Metal Speciation in Soil: Extraction of Exchangeable Cations from a Calcareous Soil with a Magnesium Nitrate Solution

The exchangeable fraction of metals in a calcareous soil was studied with a magnesium nitrate solution and its extraction procedure was optimised. Parameters like extraction time, pH and concentration of the extractant solution, number of extractions or soil/solution ratio were examined. Experiments showed that after a 1-hour extraction, an equilibrium was established between extracted and re-sorbed metal. Moreover, carrying-out successive extractions re-sorbed quantities and maximum extracted ones could be estimated. Initial pH was fixed at 7 to avoid carbonates dissolution or hydroxides precipitation. A concentration of 0.5 mol/L and a soil/solution ratio of 1/20 were chosen. Leachate analyses showed a good selectivity of the extraction toward other soil fractions.