Recycling silver

Press, 13 August 1980, Page 17

Recycling silver

Even the dark clouds of rising costs can have a silver lining — and recycling can turn silver into gold if you are in the film business.

The National Film Unit has now been credited with a return .of $30,000 made from microscopic grains of silver recovered from film processing chemicals during a three-month period ending last February’. This was earned from a collection of about 30 kg of almost pure precious metal. The unit’s laboratory director, David Appleby, admits that when the three monthly gleaning of silver was returned for sale .on the bullion market in February, the market was at an exceptionally high level.

“The price of silver went crazy. Prices rocketed from $8 a troy ounce to $5O within 12 months. Prices have slipped away from that peak, but even so the silver recovery process can be reckoned to return $BOOO to $lO,OOO every three months.

“Ten years ago this profit and the silver would have gone down the drain and out to sea,” he said. Unlike many other natural resources, the silver used in the photographic process is not destroyed by its use. A great deal of the silver can be recovered, refined, and reused. Photography consumes about a third of the total silver used by industry. Nothing has ben found to equal silver as a lightsensitive material capable of forming a photographic image. Because it is a diminishing resource its conservation is important to the photographic industry. In recent years equipment and processes have

been developed to recover this silver. The National Film Unit, with its laboratory at Avalon, Lower Hutt, is the biggest film processing complex in New Zealand, using seven million feet of film a year. The silver in every foot of 16mm colour negative film processed costs about one cent.

All the silver is removed from the colour process, unlike the black and white process which retains some .to make the image. . The silver recovered at the National Film Unit helps to offset the price of developing film. ' There are various processes available but the method chosen by the unit involves the electrolytic process. Mr Appleby says that although this method is more expensive to install, it returns 99 per cent pure silver. This means the later refining cost is minimal.

In the electrolytic method, silver is recovered from the fixing solution by passing an electric current between electrodes contained in a cell.

There are two grams of silver in a litre of fix and this passes through the cells at 30 litres a minute. When the silver ion gives up its electrical charge it becomes silver metal and is deposited on stainless steel tubes (electrodes). This is left to accumulate for a month. The stainless steel tubes are then taken from the cylinders and flexed to remove the silver. The flakes of silver are bagged, weighed, and sent to Auckland to be refined. The refining company removes the 1 per cent impurity (which is mainly moisture and traces of gelatin) and then sells the silver on the bullion market.