Determination of SO42- microquantity in carbonate rocks and formations

Author: Nino Takaishvili
Co-authors: G. Supatashvili
Keywords: carbonate rocks, microquantity of sulfates, turbidimetric method
Annotation:

In order to determine the sulfates in carbonate rocks and formations (limestones, stalactites, corals, coating etc.), due to their small content (0.01-0.3%) it is necessary to use the high-sensitivity methods. Turbidimetric method is the most acceptable from this viewpoint. Based on the optimum content of SO42- (50-150 μg in 5.0 ml) in the analysis volume the sample weight has to be within the limits of 0.1-0.5g. Its direct determination in the hydrochloric acid solution gives us the overstated results. This fact can be explained by the increase of BaSO4 suspension’s optical density in the presence of Ca2+. Solution of the task in hand is possible through Ca2+ masking, removal or via taking into account its effect on the optical density of BaSO4 suspension. The carried out studies show that turbidimetric determination of SO42- in carbonate rocks and formations has to be conducted against the background of Ca2+. The task is simplified by the circumstance that Ca2+ content in the analyzed objects is virtually constant and is close to the theoretical value (≈40%). When selecting the background concentrations of Ca2+, we have to take in account that the optical density of BaSO4 suspension is relatively stable in the analysis volume (5 ml) in the presense of 40-60 mg of Ca2+.

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