December 2007

Got Minerals?

Learn more about industrial mineral applications through numerous books, Web sites, and educational seminars.

During the past year, this column has also been about industrial minerals. The articles barely scratched the surface of the thousands of applications for the dozens of industrial minerals. If you like what you read, and want to learn more, here are some ideas.

The Society for Mining, Metallurgy, and Exploration (SME) recently released the 7th edition of Industrial Minerals & Rocks. It is a 1,548-page reference document covering more than 60 industrial minerals, rocks, and materials, including crushed stone and sand and gravel. If you want to know about the geology, mining and production methods, and uses of industrial minerals, it’s in the book. If you are a history buff, you can choose an industrial mineral and read about it in each of the seven editions to see how the industry has evolved throughout time. Better yet, the book contains chapters on aggregates, lightweight aggregates, crushed stone, and sand and gravel. Interested yet? If so, go to www.smenet.org.

If you are looking for a little lighter reading, try the Industrial Minerals Handybook, by Peter Harben. It’s jam-packed with resource descriptions, mining methods, specifications, production statistics, and other market-related issues. The handybook is available from many online bookstores or at www.peterharben.com.

And of course, the U.S. Geological Survey Minerals Yearbooks and Mineral Commodity Summaries (http://minerals. usgs.gov/minerals/pubs/commodity/) are world-famous collections of information on mineral commodities. The yearbooks are multi-page articles describing significant events in the minerals industries throughout the past year, and include numerous tables describing production volumes and values by state and product, as well as imports, exports, and so forth. The commodity summaries are a two-page roll-up of the industries. If you aren’t using these documents, you are missing out on a great resource.

If you want to get the industry take on industrial minerals, try visiting the Web site of the Industrial Minerals Association-North America (www.ima-na.org) or Industrial Minerals Association-Europe (www.ima-eu.org). These are especially informative sites to visit, especially if you are interested in sustainability.

And for educational information, the Mineral Information Institute (www.mii.org) has a Web page (look under homework help) that includes pictures and descriptions of the uses of many minerals, including the industrial minerals.

If you would like to get actively involved in the process, there are a number of annual meetings you can attend. At the SME annual meeting, the Industrial Minerals Division usually has a program of five sessions — each session with four to six papers. For those of you who don’t want to stray too far from aggregates, the Construction Materials and Aggregates Committee (CMAC) of SME organizes a five-session program. There are exhibits galore, as well as field trips and short courses. Come to the meeting at Salt Lake City (Feb. 24-27, 2008) — you won’t be bored! You can register on line at www.smenet.org.

Another annual meeting, the Forum on the Geology of Industrial Minerals, is dedicated entirely to industrial minerals. This is a much smaller, more personal meeting. The 44th Forum will be in Oklahoma during the spring of 2008. To learn more, use your Web search engine; and type in key words “forum geology industrial minerals.” You can expect a superb program on a variety of industrial minerals, including aggregates. And if you like to bring someone along, they have outstanding guest tours! I hope to see you at one of these meetings.

November 2007

Food for Thought

The consumption of soil is common among many birds and animals, including some of the two-legged variety.

My wife, Pam, and I discovered a fantastic new television series — Planet Earth. During one episode, a forest elephant plunged its trunk into the bottom of a lake, came up with a hunk of clay, popped it into its mouth, and ate it. Pam looked at me in amazement and blurted, “Wow! Even animals use industrial minerals!” 

Now, I had no intention of writing about eating dirt, but after Pam’s remark…

Geophagia — the consumption of soil — is a common behavior of many birds and animals. The dirt-eaters typically are herbivores, including antelopes, buffalo, chimpanzees, giraffes, gorillas, and zebras in Africa; peccaries and tapir in South America; deer in Europe and Asia; parrots in South America; and virtually all species of wild North American ungulates (hoofed animals), including bison, moose, and deer.

Humans have been eating soil since the beginning of man-kind. The clay recovered from a site occupied by early homo sapiens has mineralogical and nutritional characteristics like clays consumed by humans in Africa today. Hippocrates (circa 460 to 377 B.C.) wrote that pregnant women ate earth. Pliny the Elder (23 to 79 A.D.) wrote about a porridge-like cereal containing clay that had a soothing effect when used as a drug. And in Africa and the southern United States, some pregnant or nursing women still eat clay (known as pica).

Why do humans and other animals eat dirt? And how do dirt-eaters choose which soil to consume? The answer is somewhat elusive and is the subject of serious debate in the scientific literature. Six theories commonly are discussed among zoologists, anthropologists, and doctors. The first three theories involve an animal’s ability to self-medicate, which remains controversial because the evidence is mostly circumstantial or anecdotal.

