Abandoned Mine Posts

by Andy McAllister, Watershed Coordinator

Resource recovery, extracting and utilizing what had been considered “waste” or “by-product” material, has been the buzz word in AMD treatment for a few years now. Historically, the iron sludge that settles in an AMD treatment system’s settling ponds, the stuff we want to keep out of the creeks, has been seen as a waste product with no use. However, Bob Hedin of Hedin Environmental had been thinking outside of the box and spent several years looking for a way to make lemonade out of lemons. Or in this case, paint pigment out of iron oxide sludge. In the Sewickley Creek Watershed in Eastern Westmoreland County, the concept of resource recovery is becoming a reality.

The Marchand treatment system near the town of Lowber has been designed and built with resource recovery, specifically iron oxide recovery, in mind and in October 2007 Hedin and the Sewickley Creek Watershed Association celebrated the system’s first birthday. At the Marchand treatment system first anniversary celebration , Hedin recalled the very beginnings of the resource recovery process at the Marchand system,”This water is very treatable and it’s a good site. We were able to work with the watershed association to get a modest Growing Greener Grant to determine whether we could indeed, treat this water on the site”, Hedin recalled.. “That ended up leading into a full scale proposal to DEP to design, permit, and build the treatment system. We’re confident we could make good iron sludge here,” Hedin stated. “We were finished in October 2006 and the water was turned on and it’s been running for one year now”, Hedin explained. “It’s working like a charm”.

In seven years, when the settling ponds have about a foot and a half of iron sludge in them, Hedin will return with his trucks and pumps to remove the accumulated sludge, dry it out, and take it away to be processed into pigment. In traditional systems, the accumulated iron sludge waste product has to be removed from the settling ponds and disposed of. With resource recovery guiding the process, the watershed association gets long term maintenance and the sludge gets used rather than dumped into a landfill.

Unfortunately, not all iron oxide sludge coming from Abandoned Mine Drainage is appropriate for use as pigment. The quality of the irox oxide must be appropriate for its destined use as pigment for paints and stains. Also, how the mine drainage is treated plays a vital role in determining whether or not a particular sludge is suitable to be used for pigment.

Marchand treatment system ponds at Lowber.  Photo:  WPCAMR 

For more information:

The Sewickley Creek Watershed Association

Environoxide pigments

Hedin Environmental

by Bruce Golden, Regional Coordinator

Did you ever wonder why there’s such a wide range in the chemical make-up of coal mine drainage discharges? It’s because
there’s a great diversity in the mining environments in which mine drainage is formed. This multipart series of AMP will
explore, on an introductory level, the connection of mine drainage characteristics with the mining environments that created
it. It’s not meant to be rigorous, but to mainly get you thinking about the kinds of things that can happen underground that
are influential in the making of polluted water.

Part 5. Waste Coal Piles… Efficient AMD Factories

In the last three installments, I showed how the mineral pyrite is chemically reactive in the wet oxidizing environment we live in and depend on. Pyrite, as you’ll recall, is typically present in small percentages in coal and surrounding geologic strata. In its natural state, there is little opportunity for water and air to get to the pyrite, thus it’s protected from chemical reactions. Mining changes that big time.

Since the Abandoned Mine Drainage problems we currently deal with were created a long while ago, some dating back to the mid 1800s, it’s instructive to visit some of the mining processes of yesteryear to see if we can figure out how those processes have led to present day problems.

The first mining environment we’ll examine is waste coal piles. These man-made small black mountains go by a slew of colloquial names including gob piles, boney piles, slate dumps, slag heaps, and (as our friends in eastern PA’s anthracite region like to call them) culm banks. I once met a woman who called the pile close to her home Dmitri. I didn’t ask. Whatever we call them, they’re made up of the unwanted stuff discarded following the coal extraction process which most likely came from underground deep mines.

Thousands of waste piles accumulated over the course of mining in Pennsylvania. They are usually located in the vicinity of the old mine portals, as this was the most convenient and economical way of disposal. The piles are generally made up of a good bit of coal and a bunch of stuff that isn’t, including rocks called shale that are very commonly found adjacent to coal seams. (Note to my local newspaper: there’s no slate in waste coal. Please stop calling the piles slate dumps and the stuff in them slate. And while we’re at it, the orange stuff polluting streams isn’t sulfur. ) Why was so much coal discarded back in the old days? First, the separation techniques weren’t that great, and second, smaller pieces of coal had little economic value because the furnaces that burned coal required bigger chunks.

Anyway, throughout coal county it’s still fairly common to see these big, ugly, gray-black, steep-sided, highly eroded, loose-material, get-you-real-dirty, hard-to-walk-on piles with very little vegetation just sitting there as they have for decades. Their size varies greatly from one defunct mining operation to the next. Those associated with larger coal operations are really big and are measured in millions of tons. Sometimes, you’ll see pinkish-orangish streaks and patches in the piles. That’s the residue (sometimes called red dog) from the coal in the pile catching fire, sometimes spontaneously (that pesky oxidizing environment at work again) with a long slow burn that may have taken years to complete.

