jarosite molar volumes & schwertmannite thermo data

[csa08]

I just have a quick question regarding the molar volume in 'thermo.dat' of the jarosites

 

I have coppied and pasted the values:

 

Jarosite-K type= sulfate

formula= KFe3(SO4)2(OH)6

mole vol.= 153.200 cc mole wt.= 500.7983 g

5 species in reaction

2.000 SO4-- 3.000 Fe+++ 6.000 H2O

1.000 K+ -6.000 H+

-5.8197 -8.8889 -12.4748 -15.7308

-18.9953 -21.8913 500.0000 500.0000

 

Jarosite-Na type= sulfate

formula= NaFe3(SO4)2(OH)6

mole vol.= 469.050 cc mole wt.= 484.6898 g

5 species in reaction

2.000 SO4-- 3.000 Fe+++ 6.000 H2O

1.000 Na+ -6.000 H+

-4.8714 -4.8714 500.0000 500.0000

500.0000 500.0000 500.0000 500.0000

 

 

My question is how would one obtain a Jar-Na mol vol of 469.050 cc? while Jar-K is 153.200 cc and they are roughly the same mol wt and density.

 

I am also trying to add schwertmannite to this dataset if anyone knows of thermo data that contains it - I am using GWB v6.

 

Thankyou!

 

AJ

[Tom Meuzelaar]

My question is how would one obtain a Jar-Na mol vol of 469.050 cc? while Jar-K is 153.200 cc and they are roughly the same mol wt and density.

 

I am also trying to add schwertmannite to this dataset if anyone knows of thermo data that contains it - I am using GWB v6.

 

Thankyou!

 

AJ

 

Hi AJ:

 

1. The densities reported for K and Na jarosite in the extended LLNL dabase (thermo.com.v8.r6+.dat) are much closer in magnitude, so you might consider using this data instead. To further investigate why the apparent discrepancy exists, you'll want to refer to the p. 10 (thermodynamic datasets) and p. 98 (section A.8, Further Reading appendix) of the v7 GWB Essentials guide.

 

2. I could not find an entry for Schwertmannite in any of the default databases supplied with the software, or what appears to be an analog, so I'd recommend referring to the literature. A quick internet search yielded the following:

 

• Bigham, JM, Schwertmann, U, Carlson, L, Murad, E (1996) Schwertmannite and the chemical modeling of iron in acid sulfate waters. Geochimica et Cosmochimica Acta 54, 2743-2758 (link)
  
• Kawano, M, and Tomita, K (2001), Geochemical modeling of bacterially induced mineralization of schwertmannite and jarosite in sulfuric acid spring water. American Mineralogist, v. 86; no. 10; p. 1156-1165 (link)
  

 

Maybe others familiar with acid-sulfate systems can provide additional insight....

 

Regards,

 

Tom Meuzelaar

RockWare, inc.