The formation of phosphate binders in systems based on orthophosphoric acid and the most common refractory fillers in foundry technology (quartz dust, zircon ZrSiO4, and kyanite-sillimanite Al2SiO5) has not been previously studied. The phase composition of these inorganic binders was studied, and the formation of silicon SiP2O7 and zirconium ZrP2O7 pyrophosphates was confirmed. The study by differential thermogravimetric analysis in the temperature range of 20–1000°С established the fact that the formed binders are thermally stable and do not emit harmful gaseous substances. The obtained results of the studied binders make it possible to develop new environment-friendly core mixtures of thermal hardening.