1. Mineral supplement: Researchers have observed that animals, when presented with piles of soil, each pile containing different minerals, could recognize and choose the pile of soil with the mineral needed by their bodies.

2. Stomach acid buffer: When some hoofed animals eat a diet low in fiber, their rumens become so acidic that they kill helpful bacteria essential for digestion. Some of those animals buffer or neutralize the acid by eating highly alkaline soils similar to over-the-counter antacids.

3. Diarrhea: Bacteria and parasites release toxins that cause diarrhea. Researchers studying wild chimpanzees noticed that some of the animals suffering from severe diarrhea were eating soils rich in clays that bind the toxins. The clays are similar to those used in over-the-counter diarrhea medicines.

4. Grit: Many birds eat grit (small particles of stone) to aid digestion because birds don’t have teeth to chew their food. The grit stays in the gizzard, a muscular pouch just above the intestine that grinds the seeds that the bird has eaten.

5. Toxins: Wild fruits and nuts usually are bitter, astringent, sour, or poisonous. The seeds wild parrots eat are mostly inedible by other birds, but parrots can eat them because they also eat soils containing clay minerals that bind plant toxins.

6. Hunger: Some humans consume soil to assuage hunger. For example, the Ottomac Indians of South America made soil balls and ate more than one pound per day during the flood season, when finding food was difficult.

While some animals may instinctively eat dirt, humans have the ability to learn through experience. The bitter, toxic wild potatoes eaten by some South American Indians contain an alkaloid that causes stomach pains and vomiting. However, they have learned to make the potatoes edible by consuming them with clay that adsorbs the alkaloids.

Food for thought!
 

October 2007

Watching Paint Dry, Part 2

A little bit of trim highlights the importance of many minerals in paint quality, color, and workability.

After reading last month’s column titled, “Watching Paint Dry,” some of you may have come to the conclusion that I just sit around while my wife paints the house. Au contraire! Why, just the other night when Pam was painting the woodwork in our house, I seized the opportunity to explain how industrial minerals improved the quality of the paint she was so carefully applying to the baseboards.

I told Pam that almost all paints use titanium dioxide (TiO2) particles as the basic whitening pigment. TiO2 is expensive, and very fine particles of less-expensive calcium carbonate (limestone) are added to the paint formulation to separate the individual TiO2 particles. This creates an optimum spacing that maximizes the covering power of the TiO2. Calcium carbonate is used extensively in oil-based exterior house paints and in interior and exterior latex flats and semi-gloss enamels, particularly in pastel colors.  Dark color exterior paints generally limit the amount of calcium carbonate because it is susceptible to acid rain and tends to “frost” or “chalk” when repeatedly wetted by rain or sprinklers.

I knew Pam would be thrilled to learn that talc is used in both latex and oil-based paints because it has a platy shape, which improves brushability, leveling, and sag resistance of the wet paint. The talc plates align with her brush strokes and form a barrier that improves the ability of the paint to resist humidity. I also said another advantage is that talc helps keep pigments suspended in the paint and that she would not have to stir it as much.

Ground quartz is another industrial mineral commonly used in paint. It is a relatively low cost, very hard, high-brightness extender that is well suited for primers where surface hardness, roughness, and wearability are desirable. It is non-chalking and unaffected by exposure to ultraviolet light, so it improves the weatherability of exterior paints.

I was on a roll, and launched into ground mica, that same flakey stuff used in toothpaste (see Carved In Stone, Aggregates Manager, February 2007). Mica is flexible and passes on that flexibility to paint. As the dry paint film ages, mica reduces the internal stresses from thermal expansion and contraction. It is used in exterior paint and wood stains because it controls moisture, weathering, and ultraviolet (UV) degradation.

I told Pam that the coolest use of mica is as nacreous (pearlescent) pigment in automotive paint. Nacreous pigments are made by coating mica platelets with TiO2 and then overcoating with a thin, transparent film of a light-absorbing colorant. The nacreous pigment is what gives our car a two-tone metallic effect.

Pam finished the baseboards faster than I had hoped. I did not have time to tell her that kaolin has excellent hiding power because the processed clay particles overlap one another; wollastonite has needle-like particles for low sheen and film reinforcement; barite is used for heat resistance; feldspars have angular blocky particles that interlock and pack tightly, thus strengthening dried paint; or that adding diatomite particles to paint results in irregular texturing of the coating surface, which improves sanding properties and adhesion of subsequent coats.

As Pam was washing out her brush, she told me to “hop in the nacreous-coated van, go to the store, and buy some volatile liquid containing a polymer emulsion and finely ground quartz.” Cool!

But unfortunately, I might have overdone it. She then suggested that I could apply it over the uncoated drywall surface in our closet.

Oops!

