Restoration of the properties of organomineral gels in dried soil samples

It was previously established that soil drying changes their properties and, in particular, the characteristics of a specific soil organic substance – humic substances (HS). HS is the basis of soil organomineral gels that cover and bind soil particles. When water is removed from the soil, hydrophobization and compression of gels occur, as a result of which the properties of soil samples may change. The restoration of soil gels of air-dry samples should reduce the discrepancy between the data obtained when studying the soil properties of dried and non-dried soil samples. The purpose of the work is to find ways to restore the structure of soil gels. Samples of 6 types of soils were studied. Methods of vibration viscometry, laser diffractometry, scanning electron microscopy (SEM), photocolorimetry and conductometry were used in the work. It has been found that drying of soil samples increases the size of supramolecular formations (SMFs) from the soil and reduces the viscosity of soil pastes, a parameter characterizing the structure and ability of gels to swell. To restore the structure of soil gels, it is proposed to reduce the size of the SMFs from the HS to the initial ones. SMFs separation of air-dry samples was carried out by moistening the soils and subsequent treatment with various influences: temperature, ultrasound and freezing. Using SEM, it is shown that heating and ultrasound treatment do not reduce, but increase the size of the SMFs. Humidification of air-dry soils, exposure to moisture for 2 weeks and subsequent freezing bring the viscosity of pastes of a number of studied soils closer to the condition of samples that have not been dried. This process occurs due to the return of the SMFs size to the values of the initial soils, as evidenced by the data on the distribution of the size of suspended particles on a laser diffractometer. Thus, a method for restoring gel structures in dried soils to the state of the original soils is proposed.