Dewatering: Thickening, Filtering, CCD, Water Treatment & Tailings Disposal

Dewatering: Thickening, Filtering, CCD, Water Treatment & Tailings Disposal 2017-03-23T09:42:05+00:00
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How Silver in ARD Acid Rock Drainage AMD (10 replies)

John Koenig
1 year ago
John Koenig 1 year ago

Effects of trace silver concentrations in mine waste on ARD production

I know about the antibacterial effects of silver on human-based microbes - this has been around for centuries. I just learned that silver appears to have the same effect on acidithiobacillus ferrooxidans; e.g., bioleaching pyritic ores with silver content can be problematic with Acid Rock Drainage. Can anyone recommend a technical paper or reference that explores this phenomenon in straightforward language that a mining engineer could understand? Thanks

Victor Bergman
1 year ago
Victor Bergman 1 year ago

I seem to recall some work published in the CIM journals in the 1980's and 1990's. As silver is considered a contaminant there maybe some work done published in Groundwater and Groundwater Monitoring and Remediation. BTW do not sell yourself short - some of the most intelligent people (not all mind you, ;-), especially when I was escorting them home from the bar) have been mining engineers.

John Koenig
1 year ago
John Koenig 1 year ago

A bio-leaching expert & friend noted that the presence of chalcopyrite is an interference (which is OK for bioleaching situations) and that chloride negates the bactericidal effects of silver as well.

Bob Mathias
1 year ago
Bob Mathias 1 year ago

Chloride is a double edge sword though, adding it also mobilizes many toxic metals. Care must be taken if you are thinking of adding to the mix. Containment would be recommended.

Maya Rothman
1 year ago
Maya Rothman 1 year ago

Please understand that I'm not trying to oxidize pyrite: just the opposite. Understanding this mechanism might help to explain why some pyritic waste rock dumps or tailings ponds go acid when others do not. Silver content is not a constituent typically included in acid base accounting, eh? Maybe it should be (for metal mines).

Alan Carter
1 year ago
Alan Carter 1 year ago

I just meant specifically chloride. I understand the role of silver as an anti microbial. I do know other experiments have been done to control the bacteria in question. Some have included using waste milk so that the acid generating bacteria is out competed by other flora, for example, in ARD environments.

Tony Verdeschi
1 year ago
Tony Verdeschi 1 year ago

Maybe this will help. The microbiology is well within your reach!

https://microbewiki.kenyon.edu/index.php/Silver_as_an_Antimicrobial_Agent

The article states that the effect is due specifically to Ag+(aq), so Cl in solution will limit the free Ag+ to the solubility limit from AgCl, which, if I did the arithmetic correctly [SQRT(Ksp)* MW silver] would be about 1 mg/L in dilute solutions. That's a pretty high Ag concentration

Alan Carter
1 year ago
Alan Carter 1 year ago

This is great background - thanks. Has anyone seen a correlation between ARD production and silver content in humidity cell tests of pyritic tailings or other mine wastes?

Tony Verdeschi
1 year ago
Tony Verdeschi 1 year ago

The correlation will have to do with the origin and nature of the ore body from which the tailing is developed. There are certain styles of mineralization - obviously epithermal precious metals, for example, or the "cobalt association," and in quite a few supergene-enriched in the Cordillera (including the famous bonanza silver deposits in the western US). Of course, in those cases one would not expect to see Ag associated with high pyrite, unless it was a limited-enrichment example, like perhaps Copper Cities (see Guilbert and Park). You would expect to possibly see low levels of Ag in porphyry coppers. A review of geologic reports and exploration data (or production data) would probably identify specific targets to look at.

Helena Russell
1 year ago
Helena Russell 1 year ago

My only thought on this is that microbial oxidation of pyrite generates thiosulfate, which can dissolve silver. In certain wastes, it may be possible for the resulting silver-thiosulfate complexes to reach toxic concentrations, thereby limiting the extent of sulfide oxidation. This idea makes for interesting speculation, but I doubt that it would explain much more than a few cases, at best.

David Kano
1 year ago
David Kano 1 year ago

Interesting work at Michigan Tech found that silver sulfide minerals would interact with mercury cyanide, dissolving silver and precipitating mercury. http://digitalcommons.mtu.edu/cgi/viewcontent.cgi?article=1593&context=etds

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