> I need a copy of your report: "User's Guide to Phreeqc (Version 2")", by David L. Parkhurst and C. J.. Appelo, Water-Resources Investigations Report 99-4259, USGS, Denver, Colorado (1999) and the most recent version of the computer program to calculate equilibrium composition in aquatic systems. I have sent a copy by mail. PDF version and the program distribution are available from https://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc. > We are interested in predicting composition of the release water recovered from the oil sands tailings (originally 20 % solids, of which 50 % fines, i.e. smaller than 44 micron). After chemically treating the oil sands tailings with Ca(OH)2 and CO2, the sludge (tailings) is thickened using a suitable thickener. Both the chemical treatment and the thickener are invented by Apex Engineering Inc. of Edmonton, Alberta, Canada. > The release water composition is an important element of the whole process. This water has to be treated (with CO2 and/or Na2CO3) so that its Ca2+ ion concentration must be reduced to an acceptable level. Ca2+ ions in the water is a problem, because it reduces the bitumen extraction efficiency of the extraction (hot water or low energy) process. It should be fairly easy to model the aqueous reactions of adding CO2, Na2CO3 and Calcite precipitation. The interactions with the solids are not so clear, possibly exchange with the clays, and other unknown reactions with the surfaces of the solids and the organic residues. David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225
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