I have geochemical data of sedimentary sequence. From XRD data I got signatures of certain clay minerals like smectite and Kaolinite. But I need the quantitative analysis to find out the percentage of clay from certain sedimentary units. Also, I have XRF and ICP-MS data of the same sequence. Is there any way to get the quantitative clay percentage from major oxides/Trace/ REE?
If you have only kaolinite-group minerals and smectite-group minerals in your clay you might get an approximation as you know what the type of smectite is like (e.g, dioctahedral, trioctahedral , Mg- or Fe-enriched). If you have a kaolin mixed with smectite that contains in addition to those minerals some feldspar relics, quartz or even muscovite I do not see any realistic chance.
No way. You need to do particle size analysis of soil/sediment materials by standard chemical methods followed routinely in soil science laboratories.
Try fractionation. Article Cretaceous-Paleogene boundary (KPB) Fish Clay at Højerup (St...
After the third phase and dissolution of the smectite, you will be left with kaolinite.
Best regards,
Bratislav
Some things must be done in the laboratory practices. He can't do everything with the help of instruments. You must use selective decomposition to determine the basic geochemical associations and concentrations of metals in the smectite and kaolinite.
Prior to dissolution, the sample is finely ground in a vibrating mill to a grain size of 100 µm. In order to determine the metal concentration, the technique of gradual decomposition with appropriate mineral acids is used.
Dissolution of carbonate
An accurately measured amount of samples was added in small amounts to acetate buffer (NaOC (1.0 M) + HOAC, pH = 5) at room temperature in order to remove most of the carbonate. The solutions were stirred on magnetic stirrers for 12 h. After stirring, the solutions were centrifuged and washed until the acetate was quantitatively removed from the precipitate. The concentration of the metal is determined from the solution by ICP-OES or some other technique. In this way we determine the concentrations of metals in the form of carbonates.
Dissolution of oxides, hydroxides, sulfides, sulfates
6 M HCl was added to the accurately measured amount of non-carbonate fraction. The solution was stirred on a magnetic stirrer for 12 h. After stirring, the solution was centrifuged and washed until the chloride was quantitatively removed. The quantity of chloride removal can be checked with the help of AgNO3. The metal concentration (e.g. ICP-OES) in the above forms was determined from the solution.
Dissolving smectite
The accurately measured amount of samples after treatment with cold HCl was added in small amounts in warm (80 C) 6 M HCl. The solution was then stirred on a magnetic stirrer for 12 h. After stirring, the solution was centrifuged and washed until the chloride was quantitatively removed. Quantitative chloride removal was checked in the same way. The metal concentration in smectites (ICP-OES) is determined from the solution. Dissolution with hot HCl did not remove all the clay minerals present in the samples, but only removed the smectite.
Dissolution of kaolinite
Dissolution with hydrofluoric (HF) acid is used to remove kaolinite and other residual silicates. An accurately measured amount of insoluble residue after treatment with warm 6M-HCl was added in small portions to prevent overheating of the solution, in a mixture of 22M-HF and 12M-HCl in a volume ratio of 3: 1 (v / v), in Teflon cups. The mixture was then heated with continuous stirring to 80 ° C and, if necessary, a new mixture of acids was added until the silicate minerals were completely dissolved. The solutions were evaporated to 10 cm3 after which 10 mL of 12M-HCl was added again, to remove excess HF, by evaporation again to a volume of 10 mL. Insoluble residues were washed with deionized water, centrifuged, until negative to chlorides. The washed residues were dried at 105 oC and weighed. The difference obtained represents the amount of HF soluble fraction. This procedure removed kaolinites and possibly other silates present (> 99%). The metal concentration was determined from the solution. Insoluble residues represent an organic fraction.
The calculation of metals present in carbonates, oxides, smectites and kaolinites is quite complex because the quantities of samples dissolved in previous treatments must be calculated!