Batteries are included

Atomic absorption spectroscopy reveals the chemical cocktail of gaseous emissions produced by the incineration of spent alkaline batteries.

It was the perennial lament of children across the world on Christmas morning that toys and gadgets would be labelled "Batteries not included" and they would spend the day playing with their less electrically challenged gifts, frustrated and powerless until Boxing Day. Unfortunately, from the environmental and recycling perspective things changed and now many devices are unwrapped with a pack of short-life, non-rechargeable, batteries included.

Manuel Almeida, Susana Xará, Julanda Delgado, and Carlos Costa of the LEPAE, Faculty of Engineering, at the University of Porto, in Portugal, explain that the quantitative evaluation of emissions from waste incineration is a critical component of complete Life Cycle Assessment (LCA) studies, that must take into account end-of-life solutions for non-recyclable products, such as alkaline batteries.

With this in mind, the team has simulated the waste-incineration process of samples of AA alkaline batteries of the kind used to power everyday gadgets such as motorised toys, small flashlights, and telephones. The most relevant components of such batteries are a cathode, containing manganese dioxide, graphite and potassium hydroxide, a nickel-plated steel can as cathode collector, and an anode containing zinc, zinc oxide and potassium hydroxide as electrolyte. Other components in the batteries include a separator, a cap (both made of steel), a piece of tin-plated brass as anode collector, a PVC plastic sleeve, a polyamide grommet, a cardboard insulator, and a paper and cellophane separator.

The researchers held the batteries, which weigh around 25 grams each and are just under 10% moisture by weight, at 1000 Celsius in a refractory steel tube in a horizontal electric furnace for one hour.

The team explains that a continuous flow of air into the tube ensures an adequate oxygen supply for the incineration process and also guides any gaseous emissions to a filter system for collection of and AAS analysis of metals (arsenic, cadmium, cobalt, chromium, copper, iron, mercury, manganese, nickel, lead, antimony, tellurium, and zinc. Sulfur was measured using barium sulfate gravimetry and chloride using the Volhard method.

The researchers found that zinc accounted for the greatest emissions among the metals, perhaps not surprisingly, as it amounts to about 6.5% of the zinc content in the batteries. However, although manganese oxide is the main component of the cathode and iron comprises the cathode collector neither of these metals were present in the gas stream above negligible amounts. Mercury was present even in the second filter, a bubbler flask.

Chloride, from the polyvinylchloride sleeve of the battery was collected at approximately 36%, not surprisingly, although a considerable proportion of the hydrogen chloride formed is neutralized by potassium hydroxide, zinc and manganese oxides in the process and so not totally released in the gas stream.

Almeida and colleagues modelled the incineration process and were able to predictable some of the experimental thermodynamic data in the temperature range of 1000 to 1100 Celsius. "This analysis was done for most of potential reactions between components in the batteries as well as between them and the surrounding atmosphere and it reasonably agrees the experimental results," they say.

Currently, there is no simple, or cost-effective, method for recycling non-rechargeable alkaline batteries. Moreover, burying them in landfill is undesirable because of the potential leeching of toxic metals into the ground. But, worse still is incineration in a municipal solid waste incinerator plant. "This is not generally considered an appropriate method of disposal for this residue," the researchers conclude, "since it wastes recyclable materials and it is a source of gaseous emissions that must be cleaned by the off-gas treatment systems."

They point out that mercury and other trace elements in alkaline batteries, as well as mercury(II) chloride residues and other toxic materials in the incinerator fly ash must be trapped by the incinerator cleaning system.

An understanding of the particular by-products from the incinerated disposal of this ubiquitous waste product could be used to improve standard incineration procedures as well as management of gaseous and solid waste streams from MSW plants.