Numerical Evaluation of Granule Size Effect on Dissolution Rate of Potassium Silicates and Potassium Polyphosphate in Aqueous Solution1
- Eitaro Miwa and
- 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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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