Spectroscopic Studies of MnO2 and SiO2 Containing Soil-Active Phosphate Glasses

Abstract

FT-IR and Raman spectra were measured and structurally interpreted for glasses of the 41P2O5·8SiO2·6K2O·(26 – x) MgO·(19 – y)CaO·(x+y)MnO2 system where 0 ≤ x+y ≤ 40 mol.%, acting as slow-release fertilizers. It was shown that increasing the amount of MnO2 in the structure of the investigated glasses causes their gradual depolymerization, as is particularly apparent in the case of the phospho-oxygen subnetwork. Spectroscopic methods, on the other hand, showed no influence of manganese ions on the silicate subnetwork. Research on the chemical activity of the analyzed glasses conducted under conditions simulating a natural soil environment showed their low solubility with a simultaneous gradual increase in solubility occurring with an increasing number of manganese ions in the glass composition. It was found that this behavior resulted from the formation of less chemically stable bonds of the P–O–Mn2+ type, as compared with bonds of the P–O–Ca2+ and P–O–Mg2+ types. This is consistent with the depolymerizing influence of manganese ions on the analyzed vitreous structure as shown by the FT-IR and Raman spectroscopy and, thus, its weakening.