Abstract
Silver is an important industrial metal used in several areas such as photographic and x-ray films, jewelries, silver wares and electronic objects. Silver is used for photographic film/x-ray film because of its matchless quality as a light-sensitive material for making a photographic image. Silver is not destroyed in the photographic process and it can be reused and recovered. Results have proven that, bacterial alkaline protease can be used to extract silver in 30 min, but its activity decreases with increasing incubation period. Gelatin hydrolysis was monitored by measuring the increase in turbidity of the hydrolysate, which was accompanied by release of protein and hydroxyproline. The protease of the culture filtrate used was 97 U/ml after 30 min, but it decreased to 86.5U/ml after 60 min. After 90 min, it reached 85 U/ml. A great inactivation was recorded after 120 min; it got to 39.5 and 36.5% (U/ml) after 180 min. Gelatin layer was stripped completely within 30 min with 97 U ml-1 protease at 50°C and pH 8. At the end of the treatment, gelatin layer was completely removed and the polyester film was left clean. In addition, silver was recovered in the hydrolysate, both of which can be reused. Key words: Silver recovery, x-ray films, gelatin, alkaline protease, Bacillus subtilis.
Highlights
Alkaline protease is one of the most important enzymes in the commercial field and it occupies a large area in the field of enzyme production
It can restore this quantity of silver by dissolving gelatin layer in alkaline protease to be used for other purposes (Nakiboglu et al, 2003)
X-ray film is a rich source of silver, which is distributed in the gelatin layer
Summary
Alkaline protease is one of the most important enzymes in the commercial field and it occupies a large area in the field of enzyme production It is widely used in leather industry, diagnosis process, extraction of silver, animal diet production and food processing. X-ray films contain about 1.5 to 2% ratio of silver in gelatin-coated film made from polyester layer It can restore this quantity of silver by dissolving gelatin layer in alkaline protease to be used for other purposes (Nakiboglu et al, 2003). Silver oxidation is followed by electrolysis or chemical treatment of the gelatin layers of X-ray films. All these traditional ways are environmentally unsafe, so enzymatic analysis of the gelatin layer is preferable. The considered methods of analysis for enzymatic gelatin are the best alternatives to reduce
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