6th RC Competition

Champion and top finishers of the 2012 6th Reynolds Cup announced

The 2012 – 6th Reynolds Cup continued on from the success of the 2010 contest with seventy-four sets of three samples distributed to participants from 25 countries. Fifty nine participants returned quantitative results, 3 returned qualitative results, 2 withdrew, 9 failed to return results and one participant’s samples went missing. Sample one was clay-rich sediment representing petroleum shales; sample 2 was clay-rich material representing a nickel bearing laterite; and sample three was clay-rich material representing minerals found in bauxite deposits. The analytical challenges were again numerous, including many minerals with overlapping XRD peaks and the presence of amorphous materials. Similar to the 2010 Reynolds Cup, clay minerals/phyllosilicates were judged more strictly by requiring participants to quantify to a greater level of detail in terms of clay mineral/phyllosilicate classification. It’s pleasing to see that many of the participants are updating their skills, which is evident by a significant reduction in the overall bias compared with the 2010 contest.

The Reynolds Cup round robin contest affords participants an unrivalled opportunity to test their proficiency in quantitative mineralogy. Each participant will receive a summary of the complete field of entries, with the identities of individual participants kept confidential. In addition summary information on the minerals used in the mixtures will also be distributed to participants. We hope this feedback will encourage participants to continually improve their methods particularly when clay minerals are a major component.

Therefore, we are pleased to announce that the 2012 6th Reynolds Cup ‘Champion’ is Michael Plötze, from Zurich, Switzerland.

Michael Plötze studied Mineralogy/Geochemistry at the Technical University Bergakademie Freiberg (Germany). Since 1998 he is employed at the ETH Zurich (Switzerland) and head of the ClayLab at the Institute for Geotechnical Engineering. His main research topics are the investigation of alteration of clay minerals and the modification of the physicochemical properties of clays during physical and chemical treatment as well as the initial soil/clay formation in weathering. The quantitative phase analysis of soils and rocks is of course one of the most important tools in his work.

Steve Hillier, Helen Pendlowski and Ian Phillips Second place went to Steve Hillier, Helen Pendlowski and Ian Phillips from Aberdeen, Scotland. Steve and his team from The James Hutton Institute, Aberdeen Scotland are no strangers to the Reynolds Cup, having placed in the top 3 in all but the 2010 contest in which they prepared the samples.

Reinhard Kleeberg and Robert Möckel Third place went to Reinhard Kleeberg and Robert Möckel from Freiberg, Germany . Reinhard is also no stranger to the Reynolds Cup placing in the top 3 in all but the 2004 contest in which he prepared the samples. Since 1987 Reinhard has been head of the “Mineralogical laboratory” of the Mineralogical Institute at the Technical University Bergakademie, Freiberg, Germany. His team mate Robert Möckel is from the Helmholtz Institute, Freiberg Germany.

Falling just short of the top 3 finishers but deserving honourable mentions for their great efforts are; Youjin Deng from Texas A&M; in 4th place, USA. In 5th place was the team of Kristian Ufer, Stephan Kaufhold and Reiner Dohrmann from BGR/LBEG, Hannover, Germany and in 6th place was Rieko Adriaens and Gilles Mertens: “KULeuven University Clay lab” and “Qmineral”, Heverlee, Belgium.

Congratulations to all our participants and particularly to our winners!
And this is how they did it.

Michael described his procedure as follows:

1) Homogenization of the sample

2) Sample examination by optical microscopy and qualitative check for carbonates with HCl and magnetic minerals with a permanent magnet.

3) The tool used for quantification was only XRD and Rietveld refinement of XRD-patterns from randomly oriented specimens (front loaded with a blade). The Rietveld program used was AutoQuan (BGMN), with very careful selection of models and refined parameters (refinement range, background, real structure parameters).

3a) Micronizing of an aliquot of 1.5g of the whole sample in ethanol with a McCrone micronizing mill and oven drying at 60 °C.

3b) Collecting of X-ray pattern of randomly oriented specimen

3c) Adding Zincite (final content 20wt%) for quantification of amorphous content.

3d) Collecting of X-ray pattern of randomly oriented specimens XRD with CoKalpha, solid state detector, automatic divergence and antiscatter slit, 4° soller slits primary and secondary, 2-90°2Theta range, step size 0.02°2Theta, counting time 10s per step (instead of 4 s as is the usual routine at ClayLab)

4) Fractionation from 2 g of the whole sample by wet sieving and sedimentation (in Na-polyphosphate): >63 µm, 63-2 µm and <2 µm

5) Exchange of the clay fraction into Ca-form

7) For (clay) mineral identification: XRD of oriented specimens (smear slides from milled 63-2 µm and from the clay fraction on single crystal silicon wafers): simple air dried and after different treatments: ethylene glycol, formamide time dependent for halloysite and kaolinite, guanidine for vermiculite, heated at 350 and 550 °C respectively., Reynolds Cup sample two was also heated after K exchange as a check of HIV

8) Collecting of X-ray pattern of randomly oriented specimen of the 63-2 µm and the clay fraction for a “special look” on the 060 region

Steve Hillier said:

