Lead Processing Technology

PRIMARY LEAD PROCESSING:
Primary Lead production begins with sintering. Concentrated Lead ore is fed into a sintering machine with iron, silica, limestone fluxes, coke, soda ash, pyrite, zinc, caustics or pollution control particulates. The mixture is blasted with hot air to burn off the Sulphur and sent to the smelter.

Lead is usually smelted in a blast furnace using the carbon from the sintering machine to provide the heat source. As melting occurs, several layers form in the furnace. The molten Lead layer sinks to the bottom of the furnace. A layer of the lightest elements, including arsenic and antimony, floats to the top and is referred to as the "speiss." A "matte" layer also forms from the copper and metal sulfides. Finally, a layer of blast furnace slag, which contains mostly silicates, also forms. The speiss and the matte are usually sold to copper smelters where they are refined for copper processing. The slag is stored and partially recycled, if the metal content is sufficient.

The Lead from the blast furnace, called Lead bullion, and then undergoes the drossing process. The bullion is agitated in kettles then cooled to 700-800 degrees. This process results in molten Lead and dross. Dross refers to the Lead oxides, copper, antimony and other elements that float to the top of the Lead. Dross is usually skimmed off and sent to a dross furnace to recover the non-Lead components which are sold to other metal manufactures.

Finally, the molten Lead is refined. Pyrometallurgical methods are usually used to remove the remaining non-Lead components of the mixture. The non-Lead metals are usually sold to other metal processing plants. The refined Lead may be made into alloys or directly cast.

SECONDARY LEAD PROCESSING:

Most of the Lead produced comes from secondary sources. Lead scrap includes Lead acetate batteries, cable coverings, pipes, sheets and Lead coated, or terne bearing, metals. Solder, product waste and dross may also be recovered for its small Lead content. Most secondary Lead is used in batteries.

To recover Lead from a battery, the battery is broken and the components are classified. The Lead containing components are processed in blast furnaces for hard Lead or rotary reverberatory furnaces for fine particles. The blast furnace is similar in structure to a cupola furnace used in iron foundries. The furnace is charged with slag, scrap iron, limestone, coke, oxides, dross, and reverberatory slag. The coke is used to melt and reduce the Lead. Limestone reacts with impurities and floats to the top. This process also keeps the Lead from oxidizing. The molten Lead flows from the blast furnace into holding pots. Lead may be mixed with alloys, including antimony, tin, arsenic, copper and nickel. It is then cast into ingots.