Mineralien / Minerals / Minerales > Allg. Diskussionen Mineralien / General discussions minerals

Cu oxidation/weathering question

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harzgeist:
Noah,

You can it imagine as follows, starting with a solution of copper sulfate.
The copper sulfate with calcium carbonate (calcite) forms copper carbonate  in a (hypothetical) interim step. This (neutral) copper carbonate decomposes with water due to (partial) hydrolysis to malachite or azurite and carbon dioxide. The pH value and the concentration of CO2 are responsible whether malachite or azurite will be formed preferably.
Knowing this, you will be easily able to write down the equations yourself  ;D

Thomas

smaragd123:
Maybe at Jennifers Location is no Calcite and so the Environment ist to acidic to form Malachite.

jennifercindrich:
Yes this would be true indeed. This area has no calcite. These answers make sense and have been very helpful.

Thank you everyone!

Jennifer

harzgeist:
Hi Noah


--- Zitat ---Maybe at Jennifers Location is no Calcite and so the Environment ist to acidic to form Malachite.
--- Ende Zitat ---

Yes, that will be the case, due to much decomposing pyrite, mainly. So why just pyrite?
The pyrite is composed of Fe and S in the ratio of 1:2. The most oxydated product of weathering is iron(III)sulfate with a ratio of 2:3. With other words, pyrite contains more S than be bound by the contained iron. The overstanding S causes an acidic environment.

As to the equations you asked for
First let us use an other scription
for malachite CuCO3*Cu(OH)2
for azurite 2CuCO3*Cu(OH)2

Both are composed compounds of copper carbonate and copper hydroxide.
Copper carbonate can be formed from copper sulfate and calcite

CuSO4+CaCO3 <-> CuCO3+CaSO4

Copper carbonate decomposes hydrolytic

CuCO3+H2O <-> Cu(OH)2+CO2

This equations can run in both directions and are in an equilibrium state. According to the rules of the lae of mass action a low pH value and/or a high concentration of CO2 shift this equilibrium to the left side and prefers the forming of azurite.

Thomas

smaragd123:
OK thank you.

Aber werden Malachit und Azurit in den meisten Fällen nicht durch primäre Sulfide gebildet. Um aus denen Kupfercarbonat entstehen zu lassen braucht man doch ein saures Mileu, bzw. Schwefelsäure oder?
 

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