Would NH4OH reduce&dissolve metals such as iron in regolith?

From: Coos Haak
Fe++ and Fe+++ are the only stable forms of iron in aqueous solution.
Iron metal is definitily not.

I'm confused. I was under the impression that banded iron deposits,
dated from the time when the Earth's ocean first changed from anoxic to
oxic condition, due to cyanobacteria venting oxygen from photosynthes
into the ocean, were precipated iron oxide. The neutral iron was
previously dissolved nicely in the anoxic water, but the iron oxide
isn't as soluble as neutral iron was so much of the iron oxide had to
precipate out. Am I mistaken??

See above, and your high school chemistry book.

That book belonged to the school district so couldn't be kept by me.
But in any case, that book assumed there's an atmosphere of 20% free
oxygen (O2) around any water, with lots of the oxygen dissolved in all
samples of water, that oxygen reacting with any neutral iron to yield
iron oxide just as it did when cyanobacteria first released lots of O2
into the water. So I wouldn't trust that book to say the right thing
about what's stable or not in a reducing atmosphere with virtually no
O2 whatsoever.

wrote:
The neutral iron was
previously dissolved nicely in the anoxic water, but the iron oxide
isn't as soluble as neutral iron was so much of the iron oxide had to
precipate out. Am I mistaken??

Correction: Fe(+2) vs. Fe(+3), not 'neutral iron' (which isn't soluble
in water -- does your spoon dissolve in your coffee?)

Paul

From: "Paul F. Dietz"
Correction: Fe(+2) vs. Fe(+3)

See later below.

not 'neutral iron' (which isn't soluble in water -- does your spoon
dissolve in your coffee?)

That's not a valid argument. The ocean is miles deep, immense volumes
of water, and a solubility of some tiny bit that wouldn't be observable
when dipping a spoon in coffee might add up to a large total amount of
iron dissolved in the ocean.

Also, I don't drink coffee, so referring to my coffee is meaningless.

However after I posted that earlier article, before I saw your response
just now, I was researching a related matter, looking for a definitive
source for the source of the oxygen atoms that get incorporated into
carbohydrates (apparently they come from the hydrogen donor such as
water, not at all from the CO2), when I discovered:

Subject: ADMIN: Introduction to Evolution FAQ
http://www.google.com/groups?selm=c2...&output=gplain
After the advent of photosystem II, oxygen levels increased. Dissolved
oxygen in the oceans increased as well as atmospheric oxygen. ...
Initially, when oxygen began building up in the environment, it was
neutralized by materials already present. Iron, which existed in high
concentrations in the sea was oxidized and precipitated. Evidence of
this can be seen in banded iron formations from this time, layers of
iron deposited on the sea floor. As one geologist put it, "the world
rusted."
That's the sort of text that gave me the idea it was neutral iron
dissolved in the anoxic ocean. If the word "oxidized" refers to the
redox state (neutral - +2 - +3), then it tends to imply the iron was
neutral initially, although +3 - +3 is oxidation, but still if that
was the intended meaning the wording could have been clearer. But then
I discovered that confirms what you said, that the dissolved iron was
originally ferrous, but now I'm having trouble finding it again. Coming
up with stuff like this:

http://www.google.com/groups?selm=3b...ver.cfl.rr.com
The banded iron formations are deposits of oxidized iron ore.
Oxidation means the presence of oxygen.
Um, that's not the correct meaning nowadays. Oxidation means removing
electrons. Reduction means adding electrons. Oxidation in general
doesn't require oxygen. So I won't consider this author authorative.

Molecular oxygen oxidizes ferrous iron to ferric iron, which precipitates.
He seems to be saying what you're saying, need a more authorative
source however, sigh.

http://www.google.com/groups?selm=3B...E5%40olywa.net
... the two common forms of iron.

I actually know of at least three forms: neutral/metallic, ferrous, ferric.

The reduced form is much more soluble in water than the oxidized
form.

If he's referring to ferrous and ferric, ignoring metallic, then he's
agreeing with you. Ferrous iron isn't really reduced, except compared
to ferric iron. Ferrous is oxidized two-thirds as much as ferric iron.
On an absolute scale, it's not reduced at all, it's the opposite.

The evidence of the banded iron formations is not just that they
formed at a certain time, but also that they *did not* form *before*
a certain time. The banded iron formations are younger than the
earth. These deposits are quite clearly sediments formed in ancient
oceans. This means that just before that, the iron was soluble. That
means that it was the reduced form. The enormous quantity of banded
iron around today means that there was quite a bit of iron in the
reduced form at that time.

Nicely stated argument, modulo the confusing "reduced" without
clarifying that means ferrous (less oxidized) not absolutely reduced.

We think it was photosynthesis (you know, plants) that introduced
oxygen to the atmosphere.

