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Potential Use of Finely Disintegrated Iron Pyrite in Sodic and Iron-Deficient Soils¹

ABSTRACT

The rate of chemical oxidation of iron pyrite in water was measured as a function of particle size. Reducing the particle size greatly increased the rate of oxidation. For pyrite > 250 µm, the pH of the solution leveled off at 5 after 6 hours while the clay size pyrite dropped to pH 4 within 24 hours.

Application of pyrite to a slightly sodic, iron-deficient, loamy sand soil from Colorado changed several soil properties during a 2-mo incubation period. In these studies, pyrite was applied at 1% initially with an additional 1% after 1 mo. The soil/water ratio was 1:2. When clay size pyrite was used, the pH of the soil decreased from 8.3 to 7.8 after 1 mo and to 5.7 after 2 mo. The coarser pyrite decreased the pH only slightly. No significant change in the composition of exchangeable ions occurred during the first month, but the composition had changed sufficiently after 2 mo to flocculate the clay. The DTPA-extractable iron increased from 1.5 to 64 ppm for the finest pyrite treatment during 1 mo, copper doubled, and manganese quadrupled during this period. Finely disintegrated pyrite may be useful for reclaiming slightly sodium-affected soils or for providing slow release available iron.

Key Words: sulfur • fertilizer • mine tailings • oxidation

¹ Supported by the Colorado State Univ. Exp. Stn. and published as Scientific Ser. no. 2290.

² Former Graduate Research Assistant and Professor, respectively, Dep. of Agronomy, Colorado State Univ., Fort Collins, CO 80523. Present address of the senior author is International Fertilizer Development Center, Muscle Shoals, AL 35660.

Received for publication April 28, 1977.