Response mechanism of permeability of remolded loess to AlCl3 concentration: a new discovery

Abstract

The unique chemical properties and hydration behavior of aluminum, combined with the abundance of silicate minerals in loess, render the seepage mechanism of aluminum solutions in loess highly complex. To explore the response mechanism of the permeability of remolded loess to AlCl₃ solutions of varying concentrations, a systematic study was conducted involving permeability tests, Zeta potential measurements, water-soil interaction analyses, and SEM observations. Results showed that the saturated hydraulic conductivity (K_sat) increased slightly (by 7.6%) under deionized water (DW) seepage due to weak water-rock interactions and pore expansion. Compared to DW, K_sat increased notably under seepage of 0.001–0.005 mol/L AlCl₃ solutions, as Al³⁺ hydrolysis facilitated the dissolution of minerals and the compression of the diffuse double layer, improving pore connectivity. However, as the concentration of Al³⁺ increased, the amount of Al(OH)₃ colloids generated rose, which slightly reduced pore space and caused a weak downward trend of final K_sat. Under seepage of a 0.01 mol/L AlCl₃ solution, the high concentration of Al³⁺ intensified hydrolysis, initially expanding pore spaces. However, as seepage progressed, the aggregation of Al(OH)₃ colloids produced due to hydrolysis caused significant pore blockage, resulting in an initial increase followed by a decrease in K_sat. Under seepage of a 0.1 mol/L AlCl₃ solution, the large amount of Al(OH)₃ colloids formed due to intense hydrolysis almost completely blocked intergranular pore spaces, Limiting seepage to just 0.5 days. These findings provide theoretical insights to support engineering applications in loess regions.