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Can we produce hydrogen with basalt?


Daumic
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The oxidation of Fe2+by water

The Pourbaix diagram (1) defines the fields of existence of chemical compounds according to the pH and the redox potential of an environment. The lines on a Pourbaix diagram define the reactions of transformation of a compound in the other. An area delimited by these lines thus represents the field of existence of a compound.

The following web page (2) shows the Pourbaix diagram of iron and its hydroxides in water. One can see on this diagram that the field of stability of Fe2+ in basic environment is particularly narrow. In addition, this field overlaps the limit of stability of water. This situation shows that the Fe2+ reduces the water and produces hydrogen in basic environment. Only the slow kinetic of the decomposition of water moderates this reaction.

(1)  https://en.wikipedia.org/wiki/Pourbaix_diagram

(2)  https://chem.libretexts.org/Textbook_Maps/Inorganic_Chemistry_Textbook_Maps/Map%3A_Inorganic_Chemistry_(Wikibook)/Chapter_04%3A_Redox_Stability_and_Redox_Reactions/4.5%3A_Pourbaix_diagrams

 

Comparison basalts/peridotites

The fragility of Fe2+ in basic environment appears in nature by the reaction of serpentinization. This reaction is the oxidation of Fe2+ contained in a rock in contact with water. The peridotite, an igneous rock rare in the upper crust of Earth, is particularly sensitive to this reaction because of its very high content of MgO, about 30 %. This high percentage of Mg2+ makes water in contact with these rocks sufficiently basic to allow the oxidation of Fe2+by the water and the production of hydrogen.

According to the web page (3), the average content of FeO of the peridotites is slightly lower than that of basalts: 6.6 % for 7.1 %

One can see on this web page which the composition of basalts is not sufficiently basic to cause the oxidation of ferrous ions. The Fe2+ of basalts is stable in contact with natural water.

(3)  http://www.geolalg.com/chabou/cours4.pdf

 

Production of hydrogen with basalts

The thesis of Benjamin Malvoisin (4) studies the oxidation of the Fe2+ by water in peridotite. This work also shows the possibility of producing hydrogen using steel slags. Hydrogen is obtained by the oxidation of the Fe2+ contained in the slags by water. The high pH necessary to the reaction is due to the high content of ions calcium of the slags.

The upper crust of Earth contains much more basalt than peridotite. I propose to take the parameters described in the thesis of Mr. Malvoisin and to apply them to this source of Fe2+: basalts.

To exploit Fe2+ in basalts, the sequence could be:

-        vertical drilling to reach an underground layer of basalt,

-        horizontal drilling in the layer of basalt followed by a hydraulic fracturing,

-        injection in the well of a limewater.

The limewater is the cheaper base and confers on water in contact with basalt a pH in the order of 12 (5). It should be a sufficient pH to allow the oxidation of Fe2+of the rock. Ions hydroxylbrought by the limewater are not consumed, so the reaction should be maintained by a regular addition of water in the well.

The other parameter controlling the reaction, the temperature, is determined by the depth of the well. If the layer of basalt is at depths greater than 4000 meters, the temperature of the rock should be higher than 150°C. According to the kinetic established in the thesis of Mr. Malvoisin, this temperature should allow a sufficient speed of reaction.

Another parameter could be favourable to the reaction in the well: the oxidation of Fe2+ transforms olivine and pyroxene contained in rock into serpentine and magnetite. This passage from one mineral to another produces a swelling and generates a pressure of crystallization of 300 MPa (4). This pressure is higher than the lithostatic pressure at depths of 4000 meters. This situation could make the well autofracturing. 

The production curve of hydrogen could be similar to that of a shale gas well and thus last several years. After the end of the production, the well remains usable for the CO2 sequestration or geothermal energy.

