Mechanisms of Structural Transformation of Soils During Modification by Organic Structuring Agents

Abstract

This study investigates the mechanisms of structural transformation of loamy (typical sierozem) and sandy saline soils from the Kegeyli and Kungrad districts of the Republic of Karakalpakstan under modification with organic structuring agents of different molecular nature—an anionic surfactant (sulfanol) and a water-soluble polymer (carboxymethyl cellulose, CMC). SEM–EDS analysis revealed that the saline soil is characterized by elevated contents of C (24.78 wt.%), O (46.23 wt.%), Si (12.87 wt.%), Ca (4.41 wt.%), and the presence of Na, indicating high ionic strength and compression of the electrical double layer. The sierozem soil exhibits higher Si (19.09 wt.%) and Ca (7.01 wt.%) contents and lower carbon content (10.68 wt.%), suggesting a predominantly silicate–carbonate matrix and lower salinity. FTIR spectroscopy revealed characteristic absorption bands at 3387–3400 cm⁻¹ (O–H stretching), 1435–1452 cm⁻¹ (carbonate groups), and 998–1004 cm⁻¹ (Si–O–Si vibrations), confirming the presence of active surface sites capable of intermolecular interactions. Benzene vapor adsorption isotherms correspond to type II–IV behavior, indicating a mesoporous structure. The maximum adsorption capacity was observed at a dosage of 6 mL of structuring agent per 50 g of soil. For saline soil modified with sulfanol, adsorption reached 4.09 arbitrary units, while for the sierozem soil it reached 4.52 arbitrary units. Increasing the dosage to 8 mL resulted in a reduced increment of adsorption, indicating partial micropore blocking. It was established that sulfanol induces structural transformation primarily through a surface-energy mechanism involving adsorption and hydrophobization of pore walls, whereas CMC acts via polymer bridging and aggregate formation. The proposed colloid-chemical model explains pore-space redistribution depending on soil granulometric composition and ionic environment.