The effect of sequential removal of organic matter on the surface morphology of humin

Natural organic matter in soils interacts with surfaces of inorganic materials, primarily aluminosilicates or clay minerals, to form a strongly associated organo-mineral composite known as humin, Because of humin's insolubility, it is recognized as the primary sorbent of many anthropogenic organic compounds (AOCs) introduced into soil systems, This recognition has significant implications for understanding the fate and transport of AOCs, the effective remediation of contaminated sites, and the formulation and application of various agrochemicals. Humin was isolated from four soil samples. Surface area, surface charge, porosity measurements, and fractal analysis of small-angle X-ray scattering data were used to characterize changes in the surface properties resulting from selective removal of the various components of organic matter from humin, Organic matter was removed selectively from humin by Soxhlet extraction, disaggregation with the methylisobutylketone (MIBK) method, and bromine oxidation,The surface fractal dimensions decreased while surface area increased, and surface pore size decreased upon removal of organic matter, These results suggest that the mineral components of humin have smooth surfaces over length scales of similar to 1 to 15 nm, and that it is the organic matter coatings that are responsible for their surface roughness, The surfaces of all the components of humin were found to be dominated by micro- and mesopores that could be responsible for humin's high sorptive uptake of organic chemicals.