Well plants didn't exist yet, not even algae, only photosynthetic
bacteria. So once again I won't count that as an authorative source.

http://www.nature.com/cgi-taf/DynaPa...=doi1081023602
It
is generally believed that banded iron formations precipitated from an
ocean whose bottom waters contained significant concentrations of
dissolved ferrous iron, and that this sedimentation process terminated
when aerobic bottom waters developed, oxidizing the iron and thus
removing it from solution. In contrast, I argue here that anoxic
bottom waters probably persisted until well after the deposition of
banded iron formations ceased; I also propose that sulphide, rather
than oxygen, was responsible for removing iron from deep ocean water.

Hmm, this is just a letter to Nature, not a peer-reviewed article, so I
don't know what to make of it.

http://www.humboldt.edu/~natmus/Exhi...me/PreCam.web/
Massive amounts of oil shale were deposited ...
the seas of this time were rich in soluble ferrous ion (Fe^2+)
OK, that source looks like it can be trusted.

* Banded Iron-Formation (BIF) constitutes the majority of the
world's iron deposits. Most commonly these deposits consist of
alternating layers of black hematite and chert. ...
BIF deposits are a direct result of oxygen release by Precambrian
microbes. During much of the Precambrian the Earth's surface waters
and atmosphere were anoxic (oxygen-free) so that iron would exist
mostly in its reduced (ferrous or Fe^2+) form. Vast quantities of
ferrous iron entered the ocean surface through volcanic action,
upwelling, and run-off. Photosynthesis by cyanobacteria in the
surface waters produced oxygen which reacted with ferrous iron to
give the much less soluble ferric iron (Fe^3+), precipitating out
iron hydroxide (rust). Seasonal and/or biological cycles resulted
in intervening periods when iron or oxygen were not as available
resulting in the interlayered chert (microcrystalline quartz
precipitate).
Ah, that's not what I found yesterday (and lost and haven't found
again), but it'll suffice to confirm what you said. And to finish the
description with one word not defined the

Linkname: Dictionary.com/hematite
URL: http://dictionary.reference.com/search?q=hematite&db=*
A black or blackish-red to brick-red mineral, essentially
Fe[2]O[3], the chief ore of iron.
Hmm, that's just plain ferric oxide, not iron hydroxide. Why the
discrepancy?

The earliest evidence of life comes from chemical fossils formed only
100 million years after the end of the Hadean period of intense
bombardment by meteorites and planetesimals (3.8 bya), during which
huge impacts by planetesimals would periodically vaporize the oceans
and sterilize the Earth.

Actually that's now seriously doubted. Although the surface of the bare
Earth (where Oceans had been boiled away) were probably steralized,
deep inside the rock there might have been lots of life, similar to the
recently-discovered prokaryotes which survive quite nicely miles under
the surface, apparently using seeping volcanic gasses and pressurized
liquid water as sources of energy and food. This kind of life might
have survived the intense bombardment and re-seeded life in the
near-surface rocks after each bombardment event, and eventually
re-seeded life in the bulk of the oceans after a relatively short time
(my guess, only a few million years).

http://www.geo.msu.edu/geo333/crystalline_rocks.html
In the presence of free oxygen, very little dissolved iron would be
present in the oceans, because oxygen causes iron to form insoluble,
rustlike (ferric iron) oxides, which remain in rocks and in soils, and
which cannot dissolve to accumulate in the oceans. In the absence of
free oxygen, however, iron (ferrous iron) is readily soluble, and it
could easily have been weathered from iron-rich rocks and transported
in solution by streams to the oceans. Thus, quantities of iron
sufficient to produce the banded iron formations could only have
accumulated in the Precambrian oceans before the atmosphere and waters
of the earth attained significant concentrations of free oxygen.
Actually, the precipitation of iron in the open ocean was
accomplished by oxidizing it. In the absence of any available free
oxygen in the oceans, the oxygen necessary for this precipitation was
probably supplied by primitive, single-celled phytoplankton
(planktonic plants),
(Nit: They weren't plants, or even algae, they were bacteria.)
which had evolved the process of photosynthesis,
but which had not yet developed a means of coping with oxygen waste
produced in that process.
... Modern photosynthesizing plants exhale waste oxygen
through their cell walls; however, they do this without oxidizing
their own tissues, because they manufacture special oxygen-mediating
enzymes that counteract the poisonous effects of the oxygen. Prior to
the development of such enzymes, early Precambrian phytoplankton may
have used the abundant ferrous iron dissolved in the water all about
them as a protective oxygen sink. Oxygen produced by the organism
during photosynthesis was instantly combined with the dissolved
ferrous iron, thereby oxidizing it to ferric iron and causing it to
precipitate to the sea floor. Petrologic thin-section studies reveal
tiny spherical bodies around 30 microns in diameter in many banded
iron formations that may be the remains of the very phytoplankton that
caused precipitation of the iron.
When at last photosynthesizing plants began to manufacture
oxygen-mediating enzymes, they no longer needed to use dissolved
ferrous iron to dispose of their waste oxygen. Instead, they could
simply expel oxygen directly into the water in which they lived. Free
oxygen began to accumulate thereafter in the earth's ocean ...

