Synthesis of Lead Tungstate in (Li₂WO₄–Na₂WO₄)_eut–PbSO₄ Melts

Abstract—The structure of the crystallization surface of the (Li,Na), Pb//SO₄, WO₄ system is studied in wide concentration and temperature ranges in order to identify compositions with optimal physicochemical parameters, which can be used as the basis for the synthesis of fine lead tungstate with a high yield and purity. The (Li₂WO₄–Na₂WO₄)_eut–PbSO₄ system, which is a diagonal section of the (Li,Na), Pb//SO₄, WO₄ system, is chosen as a working system for solving the problem set in this work. For the first time, the concept of a “complex component,” which is a mixture of lithium and sodium tungstates and lithium and sodium sulfates at the vertices of the composition square is used in this work. The complex components are eutectic compositions of the corresponding lithium and sodium tungstates and their sulfates. This approach to the study of the “resulting” triple mutual (Li, Na), Pb//SO₄, WO₄ system, on the vertices of which complex components are located, allowed us to use the noticeable differences between the studied system and the initial triple mutual systems Li, Pb//SO₄, WO₄ and Na, Pb//SO₄, WO₄. The (Li, Na), Pb//SO₄, WO₄ system is shown to have a number of advantages in the melting temperature of the eutectic mixture on the side of Li₂,Na₂(WO₄)₂–Li₂,Na₂(SO₄)₂ and also in the shift of the line of phase co-crystallization, which leads to a marked increase in the lead tungstate crystallization surface. Before producing lead tungstate, we estimated the thermodynamic probability of the reactions underlying the synthesis of lead tungstate on the basis of the Temkin–Schwarzmann method and the van’t Hoff isotherm equation of the chemical reactions. The calculations show that all metabolic processes have with high negative Gibbs energies. The formed lead tungstate samples were analyzed by X-ray diffraction analysis on a Dron-6 X-ray diffractometer, and their dispersion was determined on a Fritsch Analysette 22 Nanotek Plus laser particle analyzer. The results of the theoretical analysis of the possibility of implementing this method for synthesizing lead tungstate in melts of the (Li₂WO₄–Na₂WO₄)_eut–PbSO₄ system and the experimental data for its implementation can become a basis for the development of a technology for producing fine lead tungstate powders.