A Simple, Simultaneous Gravimetric Determination of Calcite and Dolomite in Calcareous Soils.

 

             Literature pertaining to determination of calcite and dolomite is not modern, in general describes slow methods that require expensive specialized apparatus.  The objective of this paper is to describe a new method that requires no specialized equipment.  The separation of calcite and dolomite was done placing 0.2000 ± 0.0200 g. of calcareous soil, 6-mL glass vial with 4.0 mL of 4 mol L^-1 HCl-3% FeCl₂ ^.4H₂O in a 50-mL Erlenmeyer flask.  The Erlenmeyer was capped with the tubed rubber stopper and the carbonate meter (CM) initial weight recorded to the accuracy of 4 decimals.  A second weight was recorded after 30 s of reaction, a third weight was recorded after 30 min of reaction, and the last weight was taken after 22-24h.  Linear regressions and correlation coefficients for calcite and dolomite in calcite-dolomite-soil mixtures, with the modified carbonate meter (MCM) calcite and dolomite results were excellent.  Precision for calcite was <5% in 92.6% of samples, precision for dolomite was <10% in 98.8% of samples.  Recovery for calcite was 100 ± 10% in 86.4% of samples, recovery for dolomite was 100 ± 10% in 97.5% of samples.  The MCM technique efficiently separated calcite and dolomite in calcareous soils.  This procedure is recommended for routine analysis of calcite and dolomite concentrations up to 450 g kg^-1.  The MCM is easy to follow with good precision and recovery.