Application of Model Systems Containing Exchangeable Iron(III) to Study Acidity Characteristics of Strongly Acid Soils (pH(KCl) < 3.3)

摘要

Strongly acid soils (pH(KCl) < 3.3) are widespread in the northeast of European Russia and are characterized by the low precision of potentiometric measurements of the components of exchangeable acidity. The goal of our study was to identify the causes that reduce the precision of measuring the exchangeable acidity of these soils using single- and two-component model systems of aluminum and iron(III) ions in concentrations similar to those in extracts from the strongly acid soils. Using model solutions, it was shown that the high acidity of salt extracts from soils is caused by the presence of iron(III) ions. The precision of measurements of metal ions was determined by the mode of stirring of the analyzed solution (continuous or discrete), as well as by the duration of interaction of the titrant with it. This was due to the presence of disperse systems in the initial model solutions. Particle parameters (hydrodynamic diameter D 70-90 nm, zeta-potential 19-30 mV) were determined by the dynamic light scattering and laser Doppler electrophoresis. The presence of other components-organic compounds and fine particles of silicates and iron hydroxides capable of passing through the blue ribbon filter pores in the salt extracts from soils-further reduces the precision of measuring the total Al3+ and Fe3+ content (exchangeable acidity) by the potentiometric method and casts doubt on the possibility of its application. When working with strongly acid soil samples, the use of atomic emission method is recommended.