SYNTHESIS OF LEAD TUNGSTATE IN MELTS OF THE SYSTEM (Li<sub>2</sub>WO<sub>4</sub>–Na<sub>2</sub>WO<sub>4</sub>)<sub>evt</sub>–PbSO<sub>4</sub>

Abstract

The structure of the crystallization surface of the system (Li, Na), Pb // SO4, WO4 has been studied in a wide concentration and temperature range in order to identify compositions with optimal physicochemical parameters that can be used as the basis for the synthesis of highly dispersed lead tungstate with high yield and purity. The system (Li2WO4–Na2WO4)evt–PbSO4, which is a diagonal section of the system (Li, Na), Pb // SO4, WO4, was chosen as a working system for solving the task set in the work. For the first time, the concept of a “complex component” is used in the work, which is a mixture of lithium and sodium tungstates, as well as lithium and sodium sulfates at the vertices of the square of compositions. The complex components are eutectic compositions of the corresponding lithium tungstates, sodium and their sulfates. This approach to the study of the “resulting” triple mutual system (Li, Na), Pb // SO4, WO4 on the vertices of which complex components are located allowed us to take advantage of the noticeable differences between the studied system and the original triple mutual systems Li, Pb // SO4, WO4 and Na, Pb // SO4, WO4. It is shown that the studied system (Li, Na), Pb // SO4, WO4 has a number of advantages both in terms of melting temperatures of the eutectic mixture on the side of Li2,Na2(WO4)2–Li2,Na2(SO4)2, and in terms of the shift of the line of joint crystallization of phases, which leads to a noticeable increase in the crystallization surface lead tungstate. In this regard, before proceeding to the production of lead tungstate, we estimated the thermodynamic probability of the reaction underlying the synthesis of lead tungstate on the basis of the Temkin-Schwarzman method and the Van’t-Hoff isotherm equation of chemical reactions. Calculations have shown that all metabolic processes proceed with high negative Gibbs energies. The obtained samples of lead tungstate were analyzed by the X-ray phase analysis method on the X-ray diffractometer Dron-6, and their dispersion was determined on the Fritsch Analysette 22 Nanotek Plus laser particle analyzer. The presented results of a theoretical analysis of the possibility of implementing a method for synthesizing lead tungstate in melts of the (Li2WO4–Na2WO4)evt–PbSO4 system and experimental material for its implementation can become the basis for the development of technology for obtaining highly dispersed lead tungstate powders.