I was watching a video with my son filmed in a salt mine on the shores of Lake Erie where they claim the salt is being mined for use on (snowy) streets. Perhaps I should watch again more closely, but I got the impression* the salt being mined was NaCl and not CaCl. So, a few salty questions came to mine, I mean mind! :
a) Isn’t CaCl used on streets since its properties are better at melting the snow (a little exothermic action, or was I taught wrong?) AND better ability at lowering the freezing point so the melted snow doesn’t readily refreeze?
b) Do they mine CaCl?
c) How is food-grade salt “harvested”? Precipitated out from seawater, perhaps?
*by telling us the salt bed formed millions of years ago when the Great Lakes were believed to be a sea…makes me believe it must be NaCl they’re mining.
the previous post answers most of your question. i’ll add though that rock salt is often is almost always the result of an ancient sea or ocean drying up (evaporite formations,) getting coverd by sediments, and then the lighter salt “punches” upwars to form a salt dome. deep-seated domes are very stable, are nuclear bomb-proof, and sometimes act as petroleum traps. the salt often crytalizes into the cubic mineral halite.
food-grade salt is rarely pure NaCl. magnesium carbonate is added to keep it from clumping up in shakers. sodium iodide is for your thyroid.
Something I learned from a geology text recently is that some “evaporites” are actually not – they are precipitates, instead. Just as undisturbed shallow tropical seas can become saturated with calcium carbonate and lay down limestone, which happened a lot in the past and is actually happening off the Florida Keys and Bahama Banks today, hypersaline lagoons can become saturated with sodium chloride (and other salts, but the overwhelming majority of seawater salt is NaCl), and salt precipitate out of it. The scenario is unusual but sufficiently plausible to have happened over geological time. Imagine an embayment with a narrow mout open to the ocean, so that water can and does enter through it. There is no freshwater inflow, just seawater entering at the mouth. Evaporation from the surface water increases the salinity, and the hypersaline brines, being heavier than the ocean water replenishing the supply, tend to drift to the bottom – where they reach a saturation point. At that point, salt will crystallize out of the brine, just as carbonates and sulfates (less soluble) did before them. In fact, some such deposits show a pattern of limestones near the mouth, gypsum and related rocks near the middle, and halite and related rocks at the extreme end.
To what’s been said above, I’d add only that the majority of ocean salts are NaCl, so however it precipitates out it conjstitutes the majority of evaporite deposits, with gypsum (a sulfate) the second most common. KCl, MgCl[sub]2[/sub], and the other salts are extremely rare as mineral deposits, and generally are produced by chemical processes, as is CaCl[sub]2[/sub] to meet industrial needs.
I’m going to ask for a cite, less because I have any reason to doubt you than that (a) it seems economically unsound and unnecessary, and (b) I’d like to read more on it.
I remember learning that was why halite facies developed strata of different minerals in a certain sequence. But evaporites can produce the same sequence in a concentric pattern with halite in the center, when around the edges of a playa evaporation and precipitation are happening simultaneously, especially because evaporation from the edges inward concentrates more of the unprecipitated minerals, which concentration drives further precipitation.
Going to grade school near Cleveland, we were taken on field trips downtown to see sites of local history; they showed us the salt dome Whiskey Island at the mouth of the Cuyahoga (which hasn’t been an island since the army corps of engineers rechanneled the river mouth, connecting Whiskey Island to the mainland in the process); the Morton salt company owned it (I’m not sure if I remember seeing the Morton umbrella girl on the sign over Whiskey Island) and mined road salt. This was back in the 1960s. When did CaCl come into use as road salt? Way back when, they definitely used NaCl. They told us how the island got its name was the empty chambers of the salt mines proved useful for hiding contraband liquor during Prohibition. Or something.
It’s not pure, since it’s sea-water-salt (which is not pure NaCl). Even sea-salt is purified & refined. Only grey salt is not refined but even there, they take special care in harvesting it, and in general it;s cleaned.
wiki “The dilute brine of the sea was largely evaporated by the sun, and the concentrated slurry of salt and mud was scraped up. The slurry was washed with clean sea water so that the impurities settled out of the now concentrated brine. This was poured into shallow pans lightly baked from the local marine clay, which were set on fist-sized clay pillars over a peat fire for the final evaporation. The dried salt was then scraped out and sold.”
Note that the wiki article here is a bit inexact in naming. Very little of what is sold as “sea salt” (in the USA at least) is harvested this way, the salt that is- is sold in a tiny niche market in gourmet stores, and runs up to 10X the price of table salt. It’s not a very good article for this reason.
In the USA, salt that starts in the ocean but is re-dissolved, purified, and re-crystallized, is commonly sold as “sea salt”. This salt is the exact same substance as table salt, except for the price. It’s pure NaCl. (So is Kosher salt). (Note that sea salt, table salt and even Kosher salt can be iodized. But table salt is usually iodized.) Note that it’s pure white.
“Grey salt” aka Fleur de sel must conform to rather strict harvesting restrictions and indeed has a grey tinge to it and irregular clumps & crystals. It’s cleaned, but not purified. The taste is slightly different than table salt. Grey salt has a tiny amount of iodine naturally occurring.
CaCl is used to clear ice on roads at points (often as a brine), but it’s much more expensive that good old NaCl, so the vast majority (95%+ at a guess) of road salt is straight up NaCl.
There are vast beds of crude sodium chloride around the Great Lakes and elsewhere. It is extracted both by underground mining and by pumping water down into the beds and back up. It is used extensively as ice melt, by the chemical industry, and as table salt. Depending on its use, it may be dissolved, filtered, recrystalized, etc. to purify it. It also has other substances added in some cases. Sodium hydroxide and chlorine are basic to the chemical industry. One major source for them is the electrolysis of brime.
Calcium chloride is also used for ice melting, working better at lower temperatures.
If underground salt deposits are often mined via dissolution anyway, why not just start with ocean water, which is right at the surface and much more accessible?
Concentration and energy required to evaporate the water.
In solution mining you generally pump hot water down the well, dissolve the salt, so the fluid comming up is close to saturation ( accounting for the cooling, you dont want salt precipitating out in the surface return lines). You can then evaporate off a small ammont of water for maximum ammount of salt recovered. On the potash solution mining poject i worked on as a side project, the evaporation costs were significant. You would need a great deal of energy to evaporate sea water to get salt, as sea water is not that concentrated. You can go solar evaporation, but production rates can be quite low.
You can dissolve up to 39 grams of salt in 100 gms of hot water. I don’t remember the concentration of salt in the ocean, but it is much lower. Since in most cases, it is then recrystalized, the higher concentration is more economical.
Since sunshine is free, there are places where they do fill shallow ponds with sea water to produce salt.
Few techniques are overlooked in the quest for a buck.
hmmm, for calcium carbonate, the skeletons of corals and other animals with calcareous body parts consolidate into limestone at certain lattitudes and depth due to retrograde precipitation (they precipitate at warmer temperature.) that partly explains why there is little limestone formation in deeper water and higher lattitudes where the water is colder, the acidity due to carbonic acid is higher.
is there an article for this? i can imagine that in your secluded bay, even an occasional entry of sea water through tides or waves is enough to keep its salinity constant. also, near land, there is always the chance of rain run-off entering that system. i can’t imagine a dynamic littoral system increasing salinity to a point that solid salt begins to accumulate. it should be the opposite —a tendency to be brackish.
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