 

September 2007

Watching Paint Dry

Compared to some meetings, watching paint dry can be quite stimulating.

A while back I was suffering through a long, boring meeting, when I thought to myself, “This is about as much fun as watching paint dry.” What was I thinking? Watching paint dry can be quite fascinating!

Fortunately for me, my wife, Pam, loves to paint, so I get to do a lot of watching. When she selects paint, her first decision is “latex” or “oil-based” paint. That distinction refers to the volatile liquid and binder used in the paint. Volatile liquids make paint fluid for ease of application. Typically, the volatile liquid portion of “latex” paints is water with small amounts of other materials, whereas the volatile liquid used in “oil-based” paint usually is mineral spirits, alcohols, or esters.

After paint has been applied to a surface, the volatile liquid evaporates leaving a protective coating created by binders. The binder commonly used in latex paint is an emulsion of microscopic particles of polymer (plastic-like material) dispersed in water.  (Incidentally, latex paint does not actually contain latex, but has that moniker because the emulsion resembles milky-white latex from the rubber tree.) As the water evaporates, capillary attraction draws the polymer binders together, fusing them into a continuous film.

The most common binders used in oil-based paints are made with oils such as linseed oil (squeezed from flax seed), tung oil (from fruit of the Chinawood tree), and soya oil (from soybeans). These oils may be modified with chemicals to make alkyds, which dry harder and faster than oils alone.

Next, Pam chooses the paint color, which is created by mixing a variety of pigments. The pigment portion of paint includes hiding/coloring pigments and specialty pigments. Many pigments are naturally occurring industrial minerals that have been mined and processed specifically for use in paint.

The strongest white pigment, and the most frequently used hiding pigment in the paint industry, is titanium dioxide, an inorganic chemical manufactured from the minerals rutile and ilmenite. The red, yellow, brown, orange, and black pigments are manufactured from the iron minerals hematite, limonite, and magnetite, and are the predominant natural mineral coloring pigments used in paint. Other inorganic color pigments are manufactured from minerals containing zinc, chromium, cadmium, lead, or molybdenum compounds.

After selecting a color, Pam chooses the paint sheen — high gloss, semi-gloss, satin, eggshell, or flat. By increasing the amount of pigment, and by using larger particles, paint changes from high gloss (least amount of pigment and smaller particles) to flat (greatest amount of pigment and larger particles).

Throughout the paint selection process, Pam made a bunch of other choices based on the intended application of the paint. Will it be used indoors or outdoors? Will it cover metal or wood, woodwork or walls, new drywall or old paint? Paint manufacturers adjust the formulations of their paints to accommodate these and a host of other situations. Many of the adjustments involve the addition of other industrial minerals including calcium carbonate (limestone), talc (the stuff of baby powder), quartz (most sand is quartz), feldspar (a milky white or pink mineral found in many rocks), and mica (the shiny, flakey mineral found in many igneous or metamorphic rocks).

Next month, this column will address how the industrial minerals mentioned above (and others) woWatching Paint Dryt do what you want it to do. You might find the information very useful the next time you sit through a long, boring meeting.
 

August 2007

Cum Grano Salis

Sayings such as ‘taken with a grain of salt’ demonstrate salt’s value in everyday life.

Pliny the Elder’s Naturalis  Historia (circa 77 A.D.), describes how Mithradates the Great feared being assassinated by poison and made himself immune by swallowing small amounts of poison along with an antidote. To be effective, Pliny wrote, the antidote should be taken “cum grano salis” (with a grain of salt). Although Pliny did not comment on the value of the antidote, interpreters of Pliny’s work determined it to be ineffective. Thus, the phrase “taken with a grain of salt” was misconstrued to mean “taken with a dose of skepticism.”

Readers — don’t try this at home — there is no modern toxicology evidence to indicate that salt is an antidote to any poison. But the saying “taken with a grain of salt,” along with others such as “worth your salt,” and “salt of the earth,” all demonstrate the important role salt had, and continues to have, in our everyday lives.

Today, salt is one of the least glamorous industrial minerals with some of the most important uses.

The largest consumer of salt in the United States is not the food industry — it is the chemical industry, which consumes about 45 percent of the salt produced. Salt, which is made of sodium (Na+) and chlorine (C-1), can be mixed with water (H2O) and transformed by electrolysis into caustic soda (NaOH), hydrogen (H2), and chlorine gas (C12).

Caustic soda has numerous uses, especially in the pharmaceutical, food processing, and tobacco industries, and is the feedstock for numerous other chemical products. Hydrogen commonly is combined with some of the chlorine to make hydrochloric acid — the stuff you use to remove cement mortar from tile — or is used as a fuel to generate steam.