(4)  https://tel.archives-ouvertes.fr/file/index/docid/934238/filename/33513_MALVOISIN_2013_archivage.pdf

(5)  https://en.wikipedia.org/wiki/Limewater

 

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According  Fe + 2 H+ => Fe2+ +  H2 the standard potential is-0,402 V . The standard potential of 2 Fe2+ + 2H+ => 2Fe3+ + H2  is+0,771 V

From this value alone it can not work. To reduce a metal you need a negativ redox potential. 

With other words the first reaction is working the second not, it would go in opposit way. In rocks you don't have metallic iron, so this doesn't work in my opinion.

 

Edited by chenbeier
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7 hours ago, chenbeier said:

According  Fe + 2 H+ => Fe2+ +  H2 the standard potential is-0,402 V . The standard potential of 2 Fe2+ + 2H+ => 2Fe3+ + H2  is+0,771 V

From this value alone it can not work. To reduce a metal you need a negativ redox potential. 

With other words the first reaction is working the second not, it would go in opposit way. In rocks you don't have metallic iron, so this doesn't work in my opinion.

 

Yes, according the standard potentials for Fe3+/Fe2+ (+0.771 V) and H+/H2 (0V by definition), the oxidation of Fe2+ by water seems impossible but the reaction is pH dependent.

 The potential of the reaction (Fe2+ + H+ > Fe3+ + ½ H2) change with the pH according to the formula :

 E = E0 – 0.06 pH

 The potential of the reaction change with pH : 

pH                 potential

0                   0,771

2                   0,651

4                   0,531

6                   0,411

8                   0,291

10                 0,171

12                 0,051

14                 -0,069


 As you see in this chart, the reaction becomes possible when ph is strongly basic.

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It is an interesting idea.

Have you any information on the economics for isntance how much hdrogen you might obtain for how much limewater injection?

How would you trap and store the hydrogen, bearing in mind it is the second smallest and lightest of all gases?

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12 hours ago, Daumic said:

Yes, according the standard potentials for Fe3+/Fe2+ (+0.771 V) and H+/H2 (0V by definition), the oxidation of Fe2+ by water seems impossible but the reaction is pH dependent.

 The potential of the reaction (Fe2+ + H+ > Fe3+ + ½ H2) change with the pH according to the formula :

 E = E0 – 0.06 pH

 The potential of the reaction change with pH : 

pH                 potential

0                   0,771

2                   0,651

4                   0,531

6                   0,411

8                   0,291

10                 0,171

12                 0,051

14                 -0,069


 As you see in this chart, the reaction becomes possible when ph is strongly basic.

Ok, but I dont think in natural Rocks you have a pH of 14 . This can be achieved only with high concentratete NaOH or KOH. 

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22 hours ago, studiot said:

It is an interesting idea.

Have you any information on the economics for isntance how much hdrogen you might obtain for how much limewater injection?

How would you trap and store the hydrogen, bearing in mind it is the second smallest and lightest of all gases?

To evaluate the quantity of hydrogen economically recoverable by oxidation of Fe2+ in basalts, one can make comparisons with the exploitation of shale gas in the United States. The web page (1) brings elements of calculation. The following chart was established with the data provided by this web page. The methane concentrations estimated in several deposits of shale are expressed on the web page in scf/ton (standard cubic feet/ton). I converted the unit of these data into kg/ton. 

 

Barnett

Ohio

Antrim

New Albany

Lewis

CH4 in scf/ton

325

80

70

60

30

CH4  in kg/ton

6,5

1,6

1,4

1,2

0,6

The exploitation of this type of deposit by hydraulic fracturing has caused a fall in the price of gas in the United States. Most of this gas is used to produce electricity. The essential property of gas for this production is its heat of combustion.

The oxidation of FeO by water produces magnetite according to the reaction:

3 FeO + H2O  >  Fe3O4 + H2

One needs 216 g of  FeO to produce 2 g of H2. The average content of basalts of FeO is 7 %. A ton of basalt thus contains 70 kg of FeO. The oxidation of this Fe2+by water can release 0.6 kg of H2 / ton of basalt.

