Humic acid-, ferrihydrite-, and aluminosilicate-coated sands for column transport experiments

Abstract

Interactions of chemicals with soil minerals are often studied in batch systems. Dynamic flow systems are often limited by the low hydraulic permeability of the soil constituents, such as clays, when packed into columns. However, if clay minerals and organic matter can be immobilized on an inert support, then dynamic flow experiments can be performed. In this study, we investigate the feasibility to produce porous media with similar hydrodynamic properties, but different surface characteristics. Four minerals (ferrihydrite, kaolinite, illite, and smectite) and a humic acid were coated on silica sand grains. Coated grains were packed into columns and the hydrodynamic properties of the media were determined with anionic tracers. The hydrodynamic properties of the various coated silica sands were similar, suggesting that porous media with similar spatial structure, but different surface characteristics, could be produced. Coating of clay minerals was shown to cause anion exclusion of anionic tracers when high surface charge clays or high clay loadings for the coating procedure were used. The specific surface area of the coating materials inside the porous medium could be changed by varying the particle size of the silica grain support. Coating of different materials onto silica sand grains allows to study interactions of chemicals and colloids with dynamic flow experiments in a porous medium with defined structure.