Lead Recycling Plant

The Lead Bullion is fed into a refining kettle. Lead bullion contains many other metallic impurities including antimony, arsenic, copper, tin and zinc.

Refining Process of Lead in Detail :

• Removal of Copper : Copper is the first of the impurities to be removed. The lead bullion is melted at about 300-600 °C and held just above its melting-point when solid copper rises to the surface and is skimmed off. Sulfur is stirred into the melt to facilitate the operation by producing a dry powdery dross which is more readily removed. Once copper has been removed, there are a number of processes available for the extraction of the other impurities from the bullion. These include, in which elements are removed one or more at a time in several stages.
• Removal of antimony, arsenic and tin : After the removal of copper, the next step is to remove antimony, arsenic and tin. There are two methods available — the softening process (so-called since these elementsare standard hardeners for lead) and the Harris process. In the softening process, the lead bullion is melted and agitated with an air blast, causing preferential oxidation of the impurities which are then skimmed off as a molten slag. In the Harris process, the molten bullion is stirred with a flux of molten sodium hydroxide and sodium nitrate or anothersuitable oxidizing agent. The oxidized impurities are suspended in the alkali flux in theform of sodium antimonate, arsenate and stannate, and any zinc is removed in the form of zinc oxide.

• Removal of silver, gold & Bismuth : After the removal of antimony, arsenic and tin, the softened lead may still containsilver and gold, and bismuth. The removal of the precious metals by the Parkesprocess is based on the fact that they are more soluble in zinc than in lead. In this process,the lead is melted and mixed with zinc at 480 °C. The temperature of the melt is graduallylowered to below 419.5 °C, at which point the zinc (now containing nearly all the silverand gold) begins to solidify as a crust on the surface of the lead and can be skimmed off.
  An alternative procedure, the Port Pirie process, used at the Port Pirie refinery in Australia,is based on similar metallurgical principles.

• Removal of zinc : The removal of the precious metals leaves zinc as the main contaminant of the lead.It is removed either by oxidation with gaseous chlorine or by vacuum distillation. Thelatter process involves melting the lead in a large kettle covered with a water-cooled lidunder vacuum. The zinc distils from the lead under the combined influence of temperatureand reduced pressure and condenses on the underside of the cold lid.
  Refined lead is poured into moulds and ingots are formed. These ingots are then sent to storage. For integrated Production of Lead Oxide, Refined Lead is casted into Balls. (to be fed directly to Lead oxide Ball Mill).