Optimized sequential extraction for carbonates: Quantification and δ13C analysis of calcite, dolomite and siderite

- A sequential extraction method was optimized and tested for quantifying calcite, dolomite and siderite in sediments.
- Method allows to determine δ13C signature of individual carbonates in mixtures.
- An idealized kinetic model was used for identifying optimal pH and temperature conditions for separating carbonates.
- The grain size distribution constrains the possibility to separate carbonates by acid digestion.
- Carbonate quantification involves combining the determination of the released CO2 and the amount of dissolved metal ions.

Siderite is present in diverse types of rocks and sediments, but its quantification is cumbersome when present in relatively low contents. A new analytical method for the sequential separation of different carbonate phases is presented. The separation, quantification and characterization of the carbonates is based on different kinetic reactions during acid digestion in combination with monitoring the solution composition and the concomitant release of CO2. Trapping the released gasses permits the isotopic characterization (δ13C) of the different phases. Based on published rate laws, an idealized model was built to identify pH and temperature conditions for optimal separation of the various carbonates by taking the size distribution of carbonate particles into consideration. Results from the theoretical survey were implemented in an extraction scheme, which was optimized and evaluated by tests on pure mineral phases and their mixtures. Further tests on a diverse array of sediment and rock samples validated the specificity and reproducibility of the method.