Synthesis and thermal behavior of double copper and potassium pyrophosphate

This paper presents the synthesis and thermal behavior of double copper and potassium pyrophosphate, which can be used as a PK fertilizer containing copper as micronutrient. In order to find the conditions for the synthesis of this compound from copper sulphate and potassium pyrophosphate, various Cu2+:P2O74− molar ratios (0:1–2:1), various molar concentrations of the solutions (0.075; 0.1; 0.15 and 0.2 mol L−1) and various temperatures (25, 50, 75 and 100 °C) have been used. The solid product synthesized in optimum conditions for the separation of micronutrient copper from the reaction mass (Cu2+:P2O74− molar ratio 1:1, concentration 0.1 mol L−1) was subjected to a complex study: chemical analysis, thermal analysis, energy dispersive X-ray spectroscopy, scanning electron microscopy and X-ray diffractometry. During heating up to 1000 °C, K2Cu3(P2O7)2·3H2O loses the crystallization water; several transformations of the phosphates also take place: the decomposition of pyrophosphates to ortho-phosphates; the transformation of ortho-phosphates; the polymerization of a fraction of ortho-phosphates to amorphous phosphates with longer chains; the reorganization of ortho-phosphates and poly-phosphates to pyrophosphates and their crystallization. The decomposition mechanism was confirmed when using the X-ray diffraction patterns of the compound, thermally treated at several temperatures.