On the dissolution of iron minerals in Tamm's reagent

The kinetics of iron minerals' dissolution is the reason for the considerab le variability in Tamm's reagent efficiency. The selected period of treatme nt (2 h) is very short and fits the steep segment of the kinetic curve. Dif ferent chemicals, e.g., soil reducers and complexing agents, as well as Fe- II ions, catalyze the dissolution of iron minerals. The solubility of mixed iron minerals in the Tamms's reagent differs substantially from that of in dividual minerals. The solubility of hematite alpha Fe2O3 may increase by a factor of 30 in the presence of siderite. The hematite solubility also ris es with the magnetite Fe3O4 present. Calcite CaCO3 raises the oxalate solub ility of siderite and magnetite. The pH value of the Tamm's extract is rela tively permanent; however, its redox potential (pe) varies considerably dep ending on the oxidation-reduction status of soil. The reduction processes i n soils lead to a sharp increase in the solubility of Fe(III) minerals.