LEAD RECYCLING

Production of Recycled Lead. Lead has the highest rate of recycling of all metals. Because of its corrosion resistance, lead scrap is available for recycling decades or even centuries after it is produced. New environmental regulation in many countries has greatly reduced the dissipative uses for lead such as paint, leaded gasoline, pigments, stabilizers, solder, and ammunition.

At present time, just under half of the total world lead production of 7.62 million tons comes from recycling of scrap materials.

Lead has the highest rate of recycling of all metals. Because of its corrosion resistance, lead scrap is available for recycling decades or even centuries after it is produced. New environmental regulation in many countries has greatly reduced the dissipative uses for lead such as paint, leaded gasoline, pigments, stabilizers, solder, and ammunition.

At present time, just under half of the total world lead production of 4.7 million tons comes from recycling of scrap materials. There has been very little change in recent years in the total amount of lead production or in the percentage of recycled lead. Only in the past few years has the amount of recycled lead increased. The rate of lead production from scrap materials is expected to increase dramatically in the future.

Sources of Lead Scrap

The major source of scrap lead for recycling in the United States and throughout the world is lead acid batteries. Scrapped lead acid batteries and the associated manufacturing plant scrap represent over 90% of the contained lead available for recycling. Used automobile batteries represent about 85% of the lead acid battery scrap materials. Other lead recycled scrap materials are sheaths from telephone and power cable, lead pipe and sheet, weights (particularly automobile and truck wheel weights), anodes, printing metals, dross’s, residues, sludge’s, and dusts.

In Europe and throughout most of the rest of the world, scrapped lead acid batteries represent only about half of the lead scrap input to recycling plants. Scrap cable covering, lead sheet and pipe, and miscellaneous metal scrap items represent a much higher percentage of input scrap to recyclers in these countries than those in the United States. As the number of vehicles increases, the percentage of scrap represented by lead acid batteries will increase.

Battery-Recycling

The battery-recycling has changed dramatically over the past ten to twenty years. The changes have resulted from environmental regulation, changes in battery-processing technology, changes in battery distribution and sales techniques, changes in lead-smelting technology, and changes in the lead alloys used in the batteries.

Battery Scrap Collection and Processing. In the 1970s, batteries were distributed primarily through full-service gasoline stations. Smaller amounts were distributed through hardware stores, automobile supply stores, and mass merchandise outlets. The scrap batteries were recovered by the service stations and sold to scrap dealers, who also recovered batteries from wrecked or worn-out automobiles. The scrap dealers then sold the batteries to battery breakers and smelters. The higher lead content of the battery plates made it cost-effective to ship plates longer distances than whole batteries.

Environmental Regulations. In the 1980s, environmental legislation was passed regulating lead acid battery recycling. Rules were promulgated regarding the storage, processing, and transportation of batteries and battery scrap. Batteries and battery components are considered hazardous waste after arrival at a battery breaker or smelter if they are cracked or leaking acid, or if they are disposed of in landfills. Scrap batteries can be stored for only 90 days, after which they must be sent to a recycler or disposed of in a hazardous-waste landfill. Because only permitted processors can break batteries, the number of battery breakers has declined markedly. Only a few breakers still remain. Battery breaking is now performed mainly by lead smelters.

Battery-Breaking Processes. In the 1970s, most battery breakers used saws for decasing. In this process, the top is severed, the acid is drained, and the plates are dumped from the case. The lead posts are recovered from the tops by crushing and separation. This process is still utilized by many lead smellers in the United States and throughout the world.

In the late 1970s and early 1980s, several mechanical processes were developed to break the batteries. Technologies were developed to crush the whole batteries, separate the case from the lead-bearing materials, separate the hard rubber (ebonite) and separators from the plastic cases, and, in some cases, separate the paste portion of the battery from the metallic. The acid is neutralized in a separate procedure.

A recent innovation desulfurizes the paste, produces lead carbonate, recovers sodium sulfate crystals, and recycles the H2O. Virtually all battery-wrecking processes now recycle the polypropylene battery cases. Battery breakers process from 5000 to more than 50000 spent automobile batteries per day.

Lead-Smelting Processes The major smelting processes to recycle lead scrap involve the use of blast furnaces, short rotary furnaces, long rotary kilns, reverberatory furnaces, electric furnaces, and top-blown rotary furnaces.

Blast Furnaces. For many years blast furnaces were the primary furnace for recycling lead. Blast furnaces are used to recycle slag, dross, and residues from other processes. Blast furnaces require metallurgical coke, produce large volumes of gas that must be filtered, require a special charge, require afterburners to burn carbon monoxide contained in off-gases, and produce slag and matte that, in some cases, may be considered hazardous materials. Blast furnaces produce a bullion that is high in antimony; this bullion can be readily refined into lead-antimony alloys.

Rotary Furnaces. In most of the world other than the U.S., rotary furnaces (long, short, and top blown) have replaced blast furnaces as the major smelting vessels for lead recycling. Rotary furnaces are very versatile. They can accept virtually any type of lead-bearing feed material, including battery scrap, dust, dross, scrap lead, and sludge. Rotary furnaces can use any carbon source such as coal, coke, or ebonite as reducing agent, and they can use a variety of fuels, such as oil, coal, or gas. Because they are batch furnaces, rotary furnaces can be operated in stages to produce low-impurity bullion for refining to pure lead, or they can completely reduce the charge to recover all metal values for production of lead-antimony alloys. Rotary furnaces generally use Na2CO3 and iron as fluxes, which produce a fluid, low-melting slag.

Scrap as Charge for Primary-Lead Furnaces. Recycled battery scrap, particularly the paste portion, is often added in small amounts to the charge of sinter machines in primary-lead smelters. New lead-smelting processes can utilize lead battery paste as a substantial portion of the charge.

Lead Sweat Furnaces. Small amounts of lead are recycled via lead sweat furnaces. The primary materials recycled in sweat furnaces are lead-coaled power and communications cable, lead sheet and pipe, and other products that contain lead as a coating or as part of a complex part. The process is performed at relatively low temperatures and produces both metal for refining and dross; the dross is recycled to smelters.

Specifications for Recycled Lead
Throughout much of the world, two lead specifications prevail: one with a minimum of 99.99% Pb and the other with a minimum of 99.97% Pb. The major impurities in lead are antimony, arsenic, bismuth, copper, nickel, silver, tin, and zinc. Recently, selenium and tellurium have been added as important impurities.

Primary-lead companies generally produce the 99.99% Pb grade, whereas recyclers produce the 99.97% Pb grade. The major difference in the lead grades is that recyclers generally do not remove the bismuth and silver in their refining process. Recycled lead generally contains sufficient bismuth to preclude reaching 99.99% purity.

Gas-Producing Impurities. More important than restrictions of bismuth and silver in lead specifications has been the restriction of elements that increase gas generation in lead acid batteries. Elements that promote decomposition of the electrolyte and production of gas upon charging are specified at very low levels regardless of the overall purity of the lead. The specification for pure lead for battery oxide restricts antimony, arsenic, nickel, and tellurium to low levels, whereas nongassing impurities such as bismuth, silver, and copper are permitted at higher levels. In the most restrictive specifications, all the gas-producing impurities are restricted to a content of 1 ppm or less.

Government Regulations Regarding Recycling
The lead industry, and particularly the lead recycling industry, must conform to increasingly stringent environmental regulations. Lead acid batteries, the major raw material of recyclers, have been declared a hazardous waste. Because batteries are the largest source of lead, they constitute the major source of lead contamination in landfills and incinerators.