This value is in the low part of concentration range of shale gases given higher:

 

Barnett

CH4

Ohio

CH4

Antrim

CH4

New Albany

CH4

Lewis

CH4

Basalt

H2

Concentration  or generation   in kg/ton

6,5

1,6

1,4

1,2

0,6

0,6

But heat of combustion relativizes this low value. With equal mass, the heat of combustion of hydrogen is more twice the higher than that of methane:

 

CH4

H2

Heat of combustion in MJ/kg

50,01

120,5

The following chart presents the methane concentrations and the possible production of hydrogen expressed in MJ/ton.

 

Barnett

CH4

Ohio

CH4

Antrim

CH4

New Albany

CH4

Lewis

CH4

Basalt

H2

Concentration  or generation  in MJ / ton

328,5

80,9

70,8

60,7

30,3

78,1

In this way, the data are more favourable to basaltic hydrogen.

(1) https://spec2000.net/17-specshgas.htm

 

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30 minutes ago, chenbeier said:

I still  dont beleave it will work. In alkaline solution Fe2+ and Fe3+ are existing as Hydroxides/oxides, there is no movement of ions. So far no hydroxicomplex known. 

What you believe will not influence the rocks.
It's plausible, but I see a couple of factors.

To get the reaction to take place at any useful rate you need to raise the temperature.

That affects both the oxidation potential, and it's rate f change with pH.

So the data you have simply don't apply.

It's true that, with Ca(OH)2 you can just about get the pH to near 14. Ba(OH)2 might be a better bet.

 

However, the only practical way to get the Ca(OH)2 is by heating limestone.

And that generates CO2.

 

So, does the energy recovered as H2 save CO2 overall, once you account for that?
 

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And again Fe(OH)2 or Fe(OH)3 is not much solouble. You need the reaction 2 Fe2+ + 2 H+ =>2 Fe3+ + H2 . In alkaline solution at pH 14 not much H+ available.

I am also wondering where this formula  E = E0 – 0.06 pH was developed from Nernst law.  I am missing the the log(Fe2+/Fe3+) in it. To many question marks??????

Edited by chenbeier
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On 25/10/2018 at 12:02 PM, chenbeier said:

Ok, but I dont think in natural Rocks you have a pH of 14 . This can be achieved only with high concentratete NaOH or KOH. 

It is not necessary to reach this pH of 14. At pH 12, the potential of the reaction is zero. That means the reaction is equilibrated:

Fe2+ + H+ < > Fe3+ + ½ H2

In water at this pH 12, Fe2+ and Fe3+ are not soluble and thus remain fixed in the rock. The hydrogen produced is soluble in hot water. If limewater is put into circulation in the well, we can extract the hydrogen. The removing of H2 of the well displaces the reaction on its right wing and thus permits the continuation of the ferrous oxidation.

10 hours ago, chenbeier said:

And again Fe(OH)2 or Fe(OH)3 is not much solouble. You need the reaction 2 Fe2+ + 2 H+ =>2 Fe3+ + H2 . In alkaline solution at pH 14 not much H+ available.

I am also wondering where this formula  E = E0 – 0.06 pH was developed from Nernst law.  I am missing the the log(Fe2+/Fe3+) in it. To many question marks??????

( Fe2+ + H+ > Fe3+ + 1/2 H2 ) is a simplified writing of the reaction.

The real reaction is : 

3 FeO + H2O > Fe3O4 + H2

___________

The formula ( E = E0 - 0.06 pH ) is developped from Nernst law to see the effect of pH on the potential. The formula is obtained by considering the concentrations of Fe2+ and Fe3+ equal.

You can see (but french text):

http://www.chimie-briere.com/pcemoxred/OXYDO.htm

 

 

 

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15 hours ago, Daumic said:

It is not necessary to reach this pH of 14. At pH 12, the potential of the reaction is zero. That means the reaction is equilibrated:

Fe2+ + H+ < > Fe3+ + ½ H2

In water at this pH 12, Fe2+ and Fe3+ are not soluble and thus remain fixed in the rock. The hydrogen produced is soluble in hot water. If limewater is put into circulation in the well, we can extract the hydrogen. The removing of H2 of the well displaces the reaction on its right wing and thus permits the continuation of the ferrous oxidation.