Because a waste coal pile’s origin is an accumulation of loose, relatively small material, it’s prone to shifts in the material. Think of mini landslides and being loose underfoot. Furthermore, because vegetation has trouble establishing and sustaining itself in this rather inhospitable growth medium, the piles are commonly devoid of most plant life. Without a good root system to stabilize the material, the material remains unstable over time. This is a perfect recipe for erosion. In fact, deep erosion gullies are a prominent feature of waste piles. This can result in siltation problems for adjacent streams. Those streams can also take on a decidedly orange color which, of course, is a very good indicator of AMD. Let’s see how that happens.

We’ll change gears and zero in on a small chunk of coal that might be found in a waste pile. For illustration’s sake, let’s assume it’s a perfect cube, say one inch on a side. That means that each face of our coal cube has an area of one square inch. Since cubes have 6 faces, our cube of coal has a surface area of 6 square inches. Now, the only pyrite contained in our coal cube having any opportunity to undergo that pyrite oxidation reaction we talked about several installments earlier is the pyrite located at the cube’s surface, on those 6 square inches. Water and oxygen can’t get to the pyrite located in the cube’s interior. The places on the cube’s surface where pyrite is exposed are the only places where oxygen, water, and pyrite can all team up and thus the only place that pyrite oxidation reaction can occur. Those 6 square inches of surface area on our cube puts an upper limit on the amount of pyrite that can oxidize on that piece of coal.

Okay, now let’s say we take our cube and carefully split it in two, making the split parallel to a cube face. We wind up with two rectangular solid chunks of coal. I think we can all agree that the original 6 square inches of surface area of the combined two pieces are still intact. In addition we have two new faces resulting from the split, each one having one square inch of surface area. So the two chunks of our carefully constructed mind experiment now have a combined surface area of 8 square inches. If we do a little ciphering, that comes out to a 1/3 increase in surface area with the opportunity of having exposed pyrite that can react. More exposed pyrite raises the limit of the amount of pollution that can be formed. Note: In the real world, we don’t see perfect cubes and often cracks, fissures, or fractures allow water to penetrate the interior regions of solid coal.

To generalize, when a solid is fractured or broken up into smaller pieces, the resulting surface area will increase. We’ve also seen that the pyrite reaction is dependent on having the pyrite exposed on a surface. Putting these facts together, it becomes clear that a waste coal pile, made up of lots and lots of relatively small broken-up chunks, is going to have an enormous amount of surface area with exposed pyrite which can be available to react when united with water and oxygen.

A waste coal pile is usually quite porous to water infiltration. This is particularly ominous when it comes to AMD formation. When it rains, water can easily find its way to a tremendous amount of exposed pyrite. On the pile’s outermost surface, the supply of atmospheric oxygen will be substantial. As water infiltrates into the pile’s interior regions atmospheric oxygen will become more scarce, yet water itself can transport oxygen in the form of dissolved oxygen. Even with available oxygen being the limiting factor, the initiating and most important reaction of AMD formation, the oxidation of pyrite, has tremendous opportunity to occur. Furthermore, pyrite not reacting during one rain will have the opportunity during the next, or the next, or the next after that. For piles that can interact with ground water, the situation is even worse: an almost continual source of water available as a reactant in pyrite oxidation (limited only by available oxygen).

The pyrite oxidation reaction occurs in copious amounts when it rains. The other AMD reactions described in previous installments, i.e. the ferrous to ferric oxidation and the hydrolysis of ferric ions, may also occur in or on the pile. The extent to which they occur will depend on the amount of available oxygen, the pH, and the presence of certain bacteria in the water. In addition, some complex chemical reactions (which are beyond the scope of this article) may result in the formation of highly reactive sulfate salts, easily visible as a light greenish-yellow solid. In essence, these solids are concentrated instant AMD, ready to dissolve during the next rain. No matter what, once the initiating pyrite oxidation reaction has occurred, the AMD express has left the station.

To sum things up, waste coal piles can be very prolific producers of AMD because of the tremendous amounts of exposed pyrite. Just add wind and rain with a dab of chemistry and you’ve got a pollution factory.

By Andy McAllister, Watershed Coordinator

As most people who are involved in watershed work know, we watershed folks love acronyms. Even the invertebrates can’t escape our penchant for acronyms. In this edition of Abandoned Mine Posts, we continue our Life in Our Streams series and examine a group of aquatic invertebrates with a unique acronym.

