Bentonite Mineralogy Part 1: Methods of Investigation - Posiva

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charge. Therefore, more exchangeable cations should be released at pH 7 than at pH 4.
This is not always the case (Table 7-12). As compared to results obtained with the
BaCh and NH4-acetate methods, more magnesium was leached from all samples and
more calcium was leached from the Milos and Friedland samples than with the
ammonium acetate method. In case of sodium, the results are much the same. Only from
sample MX-80 less Na was leached with the Cu-method than with the barium chloride
and the ammonium acetate methods. Sample error can explain these differences;
portions of the same homogenized sample were used for leaching with BaCh and NH4acetate
whereas a different portion was homogenized for leaching with Cu (II)
ethylenediamine, CsCl and LiCl.
Leaching with two concentrations of CsCl gave confusing results (part of the results in
table 7-14). The 0,1 M CsClleached much more divalent cations Ca and Mg (up to 6x)
and very little Na as compared to the 0,01 M CsCl. Leaching with LiCl (Table 7-13)
gave more reliable results that much resemble those received with BaCh.
Table 7-12. Exchangeable cations and cation exchange capacity, per dry material of
four samples as determined with 0, 05 M Cu(II) ethylenediamine at pH 4 and pH 7.
CupH4 Ca2+ K+ Mg2+ Na+ CEC
cmol+/kg cmol+/kg cmol+/kg cmol+/kg cmol+/kg
MX-80 34,0 1,33 14,3 53,1 103
Kutch 8937 20,5 0,68 30,4 55,3 107
Milos H 95,0 1,13 27,1 23,9 157
Friedland 11,5 1,95 8,22 22,6 44,3
CupH7 Ca 2 + K+ Mg2+ Na+ CEC
cmol+/kg cmol+/kg cmol+/kg cmol+/kg cmol+/kg
MX-80 36,0 1,33 16,4 55,3 109
Kutch 8937 24,0 0,56 35,34 55,3 115
Milos H 99,0 1,18 24,7 24,8 150
Friedland 11,0 2,15 6,9 22,2 42,3