monomethyl arsenic

[Scarlet]

please, I want to enter the element (monomethyl arsenic and dimethyl arsenic) on solution but I do not know how to do.
thank you

[John Mahoney]

You enter them just like any other component. 

 you need to define them in a SOLUTION_MASTER_SPECIES  block and then put them in a  SOLUTION_SPECIES block.  You might want to check the formula weights.   When I set this up about a year ago I also left the alkalinity factors at zero, that might need to be changed.  but I would have to look into that.   My feeling is that unless there are really large amounts of these compounds in your solution then they will not impact the distribution of alkalinity.  If you are in low ppm concentration or less  for these compounds  and have reasonably high alkalinities  (dominantly carbonate alkalinity) you can probably get away with 0.0 values. 


SOLUTION_MASTER_SPECIES
Dmasv    Dmasv-   0.0     Dmasv  136.92

Mmasv    Mmasv-2   0.0     Mmasv  139.92

SOLUTION_SPECIES
Dmasv-  = Dmasv-
log_k 0.0

Dmasv- + H+ = HDmasv
log_k  6.14

Mmasv-2  = Mmasv-2
log_k 0.0

Mmasv-2 + H+ = HMmasv-
log_k  8.77
 
Mmasv-2 + 2H+ = H2Mmasv
log_k  12.97

As these are set up above they behave as independent components.  They are not linked to any other form of arsenic or even to each other.  So they behave essentially as independent "elements".  This is because as  I set up the SMS lines, I did not define the formula weights as a type of arsenic (which would be 74.922 g/mol for the element weight for As).    The reactions were taken from Lafferty and Loeppert (2005). Nor are there any type of reactions that couple these back to arsenic forms. 

I also have done some PhreePlot fits for sorption onto ferrihydrite from the L and L paper (more as an exercise so far).  Using the diffuse Layer model.   But you did not ask about that so I decided to just answer the question. 

Lafferty, B.J., and Loeppert, R.H., 2005. Methyl arsenic adsorption and desorption behavior on iron oxides.  Environ. Sci. Technol.  vol. 39, no. 7, p.  2020-2127.   

[Scarlet]

thank you very much for your answer, I entered the database as it should.
but I do not know how to enter the value of DMA and MMA.

[John Mahoney]

You will need to add the Solution_master_species and SOLUTION_SPECIES blocks at the top of the  inputfile,  or in the default database.

I did not see SMS or SS blocks listed in the workspace (Left side of file) you just showed the SOLUTION block.  Alternatively,  if you put the Components in the selected database then they should have show up. 

Then I think the Program will find them and add them to the element list in the solution block. 


OR iust  copy this and paste into a blank pqi file and then you should be able to use the dropdowns.


SOLUTION_MASTER_SPECIES
Dmasv    Dmasv-   0.0     Dmasv  136.92

Mmasv    Mmasv-2   0.0     Mmasv  139.92

SOLUTION_SPECIES
Dmasv-  = Dmasv-
log_k 0.0

Dmasv- + H+ = HDmasv
log_k  6.14

Mmasv-2  = Mmasv-2
log_k 0.0

Mmasv-2 + H+ = HMmasv-
log_k  8.77
 
Mmasv-2 + 2H+ = H2Mmasv
log_k  12.97

SOLUTION 1
    temp      25
    pH        7
    pe        4
    redox     pe
    units     mmol/kgw
    density   1
    Dmasv     0
    Mmasv     0
    -water    1 # kg

[Scarlet]

thank you very much Mr John,for your answer
after run,I find this result (Attach)

[John Mahoney]

Your equations do not match the ones I put on the earlier email. 

you are missing this equation

Mmasv-2  = Mmasv-2
log_k 0.0

The equation above is critical to the setup as it essential defines the component

and you have two of the following reaction with different log_k values

Mmasv-2 + H+ = HMmasv-
log_k  8.77

[Scarlet]

Hello Mr John, please can I have your email?

[Scarlet]

I brought in the elements, and found the elements in the solution table.
but after I returned my results I did not find the DMA and MMA in the OUTPUT results

[John Mahoney]

my email is jmahoney@mahoneygeochem.com

[Scarlet]

Thanks Mr.John.my email is: lami.elalaoui@gmail.com