Malmö, ABM meeting May 2012 Publication of the ABM ringtest studies on CEC and exchangeable cations Dohrmann, R. BGR/LBEG

Malmö, ABM meeting May 2012

Publication of the ABM ringtest studies onCEC and exchangeable cations

Dohrmann, R. BGR/LBEG


2 papers were accepted by Clays and Clay Minerals:

Interlaboratory CEC and exchangeable cation study of bentonite buffer materials: I. Cu(II)-triethylenetetramine method

Interlaboratory CEC and exchangeable cation study of bentonite buffer materials: II. Alternative methods

Dohrmann, 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


Motivation and questions

• 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)?


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…

Mg2+ a few meq/100 g

larger at contact


I. Cu-trien method


5 labs participated, Cu-trien details

water buffer %/Cu-trien max possible elemental Lab . (M) (mL) (mL) (mL) bentonite COX adsorbed (max.) CEC (meq/100 g) analysisLab 1 0.015 10 25 - ≈ 60 % ≈ 145 ICPLab 2 0.015 20 50 - ≈ 60 % ≈ 145 ICPLab 3-1 (setup1) 0.01 10 50 - 83% 107 AASLab 3-2 (setup1) 0.01 20 40 - 42% 213 AASLab 4 0.02 5 44 1 130-140 500 58% 152 AASLab 5 0.01 10 50 - 80+120 200+300 50%+34% 177 (120 mg) ICP

Cu-trien

200400 ± 50

200

sample mass (mg)

200

Lab technique 1 time (min) technique 2 time (min) technique 3 time (min)Lab 1 hand-shaking 15 sonication 10 rocking platform 30Lab 2 vibrating table 120 vibrating table 30Lab 3-1 shaker 120Lab 3-2 shaker 120Lab 4 sonication 3 30 times end-over, manuallyLab 5 end-over-end shaking 120

before Cu-trien addition after Cu-trien addition


Exchange population, precision (1)

Ca2+ data inaccurate, but partly with good precision

Ca2+ data inaccurate, but partly with good precision

exchangeable cation MX80 COX Dep. CAN ASHApopulationNa+/CEC (VIS) (%) 70 24 27 73K+/CEC (VIS) (%) 2 16 2 1Mg2+/CEC (VIS) (%) 8 32 30 16Ca2+/CEC (VIS) (%) 36 170 66 24control sum (%) 116 242 125 114

MX80 COX Dep. CAN ASHA

Na+ 58.4 2.6 22.3 63.3standard deviation 2.1 0.4 1.6 2.3

K+ 1.8 1.7 1.6 0.5standard deviation 0.4 0.2 0.3 0.2

Mg2+ 6.9 3.4 24.3 13.8standard deviation 0.5 0.4 0.7 0.6

Ca2+ 29.9 18.5 54.2 20.6standard deviation 1.1 4.6 2.1 0.4

CEC (VIS) 83.9 10.9 82.2 86.5standard deviation 1.5 0.7 1.9 2.1

CEC (ICP/AAS) 84.8 12.1 82.6 86.3standard deviation 3.9 2.8 3.8 3.7


Precision (standard deviation)

bentonites

COX

0.0

1.0

2.0

3.0

4.0

5.0

stan

dard

dev

iatio

n (m

eq/1

00 g

)

NaK Mg

CE

C (

VIS

)

CE

C (

ICP

/AA

S)

Ca


Conclusions Cu-trien

• 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


II. Alternative methods

without COX


Details of alternative methods

Cu-trien'5xcalcite'

Lab (mL) n (mg)Lab 1 0.50 *) ⅓ of 25 3 500 ICPLab 2 0.15 *) ⅓ of 50 3 800±50 ICPLab 4 1.0 25 6 100 KjeldahlLab 5 0.01 50 1 400+600 ICP*) the total volume used was 25 mL respectively 50 mL, which was added in three portions of approximately equal volume

(M)elemental analysis

NH4Ac NH4Clrepetitions sample mass

Lab technique 1 time (min) technique 2 time (min) technique 3 time (min)

Lab 1 hand-shaking 10sonication (homogenizer probe)

