The principal lead mineral extracted and refined for the production of primary lead is galena, which, depending upon the nature of the deposit in which it is found, will contain greater or lesser amounts of other metal values including, inter alia, arsenic, antimony, copper, silver, gold, etc. In order to produce pig lead of marketable purity and/or to promote overall economy in refining, these metal values are recovered. Briefly, the lead sulfide concentrate is roasted to remove sulfur and melted in a suitable reduction furnace to produce an impure lead base bullion. The refinery flow sheet will be adapted to handle the particular bullion being refined and can vary considerably depending upon the kind and amount of impurity to be removed. A useful device for carrying out many refining operations is the drossing kettle which may take the form of a hemispherical container made of steel which may be heated by a furnace. The kettle may be fitted with a stirrer. Because of the high density of lead, the products of the various refining reactions will almost invariably report to the dross on the surface of the lead bath. The dross thus acts to concentrate metals removed from the bath by refining reactions. The dross may be removed readily from the bath and be worked up to recover metal values therefrom.
Sulfur is generally present in basic lead bullion and a convenient way to remove such sulfur and other impurities is to treat the sulfides contained with metallic sodium. This has been accomplished by stirring the bath to create a vortex and inserting sticks of sodium metal into the bath. Because of the high density of molten lead, it is difficult to create a deep vortex in a lead bath unless energetic stirring is used. This creates an energy cost. Even with energetic stirring, there is a tendency for escape of sodium vapor. Since sodium melts at 97.5.degree. C. and lead melts at 327.degree. C., sodium exerts an appreciable vapor pressure at the temperature of the lead bath. This is undesirable from the environmental viewpoint and for personnel safety reasons and leads to losses of sodium, a relatively expensive material.
The invention provides a solution to the aforementioned problems and provides increased recovery of sodium, elimination of the dust and fume problem, reduced cost and improved safety and handling ease.
USPTO Backgrounds
USPTO Backgrounds