Co-precipitation

[Christophe Simbo]

In acide drainage and buffering in Task3 "Co-precipitation", I cannot understand where some figures were found and to make my question more clearer, I attach the part that difficult to understand on there. Where can I find the sorbed and in solution quantities of species? I tried to click on "view results" I did not find them nor are they found in graphs. 

Does  0.005 moles of the strongly binding surface/mole of precipitate refer to As(OH-)4 as 0.2/ 25.4 = 0.007 and that of 0.2(weakly binding surface) refer to Na+ and Ca2+?

 

Thank you

[Jia Wang]

Dear Christophe,

In the React app, the results file output a dataset in tabular form. You can scroll down and see the concentrations of various basis species sorbed and in fluid and more information(e.g. mineral saturation state, reactants, gasses, etc..) at each reaction step.

However, another way to retrieve numerical data is to use Gtplot and copy and paste the data onto an excel spreadsheet. You can select ‘Plot Results’ in the Results pane and Gtplot will open up. Double-click in the plot to open the XY Plot Configuration dialog. Select the desired X and Y axis parameters and click apply to modify the plot. For example, you can plot one or many components in fluid as the Y-Axis parameter and Rxn progress on the X-Axis. To obtain numerical data for this data, you can click Edit --> Copy as -->  Spreadsheet and the paste the data in an excel spreadsheet. For more detailed instructions, you can refer to the ‘How do I retrieve numerical data from my plots?’ on the GWB Tutorials webpage and section 6.7 in the GWB Reaction Modeling Guide.

The number of moles regarding strongly and weakly binding surfaces refers to the sorption site density available on the sorbing mineral. In this case, for every mole of ferric hydroxide precipitated, there is 0.005 moles of strongly binding surface sites and 0.2 moles of weakly binding surface sites available.

Hope this helps.

Best,

Jia Wang

[Christophe Simbo]

Thank you for your reply Dear Wang.

If I have asked that question it's because I did as you described up here based on the graph pH versus sorbed fraction.May be it's not the appropriate XY plot. If so, could you enlighten me 

what XY plot that can yield the maximum sorbed and in solution components of the solutes .

 

Thank you

[Jia Wang]

Dear Christophe,

The maximum sorbed capacity for each metal is calculated outside of React. From Gtplot or the text output file of the simulation, you can see that there are 0.89 mmoles of Fe(OH)3ppd precipitated. Then in the surface dataset (FeOH+.sdat) you can find the sorbing density, which is 0.005 mol of strong sites and 0.2 mol of weak sites per mole of Fe(OH)3ppd. Then you look at each metal and see if they sorb onto weak, strong, or weak and strong sites. To calculate the maximum capacity for each metal, assume that there is only one metal sorbing to the mineral surface at a time. Just multiply the mineral mass by the site density of each appropriate site and convert to mg/kg. For As(OH)4-, it's 0.00089 mol/kg * .2 mol sites/mol * 142.951 g/mol * 1000 g/kg = 25.4 mg/kg. For metals that include strong sites, include those as well.

The ‘in solution’ component concentrations are reported directly by React under ‘Components in fluid’. You can select to plot ‘Components in fluid’ vs. pH in the XY Plot Configuration dialog in Gtplot and export the numerical data using the method described in my previous response. Alternatively, you can also open the text output file and look for the concentrations of the desired components at each time step listed under ‘Original basis’ text block in the column ‘in fluid’.  

Hope this helps.

Best,

Jia Wang

 

[Christophe Simbo]

Thank you so much for your reply.

In the same line, I would like to know the contrast between the non-reacting solute and the sorbed particulate and the particulate in solution(the latter two are understandable) .As in the below figures(Sorbing Solutes section), It is said that the non-reacting curve is in blue. I was trying to retrieve data from the non-reacting component of the solutes but I couldn't find any.

[Jia Wang]

Dear Christophe,

The green and the blue lines are from two separate X1t simulations. The blue lines in the plot of your screenshot is the result of Pulse.x1t from the mass transport section, where Pb++ is a non-reacting solute because the change in concentration is not associated with any chemical reactions. To attain the numerical data for this simulation, you can simply run the Pulse.x1t example without sorption. You can view the mass transport section (linked above) for more details. Then plot Pb++ (mmol/kg) on the y-axis and distant along the x-axis. Simply click Edit --> Copy as -->  Spreadsheet and the paste the data in an excel spreadsheet.

In the case of the green line, the simulation is accounting for sorption of Pb++. In this case, I think you’re referring to the sorbed particulate as the amount of Pb++ that is sorbed based on the distribution coefficient Kd from the database. Therefore, the particulate in solution would be the Pb++ remaining in the dissolved phase.

Hope this helps.

Best,

Jia Wang

[Christophe Simbo]

Thank you!