The Optimization and Comparison of Calcimetry and Back Titration Methods for Determination of Calcium Carbonate Equivalent in Calcareous Soils

Abstract

ABSTRACT This study was conducted to optimize the calcimetry method (CM) and back titration method (BTM) for determination of calcium carbonate equivalent (CCE) in calcareous soils. For this purpose, 12 soil samples with wide CCE ranges and various physiochemical properties were selected to investigate the effect of contact time, sample preparation, soil-to-HCl ratio, heating, and HCl concentration on CCE measured by CM and BTM. Afterward, the optimized methods were compared by analysis of 100 calcareous soil samples. Results showed that the sample preparation is a key parameter affecting CCE determination, and the complete crushing of the sample without sieving led to the best results. Improper soil-to-hydrochloric acid (HCl) ratio led to overestimation of CCE. The kinetic experiment results revealed that the CCE dissolution in HCl was fast, and equilibrium was established in less than 5 minutes. The optimized BTM involved weighing 1–10 g of ground soil (depending on CCE content), adding 20 mL of 1 N HCl, heating for 5 minutes on a hotplate, and titrating by 1 N NaOH in the presence of phenolphthalein. The optimized CM involved weighing 1–5 g ground soil and adding 7 mL of 4 N HCl with a contact time of 5 minutes. The BTM and CM were highly correlated (r = 0.991) in the determination of CCE in a wide range of calcareous soils (100 soil samples), and the relevant regression equation can be employed as a transfer function to convert the BTM to CM results.