Chlorine is well known for producing safe drinking water and its use in common household bleach. But chlorine has many manufacturing applications, including the production of paper, dyestuffs, textiles, medicines, antiseptics, insecticides, solvents, paints, and plastics. All of these products ultimately owe their existence to plain old salt.

More than likely, you already know that salt (especially if you have high blood pressure and are trying to avoid it) is widely used in food processing. Salt acts as a flavor enhancer and tenderizer, and it is liberally used in processed food. It is used as a preservative because it inhibits the growth of bacteria. The fermentation, color, and texture of cheese is controlled with salt. It reacts with certain proteins to help bind processed and formed meats. Salt controls the fermentation of bread dough and provides uniform texture, grain, and strength to the dough.

When oil and gas drilling encounters salt formations, salt is added to the drilling fluid to saturate the solution, thus minimizing dissolving the salt strata. It is also used to increase the setting rate of concrete in casings, to increase drilling fluid density, and as a flocculent to cause clay particles in drilling fluid to settle out of suspension.

Salt is used for highway deicing, in water softeners, and as a supplement for livestock. There are dozens of household uses including polishing silver, killing weeds, removing mildew, refreshing stinky drain pipes…the list goes on and on and on.

Salt is even found in our bag of superstitions. Some people fear bad luck will befall them if they drop salt on the floor. They also believe the bad luck can be averted if you throw some of the spilt salt from your right hand over your left shoulder.

But take that cum grano salis.

July 2007

Lime: Part 3

Manufacturing an ancient industrial mineral. 

The process of heating lime-stone (calcination), which results in the production of lime and carbon dioxide, has remained unchanged since antiquity, although technology has evolved significantly. Calcium carbonate (CaCO3) is the basic ingredient for the manufacture of lime. The material of choice commonly is stone considered suitable for burning into lime (hence the name “lime stone”) although coral or shell are occasionally used.

Lime-burning requires immense quantities of fuel, and even though coal, oil, and gas are generally used in modern calcination processes, wood was the fuel of choice throughout most of antiquity. It is interesting to note that much documented deforestation of southern Britain during the Middle Ages has been blamed on the harvesting of forests to fuel the royal lime kilns. Some of the Mayan forests are reported to have met a similar fate.

Lime-burning takes place in a kiln, and kiln technology has improved greatly throughout time. The simplest type of kiln was a ‘pit kiln’ — essentially a covered hole in the ground filled with fuel and limestone or shells. The first major advancement was a ‘flare kiln’ (sometimes known as an intermittent kiln) that was a permanent masonry structure filled with layers of fuel and stone. After it was fired, the kiln was allowed to cool completely before the lime was removed. The next major advancement was to keep the limestone and fuel separate. This was accomplished in a “draw kiln” (also known as a continuous kiln), a masonry structure that contained chambers or “pots” within which the burning of the fuel and limestone took place. Limestone could be added to the top of the kiln, and holes or “eyes” at the base of the pot allowed for refueling as well as access to draw out the lime.

Lime burning was nasty work.

“At frequent intervals [the lime burner] flung back the clashing weight of the iron door, and, turning his face from the insufferable glare, thrust in huge logs of oak, or stirred the immense brands with a long pole. Within the furnace were seen the curling and riotous flames, and the burning marble, almost molten with the intensity of heat; while without, the reflection of the fire…showed in the foreground…the athletic and coal-begrimed figure of the lime-burner.” — From Ethan Brand, by Nathaniel Hawthorne, 1852

One of the worst processes of lime burning was handling the hard cake of quicklime (calcium oxide) that had to be removed from the kiln and added to water. The immediate reaction was intense heat and a shower of caustic specks of slaked lime (calcium hydroxide) that could cause horrible burns and, if it entered the eyes, would often cause blindness. This phenomenon was described by Pliny the Elder, who wrote that he could not understand “why lime, which is obtained through burning of stone by fire, burns once more upon contact with water.” (Historia Naturalis, 77 A.D.)

Historically, limestone was usually prepared where it was to be used, which accounts for the very large number of old lime kilns.

At the start of the 20th century, there were about 1,000 lime-burners that collectively produced about 2 million tons of lime per year. Lime is reactive and therefore is much more difficult to store or transport than limestone. Consequently, it was usually prepared where it was to be used, which accounts for the very large number of old lime kilns. But the development of modern transportation networks, in combination with modern technology, made local kilns unprofitable, and they gradually died out. 

Today, lime burning commonly takes place in safe, modern, efficient plants. And while the amount of lime annually consumed in the United States has increased 10-fold to about 20 million tons per year, the number of operations has decreased 10-fold to about 100 operations.

June 2007

Lime: Part 2

The history of an ancient industrial mineral. 

