PhreeqcUsers Discussion Forum

Conceptual Models => Example input solutions => Topic started by: Scarlet on June 01, 2020, 12:39:54 PM

Title: difference between ionic forms
Post by: Scarlet on June 01, 2020, 12:39:54 PM
hello,
please , why in the output we find the metal and ionic form of the elements?

Pb
PbOH+
Pb
PbOH+
Pb(OH)2
Pb+2
PbSO4

Title: Re: difference between ionic forms
Post by: dlparkhurst on June 01, 2020, 03:23:01 PM
I assume you are looking at the section of the output labeled "Distribution of species". You are looking at the output for an ion-association model. This type of model uses aqueous ion-pairs and complexes (multiple-ion aggregates) along with activity coefficients to account for the nonideality of aqueous solutions. Hopefully, the set of aqueous species is a representation of the microscopic state of the solution, where, in your case, some of the lead occurs as Pb+2 ion, but some is aggregated with OH- as an ion pair PbOH+, and some forms a group Pb(OH)2. This picture of a solution may or may not be right, but the ultimate goal is to estimate the solubility state of minerals.

Note that the Pitzer approach (not available for Pb with PHREEQC databases) for the most part does not rely on ion pairs and complexes, but rather accounts for non-ideality by a number of interaction parameters.
Title: Re: difference between ionic forms
Post by: Scarlet on June 01, 2020, 06:49:38 PM
Thank you so much professor, and for the element HCO3-, how to add it to the table?
Title: Re: difference between ionic forms
Post by: dlparkhurst on June 01, 2020, 07:27:14 PM
Assuming lead carbonate complexes are defined in SOLUTION_SPECIES in the database that you are using, PbCO3 and other species will appear in the output when both Pb and C are present in the solution.
Title: Re: difference between ionic forms
Post by: pauloalpe on September 13, 2020, 06:51:59 AM
Hi all,

I'm with a similar question.

Can we assume that the concentration reported as Pb+2 on phreeqc is the total of Pb ions forming ion-pair with non specific anions? If not, what this value represents?

Paulo.
Title: Re: difference between ionic forms
Post by: dlparkhurst on September 13, 2020, 07:16:02 PM
If you are asking about a chemical analysis, the reported Pb is assumed to be the total dissolved Pb in solution.

If you are asking about the section "Distribution of species" in PHREEQC output, the total dissolve Pb appears next to "Pb". Below are ions and ion pairs calculated to be present in solution. Pb+2 as a dissolved ionic species is a fraction of the total Pb in solution.