1 / 19

Analysis of CEC and Exchangeable Cations Studies: Methods and Precision Analysis

This publication discusses the interlaboratory CEC and exchangeable cation studies on bentonite buffer materials, focusing on methods, precision, and accuracy. The results indicate discrepancies and suggest ways to evaluate the real differences.

louisee
Download Presentation

Analysis of CEC and Exchangeable Cations Studies: Methods and Precision Analysis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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)

More Related