Sedimentation and Transport of Different Soil Colloids: Effects of Goethite and Humic Acid

Abstract

Soil colloids significantly facilitate the transport of contaminants; however, little is known about the effects of highly reactive iron oxide and the most representative organic matter on the transport of soil colloids with different physicochemical properties. This study investigated the effects of goethite (GT) and humic acid (HA) on the sedimentation and transport of soil colloids using settling and column experiments. The stability of soil colloids was found to be related to their properties and decreased in the following order: black soil colloids (BSc) > yellow soil colloids (YSc) > fluvo-aquic soil colloids (FSc). Organic matter increased the stability of BSc, and ionic strength (Ca2+) promoted the deposition of FSc. Colloids in individual and GT colloids (GTc) coexistence systems tended to stabilize at high pH and showed a pH-dependence whereby the stability decreased with decreasing pH. The interaction of GTc and kaolinite led to a dramatic sedimentation of YSc at pH 4.0. HA enhanced the stability of soil colloids, especially at pH 4.0, and obscured the pH-dependent sedimentation of soil colloids. The transport ability of soil colloids was the same as their stability. The addition of GT retarded the transport of soil colloids, which was quite obvious at pH 7.0. This retardation effect was attributed to the transformation of the surface charge of sand from negative to positive, which increased the electrical double-layer attraction. Although sand coated with GT–HA provided more favorable conditions for the transport of soil colloids in comparison to pure sand, the corresponding transport was relatively slow. This suggests that the filtration effect, heterogeneity, and increased surface roughness may still influence the transport of soil colloids.

Effect of Agricultural Organic Inputs on Nanoplastics Transport in Saturated Goethite-Coated Porous Media: Particle Size Selectivity and Role of Dissolved Organic Matter

“…These inputs are sustainable, environmentally friendly, economical fertilizers that can increase crop yield and effectively improve soil quality by increasing soil organic carbon sequestration. − Moreover, dissolved organic matter (DOM) released from organic inputs can readily adsorb on clay minerals, Fe oxides, and the surface of nanoparticles; hence, they significantly alter the surface chemistry and retention–repulsion properties of the water–sand–nanoparticle system. Therefore, DOM is a crucial substance in soils and can regulate the transport of nanoparticle and colloids. ,,− Furthermore, DOM from different sources exhibits complex composition and diversified characteristics. Our previous studies suggest that humification, size, and morphology of DOM or humic acid (HA) are essential for controlling the transport of ferrihydrite nanoparticles. ,, For plastics, HA improves the stability of MPs, while organic matter and Fe mineral colloids promote NPs agglomeration via bridging or neutralization. , The large particle size lead to low heteroaggregation rate of NPs with DOM, wherein 200 nm NPs show higher stability than 50 nm NPs .…”

Modeling of formation damage during smart water flooding in sandstone reservoirs

“…In equation ( 5 ), London-van der Waals force is calculated as below 30 : where is the Hamaker constant which is expressed for particle-water–sand as follow 31 : …”

Co-transport of polybromodiphenyl ethers and soil nanoparticles in saturated porous media: implications for the risks of polybromodiphenyl ether spreading in groundwater

“…[18][19][20] Particularly, physicochemical properties of soil nanoparticles, including the size and chemical components, vary significantly among PBDE-contaminated sites. 21,22 It is expected that the extents to which soil nanoparticles enhance PBDE transport in groundwater will vary substantially at contaminated sites consisting of different geological settings. To date, no studies have been carried out to understand the significance of soil nanoparticles-facilitated transport of PBDEs in groundwater, as affected by the types of soil nanoparticles and the properties of the porous media.…”