Page 203 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

Components of a lead-acid battery

A lead-acid battery is made up of the following components, enclosed within a plastic or ebonite box or casing.
There are positive and negative terminals made of lead, which provide the connection points to external devices.
There are sets of positive and negative plates kept apart by plate separators - porous sheets of PVC or polyethylene
plastic, glass microfiber, or phenolic resins that allow the free movement of the ions in the electrolyte solution. The
positive plates are grids made of lead or lead alloy coated with porous metallic lead paste, and the negative plates
are lead grids coated with lead dioxide paste. A series of negative and positive plates plus separators makes up
a battery element, and the battery elements are separated by plates of the same material as the battery box.
The elements are bathed in a sulfuric acid electrolyte solution, which can be topped up via the plugs. In sealed
batteries the electrolyte is either a gel or is soaked onto glass microfiber separators.
The average amount of lead in automotive batteries can range from 2 to 13 kg, depending on the size of the
vehicle

Steps in the recycling process
Almost all parts of a lead-acid battery can be recycled. The main steps in the recycling process are as follows:
• Collection and transportation of the batteries to a recycling facility
• Separation of the component parts of the batteries smelting and refining of the lead components
• Washing then shredding or melting of the plastic components

• Purification and treatment of the sulfuric acid electrolyte
• Treatment and disposal of waste
The batteries are mechanically or manually broken up to separate out the acid and component parts. The lead
components are conveyed to the furnace for smelting. After smelting the slag is removed and the molten unrefined
lead may be poured into moulds and cooled or it may immediately be directed to a holding kettle (cast-iron pot)
to keep it molten prior to refining. The aim of the refining process is to produce lead of high purity or to produce
alloys (requiring the addition of specific trace elements to the refining kettle) that can be used to make a new lead
battery. The molten lead is then cast into moulds and allowed to cool
Recyclable plastic components are washed then shredded or ground and melted. The molten plastic is extruded
into pellets, which can then be used in the manufacture of other plastic goods, including new battery casings.
In many smaller recycling facilities in low- and middle-income countries, the plastic battery cases are often not
recycled and may be dumped or burned The electrolyte may be recovered for re-use or neutralized with alkali and
treated to remove lead and other contaminants before being released into the sewage system. Alternatively, the
solution may be purified and sodium sulfate extracted for use in making detergents and other products

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CITS : Automotive - Mechanic Diesel - Lesson 57 - 61