The extraction of carbonate components from soils and sediments: an experimental investigation by using different leaching acids

Carbonate components in soils and sediments play a crucial role in the study of surface processes and the reconstruction of paleoclimates. The extraction of carbonate components from soils and sediments is often carried out using different types of acids. However, which reagents can effectively extract the carbonate components while minimizing the destruction of non-carbonate minerals in soils and sediments has not been fully explored yet.

The present study conducted a series of conditional leaching experiments on six standard soil and sediment samples with diverse geological backgrounds and varying carbonate contents.

The results revealed that dilute acetic acid (HOAc, 0.5 mol/L) performed better than acid solution (HCl) and acetic acid buffer solution (NaOAc-HOAc) in promoting the complete dissolution of carbonate minerals and avoiding the dissolution of clay minerals. It was also observed that pre-treating the samples with neutral ammonium acetate buffer solution (NH₄OAc) or potassium chloride buffer solution (KCl) was necessary to remove exchangeable components. The Mg/Ca ratios of the silicate components after leaching carbonate in the standard soil and sediment samples we used exhibited significant differences (ranging from 0.41 to 1.60).

The dilute acetic acid (HOAc, 0.5 mol/L) is advisable for the extraction of carbonate components from soils and sediments, and the pre-treatment of removing exchangeable components is essential for samples with low carbonate content. It is more reasonable to use the element ratios of the dilute acid insoluble fraction or the average compositions of minerals in soils and sediments for individual correction for the contribution of the silicate components.