Composition and solubility of crystalline and glassy phases in potassium silicate fertilizer.
1995
Ando J. | Izumi K. | Ozawa N. | Esaki M.
A mixture of fly ashes from domestic and imported coals was blended with potassium carbonate and calcium and magnesium hydroxides and calcined at 850-950 degrees C for 10-50 min to give potassium silicate fertilizer containing 22 x 10(-2) kg kg(-1) K2O, 13 x 10(-2) kg kg(-1) Cao, 5 x 10(-2) kg kg(-1) MgO, 37 x 10(-2) kg kg(-1) SiO2, 18 x 10(-2) kg kg(-1) Al2O3. The citric solubility of K2O reached 93-94%, while 0.5 mol L(-1) HCl solubility of SiO2 reached 70-90%. Major compounds in the products were K2O.Al2O3.2SiO2 (KAS2), K2O.Al2O3 (KA), K2O.CaO.SiO2 (KCS), and 3CaO.MgO.2SiO2 (C3MS2), all of which were soluble in citric acid and 0.5 mol L(-1) HCl. Quantitative X-ray analysis of the compounds using spinel as an internal standard showed that the crystalline compounds contained 50-70% of the total K2O, indicating that a considerable portion of K2O was present in a glassy phase. Tests on synthetic potassium silicate glass containing CaO, MgO and Al2O3 showed that the glass was highly soluble when the O/Si atomic ratio was larger than 3.1 and was hardly soluble when the ratio was smaller than 2.9.
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