Can pyrite / iron sulphite dissolve in sulfuric acid?

Question

Can pyrite / iron sulphite dissolve in sulfuric acid?

Answer 1

Also, you can't neglect microorganisms when dealing with pyrite decomposition.  There are sulfur-oxidizing bacteria that digest pyrite and other sulfides to obtain energy.  They oxidize the sulfide to sulfate, producing sulfuric acid and iron sulfates.  This is a major source of acid mine drainage that can pollute rivers.

Sometimes, samples of pyrite (after collection from the mine) will be observed to decay, forming a crust of iron sulfates and sulfuric acid.  The decay has been reported to spread between adjacent specimens, and one theory is that bacteria are responsible for the reaction and are able to transmit the "disease" to other pieces of pyrite.

So even if the reaction with sulfuric acid is slow, the presence of these bacteria might speed up the dissolution and even replenish the sulfuric acid.

Answer 2

Pyrite is not iron sulfite, it is iron disulfide (FeS2). This can be considered to consist of Fe2+ ions and disulfide ions, S2(2-) (similar to peroxide ions, O2(2-)). Since this anion is very basic, it can dissolve in acids, hence, we would expect:

FeS2(s) + H2SO4(aq) -----> FeSO4(aq) + H2S2(?)

However, I gather that H2S2 is unstable; so I would guess that it would decompose to H2S and free sulfur. Then again, I don't know for sure, because there's almost no information available about it.

Still, there is a reference in some book I have to pyrite reacting with an acid drip, eventually causing a fire. So, I would conclude that there is a reaction, although you probably shouldn't try it with more than a few drops of acid, in case the highly toxic H2S is given off.