Reversibility of the Hardening Process of Plinthite and Petroplinthite in Soils of the Araguaia River Floodplain under Different Treatments

Abstract

ABSTRACT:Although ferruginous materials occur frequently in soils of tropical regions, information about the reversal of the hardening process of these materials is scarce. This study assessed the influence of different chemical treatments and periods of immersion on the reversibility of the hardening process of plinthite and petroplinthite in soils of the Araguaia River plain. Soil samples were collected from the plinthic horizons in 0.10 m high and 0.15 m diameter PVC cylinders and divided into subsamples with a rock hammer. Homogeneous petroplinthite samples were also collected and broken into subsamples with a rock hammer. The plinthite and petroplinthite subsamples were subjected to five immersion treatments: distilled water, calcium carbonate solution, sodium hydroxide solution, sodium hydroxide solution + sodium hexametaphosphate, and acidic solution. The subsamples were immersed for 20, 40, 80, and 160 days. The dispersion and stability degrees and compressive strength in these subsamples were assessed. The wet aggregate stability test indicated no impact on the structural stability of plinthite and petroplinthite subsamples subjected to the treatment with different chemical agents, demonstrating the non-reversibility of the hardening process of these materials of the Araguaia River floodplain, under the studied conditions.

Toposequent Effect on Soil Morphology and Classification of Ultisol Soil in the Ayer Hitam Forest Reserve, Peninsular Malaysia

“…However, at the P3 observation point, the plinthite horizon properties (colored red at depth > 100 cm) were found. Martins et al (2018) stated that plinthite could be found in flat or slightly sloping areas, has high Fe, and is often exposed to seasonal groundwater levels. Plintithe is formed from the accumulation of iron hydroxide, quartz, and kaolinite.…”

“…The presence of iron in the plintithe is due to anaerobic water conditions. The iron ion content is transported, and precipitation occurs, forming soft clayey iron oxide, which hardens after drying (Martins et al 2018). Almost all soil profiles (P1 to P5) at a depth of more than 100 cm showed evidence of clay eluviation due to the lessivage process.…”