1.5 rocking platform 30

Lab 2sonication (ultrasonic bath)

15 vibrating table 120

Lab 4 end-over-end shaking 1.) 1000; 2.-5.) short Lab 5 end-over-end shaking 120

dispersion after index cation addition


Exchange populationexchangeable cation MX80 Dep. CAN ASHApopulation

Na+/CEC (%) 69 27 67K+/CEC (%) 2 2 1Mg2+/CEC (%) 8 27 15Ca2+/CEC (%) (all labs) 26 49 20control sum (%) 105 105 103

Na+/CEC (%) 69 27 67K+/CEC (%) 2 2 1Mg2+/CEC (%) 8 27 15Ca2+/CEC (%) (all) 20Ca2+/CEC (%) (only lab 2 and 5) 24 46control sum (%) 103 102 103

only most plausible Ca 2+ results

results of all labs


Accuracy?

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

MX80 Dep. CAN ASHA

Na+ 58.8 *22.4 *60.8standard deviation 1.4 1.2 3.9

K+ 1.7 1.7 0.5standard deviation 0.1 0.2 0.1

Mg2+ 6.7 */***22.8 *13.4standard deviation 0.8 1.5 0.8

Ca2+ **20.2 **/***38.8 **18.6standard deviation 1.6 1.4 0.8

CEC 84.6 83.9 90.8standard deviation 2.1 0.5 3.3


Conclusions alternative methods

• 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


Thank you


What is a real difference?

• If lab A and lab B use the same method:– result A result B: good precision (± small deviation)– result A result 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 for good precision– result A result 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 an accurate/precise CEC result?

0

20

40

60

80

100

120

different CEC methods

CE

C (

meq

/100

g)

Reuverton (BGR/LBEG standard)

Ag

TU

(m

od

)

Am

mo

niu

m a

ceta

te

bar

ium

ch

lori

de

Cu

-tri

en

Co

-Hex

amin

e

Ag

TU

cal

cite

Cu

-tri

en c

alci

te

Co

Hex

cal

cite

Cu

-tri

en 5

xcal

cite

0

20

40

60

80

100

120

different CEC methods

CE

C (

meq

/100

g)

ammonium acetate, 0.5 g and 2 g

barium chloride, 0.5 g

barium chloride, 2 g

calcareous hectorite (CMS source clay)

Compensation of two sources of error, occasionally good agreement


Example for good precision, single lab (38 bentonites)

y = 1.00 x - 0.0

R2 = 0.994

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70

Cu-trien5xCc 1. series

Cu

-tri

en

5x

Cc

re

pe

titi

on

Na y = 1.00 x + 0.0

R2 = 0.987

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0.0 1.0 2.0 3.0 4.0 5.0 6.0


Cu

-tri

en

5x

Cc

re

pe

titi

on

Ky = 0.99 x - 0.1

R2 = 0.9997

0

10

20

30

40

50

0 10 20 30 40 50


Cu

-tri

en

5x

Cc

re

pe

titi

on

Mg

y = 1.00 x - 0.5

R2 = 0.998

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70 80


Cu

-tri

en

5x

Cc

re

pe

titi

on

Cay = 0.98 x + 0.4

R2 = 0.979

0

20

40

60

80

100

120

0 20 40 60 80 100 120


Cu

-tri

en

5x

Cc

re

pe

titi

on

sumy = 0.98 x + 0.9

R2 = 0.987

0

20

40

60

80

100

120

0 20 40 60 80 100 120


Cu

-tri

en

5x

Cc

re

pe

titi

on

CEC


exch

ange

able

catio

n po

pula

tion

(%)

Na+ K+ Mg2+ Ca2+ control Ca2+ (*) control

MX80 Dep.CAN ASHA

sum sum (*)

exch

ange

able

catio

n po

pula

tion

(%)

Na+ K+ Mg2+ Ca2+ control Ca2+ (*) control

MX80 Dep.CAN ASHA

sum sum (*)

Documents

Malmö, ABM meeting May 2012 Publication of the ABM ringtest studies on CEC and exchangeable cations Dohrmann, R. BGR/LBEG