Amorphous silica prepared from olivine for soil structure improvement: Characterization and mechanism

Soil structure is an important index to maintain soil function, and the construction of stable soil aggregate structure is of great significance for the improvement of soil quality. Olivine, an abundant yet underutilized mineral resource in mining waste, holds application potential in soil amelioration. This study innovatively utilizes olivine-containing slag (a mining byproduct) to synthesize amorphous silica (APS), addressing the dual challenges of waste recycling and soil degradation. The prepared APS was characterized by X-ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy. The results showed that APS had amorphous nanostructures and high purity. The Si-OH bending vibration absorption peak and the-OH antisymmetric stretching vibration peak of the structural water reflected its sol characteristics. The effects of APS on soil composition were maintaining the acid-base balance, increasing cation exchange capacity (CEC) content, maintaining soil organic matter (SOM) stability, and enhancing the effectiveness of soil available silicon (SAS) in soil. The effect of APS on soil structure was reflected in the decrease of bulk density (BD), the increase of specific gravity (SG), the improvement of soil porosity (SP), and the water retention rate (WRR). At the same time, APS could significantly increase the percentage of non-water-stable aggregates (NWSAs) and water-stable aggregates (WSAs) in different types of soil, and the effect was the most obvious in aeolian sandy soils, reaching 24.29% and 12.24%, respectively. APS formed a more stable clay-cation-organic matter structure with soil particles, clay minerals, and organic matter to promote the formation of soil agglomeration structure and thereby improve soils.