Lead-acid batteries which are primarily used to generate electricity are made up of a series of identical cells. In each of the identical cells there is a set of positive and negative plates which are called electrodes. Lead–acid batteries are firstly invented by French physicist Gaston Plante in 1859 which are the oldest type of rechargeable batteries. Their ability to supply high currents means that the cells maintain a relatively large power-to-weight ratio although they have a very low energy-to-weight ratio and a low energy-to-volume ratio. Due to these features & benefits, along with their low cost, make them attractive to be used in motor vehicles to provide the high current required by automobile starter motors.

Recycling of Lead Acid Batteries

Recycling of battery is an activity which aims at the safety of the environment by reduction of number of batteries which we dispose off as municipal solid waste dumping sites. Batteries contain a number of heavy metals and toxic chemicals which can hamper the environment and their dumping has raised concern over risks of soil contamination and water pollution.

Lead-acid battery recycling has become the most successful recycling programs in the world today other than recycling of aluminium, glass, paper, plastic etc. In the United States 97% of all battery lead was recycled between 1997 and 2001. For the prevention of lead emissions into the ambient environment it is necessary to adopt an effective pollution control system. Continuous improvements in the technologies of battery recycling plants and furnace designs is required to keep pace with emission standards for lead smelters.

The very first step in process of recycling of lead acid batteries is sorting in which recyclable batteries are sorted into chemistries. During this process it is determined whether the spent battery intact or damaged. There is no effect of this determination one the recycling process because both intact and damaged batteries are recycled separately. Collection centers place lead acid, nickel-cadmium, nickel-metal-hydride and lithium-ion batteries into designated drums, sacks or boxes. It would be profitable for the battery recyclers that if they get steady stream of batteries, sorted by chemistry at no charge.

Image: http://www.batterycouncil.org

The battery is then broken apart in a hammer mill. Hammer mill is a machine that hammers the battery into pieces. The battery gets broken down into pieces which contain plastic, metals and acid. This is kept into a vat, where the lead and heavy materials settles down to the bottom while the plastic rises to the top. At this point, the polypropylene pieces, which make the outer jacket of the batteries, are scooped away and the liquids are drawn off, leaving the lead and heavy metals. From here each of the materials goes into a different “stream.” After this recycling is done for three different materials (plastic, lead and sulphuric acid) that at three different designated places.

Recycling of Plastic

The outer jacket of the batteries is made of polypropylene which is a thermoplastic. For the recycling purpose polypropylene pieces are first washed, then blown dry and sent to a plastic recycler. The purpose of using plastic recyclers is to melt these polypropylene pieces into an almost-liquid state. The molten plastic is then put through an extruder in order to produce small plastic pellets of a uniform size. Recyclers sell these pellets to the manufacturer of battery cases to earn profit, and the process begins again

Recycling of Lead

In the process of recycling of lead, lead grids which are made up of lead oxide and other lead parts are cleaned by washing or any other means, melted together in smelting furnaces powered by coal. Once the lead becomes molten it is then poured into ingot molds. Ingots are the carrying vessels which are made up of metals having different carrying capacities. Large ingots, weighing about 2,000 pounds are called hogs. In the contrast, smaller ingots, weighing 65 pounds, are called pigs. Molten lead is poured into ingots and is allowed to undisturbed. After few minutes, the impurities, which are known as dross, float to the top of the still-molten lead in the ingot molds. The dross is scraped away using scraper and the ingots are left to cool. When these ingots are cooled, they are removed from the molds and sent to battery manufacturers. Battery manufacturers re-melt and reuse these ingots in the production of new lead plates and other parts for new batteries.

Recycling of Sulphuric Acid

There are two possible ways to handle the acid of an old battery:

First method suggests about the neutralization of the acid using an industrial compound which is similar to household baking soda. As soon as it is added to the acid, this turns the acid into water. Once the water is formed, it is treated using municipal water treatment methodologies; disinfected and tested to be sure it meets clean water standards. Then it is released into the municipal sewer system.

Another way to treat acid is to process it using industrial chemicals. After the processing it gets converted into sodium sulfate which is an odorless white powder. This powder has a high demand in laundries as laundry detergent and in the manufacturing of glass and textile also.

Conclusion

The recycling of lead-acid batteries is environmentally safe and sound. The process does not allow the harassment of the nature and stops the acid from spill on the ground and thus prevents the contamination of the soil in the nature. Lead has been recognized as hazardous pollutant which is also ceased at the recycling centre. The most common pollutant plastic, which is a non-biodegradable, is also recycled into useful products. In total, the recycling of the lead-acid batteries has proved itself safe to environment. This is highly regulated and practiced at the state, national and international levels. Through this we can dispose off spent batteries free of cost which sounds very pleasing.