Rounding the Four Corners – March 2012

Potash

By Larry Larason

While I was sprinkling some de-icer crystals on the shadowed part of my driveway, I wondered, “Just what is in this stuff?”  I figured it wasn’t salt [sodium chloride, NaCl], so I checked the bag and found it was potassium chloride [KCl].  Potash.  Potassium is one of the three nutrients needed by all plants, and potash is used as a fertilizer, so when the snow melts and dissolves the potash, it fertilizes the weeds that grow wherever it runs off.  Hmmm.  Well, that’s better than using sodium salt, which is bad for plants.  We want healthy weeds instead of no ground cover, I guess.

In the Four Corners we don’t hear a lot about potash, but in the region around Carlsbad it’s a big deal.  The mining companies in southeast New Mexico employ about 1000 people.  And the mines contributed more than $3 million annually in severance tax to the state budget in 2000 through 2004.  Potash may not be as glamorous as gold or silver, but it is a moneymaker, and demand is increasing worldwide.

Gallup Journey Rounding the Four Corners

Potash plants form the most visible alteration of the natural environment between Moab and the Canyonlands in this 1972 photo.

Why does it have such a dumb name?  Because in the old days the way to produce it was by soaking wood ash in a pot or kettle.  When the ashes were removed, a chemical rind called pot ash containing salts of potassium was left in the kettle.  It was used in making glass and soap, as a fertilizer, and was a valuable commodity then.  The first patent in the United States was granted in 1790 for an improvement in the making of potash.  The name of potassium was adapted from potash: drop the H, double the S, add “–ium” to denote an element, and, importantly, put the accent on the second syllable or it will sound funny.

As early as the 1600s in England, spreading wood ashes on the soil was recommended to improve crop yields, although the reason it worked wasn’t understood.  Potassium was only discovered in 1807.  In some wetter parts of the country spreading wood ash on the garden is still a good idea, but most people don’t burn much wood these days.

Now, most potash is mined.  Seawater contains potassium salts, not as much as sodium salts, but enough that it can become concentrated when the water evaporates.  I wrote about the process in an earlier column about the Pennsylvanian age salt deposits in Utah [GJ: August, 2006], but here is a brief recap: When seawater is isolated and evaporating it cannot hold the dissolved minerals.  First the carbonates precipitate out as limestone [calcium carbonate], then the sulfates as gypsum/anhydrite.  Finally, as more water evaporates, the chlorides drop out as sodium and potassium salts.  New Mexico’s salt and potash were deposited during the Permian Period, but the process is much the same.

Nearly 90% of potash is used as agricultural fertilizer.  Mined potash is contaminated by sodium salt, so it must be purified by a variety of means.  Several potassium compounds fit under the potash umbrella, including potassium carbonate and sulfate.  Different compounds are preferred as fertilizer for different crops and soil types, but the important point is to add water-soluble potassium to the soil.  Plants cannot grow without it, and it is quickly depleted by intensive agriculture.

The mines in New Mexico were first worked in 1931.  These mines still supply almost 80% of our domestic potash production.  Since the potash is shallowly buried, it is mined in shafts and tunnels less than 2000 feet deep.  In other locations, Utah and Michigan, where it is deeper, it is extracted by solution mining: water is pumped down into the salt strata, left in place for up to a year in order to dissolve the salt, and then the brine is brought to the surface and evaporated to yield crystalline salts.

The 425-square-mile ”Potash Area” in New Mexico has been considered a strategic resource since 1934.  As such, it is mostly protected from drilling for petroleum or gas.  This decision was reinforced in 1973 when gas leaking from a well caused an explosion in a mineshaft that injured ten miners.  New regulations were put in place soon after.  The rising price of oil has led to about five oil wells per square mile in places just outside the Potash Area, but comparatively few within it.  Horizontal drilling may enable the oil industry to tap the petroleum reservoirs, which are much deeper than the salts.  The price of potash and worldwide demand for it has been rising as well, so it is wise to protect this resource.

Potash is also mined near Moab, Utah.  The deposits are deeper there, 2000-3000 feet.  The original mine was worked with heavy equipment, but the tunnels were about 100 degrees F, and the rocks contain dangerous gases.  After an explosion killed 18 workers, the company converted to solution mining.

U.S. production is only about 1/5 of what is used in our country.  The rest is imported, mostly from Saskatchewan, Canada.  So any newly discovered deposits are tempting targets for mining companies.  Arizona has potash in the Holbrook Basin; exploratory drilling has revealed that maybe as much as 25% of the national reserves are located there.  Unfortunately, much of it lies beneath the Petrified Forest National Park.  In 2004 Congress expanded the boundaries of the Petrified Forest; however, they never appropriated the money necessary to purchase the private and state land inside the new boundaries.  At least one rancher with 64,000 acres was willing to sell to the government, but now he is getting antsy.  In fact, he has leased with a potash exploration company, which is drilling wells to assess the potential.  Stay tuned for some interesting legal questions.

The salt that underlies and interfingers with the potash has uses as well.  Table salt is produced by solution mining near Glendale, Arizona.  And solution cavities are used to store liquid petroleum gas.  There are eleven of these storage caverns near Holbrook.  The Waste Isolation Pilot Plant [WIPP] stores radioactive waste in tunnels cut into salt beds in the southeast quadrant of New Mexico’s Potash Area.

And speaking of radioactivity, potassium has an isotope, 40K, that is radioactive.  Bags of potassium chloride used as a salt substitute for high blood pressure patients, are radioactive enough to use in classroom demonstrations of atomic decay.  If you’re squeamish, like me, there are things going on in your body all the time that you’d really prefer not to think about; here’s another: at least 4000 potassium atoms break down every second somewhere beneath your skin.  Kaboom!  But you can’t live without potassium.  So enjoy your mutations!

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