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Author: Subject: interesting iron pyrite reaction
bilcksneatff
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[*] posted on 28-11-2007 at 04:22
interesting iron pyrite reaction


I read somewhere that you could oxidize iron pyrite to FeSO4 with H2O2. So, I mixed a little bit of FeS2 with 27% H2O2. Nothing happened, but I decided to let it sit. I came back about 1/2 an hour later. That time, lots of bubbles were coming out of the H2O2 and it had turned a brown color (almost like coca-cola). I'm fairly sure the gas was SO2. Also, I checked the pH of the liquid: it was around 1-2. My guess is that the SO2 dissolved in some of the H2O2, creating H2SO4. I came up with possible reactions:

FeS2 + 6H2O2 --> FeSO4 + SO2 + 6H2O
SO2 + H2O2 --> H2SO4
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woelen
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[*] posted on 28-11-2007 at 04:49


No, the gas definitely is not SO2. It is O2, due to decomposition of the H2O2.

Iron is oxidized from +2 to +3 oxidation state.
The disulfide ion is oxidized to sulfate (indeed producing acid as well)

The reaction products will be a complex mix. It will contain Fe(2+), Fe(3+), sulfate, sulfide, sulphur and maybe even some oxide and hydroxide, due to hydrolysis of the iron(III).

This is not a suitable way for making pure FeSO4.




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bilcksneatff
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[*] posted on 28-11-2007 at 12:35


Really? I could've sworn that I smelled SO2! I guess it was from somewhere else. Thanks for clearing that up woelen.

Which of the products would cause the colors? I looked at the resulting mix today (did the experiment yesterday) the liquid now has a yellowish color.

[Edited on 28-11-2007 by bilcksneatff]
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[*] posted on 28-11-2007 at 14:30


Fe(II) is lightly colored, if at all; solutions typically have a light blue or green color.
Fe(III) is yellow to orange, the color of its hydroxy- species. (Fe(H2O)6(3+), the "plain" ion just dissolved in water, is purple and very acidic; the hydroxy ions, like FeOH(2+) and Fe(OH)2(+), are mildly acidic and much more commonly seen, having a yellow/orange color.)
Fe2O3, or from solution, more likely Fe(OH)3 -- is yellow to orange to brown, a rusty colored precipitate.
There may be still other products, for instance yellow sulfur powder, adducts (does iron form a sulfite complex?), etc.
SO2 is certainly a possibility. Probably not much is produced, as Fe(III) and H2O2 both will oxidize it. It would help that SO2 is a gas, allowing a small amount to evaporate from the solution before it reacts. Alternately, if the peroxide ran out, a limited amount of oxidation may be going on, especially reduction of Fe(III), and to a lesser extent, reduction of sulfate (SO4(2-)) with pyrite to things like thiosulfate and sulfite and so on.

Tim




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