The history of lime is a fascinating story that involves the serendipitous discovery of an industrial process, the development and transfer of that knowledge, and the technological advances stimulated by the unprecedented market-driven growth of the industry.

Way back in the mists of time, soon after man learned to make fire and used stone to build his fireplaces, he probably observed that a certain kind of rock (limestone), when subjected to intense heat, changed its composition to lime, and when that lime was mixed with water and dried, it changed back into a rock with a hardness similar to that of the original stone. 

Perhaps as long as 14,000 years ago, lime, made in the Middle East by burning small chunks of limestone in an open fire, was used to make adhesives for tools. By about 10,000 years ago, the use of lime was widespread throughout the Middle East. But unlike the serendipitous discovery of lime, this did not happen by chance. Except in very rare instances, lime is a manufactured product, and the technology needed to create it is not apparent from within the rock or the product itself. The technology of lime-burning had to be passed on from skilled practitioners to the untrained. The establishment of agriculture, a sedentary lifestyle, and the emergence of cities throughout the Middle East created a demand for lime, as well as a receptive audience eager to learn the techniques of lime-burning.

The ancient Egyptians and Greeks both used lime. The Romans almost certainly inherited the technology of lime manufacture from the Greeks, but they altered and perfected its use. By about 2,500 years ago, they had established sophisticated lime-burning technology.

During the Middle Ages, the demand created by the construction of castles, city walls, and religious buildings resulted in significantly increased lime production. Lime kilns were used throughout parts of Europe from medieval periods right through to the 18th and 19th centuries.

Like many innovative technologies, the calcination of limestone was discovered several times over a wide geographical area. The use of lime made from shell was recorded 4,000 years ago in ancient China. Polynesians made lime from coral. On the other side of the world, the Maya constructed temples decorated with multicolored stucco made from lime. They also made books out of tree bark coated with lime and prepared corn by soaking dried kernels in a solution of water and lime.

Thousands of years ago, lime was made by burning small chunks of limestone in an open fire and was used to make adhesives for tools.

Speaking of the Americas, the colonists brought a long history of lime manufacturing to the New World. Lime was made by Spanish settlers at St. Augustine, Fla. (1565), and by English settlers at Jamestown (early 1600s), who used burned oyster shells in pit kilns.  In January 1662, the first permanent masonry lime kiln in American began operating in Providence, R.I.

During the 1800s, towns and cities in North America and Europe were burgeoning with people working in expanding industries such as iron and steel manufacturing, chemicals, textiles, dyeing, and papermaking. All these industries needed burnt lime in their production processes. Meanwhile, expanding populations required vast amounts of food, and the associated agricultural boom led to even greater efforts to improve soil fertility. Here, again, lime came into great demand.

At the beginning of the 20th century, more than 90 percent of the lime consumed in the United States went for construction or soil amendments. But the growth of the chemical industries, particularly during the latter half of the 20th century, tipped the balance to where, today, more than 90 percent of lime is consumed for chemical and industrial uses.

Next month, this column will look at how lime-burning technology has changed throughout time.

May 2007

Lime: Part 1

Modern applications for an ancient industrial mineral.

Sometimes, after a hard day at work, I like to cozy up in my easy chair, have a nice hot cup of coffee, turn on the reading lamp, and browse through the latest issue of Aggregates Manager. Luckily for me, the world enjoys a healthy lime industry — otherwise I’d be up the creek without a paddle. Lime is an important industrial mineral with numerous construction, chemical, industrial, and environmental uses. Let’s see how lime affects the quality of my evening.

I am nice and comfortable inside our house that is covered with stucco. Lime is a major constituent in stucco that enhances the strength, durability, and workability of the product.

Lime was used during the tanning process to loosen the hair from the hides that make up the leather on my easy chair. Lime was added as a flux to remove impurities from the molten steel that was used to make the springs.

My coffee is brewed from municipal water that was clarified with lime. The dairy farm that provided the cream for the coffee amends the soil in its fields with lime. Plus, the coffee is sweetened with sugar refined using lime to remove impurities from the product stream.

The light bulb in the reading lamp comes on because the electric cord contains copper made from ore that was beneficiated using lime. The electricity to power the light bulb came from a coal-fired generating facility that employs flue gas desulphurization (FGD) whereby lime is injected into the flue gas to remove acidic gases such as sulfur dioxide and hydrochloric acid.

The paper in Aggregates Manager is made using lime to produce calcium hypochlorite to bleach the paper pulp, and to coagulate impurities in plant process water. Lime is also used to make precipitated calcium carbonate (PCC), a specialty filler used in premium-quality papers.

