Modelling geochemical speciation of uranium in sediments

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From: Hlanganani Tutu

Subject: Modelling geochemical speciation of uranium in sediments

I need your help and advice on how I can do thermodynamic modelling of uranium speciation in sediments. Is it proper for instance if I measure the temperature, pH and redox potential of the moist sediment and then leach with deionised water (shake test) and measure sulphates and uranium in the leachate. Finally, I use these results to construct the Eh-pH diagrams. I'm studying the geochemical speciation of uranium in mine tailings and am using GWB release 4.0.1 for modelling.

 

From: Armand R. Groffman

Subject: Re: Modelling geochemical speciation of uranium in sediments I worked on a uranium mill tailings project in the USA (UMTRA) and here is what we did to determine U-speciation in pore fluids: Collect pore fluids with a suction lysimeter. If that is not possible performed DI batch tests. If sulphate is the overwhelming anion it is most likely the major complexing agent. Also check into alkalinity. If you need more detail then collect and analyze the pore fluids for organic carbon, major cations and anions (+ NO3), and trace elements including Fe, Mn, and sulfide. Look into the milling process to understand what residual organic products would be in solution and analyze for them or their degradation products. pH is easy. For redox use an ORP probe (a bit wonky) or if the tailings are not too acidic you may be able to determine redox by measuring Mn, Fe, or S-. This may be a better way to understand the redox potential of the system. Your model output will provide

speciation and ppt products.