Emission of Fluorides From Industrial Processes—A Review

Abstract

An investigation has been made of atmospheric pollution by fluorides emitted from industrial processes in which fluorine compounds are mannfactured. Thermodynamic considerations and previous studies indicate that the principal mechanism of liberation of fluorides in high-temperature processes is pyrohydrolysis, which results in formation of HF. The principal variables in pyrohydrolysis in most industrial processes appear to be the equilibrium of the reaction, the water vapor concentration in the process atmosphere, and the factors determining mass transfer. Significant formation of SiF4 appears to be limited to cases involving thermal decomposition of fluosilicates or reaction of fluorides and silica with acids at relatively low temperatures. Formation of volatile metal fluorides may be a significant mechanism of liberation in some cases but is generally of less importance than pyrohydrolysis. By analogy to known cases, it should be possible to make order-of-magnitude estimates of the probable fluorine emission from a given process if the quantity of input fluorine is known or can be estimated.