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Modeling Transport Kinetics in Clinoptilolite-Phosphate Rock Systems

Dep. of Agronomy, Oklahoma State University, Stillwater, OK 74078

L. R. Hossner

Dep. of Soil and Crop Sciences, Texas A&M University, College Station, TX 77840

D. W. Ming and D. L. Henninger

NASA Johnson Space Center, Houston, TX 77058

* Corresponding author.

ABSTRACT

Nutrient release in clinoptilolite-phosphate rock (Cp-PR) systems occurs through dissolution and cation-exchange reactions. Investigating the kinetics of these reactions expands our understanding of nutrient release processes. Research was conducted to model transport kinetics of nutrient release in Cp-PR systems. The objectives were to identify empirical models that best describe NH₄, K, and P release and define diffusion-controlling processes. Materials included a Texas clinoptilolite (Cp) and North Carolina phosphate rock (PR). A continuous-flow thin-disk technique was used. Models evaluated included zero order, first order, second order, parabolic diffusion, simplified Elovich, Elovich, and power function. The power-function, Elovich, and parabolic-diffusion models adequately described NH₄, K, and P release. The power-function model was preferred because of its simplicity. Models indicated nutrient release was diffusion controlled. Primary transport processes controlling nutrient release for the time span observed were probably the result of a combination of several interacting transport mechanisms.

Received for publication August 23, 1993.