does not require isotopic separation as uranium does.

The great exploration boom in progress with rare earth elements would facilitate thorium supply. Thorium and uranium are commonly found in rare earth ores and, to the dismay of extractive metallurgists since the Manhattan Project, these elements tend follow along in rare earth extraction process. The isolation of thorium was developed long ago.  Point is, since so many rare earth element extraction process streams are either in operation or are pending, now is the time to accumulate thorium.

At present however, thorium is a troublesome and undesired radioactive metal whose isolation and disposal can be quite problematic. The best process schemes partition thorium away from the value stream as early in the process as possible and channel it into the raffinate stream for treatment and disposal in the evaporation pond.

The specific activity of natural thorium is 2.2 x 10^-7 curies per gram (an alpha emitter). The specific activity of natural uranium is 7.1 x 10^-7 curies per gram.  Alpha emitters pose special hazards in their handling. Dusts are a serious problem and workers must be protected especially from inhalation or ingestion. While alpha’s are not difficult to shield from, their low penetration through ordinary materials or even air makes them a bit more challenging to detect and quantitate relative to beta’s and gamma’s. In spite of the mild radioactivity of thorium, managing the occupational health of workers is known technology in practice in the nuclear industry.

Regrettably, most of the world’s nuclear power infrastructure is geared to uranium and plutonium streams. Thorium, the red-headed stepchild of the actinides, is thoughtlessly discharged to the evaporation ponds or to the rad waste repository- wherever that is- to accumulate fruitlessly. If we’re digging the stuff up anyway, why not put it to use? It is a shame and a waste to squander it.

The problem of the origin of Cu:Sn bronze has intrigued historians for many years. Bronze artifacts have been dated to 5000 BCE on the Iranian Plateau.  It is thought that the earliest bronzes were arsenical in nature. The presence of arsenic in copper metal or copper ore is not uncommon.

Copper can be found as the native metal but the smelting of copper ore appears to date back to ca 5000 BCE in southeastern Europe in what is now Serbia.

Most commonly today, the word bronze refers to a range of copper alloys comprising various proportions of copper (major, e.g., 88 %) and tin (minor, e.g., 12 %).  As the tin content increases, the resulting alloy changes properties and may have a unique purpose and name. For instance, a ratio of ca 2:1 :: Cu:Sn is called speculum and was prized for it’s ability to take a high polish for mirror applications.

Further down the composition range are varieties of pewter which are alloys comprised substantially of tin and a few percent of copper and antimony for hardening.  Many specalized compositions of pewter have been developed. Britanium or Britannia metal is an alloy comprised of 93 %Sn, 5 % Sb, and 2 % Cu. This alloy serves as the base metal Oscar Award Statue upon which gold is plated.  Pewters composed of Sn:Pb were commonly used as well.

Tin is not found in the metallic state in nature. It is oxophilic and occurs primarily as the tin (IV) oxide mineral, cassiterite. Tin ore was mined in Cornwall, England, for instance, for many centuries before recorded history.  Today, most of the worlds tin comes from Asia, South America, and Australia.

The jump to “engineered” bronze was a step change that involved the reduction of a tin mineral either in situ with copper or in isolation to produce discrete tin. It is thought that polymetallic copper ores were smelted, producing Cu:Sn bronze directly. Eventually, tin ore was identified as a source of smeltable metallic tin.  Why anyone would think to apply reduction conditions to a mineral as seemingly featureless and uninteresting as cassiterite is an intriguing question.

Below is a photo of the result of my first attempt at smelting a cassiterite simulant (SnO2, Aldrich). The SnO2 was treated with carbon black at 900 C for 4 hours in a covered porcelain crucible in a muffle furnace.  After a  failed attempt with a large excess of carbon, the ratio was reversed and heated for a longer period.  For the illustrated sample, the mass ratio of SnO2 to carbon black was ~2:1. All of the carbon black was consumed, leaving a white mass of needles on the granular solids.  Using a USB microscope I searched for evidence of reduction to the metallic state and found numerous examples of sub-millimeter sized pieces of metal.  The yield of metallic tin is estimated at < 1 %.