Healthy streams unaffected by pollutants such as acid rain or AMD generally have a high diversity of macroinvertebrate species representing several orders. In these healthier streams, one group of macroinvertebrates is most often well-represented. That group of macroinvertebrates is known as the EPT.

The term EPT, refers to three orders of aquatic insects that are well
known to be indicators of good water quality: Ephemeroptera, Plecoptera, and Trichoptera. These insects are more commonly known as Mayflies, Stoneflies, and Caddisflies. All have an aquatic phase in their life cycle and all of them emerge from their watery home and take to the air when they metamorphose into adults.

Mayflies (Order: Ephemeroptera)

Graceful and elegant, mayfly adults often emerge from the water in large numbers during the spring and spark feeding frenzies among resident trout.  As their order name would imply, their life is ephemeral, lasting a day or little longer.

While mayfly adults do not eat and only live long enough to ensure the survival of the species, mayfly nymphs live on the stream bottom for about a year, consuming anything from small bits of organic debris called detritus, to algae or other smaller invertebrates, depending on the individual tastes of that particular Genus. Several mayfly species are considered to be very sensitive to acidic conditions in a stream.

Stoneflies (Order: Plecoptera)

Often beautifully adorned with intricate color patterns, stonefly nymphs on the other hand, are generally carnivores, preying on anything that is smaller than they are. However as with anything, there are exceptions and while many stoneflies are predators, there are some stoneflies that do prefer to consume detritus and algae. Stonefly adults, once emerged from the stream, can and do eat plant material.

Their existence as adults, while longer than that of the mayflies, is very short. Stonefly adults can live for up to a few weeks. During that time, they mate and lay eggs to ensure the next generation of stoneflies. Many of the stoneflies had traditionally been considered to be fairly tolerant of acidic conditions in a stream compared to other macroinvertebrate groups. However, recent studies suggest that this order of aquatic insects may be more severely affected by acidification than previously believed.

Caddisflies (Order: Trichoptera)

Caddisfly larvae are the engineers of our aquatic world. Most caddisfly larvae live in cases that they construct out of sand, rock, twigs, leaf pieces, and any other kind of underwater debris. The beauty of these miniature constructions can be breathtaking. Some caddisflies generate their creations out of silk, create a net, or construct no case at all.

Caddisflies as a group can tolerate only a slight amount of acidity in
a stream however, there are a few species of caddisfly that are very
tolerant of acidic conditions.

Bruce Golden, Regional Coordinator

Did you ever wonder why there’s such a wide range in the chemical make-up of coal mine drainage discharges?  It’s because there’s a great diversity in the mining environments in which mine drainage is formed.  This multipart series of AMP will explore, on an introductory level, the connection of mine drainage characteristics with the mining environments that created it.  It’s not meant to be rigorous, but to mainly get you thinking about the kinds of things that can happen underground that are influential in the making of polluted water. 

Part 4.  That Chemical Ball Keeps on Rollin’… then Stops.

In Part 2 of AMD and Mining Environments, I talked in some detail about the first act of several in the formation of AMD.  To review, the chemical reaction that starts the whole AMD pollution ball rolling is the oxidation of pyrite in the presence of oxygen and water

which results in a complete chemical makeover with the chemical species of ferrous ions, sulfate ions, and hydrogen ions being dissolved in water. 

In the last installment of AMD and Mining Environments, I told you about the next act, the ferrous to ferric oxidation reaction,

in which ferrous ions (from the first reaction) are converted to ferric ions with a corresponding reduction in the numbers of hydrogen ions. 

So let’s move on.  Fair warning though: get yourself a cup of coffee / Jolt cola to get you through.  Who knew there could be so much to say about one stinking reaction?

Act 3. 

Even though the newly formed ferric ions (Fe3+) at least symbolically may look like (and indeed have been transformed from) ferrous ions (Fe2+), don’t be fooled into thinking that things haven’t changed a lot.  The loss of that single little electron means we’re talking about one very changed ion, one with a whole new attitude.  Ferric is all grown up and it’s time for this ion to settle down. 

You see, ferric isn’t all that enthralled with the whole aqueous scene.  The freedom with being dissolved amidst all that water, as was the case in its former ferrous life, is no longer so appealing.

The problem is a single ferric ion isn’t capable of leaving the aqueous life by itself… all because of that blasted +3 charge.  Ferric desperately needs help if it’s to escape its wild aqueous surroundings… help in the form of an offsetting negative charge. Only a complete neutralization of that charge will do.

As fate would have it, help is all around.  The very thing ferric is trying to be free of will ultimately be its salvation… water.  Water molecules find ferric quite attractive, but realize that without a significant commitment, ferric will not be interested.  Remember that nothing short of complete neutralization of’ the +3 charge will satisfy ferric.  Water by itself has no charge and nothing of interest to ferric.  However, water has a trick… it’s able to split itself into two parts: a negatively charged hydroxide ion (OH-) and a positively charged hydrogen ion (H+). 