“We were very pleased with our second place position in the 6th Reynolds Cup. Like most other contestant we relied on XRD for the quantitative analysis of the bulk sample. We backed this up by XRD analysis of oriented clay size fractions for precise identification of the clay minerals, applying a standard progression of air-dried, glycolated and heated patterns. For some reason the smectite in sample 1 failed to make an appearance in the clay size fraction and we left smectite out of the bulk analysis including only mixed-layer illite-smectite which was obvious in the clay size fraction analysis. As a result we determined far too much illite-smectite, a lesson there for sure. Our bulk analysis method is based on full pattern fitting of measured experimental patterns. Once you have your experimental patterns this is an extremely powerful method of quantitative mineralogical analysis that we have been successfully applying to soils and rocks for some time now. It probably copes more rigidly with background compared to Rietveld approaches where background is modelled separately. So it was particularly satisfying to accurately quantify the amorphous component in sample 3, which was identified by the absence of ‘enough background’. We have also abandoned the use of an internal standard having reached the conclusion that it gets in the way! The only thing we did differently to our routine methods was to count the patterns for longer and also to make XRF analyses of the samples. These were used a check on the likely accuracy of our mineralogical analysis by assuming compositions for each of the minerals identified and then calculating the chemical composition of the sample for comparison with the actual composition. Our bulk XRD methods or analysis are very firmly based around effort in sample preparation, in particular we believe that preparing all our standards and unknowns by spray drying is at the heart of our continued success in the Reynolds Cup.”

Reinhard Kleeberg and Robert Möckel described their procedure:

“We first took 0.85 g material, ground by hand in an agate mortar and measured an overview powder pattern in order to identify any critical minerals, e.g. water soluble species. For following bulk sample quantification, exactly 0.8 g of this material were mixed with 0.2 g corundum as internal standard and milled in a McCrone mill with zirconia grinding elements in water-free ethanol for 8 minutes. Additionally, 2 grams untreated sample material were dispersed in ethanol and sieved on a 20 micron screen. Both fractions < 20 and > 20 micron were also mixed with 20 wt% corundum, in order to get an independent result from these enriched fractions. The > 20 micron fraction was inspected under a microscope. Some particles have been separated and investigated by SEM/EDX. A part of the < 20 micron fraction was dispersed in water and oriented samples have been prepared by sedimentation on glass slides. No cation exchange procedures were applied. The oriented samples were measured in air-dried, glycolated and partially 400°C and 550°C heated stage. For samples 1 and 3 oriented samples were also prepared for the milled > 20 micron fraction, in order to confirm the presence of smectites in sample 1 by EG treatment and halloysite in sample 3 by formamide intercalation.

Mixed-layer mineral identification was performed by SYBILLA simulation on the EG treated oriented sample 1. The presence of two 1 nm “illite” reflections was recognized but the type of the illite could not be determined later on the powder pattern.

The main phase identification and quantification was done on the side-loaded spiked powders, measured on a URD-6 diffractometer (Freiberger Präzisionsmechanik, from 1988), Co long-fine focus tube, 40 kV 30 mA, energy disperse detector Meteor0D, automatic divergence slit irradiating 15 mm length, 3-80 °2θ, step 0.02, 10 sec/step.

The first phase identification was tried by conventional SEARCH-MATCH software ANALYZE and relational search in PDF-4+, release 2011. The quantification was performed with the Rietveld method using the programs BGMNwin and AUTOQUAN. Minor phases were identified by PC-PDF from the remaining maxima in the Rietveld difference plot.

We tried to apply our most recent structure (and disorder) models as orgeloped by Kristian Ufer for I/S, kaolinite, halloysite, talc and chlorite in the refinements. The sample 3 results of the bulk sample and the weighted fractions agreed well. For sample 2 we noticed big correlation problems of the trioctahedral mineral components, probably by the missing or wrong disorder models and any over-parametrization of our PO correction. This problem could not be solved within the contest, so we had to report any compromise results only. For sample 1 we noticed disagreement of the refinement results for the 2:1 minerals and a big scattering of the calculated “amorphous” content when different models for background were applied and the low-angle region was partially excluded from the calculation. We searched for any direct hint for an amorphous content, but we did not find anything in SEM or by organic carbon analysis. We also tried to “adjust” the chemically characteristic minerals like halite, pyrite + barite, and the carbonates by additional chemical analysis (ion chromatography of a water leachate, ICP/MS on the acid digestion, inorganic carbon analysis), but the balance from chemistry and Rietveld analysis was not precise enough to give an indirect hint to amorphous components. However, as our structure model for the hk bands of the I/S mineral “absorbed” the intensity of the missed illite1Md we consequently overestimated the mixed layer. The reason for the underestimation of the smectites and the misidentification of an amorphous component could not yet be identified. Hoping to get any additional useful information we did run thermal analysis (TG/DTA) in air and nitrogen atmosphere, but this did not help in the confirmation/elimination of the presence of an amorphous component or in the phase quantification.

In the end we learned on the shortcomings of our models for 2:1 minerals. Quantification of I/S seems to be impossible from powder patterns without controlled intercalation in the smectitic layers. The non-basal reflection profile is not specific enough for discrimination from illite. Moreover, the correlation problem of the PO correction models and incompleteness of the trioctahedral mineral structures were identified as critical issues to be resolved in further methodical work.”

2012 Principal Organizers
Mark Raven and Peter Self
CSIRO Land and Water, Adelaide, South Australia, August 2012.