Lead melting kettle

The lead is supplied by the metallurgical works in the form of pigs of about 99.8 per cent purity from the melting kettle it is fed directly to the container. Scr ip lead is often added to the lead bath in order to reduce the price of the pipes. Pure lead gives aboud 2% lead dross, whereas about 8% residue have to be taken into account in scrap lead. The dross is collected and refined by chemical works. Larger quantities of scrap lead are refined in a simple manner by heating it to a temperature of about 450 to 500 °C and skimming off the dross from the surface of the metal. 

The press of about 2,000 tons capacity is capable of extruding billets of 250 mm diameter and 1,100 mm length. The sequence of the charging operations may be automated by very simple means. A belt conveyor feeds the lead pigs into the melting kettle. The molten lead flows into two cylindrical molds from which the billets are alternately ejected through the top by a hydraulic ram. The billet is then placed in the container by a gripper which pivots with its arm round a column mounted at the side of the press. All of these operations are performed electrically and initiated from a control desk. 

In liquidation, tin is heated on the sloping hearth of a small reverberatory furnace to just above its melting point. The tin runs into a so-called poling kettle, and metals that melt sufficiently higher than tin remain in the dross. Most of the iron is removed in this manner. Lead and bismuth remain, but arsenic, antimony, and copper are partly removed as dross. 

Alloying elements such as copper, silver, and antimony have a much higher melting point than lead and thus require continuous agitation, or stirring, in the kettle to promote dissolution. Tin, on the other hand, has a lower melting point and is the easiest element to alloy with lead. 

The electrolyte for the two electrodes in the PLACID electrolytic cell is dilferent and is separated by a membrane that is permeable only to protons (H" "). On the cathode, lead chloride is stripped of its lead atom to leave chloride ions which, in turn, combine with protons passing through the membrane from the anode to reproduce hydrochloric acid. The latter is returned to the leaching bath for re-use. The electrolysis deposits lead as dendrites (spongy form of lead). The dendrites are shaken off the cathode, collected, and removed from the bath on a semi-submersed conveyor belt. The dendrites are pressed to expel excess electrolyte, and form platelets of pure lead that can be melted in a conventional refining kettle and cast into ingots of 99.99% purity. 

Coarse materials are dewatered and washed on fine mesh screens and stockpiled for further processing. Metallics may simply be melted in a pot or standard lead kettle or can be melted in a short rotary furnace, with some collection of a htharge slag to separate antimony and arsenic and produce a soft lead. Separator plastics are usually disposed of in landfill but polypropylene is thoroughly washed, and extruded as pellets for sale to battery manufacturers for new case production. 

When cathodes are lifted from the cells the head bars are removed for reuse and the lead cathodes are washed, then melted in a standard refining kettle. 

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