Site-Specific Retention of Colloids at Rough Rock Surfaces

Abstract

The spatial deposition of polystyrene latex colloids (d = 1 μm) at rough mineral and rock surfaces was investigated quantitatively as a function of Eu(III) concentration. Granodiorite samples from Grimsel test site (GTS), Switzerland, were used as collector surfaces for sorption experiments. At a scan area of 300 × 300 μm(2), the surface roughness (rms roughness, Rq) range was 100-2000 nm, including roughness contribution from asperities of several tens of nanometers in height to the sample topography. Although, an increase in both roughness and [Eu(III)] resulted in enhanced colloid deposition on granodiorite surfaces, surface roughness governs colloid deposition mainly at low Eu(III) concentrations (≤5 × 10(-7) M). Highest deposition efficiency on granodiorite has been found at walls of intergranular pores at surface sections with roughness Rq = 500-2000 nm. An about 2 orders of magnitude lower colloid deposition has been observed at granodiorite sections with low surface roughness (Rq < 500 nm), such as large and smooth feldspar or quartz crystal surface sections as well as intragranular pores. The site-specific deposition of colloids at intergranular pores is induced by small scale protrusions (mean height = 0.5 ± 0.3 μm). These protrusions diminish locally the overall DLVO interaction energy at the interface. The protrusions prevent further rolling over the surface by increasing the hydrodynamic drag required for detachment. Moreover, colloid sorption is favored at surface sections with high density of small protrusions (density (D) = 2.6 ± 0.55 μm(-1), asperity diameter (φ) = 0.6 ± 0.2 μm, height (h) = 0.4 ± 0.1 μm) in contrast to surface sections with larger asperities and lower asperity density (D = 1.2 ± 0.6 μm(-1), φ = 1.4 ± 0.4 μm, h = 0.6 ± 0.2 μm). The study elucidates the importance to include surface roughness parameters into predictive colloid-borne contaminant migration calculations.

Impact of Sodium Humate Coating on Collector Surfaces on Deposition of Polymer-Coated Nanoiron Particles

“…It therefore appears plausible that Na humate attaches onto the rougher surfaces of unwashed Dorsilit8 sand, but not onto the smoother acid-washed surfaces of glass beads and Ottawa sand. The total interaction energy as sum of the van der Waals and electrical double layer forces between colloids and glass bead collectors 34 and rough rock surfaces 35 has previously been shown to decrease with increasing collector roughness, with colloids being attached preferentially by sorption onto surfaces with a high density of small protuberances. Similarly, the attachment of Na humate to the surfaces of relatively smooth glass beads and Ottawa sand was also expected to be less than to the rougher surfaces of unwashed Dorsilit8 sand.…”

Transport of barrel and spherical shaped colloids in unsaturated porous media

“…We assessed surface roughness only qualitatively, but other authors also used quantitative approaches, e.g. vertical scanning interferometry (Darbha et al, 2010(Darbha et al, , 2012 to determine the surface roughness.…”

Measuring Surface Roughness through the Use of Digital Photography and Image Processing

“…Fischer and colleagues [28] relayed that geochemistry affects surface roughness, with the elements U, P, Cu, and Zn on black slates being inversely correlated with (the surface parameter) F. More recently, Fischer and colleagues [29] discovered a positive linear correlation between surface roughness, on surfaces of <100 nm, and adsorbed particle density. They also found a minimum roughness range (of at least 50 nm for particles with diameter of 1 µm) for initial colloid deposition, which occurred primarily at micrite (mainly calcite, but also with traces of quartz and ankerite) grain boundaries, where surface steps were established, forming small protrusions [30]. A scan area of 300 × 300 µm revealed that increased roughness increases the deposition of colloids, but chiefly at low concentrations.…”