Physical and Zeta Potential Characteristics of Erodible Lateritic Soils

Physical, mineralogical, and zeta potential studies were conducted on selected erodible lateritic soils from Belo Horizonte, Brazil. These soils are residual and highly weathered, and they have a very low amount of organic matter and an acid-soil solution natural pH in the range of 4.8-5.3. Engineers consider similar soils to cover 65% of the Brazilian surface. Soil sampling was performed at representative geological sites underlain by gneiss, dolomitic-itabiritic phyllites, and phyllites as parent materials. The soil erosion susceptibility was in the following decreasing order: MA-2 (soil developed from standard gneiss, more coarse materials); R-2 (soil developed from milonitic gneiss); VP-2 (soil developed from phyllite); BR-2 (developed from dolomitic-itabiritic phyllites and rich in hematite). Soil samples developed from gneiss, whether standard gneiss or milonitic gneiss (MA-2 and AR-2), are highly prone to erosion. They do not present a reverse surface charge, although they contain the same major mineralogical phases as the ones developed from phyllites, particularly kaolinite (probably less weathered) and hematite (probably in very small amounts). All the areas studied in this research presented slopes above 20% and sparse or no vegetation. Soil samples developed from phyllites, namely, VP-2 and BR-2 (dolomitic-itabiritic phyllites), are less erosion prone and present charge reversal, with iso-points at a soil solution pH of 4.8 and 4.4, respectively. These samples show a strong cation adsorption and a less repulsive force. In this sense, the colloidal activity may tend to diminish erosion.