Bentonite Mineralogy Part 1: Methods of Investigation - Posiva

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(ultramicrotome). This part of the work was not finished in time and the results will be
reported later.
6.4 Exchangeable cations & cation exchange capacity (CEC)
Five methods were used for the determination of exchangeable cations. All samples
were leached with 0,1 M BaCh (sample to solution ratio 1 :50) and 1 M NH4-acetate, pH
7 (sample to solution ratio 1 :50). The samples were gently crushed and sieved to pass 2
mm before leaching and dried at 40°C in a forced air oven. The N a, K, Ca and Mg
concentrations in the extracts were determined using inductively coupled plasma atomic
emission spectrometer (ICP-AES) at the Geolaboratory of the Geological Survey of
Finland, Kuopio. The CEC was calculated as sum of exchangeable elements and given
as cmol+/kg (centimoles of charge per kilogram of material, which corresponds to the
also commonly used CEC meq/1 00 g). pH of the samples was determined
potentiometrically in the BaCh extract.
The Cu-method was tested with four samples (MX-80, Kutch 8937, Milos H and
Friedland) at the Department of Geology, University of Helsinki by Dr.Phil. Antti
Vuorinen. A 0,05 M Cu(II) ethylenediamine solution was prepared (Bergaya & Vayer,
1997) and its pH adjusted to pH 4 and pH 7 with HCl and NH40H. The sample to
solution ratio was 500 mg/30 ml. The suspensions were gently shaken for 22 hours and
centrifuged for 20 min at 4 000 r/min. Final pH ranged from 4,4 to 5,1 (pH 4) and from
6,4 to 7,1 (pH 7). The elemental concentrations were measured with ICP-AES.
Exchangeable cations and CEC of the same four samples was determined also by
leaching with 0,1 and 0,01 M CsCl as well as with 1 M LiCl. Initial pH of the CsCl
solutions was 5,86 (0,1M) and 5,23 (0,01M). pH of the LiCl solution was adjusted to
7,0. The sample to solution ratio in all experiments was 500 mg/30 ml. The suspensions
were gently shaken for 22 hours and centrifuged for 20 min at 4 000 r/min. Final pH
ranged from 8,4 to 9,5 (Cs 0,1M), from 8,5 to 9,6 (Cs 0,01) and from 7,3 to 7,7 (Li).
The elemental concentrations were determined as above.
6.5 Total chemical analysis
For the total chemical analysis, all samples were pulverized in a tempered carbide-steel
grinding vessel and dried at 40°C in a forced air oven. Pressed powder pellets were
prepared and the elemental composition determined using X-ray fluoresence
spectroscopy (XRF) at the Geolaboratory of the Geological Survey of Finland, Espoo.
Total sulphur was determined with a S-analyzer and total carbon with a C-analyzer
using a combustion technique. Carbonate carbon and non-carbonate carbon were
determined with a C-analyzer using a combustion technique and treatment with HCl.
The method validation has not yet been completed and therefore the results are
preliminary. H20- was determined gravimetrically by heating the samples to 1 05°C.
Detection limits are given in tables 6-2 and 6-3.