Part way through AggMan, I read an article about highway construction. Lime is used in hot-mix asphalt to act as an anti-stripping agent, and in cold in-place recycling for the rehabilitation of distressed asphalt pavements. It is also used to stabilize sub-bases consisting of expansive clay soils.

When it comes to the aggregate business, the PCC mentioned above deserves a little more attention. It is used in the manufacture of polyvinyl chloride (PVC) plastics and thermoplastics and is also used as industrial filler in paint and inks. The rubber in your conveyors and truck tires contains PCC. And if all this is giving you an upset stomach, PCC is used in pharmaceuticals such as antacid tablets and calcium supplements.

So you can see that we all would be up the creek were it not for lime. Speaking of the proverbial creek, lime is used in sewage treatment to control pH in the sludge digester, in clarification to destroy harmful bacteria. More recently, the leading use of lime in sewage treatment is in a process referred to as bio-solids stabilization, which converts sewage sludge into a usable product sanctioned by the U.S. Environmental Protection Agency.

And if you had a paddle, it quite likely would be made of an injection molded plastic containing lime that was added to improve stress crack resistance of the plastic and facilitate the injection molding process.

Next month, this column will describe how, after a hard day at work, prehistoric man sat beside the campfire, had a cup of hot something or other, browsed through a few cave drawings, and accidentally discovered lime.

April 2007

Cast in Concrete

A historical perspective clarifies the difference between the often-confused (by the layman) cement and concrete.

The other day, our friends Carol and Tom visited us at our  new house. Tom looked at the roof and said, “What kind of shingles are those, cement?” He is a good friend, so I took advantage of his faux pas to harass him. “Actually, they are concrete shingles made of sand, fine gravel, water, and cement — the cement and water create a chemical reaction that binds the other ingredients together.” I then asked if he wanted to learn a little bit about cement and concrete. Tom begged off, and in doing so, missed a fascinating story.

In 1756, British engineer John Smeaton made the first modern concrete by mixing pebbles, powered brick, and water with lime cement. Today, about 340 million cubic yards of concrete are made in the United States every year — more than one cubic yard for every man, woman, and child.

Concrete made with lime cement has been found at archaeological sites more than 5,000 years old. Lime was made by roasting calcium carbonate to drive off carbon dioxide. When lime in the cement is mixed with water, a chemical reaction takes place that forms portlandite. The reaction goes CaO + H2O = Ca(OH)2. Then, throughout weeks or even years, the portlandite reacts with CO2 in the air to form calcium carbonate — artificial limestone! That reaction goes Ca(OH)2 + CO2 = CaCO3 + H2O.

But lime cement takes a long time to cure and does not harden in water. Furthermore, portlandite (before it converts to CaCO3) is undesirable in concrete because it is porous and has a low compressive strength.

As luck may have it, approximately 3,000 years ago, the ancient Greeks mixed lime with fine volcanic ash and water, which reacted to make a whole new substance called calcium silicate hydrate (CSH). CSH is a much more desirable binder than lime cement because it hardens fast, even in water, and is more durable than lime cement.

Roman engineers mastered cement technology. The formula for Roman cement was not significantly improved upon until 1824 when Joseph Aspdin, a British bricklayer, burned ground limestone and clay, thus creating portland cement. He gave it that moniker because of its similarity to Portland stone, a type of building stone that was quarried on the Isle of Portland in Dorset, England.

Now we get to the really fun stuff. Modern portland cement is made from calcium, silica, alumina, iron, and calcium sulfate. All of these materials can be obtained by mining, although some cement manufacturers substitute byproducts from other manufacturing industries.

The primary ingredient in cement manufacture is calcium, and the most important source is limestone. But not just any limestone will do. Many limestone deposits contain too much MgCO3 for use in portland cement. Normally, the upper limit of MgCO3 is 3 percent, although this can be less depending on magnesia content in the other raw materials.

The silica and alumina in the cement commonly are provided by shale, clay, or bauxite. Iron ore sometimes provides the iron in cement manufacturing, but many manufacturers use blast furnace flue dusts, mill scale, and fly ash. The calcium sulfate comes from gypsum.

Carefully proportioned quantities of lime, silica, alumina, and iron oxide are sintered (roasted together at nearly melting temperature — 1,400 to 1,500 degrees C). The product, called clinker, is ground to powder. A small amount of gypsum is added to the cement to slow down the hardening process. And that is portland cement, which can be mixed with sand, gravel, and water to make concrete.

The next time I see Tom, I am going to present him with a copy of this article.

March 2007

Green Glass

Industrial minerals affect the quality, chemical properties, and color of glass.

