The occurrence of a variety of mercury species is depending very much on the pH and the solubility, but also whether the aquatic system is operated under oxic or anoxic conditions.
Is there any water-soluble mercury sulfide species existing in aquatic systems particularly at pH above 8?
Thank you and Glück Auf!
Dr. Rüdiger B. Richter
Dear Bezah,
Thank you for that answer, but the question is more tricky, than referring to any water soluble mercury compound, only.
best regards
Ruediger
Mercury compounds above pH 8 are rearely soluble in water having oxidising conditions however in reducing environment mercury can be in soluble state.
At pH above 8 there is no any water soluble mercury compound, especially sulfide, since the solubility constant of mercury sulfide is very low, meaning that at very low concentrations of Hg and sulfide would participate as solid Hg-sulfide compound.
I have no particular answer for this complex question... But try to refer to Figure 7.4 Solubility of HgS(s) in the absence (a) and presence (b) of elemental S (activity set to unity) as a function of total dissolved sulfide concentrations... and 7.5 Dominance diagrams for aqueous phase species of Hg (a) and MeHg (b) as a function of pH and concentrations of S... in Book Chapter by Ulf Skyllberg in ENVIRONMENTAL CHEMISTRY AND TOXICOLOGY OF MERCURY by GUANGLIANG LIU, YONG CAI and NELSON O’DRISCOLL.
It used to be avaliable for download but I cannot find the link anymore...
Dear Prof. Slavka, thank you for your answer!
Yes, I am fully aware that mercury sulfide has a very low solubility product, but that doesn't necessarily mean, that there is not any other mercury sulfides present that has a different solubility characteristics and that is what I had asked for.
Dear Thomas,
your given Reference was quite helpful.
Thank you very much
You can use a program like MineQL (I think I spelled that correctly). We used it in my Aquatic Chemistry class to tell what species were "present" under different assumptions. HgS is highly insoluble. Methyl Mercury is highly soluble. So, you might need to look at alternate mercury compounds.
Dear Andrew,
thank you for your input. - That is an advantage of this platform, that a comprehensive input from other faculties is possible.
kind regards
Ruediger
Ruediger,
I think we should post the figures I refered to, so that if anyone else will be looking for this answer. So if you dont mind - I will extend your thread. Here are the two mentioned figures - I should have done that before.
T.
Dear Thomas,
great idea and very cooperative. This might be interesting for all those, who believe that Hg-Sulfide is cinnabarite, only.
Hg(HS)2 (aq), Hg(S2O3)2-2, Hg(S2O3)3-4, HgHS2-, HgS2-2 are the species available, depending on its Log K values, the specie may be major or minor. Mook for Visual Minteq database and also you can try Visual Minteq software for Log C - pH diagram and then decide. All the best!
Dear Aravinth,
that is almost a perfect answer! Mabrook!
Ruediger
Dr. Richter,
About 100 years ago people used to extract HgS from its ore by leaching it in an alkali solution of 1% NaOH and 4% Na2S over the course of several hours (Several patents use different formulations but the consensus is a few hundred mM of Na2S and a high pH >8). This metallurgical technique was useful in selectively targeted Hg(II) and leaching it into the aqueous phase by creating higher order complexes that were only able to be formed with Hg and no other metals which would remain precipitated as a sulphide. This method is no longer used for obvious reasons (I.e., Sulphide solutions are a hazard). Stability constants for expected species (e.g., Hg(HS)2, HgHS2-, HgS2-2 , HgS(H2S)2, etc..) are calculated in the literature and can be used for calculating speciation in solution but I would take these with a grain of salt as these to my knowledge thee species are just speculation to what is actually being formed. Albeit, many papers use these stability constants for (e.g., HgS2-2 being formed at high pH) as it does to some extent reflect solubility for practical reasons.
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