Hydroxide’s negative charge definitely has spurred ferric’s interest, yet ferric knows hydroxide’s single negative charge will never be enough to satisfy its appetite for negative charge completely.  Similarly hydroxide knows that ferric is far too much ion for it to handle by itself.  A little out of the box ionic thinking is all it takes to come up with the solution.  The wedding of ferric with not one, but three hydroxides is the ideal way to provide neutralization bliss as a compound, joined together by the attraction of their opposite charges.  Not only do the happy ions enjoy complete neutralization with their union, the miracle of phase change is bestowed on them as they make the transition from the aqueous to the solid state as the newly formed ferric hydroxide (Fe(OH)3(s)).  Music please!

The ceremony (reaction) is known as the hydrolysis of ferric ion. 

Before you raise your eyebrows of ferric taking three partners, know that this sort of nuptial is quite acceptable, indeed expected, in the world of atoms and molecules where neutralization of charge is a very proper thing.

The ceremony, unfortunately, saw some unsavory guests appear.  You may remember the Acidz, a.k.a. hydrogen ions, from the previous installment.  As a consequence of water making itself attractive to ferric by splitting into hydroxide ion, it also created its counterpart, hydrogen ion. Three new Acidz came into existence as a result of the ferric – hydroxide marriage.  Those chemical gangstas are far too often implicated with all sorts of trouble, if not now, then almost assuredly later.

Following the ceremony, the happy compound, now a respected member of the solid and stable Rust family, must say goodbye to the aqueous environment.  It’s no longer able to mix well with all the water surrounding it. Ferric hydroxide must immediately embark on the new journey of precipitation which, aided by gravity, will take it to the bottom where it will join other ferric hydroxides that have preceded it as it settles into its new neighborhood.  Should the compound remain underwater, as many do, it will join its neighbors known as the Yellowboy clan.  However, should ferric hydroxide find itself high and dry, things become unbearable for the hydroxides which still yearn to be near their former water siblings.  Inevitably, something’s got to give.  Ferric hydroxide experiences a breakup where two hydrogens and an oxygen go their own way as a water molecule, leaving a somewhat lighter, but wiser and more stable compound formally known as ferric oxyhydroxide, but informally called iron oxide among its friends.

Iron oxide can look forward to a rather uneventful existence and a marriage characterized by solid bonds that are likely to last a very, very long time.

Ferric, once a part of another long lasting union with sulfur in its marriage as the mineral pyrite, and now a part of a new union in the Rust family, is now safe because the oxidizing environment that broke up the pyrite marriage is no longer able to sing its siren song.

___

Okay, let’s review the hydrolysis of ferric ions, this time without the dramatization.  Here’s the balanced reaction.

Here’s one way to “read” the equation. “An aqueous ferric ion combines with 3 water molecules to form 1 molecule of solid ferric hydroxide and 3 aqueous hydrogen ions.”

Here are some salient points:

• This is called a hydrolysis reaction because of the reaction with water.  This general form of reaction is common with other metal ions.  I’ll again use aluminum as our example.                  
  Hydrolysis reactions of this sort produce a number of hydrogen ions equal to the  charge on the metal… 3 in this case.
• This is an acid forming reaction.  A lowering of pH is common.
• This reaction generally happens very quickly following the ferrous to ferric oxidation reaction. 
• In water, the solid ferric hydroxide particle that forms will join up with many other ferric hydroxide  particles in forming a larger particle.  How big this particle grows will determine how fast it settles.  In still water, bigger particles settle out faster.
• Ferric hydroxide  also goes by common name yellowboy.  Its color can vary from a yellow to a deep orange.  In a stream, as yellowboy settles and coats the bottom of a stream, it fills in the innumerable nooks and crannies created by pebbles, rocks and other features on the stream bottom.  In doing so, the habitats of benthic (bottom dwelling) macroinvertebrates (small creatures without backbones, a.k.a. bugs) are destroyed, creating serious food-web implications for fish.
• Given the chance to dry out, yellowboy undergoes a reaction where a water molecule is lost, forming ferric oxyhydroxide.
                               
  Similar reactions can also occur which result in various forms of rust, or iron oxides.  These compounds are commonly used as pigments.  Iron oxides will stain your skin, but don’t represent a safety hazard.
• In an oxidizing environment (as we live in with our abundance of atmospheric oxygen) rust-like compounds are pretty much the end of the line chemically.  They are very stable and not much is ikely to come along and react with them.

We’ll I’m going to stop now before I think of anything else. Thanks for hanging in there. Join me again for the next installment of AMD and Mining Environments where we’ll shift our attention to the neighborhoods where these chemical reactions take place.