Surface Area/Grain Size Relations

Figure from Horowitz, 1991

Changes in Surface Area as aFunction of Grain Size

Table from Horowitz, 1991; data from Jackson, 1979

Influence of Grain Mineralogy on Surface Area

Table from Horowitz, 1991; data fromForstner and Wittmann, 1981

Influence of Coatings on Surface Area

• Sand-sized and Larger seds.: grain coatings composed of carbonates, Fe & Mn oxides and hydroxides, and organic matter are rough in comparison to surface of the underlying particles.– Coatings may comprise <5% by weight, but account for

significant portion of the total surface area.

• Silt and clays sized particles: coatings fill in surface irregularities. Also, cement grains together, creating larger agglomerated grains. Combination of processes reduces surface area.

Based on Horowitz and Elrick, 1987

Surface Area vs. Concentration

From Oliver, 1973

Grain Size vs. Concentration

• Semi-systematic increase in concentration with finer-grained material

• Decrease in conc. In finest fraction due to coatings, composition, and agglomeration of grains

• Increase in fine sand due to dentrital minerals. Also to influx of metal enriched sediments from pollutant sources.

Data from Forstner and Wittman, 1979

Grain Size vs. Concentration

Data from Forstner and Wittman, 1979

Concentration vs. Quantity of Fine Sediment

Sizes Frequently Used

•16 μm

•62.5 μm

•63 μm

•125 μm

Data from deGroot et al., 1982

Metals per unit Mass

• Some deposits may contain so little fine-grained material that the bulk of the metal contaminant per unit mass is found in the sand-sized fraction.