ferrous sulfide

[1Sponge]

In the case where ferrous sulfide has been precipitated into a water system due to suspected sulfur corrosion of a pipe...

What does ferrous sulfate look like (outside of being a black precipitate) and how does ferrous sulfide behave? What is the typical particle size range? Does anyone know if it can be physically filtered out of water? Does it smear when warmed and stick to surfaces? (as is the case with the particles I am dealing with-I am trying to identify a black particle found in a drinking water system. It is not manganese).

 

[1Sponge]

In addition what is it ferrous sulfide dissovlable in? The specs we have found are not soluble in Freon, hexane, Acetone, methylene chloride or nitric acid.

 

[25362]

The property I'm aware of is its dangerous pyrophoricity in petroleum refineries. Hydrochloric acid may dissolve it by releasing H[sub]2[/sub]S. The iron could also be complexed with special chemicals to avoid the release of this gas.

A Google search would most probably give you the details.

 

[moltenmetal]

Take a sample of the solid and suspend it in some water. Make it acidic by adding a little sulphuric acid. Add a little hydrogen peroxide. If the black crap in the water gradually goes away leaving the water orange, it was ferrous sulphide.

In a reducing environment, it's black, insoluble and generally very finely divided. It plugs filters, carbon beds etc. readily. It's frequently present in water drawn from anaerobic aquifers- and it can be an indicator of contaminated water.

 

[dcasto]

FeS Iron Pyrite, fools gold. Iron Sulphide shows up as very fine black particles a lot like graphite. It can take 1 to 10 micron filters to get it all out. It is sometimes called black rust instead of red rust (Fe3O8).

There won't be anything you would want to use to dissolve it. It can be reacted with HCL to convert it to H2S (poison gas) and Fe + Cl. That is how we clean some vessels and lines. (A 15% HCL is circulated). For serious cleaning, mechanical scapers must be used. In bulk, FeS is a great fertilizer for crops that need sulphur.

The interesting thing is that it normally coats steel lines stopping futher reactions and corrsion to them by H2S.

 

[kenvlach]

Ferrous sulfide FeS has several forms (marcasite -- usually formed in aqueous conditionsl pyrrohtite -- with a wide range of non-stoichiometry Fe[sub]1-x[/sub]S, formed in dry conditions at higher temperatures). Besides being black, can be attracted by a magnet. It has very low solubility in water, but if cannot be filtered out, can be oxidized to sulfate & then by raising pH slightly, precipitated out as ferric hydroxide Fe(OH)[sub]3[/sub].

Ferrous sulfate FeSO[sub]4[/sub] is usually greenish (nearly white if extremely pure Reagent grade). Used for fertilizer, wastewater treatment., hexavalent chromium reduction. Converts to ferric sulfate Fe[sub]2[/sub](SO[sub]4[/sub])[sub]3[/sub] (reddish brown) upon oxidation.

FeS[sub]2[/sub] is pyrite (fools gold), is bright and shiny and yellow gold in color. Is harder (has diamond cubic crystal structure), and is rather non-magnetic.

 

[EdStainless]

You probably have an enitre range of various iron oxides, hydroxides, sulfides, and stuff in between.
I would expect to act 'greasy' because of the fine particle size. Stuff like this is very hard to folter out because it will foul filters so fast.
The trick is to control solubility. You can change pH and oxygen potential (H2O2)to keep material in solution until you want it to precipitate.

If you have much of this I would start to worry about underdeposite corrosion in you piping.

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