Dear Dr Parkhurst, Kirk Nordstrom suggested I contact you regarding some problems I am having doing mass-transfer calculations with NETPATH. Just to give you some background, I am a PhD student at the University of Cape Town, in the closing stages of writing up my thesis (hoping to be done by Christmas). My research is on the geochemistry and quality of coal mine waters in South Africa. I have sampled over 200 water bodies and done extensive analyses on these (not including isotopes). I then sampled some borehole cores on the mines to get an idea of the surrounding geology and am hoping to be able to use this information to determine the processes involved in the water-rock interactions. In other words, I would like to be able to say why the water in regions is different to others, based on the geology there. My first problem is that when I enter my data into DB and try to speciate it, I get an error message on all those waters with a low pH (i.e pH < 4.2). I have not measured any alkalinity in waters with a pH below 4.3 and therefore have enterred my alkalinity value as <0.01. Could this be the problem ? Is there some way of enterring acidity to compensate for this ? Perhaps a negative alkalinity (to indicate that it is consumed in the reaction) ? Or should I just add a miniscule amount as HCO3, so that it has some value to work with ? Secondly, the .dat file which I have does not offer some of the more important iron and aluminium minerals as a possible phase. The minerals which are not available, and that I need include ferrihydrite, jarosite, jurbanite, melanterite and schwertmannite. I have tried to enter these into the database but am not certain I have done it correctly ....... largely because I have no idea what "I1", "I2" and "I3" are, not to mention my uncertainty regarding the calculation of a redox state for these. Do you have an updated .dat file ? The one I downloaded from the web is dated August 1997. Alternatively some advice on how to enter these minerals would be greatly appeciated. Thirdly, I find that if I use an initial (rain water) and a final (mature mine water) water with no iron or aluminium (eg. pH ~7 waters), but include phases such as pyrite, goethite, gibbsite, etc, a mass balance transfer still occurs using these minerals. For example, all the pyrite converts to goethite but I can't figure out where the S goes. ALL into solution ? Similarly with the aluminium .... I can account for most of it: K-spar + kaolinite ~= albite. Is the rest in solution ? I do not want to leave the iron and aluminium phases out, as I know they do exist (XRD traces are evidence). Perhaps I should be using PHREEQC (which I used to speciate my waters and calculate SI, but know very little else about) ? I would greatly appreciate any help you can offer. Kind regards Bernadette Bernadette Azzie c/o Geology Dept. U.C.T. Private Bag Rondebosch 7700 South Africa E-mail: bazzi@xxxxxxxxxxxxxxxxx 082-576-3602 (Cell) (021) 650-2912 (O)
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