Ah, this story is slightly different from what I understood befo
What I had before is that oxygen diffused from the photosynthetic
bacteria into the surrounding water, whereupon it met ferrous iron,
combining to yield ferric iron which precipitated. Only when the
ferrous iron was all gone did the oxygen saturate the water and form
bubbles that floated all the way to the water's surface and start to
fill the atmosphere with oxygen, which initially combined with existing
methane and ammonia and carbon monoxide, and only when those were all
gone the oxygen began to exist free in the atmosphere. So per this
variant story, did the oxygen from photosynthesis initially get
eliminated by combining with ferrous iron right within the cells,
perhaps immediately adjacent to the photosynthetic site itself, rather
than combining with ferrous iron outside the cells?

Anyway, I'm convinced, I stand corrected on the form of dissolved iron,
ferrous not neutral.

So if we're processing Lunar regolith, after we first use hydrogen to
remove most of the oxygen (using electrolysis to recycle the hydrogen
and store the oxygen away), and if we next want to recover the bulk of
the iron (more than the little bit that we can get by using a magnet),
should we use some non-oxygen acid such as HCl or lesser-oxygen acid
such as sulfurous (not sulfuric) acid to dissolve the iron away as
ferrous salt (chloride or sulfite respectively), and then away from the
regolith, in a reaction chamber, add oxygen to convert ferrous to
ferric iron to precipate it out for storage?

From: (Henry Spencer)
tracer experiments using O-18 found O-18 in the released oxygen when
there was O-18 in the water, but not when there was O-18 in the CO2.
Precisely how that can be reconciled with the stoichiometry of the
net reaction, they didn't explain.

I posted a query in one of the biochemistry/evolution newsgroups,
hoping to get a definitive answer to this puzzle, but never got one, so
I've given up and come back here to summarize the minor clues I got.
Apparently, in the long chain of reactions, from the actual
photosynthesis which uses solar energy to convert ADP + PO4+ to ATP,
through the chain of uses for that energy in ATP to pry hydrogens off
some hydrogen donor (H2S, H2O, etc. depending on which kind of bacteria
we're talking about), it's the hydrogen being pried off the hydrogen
donor that releases whatever the rest of it is (S2 or O2 etc.), rather
than oxygen from the CO2 elsewhere in the chain giving off O2. The O2
from the CO2 apparently all or mostly gets incorporated in the
carbohydrate instead of released. But like I said, I couldn't get any
definitive answer to satisfy our query.

Photosynthesis is complicated, but it seems to work by prying the
hydrogens off water (thus releasing oxygen) and combining them with
CO2. That combination yields carbohydrates,

Yes, looking only at the original input to the process and the final
output, not the middle steps.

but it ought to also yield water as a byproduct

Why? What makes you think that? In particular, if the overall reaction,
after prying the H's from the H2O, is H + H + CO2 = HCOOH or something
like that, in a biochemical system evolved to be as efficient as
possible, why would any of the O's be wasted by re-combining them with
those H's to yield water again? I'm not saying it doesn't happen, I'm
just asking why you would think it ought to happen??

Are you perhaps saying that respiration, good old Kreb's citric-acid
cycle, would be going on at night when photosynthesis isn't available
for making ATP so the creature (plant/algae/cyanobacterium) would have
to find another source of ATP to keep alive, so would convert
carbohydrates and O2 back into CO2 and H2O, so tracer on the O's in the
original CO2 that went into the carbohydrate would yield traced O's in
the H2O from Kreb's respiration? But maybe just as all the O's in the
H2O went to O2 while the O's from CO2 went to carbohydrate during
photosynthesis, now during respiration all the O's from carbohydrate
went into CO2 while O's from O2 went into H2O? Just speculating how
things could come out the way that is observed based on
post-photosynthesis carbohydrate-production and Kreb's cycle being
basically inverses, not just in overall stiochemistry (sp?) but in the
paths of specific atoms (in this case O's from two sources) through the
chain of reactions both forward and backwards.

and it's not clear to me why some of that doesn't get mixed in with
the incoming water. Perhaps such mixing was too minor to be readily
detected due to the choice of experimental conditions.

If a vast majority of the respiration, or whatever you believe should
be a source of water from biochemistry, produces water where the O's
come from O2 not from carbohydrates, as I guessed above, then the
mixing is irrelevant because it re-creates H2O where the O's come from
O2 released when the original H2O gave up its hydrogen, so if O's are
not labeled in water on input it won't be labeled in O2 released in the
middle and won't be labled in water re-created later and won't be
released in O2 the second time around. Still I wish I had been able to
find an expert in the other newsgroup who would post a definitive
answer to our puzzle, sigh.