Soil Specific Surface Area Research Articles

Determination of soil specific surface area by water vapor adsorption: III Comparison of surface areas determined by water vapor and nitrogen gas adsorption

The specific surface areas of ten soil samples (clay content 1—72 %, organic carbon content 0.8—11.5 %) were determined by water vapor and nitrogen gas adsorption. The surface areas obtained by application of the BET equation to water vapor sorption at p/po 0.12—0.42 (21—195 m2/g) were, on the average, 80 % of the areas determined by water vapor sorption at p/po 0.20, range 27—229 m2/g. A BET water monolayer coverage was formed on the soil surface at p/po 0.12—0.20. The BET water area correlated closely with the one-point water area (p/po 0.20). The surface area determined by nitrogen gas adsorption ranged from 0.3 to 21 m2/g and did not correlate closely with water areas. The water surface areas were closely related to soil organic carbon content, while the nitrogen area was primarily related to soil clay content.

Determination of soil specific surface area by water vapor adsorption: II Dependence of soil specific surface area on clay and organic carbon content

The specific surface area of 60 mineral soil samples estimated by water vapor adsorption at 20 % relative humidity ranged from 12.1 ± 3.6 to 225.1 ±18.4 m2/g. Clay (range 1—72 %) and organic carbon content (0.7—14.6 %) together explained 84 % of the variation in the surface area. The regression equation predicting the specific surface area of soil was surface area (m2/g) =2.69+ 1.23clay-% +8.69org.C-%.

Determination of soil specific surface area by water vapor adsorption: I Drying of soil samples

Drying of three mineral soil samples (clay content 4—58 %, organic carbon content 1—5 %) equilibrated at 75.5 % relative humidity was studied. The soils were dried in an oven at +50°C, +70°C and + 105°C for 4 and 8 hours and in a desiccator over pure concentrated H2SO4 and P2O5. Drying over desiccants for 8 hours removed less water than drying at + 50°C. Drying over desiccants for 3—7 days was as efficient as drying at +70°C, for 14—24 days as efficient as 4 hours of drying at + 105°C. Eight hours of drying at + 105°C seemed to be too drastic, because it caused a greater weight loss in the clay sample of 5 % organic carbon content than did prolonged desiccant-drying. Drying at + 70°Cremoved as much water from fine sand which contained 4 % clay as prolonged desiccant-drying.

Destruction of Organic Matter by Hydrogen Peroxide in the Presence of Pyrophosphate and Its Effect on Soil Specific Surface Area

AbstractThe effectiveness of hydrogen peroxide in oxidizing soil organic matter was markedly increased by the presence of 0.1M sodium pyrophosphate at pH 7, with residual C after treatment being reduced up to 20 times lower compared to conventional soil peroxidation. “Electropositive” (Orange II) and external (N2) surface areas increased, whereas “electronegative” (cetyl pyridinium bromide) surface area values generally decreased after H2O2 treatment, supporting the assumption that metals released from organic matter may precipitate as hydroxide coatings that hinder further oxidation. Some soil sorption sites appear to be occluded by organic matter, so that changes in soil properties after peroxidation cannot be solely attributed to organic matter.