In your table it says still 0,051 V at pH 12. So no reaction!  Now you saying the ironions are not solouble what I also think, but how should a reaction takes place if the ions not dissolve?

 

 

15 hours ago, Daumic said:

( Fe2+ + H+ > Fe3+ + 1/2 H2 ) is a simplified writing of the reaction.

The real reaction is : 

3 FeO + H2O > Fe3O4 + H2

___________

The formula ( E = E0 - 0.06 pH ) is developped from Nernst law to see the effect of pH on the potential. The formula is obtained by considering the concentrations of Fe2+ and Fe3+ equal.

You can see (but french text):

http://www.chimie-briere.com/pcemoxred/OXYDO.htm

 

The reaction above can take place in a furnace at high temperature.

And In nature I dont think that Fe2+ = Fe3+. So the potential is still depending of the concentrations, which are not really existing, because nothing is dissolved.

In my opinion its still an adventure thesis.

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20 hours ago, chenbeier said:

Fe(OH)2 is also almost insoluble. 

There Is a pretty big difference in solubility.

http://www.wiredchemist.com/chemistry/data/solubility-product-constants

Why is anyone paying attention to the tables of data which relate to completely the wrong temperature?

I'm far from convinced that all the Fe in the basalt is there as FeO rather than a silicate.

There also seems to be a failure to understand the importance of the partial pressure of hydrogen.

 

The only sensible way to find out would b by experiment

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I dont have a laboratory.My kitchen is for cooking food and not doing chemical experiments. On the other hand I have not the equipment to drill a hole in rock some feet deep. Also to find iron in this rock.  Maybe the poster of this thread should do it.

Edited by chenbeier
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On 27/10/2018 at 1:51 PM, chenbeier said:

In your table it says still 0,051 V at pH 12. So no reaction!  

Good remark. I forgot to consider the effect of temperature on the Nernst equation. The effect of pH on the potential of reaction (Fe2+ + H+ > Fe3+ + ½ H2) is expressed by:

E = E0 – 0.06 pH

But the factor 0.06 is really the result of (R.T.ln(10)/F) at ambient temperature (see the web page (1)).

The reaction doesn’t occur at ambient temperature. According to the thesis of Mr Malvoisin (2), 150°C is a better temperature to obtain a good kinetic for the reaction. At this temperature, the value of the factor (R.T.ln(10)/F) is 0.084. So the effect of pH on the potential of reaction at 150°C is expressed by:

E = E0 – 0.084 pH

pH

Potential at 150°C

0

0,771

1

0,687

2

0,603

3

0,519

4

0,435

5

0,351

6

0,267

7

0,183

8

0,099

9

0,015

10

-0,069

11

-0,153

12

-0,237

13

-0,321

14

-0,405

According to the precedent chart, the reaction becomes possible between pH 9 and pH 10 at 150°C.

 

(1) https://fr.wikipedia.org/wiki/Équation_de_Nernst

(2) https://tel.archives-ouvertes.fr/file/index/docid/934238/filename/33513_MALVOISIN_2013_archivage.pdf

 

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10 hours ago, chenbeier said:

As above mentioned, do the experiment. 

The experiment has already been made. In his thesis, Mr Malvoisin describes the production of hydrogen by a treatment of a steel slag. The FeO contained in the slag has been oxidized by water in a furnace at 200°C / 50 MPa. This experiment (1) on the slag continues for the purpose of the production of nanoparticles of magnetite. Despite its high purity, the hydrogen produced in this condition is too expensive.

(1) https://www.linksium.fr/projet/hymagin/

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22 hours ago, John Cuthber said:

That's not difficult.

Drill a deep hole.

Add water.

Yes, temperature and pressure are provided freely by Earth with the following gradients:

- 30°C / km

- 30 MPa / km

 

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