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Tom Meuzelaar

High ionic strength solutions

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[admin notice: the below is from the former GWB users group email distribution list. This message was originally posted 12/20/2005]

Posted by: Laureen Kelly

Hi GWB user's group,

I'm currently working at obtaining funds for purchase of GWB, so I won't be

listing software versions, input files, etc. Tom Meuzelaar at RockWare has

been extremely helpful; he also suggested I post my question to the GWB

user's group:

I'm trying to do speciation modeling (at a minimum) for a soda lake (ionic

strength of 2.2 M in the monimolimnion) that contains a lot of arsenic. The

monimolimnion is highly reduced. Is there any software available that would

enable me to model typical soda lake ions/complexes at depth (reduced), as

well as arsenic? If not, is there any way to readily incorporate other

species into a database for high ionic strength solutions (i.e. Pitzer

database)? From what I've read so far, this is quite a problem. I'm not an

experienced m! odeler, and could really use the advice of someone in the know.

Thank you,

Laureen Kelly

Posted by: Mark Logsdon

Hi Laureen,

A good place to start, if you don't know it already, is Ptacek, C.J. and D.W. Blowes, 2003. Geochemistry of Concentrated Waters at Mine-Waste Sites, in J.L. Jambor, D.W. Blowes and A.I.M. Ritchie (Eds), Environmental Aspects of Mine Wastes. Mineralogical Association of Canada Short Course Series Vol 31, p. 239-252. Although Carol and Dave (both at U. Waterloo) are not explictly dicussing alkaline lakes, the discussion of the Pitzer formulation and some of the case studies may be useful to you. Carol's dissertation addressed siderite solubilty in highh-I solutions,, and she has worked extensively since then in developing and applying virial methods to systems that will be of interest to you. She and a recent student have been working in the Sherridon tailings, Manitoba, an arsenopyrire-rich tailing system with extermely high [As] in pore water. Because mine tailing almost always cross! es over from oxidized to reduced, she may have some useful info for you on this, too. The bibliography is extensive and up-to-date, including sources for work on trace species not including in databases like H-M-W and PHRQPITZ.

A couple of other sources may also help, especially when it comes to framing the conceptual models you wish to investigate. Domagalski, JL, HP Eugster and BF Jones, 1990. Trace metal geochemistry of Walker, Mono and Great Salt Lakes, in RJ Spencer and I-M Chou (Eds), Fluid-Mineral Interactions: A Tribute to H.P. Eugster. Geochemical Society, Special Publication No. 2, p. 315-353. [in fact, there are loads of work from the JHU/USGS people (many in the Domalgalski biblio) on geochemistry of saline lakes that, if you do not already know them, will be a great help.]

Also, Hamilton-Taylor, J and W Davidson, 1995. Redox-Driven Cycling of Trace Eelements in Lakes, in A. Lerman, D. Imboden and J. Gat, Physics and Chemistry of Lakes, 2nd Ed. Spinger, p. 217-263, including a section on As (p. 230-235). Even if not directly relevant to your lake, you may also find the article by Mackenzie, et al in that volume addressing marine saline lakes worthwile for background.

Any numercical model you use should be able to address redox issues, provided you can properly constrain the system. This is where the Hamilton-Taylor and Davidson article may help. The hard part (in my experience) is deciding how to handle equilibrium (or disequilibrium), and having soem real-world data (inclduing mineralogy of lake sediments (or even suspended sediment) to ground-truth your modeling assumptions may be invaluable.

Good luck.

Regards,

Mark

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