operation oaxaca: down the drain.
acid mine drainage. (030)
this is carlos.
we got news-of-a-lifetime.
i will share if i decide to proceed.
in the meantime,
i’ve narrowed my point-of-focus.
what type of waste do i want to concentrate on from mines?
the one that most relates to oaxaca and its precious metal mines:
acid mine drainage (AMD).
the next few articles i release will be an overview of this monster.
so sit back, and watch me distill on how i’ll take down the demon.
CJ
amd 101.
amd in simple terms is a bath full of metals, sludge, and acid from precious metal mines (i.e. gold, silver) or coal mines.
the water will look something like this:
and this is a picture of the mine in oaxaca (2022):
in either case,
the gold, silver, or coal mines must extract via ores.
ores are the rocks where the minerals/elements are.
but the ore has sulfide material in it.
The chemical reaction occurs when the sulfide is exposed to water and air.
and now, we have sulfuric acid.
example:
the silver ores often contain silver combined with sulfur to form a sulfide compound like “(Ag2)S”.
this is known as silver sulfide.
Ag → silver
S → sulfide
this occurs because one silver element has one valence electron in its outer shell.
one sulfur element has six valence electrons in its outer shell.
if we get two silver atoms… we can bond with the sulfur atom and give the two electrons to sulfur.
then we’ll have an ionic bond to make silver sulfide.
p.s. → the silver atoms are giving up their valence electron to the sulfur atom. so it’s an ionic bond.
sulfide → a sulfur atom that gained two electrons.
and the silver sulfide is known as monoclinic acanthite.
why?
because monoclinic acanthite is the stable form of silver sulfide below 173°C (343 °F).
and acanthite is the only stable form [of silver sulfide] in normal air temperature… which must be exposed to air in a mine.
sulfuric acid is very acidic (via the acidity constant).
acidity constant, denoted (Ka/pKa).
the lower the pKa, the stronger the acid is.
for sulfuric acid, the pKa values are −2.8 & 1.99.
that is low.
but for mining, how does sulfuric acid get into the water?
via pyrite rock.
the pyrite rock is in the silver ores.
and that sulfide converts to sulfuric acid via this reaction (for iron in this case):
and the acid mine drainage color is related to this, along with the pH of the water.
but why the red-orange color of acid water?
because at low pH values like one or two, there’s no color…
because the metal ions/minerals are dissolved within the water.
but because some minerals precipitate (aka pH goes up)… the water begins to turn color.
that color is the ions being removed/precipitated from the water and going to the river's bottom.
and when pH goes up, H+ ions decrease and OH- ions increase.
H+ → hydrogen ions.
OH- → hydroxide ions.
hydroxide ions can form insoluble metal hydroxides through a process known as precipitation.
and the pH varies from element to element.
for iron, it’s pH 3 when we see iron becoming precipitated.
as a result, the pH of acid mine drainage water is about pH 4 or lower.
and this is no bueno economically and for the environment.
this was a warning back in 2013.
about >40 hardrock mines that will generate an estimated 17–27 billion gallons of polluted water yearly.
this includes:
- perpetuity
- costly water treatment.
other unknowns.
it turns out…
there is more than one chemical reaction to create the acid mine drainage.
the one i mentioned above means this:
the erosion of pyrite includes the oxidation of pyrite by oxygen. and sulfur is oxidized to sulfate and ferrous iron is released.
this reaction generates two moles of acidity for each mole of pyrite oxidized.
the second reaction includes a transition from ferrous iron (Fe²⁺) to ferric iron (Fe³⁺).
its conversion of ferrous iron to ferric iron consumes one mole of acidity.
bacteria (thiobacillus ferrooxidans) in the water increase the rate of oxidation from ferrous to ferric iron.
this reaction rate is pH dependent with the reaction proceeding slowly under acidic conditions (pH 2–3) with no bacteria present.
and the reaction is several orders of magnitude faster at pH values near 5.
this reaction is referred to as the “rate determining step” in the overall acid-generating sequence.
another reaction that can occur in the acid mine drainage is the hydrolysis of iron.
hydrolysis → chemical reaction to split the water molecule.
three moles of acidity are generated as a byproduct.
other metals can undergo hydrolysis at approximately the same pH as iron.
the formation of ferric hydroxide precipitate (solid) is pH dependent.
solids form if the pH is above about 3.5.
but below pH 3.5, little or no solids will precipitate.
mole → avogrado’s number, 6.022 * 10²³ atoms.
another reaction is the oxidation of additional pyrite [or other metals] by ferric iron.
this process will continue until either ferric iron or pyrite [and other metals] are depleted from the solution.
in this reaction, iron is the oxidizing agent, not oxygen.
small conclusions.
i am just barely realizing this now,
and damn i’m a moron lol.
the silver ores in san jose del progreso have exceeded permissible metal limits:
- iron: 1845%
- aluminum: 955%
- thallium: 300%
- lead: 167%
why?
because there is iron in these ores.
and aluminum is one of the dissolved metals in acid mine drainage (AMD).
on top of that, acidity of the AMD is contributed by pH and iron + aluminum.
this acidity can force pH to be about pH 2–3 and begin precipitation of AMD.
and the precipitation causes the color.
this is why the mining pictures look like this:
this is known as ferric hydroxide. it’s the ferric iron.
and my hypothesis, at last, was proven right.
iron and aluminum had to come from the ores or the intended mining object.
so there is an excess of iron, aluminum, zinc, nickel, etc.
and rare earth elements.
time to get to the forefront of innovation and see the gaps.
how do we get the sludge/drainage metals outta there?
sources.
© 2024–2100 by Carlos Manuel Jarquín Sánchez. All Rights Reserved.
