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Publication of the ABM ringtest studies on CEC and exchangeable cations Dohrmann, R. BGR/LBEG

Publication of the ABM ringtest studies on CEC and exchangeable cations Dohrmann, R. BGR/LBEG.

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Publication of the ABM ringtest studies on CEC and exchangeable cations Dohrmann, R. BGR/LBEG

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  1. Publication of the ABM ringtest studies onCEC and exchangeable cationsDohrmann, R. BGR/LBEG

  2. 2 papers were accepted by Clays and Clay Minerals:Interlaboratory CEC and exchangeable cation study of bentonite buffer materials: I. Cu(II)-triethylenetetramine methodInterlaboratory CEC and exchangeable cation study of bentonite buffer materials: II. Alternative methodsDohrmann, R., Genske, D.,Karnland, O., Kaufhold, S., Kiviranta, L.,Olsson, S.,Plötze, M.,Sandén, T.,Sellin, P., Svensson, D.,Valter, M.BGR/LBEG, S&B Industrial Minerals, Clay Technology, B+Tech,ETH Zürich,SKB

  3. Large differences of results reported during 2010 meeting Lab exchange of data to clarify: How large is scattering (precision)? Which results are more plausible (accuracy)? Motivation and questions

  4. Mg2+ a few meq/100 g larger at contact What is a real difference? TR-09-29 (LOT) Svensson, 2010 (ABM meeting) Mg2+ analysis of the same ABM samples differed between different labs Mg2+ meq/100 g lab A lab BCalcigel 8.7 14.6MX80 3.6 8.6Rockle 9.7 17.2DepCAN 15.2 24.9Ikosorb 16.6 26.6…

  5. I. Cu-trien method

  6. 5 labs participated, Cu-trien details

  7. Ca2+ data inaccurate, butpartly with good precision Ca2+ data inaccurate, butpartly with good precision Exchange population, precision (1s)

  8. Precision (standard deviation) CEC (ICP/AAS) CEC (VIS) Na K Mg Ca

  9. The overall quality of the returned CEC results using Cu-trien method was good Some outliers were detected Exchange population (cations) exceeds CEC largely The most important question what is a real difference? can be evaluated based on ‚precision data‘ now Conclusions Cu-trien

  10. II. Alternative methodswithout COX

  11. Details of alternative methods

  12. Exchange population

  13. Accuracy? *: inflated by chloride-rich pore water; **: inflated by sulphate-rich pore water (gypsum dissolution); ***: questionable if inflated by dolomite dissolution.

  14. Precision of alternative methods is good Accuracy is partly not attainable, here more information than just CEC analyses are needed K+ and CEC results are (mostly) accurate Na+, Mg2+, and Ca2+ results partly inflated by chloride- or sulphate-rich pore water and soluble phases Conclusions alternative methods

  15. Thank you

  16. If lab A and lab B use the same method: result A @result B: good precision (± small deviation) result A ¹result B (difference > precision): individual error(s) note: check with standard clay If lab A and lab B use different methods: result A @result B: indication forgood precision result A ¹result B (difference > precision): option 1) individual error(s) option 2) systematic difference = operationally correct (both?) option 3) „complicated minerals“ such as zeolites (specific adsorption) or vermiculites (slow / incomplete cation exchange) What is a real difference?

  17. Compensation of two sources of error, occasionally good agreement What is an accurate/precise CEC result? ü ü

  18. Example for good precision, single lab(38 bentonites)

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