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This article in SSSAJ

  1. Vol. 41 No. 3, p. 637-640
    Received: May 24, 1976



Numerical Evaluation of Granule Size Effect on Dissolution Rate of Potassium Silicates and Potassium Polyphosphate in Aqueous Solution1

  1. Eitaro Miwa and
  2. Kiyoshi Kurihara2



The rate of potassium dissolution from spherical granules of K2O · 4SiO2, K2O · 5SiO2, and (KPO3)n was measured in water, NH4Cl and acetic acid solutions. Experimental results were analyzed using first-order kinetics, involving a rate constant (k) and the concentration at saturation (Cs). The kCs values in H2O were 3.65 × 10−2, 1.17 × 10−2, and 7.08 × 10−3 mg K/mm2 per day for K2O · 4SiO2, K2O · 5SiO2, and (KPO3)n, respectively. Extremely high kCs values were obtained for the dissolution of (KPO3)n in solvents rich in H+ or NH4+. Based on these experimental data and assumed values for Cs, the whole process of K dissolution from each material at various granule sizes in aqueous solutions was calculated by the equations given by Hixson and Crowell (1931). As much as 83 mg of K from granules up to 3.22 mm in diameter will dissolve within 4 days in 100 ml of 0.001M NH4Cl solution. Only small differences in kCs values were obtained for K2O · 4SiO2 and K2O · 5SiO2 in the solvents used. Potassium dissolution from K2O · 5SiO2 in aqueous solutions will be extended beyond 2-3 days by increasing granule size to 0.34 mm or greater.

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