Leaching of fluorine bearing minerals from lead and zinc concentrates

The lead and zinc concentrates produced from the BHP Cannington concentrator contain significant amounts of fluorine bearing minerals. In particular, only fluorite and apatite are readily removed by acid leaching in the presence of aluminium sulphate. It has been shown that the kinetics of fluorine leaching are described by a fast leaching component attributed to fluorite and a slow leaching component attributed to chlorite. Most fluorine bearing silicate minerals are insoluble with talc being the predominant insoluble fluorine bearing mineral. The liberation characteristics of the fluorine bearing minerals also affects the final fluorine content in concentrates after leaching. This paper describes how an understanding of the fluorine mineralogy in concentrates together within an understanding of the chemistry of fluorine leaching led to a reduction in the operating costs of the BHP Cannington concentrator.