As a kid growing up in Alfred, a small town in western New York, St. Patrick’s Day was a holiday that rivaled the excitement of Christmas. The New York State College of Ceramics at Alfred University, internationally renowned for its program of studies of ceramics and glass, hosted day-long festivities beginning with a parade complete with marching bands and paper-flower-covered floats. But what we all waited for was the evening open house where we could watch the artisans from Steuben Glass transform scorching hot, molten glass into beautiful blown-glass sculptures.

Back in a corner of the exhibit room, there were three or four different-sized beakers sitting on a black soapstone laboratory benchtop. The beakers contained the ingredients that went into the glass. I ignored those humble industrial minerals, as did practically everyone else in the room. But having spent part of my adult life studying industrial minerals, I know that regardless of the type of glass being made, the biggest beaker certainly would have contained sand. Not just any ordinary sand, mind you. Glass sand must contain at least 99.0 percent quartz (SiO2); some specifications may require even higher-purity sand. More importantly, it is critical that the quality of sand (and the rest of the raw materials as well) remain very consistent. Even slight variations in composition, grain size, and impurities of any of the raw materials can result in major problems.

The next largest beaker probably would have contained sodium carbonate (Na2CO3), commonly called soda ash. It acts as a flux that lowers the melting point of the glass batch approximately 200°C, thus saving energy and extending the life of the refractory. Soda ash is an important industrial compound that is also used to manufacture soaps and detergents, pulp and paper, chemicals, and many other familiar consumer products. The ancient Egyptians used natural soda ash for making glass as early as 3500 B.C. They also mixed soda ash with lime to make caustic soda and combined the caustic soda with silicate minerals from the Sinai Desert and aluminum-rich silt from the Nile River valley to produce silica-aluminate cement mortar. But that’s another story.

The third largest beaker likely contained limestone, which is added to increase the strength of the glass and its resistance to abrasion. Most limestone specifications require at least 97

percent calcium carbonate (CaCO3). It is also important to set limits on constituents that should be avoided in glass. Many types of limestone contain iron, and iron oxide that’s a byproduct of the iron discolors glass. Therefore, many specifications allow a maximum of 0.12 percent iron oxide (Fe2O3). Producers of very clear flint glass and crystal may set iron content as low as 0.04 percent. The restrictions may be so tight that some specialty glassmakers may use precipitated calcium carbonate or even reagent grade calcium carbonate to avoid iron in their product.

I do not recall how many beakers were sitting on the lab bench; after all, I was just a kid. But if there were a fourth beaker it might have been labeled “Secret Ingredients.”  (That would have caught the attention of both kids and adults!) Actually, more than 20 different industrial minerals are used in nearly 1,000 glass compositions for about 60,000 different glass products. Several of those minerals are used in glass as coloring agents or chromophors — selenium for red glass; iron for amber; chromium, vanadium, and cadmium for yellow; and cobalt and iron for blue. Oh, I almost forgot — chromium and iron for green glass. Happy St. Patrick’s Day!

February 2007

Toothpaste Trivia

Did you put rocks (and industrial minerals) in your mouth today?

During our last visit to Arizona, my wife, Pam, and I helped our grandkids, Donovan and Delaney, brush their teeth. Seizing the opportunity, I said, “Hey, see those little shiny specks? Those are rocks in your toothpaste!” The two ran off, mouths full of foamy toothpaste, loudly slurping, “Mommy, Daddy! Look! Rocks!”

The next time you are at your grocery store, take a look at the toothpaste rack. There are many different kinds of toothpaste. Each kind has a whole bunch of ingredients, and each ingredient designed to do a specific job. Toothpaste contains abrasives to scour off bacterial films, fluorides to harden the teeth against decay, chemicals to keep sensitive teeth from hurting and to keep plaque from forming, detergents to remove fatty films, water softeners to make the detergents work better, thickeners to keep it on the toothbrush, colorants and speckles to make it appealing, and a potent flavor to hide the bad tastes of the other ingredients.

Some of those ingredients really are rocks, or more appropriately, industrial minerals. For starters, those little specks in Donovan’s and Delaney’s toothpaste were little flakes of ground mica. They make toothpaste sparkly. Kids love it! 

Other ingredients serve a more functional role. Probably the most recognized ingredient is fluoride (usually sodium fluoride), which comes from a mineral called fluorspar. Fluoride protects teeth in three ways. First, fluoride can be adsorbed onto the surface of a tooth where demineralization (decay) has taken place. Once on the tooth, fluoride attracts calcium, thus speeding up tooth remineralization. Second, tooth enamel generally is made of a mineral called hydroxylapatite (Ca5(PO4)3(OH)). During remineralization, fluorine (F) replaces the hydroxyl ion (OH), making a new mineral called fluorapatite (Ca5(PO4)3F), which is more resistant to acids produced by plaque bacteria than hydroxylapatite. Third, fluoride disrupts the ability of bacteria to metabolize sugars, thus reducing the acidic demineralizing waste that bacteria produce.

