Phosphorus diffusion coefficients (D) have been measured using 32P in coal mine spoil from Glenharold, North Dakota, spoil with 10 percent leonardite, and in leonardite as functions of applied P, water-soluble P, and NH4F-extractable P. In each case the D values are in the relative order spoil > spoil + 10 percent leonardite > leonardite, and are linear functions of the amount of P. The addition of 10 percent leonardite to the spoil substantially reduces D. In order to determine the effect of different sorption capacities on the measured D values, capacity factors have been determined and used to calculate porous medium diffusion coefficients (Dp). The values of Dp are approximately the same for the spoil and the spoil with leonardite. This suggests that the reduction in D of the Glenharold spoil due to the presence of the leonardite can be almost entirely accounted for by the higher sorption capacity of the leonardite as compared to the spoil.
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