> I am modelling F- removal with calcite in a column packed with granular calcite (12 moles or ~1.2kg). The influent concentration of F- is 2300 mg/L (as NaF) using ADVECTION with 40 cells & 600 shifts (15 pore volumes). On analysis of the results I find that the entire amount of calcite is used up within 6 pore volumes!!! and therefore 455.4 GRAMS of fluoride are precipitated which would require about 200 litres of my solution. I think the problem is the distinction between the column and the cell. At each shift, a liter of water is added to the column. Six pore volumes is 6*40 = 240 liters of water. 240*2.3 ~ 500 g of fluoride, as you calculate. So at a first read, it seems like the calculation is correct. > I believe this is a due to the fact that the area of the column is not specified (or controlled) and therefore the actual volume (and hence F mass) passing through the column is much greater than it should be. > Is there a way of limiting the volume of the influent solution passing through the column or programming PHREEQ so that the surface area can be taken into account?? I think the volume of water is probably the key. Here's the way I'm guessing you should set the problem up. First, when you define EQUILIBRIUM_PHASES for the column, you should define the amount of calcite per cell, or 12/40 moles, when you use 40 cells. Second, you need to determine the water-filled pore volume of a cell and define the infilling solution to have that volume. There is no way to account automatically for changes in mineral volumes in the column. You can define the water volume in a solution in liters (really kilograms of water in the solution) in the SOLUTION data block. Here is an abbreviated data block that would model introduction of 0.25 L of water per shift. SOLUTION 0 -unit mg/L F 2300 -water 0.25 > I am using PHREEQC Interactive Alpha version 2.4.2 PhreeqcI is finally officially released. The current version is 2.6.1, available at the website listed below. David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled
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