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Ever since the nickel-cadmium battery came into existence, experts have been studying ways to recycle it. The first really widely-used batteries were of the open type. Their recovery at the end of their life was due to the ease with which they could be opened and the positive electrodes isolated so as to re-use the nickel.

Until the 50's, companies showed little interest in recovering the cadmium, which was not considered hazardous; and the negative electrodes available weighed very little. Moreover, putting complete nickel-cadmium batteries in the furnace to produce nickelbased ferroalloys posed absolutely no problem. The cadmium was vaporised on the surface, where it burned to produce cadmium oxide, which was usually released into the environment. At best, some of the dust was picked up by relatively efficient filters, in the case of zinc, lead and other forms of dust.

With the increasing demand for cadmium, for cadmium plating, pigments, and nickel-cadmium batteries, the price of cadmium remained high. Prices in the range of 4 to 5 USD per pound were by no means uncommon, with operations in the cadmium market handled by dealers specialising in "minor metals" and speculating on the price at the first opportunity.

In the 50's, electrochemical and hydrometallurgical processes were tested and used on a small scale for the production of recovered cadmium. The principle whereby the cadmium was extracted by distillation is described and used in the production of primary cadmium (coming from zinc ores).

The first plants designed to recover the cadmium from nickel-cadmium batteries appear to have started up in the early 60's. These plants used distilling furnaces charged with mainly pocket-plate negative electrodes and produced cadmium of fairly poor quality: 99.9% at best. The cadmium, which contained lead and nickel impurities, was nevertheless re-used for the production of pocket-plate nickel-cadmium batteries.

The thermal process (cadmium distillation) became inescapable with the appearance of sealed cylindrical nickel-cadmium batteries. Just as it is economically viable, technically feasible and always practical to dismantle manufactured items weighing from 1 to 20 kg so as to separate out the electrodes and only process those containing cadmium, so it would be unthinkable to open up one by one sealed elements weighing from 30 to 150 grams. Whilst a pocket-plate negative electrode only contains iron, iron oxide and cadmium in the form of cadmium oxide or hydroxide, a sealed unit contains amounts of other materials, including powdered nickel and nickel hydroxide along with various types of organic matter. Hydrometallurgical and electrochemical processes are both far too complex for such a mixture.

Plants were developed in the 70's: in Europe (2 in France and 2 in Germany), Asia, including Japan and Taiwan, and the USA. These were created either at the request of recycling companies specialising in the dismantling of industrial batteries, or at the request of the producers, mainly for the purpose of treating the waste produced by the manufacture of sealed units. However, the fact is that these projects were born, developed and then often disappeared as a result of fluctuations in the price of cadmium.

It was in the 80's that plants specifically designed for the processing of batteries and waste from nickel-cadmium batteries came into their own.

NIFE, in Sweden, had started work on its process in 1978, but it only became operational on an industrial scale in 1986.

In Japan, NIPPON RECYCLE CENTER developed its process in the 70's, although its dedicated plant specifically designed to treat nickel-cadmium batteries only came into operation in Korea in 1984.

Although the first cadmium distilling furnace built to operate the S.N.A.M. process goes back to 1965, the first S.N.A.M. plant was not built until 1982.

NIFE, one of the two largest manufacturers of industrial nickel-cadmium batteries in the world, began recycling cadmium by treating its own waste before treating its customers' spent batteries.

NIPPON RECYCLE CENTER, first in Japan and then in Korea (HANIL joint venture), initially based its activities on treating waste from the manufacture of batteries in Japan.

S.N.A.M. decided to build its plant in 1982 in order to treat waste from battery manufacture in the USA and France (SAFT) and then to process negative electrodes from nickel recovery companies engaged in the dismantling of industrial batteries.

In all of this, it is quite astonishing that very few companies producing zinc, and thus inevitably producers of cadmium, took a really serious interest in recycling cadmium:

- In Japan, in the late 80's, TOHO ZINC set up a plant for the pre-treatment of batteries and nickel-cadmium waste; this was designed to produce an impure cadmium oxide to be used in its primary cadmium production process.

- MITSUI MINING, at the request of a Japanese manufacturer of nickel-cadmium batteries, developed a distilling furnace which has remained at the prototype stage.

- In the USA, BIG RIVER ZINC developed a process designed to produce cadmium oxide directly from pocket-plate negative electrodes. It discontinued this process when the price of cadmium fell very sharply in 1991/1992.

- UNION MINIERE was involved in the second S.N.A.M. plant in 1988, but withdrew in 1992.

The situation of the nickel-cadmium battery manufacturers is different: they are rarely involved in the treatment of the waste they produce or of their customers' spent batteries, except for NIFE in Sweden and ENERGIZER in Florida, USA (which has a small unit basically designed to treat manufacturing dust and sludge from the wastewater treatment system). However, they provided the economic means for both the start-up and the growth of the main recycling companies currently in operation.

The appearance of national organisations responsible for collecting and monitoring batteries and accumulators gave fresh impetus to companies recycling nickel-cadmium batteries and also initiated the recycling of NiMH and Li-Ion batteries. In Ellwood City, PA (USA), INMETCO organised its development on the basis of its collection system, largely due to the backing of the RBRC (Rechargeable Battery Recycling Corporation).

In Germany, ACCUREC started up with the collection nationwide of nickel-cadmium batteries (Arge Bat) and has ensured its growth with the collection of all types of batteries which took over in 1998 from Arge Bat under the name of G.R.S. BATTERIEN (Stiftung Gemeinsames R├╝cknahmesystem Batterien).

Figure la gives examples of industrial NiCd cells, while Figure lb shovwcollected consumer cells or packs.

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