To calculate CIA and also plot the data on A-CN-K ternary diagram, I need to know the CaO in silicate minerals only, so reliable correcting method.
Hello Arash,
CaO has the molecular weight of 56 (atomic weights: Ca = 40; O = 16). CaCO3 has the atomic weight 100. So you have to multiply your CaO-value by the factor 100/56 to get Ca-carbonate.
In the case of Ca-phosphate I suppose it will be apatite (Ca5 (PO4)3 OH). In this case I would go back from the CaO values to Ca (CaO times 40/56 yields the Ca concentration). The molar weight of apatite is 497 (5 * Ca = 200; 3 * PO4 = 285, OH = 17 (F = 19; Cl = 35)). So the factor to calculate apatite on the base of the Ca concentration is 497/200. The factor could change a bit, if OH is substituted by F or Cl. I think the difference is negligible
I am not so sure whether these calculations are of any value for you. How could you find out, which of the bulk Ca concentration goes to carbonate and how much to apatite?
I think for the calculation of carbonate you need the sample concentration of inorganic carbon (atomic weight 12). Multiplying the C-concentration by the factor Ca/C = 40/12 you get the Ca concentration which is bound to carbonate (if you need CaO the factor would be 56/12).
In the case of phosphate you need the concentration of P; in apatite there are 5 Ca combined with 3 P. So the factor to calculate Ca from P is 200/93 (or 280/93 if you need CaO). If your analyses yield percentages of PO4 the factor to get Ca would be 200/285 (for CaO the factor is 280/285). If the analytical results are given in P2O5 I would recommend to calculate at first back to P (atomic weight = 31).
I hope I did no mistake or missed any additional aspects.
Regards
D. Zachmann
Dieter, thank you very much for your useful information. Beside P and Ca i have also the Rock-Eval Mineral Carbon values (might be used as a inorganic carbon) there is a relativley strong correlation (R2>0.6) between Ca and Mineral Carbon, but very low in case of Mg, Fe and P (R2
Hello Arash,
your data basis looks quite promising for your purposes. As you propose, mineral Carbon values might be used as inorganic carbon by which you can calculate Ca-carbonate. What about correlation of P and Ca ? Is R2 of < 0.4 for P and Mineral Carbon or P and Ca? If there is negligible C-org you could anyway combine P with Ca to form apatite, Otherwise the source of P could be C-org and there will be nearly no chance to assess for apatite.
I agree with your opinion concerning Fe and Mg. However, in the case of Mg there might be also some amount of dolomite. In this case Mineral Carbon must be recalculated for dolomite or split onto calcite and dolomite. So you need the additional information whether or not there could be dolomite (mineral phase identification by X-ray diffraction wold be very helpful). If you are sure there is no dolomite ( and C-org) you could do the calculation as described to assess for Ca bound to calcite and apatite. In the case of dolomite combined with calcite you certainly need X-ray diffraction determinations of sample powders in order to asses the ratios of calcite vs dolomite (if peak heights are good enough). Calculations for the splitting of Ca will become not easier (but also not too difficult).
Regards
D. Zachmann
thank you so much Dieter. Using mineral carbon values and supposing Calcite as a single present carbonate mineral, i calculated Ca value (in carbonates and phosphate). not very surprisingly, calculated Ca values(e.g. Ca(carbonate):6.96%--MINcarbon=2.09 ) are larger than total Ca (5.12%) obtained by ICP-ES (Dolomite!!!). But in case of Phosphate there is not any inconsistency (e.g. Ca(phosphate):0.19%) As you said, i have to perform XRD.
Regards
If the analysis was made by TG-DTG-DTA and XRF (or ICP-MS) method you can determine the CaO bounded to clay minerals by the measurement amount of the of CaO linked to the emitted CO2 during the decomposition of carbonate, subtracting the carbonate amount of CaO (CaO carb.) from total CaO (determined by XRF or ICP-MS). More information you can get in the attached article.
CaO* is the content of CaO incorporated in silicate fraction. McLennan (1993) proposed an indirect method for quantifying CaO content of silicate fraction assuming reasonable values of Ca/Na ratios of silicate material. Procedure for quantification of CaO content (CaO*) of silicate fraction involves subtraction of molar proportion of P2O5 from the molar proportion of total CaO. After subtraction, if the “remaining number of moles” is found to be less than the molar proportion of Na2O, then the “remaining number of moles” is considered as the molar proportion of CaO of silicate fraction. If the “remaining number of moles” is greater than the molar proportion of Na2O, then the molar proportion of Na2O is considered as the molar proportion of CaO of silicate fraction (CaO*).
The Formula provided by Fedo et al., 1995 to estimate the amount of CaO* that is present as Ca in silicate -bearing minerals only is CaO*=mol CaO - mol CO2 (calcite) - (0.5 x mol CO2) (dolomite) - [(10/3) x mol P2O5] (apatite)
for me it is not clear however where does the factor 10/3 for apatite come from.
Similarly, the factor 0.5 for dolomite.
any ideas?
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