The purpose of this exercise (for me) is to try gain a better sense of what problems people might have faced smelting tin in antiquity.  Using basic principles, I strongly heated the SnO2 under reducing conditions until the carbon was consumed.  What I did not expect was the large amount of white crystalline material produced. It’s composition is as yet unknown to me.

Next I will make some charcoal or even wood shavings as a reductant for authenticity sake. Who knows, maybe some carbon monoxide generation might be helpful. The muffle furnace does not simulate a reverberatory furnace very well. It could be that gases from a reducing flame are important.

Smelting of Cassiterite Simulant

The founders of the Silicon Valley startup, Planetary Resources, have announced plans for mining asteroids for valuable metals. Peter Diamandis, Eric Anderson and investors including director James Cameron and Google CEO Larry Page are behind this venture.

I’m trying to be positive here. Perhaps these fellows should visit some earthly mines and see what it takes to break actual rock and extract the value from it.

Earth bound ore bodies near the surface are commonly the result of concentration by hydrothermal flows. In the absence of water-based geothermal concentration processes, or recrystallization of PGM’s in magma chambers, the reality of economically viable ore bodies in asteroids is an open question. A lot of survey work needs to be done to answer this question.

Oh, and one more thing. When you blast rock on a largish planet like earth, the fragments fall back to the ground. This won’t happen on an itty bitty asteroid.

The talk about recovering water from asteroids to subsequently crack and make propellant is a large challenge all by itself.

I predict that civilization will slump back to a 19th century Dickensian-style world of robber barons and sharecroppers before any hardware gets to an asteroid.  Children will ask “Momma, what’s an iPad?” as they walk from their rundown subdivision to a quonset where they strip insulation from wire for copper to barter for food. It’s all so clear now …

Agilent is excited about their new 4100 MP-AES system. The initials stand for Microwave Plasma Atomic Emission Spectrometer. The instrument uses the magnetic component of the microwave energy to produce a nitrogen plasma at ca 5000 K, through which the sample is drawn. The monochrometer looks down the axis of the plasma torch. The detector is constructed to suppress blooming.

Pretty cool instrument. The setup includes a nitrogen supply which separates the nitrogen directly from air, so there is no large argon dewar to lug to remote locations like mine sites.

The MP-AES is designed to compete in the AA market. The detection limits are comparable for many elements. The kicker is that there no need for combustion gases or element specific lamps since it is a plasma emission method.

The question I have is this- is there any market left in the replacement of AA? The instrument sells for $53 k, so the pricing is very competitive with or better than ICP. I think that argon based ICP is going to feel the heat of this nitrogen plasma torch.

The bad news for chemists is that you don’t need a chemistry degree to run it. To set up methods, maybe, but the software is designed for operation by non-degreed techs.

Rhodochrosite Specimen with Galena and Pyrite (Copyright 2012 Th' Gaussling)

Rhodochrosite is a mineral composed of MnCO3. The specimen above is in no way exceptional, other than as a curio. The mass is comprised of rhodochrosite, galena, pyrite, what looks like quartz, and possibly a trace of a gold colored metal.

The photo below shows the galena, or PbS.

Same sample as above, showing the galena. (Copyright 2012 Th' Gaussling)

The photos were taken with a USB microscope.

According to an article in Mineweb, the remaining cold war era uranium will be consumed in the next few years, leaving the nuclear industry with inadequate supply streams from mining.  Thomas Drolet of Drolet & Associates Energy Services, said that in 2010 mining produced 118 million pounds of uranium against a demand of 190 million pounds. Obviously, the balance was made up from decomissioned nuclear weapons stockpiles. The article did not say whether the numbers represented lbs of U or of U3O8. The oxide is commonly cited in relation to uranium mine production.

Drolet suggests that Japan will have to restart ca 30 of its 50 or so reactors in order to meet power demand.

It is my sense that the Fukushima disaster will not be the stake in the heart of nuclear power. The location of the Fukushima plant and a list of easily identifiable design features allowed the initiation and propagation of the incident. While the future of reactor operation in Japan may be stunted, most reactors elsewhere in the world are not located in tsunami flood zones. Regrettably, some are located in fault zones. But the insatiable demand for kilowatt hours will override everything. Commercial fission will continue into the indefinite future.


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