Abstract
A rapid method for determination of organic carbon in carbonate rocks has been developed to replace the normal procedure in which carbonate samples are pretreated with hydrochloric acid to decompose carbonate minerals. The method involves dry combustion of organic material in an oxygen stream and subsequent measuring of carbon dioxide (CO2) generated.
Experimental data were obtained by changing combustion temperatures (450-900°C) and combustion time (5-15 minutes) using YANACO CHN-corder (model MT-5). Based on the difference of the decomposition rates between organic matter (coal and shale) and inorganic carbonates (calcium carbonate and dolomite), we have concluded that combustion conditions of 550°C for 15 minutes are appropriate for organic-carbon analysis of carbonate rocks. Amounts of sample needed for experiments are 10-100mg. More than 90% of the organic carbon can be detected directly under these conditions without any pretreatment of the sample, and the influence of inorganic carbon is less than 0.03% of the sample weight. This simplified method is also applicable for organic-carbon analysis of non-calcareous samples such as shales.
