PREPARATION OF H-EXCHANGED CRYPTOMLELANE TYPE MANGANESE OXIDE AND ITS APPLICATION TO SOIL POTASSIUM ANALYSIS

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Calcination of manganese carbonate-potassium-tert-butoxide mixture at 500°C and hydrothermal treatment of mixed manganese sulfate-ammonium sulfate-ammonium peroxodisulfate solution yielded cryptomelane and NH₄-cryptomelane, respectively. The structural K and NH₄ could be partially replaced with H by washing with HNO₃, where column washing with 6 mol/L HNO₃ was much more effective than batch washing with diluter HNO₃. The H-exchanged cryptomelane greatly preferred K over Ca and Mg. The presence of 0.05 mol/L of Ca and Mg did not affect the K adsorption at all. The contact of wetted soil with H-exchanged cryptomelane across membrane filter caused diffusive migration of K from the soil to cryptomelane. The amount of K transferred to the cryptomelane in 96 h was almost double the amount of exchangeable K in soil, suggesting that this will be a new method for accessing K-supplying power of soils.