Hydrated silica is the abrasive used in many types of toothpaste. It is a transparent gel and is used in clear toothpaste, including the one Lucy and Rosie (in the picture above) use. You might recognize hydrated silica by its other name — silica gel — the desiccant that comes packaged with electronics or other things sensitive to moisture. For you concrete folks, it is the same silica gel that forms during the destructive alkali silica reaction. Silica gel in toothpaste is manufactured from two minerals, quartz, and soda ash. And if you don’t like clear toothpaste, adding some titanium dioxide will make it opaque and white. Titanium dioxide comes from a mineral called ilmenite.

There are tiny crevices in a tooth that allow cold and heat to penetrate to the tooth’s nerves. Pam uses toothpaste that contains potassium nitrate, a chemical that actually blocks the crevices in the teeth, thus reducing sensitivity. Potassium nitrate is a naturally occurring industrial mineral that is also known as saltpeter, one of the main ingredients in gunpowder.

Sodium bicarbonate, another industrial mineral, is added to some toothpaste to make it feel nice in your mouth. It’s the stuff in the yellow box in the back of your refrigerator — baking soda. It combines with acids in saliva and releases carbon dioxide gas, adding to the foam produced by brushing.

There are many more industrial minerals in toothpaste, but I’ll stop now if you promise that sometime you will ask your kids or grandkids, “Did you put rocks in your mouth today?”

January 2007

Industrial Minerals

These unsung minerals are the building blocks
of our way of life.

 

“If DNA is the building block of life, then industrial minerals and rocks are literally the building blocks of our way of life.” 
— Kip Jeffery, Industrial Minerals & Rocks, 7th Edition, SME, 2006

Not long ago,  my wife, Pam, and I were  talking with Andy, a landscape architect who is designing a landscape plan for the yard at our new house. Andy knows that I am a geologist and asked a few questions. 

The conversation went something like this:

Andy: “So what do you study? Oil?”

Me: “No.”

Andy: “Gold?”

Me: “No.”

Andy: “Coal?”

Me: “No.”

I could see he was running out of guesses, so I told Andy that I study industrial minerals. I said there are three broad categories of mineral resources. One group is comprised of metallic minerals like gold, silver, copper, iron, and lead. Another consists of energy minerals such as oil, gas, coal, and uranium. The third group is referred to as industrial minerals and includes any mineral of economic value that is not a metallic or energy mineral. Simply put, industrial minerals are generally considered to be commonplace minerals.

Andy then asked, “What do you use them for?”

That question was all the opening I needed. “For landscaping!” I exclaimed. “Take NPK fertilizer, for example, the P is for phosphorous and the K for potassium. Both come from industrial minerals. Landscaping rock, flagstone, and breeze (3/8-inch minus) walkways are all industrial minerals. Plastic sprinkler pipe, landscape fabric, rubber tires on wheelbarrows, ceramic pots and glazes, bricks, rot-resistant fence posts, paint, glass lanterns are all made with industrial minerals. The concrete for retaining walls, flatwork, and other hardscape is made with aggregate and cement — both industrial mineral products.”

About that time Pam chimed in, “The value of industrial minerals produced in the United States during one year is more than twice the value of all the metallics combined. In fact, the value of aggregate alone is worth more than the metallics.” (Hmmm — all that listening to me rehearse presentations must have sunk in!)

By now Andy started to get into it. “Back to that concrete: last summer, there was a shortage, and we had to schedule deliveries about a week in advance,” he said. “That was a real problem because we had to pour concrete when we could get it — even if it was raining. That was because of that dam in China, right?”

“Right!”  Indeed, many industrial minerals are global commodities.

Andy, Pam, and I had a great time pointing to other objects and yammering on about the industrial minerals they contain. But it was getting late, and we had to move on to more mundane things like trees, shrubs, and perennials.

I assume most of you reading this column are aware of industrial minerals. But did you know that the aggregate industry could not do its job without them? The steel, copper, and aluminum used in excavating, processing, and maintenance equipment could not be manufactured without industrial minerals. That equipment, as well as conveyors, haul trucks, scale houses, and so forth all contain rubber, plastics, glass, ceramics, textiles, and paint, all of which contain industrial minerals. Even the food you bring for lunch was grown, processed, preserved, and packaged using industrial minerals. Taking all of this into account, every $1,000 spent on the mining and processing of aggregate creates a demand for nearly $50 of additional industrial minerals.

This year, Carved in Stone will explore industrial minerals — what they are, where we get them, and how we use them. And if you have a little science in your soul, you too will be able see them transform from commonplace minerals into the building blocks of our way of life.