Effects of nanocarbon on the hydraulic parameters and the solute transport process for disturbed loessial soil

Abstract

Due to its strong absorbability and significant specific surface area, the existence of nanocarbon in loessial soil could significantly affect the physical and chemical properties of the soil. The effects of nanocarbon on the hydraulic properties and solute transport parameters of the soil were investigated in this study. The soil water characteristic curves (SWCCs) were obtained using the centrifuge method in the loessial soil with various nanocarbon contents by weight (0, 0.1, 0.5, 0.7, and 1 %). Based on the soil columns experiment (5 cm in inner diameter and 20 cm in length), the saturated hydraulic conductivity (Ks) and the solute transport process for soil with different nanocarbon contents were also measured. The primary results were shown as follows: the water retention capacity increased with an increase in nanocarbon content, whereas the Ks value and the unsaturated hydraulic conductivity (K) decreased. The relationship between the Ks value and the nanocarbon content could be described by an exponential function. The Brooks–Corey and the van Genuchten models provided a good description of the SWCC of the disturbed loessial soil with various nanocarbon contents. Generally, the residual water content (θr) and the empirical parameter (α) increased with an increasing nanocarbon content, whereas the pore size distribution parameter (n) decreased. Application of nanocarbon in the soil could enhance available water capacity, and the obtained nanocarbon use amount was 0.746 % from the study. The classical convection–dispersion equation (CDE) and the mobile and immobile model (MIM) fitted the chloride transport process in the soil well. Furthermore, the average pore water velocity (v), the Peclet number (Pe), the retardation factor (R), the mobile water fraction (β), and the dimensionless mass transfer coefficient (ω) decreased, whereas the dispersion (λ) increased with the nanocarbon contents. In addition, ω could be expressed by a multiple regression equation related to the nanocarbon content and the v and β values.