webmaster Posted November 9, 2004 Share Posted November 9, 2004 From: Henry Kerfoot Subject: negative concentrations When I use the following parameters for reaction of feldspars with groundwater, I get results with [H+] 0. Is this an indication of instability due to use of too large a reaction step, or some other type of effect? I also occasionally get [O2] 0, which I assume is a reflection of the same thing.... Has anyone had experience with these types of issues? Here is the input and system information .... Basis is: H2O 1 kg solvent NO3- (swapped for NH3(aq)) total mg/l = .4 Na+ total mg/l = 8.4 K+ total mg/l = 3.5 Ca++ total mg/l = 13 Mg++ total mg/l = 4.3 Fe++ total mg/l = .18 HCO3- total mg/l = 72 SO4-- total mg/l = 6.9 Cl- total mg/l = 3.8 ( F- total mg/l = .2 SiO2(aq) total mg/l = 35 H+ pH = 7 O2(aq) total mg/l = 4 Al+++ total mg/l = .1 Mn++ activity = 1e-12 Zn++ total mg/l = .09 HPO4-- total mg/l = .1 show reactants Reactants: React .05 mol of K-Feldspar React .05 mol of Albite show variables Variables set by user: cpw = 1 cal/g C cpr = .2 cal/g C delxi = .01 density = 1 g/cm3 dxplot = .005 dxprint = .1 epsilon = 5e-11 inert = 0 cm3 itmax = 400 iterations itmax0 = 999 iterations nswap = 30 iterations nswap0 = 200 iterations simax = 3 molal TDS = 148 mg/kg theta = .6 timax = 3 molal From: Craig Bethke Subject: RE: negative concentrations I think you are confusing the concentration of a species in solution with that of a component. Whereas the concentration of a species is invariably a positive number, a component's concentration may be positive or negative. There's a section in the green book titled “Components with Negative Masses�, on page 38. If you read this (and perhaps the preceding pages, starting on page 30), I think this point will be clear. Quote Link to comment Share on other sites More sharing options...
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